Experiments in Robot Formation Control with an Emphasis on Decentralized Control Algorithms (Mechanical Project)

In this project, several algorithms and experiments involving the control of robot formations are presented. The algorithms used were focused on decentralized control. The experiments were implemented on two different experimental testbeds consisting of teams of wheeled mobile robots. The robots used are described along with their sensors and supporting hardware. Also, there is a discussion of the programming framework used to build the control software.

The first control algorithm and experiment uses a robust consensus tracking algorithm to control a formation of robots to track a desired trajectory. The robots must maintain the correct formation shape while the formation follows the trajectory. This task is complicated by limited communication between the robots, and disturbances applied to the information exchange. Additionally, only a subset of the robots have access to the reference trajectory.

In the second experiment, the same algorithm was re-implemented in a decentralized way, which more effectively demonstrated the goals of the algorithm. The second algorithm involves controlling a formation of robots without a global reference frame. In order to accomplish this, the formation description is reformulated into variables describing the relative positions of the robots, and vision-based measurements are used for control.

A homography-based technique is used to determine the relative positions of the robots using a single camera. Then a consensus tracking controller similar to the one used previously is used to distribute the measured information to all of the robots. This is done despite the fact that different parts of the information are measured by different agents.

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Development of Model for Large-Bore Engine Cooling Systems (Mechanical Project)

The purpose of this project is to present on the development and results of the cooling system logic tree and model developed as part of the Pipeline Research Council International, Inc (PRCI) funded project at the Kansas State National Gas Machinery Laboratory. PRCI noticed that many of the legacy engines utilized in the natural gas transmission industry were plagued by cooling system problems.

As such, a need existed to better understand the heat transfer mechanisms from the combusting gases to the cooling water, and then from the cooling water to the environment. To meet this need, a logic tree was developed to provide guidance on how to balance and identify problems within the cooling system and schedule appropriate maintenance.

Utilizing information taken from OEM operating guides, a cooling system model was developed to supplement the logic tree in providing further guidance and understanding of cooling system operation. The cooling system model calculates the heat loads experienced within the engine cooling system, the pressures within the system, and the temperatures exiting the cooling equipment. The cooling system engineering model was developed based upon the fluid dynamics, thermodynamics, and heat transfer experienced by the coolant within the system. The inputs of the model are familiar to the operating companies and include the characteristics of the engine and coolant piping system, coolant chemistry, and engine oil system characteristics. Included in the model are the various components that collectively comprise the engine cooling system, including the water cooling pump, aftercooler, surge tank, fin-fan units, and oil cooler.

The results of the Excel-based model were then compared to available field data to determine the validity of the model. The cooling system model was then used to conduct a parametric investigation of various operating conditions including part vs. full load and engine speed, turbocharger performance, and changes in ambient conditions. The results of this parametric investigation are summarized as charts and tables that are presented as part of this thesis.

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http://krex.k-state.edu/dspace/bitstream/2097/8721/3/ClintKendrick2011.pdf

Nonlinear Constrained Component Optimization of a Plug-in Hybrid Electric Vehicle (Mechanical Project)

Today transportation is one of the rapidly evolving technologies in the world. With the stringent mandatory emission regulations and high fuel prices, researchers and manufacturers are ever increasingly pushed to the frontiers of research in pursuit of alternative propulsion systems. Electrically propelled vehicles are one of the most promising solutions among all the other alternatives, as far as; reliability, availability, feasibility and safety issues are concerned.

However, the shortcomings of a fully electric vehicle in fulfilling all performance requirements make the electrification of the conventional engine powered vehicles in the form of a plug-in hybrid electric vehicle (PHEV) the most feasible propulsion systems. The optimal combination of the properly sized components such as internal combustion engine, electric motor, energy storage unit are crucial for the vehicle to meet the performance requirements, improve fuel efficiency, reduce emissions, and cost effectiveness.

In this thesis an application of Particle Swarm Optimization (PSO) approach to optimally size the vehicle powertrain components (e.g. engine power, electric motor power, and battery energy capacity) while meeting all the critical performance requirements, such as acceleration, grade and maximum speed is studied. Compared to conventional optimization methods, PSO handles the nonlinear constrained optimization problems more efficiently and precisely. The PHEV powertrain configuration with the determined sizes of the components has been used in a new vehicle model in PSAT (Powertrain System Analysis Toolkit) platform. The simulation results show that with the optimized component sizes of the PHEV vehicle (via PSO), the performance and the fuel efficiency of the vehicle are significantly improved.

The optimal solution of the component sizes found in this research increased the performance and the fuel efficiency of the vehicle. Furthermore, after reaching the desired values of the component sizes that meet all the performance requirements, the overall emission of hazardous pollutants from the PHEV powertrain is included in the optimization problem in order to obtain updated PHEV component sizes that would also meet additional design specifications and requirements.
Author: Emrah Tolga Yildiz
Source: Purdue University

The reuse of Design rules by Product and Process documentation – A descriptive case study (Mechanical Project)

The problem of automating design processes is often related to the difficulties with updating, maintaining and sharing the information. This thesis provides a descriptive case study of a large company’s design automation process and the difficulties of reusing already existing solutions.
The main purpose of the thesis has been to trace a product family from its specification of demands to a complete design program. An account is given of the documentation written during the product development process, of the different data storage and also how the company has implemented design automation in their process.

