bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimal Band-Limited Trajectory Planning and Control for an Inverted Wheeled Pendulum
Authors: Pathak Kaustubh , Agrawal Sunil K.
Published: April 2008

Mobile inverted pendulum robots consist of an elongated pendulum body with two motors mounted on it for driving the wheels. The velocity and position control of such a vehicle is challenging because of the coupling of the pendulum’s pitch angle from the vertical and the Cartesian motion of the vehicle. On using a nonlinear transform to effect partial feedback linearization, the system dynamics transforms to two subsystems: a linear system with the vehicle’s pitch and in-plane orientation, and a nonlinear system of internal dynamics. In this paper, the problem of utilizing such a partial feedback linearization for optimal trajectory planning of such vehicles is considered. Due to the resulting linear subsystem with vehicle pitch and in-plane orientation, these configuration variables can be controlled by a linear controller (C) using a nonlinear feedback. The planning approach presented in this paper considers the time-constant (τ) of the linear controller C explicitly. A band-limited Sinc-function interpolation is used to plan the variables in the method of collocation. This ensures that high frequency signal content which cannot be handled by the controller C, is absent in the planned trajectory, making the plan better implementable by the controller. The planned trajectory takes the vehicle from point to point, while keeping the vehicle pitch bounded and avoiding obstacles. The optimality condition considered in the algorithm is the length of the path. The optimization problem posed after collocation, is then solved using a standard Sequential Quadratic Programming (SQP) solver. Simulation results show that the tracking controller C is able to follow the planned trajectory when no initial planar Cartesian error is present.
Slip and Fall Characterization of Floors
Authors: Poczynok Peter J. , Barnett Ralph L.
Published: April 2008

During ambulation, every maneuver causes the feet to impose a tangential loading at each contact with the floor. If the frictional resistance at the contact point is less than the associated tangential loading, slipping occurs and sometimes falling. There are five disciplines, some recently developed, that enable one to develop the general theory for predicting the number of walkers who will slip within a given time period on a statistically homogeneous and isotropic floor. These include force-plate studies, floor duty cycles, tribometry, extreme value theory of slipperiness, and floor reliability theory. When used with some additional bookkeeping notions, the general theory will be extended to real floors traversed by walkers with multiple ambulation styles and wearing a variety of footwear. In contrast, conventional slip and fall theory does not account for floor usage, different footwear and various ambulation styles, nor can it be used to determine the number of walkers who actually slip on a given floor.
Three Dimensional Transient Finite Element Analysis for Microstructure Formation and Residual Stresses in Double-Pass Laser Aided DMD Process
Authors: Ghosh S. , Choi J.
Published: April 2008

Despite immense advances in Laser Aided Direct Metal/Material Deposition (LADMD) process many issues concerning the effects of process parameters on the stability of variety of properties and the integrity of microstructure have been reported. Modeling of heat flow seems to be a standard practice to couple heat flow calculations to related macroscopic phenomena such as fluid flow in the melt and solid-liquid mushy region, macrosegregation and thermal stresses. A key component in these models is the coupling between thermal and solute fields. Like macrostructural phenomena even microstructural features such as phase appearance, morphology, grain size or spacing are certainly no less important. The focus of this paper is the solute transport, in particular the manner in which process scale transport is coupled to transport at the local scale of the solid-liquid interface which requires a modeling of the redistribution of solutes at the scale of the secondary arm spaces in the dendritic mushy region. Basic microsegregation models which assume either no mass diffusion in the solid (Gulliver-Scheil) or complete diffusion in the solid (equilibrium lever rule) in a fixed arm space are inappropriate in high energy beam processes involving significantly high cooling rates. This paper aims at incorporating a model that accounts for finite mass diffusion and coarsening of the arm space. Due to the complexity and nonlinearity of LADMD process, analytical solutions can rarely address the practical manufacturing process. Consequently, this is an attempt towards a methodology of finite element analysis to predict solidification microstructure and thermal stresses. The simulation has been carried out for H13 tool steel deposited on a mild steel substrate. However, the program can easily be extended to a wide variety of steels.
Evaluation of Motor Vehicle Seatbelt Retractor Locking Devices
Authors: Hock Davis , Meyer Steven E. , Herbst Brian , Forrest Stephen , Renfroe David A. , Hutchinson Brandon , Canalichio Troy , Sances Anthony , Kumaresan Sriringham
Published: April 2008

