bluuebunny/crossref_metadata_2025 huggingface dataset:
NOx Prediction in Diesel Engines for Aftertreatment Control
Authors: Upadhyay Devesh , Van Nieuwstadt Michiel
Published: May 2008

Modern Diesel engines are faced with two major emission challenges in their quest to become an environmentally compatible source of motive power, Nitrogen Oxides (NOx) and Particulate Matter (PM). Advanced techniques, such as High Pressure Common Rail (HPCR) fuel injection combined with multiple injections per cycle, are commonly employed to minimize in-cylinder production of NOx and PM. However, to meet the EPA mandated standards it is essential that an aftertreatment system be used. Typical Diesel aftertreatment systems will employ some form of a NOx reducing catalyst and a particulate trap for PM removal. Lean NOx traps and Selective Catalytic Reduction (SCR) are examples of aftertreatment techniques frequently used in Diesel engine applications. Whatever the method of choice, knowledge of the feed-gas NOx concentration is essential for not only assessing the performance of the NOx reduction catalyst but also for defining the control strategy for the aftertreatment system with respect to the management of the reductant quantity to be injected. In the absence of a dynamic NOx emission model the control algorithm has to depend on either a NOx sensor upstream of the catalyst or a static map of the feedgas NOx level as some function of engine influence factors. While NOx sensors add to the overall system cost, creating an accurate and representative NOx map over the entire engine operating range can be a challenging task. A dynamic NOx model would, in theory solve, both of these problems, however it is essential that the model be simple and implementable in real time. A model that uses inputs that are not available from the standard measurement set is of little use for real time control applications as is a model that predicts the temporal and spatial NOx evolution in the engine combustion chamber as such models tend to be computationally expensive. However, it is essential that the model behave like a fast NOx sensor in predicting cycle averaged NOx emission. In this paper we present an approach to developing such a model and present results from model validation against vehicle data. The basic structure of the model relies on well-known mechanisms that describe the NOx creation and decomposition chemical kinetics. Simplifying assumptions are made to allow available measurements to be used as inputs to the model. This leads to a parametric model where the unknown parameters are estimated using Nelder Mead optimization routine available in Matlab®. Model validation against vehicle data is also presented.
Nonlinear Actuation Properties of Macro Fiber Composite Actuators
Authors: Williams R. Brett , Inman Daniel J. , Wilkie W. Keats
Published: May 2008

This paper presents an experimental approach to determine the effective piezoelectric strain parameters, d33 and d31, of the Macro Fiber Composite (MFC) actuator. Traditional d31 piezoceramics typically operate at low strain and electric fields levels and are thus adequately modeled using linear piezoelectric theory. However, the MFC has interdigitated electrodes which allow actuation by way of the stronger “d33” piezoelectric effect. The resulting large deformations/stresses often occur in combination with strong applied electric fields and cause the violation of some of the assumptions used in the development of linear piezoelectric theory. Specifically, the piezoelectric “d” parameters are no longer constant, but rather, as the current research indicates, depend on the applied mechanical stress and electric field.
High Resolution Separation of Proteins in a Polymeric Micro-Fluidic Chip
Authors: Horiuchi Keisuke , Dutta Prashanta , Cui Huanchun , Ivory Cornelius F.
Published: May 2008

An integrated micro-fluidic chip has been developed using Poly-di-methyl siloxane (PDMS) to separate proteins by isoelectric focusing (IEF). Soft lithography techniques, which offer rapid prototyping, easy multilayer fabrication, mass production capability and biocompatibility, were utilized to fabricate various parts of the micro-fluidic chip. Separately molded PDMS layers were bonded together to form three-dimensional microfluidic chips. The microfluidic chips were prepared for IEF by conditioning the channel with 1 M NaOH and then loading it with a solution of fluorescent proteins made using 0.4% MC, 4% broad-range ampholyte and 0.018 mg/ml protein in 18 MOhm water. Relatively large reservoirs on the acidic and basic ends of the channel were filled with anolyte (50 mM phosphoric acid) and catholyte (50 mM sodium hydroxide), respectively, and then current was applied along the axis of the channel until one or more bands of protein focused, usually in just a few minutes even at relatively low voltages. The focused bands were generally well-formed with sharp edges and were less than 100 microns across yielding a putative peak capacity in excess of 100 peaks in a 2-cm long channel.
Optimal Design Method for Brake Noise
Authors: Lee Heewook , Kikuchi Noboru
Published: May 2008

The optimization problem for the brake squeal noise consists of a complex-valued objective function (COF) and physical design variables (PDV). A direct solution has been hampered by many unknowns between the COF and PDV. Nonetheless, an optimal solution is possible if the problem is separated into two steps. In the first step, sensitivity analysis is used to calculate the optimal components’ eigenvalues capable of eliminating all unstable eigenvalues. If only the sensitive components’ eigenvalues for each unstable eigenvalue are chosen as design variables, finding an optimal solution is virtually guaranteed. Once the optimal components’ eigenvalues are found, the second step of the optimization involves the real-valued objective function. Resolving complex eigenvalues in essence allowed us to resume the conventional optimization with response surface methodology. The optimal physical dimensions are obtained using this approach.
Piezoelectric Vibration Control of Translational Flexible Beams Using Switched Stiffness
Authors: Ramaratnam Arun , Jalili Nader , Grier Matt
Published: May 2008

