Rozprawy doktorskie na temat „Loading”

Guyed masts are special type of structures that are widely used in the telecommunication industry. In the past, there was no guideline for seismic design of these types of structures in the corresponding design codes. On the other hand, in the latest &ldquo
G&rdquo
revision of the ANSI/TIA-EIA code there is a comprehensive design criterion for the seismic design of the guyed masts. However, during the design process of these structures the most common approach is to ignore the effect of seismic loading and use only the internal forces developed from the wind load and ice load analysis. In this study firstly the efficiency and accuracy of the commercial SAP2000 and PLS-TOWER software were investigated, then finite element models of three guyed masts that had been designed in Turkey with the heights 30m, 60m and 100m in the SAP2000 and PLS-TOWER software were analyzed under the effect of earthquake, wind and ice loadings. The most common design code recognized all over the world used for the design of the guyed masts is ANSI/TIA-EIA 222-G &ldquo
Structural Standards for Steel Antenna Towers and Supporting Structures&rdquo
. Thus, the corresponding sections of this code were followed during the study. The main objective of this research is to check the correctness of commercial SAP2000 and PLS-TOWER software and to investigate the effect of seismic actions on the guyed masts and also to gain a better understanding of the behavior of guyed masts under the effects of the wind, ice and earthquake loadings.

Abstract Ageing populations have made osteoporosis and fragility fractures a major public health concern worldwide. Half of all women and 30% of all men will suffer a fracture related to osteoporosis during their lifetime. While medical prevention of this immense problem is impossible at population level, it is necessary to find efficient preventive strategies. Exercise is one of the major prevention approaches because one reason behind the increasing burden of osteoporosis is the modern sedentary lifestyle. However, the optimal type, intensity, frequency, and duration of exercise that best enhances skeletal integrity are still largely unknown. We conducted a 12-month population-based randomized controlled exercise intervention in 120 premenopausal women. The aim was to investigate the effect of impact exercise on bone mineral density, geometry and metabolism in healthy women with the intention of assessing the intensity and amount of impact loading with a novel accelerometer-based measurement device. Training effects on risk factors of osteoporotic fractures, physical performance and risk factors of cardiovascular diseases were also evaluated. This study demonstrated that 12 months of regular impact exercise favoured bone formation, increased bone mineral density in weight-bearing bones, especially at the hip, and led to geometric adaptations by increasing periosteal circumference. Bone adaptations had a dose- and intensity-dependent relationship with measured impact loading. Changes in proximal femur were threshold-dependent, indicating the importance of high impacts exceeding acceleration of 4 g as an osteogenic stimulus. The number of impacts needed to achieve this stimulation was 60 per day. Impact exercise also had a favourable effect on physical performance and cardiorespiratory risk factors by increasing maximal oxygen uptake, dynamic leg strength and decreasing low-density lipoproteins and waist circumference. Changes were dose-dependent with impact loading at wide intensity range. Bone adapts to impact loading through various mechanisms to ensure optimal bone strength. The number of impacts needed to achieve bone stimulation appeared to be 60 per day, comparable to the same number of daily jumps. If done on a regular basis, impact exercise may be an efficient and safe way of preventing osteoporosis
Tiivistelmä Väestön ikääntymisen ja elintapojen muutosten myötä osteoporoosista ja osteoporoottisista murtumista on tullut maailmanlaajuinen terveysongelma. Ongelman laajuuden vuoksi murtumien lääkkeellinen ehkäisy ei ole mahdollista kattavasti väestötasolla, joten vaihtoehtoisten ehkäisymenetelmien kehittäminen on välttämätöntä. Liikunta on yksi potentiaalinen ehkäisykeino, koska yksi tärkeä tekijä ongelman taustalla on arkiliikunnan vähentyminen. Liikunnan tiedetään hyödyttävän luustoa, mutta optimaalisen liikunnan tyyppi, intensiteetti, määrä ja kesto ovat kuitenkin selvittämättä. Tämän tutkimuksen tavoitteena oli selvittää hyppyharjoittelun vaikutusta 35–40-vuotiaiden naisten luun tiheyteen, geometriaan ja aineenvaihduntaan sekä määrittää luun kannalta optimaalisen harjoittelun määrä ja voimakkuus. Tutkimuksessa selvitettiin myös harjoittelun vaikutuksia fyysiseen suorituskykyyn, sekä sydän- ja verisuonisairauksien riskitekijöihin. Toteutimme väestöpohjaisen, satunnaistetun, kontrolloidun 12 kuukauden mittaisen liikuntaintervention, johon osallistui 120 naista. Intervention aikana mittasimme hyppykuormitusten määrää ja voimakkuutta uudella kiihtyvyysanturiin perustuvalla menetelmällä. Nousujohteinen hyppyharjoittelu aiheutti kuormitetuissa luissa muutoksia, joista keskeiset olivat luuntiheyden ja luun ympärysmitan kasvu. Lisäksi luuston aineenvaihdunnassa tapahtui muutoksia, jotka osoittivat luun uudismuodostuksen lisääntyneen. Luun mukautumisen ja mitattujen iskukuormitusten välillä havaittiin annos-vastesuhde. Kuormitusten voimakkuus oli olennaista, sillä reisiluun kaulan luuntiheyden muutokset olivat yhteydessä kuormituksiin, joiden kiihtyvyys oli yli 4 kertaa maan vetovoiman (g) suuruinen. Luustomuutoksen saavuttamiseen tarvittavien kuormitusten määrä yli 4 g:n tasolla oli kuitenkin vain 60 kuormitusta vuorokaudessa, jotka voidaan turvallisesti saavuttaa normaaleilla hypyillä. Liikuntaharjoittelu paransi myös kolesteroliarvoja, maksimaalista hapenottokykyä, voimatasoja sekä pienensi vyötärön ympärystä, vaikuttaen näin positiivisesti sydän- ja verisuonisairauksien riskitekijöihin. Tutkimus osoitti luun mukautuvan muuttuneisiin kuormituksiin useiden mekanismien kautta ja mukautumisen olevan kuormitusten intensiteetistä riippuvaista. Osteoporoosin ehkäisyn kannalta tehokas ja turvallinen kuormitusmäärä näyttää olevan 60 hyppyä päivässä