The seemingly never-ending increase in popularity of the more rollover-prone Sport Utility Vehicle type vehicles (SUVs) has provided an increased focus and urgency on rollover occupant protection. Field research has made clear that traditional, contemporary motor vehicle seatbelt retractors often fail to restrain occupants as expected. Various researchers have documented laboratory tests results and cited numerous real-world case studies describing these circumstances. These studies have typically focused on the response of the retractor’s inertial acceleration sensing lockup device. This device has been shown to allow surprising amounts of seatbelt spool out during long duration accident sequences with resulting multi-directional vehicle acceleration pulses such as those seen in typical rollover crashes. Further, increased injury potential has been discussed and attributed to such webbing spool out. One commonly implemented design countermeasure, or redundancy, to the retractor’s inertial sensor is a webbing velocity sensor intended to lock up the retractor independent of vehicle acceleration. This paper reports laboratory test data evaluating a wide spectrum of webbing velocity sensor designs found in current production vehicles. This study evaluates their relative performance, corresponding injury potential and occupant protection aspects of these designs.
H
∞ Loop-Shaping Control Design and Robustness Analysis of a Hydraulic Wheel Loader
Authors: Fales Roger C. , Kelkar Atul G.
Published: April 2008

Construction, earthmoving, and agricultural equipment manufacturers are moving toward building more and more equipment with electro-hydraulic control systems. The existing industry practices for the design of control systems in construction machines primarily rely on classical designs coupled with ad-hoc synthesis procedures. Such practices lack a systematic procedure to account for unavoidable plant uncertainties in the design process as well as coupled dynamics of the multi-input multi-output (MIMO) configuration. In this paper, an H-infinity loop shaping control design method is applied to a wheel loader with an electro-hydraulic control system. This tracking control design is used to provide an automatic bucket levelling feature for a wheel loader. A MIMO nonlinear model for an electrohydraulically actuated wheel loader linkage is considered. The robustness of the controller design is validated in simulation using a complete nonlinear model of the wheel loader linkage. The simulation results are presented for both an H-infinity loop shaping design and an LQG design. The LQG design is from previous work and presented here for comparison. The effects of varying fluid parameters such as bulk modulus are considered in a robust stability analysis. The stability robustness and performance are compared for the two controller designs.
Epoxy Reinforcing for Rollover Safety
Authors: Herbst Brian , Hock Davis , Meyer Steven E. , Forrest Stephen , Sances Anthony , Kumaresan Sriringham
Published: April 2008

Roof intrusion and roof contact injury are common factors in rollovers. Rollover crashes are the most dangerous collision type for light duty vehicles, measured by the ratios of fatal and serious injuries to the number of occupants involved in tow away crashes according to the National Automotive Sampling System. Over half of those sustaining injury with the occurrence of roof intrusion were belted. NHTSA estimates that roof crush intrusion occurs, and potentially contributes to serious or fatal occupant injury, in about 26% of the rollover crashes. Modern automobile vehicles utilize thin sheet metal construction formed into complex sections, which are spotwelded together. During vehicular rollovers, the roof is subjected to multi-directional loading which generally leads to localized buckling in the sheet metal roof pillars and subsequent intrusion into the occupant’s survival space. The utilization of expanding epoxies and rigid polyurethane foams within the sheet metal sections can delay wall buckling through localized confinement. This composite system, sheet metal sections filled with epoxy, demonstrates significant enhancements in peak force and energy absorption under multiple loading conditions. 4-point bending tests on representative vehicle sheet metal sections show a 6-fold increase in peak strength with the composite systems. Inverted drop tests comparisons document the additional survival space retained using the composite sheet metal and epoxy system.
Dynamic Modeling for a Cylindrical Mobile Robot on Rough-Terrain
Authors: Reina Giulio , Foglia Mario , Milella Annalisa , Gentile Angelo
Published: April 2008

Ground autonomous mini-mobile robots have important potential applications, such as reconnaissance, patrol, planetary exploration and military applications. To accomplish tasks on rough-terrain, control and planning methods must consider the physical characteristics of the vehicle and of its environment. Failure to understand these characteristics could lead to vehicle endangerment and mission failure. This paper describes recent and current work at Mobile Robotics Laboratory of the Politecnico of Bari in the area of rough terrain mobility and traversability of autonomous vehicles. A cylindrical shaped mobile robot is presented and its rolling motion on rough terrain is studied from both theoretical and experimental prospect. A comprehensive vehicle dynamic model is proposed based on well-established physical models of mobile robot-terrain interaction. The model is experimentally validated and it allows employing the vehicle as a tactile sensor for terrain characterization and identification. Innovative vision-based-methods are also introduced for estimating relevant kinematic parameters of the vehicle motion. It is shown that the dynamic model can describe efficiently the vehicle behavior and could enhance its mobility on rough-terrain through integration with control and planning algorithms.
A Time and Frequency Domain Approach for Identifying Non-Linear Automotive Suspension System Models in the Absence of an Input Measurement
Authors: Haroon Muhammad , Adams Douglas E. , Luk Yiu Wah , Ferri Aldo A.
Published: April 2008

