Sensitivity analysis is one of the most prominent gradient based optimization techniques for mechanical systems. Model sensitivities are the derivatives of the generalized coordinates defining the motion of the system in time with respect to the system design parameters. These sensitivities can be calculated using finite differences, but the accuracy and computational inefficiency of this method limits its use. Hence, the methodologies of direct and adjoint sensitivity analysis have gained prominence. Recent research has presented computationally efficient methodologies for both direct and adjoint sensitivity analysis of complex multibody dynamic systems. Multibody formulations with joint friction were developed in the recent years and these systems have to be modeled by highly non-linear differential algebraic equations (DAEs) that are difficult to solve using numerical methods. The sensitivity analysis of such systems and the subsequent design optimization is a novel area of research that has been explored in this work. The contribution of this work is in the development of the analytical methods for computation of sensitivities for the most commonly used multibody formulations incorporated with joint friction. Two different friction models have been studied, capable of emulating behaviors of stiction (static friction), sliding friction and viscous drag. A case study has been conducted on a spatial slider-crank mechanism to illustrate the application of this methodology to real-world systems. The Brown and McPhee friction model has been implemented using an index-1 formulation for computation of the dynamics and sensitivities in this case study. The effect of friction on the dynamics and model sensitivities has been analyzed by comparing the sensitivities of slider velocity with respect to the design parameters of crank length, rod length, and the parameters defining the friction model. Due to the highly non-linear nature of friction, it can be concluded that the model dynamics are more sensitive during the transition phases, where the friction coefficient changes from static to dynamic and vice versa. / Master of Science / Mechanisms have been in existence since the earliest days of technology and are more relevant than ever in this age of robotics, artificial intelligence and space exploration. Innovations like myoelectric and neural prosthetics, legged robotics, robotic surgeries, advanced manufacturing, extra-terrestrial vehicles and so on are the modern day manifestations of the traditional mechanisms that formed the backbone of the industrial revolution. All of these innovations implement precision controlled multibody dynamic systems as part of their function. This thesis explores the modelling of such dynamic systems using different mathematical formulations. The contribution of this work is the incorporation of friction in the formulation of such systems. The performance of any dynamical system depends on certain parameters, which can be optimized to meet a certain objective criteria. This is achieved by performing a sensitivity analysis with respect to those parameters on the mathematical formulation of the mechanism. The derivation of this approach has been explored in this thesis. For the benefit of the reader, the application of this method has been discussed using a case study of a simple 3-dimensional slider crank mechanism.