A switch-shunt stiffness method for vibration attenuation of flexible beams undergoing translational base motion with a laminated piezoelectric patch attachment is presented. The piezoelectric actuator, bonded on the top surface of the flexible beam, is switched between open and short circuit configurations. This results in a variable equivalent stiffness which, in turn, can remove energy from the overall system by directly affecting the stored potential energy in the flexible beam. Initially, a single degree of freedom system is considered for validation of the switched stiffness method. The method is then applied to a flexible beam with moving base, representing a Cartesian-type one-link robot manipulator. Simulation results demonstrate favorable vibration attenuation in both cases; the single degree of freedom oscillator and the cantilever flexible beam. Several variations of the switching mechanisms are explored in an effort to achieve optimal vibration characteristics. Experimental testing is currently under investigation for validation of the simulation results presented here.
Effect of Inlet Flow Angle on Performance of Multilouvered Fin Heat Exchangers
Authors: Guo Dahai , Tafti Danesh K.
Published: May 2008

The effect of inlet flow angles on flat tube multilouvered fin heat exchangers is studied. Five inlet flow angles, α= ±25, ±45 and 0 degrees are employed with respect to the face of the heat exchanger. One louver angle θ = 25 degrees, and three fin pitches, Fp = 1.0, 1.5 and 2.0 are considered. There is a strong correlation between the response of the flow efficiency and heat transfer coefficient to inlet flow angle. Positive flow angles, which are in the same direction as the louver angle, have to undergo a smaller rotation to be aligned with louver directed flow in the bank, and exhibit better performance characteristics than negative inlet flow angles. The first-order effect of inlet flow angles is to reduce the effective mass flow rate and Reynolds number through the heat exchanger. For positive flow angles and small fin pitches, the heat transfer coefficient correlates well with the effective Reynolds number {Reeff = Re(cosα)}. However, this is not the case when flow angles are negative and the fin pitch increases. Under these conditions, the Nusselt number deviates considerably from the effective Reynolds number analogy, with a subsequent loss in heat transfer capability. For large negative inlet flow angles (α = −45), the heat transfer coefficient drops as much as 50% for a fin pitch Fp = 2.
Optimizing Design of a Force Probe With Six-Degree of Freedom
Authors: Hu Shengjun , Mei Tao , Kong Deyi , Zhang Yan , Sun Fei
Published: May 2008

A six-degree freedom force probe with double-face structure was developed based on piezoresistive effect and MEMS process. The sensor was constructed by two bonded silicon wafers which have the same structure with prior probe. A rectangular through hole was designed in the middle of the two silicon wafers in order to improve the axial sensitivity while keeping structural stability. Stress distributions caused by different forces and moments were obtained according to theoretical analysis and FEA calculation. The arrangement of piezoresistors on both sides fully utilized the symmetrical feature, and the bridge circuits were designed to detect corresponding force signals. Finally, the sensitivities of the probe to six-axis forces were calculated.
A Model for Acoustic Instabilities Induced by Vortex Shedding in Ducts
Authors: Matveev Konstantin I.
Published: May 2008

Acoustic instabilities may develop in ducts with a mean flow due to vortex shedding. A reduced-order model for vortex-structure interaction is derived in this paper. A duct with two baffles is considered as a general configuration for developing this model. Formation of vortices at the upstream baffle is affected by acoustic oscillations. A new quasi-steady model is applied for determining a moment of vortex separation in an unsteady flow. A vortex impingement on the downstream baffle is assumed to occur instantaneously in order to utilize a ‘kicked’ oscillator model. If vortex collisions with the baffle happen in the appropriate phase with an acoustic pressure perturbation, then acoustic eigen modes of the duct can be excited. Peculiarities of a numerical implementation of the model are discussed.
Robust and Adaptive Resolved Motion Control of a Hydraulic Loader Crane
Authors: Pedersen Henrik C. , Nielsen Brian , Andersen Torben O. , Hansen Michael R.
Published: May 2008

The focus of this paper is the comparison of a robust and a robust adaptive control algorithm, in connection to a resolved motion control system for a mobile hydraulic loader crane with a telescopic arm. The compared control strategies are related to the inner control loops of the system, which are controlling the velocities of the individual actuators on the mobile crane. Along with the inner loops an outer loop in the form of an algorithm for solving the problem of kinematic redundancy is used. The considered control strategies are tested on a simulation model incorporating structural flexibility of the mechanical system. Results obtained with the robust inner control algorithm are verified experimentally and it is explored how accurate the crane may be maneuvered. A comparison of the two methods is made based on the obtained results.
Cavitating Flow of Liquid Nitrogen in Horizontal Rectangular Nozzle
Authors: Ishimoto Jun , Onishi Masahiro , Tokumasu Takashi , Kamijo Kenjiro
Published: May 2008

