Dissertations / Theses on the topic 'Dynamic vehicle load'

Several aspects of vehicle-pavement interaction have been studied and discussed in this thesis. Initially the pavement response is studied through a quasi-static and a dynamic computationally efficient framework under moving traffic loads. Subsequently, a non-stationary stochastic solution has been developed in order to account for the effect of pavement surface deterioration on pavement service life.The quasi-static procedure is based on a superposition principle and is computationally favourable, as it requires only a 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.In the dynamic approach the pavement roughness and vehicle suspension system are linked to a dynamic pavement model in order to account for the dynamic effects of vehicle-pavement interaction on pavement response. A finite element method is employed in order to establish the response function for a linear viscoelastic pavement structure with dynamic effects taken into account. The developed computational procedure is applied to evaluate the effect of the pavement surface roughness on the pavement structure response to truck traffic loadings.Furthermore, the deterioration trends for the flexible pavement surface have been investigated based on field measurements of longitudinal profiles in Sweden. A predictive function is proposed for surface deterioration that is based on the average gradient of yearly measurements of the road surface profiles in Swedish road network. The developed dynamic framework is further elaborated to a non-stationary stochastic approach. The response of the flexible pavement is given for a non-stationary random case as the pavement surface deteriorates in pavement service life, thus influencing the magnitude of the dynamic loads induced by the vehicles. The effect of pavement surface evolution on the stress state induced in the pavement by moving traffic is examined numerically. Finally the effect of surface deterioration on pavement service life has been investigated and discussed in the thesis by incorporating the proposed prognostic surface deterioration model into a ME design framework. The results are discussed for different case studies with different traffic regimes. It was indicated that the predicted pavement service life decreases considerably when the extra dynamic loads, as a result of pavement surface deterioration, has been taken into account. Furthermore, the effect of performing a predictive rehabilitation process (i.e. resurfacing) has been studied by employing a LCC framework. The application of preventive maintenance was shown to be effective, especially when the deterioration rate is high.

QC 20141119

Transport regulators consider that, with respect to pavement damage, heavy vehicles (HVs) are the riskiest vehicles on the road network. That HV suspension design contributes to road and bridge damage has been recognised for some decades. This thesis deals with some aspects of HV suspension characteristics, particularly (but not exclusively) air suspensions. This is in the areas of developing low-cost in-service heavy vehicle (HV) suspension testing, the effects of larger-than-industry-standard longitudinal air lines and the characteristics of on-board mass (OBM) systems for HVs. All these areas, whilst seemingly disparate, seek to inform the management of HVs, reduce of their impact on the network asset and/or provide a measurement mechanism for worn HV suspensions. A number of project management groups at the State and National level in Australia have been, and will be, presented with the results of the project that resulted in this thesis. This should serve to inform their activities applicable to this research. A number of HVs were tested for various characteristics. These tests were used to form a number of conclusions about HV suspension behaviours. Wheel forces from road test data were analysed. A “novel roughness” measure was developed and applied to the road test data to determine dynamic load sharing, amongst other research outcomes. Further, it was proposed that this approach could inform future development of pavement models incorporating roughness and peak wheel forces. Left/right variations in wheel forces and wheel force variations for different speeds were also presented. This led on to some conclusions regarding suspension and wheel force frequencies, their transmission to the pavement and repetitive wheel loads in the spatial domain. An improved method of determining dynamic load sharing was developed and presented. It used the correlation coefficient between two elements of a HV to determine dynamic load sharing. This was validated against a mature dynamic loadsharing metric, the dynamic load sharing coefficient (de Pont, 1997). This was the first time that the technique of measuring correlation between elements on a HV has been used for a test case vs. a control case for two different sized air lines. That dynamic load sharing was improved at the air springs was shown for the test case of the large longitudinal air lines. The statistically significant improvement in dynamic load sharing at the air springs from larger longitudinal air lines varied from approximately 30 percent to 80 percent. Dynamic load sharing at the wheels was improved only for low air line flow events for the test case of larger longitudinal air lines. Statistically significant improvements to some suspension metrics across the range of test speeds and “novel roughness” values were evident from the use of larger longitudinal air lines, but these were not uniform. Of note were improvements to suspension metrics involving peak dynamic forces ranging from below the error margin to approximately 24 percent. Abstract models of HV suspensions were developed from the results of some of the tests. Those models were used to propose further development of, and future directions of research into, further gains in HV dynamic load sharing. This was from alterations to currently available damping characteristics combined with implementation of large longitudinal air lines. In-service testing of HV suspensions was found to be possible within a documented range from below the error margin to an error of approximately 16 percent. These results were in comparison with either the manufacturer’s certified data or test results replicating the Australian standard for “road-friendly” HV suspensions, Vehicle Standards Bulletin 11. OBM accuracy testing and development of tamper evidence from OBM data were detailed for over 2000 individual data points across twelve test and control OBM systems from eight suppliers installed on eleven HVs. The results indicated that 95 percent of contemporary OBM systems available in Australia are accurate to +/- 500 kg. The total variation in OBM linearity, after three outliers in the data were removed, was 0.5 percent. A tamper indicator and other OBM metrics that could be used by jurisdictions to determine tamper events were developed and documented. That OBM systems could be used as one vector for in-service testing of HV suspensions was one of a number of synergies between the seemingly disparate streams of this project.

Automated Guided Vehicles (AGV) are important components of modern automated transport systems. Increasing the system efficiency and throughput requires the use of heavy vehicles travelling at high speeds. As the AGV's payload capacity and travelling speed increases, the ensuing increase in lateral acceleration requires thorough dynamic modelling and more sophisticated controller design. To establish the sufficient level of model complexity necessary for this work, a 3-DOF nonlinear dynamic model comprising yaw, lateral, and roll motions is developed. The suspension, lateral and longtudinal load transfer, nonlinear behaviour of tires, and steering dynamics are included in this model. The model also comprises the effect of actuators, differential gear box, steering and tractive gear boxes. The model is validated through simulations and comparison with other models. A dynamic-based approach to the control of a typical transport interfactory AGV in a semi structured environment is studied. The 2-DOF side slippage free dynamic model comprising steering and actuators dynamics is used to design the controller. The input-output feedback linearization technique is employed to linearize the nonlinear dynamics of the vehicle. To improve robustness in the presence of parameter uncertainty, modelling errors and disturbance, a Boundary Layer Sliding Mode (BLSM) controller is adopted. The BLSM controller is later modified to improve performance and enhance robustness, using simultaneous variable boundary layer and multiple sliding surfaces strategies. Simulations based on the 3-DOF nonlinear model show the satisfactory results for the Modified Boundary Layer Sliding Mode (MBLSM) controller.