The inputs to many ‘real’ mechanical systems are not readily measurable. For example, the input to the tire patch of the tires of automotive road vehicles is neither measurable nor easy to estimate. As conventional system identification procedures require input measurements or at least estimates of the inputs, a new approach for nonlinear system identification of mechanical systems, in the absence of an input measurement, is presented here. This approach uses a combination of time domain (Restoring Force) and frequency domain (Nonlinear Identification through Feedback of the Outputs (NIFO)) techniques. The time domain is used to characterize the nonlinearities in the system and the observed nonlinear characteristics are used in the frequency domain to build a model of the system. The method is applied to experimental tire-vehicle suspension system data.
A Technique for Estimating Linear Parameters of an Automotive Suspension System Using Nonlinear Restoring Force Extraction
Authors: Haroon Muhammad , Adams Douglas E. , Luk Yiu Wah
Published: April 2008

Conventional nonlinear system identification procedures assume that the system behavior is nominally linear at a specific amplitude (usually low). The nominally linear parameters are then estimated at that particular amplitude and used to estimate the nonlinear parameters of the system. Many mechanical systems are not nominally linear over a broad frequency range for any operating amplitude. A new method for nonlinear system identification, in the absence of an input measurement, is presented that works in the opposite direction. Information about the nonlinear elements of the system is used to estimate the underlying linear parameters. Restoring force, boundary perturbation and direct parameter estimation techniques are combined to develop this approach. The approach is applied to data from an experimental tire-vehicle suspension system.
Impact Dynamics and Parametric Study of the Contact Event for Biped Robots
Authors: Mu Xiuping , Wu Qiong
Published: April 2008

In this paper, the impact dynamics and its effects on the contact event of a five-link biped walking on level ground are studied. The dynamic equations of both single and double impact of the biped are derived using the Newtonian approach. We improved the conventional five-link biped kinematic model such that, for the first time, the explicit solutions of the external impulses and post impact angular velocities are presented in detailed but compact form. These solutions are used conveniently to evaluate the conditions that warrant each individual type of impact. A parametric study is performed to correlate the type of impact with certain gait parameters and the results are presented in graphical form in the parameter space. Effects of variations in the parameters on the vertical impulse and post impact velocity of the trailing tip are further investigated. The ratio of the vertical and horizontal impulses is also examined, which shows the likelihood of slippage of the foot (feet). This work reveals important physical insights into the mechanisms of biped impact and facilitates motion planning and motion regulation of biped locomotion with prescribed contact phases.
Numerical Simulations of Capillary Electrokinetic Pinched Injection Separation Flows in Microchannels
Authors: Farouk Bakhtier , Yan Fang
Published: April 2008

Numerical simulations were performed to study the capillary electrokinetic flow in microchannels. A sample stream consisting of three different species is focused during the loading step and driven into a separation channel during the dispensing step. Flow fields and species distributions are simulated for both the loading and the dispensing steps in a two dimensional cross channel device. The evolution of each sample species concentration at the end of the separation channel is predicted. The separation resolution is defined from the sample species concentration band retention time and band width. Different separation performances can be obtained by manipulating the electric field strengths. A series of simulations for different electric field distributions and field magnitudes in the channel are presented. The goal of these simulations is to identify the parameters providing optimal separation performance. The effect of both loading and dispensing schemes on species concentration and separation resolution is presented.
The Usefulness of Entropic Average Temperatures
Authors: Stewart Susan W. , Shelton Sam V.
Published: April 2008

The second law Carnot efficiency, entropy balances, and many other principles of the second law are stated with assumed constant temperature heat sinks and reservoirs; i.e., assuming heat transfer across a boundary at a constant temperature. However, real world heat exchangers reject and receive heat transfer to a flowing fluid with a varying temperature making the application of many aspects of the second law inappropriate or complex. For such varying temperature cases, an entropic average temperature can be defined and easily calculated that can be substituted for the varying temperature heat sink or source temperature. The constant temperature restricted second law statements can then be used with this entropic average temperature. This entropic average temperature concept is simple to understand and is very useful in the presentation of thermodynamic concepts to new students, making it seem less abstract and more applicable to real world processes with which they are familiar. This paper serves to develop the concept and details of the entropic average temperature and show its usefulness while emphasizing its benefit for inclusion in engineering thermodynamics syllabi.
Learning Rate Effect in Neural Network for Damage Detection
Authors: Fang X. , Tang J. , Luo Huageng
Published: April 2008

Neural network is a powerful tool that can be utilized for structural damage detection and health monitoring. Since damage usually varies/reduces stiffness, frequency response variation can be used as indicator for damage occurrence. A well designed neural network can correlate frequency response variation to damage localization/severity without resorting to detailed structural modeling. While various neural network based approaches have been developed, their effectiveness, efficiency, and robustness oftentimes rely on the selection of several important parameters in the network construction. One of the key performance metrics for a neural network is the learning rate. Although the dynamic steepest descent algorithm (DSD) and fuzzy steepest descent algorithm (FSD) have shown promising possibility of improving the learning convergence speed significantly without increasing the computational effort, its performance still depends on the selection of control parameters and control strategy. In this paper, a tunable steepest descent algorithm (TSD) improving the performance of the dynamic steepest descent algorithm is proposed. A numerical benchmark example shows that the proposed algorithm significantly improves the convergence rates of the backpropagation algorithm. A structural health monitoring system incorporated with the neural network trained by the adaptive learning algorithm is developed for detecting the impact damage.
Implementation of Single and Multiple Adaptive Step Size Algorithm to ANC
Authors: Sabah Yesim , Okuma Masaaki , Okubo Minoru
Published: April 2008

