Control algorithm is developed for a satellite with flexible appendages to achieve a good pointing performance. Detailed modeling activity was carried out that consists of sensor and actuator models, disturbances and system dynamics. Common hardware found in the spacecraft such as reaction wheels, gyroscopes, star trackers etc. were included in the model. Furthermore, the Newton-Euler method is employed for the derivation of multi-body equations of motion. Evaluation of the pointing accuracy with proper pointing performance metrics such as accuracy, jitter and stability during slew maneuvers are obtained through simulations. Control strategies are proposed to improve pointing performance.

This thesis presents a preliminary design of a fully articulated five-fingered anthropomorphic human hand prosthesis with particular emphasis on the controller and actuator design. The proposed controller is a modified artificial neural network PID-based controller with application to the nonlinear and highly coupled dynamics of the hand prosthesis. The new solid state actuator has been designed based on electroactive polymers, which are a type of material that exhibit electromechanical behavior and a liquid metal alloy acts as the electrode. The solid state actuators reduce the overall mechanical complexity, risk failure and required maintenance of the prosthesis. / Graduate

Injury to the human neck is a frequent consequence of automobile accidents and has been a significant public health problem for many years. The term `whiplash' has been used to describe these injuries in which the sudden differential movement between the head and torso leads to abnormal motions within the neck causing damage to its soft tissue components. Although many different theories have been proposed, no definitive answer on the cause of `whiplash' injury has yet been established and the exact mechanisms of injury remain unclear. Biomechanical research is ongoing in the field of impact analysis with many different experimental and computational methods being used to try and determine the mechanisms of injury. Experimental research and mathematically based computer modelling are continually used to study the behaviour of the head and neck, particularly its response to trauma during automobile impacts. The rationale behind the research described in this thesis is that a computational model of the human head and neck, capable of simulating the dynamic response to automobile impacts, could help explain neck injury mechanisms. The objective of the research has been to develop a model that_,, can accurately predict the resulting head-neck motion in response to acceleration impacts of various directions and severities. This thesis presents the development and validation of a three-dimensional computational model of the human head and cervical spine. The novelty of the work is in the detailed representation of the various components of the neck. The model comprises nine rigid bodies with detailed geometry representing the head, seven vertebrae of the neck and the first thoracic vertebra. The rigid bodies are interconnected by spring and damper constraints representing the soft-tissues of the neck. 19 muscle groups are included in the model with the ability to curve around the cervical vertebrae during neck bending. Muscle mechanics are handled by an external application providing both passive and active muscle behaviour. The major findings of the research are: From the analysis of frontal and lateral impacts it is shown that the inclusion of active muscle behaviour is essential in predicting the head-neck response to impact. With passive properties the response of the head-neck model is analogous to the response of cadaveric specimens where the influence of active musculature is absent. Analysis of the local loads in the soft-tissue components of the model during the frontal impact with active musculature revealed a clear peak in force in the majority of ligaments and in the intervertebral discs very early in the impact before any forward rotation of the head had occurred. For the case of rear-end impact simulations it has been shown for the first time that the inclusion of active musculature has little effect on the rotation of the head and neck but significantly alters the internal loading of the soft-tissue components of the neck.

While human presence in cislunar space continues to expand, so too does the demand for `lightweight' automated on-board processes. In nonlinear dynamical environments, computationally efficient guidance strategies are challenging. Many traditional approaches rely on either simplifying assumptions in the dynamical model or on abundant computational resources. This research employs reinforcement learning, a subset of machine learning, to produce a controller that is suitable for on-board low-thrust guidance in challenging dynamical regions of space. The proposed controller functions without knowledge of the simplifications and assumptions of the dynamical model, and direct interaction with the nonlinear equations of motion creates a flexible learning scheme that is not limited to a single force model. The learning process leverages high-performance computing to train a closed-loop neural network controller. This controller may be employed on-board, and autonomously generates low-thrust control profiles in real-time without imposing a heavy workload on a flight computer. Control feasibility is demonstrated through sample transfers between Lyapunov orbits in the Earth-Moon system. The sample low-thrust controller exhibits remarkable robustness to perturbations and generalizes effectively to nearby motion. Effective guidance in sample scenarios suggests extendibility of the learning framework to higher-fidelity domains.