Proportional Solenoid Valves (PSV) have been successfully used in the hydraulic industry for many years due to the benefits associated with higher accuracy compared to on/off solenoid valves, and the robustness and cost compared to servo valves. Because the PSV plays an important role in the performance of a hydraulic system, a technique commonly referred to as Condition Monitoring Scheme (CMS) has been used extensively to monitor the progress of faults in the PSV. But before any CMS can be implemented on a system, it needs to be thoroughly tested for its reliability of fault detection since, a failure of the CMS to detect any potential fault can be economically disastrous, and dangerous in terms of the safety of personnel. The motivation of this research was to develop a fault simulator which could reliably and repeatedly induce user defined faults in the PSV and thereby aid in testing the efficacy of the CMS for monitoring such simulated faults.<p>Industry research has revealed that the most common mode of failure in spool valves is an increase in the friction between the spool and valve, due to wear, contamination and dirt, which renders the valve inoperable. In this research, a non-destructive fault simulator was developed which induced artificial friction faults in the PSV. The PSV consisted of two solenoids on the opposite sides of the valve spool by virtue of which, bi-directional position control could be achieved. The PSV with the spool and one of the solenoids was used as the system in which the faults were simulated, and the second solenoid was used an a fault simulator for inducing the desired friction characteristics in the system. <p>The friction characteristics induced in the valve were similar to those in the classical friction curve, i.e., stiction at low velocities and Coulomb and viscous friction at higher velocities. By employing a closed loop position control scheme, one of the solenoids was used to generate a linearly increasing velocity profile by virtue of which the desired friction characteristics could be induced in different velocity regimes. The other solenoid was used to generate the desired friction force. A closed loop force control strategy, which used the feedback from a force transducer, allowed for the accurate control of the friction characteristics. stiction was induced at low velocities by passing the required current in both the solenoids that resulted in no net force on the valve spool. Due to the absence of any driving force the spool was stalled at the desired location, thus achieving the same effect of stiction at low velocities. The coulomb and viscous friction were induced at higher velocities by employing an algorithm which was a function of the spool velocity. Different magnitudes of static, coulomb and viscous friction were induced to achieve the friction characteristics represented by the classical friction curve. Since the change in force characteristics of the valve results in a corresponding change in the current drawn by the position control solenoid, a rudimentary CMS for monitoring the current characteristics is presented. Based on the experimental results and validation using the CMS it was concluded that the fault simulator was able to accurately produce the desired frictional loading on the valve spool and was able to do so with a high degree of repeatability. Proportional Solenoid Valves (PSV) have been successfully used in the hydraulic industry for many years due to the benefits associated with higher accuracy compared to on/off solenoid valves, and the robustness and cost compared to servo valves. Because the PSV plays an important role in the performance of a hydraulic system, a technique commonly referred to as Condition Monitoring Scheme (CMS) has been used extensively to monitor the progress of faults in the PSV. But before any CMS can be implemented on a system, it needs to be thoroughly tested for its reliability of fault detection since, a failure of the CMS to detect any potential fault can be economically disastrous, and dangerous in terms of the safety of personnel. The motivation of this research was to develop a fault simulator which could reliably and repeatedly induce user defined faults in the PSV and thereby aid in testing the efficacy of the CMS for monitoring such simulated faults. Industry research has revealed that the most common mode of failure in spool valves is an increase in the friction between the spool and valve, due to wear, contamination and dirt, which renders the valve inoperable. In this research, a non-destructive fault simulator was developed which induced artificial friction faults in the PSV. The PSV consisted of two solenoids on the opposite sides of the valve spool by virtue of which, bi-directional position control could be achieved.The PSV with the spool and one of the solenoids was used as the system in which the faults were simulated, and the second solenoid was used an a fault simulator for inducing the desired friction characteristics in the system. The friction characteristics induced in the valve were similar to those in the classical friction curve, i.e., stiction at low velocities and Coulomb and viscous friction at higher velocities. By employing a closed loop position control scheme, one of the solenoids was used to generate a linearly increasing velocity profile by virtue of which the desired friction characteristics could be induced in different velocity regimes. The other solenoid was used to generate the desired friction force. A closed loop force control strategy, which used the feedback from a force transducer, allowed for the accurate control of the friction characteristics. stiction was induced at low velocities by passing the required current in both the solenoids that resulted in no net force on the valve spool. Due to the absence of any driving force the spool was stalled at the desired location, thus achieving the same effect of stiction at low velocities. The coulomb and viscous friction were induced at higher velocities by employing an algorithm which was a function of the spool velocity. Different magnitudes of static, coulomb and viscous friction were induced to achieve the friction characteristics represented by the classical friction curve. Since the change in force characteristics of the valve results in a corresponding change in the current drawn by the position control solenoid, a rudimentary CMS for monitoring the current characteristics is presented. Based on the experimental results and validation using the CMS it was concluded that the fault simulator was able to accurately produce the desired frictional loading on the valve spool and was able to do so with a high degree of repeatability.

