Dissertations / Theses on the topic 'Vibration load'

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 216-218).
This thesis studies a novel nonlinear spring mechanism that is comprised of a cantilever wrapping around a curved surface as it deflects. Static force versus displacement tests and dynamic "initial displacement" tests verified the spring theory for a large range of oscillator parameters. Various human motion energy harvester configurations that use the nonlinear spring were numerically optimized for power, robustness, and adaptivity. Based on the optimization results, both the nonlinear and linear devices studied in this thesis generate more power per volume and per mass when excited at one's hip while walking than current commercial energy harvesters. The two degree-of-freedom (2DOF) nonlinear oscillator is more adaptive to different excitation signals and resistant to power decay when parasitic damping is present than the IDOF and 2DOF linear systems. These significant advantages are caused by the 2DOF nonlinear system harvesting its optimal power at large electromagnetic damping coefficients, whereas the optimal power generation for the linear systems occurs at low electromagnetic damping coefficients. This thesis also examined what electromagnetic damping coefficients can be generated by magnet-and-coil geometries that satisfy the energy harvester constraints. The final chapter of this thesis investigates a load cell that uses the stiffening spring to maintain high resolution over a large range of forces and prevent large forces from damaging the load cell. Future work will include testing a full energy harvester prototype and exploring other applications of the nonlinear spring.
by Jocelyn Maxine Kluger.
S.M.

Background: Epidemiological studies suggest an increased incidence of osteoarthritis among workers in occupations requiring squat-lifting such as in construction, mining and farming. Squat-lifting postures can induce heavy mechanical loads on the joint, causing the articulating surfaces to deform. This can result in changes of vibration characteristics of the joint surfaces. Differences in the vibration characteristics of normal and pathological joints have been established and used in the past for classifying severity of disease. The purpose of this study was to examine the influence of cumulative mechanical load on the vibration properties of the knee joint and to gain an understanding of how these properties may relate to an increase in cumulative load placed on the joint. Methods: In this study, cumulative load was measured as the resultant knee joint torque during squat lifting, while a piezoelectric accelerometer was used to capture vibration signals from points on the knee during flexion and extension. Twelve university students were recruited for a repeated measures study. Each participant attended one session where they had to perform a series of six squat-lifting tasks on a force platform. Motion capture equipment was used to obtain kinematic data. The cumulative 3-D moment on the joint was calculated using inverse dynamics. Results: A visual inspection of an ensemble average constructed for the frequency spectrum of all participants revealed that differences may exist in the 750 Hz - 2000 Hz bandwidth for vibrations coming from the patella during flexion. Further statistical analysis by a t-test and ANOVA showed a decrease in the RMS power of the signal captured in this bandwidth before and after mechanical load was induced by squat lifting. A linear regression analysis indicated a significant correlation between cumulative 3-D moment on the knee joint and the median frequency of vibration signals from the patella during flexion in the 1000 Hz - 2500 Hz range. Conclusions: Overall, the results of this study indicate the possibility of a relationship between mechanical exposure on the knee joint and its vibration properties during joint movement. Despite the small sample size, a declining trend was observed in the normalized RMS power of signals with increase in loading. However, the quantitative nature of this relationship is not clear and the current study points towards a non-linear relationship between joint exposure and knee vibrations. Future studies must investigate this possibility using direct measures of joint loading, cartilage deformation and their relation to joint vibrations.
Master of Science

Accurate transport simulation is necessary to determine the probability that a unitary load might be disassembled or subject to severe structural changes while travelling to its destination. With the evaluations that come from accurate transport simulation companies might be able, for example, to optimize for the amount of plastic to use in the wrapping process of a unitary load. Other than the obvious immense cost reduction given by a lower incidence of product-ruining accidents during transport, optimizing plastic usage would also help avoid over-wrapping, resulting in better environmental outcomes. Currently, multi-axial simulation is more and more being adopted by companies in the hopes of representing more closely the stresses a load is subject to during transport. However, there is no international standard outlining a procedure that one might follow in order to do so, yet. This work starts from the identification of the best methods to record simulation-oriented transport data precisely and reliably. Some recordings of different types of transport have been conducted to highlight their different nature and to show an example of how to use a sensor in different contexts. Then, the main existing methods for simulating transport are analyzed and used to create a new procedure for the selection of the most suitable one, mainly depending on the availability of technological resources and transport data. Lastly, considerations about possible future improvements on this work are presented.

The unit load is the form of most commercial and industrial products during storage and distribution. A simple form of a unit load, a palletized bulk bin is commonly used to transport fruit and vegetables from the point of harvest to processing facilities. These vibration sensitive products are often subjected to damaging vibrations during this period. Most damage occurs during the large accelerations associated with resonance, which occurs when the natural frequency of the unit load matches the input frequencies commonly encountered during transportation. A computer model, called RoPUL (resonance of palletized unit loads), of a palletized bulk bin loaded with fruit, was developed using finite element analysis techniques. Unit loads consisting of palletized bulk bins of apples and peaches were tested and RoPUL was found to accurately predict the resonant frequencies of these loads. Using RoPUL, the effects of product mass, container design, and pallet design on natural frequencies can be analyzed. As the input frequencies of most transportation modes is well documented, RoPUL can be used to help design a unit load to better protects vibration sensitive products during shipment.
Ph. D.

Conventional gearbox vibration monitoring techniques are based on the assumption that changes in the measured structural response are caused by deterioration in the condition of the gears in the gearbox. However, this assumption is not valid under fluctuating load conditions, since the fluctuating load will amplitude modulate the measured vibration signal and cause the rotational speed of the system to change. In general monitoring of machines subject to fluctuating load conditions is dealt with by considering the constant load conditions on gearboxes or during free rotational tests. The need to monitor the condition of large gearboxes in mineral mining equipment has attracted greater interest in order to improve asset management. An inherent need for signal processing techniques, with the ability to indicate degradation in gear condition, under fluctuating load conditions exist. Such techniques should enable the online monitoring of gearboxes that operate under fluctuating load conditions. A continued flow of up to date information should consequently be available for asset and production management. With this research, a load demodulation normalisation procedure was developed to remove the modulation caused by fluctuating load conditions, which obscures the detection of an incipient gear fault conditions. A rotation domain averaging technique is implemented which combines the ability of computer order tracking and time domain averaging to suppress the spectral smearing effect caused by the fluctuation in speed, as well as to suppress the amplitude of the vibration which is not synchronous with the rotation of the gear shaft. It is demonstrated that the instantaneous angular speed of a gearbox shaft can be utilised to monitor the condition of the gear on the shaft. The instantaneous angular speed response measurement is less susceptible to phase distortion introduced by the transmission path when compared to conventional gearbox casing vibration measurements. A phase domain averaging approach was developed to overcome the phase distortion effect of the transmission path under fluctuating load conditions. The load demodulation normalisation and rotation domain averaging signal processing procedures were applied to both the conventional gearbox casing vibration and instantaneous angular speed measurements prior to the calculation of a smoothed pseudo Wigner-Ville distribution of the data. Statistical parameters such as the energy ratio were calculated from the distribution. These parameters could be monotonically trended under different load conditions to indicate the degradation of gear conditions.
Thesis (PhD (Mechanical Engineering))--University of Pretoria, 2005.
Mechanical and Aeronautical Engineering
unrestricted

For the reliability design of Engine Control Unit devices in motor vehicles, the knowledge of stresses occurring in the field within the product service life is essential. In addition to the environmental influences such as temperature, moisture and humidity, vibration and shock issues are in focus. To ensure the robustness of the products and they are still easily and inexpensively made, they must be interpreted appropriately in the development process. For this, the load spectra for the mechanical influences of road conditions and operating conditions are to be determined. Work will also include temperature and humidity values examined on typical installation locations. The essential everyday situations (commuters, taxi, farmer, ...) should be considered. Existing measurement technology must be combined to this end a comprehensive logger system with communication to the vehicle.