This dissertation investigates the dynamics of highway bridges subjected to heavy vehicle loads. A convolution method based on bridge mode shapes is developed to predict the dynamic response of a bridge to a given set of wheel loads. The convolution integral is solved by transformation to the frequency domain. In order to validate the bridge response calculation method, an experimental procedure, consisting of impulse tests to determine the bridge modal properties and vehicle tests, is presented. The measured modal properties of the bridges are compared against predictions from beam theory and finite element calculations. Good agreement between theory and measurement is shown. The modal parameters are combined with measured wheel loads in the convolution calculation to predict bridge responses. These predicted responses are compared with the measurements and good agreement is found. The convolution method is extended by an iterative procedure to include vehicle models and two parametric studies are performed. In the first, the importance of the dynamic interaction between vehicles and bridges is investigated, and guidelines for determining when interaction can be ignored are presented. In the second study, the effects of vehicle suspension design on bridge dynamic response are considered. Vehicles with leaf-spring and air-spring suspensions are considered.

In this study, CFD simulations of a complete truck are carried out to investigate the effect of altered simulation settings at cold climatic conditions. The aim of this study is to obtain knowledge through CFD simulations performed on a selected driving condition namely at a vehicle speed of 93 kph, an ambient temperature of -20 °C and for an engine operating at 25 % load. Data from measurement carried out in a climatic wind tunnel is available and utilized as boundary conditions for the simulations.The simulations are performed under steady state conditions utilizing the commercial software STAR-CCM+. The first simulation case (reference simulation case) is constructed through java macro-scripts as per the standard VTM settings at Scania. The results from the simulations are compared with the measurement data utilizing temperature validation probes. These probes are located around the engine and measure the air temperature in the underhood engine compartment. The results from the first simulation case show that the temperature of each probe located in front of the engine and above the engine agrees well with the measured probe temperatures. But the temperature of the remaining probes show larger differences with the measured probe temperatures. To investigate the larger differences in probe temperatures, additional simulations are carried out by changing specific simulation settings. For instance, this is achieved by including thermal radiation in the physics continua. Finally, a simulation of engine load of 100 % is carried out and the results from the simulation are compared with the measurement from the same engine load as well as the results from the measurement and simulation of 25 % engine load. The results from all the simulations indicate that additional boundaryconditions and/or different methodologies need to be explored to better replicate the cold climatic conditions in the simulations.

This thesis addresses the question of designing robust and flexible controllers to enable autonomous operation of a multirotor UAV with an attached slung load for general cargo transport. This is achieved by following an experimental approach; real flight data from a slung load multirotor coupled system is used as experience, allowing for a computer software to estimate the pose of the slung in order to propose a swing-free controller that will dampen the oscillations of the slung load when the multirotor is following a desired flight trajectory. The thesis presents the reader with a methodology describing the development path from vehicle design and modelling over slung load state estimators to controller synthesis. Attaching a load via a cable to the underside of the aircraft alters the mass distribution of the combined "airborne entity" in a highly dynamic fashion. The load will be subject to inertial, gravitational and unsteady aerodynamic forces which are transmitted to the aircraft via the cable, providing another source of external force to the multirotor platform and thus altering the flight dynamic response characteristics of the vehicle. Similarly the load relies on the forces transmitted by the multirotor to alter its state, which is much more difficult to control. The principle research hypothesis of this thesis is that the dynamics of the coupled system can be identified by applying Machine Learning techniques. One of the major contributions of this thesis is the estimator that uses real flight data to train an unstructured black-box algorithm that can output the position vector of the load using the vehicle pose and pilot pseudo-controls as input. Experimental results show very accurate position estimation of the load using the machine learning estimator when comparing it with a motion tracking system (~2% offset). Another contribution lies in the avionics solution created for data collection, algorithm execution and control of multirotor UAVs, experimental results show successful autonomous flight with a range of algorithms and applications. Finally, to enable flight capabilities of a multirotor with slung load, a control system is developed that dampens the oscillations of the load; the controller uses a feedback approach to simultaneously prevent exciting swing and to actively dampen swing in the slung load. The methods and algorithms developed in this thesis are validated by flight testing.

A racing vehicle suspension system is a kinematic linkage that supports the vehicle under complex loading scenarios. The suspension also defines the handling characteristics of the vehicle. Understanding the loads that the suspension carries in a variety of loading scenarios is necessary in order to properly design a safe and effective suspension system. In the past, the Formula SAE team at Virginia Tech has used simplified calculations to determine the loads expected in the suspension members. This approach involves several large assumptions. These assumptions have been used for years and the justification for them has been lost.

The goal of this research is to determine the validity of each of the assumptions made in the method used for calculating the vehicle suspension loads by hand. These assumptions include modeling the suspension as pinned-pinned truss members to prevent bending, neglecting any steering angle input to the suspension, and neglecting vertical articulation of the system. This thesis presents an approach to modeling the suspension member loads by creating a finite element (FE) model of the entire suspension system. The first stage of this research covers the validation of the current calculation methods. The FE model will replicate the suspension with all of the current assumptions and the member loads will be compared to the hand calculations. This truss-element-based FE model resulted in member loads identical to the hand calculations.

The next stage of the FE model development converts the truss model to beam elements. This step is performed to determine if the assumption that bending loads are insignificant is a valid approach to calculating member loads. In addition to changing the elements used from truss to beam element, the suspension linkage was adapted to more accurately model the methods by which each member is attached to the others. This involves welding the members of each control arm together at the outboard point as well as creating a simplified version of the pull rod mounting bracket on the upper control arm. The pull rod is the member that connects the ride spring, damper, and anti-roll bar to the wheel assembly and had previously been mounted on the upright. This model reveals reduced axial components of load but increases in bending moments sizable enough to reduce the resistance to buckling of any member in compression.

The third stage of model development incorporates the steer angle that must be present in loading scenarios that involve some level of cornering. An analysis of the vehicle trajectory that includes the effects of slip angle is presented and used to determine the most likely steer angle the vehicle will experience under cornering. The FE model was adapted to include the movement of the steering linkage caused by driver input. This movement changes the angle of the upright and steering linkage as well as the angle at which wheel loads are applied to the suspension. This model results in a dramatic change in member loads for loading cases that involve a component of steering input. Finally, the FE model was further enhanced to account for vertical movement of the suspension as allowed by the spring and damper assembly. The quasi-static loading scenarios are used to determine any member loading change due to vertical movement. The FE model is also used to predict the amount of vertical movement expected at the wheel center. This data can be used by the suspension designer to determine if changes to the spring rate or anti-roll bar stiffness will result in a more desirable amount of wheel movement for a given loading condition. This model shows that there is no change in the member loads due to the vertical movement of the wheel.