Proportional Solenoid Valves (PSV) have been successfully used in the hydraulic industry for many years due to the benefits associated with higher accuracy compared to on/off solenoid valves, and the robustness and cost compared to servo valves. Because the PSV plays an important role in the performance of a hydraulic system, a technique commonly referred to as Condition Monitoring Scheme (CMS) has been used extensively to monitor the progress of faults in the PSV. But before any CMS can be implemented on a system, it needs to be thoroughly tested for its reliability of fault detection since, a failure of the CMS to detect any potential fault can be economically disastrous, and dangerous in terms of the safety of personnel. The motivation of this research was to develop a fault simulator which could reliably and repeatedly induce user defined faults in the PSV and thereby aid in testing the efficacy of the CMS for monitoring such simulated faults.<p>Industry research has revealed that the most common mode of failure in spool valves is an increase in the friction between the spool and valve, due to wear, contamination and dirt, which renders the valve inoperable. In this research, a non-destructive fault simulator was developed which induced artificial friction faults in the PSV. The PSV consisted of two solenoids on the opposite sides of the valve spool by virtue of which, bi-directional position control could be achieved. The PSV with the spool and one of the solenoids was used as the system in which the faults were simulated, and the second solenoid was used an a fault simulator for inducing the desired friction characteristics in the system. <p>The friction characteristics induced in the valve were similar to those in the classical friction curve, i.e., stiction at low velocities and Coulomb and viscous friction at higher velocities. By employing a closed loop position control scheme, one of the solenoids was used to generate a linearly increasing velocity profile by virtue of which the desired friction characteristics could be induced in different velocity regimes. The other solenoid was used to generate the desired friction force. A closed loop force control strategy, which used the feedback from a force transducer, allowed for the accurate control of the friction characteristics. stiction was induced at low velocities by passing the required current in both the solenoids that resulted in no net force on the valve spool. Due to the absence of any driving force the spool was stalled at the desired location, thus achieving the same effect of stiction at low velocities. The coulomb and viscous friction were induced at higher velocities by employing an algorithm which was a function of the spool velocity. Different magnitudes of static, coulomb and viscous friction were induced to achieve the friction characteristics represented by the classical friction curve. Since the change in force characteristics of the valve results in a corresponding change in the current drawn by the position control solenoid, a rudimentary CMS for monitoring the current characteristics is presented. Based on the experimental results and validation using the CMS it was concluded that the fault simulator was able to accurately produce the desired frictional loading on the valve spool and was able to do so with a high degree of repeatability. Proportional Solenoid Valves (PSV) have been successfully used in the hydraulic industry for many years due to the benefits associated with higher accuracy compared to on/off solenoid valves, and the robustness and cost compared to servo valves. Because the PSV plays an important role in the performance of a hydraulic system, a technique commonly referred to as Condition Monitoring Scheme (CMS) has been used extensively to monitor the progress of faults in the PSV. But before any CMS can be implemented on a system, it needs to be thoroughly tested for its reliability of fault detection since, a failure of the CMS to detect any potential fault can be economically disastrous, and dangerous in terms of the safety of personnel. The motivation of this research was to develop a fault simulator which could reliably and repeatedly induce user defined faults in the PSV and thereby aid in testing the efficacy of the CMS for monitoring such simulated faults. Industry research has revealed that the most common mode of failure in spool valves is an increase in the friction between the spool and valve, due to wear, contamination and dirt, which renders the valve inoperable. In this research, a non-destructive fault simulator was developed which induced artificial friction faults in the PSV. The PSV consisted of two solenoids on the opposite sides of the valve spool by virtue of which, bi-directional position control could be achieved.The PSV with the spool and one of the solenoids was used as the system in which the faults were simulated, and the second solenoid was used an a fault simulator for inducing the desired friction characteristics in the system. The friction characteristics induced in the valve were similar to those in the classical friction curve, i.e., stiction at low velocities and Coulomb and viscous friction at higher velocities. By employing a closed loop position control scheme, one of the solenoids was used to generate a linearly increasing velocity profile by virtue of which the desired friction characteristics could be induced in different velocity regimes. The other solenoid was used to generate the desired friction force. A closed loop force control strategy, which used the feedback from a force transducer, allowed for the accurate control of the friction characteristics. stiction was induced at low velocities by passing the required current in both the solenoids that resulted in no net force on the valve spool. Due to the absence of any driving force the spool was stalled at the desired location, thus achieving the same effect of stiction at low velocities. The coulomb and viscous friction were induced at higher velocities by employing an algorithm which was a function of the spool velocity. Different magnitudes of static, coulomb and viscous friction were induced to achieve the friction characteristics represented by the classical friction curve. Since the change in force characteristics of the valve results in a corresponding change in the current drawn by the position control solenoid, a rudimentary CMS for monitoring the current characteristics is presented. Based on the experimental results and validation using the CMS it was concluded that the fault simulator was able to accurately produce the desired frictional loading on the valve spool and was able to do so with a high degree of repeatability.