Due to high specific strength and stiffness as well as outstanding energy-absorption characteristics, sandwich structures are extensively used in aircraft, aerospace, automobile, and marine industries. With the objective of finding lightweight blast-resistant sandwich structures for protecting infrastructure, we have found, for a fixed areal mass density, one- or two-core doubly-curved sandwich shell's (plate's) geometries and materials and fiber angles of unidirectional fiber-reinforced face sheets for it to have the maximum first failure load under quasistatic (blast) loads. The analyses employ a third-order shear and normal deformable plate/shell theory (TSNDT), the finite element method (FEM), a stress recovery scheme (SRS), the Tsai-Wu failure criterion and the Nest-Site selection (NeSS) optimization algorithm, and assume the materials to be linearly elastic. For a sandwich shell under the spatially varying static pressure on the top surface, the optimal non-symmetric one-core (two-core) design improves the first failure load by approximately 33% (27%) and 50% (36%) from the corresponding optimal symmetric design with clamped and simply-supported edges, respectively. For a sandwich plate under blast loads, it is found that the optimal one-core design is symmetric about the mid-surface with thick face sheets, and the optimal two-core design has a thin middle face sheet and thick top and bottom face sheets. Furthermore, the transverse shear stresses (in-plane transverse axial stresses) primarily cause the first failure in a core (face sheet). For the computed optimal design under a blast load, we also determined the collapse load by using the progressive failure analysis that degrades all elasticities of the failed material point to very small values. The collapse load of the clamped (simply-supported) sandwich structure is approximately 15%–30% (0%–17%) higher than its first failure load. Incompressible materials such as rubbers, polymers, and soft tissues that can only undergo volume preserving deformations have numerous applications in engineering and biomedical fields. Their vibration characteristics are important for using them as wave reflectors at interfaces with a fiber-reinforced sheet. In this work we have numerically analyzed free vibrations of plates made of a linearly elastic incompressible rubber-like material (Poison's ratio = 0.5) by using a TSNDT for incompressible materials and the mixed FEM. The displacements at nodes of a 9-noded quadrilateral element and the hydrostatic pressure at four interior nodes are taken as unknowns. Computed results are found to match well with the corresponding either analytical or numerical ones obtained with the commercial FE software Abaqus and the 3-dimensional linear elasticity theory. The analysis discerns plate's in-plane vibration modes. It is found that a simply supported plate admits more in-plane modes than the corresponding clamped and clamped-free plates.
Doctor of Philosophy
A simple example of a sandwich structure is a chocolate ice cream bar with the chocolate layer replaced by a stiff plate. Another example is the packaging material used to protect electronics during shipping and handling. The intent is to find the composition and the thickness of the "chocolate layer" so that the ice cream bar will not shatter when dropped on the floor. The objective is met by enforcing the chocolate layer with carbon fibers and then finding fiber materials, their alignment, ice cream or core material, and its thickness to resist anticipated loads with a prescribed level of certainty. Thus, a sandwich structure is usually composed of a soft thick core (e.g., foam) bonded to two relatively stiff thin skins (e.g., made of steel, fiber-reinforced composite) called face sheets. They are lightweight, stiff, and effective in absorbing mechanical energy. Consequently, they are often used in aircraft, aerospace, automobile, and marine industries. The load that causes a point in a structure to fail is called its first failure load, and the load that causes it to either crush or crumble is called the ultimate load. Here, for a fixed areal mass density (mass per unit surface area), we maximize the first failure load of a sandwich shell (plate) under static (dynamic) loads by determining its geometric dimensions, materials and fiber angles in the face sheets, and the number (one or two) of cores. It is found that, for a non-uniformly distributed static pressure applied on the central region of a sandwich shell's top surface, an optimal design that has different materials for the top and the bottom face sheets improves the first failure load by nearly 30%-50% from that of the optimally designed structure with identical face sheets. For the structure optimally designed for the first failure blast load, the ultimate failure load with all of its edges clamped (simply supported) is about 15%-30% (0%-17%) higher than its first failure load. This work should help engineers reduce weight of sandwich structures without sacrificing their integrity and save on materials and cost. Rubberlike materials, polymers, and soft tissues are incompressible since their volume remains constant when they are deformed. Plates made of incompressible materials have a wide range of applications in everyday life, e.g., we hear because of vibrations of the ear drum. Thus, accurately predicting their dynamic behavior is important. A first step usually is determining natural frequencies, i.e., the number of cycles of oscillations per second (e.g., a human heart beats at about 1 cycle/sec) completed by the structure in the absence of any externally applied force. Here, we numerically find natural frequencies and mode shapes of rubber-like material rectangular plates with different supporting conditions at the edges. We employ a plate theory that reduces a 3-dimensional (3-D) problem to a 2-D one and the finite element method. The problem is challenging because the incompressibility constraint requires finding the hydrostatic pressure as a part of the problem solution. We show that the methodology developed here provides results that match well with the corresponding either analytical or numerical solutions of the 3-D linear elasticity equations. The methodology is applicable to analyzing the dynamic response of composite structures with layers of incompressible materials embedded in it.

A structure comprised of two arches that lean against each other at the apex is considered. The arches are thin shells with internal pressure. This type of structure with solid arches has been used in bridges, such as the Gateway Arch Bridge in Columbus, Indiana, U.S.A., the Monongahela River Bridge in Pittsburgh, Pennsylvania, U.S.A., and a pedestrian bridge at the Pacific Tower in Paris, France. A series of leaning arches was incorporated in the frame of the Museum of the Moving Image, a temporary structure in London, England, during 1992-1994. Pressurized arch-shells made of a flexible material have been utilized as part of the framework for some transportable tent-like structures.

The behavior of a pair of pressurized leaning arch-shells with various tilt angles, boundary conditions, and loads is investigated numerically. Several types of loads are considered, including uniformly-distributed vertical loads applied over all or half of the structure (representing snow), and wind loads on the structure. The arches are pinned or fixed to the ground. Deflections, vibrations, and stability of the structures are investigated using the finite element method. The effect of the tilt angle on the response is examined, and buckling may occur for some tilt angles under vertical loading. This type of structure has not been used widely, but may be effective for various applications.
Master of Science

Tableau d'honneur de la Faculté des études supérieures et postdorales, 2015-2016
Les travaux réalisés dans le cadre de ce mémoire de maîtrise visent à décrire la source hydraulique de vibrations mesurées lors de la mise en service d’une roue Francis. Lors de l’essai de rejet de charge à partir de la puissance maximale, il a été relevé que la roue subissait des vibrations autoexcitées à l’une de ses fréquences naturelles. L’objectif de ces travaux est d’identifier le phénomène hydraulique causant l’entrée en vibrations auto-excitées de la roue submergée. Puisque la cavitation semble jouer un rôle dans cette problématique, les capacités du solveur fluide ANSYS CFX à simuler de la cavitation instationnaire ont été évaluées. De ce fait, deux géométries ayant été étudiées expérimentalement ont été simulées. Cette étude a permis de conclure que l’approche homogène, plus stable et couramment utilisée dans la littérature, ne permet pas de reproduire de façon fiable les fluctuations de pression causées par l’instationarité des cavités de vapeur. Il a cependant été montré que les simulations permettent de prédire la forme, la localisation ainsi que les mécanismes entraînant la présence de vapeur dans l’écoulement. De plus, il a été demontré que la cavitation est un phénomène particulièrement sensible et sujet à répondre en phase à une excitation oscillatoire, par exemple la vibration de la roue. Les simulations numériques réalisées durant différentes phases du rejet de charge transitoire ont entre autres permis d’identifier que lorsque les vibrations apparaissent, une forte région de vapeur se crée au bord de fuite de l’aubage, près du plafond. En augmentant le temps de fermeture du distributeur, le partenaire industriel a réussis à éliminer les vibrations problématiques. En réalisant des simulations avec différents temps de fermeture, il a été démontré que la solution proposée permet d’augmenter le niveau de pression dans le canal inter-aubes, réduisant ainsi la quantité de vapeur s’y trouvant. Cela laisse suggérer que la cause d’entrée en vibrations de la roue est la cavitation se formant durant le rejet de charge. Cependant, il est à noter que les différentes méthodologies proposées n’ont pas permis d’obtenir les fréquences d’excitation mesurées expérimentalement, essentiellement à cause de limitations liées à la modélisation de la cavitation.
The work presented in this master degree thesis aims to identify the hydraulic cause of mechanical vibrations measured during the commissioning of a Francis runner. During the test of load rejection from maximal power output regime, it was noticed that the runner entered a state of self-excited vibrations at one of its natural frequencies. The purposes of this work is to investigate the hydraulic phenomenon which causes the submerged runner to enter self-excited vibrations. Since cavitation is expected to play a role in this problematics, there was a need to evaluate the capabilities of the fluid solver ANSYS CFX to solve unsteady cavitating flows. Two geometries which had been investigated experimentally were thus simulated. It was concluded that the homogeneous approach, more robust and widely used in the literature, does not lead to a reliable prediction of the pressure fluctuations caused by cavitation. It was however shown that the simulations allowed to predict the shape, the location as well as the physical mechanisms responsible for the presence of vapor in the flow. It was also demonstrated that cavitation is a phenomenon particularly sensitive and subject to respond in phase to oscillatory perturbations, for instance the vibrating runner. The numerical simulations carried out at different phases of the load rejection transient have established that when the vibrations appear, a wide region of vapor forms at the trailing edge of the blade, near the crown. By increasing the distributor closing time, the industrial partner in this work had success in eliminating such problematic vibrations. In our case, when performing simulations with increased closing times, it was demonstrated that the solution proposed allows to increase the pressure level in the inter-blade channel, lowering the quantity of vapor it contains. This strongly suggests that the hydraulic cause of the vibrations is the cavitation forming during the load rejection. However, one can note that the proposed methodologies have not permitted to predict the excitation frequencies as measured experimentally, essentially due to limitations in the modeling of cavitation.

A three-dimensional, nonlinear dynamic analysis is conducted on a fully submerged, rigid, solid cylinder to be used as a breakwater. The breakwater could potentially be used as a single cylinder to protect small structures. Alternatively, multiple cylinders could be positioned in series to protect shorelines, harbors, or moored vessels from destructive incident water waves. The cylinder is positioned with its axis horizontal and is moored to the seafloor with four symmetrically placed massless mooring lines connected at the ends of the cylinder. The mooring lines are modeled as both linearly elastic ("regular") springs and compressionless springs. All six degrees of freedom of the structure are considered. The breakwater is modeled in air with a net buoyant force acting through the cylinder's center of gravity. The six "dry" natural frequencies of the structure are computed. Both linear and nonlinear free vibrations of the structure are considered. Linear damping is used to model the fluid and mooring damping effects. Normal and oblique harmonic wave forces at various frequencies and amplitudes are applied to the cylinder. The effects of the forcing amplitude and frequency, and the coefficient of damping, on the motion of the breakwater are studied. The results show that more erratic behavior occurs for the breakwater with compressionless springs, mainly due to the development of snap loads in the mooring lines.
Master of Science

Due to the increase of rotor size in horizontal axis wind turbine (HAWT) during the past 25 years in order to achieve higher power output, all wind turbine components and blades in particular, have to withstand higher structural loads. This upscalingproblem could be solved by applying technologies capable of reducing aerodynamic loads the rotor has to withstand, either with passive or active control solutions. These control devices and techniques can reduce the fatigue load upon the blades up to 40% and therefore less maintenance is needed, resulting in an important money savings for the wind farm manager. This project consists in a study of load control techniques for offshore wind turbines from an aerodynamic and aeroelastic point ofview, with the aim to assess a cost effective, robust and reliable solution which could operate maintenance free in quite hostile environments. The first part of this study involves 2D and 3D aerodynamic and aeroelastic simulations to validate the computational model with experimental data and to analyze the interaction between the fluid and the structure. The second part of this study is an assessment of the unsteady aerodynamic loads produced by a wind gust over the blades and to verify how a trailing edge flap would influence the aerodynamic control parameters for the selected wind turbine blade.
På grund av ökningen av rotorstorleken hos horisontella vindturbiner (HAWT) under de senaste 25 åren, en design som har uppstod för att uppnå högre effekt, måste alla vindkraftkomponenter och blad stå emot högre strukturella belastningar. Detta uppskalningsproblem kan lösas genom att använda metoder som kan minska aerodynamiska belastningar som rotorn måste tåla, antingen med passiva eller aktiva styrlösningar. Dessa kontrollanordningar och tekniker kan minska utmattningsbelastningen på bladen med upp till 40 % och därför behövs mindre underhåll, vilket resulterar i viktiga besparingar för vindkraftsägaren. Detta projekt består av en studie av lastkontrolltekniker för havsbaserade vindkraftverk ur en aerodynamisk och aeroelastisk synvinkel, i syfte att bedöma en kostnadseffektiv, robust och pålitlig lösning som kan fungera underhållsfri i tuffa miljöer. Den första delen av denna studie involverar 2D- och 3D-aerodynamiska och aeroelastiska simuleringar för att validera beräkningsmodellen med experimentella data och för att analysera interaktionen mellan fluiden och strukturen. Den andra delen av denna studie är en bedömning av de ojämna aerodynamiska belastningarna som produceras av ett vindkast över bladen och för att verifiera hur en bakkantklaff skulle påverka de aerodynamiska styrparametrarna för det valda vindturbinbladet.