The purpose of this paper is to investigate a modified adaptive step size algorithm and implement to active noise control (ANC) system. It is well-known that there is a trade-off between steady state error and convergence rate depending on the step size. This study shows that the new algorithm can track changes in dynamic characteristics of ANC system as well as produce a low steady state error. Simulation results are presented to compare the performance of the new algorithm to basic LMS algorithm. Although there have been several studies for adaptive step size algorithm, no quantitative analysis has yet been reported for real time active noise control application as far as the authors know. Experimental results are presented for a duct system. The results indicate that the new algorithm provides better performance than the fixed step size FXLMS algorithm.
Effects of Freezing on the Mechanical Properties of Blood Vessels
Authors: Grassl Erin D. , Barocas Victor H. , Bischof John C.
Published: April 2008

The mechanical properties of blood vessels are important to their ability to function properly. The effects of freezing/cooling on the mechanical properties are a concern for several reasons including preservation of vascular grafts, appropriate storage of samples prior to mechanical testing, and the effects and mechanisms of cryoplasty (cryotherapy for treatment of restenosis). Many have studied the effects of freezing vessels in the presence of cryoprotective agents (CPAs), and the results are mixed, depending on the type of artery and particular mechanical test. The few studies on freezing without CPAs have also given mixed results. To examine this issue further, we froze pig femoral arteries to −20 C in the absence of CPA, and then subjected them to uniaxial tensile testing. Our results suggest that freezing does have an effect on stress-strain properties, particularly in the low stress region corresponding to physiological conditions. The mechanisms of this change in mechanical properties may include the loss of smooth muscle viability, damage to extracellular matrix (ECM), or changes in alignment caused by ice crystal growth. Understanding these changes is important in understanding the mechanisms of cryoplasty, as well as choosing appropriate storage methods for tissues to be used in vascular grafts.
Transient Testing to Determine Heat Transfer Coefficient and Wall Thickness of Turbine Blades
Authors: Froerer Dathan , Ferguson James R.
Published: April 2008

The integrity of interior passages of cast components, such as turbine blades, is critical to the functionality of these components. Testing methods, which provide a timely judgment of the passages, is essential to the cost effective production of these parts. The goals of this project is to estimate the local internal heat transfer coefficients and wall thickness using inverse heat transfer techniques from the transient response exhibited by the exterior wall temperature to a sudden change in the air flow temperature within the passages. The desired result is a computationally efficient test that can both shorten and improve the inspection of cast turbine blades. The work described here is an initial effort examining feasibility. A first order, one dimensional heat transfer model is assumed through a thin wall. Simulated experimental data is generated from the forward heat transfer problem for a wall with initial temperatures equal to ambient room temperature with one side of the wall suddenly exposed to high temperature forced convection while the other is left exposed to ambient natural convection. Random Gaussian noise is superimposed on the simulated data. The Levenberg-Marquardt technique is examined to determine heat transfer coefficients, wall thickness, and its accuracy.
Design and Simulation of a Smart Endoscope: Part II
Authors: Choi JungHun , Sturges Robert H.
Published: April 2008

In this research, we are developing a noninvasive and safe endoscope for human colonoscopy. To minimize the invasiveness and discomfort, a smart endoscope is composed of a sheath with controllable stiffness that has an exoskeleton structure. A smart endoscope is comprised of an endoscope and a sheath. The stem has more flexibility than a conventional endoscope and the sheath portion maintains controllable flexibility. In principle, this approach could be used for other procedures. The stem of a conventional protoscope has stiffness and it can scratch the inside surface when it pushes into a human colon. It may also deform the colon’s shape. Important parameters used in designing a smart endoscope include the radius of curvature of a sigmoid colon, an appropriate unit diameter for the sheath part, and an ability to lock the units together. An analysis of the cable tensions and external forces is completed for a given configuration based on selected geometric parameters. By applying external forces to the stem of the endoscope, we can solve for the maximum external resisting forces. These are required to maintain the locking ability of the endoscope and the corresponding cable forces.
Disturbance Rejection by Optimal Feedback Control in a Laser Beam Steering System
Authors: Orzechowski Pawel K. , Gibson Steve , Tsao Tsu-Chin
Published: April 2008