In this thesis we have designed and implemented components for an autonomoussystem for material re handling in the construction business, an autonomouswheel loader. Our achievements was at the end of this thesis demonstratedon a prototype machine. Our main contribution to the autonomous wheelloader is a new software platform design, with this new platform future expansionsis made easier. We have also developed several software components forthis platform that solves tasks required for autonomous operation with the wheelloader the most important listed below.ˆ Mission state machineˆ Vision algorithm, detect and parametrizes a load receiver (in this thesis ahauler) from LiDAR scanner dataˆ Translation algorithm, translate the wheel loader to a dynamic target andthere empty the payloadLow level development on the vision system of the autonomous wheel loaderwas also required to bee able to reach the target of the thesis. We have implementeda communication driver and a API for a LiDAR scanner and a API for aservo controller. A mechanical xture have been designed in CAD, manufacturingof this xture was achieved using a CNC mill.
I det här examensarbetet har designat och implementerat komponenter till ettsystem för automatiserad materialhantering i anläggningsbranschen, en autonomhjullastare. Examensarbetet avslutas med en uppvisning av den prototyp somvi implementerat våra komponenter på. Vårt främsta bidrag till systemet är enny mjukvarudesign, med det nya upplägget har det blivit enklare att integreranya komponenter i systemet. Förutom plattformen så har vi tagit fram komponenteroch lösningar för era delsystem som krävs för autonom operation medhjullastaren, dessa har vi listat några av dessa nedan.ˆ Tillståndsmaskin för hantering av övergripande uppdrag.ˆ Bildbehandlingsalgoritmer, som utifrån LiDAR data parametriserar lastmottagaren(i detta examensarbete en dumper)ˆ Dynamisk translationsalgoritm, denna används för att genomföra en tömningssekvenspå en godtycklig koordinat.Mycket jobb har även lagts på utveckling av underliggande system och funktionalitet,bland annat har vi implementerat kommunikations protokoll och APIför en LiDAR skanner samt ett API för en servo controller. Vi har också konstrueraten mekanisk vagga för LiDAR skannern och servomotorn i CAD, dennakonstruktion tillverkade vi senare i en CNC fräs.

When loading a webpage on the Internet it is desirable that it loads as quickly as possible. This master thesis presents several strategies to try and improve the response time of a webpage by optimizing the loading of its component. The tests conducted in this master thesis showedthat using compression will significantly improve the response time of a webpage and using caching for static components will greatly improve the response time for repeated visits of a webpage.
När en webbsida laddas på Internet är det önskvärt att det går så fortsom möjligt att ladda sidan. Den här rapporten redovisar flera strategierför att försöka förbättra laddningstiden för en webbsida genom att optimeraladdningen av en webbsidas komponenter. Testen som genomförtsoch redovisas i rapporten visade att man kan minska laddningstidenför en webbsida signifikant genom att tillämpa komprimering. Testenvisade också att man genom att cacha statiska komponenter kan sparamycket tid för återkommande besök av webbsidan.

This work deals with the problem of container loading. It analyses the effectiveness of a layering approach to the problem. The approach is applied to three key areas within this field, the first being concerned solely with the production of efficient, yet stable, loading arrangements for a single container. Using this as a foundation, subsequent work considers the handling of certain practical aspects. The third area of research concerns extensions to the approach in order to tackle situations where all of the cargo needs to be stowed in a set of (several) containers. The work demonstrates that the proposed approach produces packing arrangements which are highly efficient in terms of volume utilisation, and are generally superior to results obtained from a variety of other approaches. Several modified versions of the approach are presented, but it is shown that the original algorithm (with some enhancements of secondary importance) provides a better basis for further work. Where separation of the cargo is required, e.g. when it consists of consignments for different destinations, the layering approach has some limitations. A method of column building, which overcomes these shortcomings, is presented and is shown to be complementaty to the layering approach in terms of the packing efficiency obtained. However, this method has severe drawbacks in relation to load stability. It is shown that practical criteria such as load-bearing ability of boxes and preferences relating to direct contact placements can be incorporated into the layering approach. The method developed uses opportunity cost concepts to govern the placement of boxes. It is demonstrated that the method can produce a significantly higher packing efficiency than is achieved when weight considerations are treated solely as constraints. A system of 'finetuning' is presented that allows the criteria involved to be given user-defined weighting factors. This is shown to be significantly enhanced by a mechanism which checks whether weight aspects are relevant in the current step of the algorithm. This research also demonstrates that the problem of loading multiple containers can often be optimally solved by using one of a number of techniques based on the single container layering approach. Sequential methods, in which containers are loaded one after another by the application of a single container algorithm, are examined. These are compared with procedures where simultaneous consideration is given to the loading of several containers. A computationally more complex method, based on a set covering philosophy, is also investigated as a possible approach. 'This process involves the generation of a number of single container loading configurations and subsequent selection, by integer programming, of a minimal subset which covers the total consignment. The potential of this type of approach is clearly demonstrated