We consider geometric and material nonlinearities when studying numerically, by the finite element method, transient three-dimensional electroelastic deformations of a graphite-epoxy square plate sandwiched between two piezoceramic (PZT) layers. Points on the four edges of the bottom surface of the plate are restrained from moving vertically. The two opposite edges of the plate are loaded by equal in-plane compressive loads that increase linearly with time and the other two edges are kept traction free. The plate material is modeled as orthotropic and neoHookean. For the transversely isotropic PZT the second Piola-Kirchhoff stress tensor and the electric displacement are expressed as second degree polynomials in the Green-St. Venant strain tensor and the electric field. Both direct and converse piezoelectric effects are accounted for in the PZT. The plate is taken to have buckled when its centroidal deflection equals three times the plate thickness. The dynamic buckling load for the plate is found to strongly depend upon the rate of rise of the applied tractions. With the maximum electric field limited to 1kV/mm, the buckling load is enhanced by 18.3$\%$ when the PZT elements are activated. For a peak electric field of 30kV/mm, the buckling load increased by 58.5$\%$. When more than 60$\%$ of the surface area of the top and the bottom surfaces of the plate are covered by the PZT layers, then square PZT elements placed symmetrically about the plate centroid provide a larger enhancement in the buckling load than rectangular shaped or cross-shaped PZT elements. An increase in the plate thickness relative to that of the PZT actuators decreases the effectiveness of the PZT in enhancing the buckling load for the plate. The finite element code was modified to also analyze, in time domain, transient deformations of a viscoelastic material for which the second Piola-Kirchhoff stress tensor is expressed as a linear functional of the strain history of the Green-St. Venant strain tensor. It was used to analyze three-dimensional deformations of a thick laminated plate with layers made of aluminum, a viscoelastic material and a PZT. The following two arrangements of layers are considered. In one case a central PZT layer is surrounded on both sides by viscoelastic layers and aluminum layers are on the outside surfaces. The PZT is poled in the longitudinal direction and an electric field is applied in the thickness direction. Thus shearing deformations of the PZT layer are dominant. In the second arrangement, the aluminum layer is in the middle and the PZT layers are on the outside. The poling direction and the electric field are in the thickness direction; thus its extensional deformations are predominant. Three indices are used to gauge the damping of motion of plate particles, and the effectiveness of PZT actuators in enhancing this damping. It is found that the optimum thickness of the viscoelastic layers for maximum total energy dissipation is the same for each set-up. Also, the total thickness of the PZT layers which results in the maximum value of one of these indices of energy dissipation is the same for the two set-ups. Both arrangements give the largest value of this index for a plate of aspect ratio 10. Buckling behavior of a sandwich plate containing a soft core is also studied. The effects of the ratio of the elastic moduli of the outer layers to those of the core, and of the core thickness on the buckling load are analyzed. The top and the bottom layers are connected by very stiff blocks on two opposite edges where in-plane compressive time-dependent tractions are applied.
Ph. D.

New railway lines are continuously being constructed and existing lines are upgraded. Hence, there is a need for research directed towards efficient design of the supporting structures. Increasingly advanced calculation methods can be motivated, especially in projects where huge savings can be obtained from verifying that existing structures can safely support increased axle loads and higher speeds. This thesis treats the dynamic response of bridges under freight and passenger train loads. The main focus is the idealisation of the train load and its implications for the evaluation of the vertical bridge deck acceleration. To ensure the running safety of train traffic at high speeds the European design codes set a limit on the vertical bridge deck acceleration. By considering the train–bridge interaction, that is, to model the train as rigid bodies on suspension units instead of constant moving forces, a reduction in bridge response can be obtained. The amount of reduction in bridge deck acceleration is typically between 5 and 20% for bridges with a span up to 30 m. The reduction can be higher for certain train–bridge systems and can be important also for bridge spans over 30 m. This thesis aims at clarifying for which system parameter combinations the effect of train–bridge interaction is important. To this end, a thorough literature survey has been performed on studies in train–track–bridge dynamics. The governing parameters in 2D train–bridge systems have been further studied through a parameter screening procedure. The two-level factorial methodology was applied to study the effect of parameter variations as well as the joint effect from simultaneous changes in several parameters. The effect of the choice of load model was thus set in relation to the effect of other parameter variations. The results show that resonance can arise from freight train traffic within realistic speed ranges (< 150 km/h). At these resonance peaks, the reduction in bridge response from a train–bridge interaction model can be considerable. From the screening of key parameters it can furthermore be concluded that the amount of reduction obtained with a train–bridge interaction model depends on several system parameters, both for freight and passenger train loads. In line with the European design code’s guidelines for dynamic assessment of bridges under passenger trains an additional amount of damping can be introduced as a simplified way of taking into account the reduction from train–bridge interaction. The amount of additional damping is today given as function of solely the bridge span length, which is a rough simplification. The work presented in this thesis supports the need for a refined definition of the additional damping.
Nya järnvägslinjer byggs kontinuerligt och befintliga linjer uppgraderas. Det finns därför ett behov av forskning inriktad på effektiv design av de bärande konstruktionerna. Alltmer avancerade beräkningsmetoder kan vara motiverade, särskilt i projekt där stora besparingar kan erhållas från att verifiera att befintliga konstruktioner kan bära ökade axellaster och högre hastigheter. Föreliggande avhandling behandlar broars dynamiska respons under belastning av gods- och passagerartåg. Huvudfokus är att studera modelleringsalternativ för tåglasten och vilka konsekvenser de har för utvärderingen av brobanans vertikala acceleration. För att garantera trafiksäkerhet vid höga tåghastigheter definierar de europeiska normerna en maximalt tillåten vertikal acceleration i brobanan. Genom att beakta tåg-bro-interaktion, där tågkomponenterna modelleras som avfjädrade stela kroppar istället för konstanta punktlaster, kan en minskning av brons respons erhållas. Reduktionen av brobanans acceleration är typiskt mellan 5 och 20% för broar med en spännvidd på upp till 30 m. Minskningen kan vara högre för vissa tåg-brosystem och kan vara viktigt också för spännvidder över 30 m. Denna avhandling syftar till att klargöra för vilka kombinationer av tåg-broparametrar effekten av tåg-bro-interaktion är viktig. I detta syfte har en omfattande litteraturstudie genomförts inom området tåg-spår-brodynamik. De styrande parametrarna i 2D tåg-brosystem har studerats vidare i en parameterstudie. Två-nivå faktorförsök har tillämpats för att studera effekten av parametervariationer samt den ytterligare effekten av samtidiga förändringar i flera parametrar. Effekten av valet av lastmodell sattes därmed i relation till effekten av andra parametervariationer. Resultaten visar att resonans kan uppstå från godstrafik inom ett realistiskt hastighetsintervall (< 150 km/h). Vid dessa resonanstoppar kan en betydande minskning av broresponsen erhållas med en tåg-bro-interaktionsmodell. Från studien av nyckelparametrar kan man vidare dra slutsatsen att reduktionen som erhålls med en tåg-bro-interaktionsmodell beror på flera systemparametrar, både för gods- och passargerartåg. Enligt de europeiska normernas rekommendationer för dynamisk kontroll av broar för passagerartrafik kan en ökad brodämpning introduceras som ett förenklat sätt att ta hänsyn till minskningen från tåg-bro-interaktion. Mängden tilläggsdämpning anges idag som en funktion av enbart brons spännvidd, vilket är en grov förenkling. Det arbete som presenteras i denna avhandling visar på behovet av en förbättrad definition av tilläggsdämpningen.

QC 20140429

The diploma thesis deals with dynamic analysis of cable-stayed steel pedestrian footbridge. The dynamic response of pedestrian-induced vibration was studied. The response of structure exeeded standard acceptance limit. Due to the effect of installed Tuned Mass Damper was studied. Motion equations of single and two degree of freedom model were solved in program MATLAB and the results were compared with numeric model in ANSYS.

Cette thèse porte sur l’étude du dévissage spontané d’assemblages vissés, sous sollicitations dynamiques transversales. Un travail expérimental et numérique a été réalisé pour caractériser ce phénomène, dans des conditions proches de celles des assemblages réels. Une expérimentation a permis de provoquer le dévissage d’un boulon, en soumettant l’assemblage à des vibrations transversales par rapport à l’axe de la vis. Les effets de la précharge, du traitement de surface et de la disposition des vis ont été explorés. Ces résultats ont été confrontés avec ceux obtenus par un modèle numérique détaillé utilisant la méthode des éléments finis. Cependant, en raison de la complexité de la géométrie et des difficultés de modélisation à l’échelle locale, le temps de calcul est très important et peut être prohibitif pour une étude industrielle. Afin de remédier à cette difficulté, des modèles simplifiés ont été développés, l’un avec une approche par éléments finis associés à un connecteur cinématique, et l’autre par modélisation unidimensionnelle. Ces modèles simplifiés reproduisent correctement le phénomène du dévissage spontané et confirment leur efficacité en gain de temps de calcul
This thesis focuses on the study of the self-loosening of bolted joints under transverse dynamic loads. Experimental and numerical work was carried out in order to reveal this phenomenon under conditions close to those of actual assemblies. An experiment allowed the loosening of a bolt to be caused by subjecting the assembly to transverse vibration with respect to the axis of the screw. Effects of preload, surface treatment and disposal of the screws were explored. These results were compared with those obtained by a detailed numerical model using the finite element method. However, due to the complexity of the geometry and modeling challenges at the local level, the computation time was very long and may be prohibitive for an industrial study. To remedy this problem, two simplified models were developed, one with a finite element approach associated with a kinematic connector, and one by unidimensional modeling. These simplified models correctly reproduce the self-loosening phenomenon and confirm their efficiency in terms of computation time