<div>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. </div><div>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. </div><div>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.</div><div>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.</div><div><br></div>

This article presents transient handling analysis with a full-vehicle non-linear multi-body dynamic model, having 102 degrees of freedom. A transient cornering manoeuvre, with a constant steer angle and velocity has been undertaken. The effects of aerodynamic lift and drag forces have been included in the simulation tests. The vehicle handling characteristics with and without aerodynamic forces have been compared and various observations made. The aerodynamic forces have been predicted by a k¿1 model solution of the Navier¿Stokes equations for turbulent flow. The numerical predictions for the evaluation of aerodynamic lift coefficient agrees well with the scaled-down air tunnel experimental work, using hot-wire anemometry

This article presents a simulation study into effects of compliant (flexible) components (such as the engine subframe and the lower control arm) and their deflections on the characteristics of a vehicle experiencing steering drift during straight-line braking. The vehicle front and rear suspension are modelled using multi-body dynamic analysis software. The front suspension model represents theMacPherson strut design of the vehicle and includes a rack and pinion steering system, brake system, engine subframe, and a powertrain unit. The model has been analysed under two steering control methods: fixed and free control. Suspension characteristics and the effect of deflections arising from the subframe and the lower control arm on these suspension characteristics have been analysed. The simulations confirmed that variation of component stiffness and interactions within components give rise to side-to-side deflections that could affect lateral drift during braking. It is concluded that side-to-side variation of suspension characteristics can have a detrimental effect on lateral drift during braking and that compliant components whose stiffness varies from side to side can cause different side-to-side deflections that can induce and influence variation in suspension characteristics such as toe steer angle that can lead the vehicle during braking.

Cone crushers are used in both the construction and mining industries for the production of aggregates and extraction of ores. Aggregates are used when building for example houses, roads and railways, hence the cone crushers are a vital part of modern society. To ensure the performance of the cone crusher, it is important to properly adjust the feeding conditions. Using computational methods to virtually analyze the performance of the crushers is a more time and cost efficient solution compared to physical testing. This thesis was divided into two parts, where the main objective of the first part was to use the discrete element method (DEM) to analyze the segregation in cone crushers. Three different methods were developed, which later were utilized to compare the segregation for four different feeding conditions. Two of the analysis methods only considered the segregation in the feed hopper, whilst the third method aimed to give an understanding ofthe segregation inside the crushing chamber. The two first methods could successfully be used to compare how segregated the feed material was for the four feeding conditions, however, the third method proved to be both hard to validate and highly dependent on proper material flow inside the crushing chamber. The main objective during the second part of the thesis was to investigate the possibility of running the DEM simulations coupled to a multibody simulation (MBS) software. The simulation routine was then used to compare the foundation loads for the same four feeding conditions as in the first part. The subframe was later modeled as a flexible body to analyze and compare the stresses the subframe was subject to during operation for the same four feeding conditions. Setting up and running the coupled simulation was successful. Different simulation settings were tested, anda general guideline on how those settings should be defined was set up. The actual impact the coupling had on the foundation loads and stresses in the subframe was however almost non-existent. This could probably be directly related to the fact that the crushing forces in EDEM are known to be many times smaller than what they have been measured to in experiments. This also meant that changing the feeding conditions to alter the segregation did not have a noticeable effect on the results.

No description available.

This paper presents a multidegrees-of-freedom non-linear multibody dynamic model of a vehicle, comprising front and rear suspensions, steering system, road wheels, tyres and vehicle inertia. The model incorporates all sources of compliance, stiffness and damping, all with non-linear characteristics. The vehicle model is created in ADAMS (automatic dynamic analysis of mechanical systems) formulation. The model is used for the purpose of vehicle handling analysis. Simulation runs, in-line with vehicle manoeuvres specified under ISO and British Standards, have been undertaken and reported in the paper.