This paper presents an optimal control design and experimental implementation for pointing and disturbance rejection in a laser steam steering system. The linear quadratic Gaussian (LQG) controller, which includes a stochastic disturbance model, as well as integral action, was designed and implemented to compensate for disturbances due to atmospheric turbulence in the optical path and mechanical vibration of the laser and optical components. The control design also considers the situation where the stochastic disturbances applied to the two beam axes are correlated and renders a multi-input-multi-output (2-by-2) output feedback controller. The experimental system consists of a two-axis tilt mirror driven by piezo-electric actuators for controlling the laser beam, a second actuated tilt mirror to generate disturbances, a position sensing device that senses the location of the beam on a target plane, and a real time computer for digital control. System identification is used to determine a state space model of the beam steering system for use in control system design. Experimental results are presented to demonstrate the effectiveness of the LQG optimal disturbance rejection for the prescribed stochastic disturbances.
Repetitive Learning Control for Precision Machining of Complex Profiles
Authors: Krishnamoorthy K. , Tsao Tsu-Chin
Published: April 2008

A fast converging Repetitive learning control scheme is proposed to track non circular piston profiles with sharp discontinuities. Modern piston profiles have sudden jumps and discontinuities which introduce large transient errors in tracking. This is handled by the learning control scheme built on top of the inner loop PD control. Simulations show that the learning scheme results in monotonic error convergence. The control law has an adjustable scalar which determines the convergence rate. The scheme involves filtering the control and tracking error values from the previous cycle to generate the learning control for the current cycle. The learning control algorithm generated a modified reference for the inner loop stabilizing feedback. We also show that Feedforward schemes based on stable plant inversion can be brought under this scheme by choosing appropriate learning filters. We also derive sufficiency conditions for stability of the proposed scheme.
Leg Stretcher for Rehabilitation
Authors: McGee Michael , Shakerin Said
Published: April 2008

To alleviate some of the problems associated with upper motor neuron diseases, passive movement and stretching are often prescribed. However, the patient has to make continual and frequent visits to a physical therapist, which is expensive and inconvenient. Therefore, there is a need for devices by which the patient can self-administer some of the prescribed exercise(s) at home. In this paper, the design of a portable unit for self-administered stretching of thigh muscles is presented.
Nonlinear State Monitoring With Karhunen-Loe`ve-Transform
Authors: Glo¨smann Philipp , Kreuzer Edwin
Published: April 2008

Nonlinear dynamical systems often appear to have uncorrelated output. This characteristic leads to the idea of analyzing the dynamics of nonlinear systems with methods developed for random processes. The Karhunen-Loe`ve-Transform (KLT) was designed to detect coherent structures in random process data. It can also be applied for state monitoring of complex systems. This paper gives a short review on the mathematical concept of the KLT and discusses an approach to characterize the dynamics of nonlinear systems based on experimental data.
Baseline, Exhaust-Fired, and Combined Operation of Desiccant Dehumidification Unit
Authors: Petrov Andrei Yu. , Zaltash Abdolreza , Vineyard Edward A. , Labinov Solomon D. , Rizy D. Tom , Linkous Randall L.
Published: April 2008

The performance of a commercially available direct-fired desiccant dehumidification unit (DFDD) has been studied as part of a microturbine generator (MTG)-based Integrated Energy System (IES) at Oak Ridge National Laboratory (ORNL). The IES includes a second-generation air-to-water heat recovery unit (HRU) for the MTG. The focus of these tests was to study the performance of a DFDD in baseline (direct-fired with its natural gas burner) mode and to compare it with a DFDD performance in the exhaust-fired and combined modes as part of the ORNL IES, when waste heat received from the MTG was used for desiccant regeneration. The baseline tests were performed with regeneration air heated by a natural gas burner (direct-fired). The testing of the waste-heat, or exhaust-fired DFDD as part of IES involved using the exhaust gas from the HRU for regeneration air in the DFDD after hot water production in the HRU. Hot water from the HRU was used to produce chilled water in an indirect-fired (water fired) absorption chiller. The combined DFDD was the combination of natural gas burner and exhaust-fired testing. The study investigated the impact of varying the process and regeneration conditions on the latent capacity (LC) and latent coefficient of performance (LCOP) of the DFDD, as well as overall IES efficiency. The performance tests show that LC increases with increasing dew point (humidity ratio) of the process air or the increased amount of waste heat associated with increased MTG power output. In addition, baseline LC was found to be three times higher than the LC in the exhaust-fired mode of operation. LCOP in baseline operation is also almost three times higher than that obtained in the exhaust-fired mode (55.4% compared to 19%). But, at the same time, addition of the DFDD to the IES with the MTG at maximum power output increases the overall IES efficiency by 4–5%. Results of the combined tests performed at a reduced MTG power output of 15 kW (51,182 Btu/h) and their comparison with the baseline and exhaust-fired tests show that activation of the DFDD gas burner during exhaust-fired tests increases the LC over the baseline value from 91,514.9 Btu/h (25.8 kW) to 101,835.8 Btu/h (29.8 kW). The LCOP during the combined mode is less than the “baseline” LCOP, because in addition to gas input, the low-grade MTG/HRU exhaust heat input to the DFDD are also being considered. The overall IES efficiency during the combined mode is approximately 8% higher than without the DFDD integrated into the IES.
A Lyapunov Controller for a Varying Length Flexible Cable System to Supress Transverse Vibration
Authors: Zhang Yuhong , Agrawal Sunil
Published: April 2008