Whilst mechanical impact is known to be essential for cartilage maintenance, it has been noted that altered joint loading and increased force may lead to cartilage degradation and increase the risk for the development of osteoarthritis (OA). This study investigated the cellular responses of chondrocytes to mechanical impact, and the effects of possible chondroprotective agents for OA preventative strategies in individuals exposed to high impact, repetitive loading. Single-impact mechanical trauma (force 1.14 N, pressure 6.47 KPa) was determined to induce biphasic decrease in cell volume to 647.38±60.38 μm3 at 2 h and 516.52±38.86 μm3 at 48 h, the initial phase of which was observed to be an active mechanotransduction mechanism, termed Impact-Induced Volume Decrease (IIVD), and the subsequent phase to be Apoptotic Volume Decrease (AVD). The newly defined IIVD was concluded to be dependent upon the PKC/PLCβ3 pathway, and possibly mediated by intracellular Ca2+ store release and Volume Sensitive Organic Anion Channel (VSOAC) activity. Furthermore, mechanical impact was observed to induce a rapid decrease in F-actin from 1.19±0.13 MU to 0.87±0.02 MU, termed Impact-Induced Actin Decrease (IIAD) and associated with the biphasic rise in cell death at rates of 2.75±0.41 %.h-1 and 0.66±0.03 %.h-1. Both in vivo exercise and in vitro mechanical load induced a release IL-1β (20.67±2.58 % and 5.86±0.21 AU), MCP-1 (25.69±0.53 % and 1.45±0.01 AU) and IL-10 (8.97±2.40 % and 5.55±0.28 AU), with in vivo concentrations correlating with joint magnitude and strike patterns. Decreased levels of IL-1β and MCP-1 (to 9.60±2.34 % and 9.01±2.34 %, respectively) observed in the evening were further confirmed using a hyperosmotic-treated in vitro model of prolonged static-loaded cartilage with evidence for a IL-1β-dominated paracrine loop between articular cartilage and mononuclear phagocytes. In vitro, chondroprotective and antiinflammatory actions of chondroitin sulphate, glucosamine sulphate, REV 5901 and Tamoxifen were associated with a reduction in pre-impact cell volume (average of 31.91±4.19 %) and increased pre-impact actin levels (average of 39.92±9.29 %). Anti-inflammatory agents, curcumin and dexamethasone exhibited less effective chondroprotective actions, via inhibition of IL-1β (average of 83.45±1.30 %) and thus apoptosis. To conclude, high impact exercise is recommended with a place for chondroprotective properties of chondroitin, glucosamine sulphate and/or curcumin in high-risk groups before OA onset.

The long bones grow by the process of endochondral ossification, which occurs at the growth plate. This process is regulated by biological factors and mechanical factors. The biological factors which contribute to endochondral ossification process are genes, hormones, nutrients etc. The mechanical factor is the load acting on the bone. The major forces on the bone are due to joint contact load and muscle forces, which induce stresses in the bone. Carter and Wong proposed in a theory that cyclic or intermittent octahedral shear stress promotes the bone growth and cyclic or intermittent hydrostatic compressive stress inhibits the bone growth. Previously this theory has been used to predict the morphological development of long bones, but with studies using simplified femur and growth plate models. Furthermore, the Carter and Wong theory has a limitation that it does not intrinsically incorporate the resulting growth direction.In the first study, the importance of a subject-specific growth plate over a simplified growth plate has been studied, and growth has been simulated using two different growth direction models: Femoral neck shaft deformation direction and minimum shear stress direction. This study favors the minimum shear stress growth direction model, as it is less sensitive to applied boundary condition than the femoral neck shaft deformation direction model.The second study aims to understand how different muscle groups affect the bone growth tendency. Subject-specific femur and growth plate models of able-bodied children were used. The muscle forces and associated hip contact force from specific muscle groups were applied, and neck shaft angle and femoral anteversion growth tendencies were predicted. This study indicated a tendency for reduction of neck shaft angle and femoral anteversion. Hip abductor muscle forces contribute most, and hip adductor muscle forces least, to bone growth rate.Accurate prediction of bone growth tendency and knowledge of the influence of different muscle groups on bone growth tendency may help in better treatment planning for children at risk of developing bone deformity problems.

QC 20151201

In this paper several Markov models have been created for simulating queues at loading docks with discrete time Markov chains and a optimization algorithm in regard to server capacity has been presented. The queuing systems have been modeled with exponential and Erlang-2 distributed service rate. They have also been modeled for one class or a simplification of two classes. An attempt was made to find a scaling factor for the service rate to use the one class exponential model to replicate the other models. This was suÿciently successful done with derivation and linear regression. The optimization was done with a greedy approach. It was computationally eÿcient, but could not guarantee global optimality.
I den här studien har flera Markov-modeller skapats för att simulera av köer vid lastkajer med hjälp av diskreta tidsmarkovkedjor och en optimeringsalgo-ritm med avseende på betjäningskapacitet har presenterats. Kövsystemen har modellerats med exponentiell och Erlang-2-distribuerad betjäningsintensiteten. De har även modellerats för en klass eller en förenkling av två klasser. Ett försök gjordes för att hitta en skalfaktor för betjäningsintensiteten för att använda den en klass exponentiella modellen för att replikera de andra modellerna. Detta var tillräckligt framgångsrikt gjort med härledning och linjär regression. Optimeringen gjordes med en girig inställning. Det var beräkningsmässigt ef-fektivt, men kunde inte garantera global optimalitet.

Graphic Processing Units (GPUs) are getting more powerful and are currently capable of displaying millions of polygons at a steady frame rate. The challenge is however, to display unique and interesting data while navigating in a 3D world. This task consists of both selecting which data to display, as well as storing all the required data.This thesis focuses on efficient methods for displaying portions of large terrain textures, by loading the textures incrementally, and thereby avoid some of the storage limitations of current graphics hardware and increase the detail level of the terrain rendered. These methods include algorithms for selecting the parts of the terrain to display, loading the data in time when it's needed and present the data in an appropriate quality while maintaining performance. How the camera behaves plays a key role in these algorithms.The process of displaying large terrains is divided into a multi step process, where coarser algorithms detect the active region of the terrain, then more accurate algorithms calculate which portions to load, and then the most precise algorithms aim to only display the necessary data. Camera movement is also taken into account in this process, and the algorithms attempt to fetch the necessary data in time before it's needed, which is a novel approach. The proposed implementation is compared to related approaches such as Virtual Texturing, a comparable methods which rely on feedback when required data is missing during rendering.

