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1
Browning, Stephen E. "Computer Program for the Analysis of Loads on Buildings Using the ASCE 7-93 Standard Minimum Design Loads on Buildings and Other Structures". Master's thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/37170.
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A computer program for the analysis of loads on buildings is developed. The program determines wind loads, earthquake loads, and snow loads according to the ASCE 7-93 Standard Minimum Design Loads for Buildings and Other Structures (ASCE 7-93). The program is developed using the object-oriented programming methodology and runs on the Microsoft Windows 95 graphical environment. It is a valuable and useful tool for determining loads on buildings.Master of Engineering
2
Bisha, James Victor. "The Effect of Load Stabilizer Selection on Load Shift Within Unit Loads". Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/33035.
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Research on unit load stability aids manufacturing facilities in selecting the most efficient load stabilizer when shipping their products to market. This studyâ s objective was to compare the performance a variety of different commonly used load stabilizers to stretch hooding. Stretch hooding is a method of load stabilization in which a tubular film is heat sealed at the top, stretched by four mechanical arms to a desired width, pulled down over the unit load. The film is slowly released as the arms descend, and is released under the pallet.
400ga stretch hooding, 80ga and 63ga stretch wrap and strapping were tested. Twenty unit loads for both vibration and impact testing were used, with 5 replications per load stabilizer. Container displacement and pallet-container displacement were measured, and the number of tares in the load stabilizer film, on the corners of the test units, after testing, was noted.
Container displacement was significantly greater during impact testing than in vibration testing. Strapping was the most effective stabilizer during vibration testing because of its ability to restrict vertical displacement. The stretch hooding was the most effective stabilizer during impact testing because of its ability to restrict horizontal displacement.Master of Science
3
Hajigholi, Pedram. "Optimal block loads of dynamic load history for fatigue durability testing". Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-67746.
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During a vehicle’s life it is experiencing complex loading from both driving and road conditions. This accumulating of loading might be damaging to the vehicle, leading to possible material fatigue cracking, hence it is a major importance to take it into account. During the design phase the vehicle will be tested on a rig to check the durability and fatigue life. This is done on the system as a whole or at component level. But as it is difficult to reproduce the actual complex loading, a much simpler loading sequence is applied on the component(s) during these tests. The purpose of this master thesis is to use an optimization software called HEEDS, which is based on a mathematical model that is applied in the software, to identify a possible multi-level block sequence which would generate the same fatigue damage as the reference complex loading sequence. This work is fully performed in calculation software, without using actual physical testing. The selected component is a front suspension low control arm (LCA) for which life is checked at various locations. The objective is to have the relative error identified as a relative ratio.
4
Zhou, Xiao Yi. "Statistical analysis of traffic loads and traffic load effects on bridges". Phd thesis, UNIVERSITE PARIS-EST, 2013. http://tel.archives-ouvertes.fr/tel-00949929.
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Une grande majorité (85%) des ponts français a une portée inférieure à 50 m. Pour ce type d’ouvrage d’art, la charge de trafic peut être déterminante pour la conception et le recalcul. Or, en Europe, le fret routier a augmenté de 36.2% entre 1995 et 2010, et la croissance annuelle du volume transporté par la route a été évaluée à 1.7% entre 2005 et 2030. Il est donc essentiel de s’assurer que les infrastructures européennes sont en mesure de répondre à cette demande croissante en capacité structurelle des ouvrages. Pour les ouvrages neufs, les modèles de trafic dans les normes ou les législations pour la conception des ponts incluent une marge de sécurité suffisante pour que la croissance du trafic soit prise en compte sans dommage par ces ouvrages. Mais pour les ouvrages existants, la résistance structurelle aux trafics actuels et futur est à vérifier et une priorisation des mesures doit être faite pour assurer leur intégrité structurelle et leur sécurité. De plus, afin de préserver leur infrastructure tout en ne menaçant pas leur compétitivité nationale, certains pays réfléchissent à l’introduction de poids lourds plus longs, plus lourds, ce qui permet de réduire le nombre de véhicules pour un volume ou un tonnage donné, ainsi que d’autres coûts (d’essence, de travail, ..), ce qui justifie encore plus les calculs effectués. Pour répondre à ce genre de problématique, différentes méthodes d’extrapolation ont déjà été utilisées pour modéliser les effets extrêmes du trafic, afin de déterminer les effets caractéristiques pour de grandes périodes de retour. Parmi celles-ci nous pouvons citer l’adaptation d’une gaussienne ou d’une loi de Gumbel sur la queue de distribution empirique, la formule de Rice appliquée à l’histogramme des dépassements de niveaux, la méthode des maxima par blocs ou celle des dépassements de seuils élevés. Les fondements et les utilisations faites de ces méthodes pour modéliser les effets extrêmes du trafic sur les ouvrages sont donnés dans un premier chapitre. De plus, une comparaison quantitative entre ces méthodes est réalisée. Deux études sont présentées, l’une basée sur un échantillon numérique et l’autre sur un échantillon réaliste d’effets du trafic. L’erreur induite par ces méthodes est évaluée à l’aide d’indicatifs statistiques simples, comme l’écart-type et les moindres carrés, évalués sur les valeurs caractéristiques et les probabilités de rupture. Nos conclusions sont, qu’en général, les méthodes sont moins précises lorsqu’il s’agit de déterminer des probabilités de rupture que lorsqu’elles cherchent des valeurs caractéristiques. Mais la raison peut en être les faibles probabilités recherchées (10-6 par an). De plus, bien qu’aucune méthode n’ait réalisée des extrapolations de manière correcte, les meilleures sont celles qui s’intéressent aux queues de probabilités, et en particulier des dépassements au-dessus d’un seuil élevé. Ainsi une étude de cette dernière méthode est réalisée : en effet, cette méthode, nommé "dépassements d’un seuil élevé", considère que les valeurs au-dessus d’un seuil correctement choisi, assez élevé, suit une distribution de Pareto généralisée (GPD). Cette méthode est utilisée de manière intensive dans les domaines de l’hydrologie et la finance, mais non encore appliquée dans le domaine des effets du trafic sur les ouvrages. Beaucoup de facteurs influencent le résultat lorsqu’on applique cette méthode, comme la quantité et la qualité des données à notre disposition, les critères utilisés pour déterminer les pics indépendants, l’estimation des paramètres et le choix du seuil. C’est pour cette raison qu’une étude et une comparaison des différentes méthodes d’estimation des paramètres de la distribution GPD sont effectuées : les conditions, hypothèses, avantages et inconvénients des différentes méthodes sont listés. Différentes méthodes sont ainsi étudiées, telles la méthode des moments (MM), la méthode des moments à poids (PWM), le maximum de vraisemblance (ML), le maximum de vraisemblance pénalisé (PML), le minimum de la densité de la divergence (MDPD), la méthode des fractiles empiriques (EPM), la statistique du maximum d’adaptation et la vraisemblance des moments (LM). Pour comparer ces méthodes, des échantillons numériques, des effets de trafic simulés par Monte Carlo et des effets mesurés sur un ouvrage réel sont utilisés. Comme prévu, les méthodes ont des performances différentes selon l’échantillon considéré. Néanmoins, pour des échantillons purement numériques, MM et PWM sont recommandées pour des distributions à paramètre de forme négatif et des échantillons de petite taille (moins de 200 valeurs). ML est conseillé pour des distributions à paramètre de forme positif. Pour des effets du trafic simulés, ML et PML donne des valeurs de retour plus correctes lorsque le nombre de valeurs au-dessus du seuil est supérieur à 100 ; dans le cas contraire, MM et PWM sont conseillés. De plus, comme c’est prouvé dans l’étude de valeurs réelles mesurées, les valeurs a priori aberrantes ("outliers") ont une influence notable sur le résultat et toutes les méthodes sont moins performantes. Comme cela a été montré dans la littérature, ces "outliers" proviennent souvent du mélange de deux distributions, qui peuvent être deux sous-populations. Dans le cas de l’effet du trafic sur les ouvrages, cela peut être la raison d’une estimation des paramètres non correcte. Les articles existant sur le sujet soulignent le fait que les effets du trafic sont dus à des chargements indépendants, qui correspondant au nombre de véhicules impliqués. Ils ne suivent pas la même distribution, ce qui contredit l’hypothèse classique en théorie des valeurs extrêmes que les événements doivent être indépendants et identiquement distribués. Des méthodes permettant de prendre en compte ce point et utilisant des distributions mélangées (exponentielles ou valeurs extrêmes généralisées) ont été proposées dans la littérature pour modéliser les effets du trafic. Nous proposons une méthode similaire, que nous appelons dépassement de seuils mélangés, afin de tenir des différentes distributions sous-jacentes dans l’échantillon tout en appliquant à chacune d’entre elles la méthode des dépassements de seuil. Pour des ponts ayant des portées supérieures à 50 m, le scénario déterminant est celui de la congestion, qui n’est pas ce qui est étudié ici. De plus, le trafic n’est pas la composante déterminante pour la conception des ponts de longue portée. Mais des problèmes de fatigue peuvent apparaître dans certains ponts, tels les ponts métalliques à dalle orthotrope, où l’étude du trafic peut devenir nécessaire. Ainsi nous avons fait une étude de l’influence de la position des véhicules sur le phénomène de fatigue. Pour cela, quatre fichiers de trafic réels, mesurés en 2010 et 2011 par quatre stations de pesage différentes, ont été utilisés. Ils ont mis à jour des comportements latéraux différents d’une station à l’autre. Si nous les appliquons au viaduc de Millau, qui est un pont métallique à haubans et à dalle orthotrope, nous voyons que l’histogramme des effets et l’effet de fatigue cumulé est beaucoup affecté par le comportement latéral des véhicules. Ainsi, des études approfondies utilisant les éléments finis pour modéliser les ouvrages et des enregistrements de trafic réel, peuvent être utilisées pour pré-déterminer quels éléments, donc quelles soudures, doivent être examinés dans les ponts afin d’estimer leur santé structurelle.