Modeling and controller design for a flexible cable transporter system, with arbitrarily varying cable length is presented using Hamilton’s principle and Lyapunov theory. The axial velocity of the system is assumed to be arbitrary in the model. This is different from existing literature where the axial velocity is assumed either constant or is prescribed. The governing equations are coupled non-linear partial differential equations (PDEs) and ordinary differential equations (ODEs), and boundary conditions. The interactions between the cables and the slider, pulleys, and motors are included in the model. Numerical solution of the governing equations is obtained using Galerkin’s method. Based on the Lyapunov stability theory, we propose boundary controllers and the control law for an actuator within the domain to suppress the transverse vibration of the cables, while achieving the slider goal. The proposed controllers dissipate the vibratory energy and guarantee asymptotic stability of the closed-loop system. Simulation results demonstrate the effectiveness of the proposed controllers.
Kinematic Analysis and Evaluation of Wheelchair Mounted Robotic Arms
Authors: McCaffrey Edward J. , Alqasemi Redwan M. , Dubey Rajiv V.
Published: April 2008

There has been significant progress in bringing commercially-viable wheelchair mounted robotic arms (WMRA) into the marketplace in the past 30 years. This paper focuses on kinematic analysis and evaluation of such robotic arms. It addresses the kinematics of the WMRA with respect to its ability to reach common positions while performing activities of daily living (ADL). A procedure is developed for the kinematic analysis and evaluation of a wheelchair mounted robotic arm. In addition to developing the analytical procedure, the manipulator is evaluated, and design recommendations and insights are obtained. Current commercially-available wheelchair mountable robotic manipulators have been designed specifically for use in rehabilitation robotics. In an effort to evaluate two commercial manipulators, the procedure for kinematic analysis is applied to each manipulator. Design recommendations with regard to each device are obtained. This method will benefit the researchers by providing a standardized procedure for kinematic analysis of WMRAs that is capable of evaluating independent designs.
Shape Preserving Global Parameterization for CAD/CAM/CAE
Authors: Lee Chen-Han , Lu Lingyun , Dym Jon , Yin Guangyan
Published: April 2008

CAD/CAM/CAE applications often deal with open or closed shells of faces (surfaces). Each face has it’s own 2-D parameter space that may not be rectangular. In many applications we need to merge the individual parameter spaces into a single global parameter space that resembles the model shape in the 3-D physical space. In this paper, we present a method of building such shape-preserving global parameterization (of a shell of faces) that is suitable for CAD/CAM/CAE applications.
Actively Cooled Current Leads for Superconducting Electronics Using Mixed-Gas Joule-Thomson Refrigeration
Authors: Nellis Gregory F. , Pfotenhauer John M. , Klein Sanford A.
Published: April 2008

Electrical leads used for the supply of current to superconducting magnets and electronics must span the temperature range from room temperature to cryogenic temperatures. Because the conventional materials used for such purposes (e.g., copper and aluminum) have both a finite electrical resistance and a significant thermal conductivity, operation of the leads results in both thermal generation and conductance. The resulting thermal loads must be removed from the cryogenic environment. This paper describes a method for integrating cryogenic refrigeration technology with current leads in an efficient and practical manner. The key to this concept is the use of a mixed-gas cooling cycle that absorbs the distributed refrigeration load continuously over the temperature range that it is generated, as opposed to allowing it to pass down to the cold end of the lead where the same energy flow constitutes a much higher entropy load on the cryocooler. Additional benefits of this technology include a more isothermal electronic package, as well as improvements in reliability, and reduction in size and mass. Mixed-gas working fluids can be used within Joule-Thomson devices to achieve a greater refrigeration effect for the same pressure span than is possible with a pure substance. This paper describes a computational tool that allows the composition of gas mixtures to be optimized for the case where the refrigeration load is not completely concentrated at the cold end, as is typically the case, but rather the refrigeration load is distributed over the entire temperature range. A genetic optimization algorithm was found to be the most robust and reliable technique for identifying optimum gas mixture composition. The thermodynamic advantage associated with accepting the refrigeration load at the temperature of its origin, rather than at the cold end, is quantified.
Cooling Flow Simulation in the Enclosure of Mobile Generator
Authors: Xie J. , Amano R. S.
Published: April 2008

