bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of Inclined Fin-Tube Heat Exchanger for Compact Air Conditioner
Authors: Kanematsu Haruaki , Murakami Kazuhiko
Published: May 2008

For saving space at an office or a clean room, it is needed to reduce the space of an air conditioner. It is effective to miniaturize a heat exchanger because it occupies the large space in the air conditioner. Three types of a heat exchanger that are an in-line tube and cut fins type, a staggered tube and cut fins type and a staggered tube and uncut fins type were investigated as four inclined angle tests of 0, 45, 60 and 80 degrees in a heat wind tunnel. The coefficients of flow friction and heat transfer rates were obtained from these experiments, and the characteristics of inclined heat exchanger were clarified by effects of tube arrangements, fin types and inclined angles against flow direction. As a numerical approach, two-dimensional steady models were applied on the staggered tube and the in-line tube by using BFC (Boundary-Fitted Coordinate Method); BFC is available to make grids for any install angle of the heat exchanger. The results of the numerical analysis visualized flow patterns and heat transfer in these heat exchangers. In case of 80-degrees angle, the flow makes dead area in a part of the heat exchanger, and it causes reducing performance of the heat exchanger. These results are available for improve a compact high performance heat exchanger.
Heat Transfer in Wavy Duct With Different Corrugation Angle
Authors: Hwang Sang Dong , Kim Han Ho , Cho Hyung Hee , Chen Seung Bae
Published: May 2008

The present study investigates the effects of duct corrugation angle and flow velocity on the convective heat/mass transfer characteristics in wavy ducts applied in a primary surface heat exchanger. Local heat/mass transfer coefficients on the corrugated duct sidewall are determined using a naphthalene sublimation technique. The flow visualization technique is used to understand the overall flow structures inside the duct. The corrugation angles of the wavy ducts are 145° and 130°, and the duct aspect ratio is fixed at 7.3. The Reynolds numbers, based on the duct hydraulic diameter, vary from 1,000 to 5,000. The results show that secondary vortex flow cells, called Taylor-Go¨rtler vortices, exist periodically in the wavy duct. Therefore, non-uniform distributions of the heat/mass transfer coefficients are obtained on the duct walls. On the pressure-side wall, high heat/mass transfer cell-shaped regions appear due to the secondary vortex flows for both corrugation angles. On the suction-side wall, the heat transfer coefficients are lower than those on the pressure-side wall. The wavy duct with the corrugation angle of 130° has the stronger strength of the secondary vortex cells resulting in higher heat/mass transfer rates on the duct wall because the sharp turn enhances the development of the secondary flow cells.
Power Oriented Modeling of a Common Rail Injector
Authors: Morselli Riccardo , Corti Enrico , Rizzoni Giorgio
Published: May 2008

The common rail injection system has allowed torque and power performance of diesel engines to improve greatly, while reducing fuel consumption and conforming to emissions standards. This paper proposes a simple but effective energy-based model of a common rail injector as a basis for the implementation of the advanced fuel injection control strategies. The proposed model has been validated comparing the simulation results with real experimental data. The obtained results show how the dynamic behavior of the injector is well captured by the model.
Hybrid Modeling and Control of a Direct Injection Stratified Charge Engine
Authors: Bemporad Alberto , Giorgetti Nicolo` , Kolmanovsky Ilya , Hrovat Davor
Published: May 2008

This paper illustrates the application of hybrid modeling and optimal control to the problem of air-to-fuel ratio and torque control in advanced technology gasoline direct injection stratified charge (DISC) engines. DISC engines have two discrete modes of operation, stratified and homogeneous, and their dynamic behavior can be easily captured by a hybrid model. We show that the design flow (hybrid modeling and controller synthesis) is simple in terms of problem setup and tuning, provides good closed-loop performance, and leads to a control law that can be implemented on automotive hardware as a piecewise affine function of the measured and estimated quantities.
Predictive Modeling for Rollover Warning of Heavy Vehicles
Authors: Hyun Dongyoon , Langari Reza
Published: May 2008

A predictive model to determine the rollover threat of heavy vehicles is proposed. The purpose of this model is to predict the rollover threat sufficiently in advance of the actual event so as to enable the driver to react accordingly. The Load Transfer Ratio (LTR) is used as a rollover threat index in this model. In order to facilitate a practical implementation of the proposed approach, a predictive model is established using a simple roll-plane model of the vehicle in conjunction with an online parameter identification strategy. This is to address the inherent issues involved in assessing certain key parameters in the proposed predictive model. The proposed predictive model and the associated parameter-identification algorithm are verified using a 14 degrees-of-freedom vehicle simulation model previously developed as a part of a broader study on heavy vehicles undertaken at Texas A&M University and supported by Texas Transportation Institute (TTI).
A Panoramic View of Fault Management for Longitudinal Control of Automated Vehicle Platooning
Authors: Lu Xiao-Yun , Hedrick J. Karl
Published: May 2008