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Kristensson, Jonathan. "Load Classification with Machine Learning : Classifying Loads in a Distribution Grid". Thesis, Uppsala universitet, Institutionen för teknikvetenskaper, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-395280.
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This thesis explores the use of machine learning as a load classifier in a distribution grid based on the daily consumption behaviour of roughly 1600 loads spread throughout the areas Bromma, Hässelby and Vällingby in Stockholm, Sweden. Two common unsupervised learning methods were used for this, K-means clustering and hierarchical agglomerative clustering (HAC), the performance of which was analysed with different input data sets and parameters. K-means and HAC were unfortunately difficult to compare and there were also some difficulties in finding a suitable number of clusters K with the used input data. This issue was resolved by evaluating the clustering outcome with custom loss function MSE-tot that compared created clusters with subsequent assignment of new data. The loss function MSE-tot indicates that K-means is more suitable than HAC in this particular clustering setup. To investigate how the obtained clusters could be used in practice, two K-means clustering models were also used to perform some cluster-specific peak load predictions. These predictions were done using unitless load profiles created from the mean properties of each cluster and dimensioned using load specific parameters. The developed models had a mean relative error of approximately 8-19 % per load, depending on the prediction method and which of the two clustering models that was used. This result is quite promising, especially since deviations above 20 % were not uncommon in previous work. The models gave poor predictions for some clusters, however, which indicates that the models may not be suitable to use on all kinds of load data in its current form. One suggestion for how to further improve the predictions is to add more explanatory variables, for example the temperature dependence. The result of the developed models were also compared to the conventionally used Velander's formula, which makes predictions based on the loads' facility-type and annual electricity consumption. Velander's formula generally performed worse than the developed methods, only reaching a mean relative error of 40-43 % per load. One likely reason for this is that the used database had poor facility label quality, which is essential for obtaining correct constants in Velander's formula.
6
Cong, Jing [Verfasser]. "Load Specification and Load Generation for Multimedia Traffic Loads in Computer Networks / Jing Cong". Aachen : Shaker, 2006. http://d-nb.info/1170529038/34.
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Dennis, Gary. "Spinal Loads in Team Lifting". Thesis, Griffith University, 2003. http://hdl.handle.net/10072/367181.
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In the first experiment, spinal loads during individual and two-person team lifting tasks were compared. Ten healthy male subjects performed symmetrical individual lifts with a box mass of 15, 20 and 25 kg and symmetrical two-person team lifts with 30, 40 and 50 kg from the floor to standing knuckle height. Results indicated that the torque and compression force experienced by the lumbar spine were approximately 20% lower during team lifts compared to the load-matched individual lifting tasks. The two main and equal contributing factors reducing spinal load during team compared to individual lifting tasks were: (i) the increased horizontal pulling force and (ii) the ability of the team to hold the load at the ends of the box, which reduced the moment arm of the load. The second experiment assessed the effect of relative team member height (matched versus unmatched) on lumbar spinal loads during two-person team lifting tasks. Twelve young healthy male subjects performed matched and unmatched team lifts with two box masses (30 and 60 kg) and three initial box heights (0, 20 and 40 cm). Matched team members had standing heights within 5%, whilst unmatched teams had an average standing height difference of 25 ± 2.5 cm. Although spinal loads were reduced for the shorter subjects and increased for the taller subjects at the end of the lift, no significant difference was found in the maximum spinal loads incurred during matched compared to unmatched lifting conditions. In the final experiment the relationship between load mass distribution and the relative spinal loads incurred by each of the individual team members during two-person team lifting tasks was examined. Two-person lifting teams were required to lift a box containing a mass of 30 kg or 60 kg from the floor to standing knuckle height. Adjusting the position of the centre of mass within the box by ± 15 cm and ± 7.5 cm relative to the evenly distributed position (0 cm) yielded three load mass distribution ratios (69:31, 59:41 and 50:50), which represented the percentage of the total mass lifted by each team member. Although the spinal load incurred by the team member lifting at the heavier end of the load was greater than for the person at the lighter end of the load, the difference between the spinal loads incurred by each team member was not as great as the difference in the asymmetric distribution of the load mass. Subsequent investigation of the factors influencing spinal load indicated that the spinal loads experienced by the team member at the heavier end of the load was less than expected because they generated a larger horizontal pulling force than their lifting partner. Consequently, during the lift the load translated toward the team member at the heavier end of the load, which combined with the larger horizontal pulling force reduced the extensor torque required at the lumbar spine. Overall, results from this study have demonstrated that: (i) the lifting strategy used by two-person teams is distinguished from individual lifts by a greater use of horizontal pulling forces applied to the load and a decreased distance between the load and the lumbar spine, (ii) both the horizontal pulling force and the position of the hands on the load in team lifting have a load relieving effect on the lumbar spine and (iii) two-person team lifts performed by team members of unmatched standing height and with asymmetrical load mass appear to be coordinated in a manner that partially mitigates the increased spinal loads for the team member at increased risk of spinal injury.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Physiotherapy and Exercise Science
Griffith Health
Full Text
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Lindegård, Andersson Agneta. "Associations between working techniques, physical loads and psychosocial loads during VDU-work /". Stockholm : Arbetslivsinstitutet, förlagstjänst, 2004. http://ebib.arbetslivsinstitutet.se/ah/2004/ah2004_05.pdf.
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Asgarifard, Aniran. "Static Machines, Fragile Loads". Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/71804.
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Ramps are usually perceived as utilitarian objects emerging from standardized guidelines for architecture and landscape architecture. But closer examination reveals they can be quite beautiful and poetic. What we commonly call ramps, Galileo referred to as inclined planes, counting them as one of six classical simple machines in Le Meccaniche (On Mechanics) . Because inclined planes are actually static machines that do not require any energy to run.
They do not discriminate among users. This thesis explores the work of the ramp in moving fragile loads, such as human beings.Master of Landscape Architecture
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McColl, Chance C. "A matched-harmonic confluence approach to rotor loads prediction with comprehensive application to flight test". Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45837.
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Future management of helicopter fleets will be more heavily based on individual component damage tracking and less on legacy usage monitoring (flight parameter-based) methods. This enhances health assessment capabilities by taking into account the actual loads on a component-by-component basis. However, accurate loads prediction in rotating frame components remains a challenge. Even with advanced computational fluid dynamics (CFD) techniques, prediction of the unsteady aerodynamic loads acting on the rotor blades is computationally intensive and problematic in terms of accurate loads prediction across the entire flight regime of the helicopter. High-speed flight can potentially introduce both shock and near-stall effects within a given rotor rotation. Low-speed flight can include blade-vortex interaction effects, wherein flow from a given blade (vorticity loading from tip vortices) impinges upon the preceding blade, causing unsteady aerodynamic loading that is difficult to quantity and predict numerically. Vehicle maneuvering can produce significantly higher blade pitching moments than steady flight. All of these regimes combine to represent the loading history of the rotor system. Therefore, accurate loads prediction methods, in terms of matching peak-to-peak, magnitude, phase, as well as vibratory/harmonic content, are required that capture all flight regimes for all critical structural components.
This research focuses on the development of a loads prediction method, known as the Load Confluence Algorithm (LCA), and its application to the analysis of a large set of flight test data from the NASA/US Army UH-60A Airloads Program. The LCA combines measured response at a prescribed set of locations with a numerical model of the rotor system. For a given flight condition (steady flight, maneuvers, etc.) the numerical simulation's predicted loads distribution is iteratively incremented (by harmonic) until convergence with measured loads is reached at the prescribed locations (control points). Predicted loads response at non-instrumented locations is shown to be improved as well, thus enhancing fatigue lifing methods for these components.
The procedure specifically investigates the harmonic content of the applied loads and the improved prediction of the harmonic components. The impact of the enhanced accuracy on loads predictions on component structural fatigue is illustrated by way of an example.
Results show that, for a limited sensor set (two 3-axis sensors per blade), blade loads are accurately predicted across a full range of flight regimes. Hub loads are best modeled using the pushrod as the control point. Results also show that load magnitude has a tremendous influence on damage, with a 25% over-estimation of vibratory load resulting in a damage factor of nearly 3. This research highlights the importance of accurate loads prediction for a rotorcraft life tracking program. Small inaccuracies in loads lead to dramatic errors in damage assessment.
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Islam, Shariful. "Load Rating Study of Effects of Special Hauling Vehicle Loads on Ohio Bridges". University of Toledo / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1544818358028013.
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Jansson, Natascha. "Analysis of Dynamic Flight Loads". Licentiate thesis, KTH, Flygdynamik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-94881.