The results have been reached through a series of interviews as well as previous studies and material from the company. From an analysis of the results proposed solutions are given and focus on the low quality the documentation has and how it is a result of a rapid growth within the company.

Author: Andersson, Emma

Source: Jönköping University


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http://www.mediafire.com/file/b955a9m9ep73c69/FULLTEXT01.pdf

Mass Transfer and GDL Electric Resistance in PEM Fuel Cells (Mechanical Project)

Many modeling studies have been carried out to simulate the current distribution across the channel and shoulder direction in a proton exchange membrane (PEM) fuel cell. However the modeling results do not show agreement on the current density distribution. At the same time, no experimental measurement result of current density distribution across the channel and the shoulder direction is available to testify the modeling studies.
Hence in this work, an experiment was conducted to separately measure the current densities under the channel and the shoulder in a PEM fuel cell by using the specially designed membrane electrode assemblies. The experimental results show that the current density under the channel is lower than that under the shoulder except when the fuel cell load is high. Afterwards two more experiments were carried out to find out the reason causing the higher current density under the shoulder. The effects of the electric resistance of gas diffusion layer (GDL) in the lateral and through-plane directions on the current density distribution were studied respectively. The experimental results show that it is the through-plane electric resistance that leads to the higher current density under the shoulder.

Moreover, a three-dimensional fuel cell model is developed using FORTRAN. A new method of combining the thin-film model and homogeneous model is utilized to model the catalyst layer. The model is validated by the experimental data. The distribution of current density, oxygen concentration, membrane phase potential, solid phase potential and overpotential in a PEM fuel cell have been studied by the model. The modeling results show that the new modeling method provides better simulations to the actual transport processes and chemical reaction in the catalyst layer of a PEM fuel cell.

Author: Wang, Lin

Source: University of Miami


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http://www.megaupload.com/?d=1CWH7HT5

Biomechanics of the Intervertebral Disc: The Effects of Load History on Mechanical Behavior (Mechanical Project)

Degenerative disc disease is associated with back pain, and can be a debilitating disorder. In addition to the biological contributions of genetics and aging, mechanical factors have been implicated in accelerating the progression of disc degeneration.

Two studies were performed in order to explore the effects of various loading conditions on disc biomechanics. The first study explores the effects of compressive historical loads and disc hydration on subsequent creep loading and recovery. The second study investigates the restorative powers of creep distraction between compressive loading periods. In both cases three commonly applied mathematical models were employed to characterize disc behavior and the effectiveness of each model was validated.

The studies confirm that hydration level has a significant impact on disc stiffness and time dependent behavior. Distraction and conditioning phases are shown to have a significant impact on hydration level and thus subsequent mechanical behavior.

Introduction:

The Intervertebral Disc:

The intervertebral disc (IVD) is found between two subsequent vertebral bodies allowing the spine to flex and twist while supporting gravitational and muscular loads. A motion segment is comprised of an intervertebral disc and its two neighboring vertebral bodies. The mechanical properties of the disc are imperative to its normal operation. The disc is comprised of several components that each contribute to the mechanical properties. Degradation of these components can lead to reduced mechanical performance as well as pain.

The disc degenerates naturally as a normal part of aging, but the relationship between degeneration and pain is not fully understood. Studies are focused on differentiating between natural aging and the debilitating effects of more extreme degeneration. The effects of degeneration on the mechanical behavior of the disc may be a contributing factor to pain. Degeneration can lead to degraded biomechanics in terms of increased flexibility, decreased fluid pressurization, and lower disc height. Severe disc degeneration involves the degradation of the components of the disc and can lead to herniation, spinal stenosis, and degenerative spondylolisthesis.

Author: Adam Shabtai Gabai

Source: University of Maryland

Design of 120cc Single Cylinder Experimental Engine for Analysis of Intake Swirl and Multiple Ignition Sites (Mechanical Project)

The intent of this thesis is to design, build, and test a cylinder head with variable swirl and ignition sites. The design aspect used Solid Works Floworks to model airflow within the head and cylinder. Swirl rate and volumetric flow rate were calculated from the results. Many design iterations took place before a suitable design was accomplished.
Once the suitable design was reached, it was built using the rapid prototyping method known as 3-D printing (Fused Deposition Modeling). Valve guides and seats were installed in the head. Then valves, springs, and retainers were installed to allow for testing. The inlet was created using stereo-lithography due to its smooth surface finish and thin walls. A pin wheel swirl measuring device was built to measure tangential rotation rate of gasses in the cylinder. The experimental head was tested on the University of Miami flow bench in the Internal Combustion Engines Laboratory.
The results of the experimental work and theoretical modeling were compared. The results matched closely. The difference between experimental and theoretical values for high swirl flow rates were less than 3% error and the swirl ratio was less than 10%. For the low swirl scenario, error was less than 30%. The measured flow rate for the high swirl scenario was 28.87 CFM and the swirl ratio was measured as 2.87. SolidWorks Floworks created accurate results for the high swirl scenario and further experimentation should be conducted for different geometries.

Author: Seemann, Patrick

Source: University of Miami

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