Little information is available in the literature concerning an ergonomic systems view of industrial seats. This study has been aimed at expanding knowledge of industrial seat design. For this purpose, a model for evaluating industrial seats has been proposed, listing demands and restrictions from the task and the workplace. It also includes responses and effects on the sitter, and methods of measurement for evaluating industrial work seats. The appropriateness of work seat design has been assessed in laboratory and field studies, using methods to measure body loads, their effects and responses. These have been body height shrinkage, biomechanical methods, subjective assessment, and posture assessment. The shrinkage method, including equipment and procedures, has been developed in this project. It assesses the effect of loads on the spine in vivo by using body height changes as a measure of disc creep. The results are well correlated with spinal loads. The method is sensitive enough to differentiate between spinal loads of 100 N difference. The results are also related to the perception of discomfort. Biomechanical methods have been developed for calculating compressive, shear, and momental loads on the spine. Ratings of discomfort, body mapping, interviews, video recordings, and prototype equipment for the recording of head posture have also been used. The methods have been shown to be appropriate for seat evaluation. Work seats have been evaluated in different tasks, incorporating back-rests of different height, width and shape, conventional seat pans and sit-stand seats. It has been shown that advantageous chair features could be referred to each particular task. The tasks evaluated included forward force exertion (high backrests advantageous), vision to the side (low backrests advantageous), work with restricted knee-room (seats allowing increased trunk-thigh angle advantageous), grinding (high, narrow backrests advantageous), punch press work (increased seat height advantageous), and fork lift truck driving (medium height backrest advantageous). The work task has been shown to be a major influence on seat design, and must therefore always be thoroughly considered.

Over the last decade it has become increasingly popular to provide large public areas with gracefully designed 'flexible' staircases. One inherent characteristic of this type of construction is a low stiffness to mass ratio and hence a low natural frequency when compared to more traditional designs. A number of staircases have been found to be dynamically responsive to pedestrian traffic resulting in costly repairs. The objective of this thesis was to investigate the differences between human induced loading on floors with that on stairs. Experimental work carried out on a purpose built staircase showed that forces up to 3 times the static body weight were generated during fast descents while forces up to 2.5 times the static body weight were generated during fast ascents. The work also showed that first harmonic values generated while ascending were slightly higher than for descending whilst second harmonic values were up to 3 times greater for fast descents than for fast ascents. When compared with floor testing, stair testing produced first harmonic values nearly 2.5 times greater with second, third and fourth harmonic values nearly 3 times greater. The harmonic results for the flat testing were also incorporated into a new mathematical expression to predict peak accelerations on simply supported floors and footbridges. The experimental results were duplicated analytically by developing a computer program to calculate the vertical ground reaction forces from body segment positional data. Following a Newtonian approach, the predicted first harmonic values were 20% to 30% lower than actual while the second harmonic values were approximately the same. Monte Carlo simulation techniques were also used to model the effects of group loading on stairs. The simulations predicted enhancement factors (a multiplier on single subject loading) of 3 to 6 for smaller groups(< 9 people) and 4 for larger groups(> 25 people). If the experimental/analytical results are combined with the group loading predictions, the harmonic values for groups ascending or descending flexible staircase could be substantially increased. These results demonstrate that loading data from floors is highly inappropriate for staircase design.

Impact loads have been implicated in the initiation of secondary osteoarthritis but in the absence of defined injury this is difficult to rest rigorously.  The response to controlled impacts of samples of cartilage and bone in isolation and together, may yield valuable insights into how tissue properties may influence degenerative changes associated with osteoarthritis. A rigid instrumented drop tower was constructed and interfaced to a LabVIEW software oscilloscope modified to capture and store data to disk.  Controlled impact loads were applied to cores of articular cartilage, both isolated and in situ on the underlying bone or bonded to substrates of different material properties.  Bovine tissue from the carpometacarpal joint and human cartilage from elderly femoral heads was used.  The response of the samples was investigated in terms of a dynamic stiffness, energy absorbed and coefficient of restitution.  In addition the quasistatic modulus was measured from compression tests in order to compare the values for the stiffness of cartilage and bone at different rates of stress and strain.  Composition analysis was then performed on human cartilage samples to investigate if there was any correlation between the biochemical constituents and mechanical factors. The dynamic stiffness of the cartilage samples was governed by peak stress and did not show a high sensitivity to strain rate.  Cartilage had good force attenuating properties in situ on bone and the substrates.  The greater volume of the stiffer underlying substrate dominated the response of the composite samples.  For the human cartilage samples the dynamic stiffness was most correlated to percentage collagen whereas the quasistatic modulus was most correlated with water content.  Overall the biochemical composition was a poor predictor of stiffness which indicates the importance of interactions between the matrix constituents in the tissue response to an applied load.

The response of an Echinodome to static and dynamic point loads, and explosive type loadings was examined both theoretically and experimentally. The finite element method of analysis was employed in the theoretical investigation. Semi-loof thin shell elements were used to model a GRP prototype on which the experiments were performed. The stress distribution of the Echinodome under a static symmetric point load were investigated both experimentally and theoretically. Then the Southwell technique was employed in estimating the critical buckling load from deflection measurements. Experimental estimates were then compared with the numerical predictions in the form of non-linear collapse and non-linearbifurcation buckling loads. A free vibration was performed to determine the structural natural frequencies and typify the mode shapes. The shock response spectra of several pulse shapes were determined using the finite element method. The most severe loading function was established to be a step loading with infinite duration and zero ramping time and was then employed as the load-time history in an axisymmetric and symmetric non-linear dynamic buckling analysis. The dynamic collapse buckling loads were found to be smaller in magnitude than their static correspondents. A modal testing was then carried out on the Echinodome prototype to determine the experimental modal parameters (natural frequencies, damping values and mode shapes). Newly developed correlation techniques were adopted in the comparison of the experimentally derived parameters with those predicted and poorly modelled regions were identified. Great improvement was achieved by correcting the experimental data and updating the finite element model's boundary conditions. A set of underwater free field experiments was performed to determine the pulse characteristics for a specific explosive charge, followed by another set while the prototype was in a floating submerged state and acting as the target for the same explosive charge. A theoretical simulation was accomplished by employing a finite element-boundary element approximation for the modelling of the structure and infinite fluid media respectively. Measured responses were compared with the numerical predictions and means of acquiring better theoretical approximations are mentioned. The loading conditions to be experienced by an underwater LNG Echinodome vessel are reviewed with emphasis on accidental dynamic loads (impact and explosion). A state of the art storing configuration is proposed for the Echinodome in order to limit the extent of damage and hence minimise risk during upset conditions. Finally, appropriate design, construction and prestressing procedures were recommended.