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This thesis deals with the determination of loads on an aircraft struc- ture during flight. The focus is on flight conditions where the loads are significantly time-dependent. Analysis of flight loads is primarily motivated to ensure that structural failure is avoided. The ability to ac- curately determine the resulting structural loads which can occur during operation allows for a reduction of the safety margins in the structural design. Consequently it is then possible to decrease the aircraft struc- tural weight. The demand for safe and fuel efficient aircraft creates a desire for efficient and accurate methods for determining the structural loads. The first paper of this thesis discusses the use of control laws for robust atmospheric turbulence load alleviation in the time domain. A numerical aircraft model including structural elasticity and unsteady aerodynamic effects is used. A limited set of longitudinal flight mechanic degrees of freedom are considered and two methods for structural load analysis are compared for evaluation of the wing root bending moment. In the second paper a method to perform time domain simulation of both motion of center of gravity and elastic deformation is described. The intention with the development of this simulation method is to enable efficient analysis of dynamic flight loads. A third study is finally included, where steady and unsteady pressure measurements have been carried out during wind tunnel testing. The motivation for performing these experiments is that knowledge about the aerodynamic force distribution which affect an aircraft structure is needed to correctly determine the structural loads.QC 20120529
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Kim, Hak Joon. "Estimation for tunnel lining loads". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq23005.pdf.
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Khavassefat, Parisa. "Pavement Response to Moving Loads". Licentiate thesis, KTH, Väg- och banteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-145321.
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The response of flexible pavements at vehicle-road interaction has been studied in this thesis. A quasi-static and a dynamic framework for analysing the pavement structure under moving load has been developed. Both frameworks are general, robust and computationally efficient. The quasi-static procedure is based on superposition principle and is computationally favourable, as it requires only reduced incremental problem to be solved numerically. Using the developed framework the effect of vehicle configuration and traffic characteristics on the damage induced in pavements is investigated numerically. It is shown that the developed numerical model provides a more accurate explanation of different distress modes. Moreover the conventional analysis and design methods with layered linear elastic behaviour assumption for asphalt layer are unable to capture several important aspects of pavement response. In the dynamic analysis approach the pavement roughness and vehicle suspension system is linked to a dynamic pavement model in order to account for the dynamic effects at vehicle-road interaction on pavement response. A finite element method is relied upon in order to establish the response function for a linear viscoelastic pavement structure with dynamic effects taken into account. The computational procedure developed is applied to evaluate the effect of the pavement surface roughness on the pavement structure response to truck traffic loading. Stress field parameters governing fracture initiation in asphalt layers are reported for two measured road roughness profiles. It is shown that the dynamic effects at vehicle-road interaction may have a profound influence on the stresses induced in flexible pavements; therefore these effects need to be taken into account for accurate prediction of the road performance in the field.QC 20140516
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Al-Battal, Nader. "Flow control for loads control". Thesis, University of Bath, 2019. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.767607.
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During gust encounters and turbulence aircraft are subject to extreme loads that dictate the structural requirements. Amelioration of these loads would allow reduced structural weight and therefore greater efficiency. Flow control is used for controlling the extreme loads at the fluid-structure interface. Two versions of the jet flap, normal and upstream blowing from the upper surface are studied under steady state conditions to illustrate the effectiveness of these devices at mitigating lift loads. The upstream blowing jet flap is further investigated through periodic and transient activation to demonstrate the feasibility for controlling transient gust encounters. These measurements include force, pressure and Particle Image Velocimetry measurements at a Reynolds number of 660,000 for a NACA 0012 airfoil.
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Seale, Sandra Hull. "Dynamic loads in layered halfspaces". Thesis, Massachusetts Institute of Technology, 1985. http://hdl.handle.net/1721.1/70618.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1985.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.
Bibliography: leaves 209-213.
by Sandra Hull Seale.
Ph.D.
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Ali, Sk Sekender. "Concentrated loads on solid masonry". Thesis, University of Newcastle upon Tyne, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335631.
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Karimi, Kambiz. "Clustering analysis of residential loads". Kansas State University, 2016. http://hdl.handle.net/2097/32616.
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Master of ScienceDepartment of Electrical and Computer Engineering
Anil Pahwa
Understanding electricity consumer behavior at different times of the year and throughout the day is very import for utilities. Though electricity consumers pay a fixed predetermined amount of money for using electric energy, the market wholesale prices vary hourly during the day. This analysis is intended to see overall behavior of consumers in different seasons of the year and compare them with the market wholesale prices. Specifically, coincidence of peaks in the loads with peak of market wholesale price is analyzed. This analysis used data from 101 homes in Austin, TX, which are gathered and stored by Pecan Street Inc. These data were used to first determine the average seasonal load profiles of all houses. Secondly, the houses were categorized into three clusters based on similarities in the load profiles using k-means clustering method. Finally, the average seasonal profiles of each cluster with the wholesale market prices which was taken from Electric Reliability Council of Texas (ERCOT) were compared. The data obtained for the houses were in 15-min intervals so they were first changed to average hourly profiles. All the data were then used to determine average seasonal profiles for each house in each season (winter, spring, summer and fall). We decided to set three levels of clusters). All houses were then categorized into one of these three clusters using k-means clustering. Similarly electricity prices taken from ERCOT, which were also on 15-min basis, were changed to hourly averages and then to seasonal averages. Through clustering analysis we found that a low percent of the consumers did not change their pattern of electricity usage while the majority of the users changed their electricity usage pattern once from one season to another. This change in usage patterns mostly depends on level of income, type of heating and cooling systems used, and other electric appliances used. Comparing the ERCOT prices with the average seasonal electricity profiles of each cluster we found that winter and spring seasons are critical for utilities and the ERCOT price peaks in the morning while the peak loads occur in the evening. In summer and fall, on the other hand, ERCOT price and load demand peak at almost the same time with one or two hour difference. This analysis can help utilities and other authorities make better electricity usage policies so they could shift some of the load from the time of peak to other times.
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Perng, Horng-Linn. "Damage accumulation in random loads". Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184822.
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An equivalent constant amplitude fatigue loading (Miner's stress) is developed for stationary random amplitude loadings. The effects of rainflow cycle counting and fatigue crack closure are included. A method for determining the opening stress in a random loading is also proposed. This research takes a fatigue damage factor approach. The damage factor is defined as the ratio of the wide band rainflow fatigue damage to the equivalent narrow band fatigue damage. The mathematical form of the damage factor equations is derived from theoretical derivations using the analytically tractable local range cycle counting method. Simulations of stationary Gaussian random processes are used to empirically derive the values of certain parameters dependent on the spectral shape for the rainflow cycle counting equations. There are five tasks in this research. (1) A simulation program for generating a Gaussian process has been written and is used to generate random loading histories for this study. (2) A previously proposed rainflow damage factor has been verified and refined with these simulations, without considering crack closure. (3) Using a sinusoidal approximation, the joint probability density functions between peaks, valleys and rises counted by the local range method are derived. (4) The resulting joint probability distributions are used to determine the theoretical damage with crack closure; simulations are again used to calibrate the parameters for rainflow stress cycles. (5) A procedure for finding an equivalent constant fatigue crack opening stress for stationary random loadings is described. An example application of the procedures and equations is given.
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Chen, Emily. "Thermal Loads in Space Turbines". Thesis, Luleå tekniska universitet, Rymdteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-75719.
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Prediction of thermal loads within cavities in space turbine, has as been a challenging task in aspects of achieving accurate and reasonable estimations that are crucial for design concepts. The difficulty lies within the turbulent flow and its thermal interaction with the structure inside such section. It does not exist a method that works perfectly for prediction of thermal loads in any cavity and the taken approach to perform this kind of analysis has been differently chosen. The objectives of this work have been to improve methods for assessment of thermal loads in space turbines, especially calculation of the heat transfer coefficient and bulk temperature. As the thesis was conducted at GKN Aerospace Sweden, Trollhättan, one of theirs demonstrator turbine was chosen for the study case. Its first stage rotor blade and the nearby cavity were the main research regions. The flow can enter and exit the cavity through one slot and is characterized with a very low axial speed. For the studied regions, the wall surface has been subdivided into a number of segments. With prescribed wall temperatures and use of computational fluid dynamics (CFD) to compute the wall heat flux at the sections, the heat transfer coefficient and bulk temperatures were determined in three different ways. One of them was based on evaluating one single CFD result and derive the thermal loads from formulas. The others used by point-plotting approach, whereas one of them focused on formulating a model that describes the thermal interaction between the section walls. The results demonstrate that this model was able to predict a section's wall heat flux as a function of the wall temperatures in fair agreement with CFD results for a range of temperature variations. Further more, some of the predicted heat transfer coefficient at a section shows to be highly sensitive to the prescribed wall temperatures in the cavity and rotor blade.
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Yang, Yang. "Scheduling divisible loads in multiple rounds /". Diss., Connected to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2005. http://wwwlib.umi.com/cr/ucsd/fullcit?p3174407.
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Thesis (Ph. D.)--University of California, San Diego, 2005.Title from first page of PDF file (viewed February 28, 2006). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references ( p. 159-170).
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Sæterstad, Marie Lunde. "Dimensioning Loads for a Tidal Turbine". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-13637.