This paper proposes some principles for fault management of longitudinal control of automated vehicles in AHS. Systems faults may be broadly divided into software and hardware. Software fault management is briefly addressed. These faults can be avoided by proper controller design, rigorous algorithm development, correct and robust code construction, simulation and real-time run test. Emphases are put on hardware faults. Hardware faults which may appear in practice are classified according to their likelihood of appearance, impact on safety, robust stability within controller bandwidth and maneuverability. The most prominent cases are those when communication and/or radar are in fault. From control viewpoint, they have very strong impact on string stability. The main difficulties in these cases are: (a) Some or all of the three parameters: relative distance, speed and acceleration, are not directly available; (b) Measurements of these parameters contains some noise; (c) Filtering and estimation of these parameters lead to some time delay and discrepancy. General principle of control strategy for each fault case is proposed. Corresponding string stability of the platoon is briefly analyzed. Consideration in this paper is in higher level. To practically implement each of these strategies will be addressed in future works.
Effect of Jet-to-Jet Spacing in Impingement Arrays on Heat Transfer
Authors: Ekkad Srinath V. , Gao Lujia , Hebert Ryan T.
Published: May 2008

Detailed heat transfer measurements are presented for jet impingement through arrays of jet holes. The effect of jet-to-wall spacing, hole-to-hole spacing are studied for inline arrays of holes. The axial and spanwise spacing (S/D) of holes are varied to produce square and rectangular arrays of holes. The results are presented at a jet average Reynolds numbers of 5000, 10000, and 15000. The jet-to-wall spacing is varied from 1 to 5. The arrays of 25 holes are placed to create four different configurations. The first configuration has an axial jet-to-jet spacing (SX/D) of 4 and a jet-to-jet spanwise spacing (SY/D) of 4, the second configuration has a SX/D of 8 and SY/D of 4, and the last configuration has a SX/D and SY/D of 8. Detailed heat transfer measurements are obtained using the transient liquid crystal technique. Results show that increase in jet-to-wall spacing reduces cross-flow effect. Results also show that the increase spacing between jets increases lateral spreading.
Heat Transfer Coefficient on the Squealer Tip and Near Squealer Tip Regions of a Gas Turbine Blade
Authors: Kwak Jae Su , Han Je-Chin
Published: May 2008

Detailed heat transfer coefficient distributions on a squealer tip of a gas turbine blade were measured using a hue detection based transient liquid crystals technique. The heat transfer coefficients on the shroud and near tip region of the pressure and suction sides of a blade were also measured. Tests were performed on a five-bladed linear cascade with blow down facility. The blade was a 2-dimensional model of a first stage gas turbine rotor blade with a profile of a GE-E3 aircraft gas turbine engine rotor blade. The Reynolds number based on the cascade exit velocity and axial chord length of a blade was 1.1×106 and the total turning angle of the blade was 97.7°. The overall pressure ratio was 1.23 and the inlet and exit Mach number were 0.25 and 0.59, respectively. The turbulence intensity level at the cascade inlet was 9.7%. The heat transfer measurements were taken at the three different tip gap clearances of 1.0%, 1.5% and 2.5% of blade span. Results showed that the overall heat transfer coefficient on the squealer tip was higher than that on the shroud and the near tip region of the pressure and suction side. Results also showed that the heat transfer coefficients on the squealer tip and its shroud were lower than that on the plane tip and shroud, but the heat transfer coefficients on the near tip region of suction and pressure sides were higher for the squealer tip case.
Nanoscale Energy Transport in Information Technology Research With an Application to High-Density Data Storage Devices and Systems
Authors: Asheghi Mehdi , Yang Yizhang , Sadeghipour Sadegh M. , Bain James A. , Barmak Katayun , Jhon Myung S. , Gellman Andrew J. , Schlesinger Ed , Zhu Jian-Gang , White Robert M.
Published: May 2008