The fundamental characteristics of the two-dimensional cavitating flow of liquid nitrogen through a horizontal rectangular nozzle are numerically and experimentally investigated to realize the further development and high performance of new multiphase cryogenic fluid applications. First, the governing equations of the cavitating flow of liquid nitrogen based on the unsteady thermal nonequilibrium two-fluid model are presented, and several flow characteristics are numerically calculated, taken into account the thermodynamic effect of cryogenic conditions. Next, the flow visualization measurement on unsteady cavitating flow of liquid nitrogen through a rectangular nozzle installed in a horizontal duct is carried out to clarify the basic cryogenic two-phase flow structure and fundamental characteristics of the transient growth process of cryogenic cloud cavitation.
Empowering Effective Teamwork for Machine Risk Reduction in the Workplace
Authors: Etherton J. R.
Published: May 2008

The need for teamwork creates new requirements for engineers who use the new ANSI guidelines (B11 TR3-2000) for reducing risks associated with machines. Specifically, the guidelines state that “...a team of involved personnel (e.g., operators, maintenance, engineering) should participate in the risk assessment and reduction effort.” The goal of such teams is to achieve tolerable risk. If they are to be effective team members, engineers will need skills in team leadership; identifying tasks and their associated hazards; using risk assessment tools; developing consensus about degree of risk; and selling the team’s proposed risk reduction measures to management. This paper describes the stages of the TR3 process and focuses on engineering leadership skill development. Leadership must face the challenges of change and instill a sense of trust in the process so that a machine risk assessment team’s injury reduction work can be effective.
Dynamic Contribution of Tires in Vehicle Suspension Modeling: An Experimental Approach
Authors: Catania Giuseppe , Zanarini Alessandro
Published: May 2008

An analytical-experimental approach is followed to obtain the dynamic model of a car vehicle, taking into account the full dynamic contribution due to tires. Linearized and condensed vehicle equations of motion are first introduced. The experimental modal model of a car tire, consisting of limited sets of eigenfrequencies and eigenshapes is then experimentally estimated in the frequency range Δftire=0÷300 Hz, starting from a restricted set of experimental degrees of freedom (d.o.f.). The tire is locally loaded to simulate the displacements due to gravitational loads and road contact occurring in operating conditions. Elastic coupling between the car structural model and the tire modal model is thus obtained; a linear, complex eigenproblem is thus formulated, and eigenfrequencies related to the full system are obtained as well. Results are reported and discussed in detail.
High Strain Rate Compressive Properties of Soft Tissue
Authors: Van Sligtenhorst Caleb R. , Cronin Duane S. , Brodland G. Wayne
Published: May 2008

High strain rate material properties and constitutive equations are essential for the development of numerical and physical models to assess the performance of soft materials subject to high rate deformation, with potential applications including protective equipment and vehicle crashworthiness. However, these properties are not available for many soft tissues. This is because specialized testing methods must be employed to obtain the necessary data. Fresh bovine tissue from the semimembranosis muscle was obtained and tested using a polymeric Split Hopkinson Pressure Bar. Samples were tested from 1.4 to 200 hours post mortem to observe the effect of rigor and other possible temporal effects on the material properties. Since this muscle had relatively uniform fiber orientation, it was possible to obtain specimens with fiber directions parallel, perpendicular, and at 45 degrees to the compression axis. The stress-strain curves for the muscle were concave upwards, as is typical of soft tissues at high strain rates. Fiber orientation was determined to have negligible effect at the tested strain rates. The testing revealed that the stiffness of the tissue increased with post mortem time until approximately 6 hours. At times greater than 200 hours post mortem, the tissue properties were found to be very similar to the properties of fresh tissue. These findings suggest that properties of fresh tissue might be estimated using more easily obtained post-rigor tissue.
Virtual Lash Adjuster for an Electromechanical Valve Actuator Through Iterative Learning Control
Authors: Peterson Katherine S. , Stefanopoulou Anna G. , Wang Yan , Megli Tom
Published: May 2008

The reduction of impacts which occur in electromechanical valve actuators due to the presence of valve lash have been largely neglected in the literature. Instead, the majority of work in this area has focused on impacts occurring elsewhere. As such, a controller is presented here to account for the impacts which occur during the release phase of the valve opening due to the presence of valve lash. A combination of feed forward and iterative learning control are used to achieve trajectory tracking during the release bounding the impact velocity by 0.4 m/s.
New Evolutionary Techniques for Optimization of Energy Systems Utilizing Computational Fluid Dynamics
Authors: McCorkle Douglas S. , Bryden Kenneth M.
Published: May 2008