This thesis explores two aspects of modeling the behavior of joint friction in structures. The first aspect deals with the accurate and efficient simulation of a simple system that incorporates the LuGre friction law. Energy transfer and dissipation in a structural joint model is the second topic of this thesis. It is hypothesized that friction could serve to pump energy from one frequency to higher frequencies where it might be dissipated more quickly. Motivation for this study stems from the need to have accurate models of high-precision space structures. Because friction at connecting joints plays a major role in the damping capacity of the structure, a good understanding of this mechanism is necessary to predict the vibratory response and enhance the energy dissipation of the structure. Simulation results of a dynamic system with LuGre friction show that the system is relatively well-conditioned when the slip velocity is small, and ill-conditioned for large slip velocities. Furthermore, the most efficient numerical method to simulate this system is determined to be an implicit integration scheme. To study the energy transfer and dissipation, two models of a jointed structure with friction are considered. Results from the steady-state forced responses of the two structural systems indicate that friction converted low frequency, single harmonic excitation to multi-harmonic response through internal resonances. However, differences in energy dissipation results between the models show that the response of a frictional system is highly sensitive to system parameters and friction laws. Conclusions and suggestions for future research are also discussed.

This thesis documents the development of a novel nonlinear controller for servo pneumatic actuators that give good reference tracking at low speed motion, where friction has strong effect to the system behaviors. The design of the nonlinear controller presented in this thesis is based on the formalism of Lyapunov stability theory. The controller is constructed through a dynamical adaptive backstepping-sliding mode control algorithm. The conventional Lyapunov-based control algorithm is often limited by the order of the dynamical system; however, the backstepping design concept allows the control algorithm to be extended to higher order dynamical systems. In addition, the friction is estimated on-line via the Lyapunov-based adaptive laws embedded in the controller; meanwhile, the sliding mode control provides high robustness to the system parameter uncertainties. The simulation results clearly demonstrating the improved system performance (i.e., fast response and the reduced tracking error) are presented. Finally, the integration of the controller with a Lyapunov-based pressure observer reduces the state feedback of the servo pneumatic actuator model to only the piston displacement.

This thesis documents the development of a novel nonlinear controller for servo pneumatic actuators that give good reference tracking at low speed motion, where friction has strong effect to the system behaviors. The design of the nonlinear controller presented in this thesis is based on the formalism of Lyapunov stability theory. The controller is constructed through a dynamical adaptive backstepping-sliding mode control algorithm. The conventional Lyapunov-based control algorithm is often limited by the order of the dynamical system; however, the backstepping design concept allows the control algorithm to be extended to higher order dynamical systems. In addition, the friction is estimated on-line via the Lyapunov-based adaptive laws embedded in the controller; meanwhile, the sliding mode control provides high robustness to the system parameter uncertainties. The simulation results clearly demonstrating the improved system performance (i.e., fast response and the reduced tracking error) are presented. Finally, the integration of the controller with a Lyapunov-based pressure observer reduces the state feedback of the servo pneumatic actuator model to only the piston displacement.

Different contact surface parameters and operating characteristics are observed during the deep drawing process. It is not possible to find a formulation that can be used for all lubrication regimes. Therefore, several friction models have been developed in order to overcome this problem. In this study, a math program is developed which combines Wilson&rsquo / s and Khonsari&rsquo / s friction models in a new model in order to increase accuracy and efficiency in friction calculations. By comparing the results of both friction models, the film thickness ratio of 0.035 is introduced for 0.15 &mu / m standard deviation of surface summits. Below the ratio of 0.035, Khonsari&rsquo / s model gives more accurate results since asperity friction is dominant and the model is based on asperity contact. Above the ratio of 0.035, Wilson&rsquo / s model gives more accurate results since hydrodynamic friction is dominant and the model is based on lubricant flow. In this study, a finite element program is used to simulate 50 mm cylindrical and 50.5x50.5 mm square shallow drawing processes which are performed in single stage. The final cup depths are selected as 18 mm and 23 mm for square and cylindrical cup drawing respectively. The FEM model and the program codes developed are verified by the previous studies in literature. After verification, the simulation results of the cylindrical and square cup drawing are input to a math program which calculates local friction coefficients using the combined friction model. Finally, the combined friction model and the results are further discussed.