This thesis concludes by presenting the most important changes that must occur in member load calculations to determine the proper suspension loading under a variety of loading scenarios. Finally, a discussion of future research is offered including the importance of each area in determining suspension loads and recommendations on how to perform this research.
Master of Science

The present study has the objective of evaluating the effect of lubricant features on the friction coefficient by using three different lubricants (two synthetics and one mineral), which are used in automotive transmissions. In order to perform experiments, it was used a ball-on-disc system. The disc was manufactured with the same mechanical properties as transmission gears and the ball was made of 52100 SAE steel. The test parameters were defined based on a dynamic analysis conducted using \"ISOCAD\" which takes into account the geometry of the gear and vehicle dynamics (applied force and speed) during the tribological experiments. In order to set the temperature parameter, the lubricant testing temperature of a standard fuel economy was used. Experiments were conducted in two different lubrication conditions: i (starved) and ii (fully flooded). After the parameters were defined, it was possible to calculate the oil film thickness and, thus define the lubrication regime reached in each condition. Mixed and/or boundary lubrication was obtained in all the tests. Results showed the relationship between the speed and the specific oil film using a Khonsari and Masjedi formulation (2014), which takes into account the effect of surface roughness and, it is based on Downson and Higginson\'s (1981) formulation. The chemical analysis of the lubricant showed a relationship between friction coefficient and the additives used in lubricants. These results also showed the oil performance under different temperatures, speeds and loads. The best results were obtained for a synthetic lubricant.
O presente estudo tem o objetivo de avaliar o efeito de propriedades dos lubrificantes sobre o coeficiente de atrito. Para tanto foram testados três lubrificantes diferentes (dois sintéticos e um mineral), que são utilizados em transmissões automotivas. Os experimentos foram conduzidos utilizando um sistema tribológico denominado \"ball-on-disc\". Os discos foram fabricados com as mesmas propriedades mecânicas das engrenagens de transmissão, já as esferas foram fabricadas com aço SAE 52100. Os parâmetros de teste foram definidos com base na análise dinâmica conduzida utilizando o software \"ISOCAD\", que leva em conta a geometria da engrenagem e a dinâmica do veículo (força aplicada e velocidade) durante os ensaios tribológicos. Para definir os parâmetros de temperatura, foram utilizadas as mesmas temperaturas encontradas durante o ensaio de economia de combustível padronizado. Experimentos foram realizados em duas condições de lubrificação diferentes: i) fornecimento limitado de lubrificante, ou \"Starved\" e ii) condição de lubrificação imersa, ou \"Fully flooded\". Depois dos parâmetros definidos, foi possível calcular a espessura de filme de óleo, de forma a definir o regime de lubrificação alcançado em cada condição. Lubrificação mista e limítrofe foi obtida todas as condições de testes. Os resultados mostraram a relação entre a velocidade e o filme de óleo específico usando uma formulação de Khonsari e Masjedi (2014), que leva em conta o efeito da rugosidade da superfície e baseia-se na formulação de Downson e Higginson (1981). A análise química do lubrificante mostrou que existe uma relação entre o coeficiente de atrito e os aditivos utilizados nos lubrificantes. Estes resultados também mostram o desempenho dos lubrificantes em diferentes temperaturas, velocidades e cargas. Os melhores resultados foram obtidos para um lubrificante sintético.

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

QC 20140429

The thesis describes function and characteristics of spring and damper, their particular way and margin of influence on vehicle behavior in selected riding maneuvers. The goal is to maintaining maximal grip, control, and achieve predictable vehicle handling.

Since the last United Nations Climate Change Conference in 2015 in Paris (the COP 21), world leaders acknowledged climate change. There is no need any more to justify the switch from fossil fuel-based to renewable energy sources. Nevertheless, this transition is far from being straightforward. Besides technologies that are not yet mature -- or at least not always financially viable in today's economy -- the power grid is currently not ready for a rapid and massive integration of renewable energy sources. A main challenge for the power grid is the inadequacy between electric production and consumption that will rise along with the integration of such sources. Indeed, due to their dependence on weather, renewable energy sources are intermittent and difficult to forecast with today's tools. As a commodity, electricity is a quite distinct good for which there must be perfect adequacy of production and consumption at all time and characterized by a very inelastic demand. High shares of renewable energy sources lead to high price volatility and a higher risk to jeopardize the security of supply. Additionally, the switch to renewable energy sources will lead to an electrification of loads and transportation, and thus the emergence of new higher-consumption loads such as electric vehicles and heat pumps. These new and higher-consumption loads, combined with the population growth, will cause over-rated power load increases with less predictable load patterns in the future.This work focuses on issues specific to the distribution power grid in the context of the current energy transition. Traditional low-voltage grids are perhaps the most passive circuits in power grids. Indeed, they are designed primarily using a fit and forget approach where power flows go from the distribution transformer to the consumers and no element has to be operated or regularly managed. In fact, low-voltage networks completely lack observability due to very low monitoring. The distribution grid will especially undergo drastic changes from this energy transition. Distributed sources and new high-consumption -- and uncoordinated -- loads result in new power flow patterns, as well as exacerbated evening peaks for which it is not designed. The consequences are power overloads and voltage imbalances that deteriorate grid components, such as a main asset like the medium-to-low voltage transformer. Additionally, the distribution grid is characterized by end-users that pay a price for electricity that does not reflect the grid situation -- that is, mostly constant over a year -- and allow little to no actions on their consumption.These issues have motivated authorities to propose a global approach to ensure security of electricity supply at short and medium-term. The latter requires, among others, the development of demand response programs that encourage users to take advantage of load flexibility. First, we propose adequate electricity pricing structures that will allow users to unlock the potential of such demand response programs; namely, dynamic pricings combined with a prosumer structure. Second, we propose a fast and robust two-level optimization, formulated as a mixed-integer linear program, that coordinates flexible loads. We focus on two types of loads; electric vehicles and heat pumps, in an environment with solar PV panels. The lower level aims at minimizing individual electricity bills while, at the second level, we optimize the power load curve, either to maximize self-consumption, or to smoothen the total power load of the transformer. We propose a parametric study on the trade-off between only minimizing the individual bills versus only optimizing power load curves, which have proven to be antagonist objectives. Additionally, we assess the impact of the rising share of flexible loads and renewable energy sources for scenarios from today until 2050. A macro-analysis of the results allows us to assess the benefits of load flexibility for every actor of the distribution grid, and depending on the choice of a pricing structure. Our optimization has proved to prevent evening peaks, which increases the lifetime of the distribution transformer by up to 200%, while individual earnings up to 25% can be made using adequate pricings. Consequently, the optimization significantly increases the power demand elasticity and increases the overall welfare by 10%, allowing the high shares of renewable energy sources that are foreseen.
Doctorat en Sciences de l'ingénieur et technologie
info:eu-repo/semantics/nonPublished