Optimization techniques that search a solution space without designer intervention are becoming important tools in the engineering design of many thermal fluid systems. Evolutionary algorithms are among the most robust of these optimization methods because the ability to optimize many designs simultaneously makes evolutionary algorithms less susceptible to premature convergence. However application of evolutionary algorithms to thermal and fluid systems described by high fidelity models (e.g. computational fluid dynamics) has been limited due to the high computational cost of the fitness evaluation. This paper presents a novel technique that combines two technologies used in the optimization of thermal fluids systems. The first is graph based evolutionary algorithms that are implemented to help increase the diversity of the evolving population of designs. The second is an algorithm utilizing a feed forward neural network that develops a stopping criterion for computational fluid dynamics solutions. This reduces the time required for each future evaluation in the evolutionary process and allows for more complex thermal fluids systems to be optimized. In the system examined here the overall reduction in computational time is approximately 8 times.
Limits of Performance for Alternate Fuel Energy to Mechanical Work Conversion Systems
Authors: Adebiyi George A.
Published: May 2008

The major alternatives for producing work from the chemical energy of fuels include combustion systems and fuel cells. Combustion systems are subject to several performance limiting constraints. Key amongst these is the fact that combustion is an uncontrolled chemical reaction and is typically highly irreversible. The requirement to operate below the metallurgical limit adds to the irreversibility or exergy consumption in practical combustion systems. Furthermore, the use of heat exchangers, which must have finite temperature differences between fluid streams, compounds the exergy consumption. The fuel cell conversion system is a major alternative to combustion systems. It operates as a direct conversion device and is often cited as having a potential for 100% second-law efficiency. Realistically, however, the chemical reactions involved are not reversible. More importantly, the available fuel resources must be reformed to make the chemical energy of the fuel convertible to work; such processes require significant exergy input that must be factored into the determination of the overall exergy conversion efficiency attainable. This paper gives a first- and second-law analysis of the alternate systems for conversion of fuel exergy to mechanical work thus providing a more realistic comparison of the potential of both systems.
Analysis of Flexible Joints for Micromachined Devices
Authors: Johnstone Robert W. , Parameswaran Ash
Published: May 2008

In micromachined devices, surface forces are often stronger than inertial forces. This is a serious disadvantage to conventional designs for prismatic and revolute joints in micromachines. Made from multiple pieces, conventional designs including a lot of sliding contact, which is a serious reliability concern due to stiction and wear problems. To eliminate the sliding contact, Fettig, Wylde, Hubbard, and Kujath investigated the use of compliant devices that closely mimic the behavior of traditional prismatic and revolute joints. In particular, they fabricated and tested a number of surface micromachined flexible joints. They were able to provide empirical data on the transverse, lateral, and rotational spring constants for the joints they fabricated. However, designers typically need to optimize device dimensions to meet their design requirements. To this end, the structures investigated by Fettig et al were analyzed. This paper will present expressions for predicting all three of the stiffness constants for the flexible joints.
Dynamic Modeling of a Thermally-Driven Micro Diffuser Pump
Authors: Sun Chen-li , Pisano Albert P.
Published: May 2008

In this study, we present the dynamic modeling of a micro diffuser pump by employing the commercial software package CFDRC. Two types of time-dependent pressure boundary conditions are applied to the inlet. Sinusoidal and square wave functions with various amplitudes and frequencies are used. The results indicate a rectification effect such that a net flow in the divergent direction of the diffuser is gained over the time. In addition, the model is able to show the correlation of flow rate with frequency by flow circulation effects. This impact of the transient flow on the pumping performance is discussed. The modeling results are also compared to experimental data found in the literature. The net flow rates predicted by the 3D modeling are found to have good agreement at low excitation frequencies. To evaluate the validity of the imposed pressure boundary condition, the heat transfer model of the evaporation process is used.
Numerical Simulation of Microscale Ion-Driven Air Flow
Authors: Schlitz Daniel J. , Garimella Suresh V. , Fisher Timothy S.
Published: May 2008

Ion-driven air flow is a novel method of pumping air at microscale dimensions using the concept of ion drag. The method employs a series of micro-fabricated electrodes to generate strong electric fields that pump unipolar ions through air. Ions collide repeatedly with neutral molecules, thus generating bulk motion of the gas. Meso-scale motion is obtained by changing the voltage of electrodes rapidly over time to create a nearly continuous force on the ions. One application of this technology involves generation of air flow through microchannels or other micro-featured surfaces to create compact, high flux heat sinks for electronics cooling. A numerical model of the fluid-ion-electric field interaction has been developed. The momentum and continuity equations are supplemented with equations for electric charge transport and for electric potential. The momentum equations are coupled through a body-force term to the charge transport and electric field equations, both of which are coupled to the momentum equations and to each other through source and convection terms. The model describes the one-dimensional, time-dependent flow of air and ions between evenly spaced microscale planar electrodes, of which the voltages are switched at frequencies on the order of 1 MHz. The flow is investigated to determine the effect of switching frequency on maximum velocity and pressure head.
Investigation of the Flow Mal-Distribution in Microchannels
Authors: Teng Jyh-Tong , Chu Jiann-Cherng , Liu Min-Sheng , Wang Chi-Chuan , Greif Ralph
Published: May 2008