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The main dynamic loads on a tidal turbine are due to the tidal current variation, turbulence, wave-current interaction and wake from the tower and upstream turbines. The design of the turbine is highly dependent on the dynamic loads acting on the turbine's blades and its structure. Cyclic loading and unloading of any material over a period of time will lead to fatigue and structural damage. In this work dimensioning loads for NTNU's 1 MW reference tidal turbine are calculated due to the vertical no-slip current velocity profile, wave-current interaction, the horizontal and vertical velocity component due to the waves, turbulence and the tidal wave. Based on mathematical models the dimensioning loads for the turbine are calculated with a Matlab code written for this work. The influence of each of the components causing a dynamic load on the tidal turbine blades is evaluated and analyzed with the rainflow counting algorithm, which can be used for fatigue analysis.Results from Matlab calculations are compared to experimental results in order to validate the Matlab code. In the comparison the trends are the same for calculation and experimental results, oscillating curves with the same period. It is noticed that in large waves the Matlab code predicts very well the dynamic loads in terms of mean and peak-to-peak values.For the thrust force and the shaft torque the horizontal component of the velocity due to the waves has the largest influence on the peak-to-peak values and the turbulence induces a high number of cycles. For the pitch moment as well the horizontal component due to the waves has the largest influence on the peak-to-peak values, but also the vertical component has a certain influence. For the pitch moment the consistently main oscillations inducing cyclic loading are due to the vertical no-slip current velocity profile. This is also the case for the yaw moment, but here the vertical wave component has the largest influence on the peak-to-peak values. For calculation with the tidal wave it is noticed that higher velocities gives higher maximum values. The Matlab code is a reliable and fast tool. Despite the simplifications done in the calculations, it calculates the dimensioning loads for a tidal turbine with a good accuracy.
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Havn, Jarle. "Wave Loads on Underwater Protection Covers". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-16225.
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Submerged structures in shallow water can be exposed to large hydrodynamic wave- and current forces. An estimate of the total external loads will be important for the design and robustness of the structures. The aim will also be to achieve more correct estimates in accordance with the physical loads. In the present work, wave forces on submerged protection covers over offshore pipelines in shallow water have been investigated. Protection covers have usually a small dry weight. In some cases, it can last some time before stabilizing gravel is dumped on the covers and the covers will in the mean time be freely exposed to the hydrodynamic forces. In order to investigate the shallow water forces, two simplified protection covers were studied with both a numerical CFD analysis and performed experiments in a wave tank. A rectangular and a half circular geometry was chosen for the simplified covers. A Numerical Wave Tank (NWT) modeled with Computational Fluid Dynamics (CFD), can be used to make similar analysis as performed experiments in a physical wave tank. The use of numerical analysis can reduce both cost and time in comparison with physical experiments. In the present work a two dimensional numerical wave tank was investigated with the numerical CFD software ANSYS CFX. Further the numerical wave tank was used to investigate the dynamic wave forces on the simplified protection covers. Numerical wave elevation and numerical forces was compared with a theoretical approach. A modeled numerical piston or flap wavemaker gave reasonable wave elevation and was found usable to produce numerical waves. A comparison with results by Silva et al. (2010) gave almost similar results. Time series of wave elevation was found to be in good agreement with both theory and experiments. Numerical wave forces on the simplified covers gave good results compared with linear theory. Theoretical horizontal added mass coefficient was found to Ca,1= 1,53 for the rectangular cover and Ca,2= 1,145 for the half circular cover. Similar in CFD the horizontal added mass coefficients was found to be Ca,1= 1,4 and Ca,2= 1,18 respectively. The vertical forces from CFD was a small value larger than the theoretical linear vertical Froude-Kriloff forces. The experimental tests was performed in the student wave tank at MARINTEK in Trondheim. Wave elevation from two wave probes and vertical force from three force transducers was measured. The wave elevation was compared with both numerical and theoretical wave elevation. The damping along the tank length was found to be similar as in the CFD analysis of around 1%/m. Due to different experimental setup and numerical modeling the vertical forces was not comparable. Non dimensional vertical forces and overturning moment was found from the performed experiments. Largest forces was measured on the rectangular cover. Largest non dimensional forces and overturning moment was found for the half circular cover.
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Holm, Herman. "Ice-Induced Loads on Ship Hulls". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18651.
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The calculation of ice-induced loads on ships is still mainly based on empirical models. In order to gain a better physical understanding of the loading on ice-going vessels, Det Norske Veritas launched an <i>ice load monitoring<i> project involving full scale trials with the coastguard vessel KV Svalbard during the winters 2006, 2007 and 2011. The results from the full scale measurements conducted with KV Svalbard has been topic of several earlier master's thesis at NTNU,The master thesis consists of four parts. The first part is a literature review of the mechanical and physical properties of sea ice.The second part is a review of the rule sets developed by DNV and the IACS regarding vessels operating in ice infested waters. Both design principles and numerical values have been evaluated. The main difference between the designs principles used, is that IACS base their rules on a plastic method of approach, while DNV uses an elastic method. Despite the difference in the design principles, when comparing their numerical values turned out to be quite similar. The DNV rules are in general most conservative for the smaller vessels and the IACS rules the most conservative for large vessels. The third part consists of a finite element study of a part of the bow on KV Svalbard. A systematic load scheme is used, consisting of 102 load cases. For each of the stress factors there where made graphs that showed the stress at the sensor location when moving the patch load. The sensor mounted on the frame were able to measure load that was within the frame loading area and sensor mounted on the stringer could measure stress for all of the load cases in the horizontal directions. One of the explanations for this is that the stringer transfers stress from the load patch area that could be measured by the sensors.The last part consists of a comparison between measurements from the full scale trials and the results from the 102 load cases. This comparison is done through a weighted summation method where 5 different load cases are combined to represent the measured result, and a load factor is calculated for each load case for its contribution of the measured results. The stress component used in this comparison is the shear stress tau xy The load cases were tested against the 11 measurements from the full scale trials. There were in total 11 load cases that gave positive factors for all of the 11 measurements at the same time. A figure was made to show which load cases were likely to contribute in the solution of the load cases. Load cases inside the frame loading area have the largest load factors for the solution of measurements.This load decision scheme is very sensitive to the selection of load cases and boundary conditions. A change of the boundary conditions for the model was tried out for 7 load cases, and with changed boundary conditions, only 5 gave positive load factors.The results of this thesis shows that is possible to find many solution to the measured result by combining many load case, but is it not possible to decide <i>the<i> solution.
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Bransby, Mark Fraser. "Piled foundations adjacent to surcharge loads". Thesis, University of Cambridge, 1995. https://www.repository.cam.ac.uk/handle/1810/251968.
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Lone, Mohammad Mudassir. "Pilot modelling for airframe loads analysis". Thesis, Cranfield University, 2013. http://dspace.lib.cranfield.ac.uk/handle/1826/10388.
Pełny tekst źródłaStreszczenie:
The development of large lightweight airframes has resulted in what used to be high frequency structural dynamics entering the low frequency range associated with an aircraft’s rigid body dynamics. This has led to the potential of adverse interactions between the aeroelastic effects and flight control, especially unwanted when incidents involving failures or extreme atmospheric disturbances occur. Moreover, the pilot’s response in such circumstances may not be reproducible in simulators and unique to the incident. The research described in this thesis describes the development of a pilot model suitable for the investigation of the effects of aeroelasticity on manual control and the study of the resulting airframe loads. After a review of the state-ofthe- art in pilot modelling an experimental approach involving desktop based pilot-in-the-loop simulation was adopted together with an optimal control based control-theoretic pilot model. The experiments allowed the investigation of manual control with a nonlinear flight control system and the derivation of parameter bounds for single-input-single-output pilot models. It was found that pilots could introduce variations of around 15 dB at the resonant frequency of the open loop pilot-vehicle-system. Sensory models suitable for the simulation of spatial disorientation effects were developed together with biomechanical models necessary to capture biodynamic feedthrough effects. A detailed derivation and method for the application of the modified optimal control pilot model, used to generate pilot control action, has also been shown in the contexts of pilot-model-in-the-loop simulations of scenarios involving an aileron failure and a gust encounter. It was found that manual control action particularly exacerbated horizontal tailplane internal loads relative to the limit loads envelope. Although comparisons with digital flight data recordings of an actual gust encounter showed a satisfactory reproduction and highlighted the adverse affects of fuselage flexibility on manual control, it also pointed towards the need for more incident data to validate such simulations.
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Stålnacke, Per. "Nutrient loads to the Baltic Sea /". Linköping : Univ, 1996. http://www.bibl.liu.se/liupubl/disp/disp96/arts146s.htm.
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Earl, Timothy J. "Modelling nutrient loads from British catchments". Thesis, University of Essex, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.495764.
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Reeves, P. "Wind loads on semi-submersible platforms". Thesis, University of Strathclyde, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382429.
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Heathcote, Daniel. "Aerodynamic loads control using mini-tabs". Thesis, University of Bath, 2017. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760920.