A thermal and airflow simulation model is developed for three-dimensional cooling flow study of ventilation and heat transfer inside a mobile generator’s enclosure. The purpose of this design is to achieve better sound attenuation while keeping proper cooling of the engine and generator. This paper focuses its objectives on the adjustment and improvement of cooling performances of some design factors like vent size, vent positions, fan’s flow rate and airflow route based on the CFD approach. A zero-equation HVAC turbulence model was employed and the simulation results were compared with the standard k-ε model. Numerical results show that the proper distribution in the intake vents helps in achieving uniform cooling flow distributions by avoiding the occurrence of hot spots on the engine and generator surfaces. Pressure drop through muffler and radiator are both important factors. Effective flow path arrangement is also found to be one of the most fatal factors in the thermal and noise management.
Energy Savings and Pollution Reduction by Coupling a Three-Kiln Brick Production System for the Construction Industry
Authors: Cha´vez Rosa H. , de J. Guadarrama Javier , Carapia Leticia , Herna´ndez-Guerrero Abel
Published: April 2008

Atmospheric pollution is one of the most important environmental problems, becoming a phenomenon that could reach levels of serious consequences with irreversible environmental impacts. In Mexico, like in several other countries, brick makers carry out brick production by burning mixtures of different heavy fuels. Because of the wide variety of fuels used it is necessary to determine what types of residual gases are generated, in order to propose remedial treatments in production or to introduce substitution technologies. These preventive actions need to be put in place in order to comply with the Ecological Balance and Environment Protection General Law. Brick kilns emit pollutant gases and particles that remain in the air causing a serious health hazard to the near-factory residents. Amongst these pollutants are carbon monoxide (CO), sulfur oxides (SOx) and hydrocarbons. This paper presents the results of the analysis of a novel 3-kilns coupled system. This experimental analysis includes the determination of the combustion products for gases and particulate matter generated from the burning of the heavy fuels using Gas Chromatography and Scanning Electron Microscopy. Field data also allowed the determination of energy savings for this system, mainly due to the reduction of the consumption of fuel. Fortunately these results show a combined 30% energy savings and a reduction of pollutants and particle emissions.
A Numerical Study of Unsteady Natural Convection in a Rectangular Enclosure: The Effect of Compressibility
Authors: Akyuzlu K. M. , Pavri Y. , Antoniou A.
Published: April 2008

A two-dimensional, mathematical model is adopted to investigate the development of buoyancy driven circulation patterns and temperature contours inside a rectangular enclosure filled with a compressible fluid (Pr=1.0). One of the vertical walls of the enclosure is kept at a higher temperature then the opposing vertical wall. The top and the bottom of the enclosure are assumed insulated. The physics based mathematical model for this problem consists of conservation of mass, momentum (two-dimensional Navier-Stokes equations) and energy equations for the enclosed fluid subjected to appropriate boundary conditions. The working fluid is assumed to be compressible through a simple ideal gas relation. The governing equations are discretized using second order accurate central differencing for spatial derivatives and first order forward finite differencing for time derivatives where the computation domain is represented by a uniform orthogonal mesh. The resulting nonlinear equations are then linearized using Newton’s linearization method. The set of algebraic equations that result from this process are then put into a matrix form and solved using a Coupled Modified Strongly Implicit Procedure (CMSIP) for the unknowns (primitive variables) of the problem. A numerical experiment is carried out for a benchmark case (driven cavity flow) to verify the accuracy of the proposed solution procedure. Numerical experiments are then carried out using the proposed compressible flow model to simulate the development of the buoyancy driven circulation patterns for Rayleigh numbers between 103 and 105. Finally, an attempt is made to determine the effect of compressibility of the working fluid by comparing the results of the proposed model to that of models that use incompressible flow assumptions together with Boussinesq approximation.
Experimental Study of the Gas Entrapment Process in Closed-End Microchannels
Authors: Pesse Ana V. , Warrier Gopinath R. , Dhir Vijay K.
Published: April 2008

Earlier studies have shown that for cavities present on any heater surface to become active nucleation sites during boiling, they should entrap gas. The liquid penetrates the cavity due to the capillary and surface forces, but the exact physical mechanisms have not been fully quantified. The physical mechanisms of the gas entrapment process in closed-end microchannels, representing nucleation sites, are investigated in this study. Aside from the fluid properties, the width, length and depth of the cavities, as well as the static contact angle of the test liquid with the solid are considered as main parameters that influence the gas entrapment process. Test pieces consisted of micromachined silicon dices with glass bonded on top. Widths of 50, 30, 15 and 5μm were chosen based on size distribution probability. The mouth angle was 90° in all cases. Test pieces were held horizontally under a microscope equipped with a CCD camera. A drop of liquid was placed at the entrance of the microchannel and capillary and surface forces drive the liquid into the microchannel. Experiments show two main filling behaviors: (1) A uniform meniscus forms at the entrance and moves inwards, (2) Two menisci: one at the entrance and the other at the closed end of the microchannel. In some cases droplet formation at the walls was observed. A single meniscus typically forms for higher contact angles, while two menisci form for lower contact angles. In all cases, after a sufficient time interval (hours to days) the microchannel was completely flooded. In general, for a given depth, wider microchannels take longer to fill. Surface cleanliness and fabrication process also play a role in modifying the contact angle and hence the time taken to fill the microchannel. A comparison of the interface advancement in the microchannel with a simple mass diffusion model shows reasonable agreement.
Simulation of Pendant Droplets and Falling Films in Horizontal Tube Absorbers
Authors: Killion Jesse D. , Garimella Srinivas
Published: April 2008