This study examines the mal-distribution problem in microchannel manifolds. The tubes are of triangular shape with hydraulic diameter of 25 and 50 μm. Ranges of the Reynolds number are from 0.1 to 9. The test results indicate that the mal-distribution decreases with the rise of flow rate. For an inlet flow rate of 0.1 mL/min at the distributor inlet, the maximum difference of the translational velocity among manifolds is about 45%. The difference is reduced to 33% if the flow rate is increased to 0.153 mL/min. The maximum translational velocity inside the manifolds is located at the edge of the manifolds and the center portion has the smallest translational velocity. This is because of the spread and turn around water that helps to contribute the increase of flow rate nearby the edge.
Characterization of Balloon-Jointed Micro-Fingers
Authors: Lu Yenwen , Kim Chang-Jin
Published: May 2008

A micro-finger structure articulated by pneumatically controlled micro balloon joints is characterized for its force capability. The micro-finger, being developed as a building component for future micro-robotics, is made of thick (>100 μm) silicon segments closely jointed by micro balloons made of Parylene thin film. The thick silicon structure and the small gap in between provide strength and stiffness that are desirable in micro-robots. The force characterization of the microfingers, obtained from a simple experimental setup, demonstrates that the micro-finger can apply 1.2 mN force at 60 psi pneumatic actuation. The effective stiffness of the micro-finger is also obtained. The increasing stiffness under higher pressure suggests that the micro-fingers can exert stronger force by increasing pressure, showing the advantage of the active grasping mechanism.
Classification of Corrosion Detected by Acoustic Emission
Authors: Saenkhum N. , Prateepasen A. , Keawtrakulpong P.
Published: May 2008

This paper presents an Acoustic Emission (AE) to detect pitting corrosion in stainless steel. The AE signals were analyzed to reveal the correlation between AE parameters and severity levels of pitting corrosion in austenitic stainless steel 304 (SS304). In this work, the corrosion severity is graded roughly into five levels based on the depth of corrosion. Relationships between a number of time-domain AE parameters and the corrosion severity were first studied and key parameters identified. The corrosion severity was also categorized into three stages: initial, propagation and final stages based on the source mechanisms of the AE signals. We identified these stages from the frequency-domain characteristic of the AE signal and the visual characteristic of the corroded pits in each level of corrosion severity. A number of measures were employed to quantify such characteristics and the source mechanisms hypothesized. To demonstrate the usefulness of such parameters, a feed-forward neural network was used to classify the corrosion severity. Preprocessing and verification techniques were provided to facilitate and to maintain the generalization capability of the network. The classification performance is excellent and demonstrates that the AE technique and a neural network can be efficiently used to detect and monitor the occurrence of corrosion as well as to classify the corrosion severity.
A Novel 3-DOF Micromanipulator
Authors: Chang Heng-Chung , Tsai Julius Ming-Lin , Tsai Hsin-Chang , Fang Weileun
Published: May 2008

In this study, a stiff HARM (high aspect ratio micromachining) manipulator is reported. Since the micromanipulator is made of single crystal silicon, it has superior mechanical properties. The micromanipulator is consisted of a position stage and a robot arm. Moreover, the robot arm is monolithically integrated with the position stage through the micromachining fabrication processes. Hence, its in-plane and out-of-plane positions are precisely controlled by two comb drive actuators and a vertical comb, respectively. In applications, the robotarm, which has three degrees of freedom (DOF), can be exploited as a micromanipulator.
Heat Transfer and Flow Characteristics of a Rib With a Slit
Authors: Tariq Andallib , Panigrahi P. K.
Published: May 2008

The present investigation is an experimental study of convective heat transfer in the entrance region of a rectangular channel with a single surface mounted slit rib. The open area ratios of the slit rib set during the experiment are equal to 10, 20, 30, 40 and 50%. Hotwire anemometry (HWA) and resistance thermometry (RTD) have been used for velocity and temperature measurement respectively. Both mean and turbulent statistics of the velocity and temperature fluctuations have been reported. Smoke visualization has also been carried out to obtain a qualitative picture of the flow field behind the rib. The surface Nusselt number has been determined from liquid crystal thermography (LCT). The Reynolds number based on the hydraulic diameter of the channel has been set at Re = 32,100. The nature of the flow through the slit and its interaction with the shear layer from the top of the rib depend on the size of the slit. For the slit rib with higher open area ratio (β = 40 and 50%), the bottom part of the slit rib behaves like an independent small rib with its own reattachment region. At smaller open area ratio (β = 10, 20 and 30%), the flow through the slit manipulates the reattaching shear layer from the top of the rib. The size of the slit and its location from the bottom channel surface are the primary parameters responsible for the modification and manipulation of the flow behavior of a slit rib in comparison to the solid rib.
An Integrated Approach for Numerical Simulation of Full Vehicle Behaviour During Transient Dynamic Maneuvers on Arbitrary Obstacles and Road Surfaces
Authors: Duni E. , Monfrino G. , Saponaro R. , Caudano M. , Urbinati F. , Spinelli M. , Pizzuto A.
Published: May 2008