Efterfrågan på höga byggnader ökar i städerna och eftersom hållbarhet är ett viktigt ämne i samhället har intresset för och användandet av trä i höga byggnader ökat de senaste åren. Träbyggnaders flexibilitet och låga vikt gör att svängningar orsakade av horisontella dynamiska vindlaster i bruksgränstillståndet kan uppfattas som störande av personer som vistas i byggnaden och därav bli styrande för dimensioneringen av byggnaden. I detta examensarbete studeras en hybridlösning som använder sig av en vertikalt bärande och horisontellt stabiliserande kärna av KL-trä samt byggs upp med lätta prefabricerade volymelement. Syftet med arbetet är att ta fram en lämplig uppbyggnad och studera dess dynamiska egenskaper samt studera hur förändringar av kärnans parametrar och uppbyggnad påverkar de dynamiska egenskaperna. Målet är att erhålla svar på maximalt antal våningar för respektive alternativ uppbyggnad samt utöka förståelsen på kärnans inverkan på byggnadens dynamiska respons. Byggnaden modelleras upp enligt fyra olika huvudstrukturer där Struktur 1 är byggnadens grundmodell enligt dess enklaste uppbyggnad, inom Struktur 2 varierar KL-träkärnans väggtjocklek, inom Struktur 3 varierar KL-träkärnans storlek och inom Struktur 4 adderas horisontalstabiliserande väggar till KL-träkärnan. I alla modeller antas volymelementen ej bidra till byggnadens globala stabilitet och därför modelleras de in som massor. De olika strukturerna modelleras upp i FEM-programvaran Robot Structural Analysis där en modalanalys utförs för att erhålla byggnadens egenfrekvenser och svängningsmoder. Därefter beräknas toppaccelerationen hos svängningarna, orsakade av dynamisk vind, på golvbjälklaget i byggnadens översta våning ut för hand för att jämföras mot komfortkrav i ISO 10137. Resultaten visar att byggnaden generellt sett har låga egenfrekvenser vilket beror på en förhållandevis hög massa och relativt låg styvhet hos strukturen. Struktur kan uppföras till 20 våningar under de förhållanden som använts i beräkningarna. Förändringar i kärnans tjocklek förstyvar byggnaden något vilket gör att Struktur 2 bör kunna uppföras ett par våningar högre. Förändringar i kärnans storlek visar sig ha en relativt stor påverkan på byggnadens styvhet och därför kan Struktur 3 uppföras till 24 våningar då kärnan är 25 % större i alla riktningar. För Struktur 1, 2 och 3 sker svängning först i y-led, sedan i x-led och sist som vridning kring z-axeln. För Struktur 4 visar sig styvheten påverkas mycket av att stabiliserande väggar adderas till kärnan, dock kan även svängningsriktningar för första och andra svängningsmod förändras och det bör kontrolleras så att problem med vridningssvängningar inte uppkommer. Om stabiliserande väggar läggs till i y-riktning, x-riktning samt del av fasad kan Struktur 4 uppföras hela 28 våningar, med förhållandevis god marginal. Som förslag på fortsatt arbete bör en statisk dimensionering utföras för att vidare utreda om uppbyggnaden är lämplig vad gäller bland annat tvärsnittstorlekar och infästningar. Dessutom bör det undersökas om och hur volymelementens styvhet kan användas för att bidra till strukturens globala stabilitet. Då kärnans storlek har en stor påverkan på byggnadens styvhet bör det utredas ifall lämpliga planlösningar kan arbetas fram med större eller till och med dubbel kärna för att sedan utföra en dynamisk dimensionering på strukturen. Då planlösningen enligt denna och andra studier bedöms ha potential för att bygga högt, vore en jämförelse av olika planlösningar intressant där förslagsvis byggnadens yttermått och form samt placering och antal stabiliserande KL-träkärnor varierar.
The demand on high-rise buildings grows in the cities and since sustainability is an important matter in today’s society, the interest for high-rise timber buildings has grown the past years. The flexibility and weight of timber buildings makes wind-induced vibrations in serviceability limit state an issue that can be deciding for the design of the building since people can find the vibrations disturbing. In this study, a building which uses a vertically load-bearing and horizontally stabilising CLT core and is built-up with light prefabricated volume elements. The objective of this study is to produce a suitable structure and study its dynamic properties and how changes of the core’s parameters and design may change the dynamic properties of the building. The goal is to find the maximum number of floors that can be built for each alternative structure and to expand the knowledge on how the CLT core impacts the dynamic response of the building. The building is modelled by four different main structures where Structure 1 is the building’s basic and most simple model, within Structure 2 the CLT core’s wall thickness varies, within Structure 3 the CLT core’s size varies and within Structure 4 horizontally stabilising walls are added to the core. In all of the models, the volume elements are assumed not to contribute to the global horizontal stability of the building which is why they are modelled as masses. The different structures are modelled into the FEM software Robot Structural Analysis where a modal analysis is being carried out to find the building’s natural eigenfrequencies and modes of vibrations. Subsequently, the top acceleration of the wind-induced vibrations is calculated on the floor slab of the top floor by hand to be compared to comfort limits in ISO 10137. The results show that the building has low eigenfrequencies in general, which is due to the structure’s relatively high mass and low stiffness. Structure 1 can be built up to 20 floors under the conditions used in the calculations. Changes of the core’s wall thickness stiffen the building which means that Structure 2 should be able to build a couple of floors higher. Changes in the size of the core have a relatively large impact on the rigidity of the building and therefore Structure 3 can be built up to 24 floors when the core is 25 % larger in all directions. For Structure 1, 2 and 3, swaying occurs first in the y-direction, second in the x-direction and third as twist around the z-axis. For Structure 4, the rigidity is greatly influenced when stabilising walls are added to the core. However, the direction of the first and second modes of vibration can change and it should be verified that problems with twisting oscillation does not occur. If stabilising walls are added in the y-direction, x-direction and part of the façade, Structure 4 can be built up to 28 floors with a relatively good margin. As a proposal for further work, a static design should be performed to further investigate whether the structure is suitable for e.g. cross-sectional sizes and connections. It should also be examined if and how the rigidity of the volumes can be used to contribute to the global stability of the structure. As the size of the core has a major impact on the rigidity of the building, it should be investigated if a suitable floor layout can be arranged with larger or even double cores and then perform a dynamic design on the structure. As the floor layout, according to this and other studies, is considered to have great potential when building high, a comparison of different floor plans would be interesting where e.g. the external dimensions and shape of the building, as well as the placement of the CLT core and number of cores can vary.

Methode de calcul d'une force statique equivalente pour representer l'action du vent sur une structure basse type (halle industrielle), avec determination de coefficients de pression dans une approche reglementaire. Pour les structures elevees, ou l'aspect dynamique est preponderant, developpement d'un logiciel a partir du modele vickery-basu (structure elancee a section circulaire); determination des parametres aerodynamiques a partir de donnees experimentales

Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.15.04 «Шахтне та підземне будівництво». – ДВНЗ «Національ-ний гірничий університет», Дніпропетровськ, 2012.
Диссертация на соискание ученой степени кандидата технических наук по специальности 05.15.04 «Шахтное и подземное строительство». – ГВУЗ «Национальный горный университет», Днепропетровск, 2012.
Thesis for obtaining scientific degree of candidate of technical sciences by speciality 05.15.04 – «Mining and underground construction». – State Institution of Higher Education «National Mining University», Dnipropetrovs’k, 2012.
Дисертацію присвячено розв’язанню актуального науково-технічного завдання обґрунтування параметрів прогонових будов поверхні шахт з урахуванням переходу на полегшені огороджувальні конструкції на підставі закономірностей зміни динамічних характеристик. Результати комп’ютерного моделювання методом скінченних елементів та теоретичних розрахунків дозволили проаналізувати динамічні процеси у прогонових будовах галерей і встановити закономірності порушення їх міцності. Отримані експериментальним шляхом динамічні характеристики прогонових будов використано для оцінювання міцності, стійкості та витривалості динамічно навантажених конструкцій прогонових будов. Закономірності, отримані в результаті комп’ютерного моделювання динамічних процесів галерей, використано для розробки рекомендацій з визначення ширини резонансної зони та величини коефіцієнта динамічності прогонових будов у комплексі будівель і споруд поверхні шахт гірничодобувних підприємств Криворізького басейну за умови переходу на полегшені огороджувальні конструкції.
Диссертация посвящена решению актуальной научно-технической задачи обоснования параметров пролетных строений поверхности шахт с учетом перехода на облегченные ограждающие конструкции на основе закономерностей изменения динамических характеристик. В работе выполнен системный анализ современного состояния и основных тенденций развития проектирования пролетных строений на поверхности горнодобывающих предприятий. Для моделирования напряженно-деформированного состояния пролетных строений был использован вычислительный комплекс SCAD, широко используемый в практике инженерного анализа как в Украине, так и за рубежом. Проверка аналитических методов расчета методом конечных элементов в программе SCAD для ряда математических моделей показал, что принятые допущения, используемые в моделях в аналитическом методе, не оказывают значительного влияния на характер поведения и численные значения амплитудно-частотных характеристик. Результаты компьютерного моделирования методом конечных элементов и теоретических расчетов позволили проанализировать динамические процессы в пролетных строениях галерей и установить закономерности нарушения их прочности. Выполнены экспериментальные исследования напряженно-деформированного состояния пролетных строений в комплексе зданий и сооружений поверхности шахт горнодобывающих предприятий Криворожского бассейна. Полученные экспериментальным путем динамические характеристики пролетных строений использованы для оценки прочности, устойчивости и выносливости динамично нагруженных конструкций пролетных строений. Закономерности, полученные в результате компьютерного моделирования динамических процессов, использованы для разработки рекомендаций по определению ширины резонансной зоны и величины коэффициента динамичности пролетных строений в условиях перехода на облегченные ограждающие конструкции. На основании впервые установленных закономерностей изменения амплитудно-частотных характеристик пролетных строений от различного характера внешних нагрузок и геометрических параметров ограждающих конструкций решена актуальная научная задача установления закономерностей изменения жесткости и частот собственных колебаний галерей при условии перехода на облегченные ограждающие конструкции. Сопоставление теоретических и экспериментальных результатов производилось на основании сравнения частот колебаний, максимальных перемещений. Установленное удовлетворительное соответствие этих факторов является достаточным для вывода о достоверности математической модели. Внедрение эффективных ограждающих конструкций пролетных строений на основе использования разработанных рекомендаций по определению рациональной массы пролетного строения позволяет получить экономический эффект на одной транспортерной галереи 299 тыс. грн.
Thesis is devoted to the urgent scientific and technical problem explanation analysis of span structures on the mines surface characteristics with account of transition to eased cladding structures on the basis of dynamic characteristic principles. Computer simulations results by finite elements and theoretical calculation methods allowed analyzing the dynamic processes in span structures galleries and establishing principles of its strength defection. Experimentally obtained dynamic processes in span structures are used for strength, resistibility, endurance evaluation of dynamically loaded span structures. Obtained results based on the results of dynamic processes in galleries structures are used for recommendation formulation to determine the resonance zone width and dynamic index value of span structures under conditions of transition to eased cladding structures. Implementation of effective cladding structures of span structures allows reducing the cost of span structures reconstruction an average of 10…20 %.