The solar wind interaction with an icy comet is studied through a model problem. A hybrid simulation is done of a box with evenly distributed water ions and protons, where initially the water ions are stationary, and protons move with the speed of the solar wind. The purpose of the thesis is to investigate the interaction between the two species through the convective electric field, and focus is on early acceleration of pick-up ions, and deflection of the solar wind. It is relevant to the cometary case, because it enables study of the physics of this interaction, without involving other mechanisms, such as bow shock, magnetic field pile-up and draping. The species are found to exchange kinetic energy similar to a damped oscillator, where the dampening is caused by kinetic energy being transferred to the magnetic field. At early times, i.e. times smaller than the gyration time for the water ions, the solar wind does not lose much speed when it is deflected. For comparable number densities, the solar wind can be deflected more than 90° at early times, and loses more speed, and water ions are picked up faster. The total kinetic energy of the system decreases when energy builds up in the magnetic field. The nature of the energy exchange is strongly dependent on the number density ratio between water ions and protons. A density instability with behaviour similar to a plasma beam instability forms as energy in the magnetic field increases, and limits the amount of time the simulation preserves total energy, for the particular hybrid solver used. There is a discussion on the structure of the density instability, and it is compared to cometary simulations.

The anterior cruciate ligament (ACL) is one of four major intra-articular knee ligaments and plays a key role in knee stability. Rupture of the ACL is one of the most common and debilitating sport-related knee injuries. Most ACL ruptures do not involve direct collisions, but occur during landing, cutting, and pivoting tasks common to sports such as soccer, basketball, and netball. Rates of ACL rupture in young people have increased enormously in Australia over the past two decades. Generally, ACL ruptures are 3.5-4 times more frequent in female compared to male athletes. Among females, those aged 15-19 years are at highest risk of ACL rupture being ~4 times more likely to sustain injury than their pre-pubertal counterparts. Analysis of video footage of ACL injury events, cadaveric experiments, and biomechanical studies has yielded a consensus that external knee loads applied in three planes of motion (i.e., sagittal, frontal, and transverse) contribute to ACL rupture. Laboratory-based biomechanical studies that directly instrumented the ligament have been performed, albeit sparingly for obvious reasons of invasiveness, and show the ACL sustains substantial loading during non-injurious motor tasks. Moreover, studies using external biomechanical measures to examine ACL loading employing computational models have been limited, and have not included, and thus are insensitive to, an individual’s knee muscle activation patterns in muscle force estimates Valid models of the ACL and its loading profile have been challenging to create, and instrumented measures of ACL loading without concurrent modelling of the neuromusculoskeletal dynamics will fail to provide insight into the role of specific muscle and external loads in loading the ACL. Therefore, the mechanisms underlying ACL loading during dynamic motor tasks, through the interaction of muscles, contacting articular bodies, and other soft tissues, remain unclear. This deprives injury prevention and rehabilitation programs of personalized targets that are mechanistically linked to in vivo ACL loading. The purposes of this thesis were to develop and validate a computational model that can accurately estimate ACL force based on outputs of neuromusculoskeletal models in individuals with an intact ACL; determine ACL loading in drop-land-lateral jump task in mature females, therein examining the mechanisms that contribute to ACL loading, and; and determine effects of pubertal maturation on females’ ACL loading during a dynamic motor task considered provocative for the ACL. This thesis involved the development, validation, and application of a computational model to quantify ACL force during dynamic motor tasks. First, an ACL force model was developed using the most relevant, complete, and accessible cadaveric data from the literature. These data comprised measurements of ACL force or strain across various knee flexion angles in response to uni- and multiplanar external knee loads. Using a portion of these data, algebraic equations were fitted to well describe ACL loading in response to both uni- and multiplanar knee loading. The model was then validated using the remaining experimental data not used in model development. The validated ACL force model was then combined with an electromyography (EMG) -informed neuromusculoskeletal model to estimate ACL force developed during a standardised drop-land-lateral jump task performed by healthy females in laboratory conditions. Ninety-three females, aged 8 to 20 years, volunteered to participate in this study. All participants were recreationally active and had no history of lower limb injury or knee pain. Participants were divided into 3 groups: pre-, early/mid-, or late/post-pubertal based on Tanner’s pubertal classification system. Each participant attended a laboratory-based testing session, wherein three repeated trials of a standardized drop-land-lateral jump from a box with box height set to 30% of their lower limb length, while 3D motion capture, ground reaction forces, and surface EMG were acquired. For purposes of calibrating the EMG-informed neuromusculoskeletal model, three trials of running at a natural self-selected style (speed range from 2.8 to 3.2 m.s-1) were performed. These laboratory data were then used in a neuromusculoskeletal model to estimate ACL loading. The OpenSim modelling software was used to scale a generic anatomical model to match each participant’s gross dimensions, mass, and inertia, followed by morphometric scaling to preserve fibre and tendon operating ranges, and last adjust each muscle’s maximum isometric strength based on empirical relationships between mass and height with lower limb muscle volume. Using this scaled model, the external biomechanics (i.e., model motions and joint loading) and muscle tendon unit actuator kinematics (i.e., moment arms, lengths, and lines of action) were determined. The EMG signals were conditioned into normalized linear envelopes, which were combined with the OpenSim external biomechanics and muscle tendon unit actuator kinematics to drive a model in the Calibrated EMG-informed Neuromusculoskeletal Modelling (CEINMS) toolbox. The CEINMS was first calibrated and then run with an EMG-informed neural solution to estimate lower limb muscle and tibiofemoral contact forces. The muscle tendon unit kinematics and forces, along