This work describes a numerical methodology based on the finite element method used for the transient dynamic simulation of the full vehicle rolling on different kind of obstacles. Some issues related to the tire finite element model development and its validation, by numerical-experimental comparison, have been discussed. The strategy to combine the static simulations such as the tire inflating, the vehicle weight application and suspension pre loading, with transient dynamic analysis of the car rolling over the obstacle has been chosen. The methodology, based on integration of Abaqus Implicit and Explicit codes, has been successfully applied for the dynamic simulation of Fiat Punto car passing over comfort and pothole obstacle; it is in a good stage of development for a bump obstacle (misuse airbag test).
Validation Experiments of Large Compartment Fires
Authors: McGrattan Kevin B. , Donnelly Michelle , Hamins Anthony , Johnnson Eric , Maranghides Alex , Mulholland George , Ohlemiller Tom , Widmann John , Yang Jiann
Published: May 2008

In cooperation with the fire protection engineering community, a computational fire model, Fire Dynamics Simulator (FDS), is being developed at NIST to study fire behavior and to evaluate the performance of fire protection systems in buildings. The software was released into the public domain in 2000, and since then has been used for a wide variety of analyses by fire protection engineers. An on-going need is to develop and validate new sub-models. Fire experiments are conducted for a variety of reasons, and model predictions of these experiments over the past few decades have gradually improved. However, as the models become more detailed, so must the measurements. The bulk of available large scale test data consist of temperature (thermocouple) measurements made at various points above a fire or throughout an enclosure. While it is useful to compare model predictions with these measurements, one can only gauge how closely the model reproduces the given data. There is often no way to infer why the model and experiment disagree, and thus no way to improve the model. Also, it is difficult to separate various physical phenomena in a large scale fire test so that combustion, radiation and heat transfer algorithms can be evaluated independently. For example, the heat release rate of the fire governs the rate at which energy is added to the system, convective and radiative transport distribute the energy throughout, and thermal conduction drains the system of some of the energy. The measured value of a temperature, heat flux, or gas concentration at any one point depends on all the physical processes, and uncertainties in each phase of the calculation tend to combine in a non-linear way impacting the prediction.
Hydrogen as a Fuel Supplement in a CNG Operated Vehicle Using a Simple Onboard Hydrogen Generation System
Authors: Asad Usman , Wattoo Mohammad A.
Published: May 2008

Natural gas operated gasoline engines achieve superior fuel economy on the expense of reduced engine power and increased emissions. One method of offsetting these disadvantages is by the addition of hydrogen gas up to 20% by volume to compressed natural gas (CNG) using the existing natural gas conversion systems. This offers major benefits in fuel economy, light load performance and lower emissions. The effect of supplementing CNG with hydrogen is studied along with the design of a simple hydrogen generation system for a 1.3 L bi-fuel engine. The Suzuki 1.3 L G13BA (SOHC) gasoline engine fitted with the Landi Renzo CNG pressure regulator, Type TN1 (Standard) has been used for experimentation. The system uses a small current for electrolysis of ordinary tap water for production of hydrogen. The light load performance is significantly enhanced and carbon monoxide and unburnt hydrocarbon emissions are reduced. Constraints on system design have been duly accounted for and the complete system is placed under the hood of the vehicle.
A Coupled Tube-Tissue Model for Frequency Calculation of Arterial Tubes With Tissue
Authors: Zhang Xiaoming , Fatemi Mostafa , Greenleaf James F.
Published: May 2008

Vibro-acoustography is a new noncontact imaging method based on the radiation force of ultrasound. We extend this new technique for tissue characterization of arterial vessels by vibration techniques. In this paper a theoretical model for vibration analysis of arterial vessel with tissue is developed. Experimental studies were carried out on a silicone rubber tube embedded in a cylindrical gelatin phantom of larger radius, which simulates a large artery and the tissue body. The fundamental mode is well excited by the radiation force of ultrasound. The fundamental frequency was measured 81.8 Hz for a tube-phantom structure that is quite close to our theoretical prediction of 83.3 Hz.
The Development of a Monitoring and Control System for Pulverised Coal Flames Using Neural Networks
Authors: Tan O. H. , Wilcox S. J. , Ward J. , Lewitt M.
Published: May 2008

This paper presents the results obtained from a series of experiments that have been conducted on a 150kW pf burner rig based at Casella CRE Ltd. in the United Kingdom. These experiments systematically varied the burner swirl number and the secondary air flow rate over a significant range for two different coals so that both satisfactory and ‘poor’ combustion conditions were obtained. The infra-red emissions from the flame and the combustion noise generated in the furnace chamber were measured with appropriate sensors as were the fuel and air flow rates and pollutant emissions. The signals from the sensors were analysed using signal processing techniques to yield a number of features. These in turn were employed to train a neural network to accurately estimate the gaseous emissions from the rig, such as NOx and CO. In a separate set of experiments, where the combustion process was placed in a poor condition, the sensors were coupled with the neural models and incorporated into an intelligent control system, which was able to alter the excess air level to improve the process. In this fashion simultaneous low Nox and CO levels were achieved with both coal types. This method thus uses a combination of relatively low cost sensors and artificial intelligence techniques to control the combustion of the pulverised fuel burner. It is envisaged as particularly attractive for multiple burner installations that are fed from a common manifold, where individual burner performance is not known.
Optimal Placement of Piezoelectric Sensors and Actuators for Controlled Flexible Linkage Mechanisms
Authors: Zhang Xianmin , Erdman Arthur G.
Published: May 2008