In this diploma thesis the seismic load on two different models is solved – the first model is a beam hall and the second model is a multistory building. The calculation of seismic load was performed according to standard ČSN EN 1998-1 (Eurocode 8) using the response spectrum analysis and the method of equivalent static forces (substi-tute load). For the combination of seismic responses in different directions are used SRSS and CQC rules. Models and calculations were solved in a student’s version of program RFEM 4.10 (Ing. Software Dlubal, s.r.o.). The comparison of mentioned methods in each models, also the comparison of combinative rules in calculation and the final evaluation of seismic responses on both of models are the subject of this thesis.

This master thesis deals with the dynamic analysis of a footbridge. Computational model of the footbridge was created using ANSYS software. The model was subjected to dynamic wind load in longitudal and lateral direction. Furthermore pedestrian load in lateral direction was analyzed. Afterwards, due to unsatisfactory response to the pedestrian laod, a tuned mass damper was introduced to reduce the vibration. This lead to decrease in the vibration to a satisfactory levels, as is shown in the analyses of the model.

Background Whole-body vibration (WBV) as a training modality is established in the fields of sport, fitness, rehabilitation, and clinical intervention. WBV exercises are performed thereby while standing on a motor driven oscillating platform device. Therefore, the scientific interest in WBV is a steadily increasing field in sports science and research. It has been shown that WBV training elicits various biological and physiological effects in men. Nevertheless, there are only a small number of studies examining WBV effects on neuromuscular performance of the lower extremities in elderly people. Furthermore, the results of these studies show many discrepancies that may be caused by limitations referring to the different applied training protocols and vibration loads. In addition, there is still a deficit of information for effective but safe recommendations for WBV application for trunk and neck muscles. Therefore, this doctoral thesis deals with three major aspects of WBV as an exercise modality in strength training: (1) the recommendation of optimal vibration loads (VbLs) for the lower extremities as an essential element of the WBV exercise parameters in older adults, (2) the evaluation of these VbLs in a WBV training intervention for elderly people with regard to feasibility and chronic effects on neuromuscular performance of the lower limbs, and (3) the allocation of information for effective but safe advices for VbLs for trunk and neck muscles. These aspects are further specified toward five hypotheses (H1, H2, H3, H4, and H5) by findings and limitations of the current state of literature. Methods The five hypotheses are evaluated within three research papers (studies 1 to 3). The first study (S1) evaluated the optimal VbL determined by the combination of three biomechanical variables (vibration frequency, vibration amplitude, and knee angle) in older adults (H1). Therefore, the neuromuscular activity of the quadriceps femoris and hamstring muscles in 51 healthy subjects were measured during WBV exposure using surface electromyography (EMG). Maximal voluntary contractions (MVCs) were conducted prior to the measurements to normalise the EMG signals. A three-way mixed ANOVA was performed to analyse the different effects of the biomechanical variables on muscle activity. Study 2 (S2) represents a randomised controlled trial to assess the results of S1 implemented in a WBV training protocol and therefore to evaluate the feasibility and effectiveness of a six-week WBV intervention (H2, H3, and H4). A total of 21 subjects was allocated randomly into either a WBV training or control group. While the WBV group completed a six-week WBV training programme the control group was asked not to change their current level of physical activity during the study. Before and after the intervention period, jump height was measured during a countermovement jump (CMJ). In addition, isokinetic knee extension and flexion strength parameters were recorded using a motor-driven dynamometer. The Borg scale for ratings of perceived exertion (RPE scale) was used to evaluate the intensity of WBV exercises within each training session. Changes from pre- to posttest were analysed by a paired sample t-test (within-group comparisons) and independent sample t-test (between-group comparisons). The intention of study 3 (S3) was to analyse the impact of biomechanical variables on neuromuscular activity of different trunk and neck muscles during WBV (H5) filling the lack of information in current literature. Those biomechanical variables were assumed, which current literature suggests as having the lowest risk of negative side effects on the head. Surface EMG was used to record the neuromuscular activity in 28 healthy subjects. EMG signals were normalised to prior measured MVC. Different effects of the biomechanical variables were analysed by an ANOVA for repeated measurements. Results The findings of S1 showed that the biomechanical variables affect the level of neuromuscular activity of thigh muscles in older adults in different dimensions which confirms H1. The maximum levels of muscle activity were significantly reached at high amplitude and high frequency, whereas the factor “knee angle” only significantly affected the quadriceps femoris. Furthermore, WBV led to a higher muscle activation of the quadriceps femoris (74.1 % MVC) than of the hamstring muscles (27.3 % MVC). The main findings in S2 were an increased multi-joint strength performance of the lower limbs during a countermovement jump in the WBV group, whereas values of the control group remained unchanged after the intervention, thus confirming H2. There were no statistically significant differences in isokinetic maximal strength, mean power, or work values in knee extension or flexion in both groups (rejecting H3). In addition, the subjective perceived exertion of the WBV exercises and respective training parameters ranged between moderate rating levels of 7 and 13 of the Borg scale and indicate WBV intervention as a feasible and safe training program for elderly people, which is consistent with H4. Finally, the outcomes of S3 confirmed H5 as the biomechanical variables affect the level of neuromuscular activity of the trunk and neck in different dimensions. The maximum levels of muscle activity were significantly reached at high amplitude and high frequency, while knee angles had similar effects on the VbL. WBV led to a higher muscle activation of the lower back muscles (27.2% MVC) than of neck muscles (8.5 % MVC) and the abdominal muscles (3.6 % MVC). Conclusion A maximised VbL for WBV training in older adults depends on specific combinations of the biomechanical variables (vibration frequency, vibration amplitude, and knee angle). In addition, a WBV training based on this age-specific high VbL is a feasible, suitable and effective training program for elderly people to prevent age-related reduction of muscle performance in the lower extremities. Furthermore, the combination of biomechanical variables recommended in literature as safe for preventing harmful transmissions to the head, only elicit low to moderate muscle activation of the upper body. The findings of this thesis represent fundamental research in the field of WBV and may help to improve further research in this area. Finally, this thesis may help coaches and therapists to enhance the quality of WBV training in practical application
Hintergrund Ganzkörpervibration (Whole-Body Vibration, WBV) hat sich als Trainingsanwendung im Sport-, Fitness, Rehabilitationsbereich und klinischen Bereich etabliert, wobei die Übungen dabei im Stehen auf einer Vibrationsplatte durchgeführt werden. In diesem Zusammenhang ist auch das wissenschaftliche Interesse am Vibrationstraining ein stetig wachsendes Feld in den Bereichen der Sportwissenschaft und Forschung. Bisher konnte gezeigt werden, dass Vibrationstraining verschiedene biologische als auch physiologische Reaktionen beim Menschen hervorruft. Dennoch gibt es nur wenige Untersuchungen, die sich mit den Auswirkungen des Vibrationstrainings auf die neuromuskuläre Leistung der unteren Extremitäten bei älteren Menschen beschäftigen. Des Weiteren weißen die Ergebnisse dieser wenigen Studien viele Widersprüchlichkeiten auf, welche durch die unterschiedlich verwendeten Trainingsvorgaben und Vibrationsbelastungen verursacht sein könnten. Darüber hinaus besteht noch ein großes Defizit an grundlegenden Informationen hinsichtlich effektiver, aber dennoch sicherer Vorgaben in der Anwendung des Vibrationstrainings im Bereich der Rumpf- und Nackenmuskulatur. Vor diesem Hintergrund beschäftigt sich die vorliegende Dissertation mit drei wesentlichen Aspekten des Vibrationstrainings: (1) die Empfehlung von optimalen Vibrationsbelastungen (VbL) als wesentlicher Bestandteil des Vibrationstrainingsplans der unteren Extremitäten älterer Menschen, (2) die Evaluierung dieser VbL anhand einer auf Vibrationstraining basierter Intervention mit älteren Menschen hinsichtlich Durchführbarkeit und Auswirkungen auf die neuromuskuläre Leistung der unteren Gliedmaßen, und (3) Angaben für effektive und sichere VbL für Rumpf- und Nackenmuskulatur bereitzustellen. Mit der Aufarbeitung von Ergebnissen und Defiziten des aktuellen Forschungsstands werden diese Aspekte durch die Formulierung von fünf Hypothesen (H1, H2, H3, H4, and H5) weiter spezifiziert. Methodik Die fünf Hypothesen werden in drei wissenschaftlichen Veröffentlichungen (Studie 1 bis 3) untersucht. Die erste Studie (S1) befasste sich mit der optimalen VbL für ältere Personen (H1), welche durch die Kombination von drei biomechanischen Variablen (Vibrationsfrequenz, Vibrationsamplitude und Kniewinkel) bestimmt wird. Hierzu wurde die neuromuskuläre Aktivität der vorderen und hinteren Oberschenkelmuskulatur von 51 gesunden Probanden unter Vibration mittels Oberflächen-Elektromyografie (EMG) gemessen. Vor den Messungen wurden maximale muskuläre Kontraktionen durchgeführt, um die EMG zu normalisieren. Um die unterschiedlichen Auswirkungen der biomechanischen Variablen zu analysieren wurde eine drei-faktorielle Varianzanalyse durchgeführt. Studie 2 (S2) entspricht einer randomisierten kontrollierten Studie, welche die Ergebnisse aus S1 in einem Trainingsplan verwendet, um die Durchführbarkeit und Effektivität eines sechs wöchigen Vibrationstrainings zu untersuchen (H2, H3, und H4). Hierfür wurden 21 Probanden zufällig einer Vibrationstrainings- oder einer Kontrollgruppe zugeteilt. Während die Vibrationsgruppe ein sechs wöchiges Vibrationstraining absolvierte, wurden die Teilnehmer der Kontrollgruppe gebeten ihre körperliche Aktivität während des Studienzeitraums nicht zu verändern. Vor und nach dem Untersuchungszeitraums wurde die Sprunghöhe während eines „countermovement jump“ (CMJ) erfasst. Weiterhin wurden isokinetische Kraftmessgrößen der Kniegelenkbeugung und –streckung an einem Dynamometer ermittelt. Die Borgskala zur Erfassung des subjektiven Belastungsempfindens wurde eingesetzt, um die Intensität der Übungen des Vibrationstrainings innerhalb einer Trainingseinheit zu messen. Veränderungen der Messgrößen zwischen Eingangs- und Abschlusstest wurden statistisch mit einem t-Test für abhängige (innerhalb einer Gruppe) und einem t-Test für unabhängige Stichproben (zwischen den Gruppen) untersucht. Ziel der dritten Studie (S3) war es den Einfluss der biomechanischen Variablen auf die muskuläre Aktivierung verschiedener Rumpf- und Nackenmuskeln (H5). Hierzu wurden solche biomechanische Variablen ausgesucht, welche laut derzeitigem Wissensstand jeweils das geringste Risiko von Nebenwirkungen für den Kopf ausüben. Mittels Oberflächen-EMG wurde die muskuläre Aktivität von 28 Probanden erfasst. EMG Signale wurden zu vorangegangenen MVC Messungen normalisiert. Die Unterschiedlichen Effekte der biomechanischen Variablen wurden mittels einer Varianzanalyse für Messwiederholungen analysiert. Ergebnisse Die Ergebnisse von S1 konnten zeigen, dass die biomechanischen Variablen den neuromuskulären Aktivierungsgrad der Oberschenkelmuskulatur bei älteren Personen unterschiedlich beeinflussen und somit H1 bestätigen. Der höchste Grad der Aktivierung wurde deutlich mit einer großen Amplitude und hohen Frequenz erreicht, wobei der Kniewinkel ausschließlich die vordere Oberschenkelmuskulatur beeinflusst. Zudem, führte der Vibrationseinfluss zu einer größeren Muskelaktivität der Oberschenkelvorderseite (74.1 % MVC) als der –rückseite (27.3 % MVC). Die Resultate von S2 hinsichtlich des CMJ Tests bestätigen H2, da es in der Vibrationstrainingsgruppe zu einer gesteigerten gelenksübergreifender Kraftleistung in den Beinen kam, aber keine Veränderungen in der Kontrollgruppe feststellbar waren. Hingegen kam es in keiner Gruppe zu statistisch signifikanten Veränderungen der isokinetischen Messgrößen (Maximalkraft, Kraftleistung, Muskelarbeit), wodurch H3 abgelehnt wird. Das subjektive Belastungsempfinden der Übungen und des Belastungsgefüges des Vibrationstrainings liegt zwischen moderaten Bewertungsstufen von 7 bis 13 der Borgskala und weist daraufhin, dass Vibrationstraining ein praktikables und sicheres Übungsprogramm für ältere Menschen ist und somit H4 bestätigt. Die Ergebnisse von S3 konnten H5 bestätigen, da die biomechanischen Variablen den neuromuskulären Rumpf- und Nackenmuskulatur unterschiedlich beeinflussen. Der höchste Grad der Aktivierung wurde deutlich mit einer großen Amplitude und hohen Frequenz erreicht, wobei der Kniewinkel sich ähnlich auf die VbL auswirkt. Der Vibrationsstimulus führte zudem zu einer höheren Aktivierung der unteren Rückenmuskulatur (27.2% MVC) als der Nacken- (8.5 % MVC) und Bauchmuskulatur (3.6 % MVC). Schlussfolgerungen Die maximale muskuläre Belastung älterer Personen in einem Vibrationstrainings hängt von bestimmten Kombinationen der biomechanischen Variablen (Vibrationsfrequenz, Vibrationsamplitude und Kniewinkel). Zudem ist ein Vibrationstraining, das auf altersspezifischen Vibrationsbelastungen basiert ein machbares, angemessenes und effektives Trainingsprogramm für älteren Menschen, um einem altersbedingten Abnehmen der muskulären Leistungsfähigkeit vorzubeugen. Weiterhin führt die Verbindung von biomechanischen Variablen, welche laut bisherigem Forschungsstand als sicher gegen schädliche Vibrationsübertragungen zum Kopf gelten, nur zu leichten bis moderaten Muskelaktivierung im Oberkörper. Die Ergebnisse dieser Dissertation liefern einen Beitrag zur Grundlagenforschung auf dem Gebiet des Vibrationstrainings und können weiteren Forschungsarbeiten hilfreich sein. Darüber hinaus kann diese Arbeit helfen die Qualität von Vibrationstrainingsangeboten zu verbessern und somit zum praktischen Nutzen beitragen