By all measures, the data storage industry is one of the most important components of the Information Technology (IT) revolution. In recent years, many of the emerging technologies rely heavily on energy transport at extremely short time and length scales as a mean to overcome the superparamagnetic limit - a serious impediment to future advancement of storage technology. Additionally, thermally induced failure and reliability issues at the nanoscale are becoming increasingly important due to rapid device miniaturization in data storage applications. Further advances in high-technology data storage systems will be difficult, if not impossible, without rigorous treatment of nanoscale energy transport. This manuscript reviews the thermal design issues and challenges in thermally assisted magnetic disk recording, thermally assisted scanned probe recording, phase change optical data recording, magnetoresistive random access memory (MRAM) and giant magnetoresistive (GMR) heads. Relevant thermally induced failures in GMR heads, write coil, interconnects and MRAM will be discussed as well.
Marangoni and Variable Viscosity Phenomena in Picoliter Size Solder Droplet Deposition
Authors: Dietzel M. , Haferl S. , Ventikos Y. , Poulikakos D.
Published: May 2008

This numerical investigation studied the effects which the temperature dependence of surface tension (Marangoni phenomenon) and viscosity has on the spreading, the transient behavior and final post-solidification shape of a molten Sn63Pb solder droplet deposited on a flat substrate. A Lagrangian finite element formulation of the complete axisymmetric Navier-Stokes equations was utilized for the description of the droplet behavior. Linear temperature dependence for the surface tension and an exponential dependence for the viscosity were assumed. The initial droplet temperature was varied in 50K steps from 200°C to 500°C, whereas the substrate temperature was kept constant at 25°C. This varied the initial Reynolds number Re0 from 360 to 716 and the Marangoni number Ma from −9 to −49. The initial Weber number We0 and initial Prandtl number Pr0 were for all cases O(1) and O(10−2), respectively. The impact velocity and the droplet diameter remained unchanged in all cases examined at 1.5 m/s and 80 microns. A major finding of the work was that, contrary to intuition, the Marangoni effect decreased droplet spreading monotonically. Due to the Marangoni effect, surface tension forces instead of freezing arrested spreading. Droplet receding during recoiling was aided by the Marangoni effect. On the other hand, the change of viscosity with temperature showed no significant influence on the outcome of the droplet impact.
Nanoscale Quantitative Thermal Imaging of Electronic Devices
Authors: Zhou Jianhua , Yu Choongho , Hao Qing , Kim Dohyung , Shi Li
Published: May 2008

This paper investigates a new method for quantitative nanoscale thermal imaging of electronic devices. Different from previous works that utilized a thermal sensor fabricated on a scanning probe to obtain surface thermal images, the current approach employs a tunneling thermocouple made of a metal tip and an ultra-thin metal film deposited on the sample surface. The metal tip has a negligible Seebeck coefficient; while the metal film can be Bi2Te3 or a semiconducting polymer that has very high Seebeck coefficient and low thermal conductivity. Unlike the probe with a built-in thermal sensor, the measured thermoelectric voltage by the tunneling thermocouple is not affected by the tip-sample contact thermal resistance and air conduction, allowing quantitative temperature measurement with a spatial resolution limited by the metal film thickness, which can be 10–20 nm. We have tested the new approach using Ir or Pt-Ir -coated atomic force microscope (AFM) tips to obtain the surface temperature profiles of interconnect structures coated with a thin Cr film. The measured surface temperature gradient is larger and the maximum measured temperature is 60% higher than the corresponding values obtained by a thermal probe with a built-in thermocouple fabricated at the tip end. The two thermal imaging methods are currently being used to measure temperature distribution on the cross section of a 130 nm-technology silicon-on-insulator field-effect transistor.
Simulation of Single-Event Failure in Power Diodes
Authors: Walker D. G. , Fisher T. S. , Al-badri A. M. , Schrimpf R. D.
Published: May 2008

Single-event burnout (SEB) is a catastrophic failure mechanism in power diodes that is initiated by the passage of a heavy ion through a diode in a current-blocking state. In this work, the physical mechanism responsible for device failure during SEB is investigated using transient, coupled electro-thermal, device simulations. For the first time, the effects of a thermal feedback mechanism have been examined and deemed crucial to predicting possible failure in power diodes. Results indicate that device failure is predicted for large blocking voltage near breakdown with a linear energy transfer (LET) of 30MeV/mg/cm2 only when thermal effects are included. However, without inclusion of the thermal model, no device failure is predicted. These results correspond to experimental observations better than any previous work.
Rheological Study of Micro Particle Laden Polymeric Thermal Interface Materials: Part 2 — Modeling
Authors: Prasher Ravi S. , Shipley Jim , Prstic Suzana , Koning Paul , Wang Jin-Lin
Published: May 2008