The primary purpose of this research is to investigate the effectiveness of a scaled roller rig for accurately assessing the contact mechanics and dynamics between a profiled steel wheel and rail, as is commonly used in rail vehicles. The established creep models of Kalker and Johnson and Vermeulen are used to establish correction factors, scaling factors, and transformation factors that allow us to relate the results from a scaled rig to those of a tangent track. �Correction factors, which are defined as the ratios of a given quantity (such as creep coefficient) between a roller rig and a track, are derived and used to relate the results between a full-size rig and a full-size track. Scaling factors are derived to relate the same quantities between roller rigs of different scales. Finally, transformation factors are derived by combining scaling factors with correction factors in order to relate the results from a scaled roller rig to a full-size tangent track. Close-end formulae for creep force correction, scaling, and transformation factors are provided in the thesis, along with their full derivation and an explanation of their limitations; these formulae can be used to calculate the correction factors for any wheel-rail geometry and scaling. For Kalker's theory, it is shown that the correction factor for creep coefficients is strictly a function of wheel and rail geometry, primarily the wheel and roller diameter ratio. For Johnson and Vermeulen's theory, the effects of creepage, scale, and load on the creep force correction factor are demonstrated. �It is shown that INRETS' scaling strategy causes the normalized creep curve to be identical for both a full-size and a scaled roller rig. �It is also shown that the creep force correction factors for Johnson and Vermeulen's model increase linearly with creepage, starting with the values predicted by Kalker's theory. �Therefore, Kalker's theory provides a conservative estimate for creep force correction factors. �A case study is presented to demonstrate the creep curves, as well as the correction and transformation factors, for a typical wheel-rail configuration. �Additionally, two studies by other authors that calculate the correction factor for Kalker's creep coefficients for specific wheel-rail geometries are reviewed and show full agreement with the results that are predicted by the formulae derived in this study. �Based on a review of existing and past roller rigs, as well as the findings of this thesis, a number of recommendations are given for the design of a roller rig for the purpose of assessing the wheel-rail contact mechanics. �A scaling strategy (INRETS') is suggested, and equations for power consumption of a roller rig are derived. Recommendations for sensors and actuators necessary for such a rig are also given. Special attention is given to the resolution and accuracy of velocity sensors, which are required to properly measure and plot the creep curves. / Master of Science

No description available.

La dynamique des structures assemblées est un sujet de recherche actuel. En particulier, une prédiction correcte de l'amortissement apporté par les liaisons vissés est devenu une condition essentiel pour un certain nombre d'applications, comme par exemple les avions et les véhicules spatiaux. En effet, pour ces applications, l’utilisation de matériaux avec un coefficient d'amortissement plus élevée, comme des matériaux visco-élastiques, est limité par les conditions de fonctionnement.Ces travaux apportent deux contributions principales. La première porte sur la phase de conception et modélisation, avec la création d'un système de connecteurs pour la reproduction des comportements normal et tangentiel d'une liaisons vissée. Cela est accomplie en considérant seulement les données physiques de la liaison et des surfaces en contact.La deuxième contribution concerne l’évaluation des propriétés dynamiques non-linéaires des assemblages. Un set d'outils de post-traitement utilisant le filtre de Kalman est développé pour réaliser une analyse modale non-linéaire pour les types d'essais les plus communs: les essais aux chocs, les essais en balayage sinus, et les essais en sinus aléatoire.Les méthodes développées ont été appliqués et évaluées sur une structure boulonnée réel, en soulignant les avantages et les inconvénients. Notamment, le filtre de Kalman permet une meilleure précision sur les paramétrés identifiés, mais le procédé d’initialisation du filtre est le problème principal. Une automatisation partiel de l’initialisation est prévu, ainsi que des conseils pratiques grâce à l’expérience acquise sur le sujet. / Bolted structures dynamics is an ongoing research topic. In particular, a correct prediction of the damping provided by bolted joints has became an essential requirement for a certain number of applications, such as aircrafts and space vehicles. In fact, for these applications, the use of materials with higher damping coefficients is limited by environmental conditions.This work provides two main contributions. The first one concerns the design and modeling phase, with the creation of a finite element connectors' system, that reproduces the bolted joint normal and tangential behaviors. The latter is accomplished only by taking into account readily available physical data, such as the bolted joint dimensions and the properties of the surfaces in contact. The second contribution regards the evaluation of assembled structures' nonlinear dynamic properties. A set of post-processing tools making use of the Kalman filter is developed to perform a nonlinear modal analysis for the most common types of experimental tests: impact hammer tests, sweep sine tests, and random vibration tests.The developed methods are then applied and evaluated on a real bolted structure, pointing out advantages and drawbacks. In particular, the Kalman filter allows for a higher accuracy in the determination of modal parameters, but the filter initialization is the main problem. A partial automation of the initialization task is provided, together with practical tips thanks to the experience gained on the subject.