Concevoir un composant automobile et s’assurer que celui-ci atteindra un niveau de fiabilité cible requière une connaissance précise de la variabilité des chargements que ce composant est susceptible de rencontrer dans son environnement d’utilisation. La grande diversité des chargements appliqués à différents véhicules par différents clients, ou à un même véhicule tout au long de son historique d’utilisation, représente un défi statistique majeur. Généralement, l’acquisition d’information relative à la variabilité des chargements imposés aux composants des véhicules, repose sur la réalisation de campagnes de mesures. La complexité, la durée et le coût de telles campagnes limite naturellement la taille des échantillons statistiques constitués et les chargements enregistrés sont inévitablement dépendants du véhicule utilisé pour la mesure.Le travail présenté dans ce manuscrit explore la possibilité de changer fondamentalement d’approche, en se basant sur la simulation plutôt que sur la mesure et en concentrant l’effort d’analyse statistique non pas directement sur la variabilité des chargements mais sur la variabilité des facteurs qui les déterminent. Dans ce but, des modèles stochastiques sont proposés pour décrire l’évolution de la géométrie des surfaces de routes rencontrées par les véhicules ainsi que l’évolution de la vitesse à laquelle les conducteurs les parcourent. La caractérisation de la variabilité de ces facteurs est couplée à la notion de situations de vie. Ces dernières permettent de segmenter l’historique d’utilisation des véhicules, afin de faciliter l’analyse statistique de leur évolution au sein d’une population de clients. Pour finir, la réponse dynamique du véhicule à l’excitation générée par la route est déduite par la simulation.Des données statistiques relatives à la variabilité des facteurs de route et de vitesse sont évidemment nécessaires. L’information sur les routes parcourues peut par exemple être acquise à moindre coût au moyen d’une méthode d’estimation des profils de route proposée dans ce manuscrit. Cette information peut ensuite être exploitée afin de constituer, par la simulation, à un coût très faible et pour n’importe quel véhicule dont les caractéristiques sont connues, un échantillon d’historiques de chargements aussi important que souhaité. Cette méthodologie basée sur la simulation offre la possibilité d’analyser plus largement la variabilité des chargements de fatigue provenant de la route, l’influence des différents facteurs qui les déterminent ainsi que l’effet sur la fiabilité des composants du véhicule étudié
In order to design vehicle components that will achieve a prescribed reliability target, it is imperative to possess a precise description of the variability of the loads to which such components may be subjected within the environment in which they are used. The strong diversity of the loads imposed on different vehicles by different customers, or on a particular vehicle throughout its life, constitutes a formidable statistical challenge. Generally, the acquisition of information about the load variability experienced by vehicle components is based on the use of load measurement campaigns. The complexity, duration and cost of such campaigns naturally limit the size of the statistical samples that may be collected. Moreover, the recorded load histories are inevitably dependent on the vehicle used for the measurements.The work presented within this manuscript explores the possibility of a fundamental change in the approach to load characterisation. The objective is to make use of simulation rather than measurements and focus statistical analysis efforts not directly on load variability itself but on the variability of the factors that determine such loads. Stochastic models are proposed to describe the evolution of the geometry of road surfaces covered by vehicles, as well as the evolution of vehicles’ speed on those road surfaces. The characterisation of the variability of such factors is performed in combination with the use of life situations. The latter may be employed to divide the load histories associated to different vehicles, within a population of customers, and analyse their variation more easily. Eventually, the dynamic response of the vehicle to the excitation imposed by the road can bederived through simulation.Statistical data on the variation of the road and speed factors obviously have to be acquired in order to apply the methodology. For example, road-related information may be obtained through the use of a road profile estimation algorithm proposed within the framework of this manuscript. Such information may then be exploited to constitute, through simulation, an arbitrarily large set of load histories at a very low cost and for any vehicle whose mechanical characteristics are known.The proposed methodology based on simulation enables us to study more extensively the variability of road-induced fatigue loads, the influence of the different factors that determine such loads, as well as the effect they have on the reliability of any considered vehicle component

La problématique de cette thèse réside dans la caractérisation et le maintien de la stabilité des Véhicules Légers Tout Terrain (VLTT). Elle se concentre plus particulièrement sur le développement de systèmes de sécurité actifs capables à la fois de prévenir le conducteur des risques encourus mais aussi de les limiter afin d'assurer l'évolution du véhicule dans une zone de stabilité prédéfinie. Comme le cadre expérimental privilégié est l'application à la stabilité des quadricycles légers à moteurs, plus connus sous le terme anglophone "quad", une des contraintes du projet a été de se limiter à un système sensoriel bas-coût afin d'être en mesure d'industrialiser un tel système. En premier lieu, les métriques de stabilité (Transfert de Charge Latéral et Longitudinal : TCLa et TCLo) ont été choisies grâce à une étude préliminaire sur la stabilité des VLTT. Par la suite, une modélisation 2D en roulis et en tangage avec la prise en compte des déplacements du pilote sur le véhicule sont présentées, ce qui permet d'estimer respectivement le TCLa et le TCLo uniquement à partir de la mesure de l'accélération latérale et longitudinale. Étant donné que pour la suite des travaux, l'anticipation du risque de renversement latéral est nécessaire, un modèle 2D en lacet du véhicule est proposé afin d'obtenir un modèle analytique décrivant la dynamique latérale du véhicule. La suite du mémoire présente les différentes techniques d'observation proposées pour l'estimation des variables et paramètres non-directement mesurables du modèle en lacet du véhicule et qui influencent sa stabilité latérale : les glissements, les conditions d'adhérence et les inclinaisons du véhicule. Plusieurs observateurs ont été proposés, dont le dernier permet de considérer des conditions d'adhérence différentes entre les essieux avant et arrière en utilisant plus largement les accélérations mesurées. Cela permet d'intégrer les passages de sous- à sur-vireur qu'il est essentiel de considérer quand on étudie la stabilité de ce type de véhicule. Ainsi, l'estimation des glissements est toujours pertinente, ce qui permet d'obtenir par la suite une meilleure prédiction de la métrique de stabilité latérale (TCLa) quel que soit le comportement du véhicule. Puis en s'appuyant sur les estimations des observateurs couplées aux modèles dynamiques du véhicule et sur l'extrapolation des commandes du conducteur sur un horizon de prédiction, il est possible de prédire les évolutions du TCLa. Cette valeur prédite ainsi que les estimations en ligne des métriques de stabilité constituent alors le point d'entrée pour la synthétisation d'un système de sécurité actif dédié aux VLTT. Celui-ci est basé sur la génération d'un retour d'effort au niveau de la gâchette des gaz permettant soit d'informer le pilote du risque encouru par la création d'une sensation de dureté, soit d'imposer le retour complet de la gâchette des gaz, ce qui implique une diminution de la vitesse et donc la réduction du risque. Finalement, dans le cas où il est possible de maîtriser la vitesse du véhicule par l'installation d'un système de rétroaction sur les freins (Quad haut de gamme ou robot mobile), les derniers travaux présentés s'intéressent aux techniques de commande prédictive à modèle afin de calculer en temps-réel la vitesse maximale admissible, qui assure l'évolution du critère de stabilité choisi dans un domaine de stabilité. Les modèles, les observateurs, la prédiction du TCLa et les 2 systèmes de prévention présentés dans ce mémoire ont été validés et testés au travers de simulations avancées et d'essais expérimentaux réalisés sur un quad agricole et un robot autonome. Il apparaît alors qu'en plus d'être efficace pour la prévention des risques de renversement à hautes dynamiques, le système de sécurité est industriellement viable. Cela a été rendu possible grâce à une conception reposant uniquement sur des actionneurs et un système sensoriel, dont les coûts sont en adéquation avec le prix d'un VLTT.