Currently there are no models to predict the thickness or the bondline thickness (BLT) of particle laden polymeric thermal interface materials (TIM) for parameters such as particle volume fraction and pressure. TIMs are used to reduce the thermal resistance. Typically this is achieved by increasing the thermal conductivity of these TIMs by increasing the particle volume fraction, however increasing the particle volume fraction also increases the BLT. Therefore, increasing the particle volume fraction may lead to an increase in the thermal resistance after certain volume fraction. This paper introduces a model for the prediction of the BLT of these particle laden TIMs. Currently thermal conductivity is the only metric for differentiating one TIM formulation from another. The model developed in this paper introduces another metric: the yield stress of these TIMs. Thermal conductivity and the yield stress together constitute the complete set of material parameters needed to define the thermal performance of particle laden TIMs.
Application of the Lattice-Boltzmann Method to Sub-Continuum Heat Conduction
Authors: Zhang Wei , Fisher T. S.
Published: May 2008

The Lattice Boltzmann Method (LBM) is introduced in this paper as a method to simulate heat conduction across broad length scales in which continuum and sub-continuum effects exist. The paper describes the implementation of the method in both one and two dimensions. Results are presented for cases involving problems with existing solutions and show close agreement with both continuum and subcontinuum solutions of one-dimensional heat transfer through thin films. Results for a two-dimensional continuum problem agree with a known solution to within one percent. These results, combined with relative small computational effort, indicate that the LBM is a useful analysis tool for simulation of multiscale heat conduction.
An Improved Computational Procedure for Sub-Micron Heat Conduction
Authors: Murthy J. Y. , Mathur S. R.
Published: May 2008

Popular numerical techniques for solving the Boltzmann transport equation (BTE) for sub-micron thermal conduction include the discrete ordinates method and the finite volume method. However, the finite wave speed associated with the BTE can cause large errors in the prediction of the equivalent temperature unless fine angular discretizations are used, particularly at low acoustic thicknesses. In this paper, we combine a ray-tracing technique with the finite volume method to substantially improve the predictive accuracy of the finite volume method. The phonon intensity is decomposed into ballistic and in-scattering components. The former is solved using a ray tracing scheme, accounting for finite wave speed; the latter is solved using an unstructured finite volume method. Comparisons between this new technique and traditional finite volume formulations are presented for a range of acoustic thicknesses, and substantial improvement is demonstrated.
Electron Transport and Anode Heating Due to Field Emission From Carbon Nanotubes
Authors: Walker D. G. , Fisher T. S.
Published: May 2008

Carbon nanotubes (CNT) are being considered for field emission applications because of their low turn-on voltage and ability to support large current densities. The localization of emission and large currents from CNTs result in significant anode heating. The present work investigates the electron energy distribution at the anode surface through simulation of the field emission process and the trajectory of electrons across the vacuum gap. Field emission is modeled by Fowler-Nordheim-like expressions where the emission site is assumed to be a ring with the diameter of a nanotube. The electron trajectory is determined through a Monte Carlo simulation including Coulomb interactions between electrons. Results indicate that the electron beam spreads due to Coulomb interaction, but that the initial ring is preserved. In fact, the ring diameter at the anode spreads to 3μ per 10μ of vacuum gap in a field of 10 Vμm. This estimate matches well with reported observations. Further, the spreading becomes more significant with increased fields due to the higher current density of field emitted electrons.
Dynamics of Thermal Energy Storage in Integrated Energy Systems With On-Site Power Generation
Authors: Jalalzadeh-Azar Ali A. , Anderson Ren , Slayzak Steven J. , Ryan Joseph P.
Published: May 2008

Integrated energy systems (IES) incorporating on-site power generation provide opportunities for improving reliability in energy supply, maximizing fuel efficiency, and enhancing environmental quality. To fully realize these attributes, optimum design and dynamic performance of integrated systems for a given application have to be pursued. Whether referred to as cogeneration, combined heat and power (CHP) or building cooling, heating, and power (BCHP), integrated energy systems manifest effective energy management aimed at closing spatial and temporal gaps between demand and supply of electrical and thermal energy. This is accomplished by on-site power production and utilization of the resulting thermal energy availability for thermally-driven technologies including desiccant dehumidification, absorption cooling, and space heating. The notion that the demands for thermal and electrical energy are not always congruent and in phase signifies the importance of considering thermal energy storage (TES) for integration. This paper explores the potential impact of implementing TES technology on the overall performance of integrated energy systems from the first- and second-law perspectives. In doing so, the dynamics of packed bed thermal energy storage systems for potential energy recovery from the exhaust gas of microturbines are investigated. Using a validated simulation model, the transient thermal response of these TES systems is examined via parametric analyses that allow variation in the thermal energy availability and physical characteristics of the packed beds. The parasitic electrical energy requirement associated with the pressure losses in the packed beds is included in the performance assessment. The results of this study are indicative of the promising role of TES in integrated energy systems.
Development of a Breadboard System for Process Control Design: Part I
Authors: Mountain Jeffrey R.
Published: May 2008