with the joint loads were then incorporated into the validated ACL force model to quantify ACL force. For each participant, the contribution of muscle and intersegmental loads to ACL forces were calculated across the stance phase of the drop-land-lateral jump task. Specific statistical analyses were run to address each of the research questions and encapsulated as a series of research manuscripts in the format of journal articles. The first study developed and validated a computational model that predicted the force applied to ACL in response to multiplanar knee loading that was estimated by a subject-specific neuromusculoskeletal knee model, as described above. The study demonstrated these models’ utility by applying it to a sample of motion capture data. First, a three-dimensional (3D) computational model was developed and validated using available cadaveric experimental data to estimate ACL force. The ACL force model was valid as it well predicted the cadaveric data, showing strong statistical correlation (r2=0.96 and P<0.001), minimal bias, and narrow limits of agreement. Second, by combining a neuromusculoskeletal model with the ACL force model, it was revealed that during a drop-land-lateral jump task the ACL is primarily loaded through the sagittal plane, mainly due to muscular loading. The computational model developed in study one was the first validated accessible tool that could be used to develop and test knee ACL injury prevention programs for people with normal ACL. The method used to develop this model can be extended to study the abnormal ACL upon the availability of relevant experimental data. The paper describing these results was published as Nasseri A., Khataee H., Bryant A.L., Lloyd D.G., Saxby D.J. Modelling the loading mechanics of anterior cruciate ligament, Computer Methods & Programs in Biomedicine, 184 (2020) 105098. doi: 10.1016/j.cmpb.2019.105098. Study two determined ACL force and the key muscular and biomechanical contribution to this ACL loading in a standardized drop-land-lateral jump task performed by sexually mature young females. Three-dimensional whole-body kinematics, ground reaction forces, and muscle activation patterns from eight lower limb muscles were collected during dynamic tasks performed by healthy females (n=24), all who were recreationally active. Collected data were used to model the external biomechanics, muscle-tendon unit kinematics, and muscle activation patterns using established biomechanical modelling software packages (i.e., OpenSim and MotoNMS). These biomechanical and electromyographic data were then used to calculate the lower limb muscle, joint contact and the ACL forces through an EMG-informed neural solution combined with a validated ACL force model. Peak ACL force (2.3 ± 0.5 BW) was observed to occur at 14% of the stance phase during the drop-land-lateral jump task. The ACL force was primarily developed through the sagittal plane, and muscles were the dominant source of ACL loading. The main ACL muscular antagonists were the gastrocnemii and quadriceps, while the hamstrings were the main ACL agonists. Our results highlighted the important role of gastrocnemius in ACL loading, which could be considered more prominently in ACL injury prevention and rehabilitation programmes. The paper describing these results is accepted for publication as Nasseri A., Lloyd D.G., Bryant A.L., Headrick J., Sayer T.A., Saxby D.J. Mechanism of anterior cruciate ligament loading during dynamic motor tasks. Medicine and Science in Sports and Exercise. Study three determined and compared ACL loading during a drop-land-lateral jump task in females across three pubertal stages of maturation. Further, the relative contributions to ACL force from three planes of motion (sagittal, frontal, and transverse) were compared. In this, sixty-two participants were divided into pre-pubertal (n=19), early/mid-pubertal (n=19) or late/post-pubertal (n=24) groups based on Tanner’s pubertal classification system. Each participant completed a biomechanical testing session wherein we collected three-dimensional body motion, ground reaction forces, and EMG during drop-land-lateral jump task. Using these data, the aforementioned ACL force and neuromusculoskeletal knee model was used to assess ACL loading and the key contributions to this loading. To analyse the ACL force in a continuous manner, statistical parametric mapping (SPM) analysis was used. SPM ANOVA and post-hoc t-tests were used to compare total ACL force and contributors to this force over the stance phase of the drop-land-lateral jump task between three groups of females across maturation. Compared to pre- and early/mid-pubertal, females in late/post pubertal group showed significantly higher ACL force during a large percentage of the stance phase, which encompassed the peak ACL forces. The forces developed through sagittal and transverse planes were significantly higher in late/post-pubertal group compared to the two other groups over large percentages of the stance phase. The contribution of the frontal plane mechanisms to ACL force was not significantly different across sexual maturation, while the pre- and early/mid-pubertal groups were not significantly different for any of the outcome measures. The larger ACL forces observed in late/post-puberty group (14-20 years) may partially explain the higher rate of ACL injury in females aged 15-19 years in the last decades. In addition, it has been shown that ACL growth plateaus at the age of 10, prior to full sexual maturation and cessation of growth in stature. Thus, females in late/post pubertal group are potentially heavier, have similar sized ACL, but with greater ACL forces compared to their less sexually mature counterparts. These reasons together could be the foundation, at least in part, for the higher ACL forces observed in this group. The manuscript describing these results is under review as Nasseri A., Lloyd D.G., Minahan C., Sayer T.A., Paterson K., Vertullo C.J., Bryant A.L, Saxby D.J. Effects of pubertal maturation on anterior cruciate ligament forces during a landing task in females. American Journal of Sports Medicine. In conclusion, a computational ACL force model was developed and validated that provided a platform for integration of external biomechanics, muscle and joint contact forces to calculate in vivo ACL force. This ACL force model enabled examination of the ACL loading mechanism by exploring the main muscular and biomechanical contributions to ACL loading; and the effects of pubertal maturation on ACL loading in females. The variability in the magnitude and contributions to ACL force across a wide age range of participants suggest estimation of ACL force is necessary to understand the potential ACL injury mechanisms and design ACL injury prevention programs, rather than relying on external biomechanics that are proposed as surrogates of ACL injury.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School Allied Health Sciences
Griffith Health
Full Text