This thesis presents a state-of-the-art-review and twodifferent approaches for solving the moving load problem ofcable-stayed and suspension bridges. The first approach uses a simplified analysis method tostudy the dynamic response of simple cable-stayed bridgemodels. The bridge is idealized as a Bernoulli-Euler beam onelastic supports with varying support stiffness. To solve theequation of motion of the bridge, the finite difference methodand the mode superposition technique are used. The second approach is based on the nonlinear finite elementmethod and is used to study the response of more realisticcable-stayed and suspension bridge models considering exactcable behavior and nonlinear geometric effects. The cables aremodeled using a two-node catenary cable element derived using"exact" analytical expressions for the elastic catenary. Twomethods for evaluating the dynamic response are presented. Thefirst for evaluating the linear traffic load response using themode superposition technique and the deformed dead load tangentstiffness matrix, and the second for the nonlinear traffic loadresponse using the Newton-Newmark algorithm. The implemented programs have been verified by comparinganalysis results with those found in the literature and withresults obtained using a commercial finite element code.Several numerical examples are presented including one for theGreat Belt suspension bridge in Denmark. Parametric studieshave been conducted to investigate the effect of, among others,bridge damping, bridge-vehicle interaction, cables vibration,road surface roughness, vehicle speed, and tuned mass dampers.From the numerical study, it was concluded that road surfaceroughness has great influence on the dynamic response andshould always be considered. It was also found that utilizingthe dead load tangent stiffness matrix, linear dynamic trafficload analysis give sufficiently accurate results from theengineering point of view.
QC 20100511

This thesis develops dynamic models for the two-mode FWD EVT, develops a control system based on those models that is capable of meeting driver torque demands and performing synchronous mode shifts between different EVT modes while also accommodating preferred engine operating points. The two-input two-output transmission controller proposed herein incorporates motor-generator dynamics, is based on a general state-space integral control structure, and has feedback gains determined using linear quadratic regulator (LQR) optimization. Dynamic modeling of the vehicle is categorized as dynamic modeling of the mechanical and electrical subsystems where the mechanical subsystem consists of the planetary gear sets, the transmission and the engine whereas the electrical subsystem consists of the motor-generator units and the battery pack. A discussion of load torque is also considered as part of the mechanical subsystem. With the help of these derived dynamic models, a distinction is made between dynamic output torque and steady-state output torque. The overall control system consisting of multiple subsystems such as the human driver, power management unit (PMU), friction brakes, combustion engine, transmission control unit (TCU) and motor-generator units is designed. The logic for synchronous mode shifts between different EVT modes is also detailed as part of the control system design. Finally, the thesis presents results for responses in individual operating modes, EVT mode shifting and a full UDDS drive cycle simulation.

Loads determination for external stores on fighter aircraft is an important task for manufacturers in ensuring the safe operation of their aircraft. Due to the large number of possible store combinations, wind tunnel tests – the primary approach to obtaining loads data – cannot be performed for all configurations. Instead, supplementary techniques to estimating loads are necessary. One approach is to use information from another store and adapt it, using so-called scaling methods, to the non-tested store. In this thesis, a scaling method combining the results of computational fluid dynamics (CFD) simulations, for both a non-tested and a reference store, with existing wind tunnel data for the reference store, is thoroughly examined for a number of different stores, angles of attack, sideslip angles and Mach numbers. The performance of the proposed scaling method is assessed in relation to currently used scaling methods, using non-parametric and multivariate statistics. The results show no definitive improvement in performance for the proposed scaling method over the current methods. Although the proposed method is slightly more conservative, considerable variability in the estimates and an increased time consumption for scaling leads the author to advise against using the proposed method for scaling aerodynamic loads on external stores.
Lastbestämning för yttre utrustning på stridsflygplan är en viktig uppgift för att tillverkarna ska kunna garantera säkerheten för sina flygplan. Då antalet möjliga utrustningskombinationer är mycket stort, kan inte vindtunneltester – normalt den främsta metoden för att erhålla lastdata – utföras för alla konfigurationer. Således behövs kompletterande metoder för att skatta laster. Ett alternativ är att använda data från en annan utrustning och anpassa den, med hjälp av så kallade skalningsmetoder, till den icke-testade utrustningen. I detta examensarbete behandlas en skalningsmetod som kombinerar resultaten från numeriska strömningsberäkningar – så kallade CFD-simuleringar – för både en testad och en icke-testad utrustning med befintliga vindtunneldata för den testade utrustningen. Metoden undersöks grundligt för ett antal olika utrustningar, anfallsvinklar, sidanblåsningsvinklar och Machtal. Prestandan hos den föreslagna skalningsmetoden utvärderas i relation till nu använda skalningsmetoder, baserat på icke-parametrisk och multivariat statistik. Resultaten visar inga definitiva förbättringar av prestanda för den föreslagna skalningsmetoden jämfört med de nuvarande metoderna. Även om den föreslagna metoden är något mer konservativ, så föranleder betydande variationer i skattningar och en ökad tidsåtgång för skalning författaren att avråda från att använda den föreslagna metoden för skalning av luftlaster på yttre utrustning.