The optimal placement of sensors and actuators in the active vibration control of flexible linkage mechanisms is studied. Based on the concept of the controllability and the observability of the controlled subsystem and the residual subsystem, the objective functions are proposed aiming at the maximization of the controllability and the observability of the controlled modes and minimization of those of the residual modes. The optimal model is solved using the modified constrained variable metric method. Numerical example shows the validness of the proposed modeling.
Experimental and Numerical Film Effectiveness Downstream a Row of Compound Angle Film Holes
Authors: Khanicheh A. , Taslim M. E.
Published: May 2008

High component lifetimes of modern gas turbines can be achieved by cooling the airfoils effectively. Film cooling is commonly employed on the airfoils and other engine hot section surfaces in order to protect them from the high thermal stress fields created by exposure to combustion gases. Complex geometries as well as optimized cooling considerations often dictate the use of compound-angled film cooling hole. In the present experimental and computational study, the effects that two different compound angle film cooling hole injection configurations have on film cooling effectiveness are investigated. Film cooling effectiveness measurements have been made downstream of a single row of compound angle cylindrical holes with a diameter of 7.5 mm, and a single row of compound angle, diffuser-shaped holes with an inlet diameter of 7.5 mm. The cylindrical holes were inclined (α=25°) with respect to the coverage surface and were oriented perpendicular to the high-temperature airflow direction. The diffuser-shaped holes had a compound angle of 45 degrees with respect to the high temperature air flow direction and, similar to the cylindrical film holes, a 25-deg angle with the coverage surface. Both geometries were tested over a blowing ratio range of 0.7 to 4.0. Surface temperatures were measured along four longitudinal rows of thermocouples covering the downstream area between two adjacent holes. The results showed that the best overall protection over the widest range of blowing ratios was provided by the diffuser-shaped film cooling holes. Compared with the cylindrical hole results, the diffuser-shaped expansion holes produced higher film cooling effectiveness downstream of the film cooling holes, particularly at high blowing ratios. The increased cross sectional area at the shaped hole exit compared to that of the cylindrical hole lead to a reduction of the mean velocity, thus the reduction of the momentum flux of the jet exiting the hole. Therefore, the penetration of the jet into the main flow was reduced, resulting in an increased cooling effectiveness. A commercially available CFD software package was used to study film cooling effectiveness downstream of the row of holes. Comparisons between the experimentally measured and numerically calculated film effectiveness distributions showed that the computed results are in reasonable agreement with the measured results. Therefore, CFD can be considered as a viable tool to predict the cooling performance of different film cooling configurations in a parametric study. A more realistic turbulence model, possibly adopting a two-layer model that incorporates boundary layer anisotropy, in the computational study may improve the predicted results.
Finite Element Analysis of the Covered Microstent
Authors: Gu Linxia , Kumar Ashok V. , Santra Swadeshmukul , Mericle Robert A.
Published: May 2008

Traditional minimally-invasive endovascular procedures like coiling are inadequate for the effective treatment of may wide-necked, fusiform aneurysms and arteriovenous fistulae (AVF) in the brain. An endovascular approach of placing a covered microstent across the intracranial aneurysm neck and AVE rent is promising. Unlike bare stents (stent without cover), covered microstents will have the capability of completely preventing blood flow into the aneurysm cavity of AVF rent. The strategy will restore normal vessel morphology and blood flow.
Multidimensional Hidden Slow Variable Tracking in a Hierarchical Dynamical System
Authors: Chelidze David
Published: May 2008

In this paper, we present a novel method for multidimensional damage identification based on a dynamical systems approach to damage evolution. This approach does not depend on the knowledge of particular damage physics, and is appropriate for systems where damage evolves on much slower time scale then the directly observable dynamics. In an experimental context, the phase space reconstruction and locally linear models are used to quantify small distortions occurring in a dynamical system’s phase space due to damage accumulation. These measurements are then related to the drifts in damage variables. A mathematical model of a harmonically driven cantilever beam in a force field of two battery-powered electromagnets is used to demonstrate validity of the method. It is explicitly demonstrated that an affine projection of the described damage metric accurately tracks the two competing damage processes. For practical damage identification purposes, the tracking data is analyzed using the proper orthogonal decomposition (POD) and optimal tracking (OT) methods. Both methods correctly identify the two dominant damage modes. However, the OT is more impervious to changes in fast-time dynamics and provides a significantly better signal-to-noise ratio. The OT-based damage observer is demonstrated to be within a linear transformation from the actual damage states.
Characterization of the Thermodynamic Working Cycle in a MEMS-Based Micro Heat Engine
Authors: Whalen S. A. , Weiss L. W. , Richards C. D. , Bahr D. F. , Richards R. F.
Published: May 2008