Recent literature suggests that the droplets that form in horizontal-tube, falling-film absorbers play a major role in the absorption process. The performance of such absorbers is critical to the performance of many absorption heat pump systems. The simulation of droplets of aqueous Lithium Bromide pendant from horizontal tubes was performed by numerically solving the equations of motion on a fixed 3-D grid. The so-called volume of fluid method was used to handle the interface between the liquid and vapor phase. Results are compared with simplified axisymmetric models and with high speed video taken during flow visualization experiments. The results show that simplified axisymmetric models do not satisfactorily represent the evolution of the droplets under horizontal tubes, and that the 3-D numerical model appears to accurately match the important characteristics of droplet formation, detachment and impact observed in the experiments.
Analysis of Heat-Driven Cooling Production Coupled to Power Generation for Increased Electrical Yield
Authors: Lindmark Susanne , Martin Viktoria , Westermark Mats
Published: April 2008

In striving for sustainable energy systems, the development of advanced technologies for combined heat and power generation is a critical factor. In many regions of the world there is a demand for heating only during a small part of the year and the yearly peak of power demand often occurs during the cooling season. Hence, the concept of trigeneration, i.e. the combined generation of power, heat and/or cooling is of great interest when it comes to obtaining a high yearly overall efficiency. In this paper, system studies are used to evaluate different types of trigeneration systems and the potential for an increasing electrical yield. The trigeneration systems consist of different types of gas engines coupled to different types and numbers of absorption chillers. The concepts are compared with regards to: the potential for increasing the overall electrical yield for a plant; cost-effectiveness; and environmental impact in terms of avoided CO2. Results indicate that the use of a humidified gas engine coupled to absorption chillers is a cost-effective and environmentally promising method to increase the electricity yield of a power cycle.
Characterization of High Porosity Open-Celled Metal Foam Using Computed Tomography
Authors: Schmierer Eric N. , Razani Arsalan , Keating Scott , Melton Tony
Published: April 2008

High porosity metal foams have been the subject of many investigations for use in heat transfer enhancement through increased effective thermal conductivity and surface area. Convection heat transfer applications with these foams have been investigated for a large range of Reynolds numbers. Common to these analyses is the need for quantitative information about the interfacial surface area and the effective thermal conductivity of the metal foam. The effective thermal conductivity of these metal foams have been well characterized, however little investigation has been made into the actual surface area of the foam and its dependence on the foam pore density and porosity. Three-dimensional x-ray computed tomography (CT) is used for determining interfacial surface area and ligament diameter of metal foam with porosities ranging from 0.85 to 0.97 and pore densities of 5, 10, 20, and 40 pores per inch. Calibration samples with known surface area and volume are utilized to benchmark the CT process. Foam results are compared to analytical results obtained from the development of a three-dimensional model of the high porosity open-celled foam. The results obtained are compared to results from previous investigations into these geometric parameters. Results from calibration sample comparison and analysis of the foam indicate the need for additional work in quantifying the repeatability and sources of error in CT measurement process.
Molecular Dynamics Study of Thermal Boundary Resistance: Evidence of Strong Inelastic Scattering Transport Channels
Authors: Stevens Robert J. , Norris Pamela M. , Zhigilei Leonid V.
Published: April 2008

With the ever-decreasing size of microelectronics, growing applications of superlattices, and development of nanotechnology, thermal resistances of interfaces are becoming increasingly central to thermal management. Although there has been much success in understanding thermal boundary resistance (TBR) at low temperature, the current models for room temperature TBR are not adequate. This work examines TBR using molecular dynamics (MD) simulations of a simple interface between two FCC solids. The simulations reveal a temperature dependence of TBR, which is an indication of inelastic scattering in the classical limit. Introduction of point defects and lattice-mismatch-induced disorder in the interface region is found to assist the energy transport across the interface. This is believed to be due to the added sites for inelastic scattering and optical phonon excitation. A simple MD experiment was conducted by directing a phonon wave packet towards the interface. Inelastic scattering, which increases transport across the interface, was directly observed. Another mechanism of energy transport through the interface involving localization of optical phonon modes at the interface was also revealed in the simulations.