This project studies the dynamic response of a composite floor system to excitations from moving fork-lift trucks. The floor system analysed is a system of precast and partially prestressed double-tee elements with a cast in-situ topping. Currently, there are concerns whether the vibrations caused by fork-lift trucks might exceed acceptable limits due to an ongoing trend towards structures of higher slenderness. This study investigates the mechanical background of the excitation and the current design of the floor system. The study is divided into three major chapters: Dynamic fork-lift truck model A dynamic load model of a fork-lift truck is developed which can be used in the analytical verification of the vibration serviceability of structures. The model is based on tests performed on four fork-lift trucks in various configurations. The tests are analysed for the spectrum of accelerations. The analysis results in a simple two-degree-of-freedom model. Its only variables are velocity and time. All other values are constant throughout a simulation and depend on the geometry of the specific fork-lift truck and its payload. The frequencies and phase delays are constants and they are verified as eigen-frequencies of a three-degree-of-freedom model. FE-simulation of vibrations of a composite floor system The fork-lift truck model is applied to a three-dimensional model of a composite floor system. The finiteelement model is developed to simulate the construction process of the composite floor system and its influence on the in-service properties of the structure. As part of this work a preliminary investigation of the damping potential of the joint between precast and cast in-situ concrete is undertaken. A linear time-step analysis of the structure is performed and the nodal accelerations are analysed for their magnitude, dependence on the excitation and frequency content. Field test In order to verify the FE-model of the floor system and the results of the dynamic analysis a field test was undertaken: a floor system was monitored under service conditions. The field data comprise the accelerations of the floor and the forklift truck and the position of the truck relative to the points of measurement. A comparison of the field data and the simulation results proves the validity of both the dynamic fork-lift truck model and the FE-model of the floor system.

Random vibration coupled with thermal cycling is a common environment for a lot of mechanical and electrical products, especially for those experiencing transportation and handling frequently. Today, random vibration plus thermal cycling have been broadly applied as an important stimulus stress to expose the latent defects during development. In addition, drop tests are also necessary for these products since an accidental drop may seriously damage them. Both random vibration and drop tests are expensive. Plate element is popular in portable and transportation related products, for example, the Printed Circuit Boards (PCBs) in equipment installed in vehicles, the Liquid Crystal Displays (LCDs) in portable computers and the skin panels near the engines in airplanes. These plate elements are subjected to random vibration and thermal cycling, and some of them may encounter a drop. Even through the deterministic vibration theory of plates has been developed a lot, the random vibration theory of plates has not been well explored yet, particularly in reliability quantification, response analysis, and thermal load effect. In this dissertation, a random vibration analysis model for packaged plates is proposed for base excited random vibration coupled with temperature loads. Based on this model, a reliability quantification model is proposed, too. Two common random vibration power spectral densities "Ideal White Noise (IWN)" and "Band Limited White Noise (BLWN)" are researched. As a result, the closed form solution for IWN is derived and the numerical procedure for BLWN is presented. By comparing the IWN results with the BLWN results, an application limit to IWN is discovered. The effects of temperature and damping on reliability are then investigated. For the drop load case, the response process and the reliability are researched, and the illustrative example is given to demonstrate the methodology. The research results of the dissertation may supply designers with guidelines and supplement testing with analytical data; therefore, the test cost can hopefully be cut down. The methodologies can be applied to the evaluation of transportation reliability.

There is a need to investigate and improve upon existing methods to predict response of sensors due to flow-induced vibrations in a pipe flow. The aim was to develop a tool which would enable an engineer to quickly evaluate the suitability of a particular design for a certain pipe flow application, without sacrificing fidelity. The primary methods, found in guides published by the American Society of Mechanical Engineers (ASME), of simple response prediction of sensors were found to be lacking in several key areas, which prompted development of the tool described herein. A particular limitation of the existing guidelines deals with complex stochastic stationary and non-stationary modeling and required much further study, therefore providing direction for the second portion of this body of work. A tool for response prediction of fluid-induced vibrations of sensors was developed which allowed for analysis of low aspect ratio sensors. Results from the tool were compared to experimental lift and drag data, recorded for a range of flow velocities. The model was found to perform well over the majority of the velocity range showing superiority in prediction of response as compared to ASME guidelines. The tool was then applied to a design problem given by an industrial partner, showing several of their designs to be inadequate for the proposed flow regime. This immediate identification of unsuitable designs no doubt saved significant time in the product development process. Work to investigate stochastic modeling in structural dynamics was undertaken to understand the reasons for the limitations found in fluid-structure interaction models. A particular weakness, non-stationary forcing, was found to be the most lacking in terms of use in the design stage of structures. A method was developed using the Karhunen Loeve expansion as its base to close the gap between prohibitively simple (stationary only) models and those which require too much computation time. Models were developed from SDOF through continuous systems and shown to perform well at each stage. Further work is needed in this area to bring this work full circle such that the lessons learned can improve design level turbulent response calculations.
Ph. D.