This work examines the conversion of thermal to mechanical energy in a micro heat engine by characterizing the heat engine’s working cycle. Results are given for dynamic measurements of pressure, volume, and temperature throughout the working cycle of the engine. Engine pressure is determined from the deformation of the two membranes in contact with the working fluid. A Michelson interferometer is used to measure the center deflection and displacement profile of both of these membranes. Pressure is determined from the membrane deflection using experimental static pressure-deflection curves. Engine temperature is measured using electrical resistance thermometry, via a micro resistance thermometer fabricated on the surface of a silicon membrane exposed to the working fluid in the engine cavity.
Design and Fabrication of High Frequency Coaxial Transmission Line
Authors: Richter Matt , Taylor Don J.
Published: May 2008

This paper discusses design considerations and fabrication challenges involved in the production of a coaxial transmission line that can transmit signals without secondary moding above 110 GHz. Specific areas highlighted include the transition into the dielectric support, the impact of tolerances on performance, and nontraditional machining techniques used in component fabrication. Full wave FEA simulations are used to explore the effect of tolerances on performance, as well as to investigate the performance of various designs for the transition to the insulating support. Additionally, the results of a cylindrical EDM turning process that is used to create a stepped center conductor with a diameter that is less than 100 microns are presented. The goal of this paper is to give insight into what the mechanical demands will be as electronics move to higher and higher frequencies.
Application of Multivariable Adaptive Control to Automotive Air Conditioning Systems
Authors: Shah Rajat , Alleyne Andrew G. , Rasmussen Bryan P.
Published: May 2008

This paper presents the application of a multivariable adaptive control strategy to a typical automotive air conditioning system. First, an experimentally validated physical model for the air conditioning cycle is introduced. This is followed by the application of a multi-input multioutput (MIMO) parameter estimation algorithm to recursively identify an equivalent discrete time state space model of the system. A Linear Quadratic Regulator (LQR) design is implemented on the estimated model with the objectives of reference tracking and disturbance rejection. Simulation studies are performed to explore the idea of modulating the electronic expansion valve opening and air flow rate over the evaporator for controlling the efficiency and capacity of a general automotive air conditioning unit. The results demonstrate the efficacy of the MIMO controller for these objectives.
Control of Oscillations in Electrically Driven Skid Steer Vehicles
Authors: Andersen Torben Ole , Hansen Michael Rygaard , Pedersen Henrik Clemmensen
Published: May 2008

This paper is concerned with the stabilization of skid steer wheeled vehicles. This type of vehicle is often characterized by a short wheelbase and without any suspension other than that of the wheels, and is therefore liable to rotational pitch oscillations. The objective of this paper is twofold. Firstly, the abovementioned oscillation phenomena are examined with a view to improve the understanding of its dependency on weight distribution, and traction characteristics of tire-surface contact. Secondly, a number of control strategies that dampens the oscillatory nature of the vehicle are derived and evaluated. The basic idea of the control strategy is to keep the angular pitch velocity at zero by increasing the motor torque when the vehicle is tilting forward and decreasing the motor torque when the vehicle is tilting backwards. The basic control design objective being to achieve the lowest possible mean square tracking error without letting the mean square input exceed its maximally permissible value. The results are experimentally evaluated by means of a small-scale vehicle.
Design and Microfabrication of Terahertz Magnetic Metamaterials
Authors: Yen Ta-Jen , Fang Nicholas , Zhang Xiang
Published: May 2008

In this work, we introduce the simulation design and microfabrication of a class of magnetic metamaterials with critical dimension of 2–6 microns and lattice constant of 30–50 microns. These metamaterials will exhibit magnetic response at 0.5–2THz. To optimize the design variables, we conducted a series of Taguchi experiments and a quasi-linear relationship of resonant frequency is established upon each design parameter. We are currently characterizing the first generation of the fabricated magnetic metamaterials using Fourier Transformed Infrared spectroscopy.
Modeling and Characterization of Micromachined Bi-Directional Electro-Thermal Vibromotors
Authors: Shih Wen-Pin , Pai Minfan , Lin Yu-Yun , Hui Chung-Yuen , Tien Norman C.
Published: May 2008

The motion of a micromachined bi-directional electrothermal vibromotor (BETV) is analyzed using an impact model which takes into account of friction and contact, as well as the compliance of the slider and the impact head. This model is shown to address several important issues on the reliable usage of BETV. These include (a) how to achieve the push or pull mode (b) avoiding multiple impacts in one actuation cycle (c) the existence of periodic solution with the same period as the thermal actuator. To test our theory, we fabricated and conducted experiments on several BETV with different geometries. Preliminary results showed good agreement between theory and experiments.