Pełny tekst źródłaStreszczenie:
Aircraft encounter increased aerodynamic loads when exposed to gusts, turbulence andmanoeuvres. Currently, these loads are mitigated through the use of ailerons and spoilers to reduce lift, in turn reducing the loads passed to the aircraft structure. However, these actuators are limited in their frequency response and cannot control loads produced by higher frequency events. Therefore, an actuator which can mitigate high frequency oscillatory loads is required, with a deployment reduced frequency, k of up to 1. One such promising load control actuator is the minitab, consisting of a small span-wise strips, similar to the Gurney flap, deployed normal to the airfoil upper surface. Key to the actuator’s high frequency response is its low inertia, meaning that a small energy input can achieve a significant effect. To investigate the efficacy of the minitab on load alleviation a series of steady state, periodic and transient measurements were conducted at a Reynolds number of 6.6 x 105. These experiments aimed to fully evaluate the effect of chordwise location, mini-tab height and angle of attack on steady state load control. The dynamic response was categorised, in terms of magnitude, phase and time delay by the periodic and transient measurements. Mini-tabs of height h/c = 0.02 and 0.04 were employed in a steady state configurationacross a range of chordwise locations to investigate the effects of mini-tab height and chordwise position. Overall, the mini-tab was found to have a lift reducing effect which increased with height. It was found that the effect of the chordwise location was highly dependent on the angle of attack. Placement close to the trailing edge induced a large effect at α = 0°, creating an effective change in camber comparable to conventional Gurney flap use. Peak suction over the lower surface increased resulting in a reduction of ΔCL = -0.48. Approaching stall, effectiveness decreased as the mini-tab became immersed in the separated flow. Placement at xf/c = 0.60 produced an almost constant lift reduction between α = 0° and 5° of ΔCL ≈ -0.60, with a gradual reduction to stall. A mini-tab positioned close to the leading edge (xf/c = 0.08) was found to separate the flow effectively at low incidences but with no noticeable change in lift observed. It was found that the flow separation produced by the mini-tab effectively eliminated the suction peak on the upper surface. However, placement close to the leading edge has increasing effectiveness towards stall, as the shear layer induced by the separation was displaced further from airfoil surface. Peak lift reduction at stall was found to be ΔCL ≈ -0.67. The optimum chordwise location for peak lift reduction is dependent on the airfoil angle of attack: the position of the mini-tab for maximum lift reduction moves towards the leading edge as the angle of attack increases. The second stage utilised a deployable mini-tab up to reduced frequencies, k = 0.79, placedat xf/c = 0.85, to assess the mini-tab’s frequency response. The force measurements indicate that the mini-tab has a decreasing effect on lift reduction with increasing actuation frequency. This trend is comparable to Theodorsen’s function, based on the change in circulation. For α = 0°, the normalised peak-to-peak lift reduction decreased from 1 for steady state deployment to around 0.6 at k = 0.79. In addition, a phase lag exists between the mini-tab deployment and the aerodynamic response which increased with actuation reduced frequency, k. However, the measured phase lag is substantially larger than Theodorsen’s prediction. Increasing the angle of attack, α reduced the mini-tab’s effect on lift while increasing the phase angle when comparing equal k values. Particle Image Velocimetry measurements indicate that the delay and reduction in effectiveness of periodic deployment is due to the presence and growth of the separated region behind the mini-tab. Overall, the mini-tab was found to be an effective, dynamic lift reduction device with the separated region behind the mini-tab key to the amplitude and phase delay of lift response. Finally, the aerodynamic response of the mini-tab was investigated during a transientdeployment. The delay in aerodynamic response to mini-tab actuation was consistent with literature. The normalised deployment period, τdeploy did not provide a significant alteration in the aerodynamic response for deployment periods below τdeploy = 3, with the aerodynamic response reaching the steady state value around τ = 6-8. The aerodynamic response of the mini-tab was approximated using a simple, 1st order system response to a ramp-step input of gradient 1/τdeploy, indicating that the aerodynamic response of the mini-tab is further delayed for higher angles of attack, due to the presence of separated flow in the vicinity of the mini-tab. PIV measurements were utilised to analyse the effect of transient mini-tab deployment, indicating a delay in the development of the separation region created by the mini-tab, producing a corresponding delay in aerodynamic response. In addition, outward deployment was found to have a slower aerodynamic response than inward deployment, as the flow was found to take to detach slower than to reattach.
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Klepsvik, Jonny. "Nonlinear wave loads on offshore structures". Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/36062.
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Sangi, Abdul Jabbar. "Reinforced concrete structures under impact loads". Thesis, Heriot-Watt University, 2011. http://hdl.handle.net/10399/2485.
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33
Eccles, Lee H. "PRESSURE BELT FOR WING LOADS MEASUREMENT". International Foundation for Telemetering, 2001. http://hdl.handle.net/10150/606396.
Pełny tekst źródłaStreszczenie:
International Telemetering Conference Proceedings / October 22-25, 2001 / Riviera Hotel and Convention Center, Las Vegas, NevadaBoeing Commercial Airplanes has used many methods in the past to measure the structural loads on the wings of its airplanes. The most recent approach is to use arrays of MEMS pressure sensors on the top and bottom surfaces of the wings. By knowing the difference in pressure between the top and bottom of the wings the structural loads on the wings can be calculated. It was decided that in order to build an array of 1100 sensors it would be necessary to condition the sensors and convert the analog output to a digital form at the site of the pressure measurement. This process was taken one step further by converting the output of the A/D converter into engineering units within the sensor module as well. The array is built using a flex circuit card in one foot sections that can be interconnected to form an array of up to 125 sensors. There is a sensor location every two inches on the flex circuit but not all locations are populated. This paper will describe not only the pressure belt but the lessons learned during the development and the implications that these lessons have for smart transducers in general.
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Lone, M. Mudassir. "Pilot modelling for airframe loads analysis". Thesis, Cranfield University, 2013. http://dspace.lib.cranfield.ac.uk/handle/1826/10388.
Pełny tekst źródłaStreszczenie:
The development of large lightweight airframes has resulted in what used to be high frequency
structural dynamics entering the low frequency range associated with an aircraft’s rigid body dynamics.
This has led to the potential of adverse interactions between the aeroelastic effects and
flight control, especially unwanted when incidents involving failures or extreme atmospheric disturbances
occur. Moreover, the pilot’s response in such circumstances may not be reproducible
in simulators and unique to the incident. The research described in this thesis describes the
development of a pilot model suitable for the investigation of the effects of aeroelasticity on
manual control and the study of the resulting airframe loads. After a review of the state-ofthe-
art in pilot modelling an experimental approach involving desktop based pilot-in-the-loop
simulation was adopted together with an optimal control based control-theoretic pilot model.
The experiments allowed the investigation of manual control with a nonlinear flight control
system and the derivation of parameter bounds for single-input-single-output pilot models. It
was found that pilots could introduce variations of around 15 dB at the resonant frequency
of the open loop pilot-vehicle-system. Sensory models suitable for the simulation of spatial
disorientation effects were developed together with biomechanical models necessary to capture
biodynamic feedthrough effects. A detailed derivation and method for the application of the
modified optimal control pilot model, used to generate pilot control action, has also been shown
in the contexts of pilot-model-in-the-loop simulations of scenarios involving an aileron failure
and a gust encounter. It was found that manual control action particularly exacerbated horizontal
tailplane internal loads relative to the limit loads envelope. Although comparisons with
digital flight data recordings of an actual gust encounter showed a satisfactory reproduction and
highlighted the adverse affects of fuselage flexibility on manual control, it also pointed towards
the need for more incident data to validate such simulations.
35
Perez, Tellez Adriel. "Modelling aggregate loads in power systems". Thesis, KTH, Elkraftteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-204600.
Pełny tekst źródłaStreszczenie:
The load response to voltage and frequency changeshas a considerable impact on the behaviour of the powersystem. Thus, the selection of a load model structure andits corresponding parameters is an important task in orderto study and predict the system behaviour. Currently,the Nordic Transmission System Operators (TSO) use theZIP load model, as it provides an easy and flexible way ofrepresenting the load. The main goal of the thesis has beento test two approaches for deriving ZIP model parameters,namely the component-based and measurement-basedapproaches. The former approach uses predefined parametervalues, and information on the loads electricityconsumption, whereas the latter uses measurement dataand curve-fitting techniques. In order to evaluate themethodology, a case study has been performed, wherethe two aggregation approaches were applied on anevaluation point. It was found that the aggregation bymeans of the component-based approach may result in ZIPparameters lacking physical significance. ZIP parameterswithout physical significance pose a challenge for systemplanners, who may have difficulties in accepting thesevalues as they are less intuitive than physically significantones. Furthermore, the results of the measurement-basedapproach indicate that the ZIP model has some limitationwhen it comes to the sudden load changes that it canaccommodate. This has been the case with the measuredreactive power in the case study. Based on the resultsof applying the methodology, it can be concluded thatthe component-based and measurement-based approachesprovide useful information when understanding powersystem loads.Lastens svar på spänning och frekvensförändringarhar en betydande inverkan på elkraftsystemet. Sålundaär valet av en lastmodell och dess parametrar viktigt föratt kunna studera och förutsäga systemets beteende. Förnärvarande använder de nordiska stamnätsägarna (TSO)ZIP lastmodellen, eftersom det ger ett enkelt och flexibeltsätt att representera lasten. Huvudsyftet med den häravhandlingen har varit att testa två metoder för att ta framZIP modellparametrar, nämligen en komponent-baseradoch en mätnings-baserade metod. Den tidigare metodenanvänder fördefinierade parametervärden, och informationom lasternas elförbrukning, medan den senare användermätdata och kurvanpassningstekniker. För att utvärderametoden har en fallstudie genomförts där de två metodernaapplicerades på en utvärderingspunkt. Det konstateradesatt den komponent-baserade metoden kan resultera i ZIPparametrar som saknar fysisk betydelse. ZIP parametrarutan fysisk betydelse utgör en utmaning för systemplanerare,som kan ha svårt att acceptera dessa värden eftersom deär mindre intuitiva än fysiskt betydande sådana. Dessutomindikeras det, att ZIP modellen har begränsningar när detgäller att representera stora steg i den uppmätta effektenssvar, då den mätnings-baserade metoden används. Dettaär fallet för den reaktiva effekten i fallstudien. Baserat påresultaten av tillämpningen av metoden, kan man dra slutsatsenatt den komponent-baserade och mätnings-baserademetoden ge användbar information när man vill förståkraftsystems laster.