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 193-198).
In recent years edge fracture has become a challenge in the manufacturing industry with the dramatical increase in the application of light-weight materials such as Advanced High Strength Steels (AHSS) and aluminum alloys. A premature edge cracking is observed in components with blanked/trimmed/pierced edges during the subsequent metal forming process. To understand the underlying physical mechanism and to establish a reliable CAE model, the thesis carries out a comprehensive experimental and numerical investigation on edge fracture of a commercially available DP780 steel sheet. The study reveals that it is the substantial plastic deformation introduced during the out-of-plane sheet blanking process that compromises the material ductility within the Shear Affected Zone (SAZ), and subsequently causes the edge to fracture prematurely under the in-plane edge stretching. To simulate the fracture behavior under such a complex a loading path, the fracture initiation is modeled using the concept of a scalar damage indicator that consists of two parts which are accumulated at different stages. The first one is accumulated during the sheet blanking process, referred to as pre-damage, while the second part is produced by the following metal forming. In such a modeling frame work, a corner stone is to determine the first part of pre-damage within the SAZ. This is achieved by a hybrid experimental and numerical method. Aided by microscopic examinations on cracked surfaces, the study shows that the pre-damage distribution within the SAZ follows an exponential function that drops from the critical value of unity at the edge surface to zero over the width of the SAZ. The obtained pre-damage is then introduced as the initial damage value during the following metal forming process. Based on a detail experimental characterization, a plasticity and fracture model is introduced to describe the material behavior under investigation. The model is based on the von Mises yield condition, a non-associated Hill'48 flow potential and an isotropic hardening law, together with the MMC fracture locus description with dependence on both stress triaxiality and Lode angle parameter. The proposed model successfully predict edge fracture in numerical simulation.
by Kai Wang.
Ph. D.

In questo lavoro si presenta una descrizione del processo completo di caricamento di un aereo cargo: dalla pianificazione del volo al posizionamento delle unità di carico a bordo. Il processo completo è noto in letteratura con il nome di “Air Cargo Loading Planning Problem”. Questo problema generale può essere scomposto in quattro passaggi, l’ultimo dei quali è la fase di posizionamento di unità di carico (ULD) a bordo dell’aeromobile. Questo sotto-problema viene denominato “Weight and Balance Problem” (WBP). L’obiettivo di questa tesi è stata la costruzione e implementazione di un modello di programmazione lineare intera mista (MIP) per la risoluzione del WBP applicato a un volo cargo con tragitto multi tappa, cioè il caso in cui il volo spezza il tragitto tra due aeroporti con delle fermate intermedie in cui possono essere effettuate operazioni di scarico/carico. L'obiettivo è quello di raggiungere il miglior bilanciamento possibile cercando di minimizzare il numero delle operazioni a terra negli aeroporti intermedi. Si è poi esteso questo modello al caso in cui sulla stessa tratta operi una flotta di aerei. Infine si presentano alcuni risultati ottenuti applicando il modello costruito ad alcune istanze test che simulano un piano di volo sotto tre diversi scenari.

Atherosclerotic plaque caps are composed of a composite soft tissue material that becomes subjected to cyclic loading under stenotic flow conditions. The cyclic loading causes the plaque cap to fatigue and eventually fail. The hypothesis of this work is that arteries and plaque caps may fatigue which may be predicted by a stress vs. number of cycles (S-N) curve. The S-N curve has not been determined for almost any biological soft tissue. The Specific Aim of the thesis is to quantify an S-N curve for normal arterial soft tissue collected from cyclic tension testing. Coronary arteries from porcine hearts will be tested as a material that closely models the plaque cap in non-linear elastic behavior. The S-N curve will be developed through failure testing with multiple cycles at stresses between 0.5 and 5 MPa.

The development of the next generation of Saab's multirole combat aircraft the JAS 39 Gripen includes developing a lot of new software for the aircraft's on-board computers. The new software has to be loaded into these computers routinely, in order to carry out testing on it. This is currently a slow and tedious process. In order to load the computers a protocol defined in the ARINC 615A standard is used. Today Saab uses commercial software applications implementing this protocol for the loading process. These applications have significant disadvantages, such as not being able to load several computers in parallel or only being able to load computers from a specific manufacturer. In this thesis we introduce a system using a client-server architecture that allows users to load the computers in parallel, regardless of the manufacturer. In Section 3.2.2 we show that our system reduces the time required to load the aircraft's on-board computers significantly. We also indicate some improvements that can be made in order to speed up the process even further. These improvements mainly involve improving the on-board computers themselves through the use of faster persistent storage and support for later revisions of the protocol involved.

Methods of structural optimization have been studied and developed over the last three decades. An important aspect of structural optimization pertains to the conditions under which the loads are applied. Problems in which the applied load is single and deterministic are well documented in the literature, whereas those in which the load is deterministic but varying, stochastic, or uncertain have been less studied. Although methods of structural optimization under single-loading conditions can be extended to multiple-loading cases, the computational burden imposed by these methods is often extremely high, to the point of becoming inapplicable.
In this thesis, a novel approach is introduced. We first propose the use of the concept of stiffness ellipsoid, whose boundary defines the field of displacements of a structure subject to a load with a constant magnitude, but applied in an arbitrary direction. Based on the study of the stiffness ellipsoid, an optimality criterion that determines the worst case of the structure subject to a load with a given magnitude, but applied in an arbitrary direction, is proposed. The underlying ideas are applied to the structural optimization of the roller-carrying disk of a novel class of cam-follower speed-reduction devices---Speed-o-Cam (SoC). The optimum structures obtained in this thesis are compared with the existing prototype, which was designed using established design criteria only. Results indicate an improvement of almost twice the stiffness with a mass reduction of 40% of the original prototype.
Also reported in the thesis is a novel algorithm of mesh generation, named the contour mesh generation algorithm (CMGA). The CMGA, based on the concept of penalty functions, is applied throughout the examples given in the thesis and shows a great advantage in solving structural optimization problems.