Este trabalho tem como objetivo estudar a influência da geometria de suspensão do veículo nas atitudes da massa suspensa. Apresenta um confronto entre obras e autores e está segmentada em três partes; onde na primeira parte são definidos os conceitos básicos como dive, squat, lift, anti-dive, anti-squat, anti-lift e equivalente trailing-arm; na segunda parte são apresentadas as limitações e os novos conceitos definidos por R. S. Sharp e na terceira parte é apresentado o modelo dinâmico bidimensional introduzido por Fu-Cheng Wang. Apresenta um modelo virtual em sistema de multi-corpos desenvolvido no programa ADAMS, com todos os subsistemas que compõe um veículo completo. Inova ao trazer como objeto de estudo um veículo de competição (fórmula SAE) que possui como particularidade o sistema de suspensão push-rod. Surpreende com os resultados obtidos, pois, contrariam os conceitos básicos encontrados na maioria dos livros
This work has objective study the influence of suspension geometry on the sprung mass attitudes. It presents a confrontation among works and authors and this segmented in three parts; where in the first part the basic concepts are defined, dive, squat, lift, anti-dive, anti-squat, anti-lift and equivalent trailing-arm; in the second part the limitations are presented and the new concepts are defined for R. S. Sharp and in the third part are presented the bidimensional dynamic model introduced by Fu-Cheng Wang. It presents a virtual model in system of multi-bodies developed in the program ADAMS, with all the subsystems that composes a complete vehicle. It innovates when bringing such object to study one vehicle of competition (formula SAE) that it has a particularity suspension system push-rod. It surprises with results because it’s opposite of the basic concepts which is present in the majority of books

碩士
國防大學中正理工學院
造船工程研究所
92
In this research, the important equipments and weapon systems are put in the heavy load vehicle. The heavy load vehicle will run on different roads. Therefore, the kinematic performance and safety of the vehicle are very important. Reducing the part damage, which is induced by dynamic load of the heavy load vehicle, becomes very important issue. The comfort of human being is not so significant. The 3-dimensional model of the heavy load vehicle is established, simulated, and analyzed in ADAMS (Automatic Dynamic Analysis of Mechanical System). The analyses of suspension system, which were made in ADAMS, are only in bicycle and motorcycle in previous researches. There are only few analyses of suspension system, made in ADAMS, focusing on heavy load vehicle. Therefore, in this research the analysis of suspension system of heavy load vehicle is focused on varied suspension parameters and different roads. The dynamic response of the centers of the vehicle body and cargo are also taken into account. The active control is not put into the suspension system in this research. ADAMS is applied to simulate the dynamic behavior on different roads. The varied K (coefficient of stiffness) and C (coefficient of damper) of the suspension system are continuously utilized in the simulation. Finally, the balance between smooth and stability of the maneuver are obtained in order to get the best effect on reducing vibration.

碩士
逢甲大學
土木工程學系
102
Transportation construction is a crucial indicator of the economic development of a country. Excellent transportation system planning enhances the convenience of transportation and substantially benefits national economy. All processes involving material logistics, supplying resources, and product delivery rely on a comprehensive transportation system. Therefore, bridge construction is essential in transportation construction projects, and bridge designs are the crucial basis of bridge constructions. In this study, we examined the impact load of various factors on bridge girders and investigated five factors, namely the structural system of bridges (simply supported single-span beams and two-span continuous beams), span distance, wheelbase between the central and rear wheels of a standard HS20-44 truck, truck speed, and damping ratio. Subsequently, finite element analysis software (SAP2000) was adopted to establish a series of bridge girder models. Finally, the impact coefficients obtained in this study were used to investigate the impact load of dynamic vehicles on bridge girders. The results indicated that the impact coefficients were proportional to span distance and the wheelbase and speed of the truck. Furthermore, the models developed in this study conformed to the impact coefficient regulations stipulated in the bridge design specification for highways.

Heavy vehicle load security is a very important factor for all road users, and the friction forces arising within the cargo layer and between the cargo and the trailer bed are known to offer definite resistance to the dynamic forces and moments induced by the directional maneuvers, which would affect the load security significantly. A simple load-platform friction model is proposed to study the relationship between the friction coefficients and vertical vibration, and validated with the experimental record from the tests conducted at CONCAVE research center. The dynamic friction coefficient is observed to be a function of the acceleration of vertical vibration and horizontal movement. The vertical vibration has significant influence on the magnitude of friction forces between the mating surfaces. The model further incorporates the load-deck interface friction and vertical trailer vibration, by establishing the vehicle model with dynamic friction model. The dynamic response characteristics of the friction coefficients are evaluated in terms of sinusoidal excitation and random road input. The model is utilized to study the longitudinal cargo movement under breaking maneuvers. The results of the analysis revealed the strong influences of vibration amplitude and frequency as well as deceleration rate on the potential cargo movement. The vehicle parameters are also found to influence the dynamic friction coefficients and resulting cargo dynamics.