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Svensson, Niklas. "Fatigue Analysis with Loads from MBS". Thesis, KTH, Maskinkonstruktion (Inst.), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-168720.
Pełny tekst źródłaStreszczenie:
Detta examensarbete har utförts i samarbete med Scania CV AB, en lastbils- och busstillverkare. Scania tror att en stor del i att behålla en ledande position är att erbjuda sina kunder pålitlighet, bland annat i form av livslängd. På grund av detta så är utbyggnad av kompetens och kunskap kring utmattningsanalys alltid aktuellt. Simuleringsdriven produktutveckling har dessutom ökat intresset för simuleringar tidigare i produktutvecklingen. Detta skapar nya utmaningar då det kräver att utmattningsanalyser utförs innan en fysisk prototyp finns. Då laster krävs för utmattningsanalyser är en tänkbar lösning att skapa lastfall med multibody simulations (MBS) med virtuella prototypfordon körandes en virtuell provbana.Huvudsyftet med detta arbete är att undersöka potentialen för att utföra analyser med laster från MBS. Fyra olika analysmetoder, som används inom Scania, har utförts med laster från MBS istället för från provbana. En utvärdering av metodernas robusthet och deras resultat jämfört med resultat från testrigg var tänkt att ge en indikation för vilken virtuell metod som har störst potential. Ett rammonterat inverterfäste som gått sönder i testrigg analyserades under arbetet. En modell av komponenten genererades i Abaqus och importerades i Adams för MBS. Laster som uppmättes i Adams användes för att utföra de olika utmattningsanalyserna.Det visade sig att två metoder var mer lovande än övriga: Dynamisk simulering med PSD och Superposition av modala spänningar. Men, utmattningsuppskattningarna från de genererade lasterna överensstämde inte med utfallet från det fysiska testet. I testrigg gick komponenten sönder medan analyserna indikerade att den inte skulle komma nära utmattningsbrott. Genom att jämföra lastsignalerna från testrigg och MBS uppdagades det att signalerna avvek kraftigt från varandra. Analys med testriggsignal indikerade att komponenten skulle gå sönder, vilket den också gjorde. Användande av lastsignalen från provbanan ledde däremot till ungefär samma skada som analyserna med MBS gav.Dessa resultat indikerar att det finns potential för utmattningsanalyser med virtuellt anhållna laster. Vidare undersökningar med ytterligare komponenter behöver dock genomföras innan definitiva slutsatser kan dras. Att utröna anledningen till att provet i testrigg varit tuffare än verkligheten är också av intresse.Scania is a truck and bus developer. They believe that reliability, which is strongly associated with life length, has been critical in achieving a leading position and is key to retaining it. Therefore, there is a continuous drive to increase their capability to simulate life length, specifically fatigue. Additionally, the recent popularity of simulation driven product development has created an additional interest in performing simulations earlier in the product development process. This creates a challenge since it requires fatigue analyses to be performed before prototype vehicles are available. Since loads are required for fatigue analyses, one solution is to perform a multibody simulation (MBS) of a virtual prototype vehicle on a virtual test track and derive load cases.This thesis investigated the possibility of using loads derived from MBS simulations to perform fatigue analyses. Four different simulation methods which are currently used by Scania were evaluated with MBS loads instead of physically measured loads. By comparing the methods’ results to those of physical tests, the virtual methods with the greatest potential were identified. A chassis mounted inverter bracket was analyzed in this work. The component was modeled in Abaqus, a model which then was merged into a complete bus model in Adams. Next, this model was run as an MBS over the virtual test track and load data was extracted. The component was then analyzed with different fatigue analysis methods, with the data from the MBS used as input. The fatigue results were then compared with the results of a physical shake rig test of the same component.Two methods were found to be most promising: Dynamic simulation with PSD and Superposition of modal stresses. Interestingly, the fatigue estimation for these methods substantially differed from the outcome of the physical test. The component failed in the physical test but according to the simulation it should have survived. Upon further investigation, it was found that the component was subjected to higher loads in the shake rig than on the shake track. A fatigue simulation using the signal from the shake rig agreed with the outcome of the physical test, namely failure. Analysis using the figures from the test track gave values similar to the results for analyses with MBS loads.These results suggest that this type of virtual analysis has potential. But before more definite conclusions can be drawn further investigations with more than one component need to be performed. Another path of investigation is to look at why the shake rig test is more severe than the virtual shake track.
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Zhang, Yu Ph D. Massachusetts Institute of Technology Department of Mechanical Engineering. "Wave loads on offshore wind turbines". Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/100344.
Pełny tekst źródłaStreszczenie:
Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (page 65).
Ocean energy is one of the most important sources of alternative energy and offshore floating wind turbines are considered viable and economical means of harnessing ocean energy. The accurate prediction of nonlinear hydrodynamic wave loads and the resulting nonlinear motion and tether tension is of crucial importance in the design of floating wind turbines. A new theoretical framework is presented for analyzing hydrodynamic forces on floating bodies which is potentially applicable in a wide range of problems in ocean engineering. The total fluid force acting on a floating body is obtained by the time rate of change of the impulse of the velocity potential flow around the body. This new model called Fluid Impulse Theory is used to address the nonlinear hydrodynamic wave loads and the resulting nonlinear responses of floating wind turbine for various wave conditions in a highly efficient and robust manner in time domain. A three-dimensional time domain hydrodynamic wave-body interaction computational solver is developed in the frame work of a boundary element method based on the transient free-surface Green-function. By applying a numerical treatment that takes the free-surface boundary conditions linearized at the incident wave surface and takes the body boundary condition satisfied on the instantaneous underwater surface of the moving body, it simulates a potential flow in conjunction with the Fluid Impulse Theory for nonlinear wave-body interaction problems of large amplitude waves and motions in time domain. Several results are presented from the application of the Fluid Impulse Theory to the extreme and fatigue wave load model: the time domain analysis of nonlinear dynamic response of floating wind turbine for extreme wave events and the time domain analysis of nonlinear wave load for an irregular sea state followed by a power spectral density analysis.
by Yu Zhang.
S.M.
38
Anbo, Anders. "Identification of extreme load cases for a surface drill rig by means of MBS simulations". Thesis, Uppsala University, Division of Scientific Computing, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-130228.
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This master thesis is Atlas Copco Craelius’ first step in incorporating numericalmethods in load case analysis during the development process. Atlas Copco needs toconstantly evolve and refine their methods in the design process to remain as thenumber one manufacturer of mining and construction equipment. Poor knowledge ofloads results either in structural failures or in oversized structures, both very costlyfor Atlas Copco.The main goal of this thesis is to examine the potential in MBS software by using it toidentify extreme load cases in one of Atlas Copco Craelius’ surface drill rigs, Mustang5. The MBS-software ADAMS View is used to build a model of the Mustang 5 drill rigand evaluate simulation results. The rig model is subject to motions which representreal case scenarios. The feed positioning possibilities are examined thoroughly since it was expected that the positioning has impact on the load levels. 25 different feedpositioning are simulated.The main conclusion is that the load levels are highly dependent on the feedpositioning. For example, the load levels in the boom raising cylinder can increaseseven times, if the rig is operated with the most unfavorable positioning compared tothe recommended. It could also be concluded that not only one positioning isextreme in terms of loads; it depends on which part of the boom system is beingobserved. Thus, several positioning cases have to be taken into consideration in orderto optimize the design of parts in the boom system.
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Helmers, Matthew J. "Use of Ultimate Load Theories for Design of Drilled Shaft Sound Wall Foundations". Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/36856.
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A study was performed to investigate the factors that affect the accuracy
of the procedures used by the Virginia Department of Transportation for
design of drilled shaft sound wall foundations. Field load tests were
performed on eight inch and nine inch diameter drilled shafts, and the
results were compared to theoretical solutions for ultimate lateral load
capacity. Standard Penetration Tests were run in the field and laboratory
strength tests were performed on the soils from the test sites. It was
found that published correlations between blow count and friction angle
for sands and gravels can be used to estimate friction angles for the
partly saturated silty and clayey soils encountered at the test sites.
A spreadsheet program was developed to automate the process of determining
design lengths for drilled shaft sound wall foundations. The spreadsheet
was used to investigate the effects of different analysis procedures and
parameter values on the design lengths of drilled shaft sound wall
foundation.Master of Science
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Hensley, John Eric. "Rotordynamic coefficients for a load-between-pad, flexible-pivot tilting pad bearing at high loads". Texas A&M University, 2006. http://hdl.handle.net/1969.1/4404.