Reliability quantification is one of the most important tasks in Reliability Engineering. During the design, development, and operational phase, this information can be very valuable to the product's designers, and users. The designers can use it to guide their design, find the design's weak points. Users can use it to setup maintenance plans and schedule. PCBs, as the major building block of electronic equipment, have been widely used in modern complex systems, such as aircraft, automotives, laptop computers, etc. Its reliability plays a vital role in the whole system's reliability. Thus, effective and accurate quantification of PCB's reliability becomes very essential to the whole electronic system's reliability quantification. Random vibration and thermal cycling are two common environments experienced by PCB's. As a result, quantifying the reliability of a PCB under these two environments becomes necessary. Currently, in industry, the commonly used methods to quantify the reliability of a PCB are the MIL-HDBK-217 and Bellcore type methods. However, the lack of accuracy and slow pace of updating the databases have limited the usage of these methods. In this dissertation, a Modified Stress-Strength Interference (MSSI) method is proposed to quantify the reliability of a PCB. In this method, not only the stress and the strength are assumed to be distributed, but also is the mean value of the strength, so that both the initial designed-in reliability and the reliability at any time can be quantified. Based on this method, a reliability quantification model for the PCB is developed. In this model, a PCB is divided into three parts: i.e., board, interconnects, and parts and modules mounted on the board. Seven (7) failure modes related to the board and the interconnects, and one (1) failure mode related to the module have been investigated. The dependence between these failure modes is studied and incorporated into the reliability quantification model. A three-step popcorn effect reliability quantification model is also proposed by means of considering the failure mechanism of the popcorn effect. Finally, a comprehensive example is given to demonstrate the usage of the methodology proposed in this dissertation.

Мета дисертаційної роботи полягає у визначенні напружено-деформованого стану відповідальних конструкцій будівель і споруд при впливі вібродинамічних навантажень метрополітену, які можуть призвести до часткового або повного руйнування несучих конструкцій будівлі. На основі проведених експериментально-теоретичних досліджень, вирішена наукова задача, що полягає у розробці методики оцінки вібродинамічного впливу від дії метрополітену, яка використана для ретроспективного нелінійного аналізу будівлі, на яку поширюється цей вплив. Автором запропоновано: − при новому будівництві цивільних будівель у зоні впливу метрополітену, рекомендується використовувати методику розрахунку на вібродинамічні навантаження із урахуванням фактору часу, а також проводити заходи щодо захисту конструкцій або будівель у вигляді демпфуючих пристроїв, або використовувати демпфуючі властивості ґрунту; − при проведенні реконструкції будівель, рекомендується встановлювати захисні екрани у ґрунті для запобігання негативного впливу від метрополітену на несучі конструкції будівель та споруд.
Цель диссертационной работы заключается в определении напряженно-деформированного состояния ответственных конструкций зданий и сооружений при воздействии вибродинамических нагрузок от метрополитена, которые могут привести к частичному или полному разрушению несущих конструкций здания. Автором предложено: − при новом строительстве гражданских зданий в зоне влияния метрополитена рекомендуется использовать методику расчета на вибродинамические нагрузки с учетом фактора времени, а также проводить мероприятия по защите конструкций или зданий в виде демпфирующих устройств, или использовать демпфирующие свойства почвы; − при проведении реконструкции зданий, рекомендуется устанавливать защитные экраны в почве для предотвращения негативного влияния метрополитена на несущие конструкции зданий и сооружений.
The purpose of the thesis is to determine the stress-strain state of responsible constructions of buildings under the vibrodynamic influences from the subway, that can lead to partial or complete destruction of load-bearing structures. On the basis of the experimental and theoretical researches, the scientific problem was solved. It consists in the development of methodology for estimation vibrodynamic influence from the subway, that is used for the retrospective nonlinear analysis of the building to which this influence applies. The practical value of the work consists in: take into account the factors that can influence the formation of stress-strain state of load-bearing structures under vibrodynamic impacts; provide recommendations for modeling the process of subway impact on load-bearing structures for future consideration in the design. Forecast of stress-strain state in process of designing and reconstructing of buildings allows us to estimate the possible adaptability of buildings and structures to vibrodynamic effects, in addition to traditional methods for determination of the constructive safety by the boundary states. The results of the work were used to provide recommendations in the buildings design in zone of negative impact from subway vibration on bearing structures and for the development of basic methods for protection of structures. The author suggested: − for new construction of civil buildings in zone of influence from the subway it is recommended: to use the methodology for calculating vibrodynamic loads with taking into account the time factor; to protect load-bearing structures of buildings with damping devices, or to use the damping properties of the soil; − for buildings under reconstruction, it is recommended to install protective shields in the soil to prevent the negative impact from the subway on the load-bearing structures of buildings.

In der vorliegenden Arbeit werden Holzwerkstoffe im statischen Biegeversuch und im Schlagbiegeversuch vergleichend geprüft. Ausgewählte Holzwerkstoffe werden thermisch geschädigt, zudem wird eine relevante Kerbgeometrie geprüft. Ziel der Untersuchungen ist die Eignung verschiedenartiger Werkstoffe für den Einsatz in sicherheitsrelevanten Anwendungen mit Schlagbelastungen zu prüfen. Hierzu werden zunächst die Grundlagen der instrumentierten Schlagprüfung und der Holzwerkstoffe erarbeitet. Der Stand der Technik wird dargelegt und bereits durchgeführte Studien werden analysiert. Darauf aufbauend wird eine eigene Prüfeinrichtung zur zeitlich hoch aufgelösten Kraft-Beschleunigungs-Messung beim Schlagversuch entwickelt. Diese wird anhand verschiedener Methoden auf ihre Eignung und die Messwerte auf Plausibilität geprüft. Darüber hinaus wird ein statistisches Verfahren zur Überprüfung auf ausreichende Stichprobengröße entwickelt und auf die durchgeführten Messungen angewendet. Anhand der unter statischer und schlagartiger Biegebeanspruchung ermittelten charakteristischen Größen, wird ein Klassenmodell zum Werkstoffvergleich und zur Werkstoffauswahl vorgeschlagen. Dieses umfasst integral die mechanische Leistungsfähigkeit der geprüften Holzwerkstoffe und ist für weitere Holzwerkstoffe anwendbar. Abschließend wird, aufbauend auf den gewonnenen Erkenntnissen, ein Konzept für die Bauteilprüfung unter Schlagbelastung für weiterführende Untersuchungen vorgeschlagen
In the present work wood-based materials are compared under static bending load and impact bending load. Several thermal stress conditions are applied to selected materials, furthermore one relevant notch geometry is tested. The objective of these tests is to investigate the suitability of distinct wood materials for security relevant applications with the occurrence of impact loads. For this purpose the basics of instrumented impact testing and wood-based materials are acquired. The state of the technology and a comprehensive analysis of original studies are subsequently presented. On this basis an own impact pendulum was developed to allow force-acceleration measurement with high sample rates. The apparatus is validated by several methods and the achieved signals are tested for plausibility. A general approach of testing for adequate sample size is implemented and applied to the tested samples. Based on the characteristic values of the static bending and impact bending tests a classification model for material selection and comparison is proposed. The classification model is an integral approach for mechanical performance assessment of wood-based materials. In conclusion a method for impact testing of components (in future studies) is introduced

Solar energy harvesting using photovoltaic (PV) systems has gained popularity in recent years due to its relative ease of use and its cost efficiency compared to the rest of the clean energy sources. However, to further expand the application of PV systems requires making them more desirable than the other competitive energy sources. The improvement of safety and cost efficiency are requisites for further popularization of PV system application. To satisfy these requisites it is necessary to optimally design the system against the environmental conditions. Wind action is one of the main ambient loads affecting the performance of PV systems. This dissertation aims to investigate the effects of wind load on residential scale roof mounted PV panels and their supporting structures as well as evaluating the structural response of the system to the wind-induced vibration. To achieve these goals, several full- and large-scale experimental tests were performed at the Wall of Wind Experimental Facility at Florida International University (FIU). The wind effects on different PV system and roof configurations were investigated in these tests. The results shed light on the most influential parameters affecting the wind pressures acting on the PV panel surface. In addition, the findings are presented in the form of design pressure coefficients for adoption to future building codes and wind standards. The second phase of the physical testing included the investigation of the actual response of the PV system to the wind action. Because of the dynamic properties of the PV panel, it was expected that the wind induced vibration can affect the dynamic response of the system including the acceleration at the panel surface and support reactions at the racking system to roof interface. To test this theory, two different models of the system were developed, one with the real PV panels and the other one with wooden rigid panels. Comparing the results, it was concluded that the dynamic response of the system was not considerably affected by wind-induced fluctuations. Finally, and to better understand the dynamic response of the system, an analytical model was developed using ANSYS and dynamic analysis was carried out using as input the wind induced pressure data acquired from the physical testing. At the first step, the analytical model was verified by comparing the analytical modal frequencies to the experimental natural frequencies obtained from the hammer test. It was shown that the analytical model can well represent the dynamic properties of the actual model. However, once the reaction output was compared to the loadcell data recorded during the wind tunnel test, there was a considerable discrepancy between the results. It was assumed that the deflection of the supporting structure caused this discrepancy. This assumption was verified and it was concluded that the supporting structure can significantly influence the dynamic response of the system.

This study mainly covers the finite element analysis of a micro satellite structure by considering the vibration effects at the time interval from the launching to the Earth&rsquo
s orbit landing. Micro-satellites have a great importance in the satellite industry and several developing countries deal with micro-satellite design and production. Turkey is one of these countries by conducting new satellite projects. RASAT project is one the continuing micro-satellite project, which has being developed by TÜ
BiTAK Space Technologies Research Institute. In this thesis, the RASAT satellite is taken as the model for the study. On this model, many mechanical design studies which are performed according to the specified requirements and constraints are verified by finite element analyses. These analyses cover all the essential vibration loads during launching. In the study, firstly, a finite element model of RASAT is prepared. Then, the essential analyses are performed according to the specifications required by the launchers. In the analyses, commercially available finite element software is used. Finally all the results obtained from the finite element analyses are compared with the predefined requirements and constraints. The results show that the structural design verification regarding the reliability of the structure for the desired mission has been successfully completed.

Thesis (PhD (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009.
The main research objective of this dissertation was to determine the performance parameters of particle dampers (PDs) under centrifugal loads. A test bench was developed consisting of a rotating cantilever beam with a PD at the tip. Equal mass containers with di erent depths, filled with a range of uniform sized steel ball bearings, were used as PDs. For all the tests, the total PD mass was identical. During operation the tip of the beam was displaced, and after release, the beam could vibrate freely. The decay in the vibratory motion of the tip of the beam was measured over a range of centrifugal loads. The experiments were duplicated numerically with a discrete element method (DEM) model, calibrated against the experimental data. This model could then be used for a more in-depth investigation of phenomena occurring when PDs are under centrifugal loads. From the data analysis, it can be concluded that there are two zones of damping, one with a high and one with a low damping factor. These damping zones depend on the ratio between the peak vibration acceleration and the centrifugal loading. Each zone has a limit in terms of the centrifugal loading beyond which the PD cannot function if the vibration amplitude is fixed. In the high damping zone, it was found that the excitation state of the particles was high enough for the system vibration frequency to change. In the low damping zone, there is only limited motion between the particles. The main parameters that influence the performance of the PDs are the friction between the particles themselves and with the container, the PD length/diameter aspect ratio, and the particle size. An important finding is that a PD with less layers (increase in particle size) will still function at a higher centrifugal load compared to one with a smaller number number of layers.