Stability is an important criterion in the design and performance of launch vehicles. Present day launch vehicles have become more and more flexible due to the constraints of weight reduction, necessarily imposed for enhanced performance of the vehicle. Due to higher flexibility, the launch vehicle stability becomes a concern. Instability in the launch vehicles has been noticed due to three major sources: thrust, aerodynamic forces and combustion induced instabilities. Instability in the launch vehicles may pose problem to the structural integrity leading to structural failure or it may lead to the deviation in the trajectory of the vehicle. Several structural failures of launch vehicles due to instabilities have been reported in the literature. The prediction of the structural response due to various excitations such as thrust and aerodynamic loading is essential to identify any failure scenarios and to limit the vibrations transmitted to the payload. Therefore, determination of dynamic and stability characteristics of a launch vehicle under the influence of different parameters, is of vital importance. Disciplines such as, flight mechanics (dynamics), structural dynamics, aerodynamics, propulsion, guidance and control are closely related in the design and analysis of launch vehicles. Typically, flight mechanics, guidance and control problems consider a rigid vehicle for modeling and simulation purposes. The disciplines of structural dynamics and aeroelasticity consider a flexible vehicle. In order to bring in the effect of flexibility on the flight dynamics of the launch vehicle, structural dynamics and aeroelasticity aspects need to be effected. The preliminary design of a new launch vehicle requires inputs from different disciplines and parametric studies are required to finalise the vehicle configuration. The study of the effect of different parameters on the dynamics and stability of launch vehicles is required. In this context, there is a need to develop an integrated approach that provides tools for the design and analysis of a launch vehicle. The availability of integrated modeling and simulation tools will reduce the requirement of costly prototype development and testing. In the present thesis, an attempt has been made to develop a numerical tool to conduct parametric studies for launch vehicle dynamics and stability. The developed tool is suitable for prediction of onset of instabilities under the influence of different parameters. The approach developed in this thesis is also well suited for specialized analysis of problems involving vertical launch, stage separation, engine shutdown and internal stress wave propagation related to structural integrity. Stability problems due to thrust and the aerodynamic forces (aeroelastic stability) in the launch vehicles/ missiles have been reported in the literature. Most of these works have modeled the vehicle as a beam or by using discrete degrees of freedom. In these works, the effect of thrust or aerodynamic forces on the flexible body modes is investigated and it is shown that the instability may occur in one of the bending modes due to change in the parameters such as thrust or aerodynamic forces. Traditionally, the dynamic characteristics are obtained in a body-fixed coordinate system, whereas the prediction of trajectory (rigid body dynamics) is carried out in an inertial frame of reference. Only few works have addressed the coupling of the rigid body motion and the flexible body dynamics of a vehicle. But these works also, do not consider the total derivative of displacements with respect to an inertial frame of reference. When the integrated equations of motion are derived in an inertial frame of reference, the rigid body motion and the elastic displacements are highly coupled. In this thesis, the rigid body motion and the flexible body dynamics is studied in an inertial frame of reference. The flexible body dynamics of the moving vehicle is studied in an inertial frame of reference, including velocity induced curvature effects, which have not been considered so far in the published literature. A detailed mechanics based model is developed to analyze the problem of structural instabilities in launch vehicles. Coupling among the rigid-body modes, the longitudinal vibrational modes and the transverse vibrational modes due to asymmetric lifting-body cross-section are considered. The model also incorporates the effects of aerodynamic forces and the propulsive thrust of the vehicle. The propulsive thrust is considered as a follower force. The model is one-dimensional, and it can be employed to idealized slender vehicles with complex shapes. The governing differential equations along with the boundary conditions are derived using Extended Hamilton’s principle. Subsequently, the modeling of the propulsive thrust and the aerodynamic forces are included in the formulation. In the literature, the propulsive thrust has generally been modeled as a follower force applied at the nozzle end. Few of the works in the literature have modeled the combustion process in the solid rocket motor and the liquid propellant engine in detail. This is required to understand the combustion induced instabilities. In the present thesis, the propulsive thrust is considered as a follower force and few of the combustion parameters affecting the thrust are considered. In the literature, the modeling of the aerodynamic forces acting on a launch vehicle has been carried out using general purpose computational fluid dynamics (CFD) codes or by using empirical methods. CFD codes are used to obtain the pressure and the shear stress distribution on the vehicle surface by the solution of Navier Stokes/ Euler equations. The empirical methods have been used to obtain the distributed aerodynamic forces acting on the vehicle. The aerodynamic forces are expressed in terms of distributed aerodynamic coefficients. In the present work, the modeling of the aerodynamic forces has been carried out in two different ways: using a CFD package and by using empirical methods. The stability of a system can be studied by determining the system response with time. Eigenvalue analysis is another tool to investigate the stability of a linear system. To study the stability characteristics of the system using eigenvalue analysis, a computational framework has been developed. For this purpose, the finite element discretization of the system is carried out. Further to that, two different methods are utilized for finite element discretization of the vehicle structure: Fourier Transform based Spectral Finite Element method (SFEM) and an hp Finite Element method (FEM). The conventional FEM is a versatile tool for modeling complicated structures and to obtain the solution of the system of equations for a variety of forcing functions. The SFEM is more suitable for obtaining the solution for simple 1D and 2D structures subjected to shock and transient loads, having high frequency content. In this thesis, the spectral finite element model is developed for a vehicle subjected to the propulsive thrust and the aerodynamic forces. Prediction of instability using SFEM, means solving a nonlinear eigenvalue problem. Standard computer codes or routines are not available for solving a nonlinear eigenvalue problem. A computer code has been written to solve the nonlinear eigenvalue problem using one of the algorithms available in the literature. An hp finite element model is also developed for launch vehicle. The finite element stiffness and damping matrices due to the thrust, the aerodynamic forces and the rigid body velocity and acceleration are derived using Lagrange’s equations of motion. A standard linear eigenvalue problem and a polynomial eigenvalue problem is formulated for determination of instability regimes of the vehicle. It is important to understand the influence of different parameters such as thrust, velocity, angle of attack etc. on the stability of a launch vehicle. Parametric studies are important during the preliminary design phase of a vehicle to identify the instability regimes. The design parameters can be changed to reduce the possibility of instabilities. Numerical simulations are carried out to determine the unstable regimes of a slender launch vehicle for propulsive thrust and velocity as the parameters, neglecting the aerodynamic forces. Comparison between the results based on a Fourier spectral finite element model and a hp finite element model are carried out. Phenomenon of static instability (divergence) and dynamic instability (flutter) are observed. Determination of mode shapes of the vehicle is important for deciding the placement of sensors and actuators on the vehicle. In this context, eigenvectors (mode shapes) for different end thrust and speed are analyzed. Further, numerical simulations are also carried out to determine the instabilities in a slender launch vehicle considering the combined effects of propulsive thrust, aerodynamic forces and mass variation. The finite element model simulation results for aeroelastic effects are compared with the published literature. Stability of a vehicle is analysed for velocity (free stream Mach number) as a parameter, at maximum propulsive thrust, including the effect of aerodynamic forces and mass variation. Phenomenon of static instability (divergence) and dynamic instability (flutter) are observed. With the increase in the Mach number, branching (splitting) and merging of the modes is observed. At higher Mach numbers, divergence and flutter are observed in different modes simultaneously. Numerical simulations are carried out for a typical nosecone launch vehicle configuration to analyse the aeroelastic stability at two different Mach numbers using empirical aerodynamic data. The phenomenon of flow separation and reattachment is observed at the cone-cylinder junction. The stability of a typical vehicle under propulsive thrust and aerodynamic forces is investigated using CFD derived aerodynamic data. The aerodynamic pressure and shear stress distribution for a launch vehicle are obtained from the CFD analysis. The effect of different parameters such as combustion chamber pressure, tip mass and slenderness ratio on the stability of a vehicle is studied. In the later part of the thesis, solution methodology for the time domain response for a coupled axial and transverse motion of a vehicle is developed. The axial responses (displacements and velocities) of a typical vehicle subjected to axial thrust are determined using direct integration of the equations of motion. The axial displacements due to two different thrust histories are compared. The axial velocities with time at different locations are determined. The time domain and the frequency domain responses for a representative vehicle subjected to a transverse shock force are determined using Spectral Finite Element method (SFEM). The system of equations for a coupled axial and transverse motion of a vehicle is developed. Numerical simulations are carried out to determine the coupled axial and transverse response of a vehicle subjected to axial and transverse forces. The coupling of rigid body motion with the elastic displacements is illustrated. The thesis is comprised of seven chapters. The first chapter gives a detailed introduction to launch vehicles and covers literature survey of launch vehicle dynamics and stability. The dynamics and stability related aspects of flexible structures are also discussed. In chapter 2, a detailed mathematical model of a slender launch vehicle is developed to analyze the problem of structural instabilities. Chapter 3 deals with the finite element discretization of the vehicle structure using two different methods: Fourier spectral finite element method and an hp finite element method. In chapters 4 and 5, numerical simulations are carried out to determine the instabilities in a slender launch vehicle considering the effects of propulsive thrust, aerodynamic forces and mass variation. In chapter 6, solution methodology for the time domain response for a coupled axial and transverse motion of a vehicle is developed. The last chapter gives the conclusions and the future scope of work. To summarize, this thesis is a comprehensive document, that not only describes some detailed mathematical models for launch vehicle stability studies, but also presents the effect of aerodynamic, propulsion and structural loads on the launch vehicle stability. Linear stability analysis of a representative vehicle is carried out for prediction of onset of the instabilities under the influence of different parameters such as velocity, thrust, combustion factors etc. The correlation between the stability analysis and the time domain response is established. In short, the matter presented in this thesis can serve as a useful design aide for those working in the launch vehicle design.