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The dynamic and static performance of a flexure-pivot tilting pad bearing is presented at
a load between pad configuration for various load and speed combinations. A similar
work performed on the same bearing at lower loads ranging from 0-1 MPa (0-150 psi) by
Al-Ghasem was tested, whereas the current work investigates effects in the load range
between 1-2.2 MPa (150-320 psi). The bearing design parameters include: 4 pads with
pad arc angle 72ú and 50% pivot offset, pad axial length 0.0762 m (3 in), pad radial
clearance 0.254 mm (0.010 in), bearing radial clearance 190.5 õm (0.0075 in), preload
0.25, and shaft nominal diameter of 0.11684 m (4.600 in). An important distinction
between the two sets of tests is the difference in experimental bearing radial clearance,
which for this case measured 208 õm (0.00082 in), and for Al-GhasemâÂÂs was 165.1 õm
(0.0065 in). The rotordynamic coefficients are determined experimentally using a test rig
equipped with motion and load sensors. The rig is modeled using NewtonâÂÂs laws, which
is converted from the time to frequency domain using Fourier Transform to give complex
dynamic stiffnesses. From the resulting complex dynamic stiffnesses the associated real
and imaginary components are plotted as a function of excitation frequency and curve
fitted via linear regression to give the rotordynamic coefficients. The primary objectives
were to determine whether the real component of the complex dynamic stiffnesses could
be better modeled with or without the mass coefficient and to contrast the rotordynamic
coefficients with an analytical model. Only in the load range of 1 to 2.2 MPa were the
unloaded direct mass coefficients near or at 0, which would allow for a [K][C] model to
be used. The remaining real components are better represented with the mass term. The
analytical model generally overpredicted the stiffness, damping and mass coefficients,
especially for the direct components; the trends were generally consistent.
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Spjutare, Christian. "Aerodynamic Loads on External Stores - Saab 39 Gripen : Evaluation of CFD methods for estimating loads on external stores". Thesis, Linköping University, Applied Thermodynamics and Fluid Mechanics, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-54127.
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External stores mounted on aircraft generate loads which need to be estimated before first takeoff. These loads can be measured in a wind tunnel but since the possible store configurations are basically endless, testing them all is neither economically feasible nor time efficient. Thus, scaling based on geometrical similarity is used. This can, however, be a crude method. Stores with similar geometrical properties can still behave in different ways due to aerodynamic interference caused by adjacent surfaces.
To improve the scaling performance, this work focuses on investigating two CFD codes, ADAPDT and Edge. The CFD simulations are used to derive the difference in aerodynamic coefficients, or the Δ-effect, between a reference store and the new untested store. The Δ-effect is then applied to an existing wind tunnel measurement of the reference store, yielding an estimation of the aerodynamic properties for the new store.
The results show that ADAPDT, using a coarse geometry representation, has large difficulties predicting the new store properties, even for a very simple store configuration on the aircraft. Therefore it is not suited to use as a scaling tool in its present condition. Edge on the other hand uses a more precise geometry representation and proves to deliver good estimations of the new store load behavior. Results are well balanced and mainly conservative. Some further work is needed to verify the performance but Edge is the recommended tool for scaling.
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Elliott, Robin James. "Stability and metabolic analysis of walking on cross-slopes with various vertically placed backpack loads and without loads". Thesis, The University of Utah, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10248968.
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Though many who walk along roadside cambers and hill edges may have an interest in making their travels sure and effective, those most concerned may be soldiers in the infantry. They need to be injury free and have as much energy as possible when they march into battle.
Walking on uneven ground without being injured by falling down (particularly with a heavy backpack) is generally accomplished by maintaining stability. This present study was conducted to determine an individual’s most stable position (using a stability formula which compares dynamic center of mass with center of pressure) when wearing a backpack under differing load positions - low back, middle back or high back – and differing walking angles: level, as well as along a cross-sloped surface.
Furthermore, this study investigated the stability of persons walking along a cross-slope without a load.
Finally, this study attempted to determine which combination of backpack load location and slope tilt best conserved metabolic energy.
To carry out this backpack stability research, a group of 15 participants were asked to walk along an indoor track under the varying conditions mentioned (i.e., low to high backpack load positions and level to 10 degree tilted cross-slopes). The trials of their walks were performed randomly. The participants were recorded in a motion capture system and force plates documented their stepping times and locations.
Again, the same 15 participants walked along the track under the same conditions, but without the loads to determine the effect of different cross-slope angles on their stability.
Lastly, the same participants walked the track under the various conditions wearing portable oxygen sensors to analyze their energy expenditure.
The results of these limited tests indicate no significant stability differences between 0, 5 or 10 degree angles in cross-slope walking loaded or unloaded. Nor was any significant stability differences noted between the various load locations of the backpacks. Nor was there a significant energy difference between the conditions.
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Johnson, Jeffrey Keith. "Concrete bridge deck behavior under thermal loads". Thesis, Montana State University, 2005. http://etd.lib.montana.edu/etd/2005/johnson/JohnsonJ0805.pdf.
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Marzeddu, Andrea. "Measuring impact loads on rigid coastal structures". Doctoral thesis, Universitat Politècnica de Catalunya, 2016. http://hdl.handle.net/10803/393926.
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The aim of this work is the study of laboratory effects on the measurement of wave impact induced loads on rigid maritime structures. A high number of experiments (more then 4000 using regular wave attacks) have been carried out in the small scale wave flume "CIEMito" in the laboratory of the LIM-UPC BarcelonaTech. The effects on the results of sample frequency, measurement systems and experimental layout has been deeply studied. A high number of repetitions of the same wave attack has been performed in order to have statistically robust results since the almost-random behavior of the studied phenomenon.
-Sample frequencies from 50 to 19200 Hz
- Load cells, pressure transducers and an innovative tactile pressure map
- Six different experimental layouts effects have been tested
The maximum results of force and pressures have been always measured at the maximum sample frequency. Differences of the 150% has been found between the measurements at 50 and 19200 Hz.
The total load measured considering all the width of the flume tends to sub estimate the total force measured only in a slice in the middle of the flume. Even if the average value is comparable, the pressure transducers tends to return much spread results than the load cells.
The tactile pressure mapping system stands out for his very high spatial density (196 sensels in a 49cm2 area) but an experimental specific calibration and an ad-hoc set-up are necessary for the utilization with water and in order to can collect reliable results comparable with the classic measurement systems. For this work 3 types of calibration methodology have been compared: static, instrumented pendulum and water jets. The last has to be considered the best choice and the selected for the definitive tests. Among all the results the ones to be highlighted are: the integral of pressures (the force applied over the whole sensor) acting on the tactile sensor differ from simultaneous load cell measurements by less than ±20%. The pressure mapping system tends to underestimate the pressure peak. However, if the average values of the 3, 5 and 10 highest peaks are considered they differ by up to ±10%. Has been shown a reduction effect of the pressure peak when pressure measurement systems are coupled with load cells.
A perfect set-up for these kind of measurement hasn't found yet but the combination of the three measurement systems seems to be the best possible solution. Load cells return a direct and reliable result of the total load, but the set-up could be complicated especially at large scales. The pressure mapping system neither seems to be the perfect alternative to the pressure transducers and a combined use is suggested for these experiments that require a high level of precision both in space and magnitude.
A sample frequency around 4000 Hz, for small scale experiments, present the right combination between sample density, memory storage and added signal noise for the correct characterization of the impulsive phenomenon of the wave generated violent impact loads on rigid structures. Considering a working scale in between 1/50 and 1/100, a frequency of 500Hz is proposed for measurement at full scale.