The vibrational performance of footbridges due to human-induced loads has been investigated, based on modal and pedestrian tests carried out on three prototype footbridges. Analyses using calibrated finite element models of these structures were also conducted. All test structures presented natural frequencies within the range of excitations produced by pedestrians and were therefore suitable for investigating the applicability of some current guidelines for vibration performance. In addition, the inclusion of a footbridge made of glass reinforced plastic in the test programme enabled the performance of this new type of footbridge construction to be investigated. The techniques of ambient excitation, impulse response using an instrumented hammer, and free-vibration decay were employed to obtain the modal properties of the test structures. The practicalities of using these techniques are discussed and improvements in their application are suggested. Very good agreement was obtained between the experimental and the numerical results. The calibrated numerical models were employed to investigate ways of removing the natural frequencies of the structures from the common range of pedestrian excitation, thereby improving their vibration performance. The handrails were identified as a potential way to increase the stiffness and thus the natural frequencies of a structure. In addition, use of a catenary shape or pre-camber in combination with horizontal restraint at the bearings were also shown to be useful for increasing natural frequencies since beneficial axial effects are introduced. In the case of the glass reinforced plastic footbridge, it was shown that a selective distribution of mass that could be conveniently added within the cells of the deck was the best strategy for frequency tuning. Guidelines for vibration performance are suggested, focusing on the definition of the pedestrian load and frequency ranges of interest, acceptability limits to vibration, treatment of multi-frequency component vibrations and vandal loading.

Vibration serviceability in the design of footbridges is gathering enormous prominence as comfort restrictions get enhanced. Comfort verifications are often becoming critical when considering human induced dynamic loading on lightweight structures, which are increasing in slenderness and flexibility. The aim of this work was to build up understanding about the running load effects on the response of footbridges and proving that it could imply a critical load case that would require verification. Additionally, the accuracy of potential models to estimate the structural response was evaluated. Finally, aiming for a practical application, this work provides a step forward towards the possibility of adopting a simplified design methodology to be included in the future guidelines and an insight into the potential effects of a marathon event. While the walking load case is a well-studied phenomenon, not much attention has been paid to the running induced excitation. Guidelines motivate that there is no need for verification and exceptionally, some get to suggest a time domain load model definition. The interaction phenomena as well as the effects of groups of runners in the dynamic response of the structure remain still unknown. Limiting the work to the vertical component of the response and force and based on a large set of additional assumptions, experimental and numerical analyses were performed. Three footbridges were tested and subjected to tests involving different motion forms; jumping, walking and running. On the other hand, the time domain load models available in the literature were applied accounting for the spatial displacement of each of the pedestrians along the footbridge. In the most advanced of the models, aiming to account for interaction effects, the subjects were modelled as independent mechanical systems. The results derived from the experimental study helped characterizing the running load effect on the footbridge's response and proved that there may be structures in which running could comprise a critical load case. Furthermore, the numerical analyses allowed to verify the accuracy of the suggested models and the improvement that the human structure interaction effects involve. The analyses resulted in complementary sets of conclusions that built up understanding about the running load effects on footbridges; such as the sensitivity of the estimated response to the structure's modal properties and the influence of the parameters that characterize the running motion. Finally, the suggested simplified design methodology was able to estimate, with a very reasonable error for the current case study, the calculated response by the most accurate of the models. To sum up, this work serves as a motivation to include the running load case in the guidelines and establishes a starting point for further research and simplified design methodologies based on the strategy and models suggested in this work.

Моргун, С.О. Напруженно-деформований стан конструктивно неоднорідних лопаток турбомашин при їх вібраціях [Текст]: дис. … канд. техн. наук: 01.02.04 : захищена ....: затверджена…. /Моргун Сергій Олександрович. – Запоріжжя, 2015. – 157 с.
UK: Дисертація присвячена визначенню параметрів напружено-деформованого стану конструктивно неоднорідних робочих лопаток турбомашин при їх вібраціях з використанням методу скінчених елементів. Розвинуті і теоретично обґрунтовані ефективні чисельні методи для розв’язання розглянутих в дисертації задач. Досліджено вплив геометричних характеристик лопаток, фізико-механічних властивостей матеріалу, температури газового потоку на частоти та форми коливань і напружено-деформований стан робочих лопаток турбомашин. Достовірність та адекватність розроблених математичних моделей підтверджена співставленням результатів з даними, отриманими з використанням пакету програм ANSYS та експериментально. EN: The thesis is devoted to the non homogeneous cooled single turbine blades and strain-deformed state parameters under vibration load by means of finite elements method usage. The effective numerical methods for the foregoing problems solution are also developed and theoretically approved. The turbine blades geometrical characteristics, their material physical and mechanical state and the gas flow temperature influence on their oscillation forms and frequencies, and strain-deformed state has been researched. The results of the research have been adopted by the obtained results comparison with the ANSYS program package’s solutions and experimental data. RU: Диссертация посвящена определению параметров напряженно-деформированого состояния конструктивно неоднородных лопаток турбомашин при их вибрациях с использованием метода конечных элементов. Приведена постановка и обоснование задач динамического поведения рабочих лопаток турбомашин. Развиты и теоретически обоснованы эффективные численные методы для решения рассмотреных в дисертации задач. Построены уточненные математические модели свободных и вынужденных колебаний, а также напряженно-деформированного состояния, позволяющие адекватно описывать динамическое поведение конструктивно неоднородных рабочих лопаток. Уравнения движения лопаток получены с использованием вариационного принципа Лагранжа II рода. Выполнен анализ сходимости полученных решений. Получены результаты количественного и качественного характера для лопаток с конструктивными неоднородностями, которые характеризуют особенности их поведения при вынужденных колебаниях, вызванных воздействием переменной газодинамической силы. Исследовано влияние геометрических характеристик лопаток, физико-механических свойств материала, температуры газового потока на частоты и формы колебаний и напряженно-деформированное состояние рабочих лопаток турбомашин. Достоверность и адекватность разработанных математических моделей подтверждена сопоставлением полученных результатов с данными, полученными с использованием пакета программ ANSYS и экспериментальным путем. Экспериментальные исследования частот и форм колебаний, как охлаждаемых, так и неохлаждаемых лопаток турбомашин проводились методом голографической интерферометрии. Параметры напряженно-деформированного состояния лопаток определялись на специальном вибровоздушном стенде с применением метода тензометрирования.

Thesis (M.S.)--West Virginia University, 2005.
Title from document title page. Document formatted into pages; contains x, 65 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 63-65).

碩士
國立臺北科技大學
土木與防災研究所
100
In order to understand that the impact of vibration induced by the train on the upper structure. This main purpose of this study is to measure the vibration induced by the passing train and build model by ETABS. The input data are the acceleration time histories that recorded at the location of measurement. The results of the experiment and numerical analysis will compared with each that make the model be accurated. Finally, the structure modal set with TMDS by ETABS may suppress the vibration of structure. The principle of damping vibration is that tunes TMD into the natural oscillation frequency of structure in order for inner material within TMD to vibrate in an opposite direction to an external force. This process allows vibrational energy to be absorbed by decreasing vibration of structure as a result.

碩士
中原大學
機械工程研究所
100
In this study, we discuss the microbeam which are fixed in both ends, and use electric loading of the polarization voltage DC component and the AC component to actuated it. The viscous damping is considered in this microbeam structure. Then calculate the nonlinear natural frequency ratio , linear natural frequency ratio and dimensionless coefficient of the axial force to analyze. By using Hamilton's principle to derived the governing equation of motion , the parameters of influence are included in the model, then merge parameters into non dimensional parameters. After applying Galerkin's method, governing equation of motion is simplified into Mathieu equation with time variable. Finally the effect of the driving voltage and the amplitude on the frequency ratio is discussed and verified the results with the published theoretical and experimental results, then observe the pattern of vibration .

碩士
國立成功大學
工程科學系
105
This study presents the analysis of a circular piezoelectric plate subjected to a uniform load. The circular host plate is aluminum and the bottom surface bonded with a piezoelectric plate. The governing equations and the corresponding boundary conditions of the entire system are obtained by performing Hamilton’s principle. The finite element technique is set for analyzing the behavior of the entire plate. The shape functions of one element are obtained by solving the equations of static equilibrium. The effects of thickness and area of the piezoelectric layer on the displacement of the plate and the electric charge accumulation on the bottom piezoelectric layer are to be investigated.

碩士
國立成功大學
工程科學系
107
The purpose of this paper is to investigate the dynamic response of a piezoelectric sandwich Mindlin Plate. The upper and lower layers of the sandwich plate structure are aluminum alloy plates with piezoelectric material (PZT-5H) in the middle. The stresses and strains of the structure in this paper are calculated via the Mindlin plate theory. The kinetic energy and strain energy are derived by stress and strain. The governing equations of the piezoelectric sandwich plate are derived by Performing Hamilton's Principle. The modal frequencies of the piezoelectric composite plate are obtained by analytic method. Applying a concentrated moving load on the structure obtain the displacement of the plate and the voltage on the piezoelectric layer. The velocity effect on the displacement and voltage is investigated in the thesis.

碩士
國立成功大學
工程科學系
104
This study presents the vibration analysis of piezoelectric Mindlin plate under moving load. The host plate is aluminum and the bottom surface bonded with a piezoelectric plate. The governing equations and boundary conditions of the entire system are derived from performing Hamilton’s principle. The finite element method is adopted to analyze the behavior of the entire plate. The shape functions of one element are constructed from solving the equations of static equilibrium. Newmark’s Integration Method is adopted to analyze the plate’s dynamic response. The effects of thickness and area of the piezoelectric layer on the displacement at the center of the plate and the etymology of electricity on the bottom piezoelectric layer are investigated.