Thesis (Ph. D.)--Florida State University, 2005.
Includes vita. Includes bibliographical references (p. 140-144). Also available online via the Florida State University ETD Collection website (http://etd.lib.fsu.edu/).

Indiana University-Purdue University Indianapolis (IUPUI)
Indiana University–Purdue University Indianapolis student team Jaguar has been participating in the electric Formula SAE (FSAE) vehicle competitions in the past few years. There is an urgent need to develop a design tool for improving the performance of the vehicle. In this thesis, multibody dynamics (MBD) models have been developed which allow the student team to improve their vehicle design, while reducing the required time and actual testing costs. Although there were some studies about MBD analyses for vehicles in literature, a detailed modeling study of key parameters is still missing. Specifically, the effect of suspension system on the vehicle performance is not well studied. The objective of the thesis is to develop an MBD based model to improve the FSAE vehicle’s performance. Based on the objective and knowledge gap, the following research tasks are proposed: (1) MBD modeling of current suspension systems; (2) Modification of suspension systems, and (3) Evaluation of performance of modified suspension systems. The models for the front suspension system, rear suspension system, and full assembly are created, and a series of MBD analyses are conducted. The parameters of the vehicle by conducting virtual tests on the suspension model and overall vehicle model are studied. In this work, two main virtual tests are performed. First, parallel wheel travel test on suspension system, in which the individual suspension system is subject to equal force on both sides. The test helps understand the variation in stability parameters, such as camber angle, toe angle, motion ratio, and roll center location. Second, skid-pad test on full assembly of the vehicle. The test assists in understanding the vehicle’s behavior in constant radius cornering and the tire side slip angle variation, as it is one of the important parameters controlling alignment of the vehicle in this test. Based on the vehicle’s dynamics knowledge obtained from the existing vehicle, a modified version of the FSAE vehicle is proposed, which can provide a better cornering performance with minimum upgrades and cost possible. Based on the results from the parallel wheel travel test and skid-pad test, the lateral load transfer method is used to control the vehicle slip, by making changes to the geometry of the vehicle and obtaining appropriate roll center height for both front and rear suspension system. The results show that the stiffness in front suspension system and rear suspension system are controlled by manipulating roll center height. This study has provided insightful understanding of the parameters and forces involved in suspension system and their variations in different events influencing vehicle stability. Moreover, the MBD approach developed in this work can be readily extended to other commercial vehicles and sports vehicles.

碩士
國立成功大學
土木工程學系碩博士班
93
Patching on roads results in pavement irregularity, and this makes an additional dynamic load to both vehicle and pavement systems. Dynamic load is the key factor for stress and life assessment of pavement. Because the vehicle and pavement interact as a coupled system, the dynamic response cannot be solved with either isolated pavement system or vehicle kinematic formation. A 2-D interacting model was constructed with ABAQUS to investigate how the pavement-vehicle parameters affect the dynamic responses. A quarter car model was constructed to simulate a moving load sliding on pavement with surface roughness. Besides the mass of the vehicle carriage, the tire of the quarter car was given an isolated mass as a real car. In order to make the contact interaction more factually, a linear spring was adopted to model the tire elasticity. The pavement-vehicle interacting model was also given different conditions and compared with each other to find out an optimum model.

Renewable energy is key to a sustainable future. However, the intermittency of most renewable sources and lack of sufficient storage in the current power grid means that reliable integration of significantly more renewables will be a challenging task. Moreover, increased integration of renewables not only increases uncertainty, but also reduces the fraction of traditional controllable generation capacity that is available to cope with supply-demand imbalances and uncertainties. Less traditional generation also means less rotating mass that provides very short term, yet very important, kinetic energy storage to the system and enables mitigation of the frequency drop subsequent to major contingencies but before controllable generation can increase production. Demand, on the other side, has been largely regarded as non-controllable and inelastic in the current setting. However, there is strong evidence that a considerable portion of the current and future demand, such as electric vehicle load, is flexible. That is, the instantaneous power delivered to it needs not to be bound to a specific trajectory. In this thesis, we focus on harnessing demand flexibility as a key to enabling more renewable integration and cost reduction. We start with a data driven analysis of the potential of flexible demands, particularly plug-in electric vehicle (PEV) load. We first show that, if left unmanaged, these loads can jeopardize grid reliability by exacerbating the peaks in the load profile and increasing the negative correlation of demand with wind energy production. Then, we propose a simple local policy with very limited information and minimal coordination that besides avoiding undesired effects, has the positive side-effect of substantially increasing the correlation of flexible demand with wind energy production. Such local policies could be readily implemented as modifications to existing "grid friendly" charging modes of plug-in electric vehicles. We then propose improved localized charging policies that counter balance intermittency by autonomously responding to frequency deviations from the nominal frequency and show that PEV load can offer a substantial amount of such ancillary services. Next, we consider the case where real-time prices are employed to provide incentives for demand response. We consider a flexible load under such a pricing scheme and obtain the optimal policy for responding to stochastic price signals to minimize the expected cost of energy. We show that this optimal policy follows a multi-threshold form and propose a recursive method to obtain these thresholds. We then extend our results to obtain optimal policies for simultaneous energy consumption and ancillary service provision by flexible loads as well as optimal policies for operation of storage assets under similar real-time stochastic prices. We prove that the optimal policy in all these cases admits a computationally efficient form. Moreover, we show that while optimal response to prices reduces energy costs, it will result in increased volatility in the aggregate demand which is undesirable. We then discuss how aggregation of flexible loads can take us a step further by transforming the loads to controllable assets that help maintain grid reliability by counterbalancing the intermittency due to renewables. We explore the value of load flexibility in the context of a restructured electricity market. To this end, we introduce a model that economically incentivizes the load to reveal its flexibility and provides cost-comfort trade-offs to the consumers. We establish the performance of our proposed model through evaluation of the price reductions that can be provided to the users compared to uncontrolled and uncoordinated consumption. We show that a key advantage of aggregation and coordination is provision of "regulation" to the system by load, which can account for a considerable price reduction. The proposed scheme is also capable of preventing distribution network overloads. Finally, we extend our flexible load coordination problem to a multi-settlement market setup and propose a stochastic programming approach in obtaining day-ahead market energy purchases and ancillary service sales. Our work demonstrates the potential of flexible loads in harnessing renewables by affecting the load patterns and providing mechanisms to mitigate the inherent intermittency of renewables in an economically efficient manner.
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