Following these methodologic recommendations not only will permit better and more reliable measurement but also will permit a better comprehension/evaluation of the test and analysis uncertainties. In this manner it will be possible to extrapolate, in a reliable way, scale test results to the design process of breakwaters.Esta tesis se centra en el estudio de efectos de laboratorio que tienen lugar durante la medida de impactos violentos generados por olas rompientes sobre estructuras rígidas. Para su fin, se ha llevado a cabo una extensa campaña experimental en el canal de pequeña escala CIEMito del LIM-UPC BarcelonaTech y se ha realizado más de 4000 ensayos con oleajes regulares. Se ha analizado el efecto de la frecuencia de muestreo, la tipología del sistema de medida y el layout experimental en los resultados registrados. Tras confirmar experimentalmente el comportamiento prácticamente aleatorio del fenómeno y, para poder realizar comparativas estadísticamente validas, se ha realizado un alto número de repeticiones del mismo oleaje. Se ha analizado en particular los siguientes efectos: - Frecuencias de muestreo entre 50 y 19200 kHz - Células de carga, sensores de presión y un innovador sistema táctil de medidas de presión - Seis diferentes layouts experimentales. Los máximos resultados de fuerza y presión se han medido siempre a la máxima frecuencia de muestreo y se han obtenido diferencias del orden del 150% con los ensayos muestreados a 50 Hz. La resultante medida de la fuerza en todo el ancho del canal tiende a subestimar el valor de la fuerza cuando se compara con medidas en la porción central. Aunque en valor promedio los resultados son comparables, en el caso de los sensores de presión los resultados son más dispersos en comparación con los resultados de las células de carga. El sensor táctil de presión destaca por su elevada densidad espacial (196 sensores en un área de 49cm2) pero en su contra, requiere de una calibración dinámica y un set-up particular para su utilización en agua y para que los resultados sean comparables con los de los sistemas clásicos de medida. Para este trabajo se comparó una calibración con la caída de un martillo y con la caída de un volumen controlado de agua, siendo ésta última la seleccionada para estos ensayos. Entre los resultados obtenidos se destacaque a partir de una comparativa directa entre la integral de las presiones medidas del sensor táctil calibrado y la fuerza medida en la misma área por una célula de carga, se ha evidenciado errores del orden del ±20%. El sensor táctil tiende a subestimar las presiones de pico, aunque si se consideran los valores extremos medidos, los errores son del ±10%. Se ha evidenciado también un efecto de reducción del pico de presión cuando las medidas de presión están acopladas con medidas de células de carga. Aunque no hay una alternativa perfecta para esta tipología de medidas la combinación de los tres sensores parece la mejor solución posible. Las células de carga dan un resultado directo y muy fiable de la fuerza total, pero su instalación, sobretodo en ensayos de gran escala puede ser complicada. El sensor táctil tampoco se presenta como la alternativa absoluta a los sensores de presión y se aconseja un uso combinado para ensayos que requieran más altos niveles de precisión espacial que en magnitud. Una frecuencia de muestreo entorno a 4000 Hz en ensayos a pequeña escala presenta la justa combinación entre velocidad de muestreo y cantidad de datos registrados para detectar el fenómeno impulsivo generado por el impacto violento del oleaje en estructuras rígidas. Si se considera que se ha trabajado con una escala de trabajo alrededor entre 1/50 y 1/100, se propone una frecuencia de muestreo a escala prototipo entorno a 500 Hz. El seguimiento de estas recomendaciones metodológicas permite no sólo generar unas medidas más fiables sino también permitirá una mejor comprensión/evaluación de las posibles incertidumbres en fase de ensayo y análisis de datos. Una correcta medida del fenómeno impulsivo del impacto del oleaje en estructuras rígidas aporta más fiabilidad al proyecto de estructuras rompeolas
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Ercan, Anil. "Behaviour Of Pile Groups Under Lateral Loads". Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12611804/index.pdf.
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To investigate the lateral load distribution of each pile in a pile group, the bending moment distribution along the pile and the lateral group displacements with respect to pile location in the group, pile spacing, pile diameter and soil stiffness three dimensional finite element analysis were performed on 4x4 pile groups in clay. Different Elatic Modulus values, pile spacings, pile diameters and lateral load levels used in this study. In the analysis PLAXIS 3D Foundation geotechnical finite element package was used. It is found that, lateral load distribution among the piles was mainly a function of row location in the group independent from pile spacing. For a given load the leading row piles carried the greatest load. However, the trailing row piles carried almost the same loads. For a given load, bending moment values of the leading row piles were greater than the trailing row piles. On the other hand, as the spacing increased group displacements and individual pile loads decreased under the same applied load. However, this behavior was seen more clearly in the first and the second row piles. For the third and the fourth row piles, pile spacing became a less significant factor affecting the load distribution. It is also found that, pile diameter and soil stiffness are not significant factors on lateral load distribution as row location and pile spacing.
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Longva, Vegard. "Simulation of Trawl Loads on Subsea Pipelines". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2010. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-11594.
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The main objectives in this thesis was to investigate the effect of oblique trawl board crossings, increased trawl board added mass due to seabed proximity and the effect of a more rectangular trawl board geometry. In addition a new hydrodynamic load model which handles the seabed proximity and forward speed in a more consistent way was examined. All simulations in this thesis are performed by means of the computer software SIMLA. A brief description of methods applied in SIMLA and nonlinear finite element analysis is therefore included. The thesis contains also a chapter which describes trawling concepts and trawl boards used in Norwegian waters. Design loads from trawl gears on subsea pipelines are nowadays based on recommendations from the DNV-RPF111 code. Simulation models with a 4500 kg polyvalent trawl board were established to verify the DNV recommendations for free spans of height 0 m and 1 m. The simulations demonstrated that increasing trawl board added mass due to seabed proximity did not have any influence on neither pull-over loading nor pipeline response. The effect of a rectangular trawl board geometry was most pronounced for a span height of 0 m because the duration increased by 0.5 s and the horizontal pull-over force was kept constant throughout the pull-over. A slighty larger pull-over loading compared to the polyvalent board was observed for a span height of 1 m. Oblique trawl board crossings were examined for 6 different hit angles. The major finding was that a perpendicular crossing did not predict the largest pull-over load. On a general basis the simulations for a span height of 1 m underpredicted maximum pull-over force, duration and pipeline displacement compared to the DNV-RP-F111 recommendations. The 0 m span height simulations indicate that DNV predicts a different shape of the load time history and is slightly nonconservative in terms of maximum pull-over load. The new hydrodynamic load model which includes the effect of forward speed and seabed proximity was used to simulate a perpendicular trawl board crossing. Here the span height of 0 m indicated that the DNV-RP-F111 code is nonconservative in terms of the pull-over load. The simulation for a span height of 1 m was however in very good agreement with the DNV-RP-F111 code in terms of duration and horizontal pull-over load. Therefore it is recommended that future simulations are based on the new hydrodynamic load model.
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Castellani, Michele. "Nonlinear flight loads and aeroelastic response prediction". Thesis, University of Bristol, 2017. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.720821.
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Alamin, Basher. "Analysis of construction loads on concrete formwork". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0006/MQ43645.pdf.
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Mackman, Thomas James. "Surrogate model construction for steady aerodynamic loads". Thesis, University of Bristol, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633231.
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An efficient method for predicting steady aerodynamic loads with respect to varying geometric and flow parameters is to use a surrogate model to interpolate or approximate a finite set of Computational Fluid Dynamics (CFD) simulations. Further improvements to the strategy for constructing the surrogate have the potential to provide more accurate predicted values or to reduce the number of simulations required to achieve a model of sufficient quality. This work was originally motivated by the task of providing data for calculating structural loads for civil passenger aircraft, but is directly relevant for closely related applications such as providing aerodynamic data for flight mechanics analysis, and quantification of race-car aerodynamic performance. The objective at the outset was to develop aspects toward an improved surrogate modelling strategy for predicting aerodynamic data that enables a reduction in the overall simulation budget. To this end, the fundamental topics of adaptive sampling, model parameter tuning, and practical implementation for aerodynamic data have been investigated, with the goal of developing novel methods in each of these areas, and analysing their operation. Details of an adaptive sampling method based on a combination of curvature-adaptive and space-filling components are presented, including recovery of expected behaviour for analytic functions, formulation of the space-filling component, simultaneous addition of update points; and how best to optimise the criterion efficiently for multidimensional problems. An advanced strategy for choosing locally varying interpolation parameters is then presented, which works by optimising a single value to scale a prescribed local distribution of parameters, subject to constraints on the properties of the interpolation matrix. Following this, the use of various physics-based responses to drive the sampling algorithm and techniques for mitigating noise are investigated for application to aerodynamic data.
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braswell, tom. "SPACECRAFT LOADS PREDICTIONVIA SENSITIVITY ANALYSIS AND OPTIMIZATION". Master's thesis, University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3532.
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Discrepancies between the predicted responses of a finite element analysis (FEA) and reference data from test results arise for many reasons. Some are due to measurement errors, such as inaccurate sensors, noise in the acquisition system or environmental effects. Some are due to analyst errors precipitated by a lack of familiarity with the modeling or solver software. Still others are introduced by uncertainty in the governing physical relations (linear versus non-linear behavior), boundary conditions or the element material/geometrical properties. It is the uncertainty effects introduced by this last group that this study seeks to redress. The objective is the obtainment of model improvements that will reduce errors in predicted versus measured responses. This technique, whereby measured structural data is used to correct finite element model (FEM) errors, has become known as "model updating". Model updating modifies any or all of the mass, stiffness, and damping parameters of a FEM until an improved agreement between the FEA data and test data is achieved. Unlike direct methods, producing a mathematical model representing a given state, the goal of FE model updating is to achieve an improved match between model and test data by making physically meaningful changes. This study replaces measured responses by reference output obtained from a FEA of a small spacecraft. This FEM is referred to as the "Baseline" model. A "Perturbed" model is created from this baseline my making prescribed changes to the various component masses. The degree of mass variation results from the level of confidence existing at a mature stage of the design ii iii cycle. Statistical mean levels of confidence are assigned based on the type of mass of which there are three types: •Concentrated masses – nonstructural, lumped mass formulation (uncoupled) •Smeared masses – nonstructural mass over length or area, lumped mass formulation (uncoupled) •Mass density – volumetric mass, lumped mass formulation (uncoupled) A methodology is presented that accurately predicts the forces occurring at the interface between the spacecraft and the launch vehicle. The methodology quantifies the relationships between spacecraft mass variations and the interface accelerations in the form of sensitivity coefficients. These coefficients are obtained by performing design sensitivity /optimization analyses while updating the Perturbed model to correlate with the Baseline model. The interface forces are responses obtained from a frequency response analysis that runs within the optimization analysis. These forces arise due to the imposition of unit white noise applied across a frequency range extending up to 200 hertz, a cut-off frequency encompassing the lift-off energy required to elicit global mass response. The focus is on lift-off as it is characterized by base excitation, which produces the largest interface forces.M.S.
Department of Civil and Environmental Engineering
Engineering and Computer Science
Civil Engineering MS