In moderate sea states, the predictions of the wave drift forces based on the potential theory correlate well with measurements. However, in severe wave conditions model tests have shown that there is an increase in wave drift forces as the sea states increases. Such difference is explained by the viscous drift forces acting in the waterline zone of a structure. This thesis presents an experimental study of the low-frequency surge motion loading on and response of a semisubmersible model in different sea states ranging between moderate and extreme. In addition to the experimental study, the thesis includes numerical simulations. The experimental tests were conducted in MARINTEK ocean basin with a 1/50 scale model which was moored using horizontal springs and catenary mooring lines. The environmental conditions included waves, current and combined wave and current fields. The waves used included both regular and irregular waves. In addition, decay tests were conducted in still water and in current. For irregular waves, statistical analysis of the values of mean value and standard deviation of the motion responses was carried out to investigate the effect of wave-current interaction and different sea states on these values. As for the numerical simulations, a mathematical model that is based on Morison’s approach was used to predict the dynamic surge motion loading on and responses of a semisubmersible platform. In addition, the steady and slowly varying wave forces are predicted using Pinkster’s procedure. The second numerical simulation was carried out using three-dimensional diffraction program that estimates the six degrees of freedom loading and responses in regular waves with and without the viscous damping effects. The damping of the system stems from both the hull and the mooring system. The mooring system damping was studied using the energy dissipation method to estimate the damping of the mooring line using the amplitude of the surge motion of the vessel.

In moderate sea states, the predictions of the wave drift forces based on the potential theory correlate well with measurements. However, in severe wave conditions model tests have shown that there is an increase in wave drift forces as the sea states increases. Such difference is explained by the viscous drift forces acting in the waterline zone of a structure. This thesis presents an experimental study of the low-frequency surge motion loading on and response of a semisubmersible model in different sea states ranging between moderate and extreme. In addition to the experimental study, the thesis includes numerical simulations. The experimental tests were conducted in MARINTEK ocean basin with a 1/50 scale model which was moored using horizontal springs and catenary mooring lines. The environmental conditions included waves, current and combined wave and current fields. The waves used included both regular and irregular waves. In addition, decay tests were conducted in still water and in current. For irregular waves, statistical analysis of the values of mean value and standard deviation of the motion responses was carried out to investigate the effect of wave-current interaction and different sea states on these values. As for the numerical simulations, a mathematical model that is based on Morison's approach was used to predict the dynamic surge motion loading on and responses of a semisubmersible platform. In addition, the steady and slowly varying wave forces are predicted using Pinkster's procedure. The second numerical simulation was carried out using three-dimensional diffraction program that estimates the six degrees of freedom loading and responses in regular waves with and without the viscous damping effects. The damping of the system stems from both the hull and the mooring system. The mooring system damping was studied using the energy dissipation method to estimate the damping of the mooring line using the amplitude of the surge motion of the vessel.

The finite element method in conjunction with the theory of viscoplasticity, and to a lesser extent plasticity, have been used for modelling of plasticity base progressive fracturing in transient dynamic problems. The difficulties associated with the computational modelling of wave propagation problems are discussed. The central difference method is utilised for step-by-step direct time integration of equations of motion, which is coupled with the lumped mass and proportional damping matrices. Special attention is devoted to a correct integration of energy states. Computer implementation takes advantage of modern computer languages and programming techniques, which results in a efficient and fully portable computer code. The strain softening phenomenon is explained in some detail. The consequences of the change of type in the governing of classical rate-independent continuum at the onset of strain softening are investigated. As a solution to that problem, the enrichment of the continuum with the higher-order derivatives in form of strain-rate dependent model (viscoplasticity) is explored and unique, stable and mesh insensitive results are observed for mode-I and mode-II failure problems. A constitutive model for quasi-brittle materials is proposed. The progressive damage is assumed to be isotropic and is modelled with the decohesion process. To account for different behaviour of heterogeneous materials under increasing hydrostatic pressure the degree of softening is rendered state-of-stress dependent. The model is based on the Mohr-Coulomb yield criterion and non-associated flow rule is utilised. The problems associated with non-smoothly intersecting yield surfaces for Mohr-Coulomb yield criterion are discussed with emphasis on correct evaluation of the viscoplastic parameters in singular regions.

This work explored the role of spatial grouping, set size, and stimulus probe modality using a recall task for visual, auditory, and tactile information. The effects of different working memory (WM) loading task modalities were also examined. The Gestalt spatial organizing principle of grouping showed improvements in response times for visual and tactile stimulus probes with large set sizes and apparently allowed participants to effectively chunk the information. This research suggests that tactile information may use spatial characteristics typically associated with visual information, as well as sequential characteristics normally associated with verbal information. Based on these results, a reformulation of WM is warranted to remove the constraints of the input modality on processing types. The input modalities appear to access both a spatial sketchpad and a temporally-based sequence loop. Implications for multisensory research and display design are discussed.
Ph.D.
Department of Psychology
Sciences
Psychology PhD

TELECOMUNICAÇÕES BRASILEIRAS S/A
Neste trabalho são analisados os campos modais em guias circulares contendo em seu eixo um carregamento cilíndrico dielétrico uniforme ou corrugado, identificando propriedades destes campos úteis a aplicações no projeto de ressoadores, filtros e alimentadores. Com o objetivo de apresentar uma aplicação da análise dos guias circulares com carregamento dielétrico, é feita a análise de um ressoador dielétrico cilíndrico apresentando- se sua carta modal relacionando suas freqüências de ressonância com o carregamento dielétrico.
In this work the modal fields for circular waveguides with uniform or corrugated dieletric loads are analysed, and useful properties of these fields to applications such as ressonators, filters and antenna feeders are ecamined. As an application of the analysis of dieletric loaded circular waveguides, an algorithm is developed for the determination of ressonant frequencies of dieletric loaded ressonators, and the modal chart, relating ressonant frequencies to ressonator dimensions, is evaluated.