This paper presents initial planning for the development of a process control breadboard system. The proposed system will be composed of mechatronic, thermal/fluid, and control elements that using simple hand tools can be easily reconfigured by undergraduate students. An approach for integrating the breadboard system throughout the curriculum, enhancing the design education experience beginning with freshmen and continuing through the senior capstone experience, is proposed. This system is expected to significantly enhance the ability of students to work with a thermal/fluid-based process control system, and to provide the opportunity for design/build/test realization for a variety of completely functional systems. A sampling of configurations will be presented to demonstrate how this proposed system might be used to address an open-ended design problem with external constraints. A comparison with existing educational trainer systems commonly found at academic institutions will be presented, along with preparations for a proof-of-concept adaptation to occur during the fall semester of 2002. Support for K-12 outreach activities and EC2000 professional component program criteria will also be discussed.
A First Principle Engine Model for Up-Front Design: Further Studies on Hydrodynamic Bearing Models
Authors: Ma Zheng-Dong , Perkins N. C.
Published: May 2008

The design of a conceptually new engine system requires an engineering tool that can quickly estimate effects of the design changes on NVH and durability at the very onset of the engine design cycle. In (Ma, et al., 2000 and Ma and Perkins 2001), we presented an engine modeling template (EngTmp) to support up-front design of engine systems. The EngTmp employs a recursive formulation of multibody dynamics that leads to the minimum number of equations of motion to represent engine dynamics and vibration. The engine models generated from the EngTmp thus enjoy greater computational efficiency. The objective of this paper is to provide some further discussions on the hydrodynamic bearing models employed in the EngTmp and numerical results obtained recently for the sample engine. The attention will be focused on discussing effects of employing different hydrodynamic bearing models based on the Reynolds equation.
Experimental Investigations of the Rubber-Asphalt Sliding Pair Dynamics
Authors: Bozˇic´ Ante , Petrovic´ Ivan , Peric´ Nedjeljko , Matusˇko Jadranko
Published: May 2008

A laboratory model for experimental investigations of the rubber-asphalt sliding pair has been designed with the purpose of better understanding of dynamic behavior of the friction force in the contact patch between the car tire and the road. Its design is described and some experimental results are given. These results confirm that it is essential to use a dynamic friction model in order to describe friction force in contact between the car tire and the road. Moreover, they indicate that the existing dynamic friction models night be physically incorrect regarding the change of friction coefficient for an asperity bristle passing through the contact surface.
Analysis of Torque Converter Dynamics
Authors: Deur Josˇko , Hrovat Davor , Asgari Jahan
Published: May 2008

A good understanding of the torque converter dynamic behavior in a wide range of its operation gains the understanding of overall power train dynamic behavior, and facilitates design of different torque converter and power train control and estimation strategies. A detail analysis of the torque converter dynamics based on the linearized “static” and dynamic torque converter models is presented in the paper. The analysis results in simplified linearized torque converter models convenient for control and estimation purposes, and yields a clear insight to the torque converter capability of damping the power train vibrations.
GPS-Based Real-Time Identification of Tire-Road Friction Coefficient
Authors: Hahn J. O. , Rajamani R. , Alexander L.
Published: May 2008

Vehicle control systems such as collision avoidance, adaptive cruise control and automated lane-keeping systems as well as ABS and stability control systems can benefit significantly from being made “road-adaptive”. The estimation of tire-road friction coefficient at the wheels allows the control algorithm in such systems to adapt to external driving conditions. This paper develops a new tire-road friction coefficient estimation algorithm based on measurements related to the lateral dynamics of the vehicle. A lateral tire force model parameterized as a function of slip angle, friction coefficient, normal force and cornering stiffness is used. A real-time parameter identification algorithm that utilizes measurements from a differential GPS system and a gyroscope is used to identify the tire-road friction coefficient and cornering stiffness parameters of the tire. The advantage of the developed algorithm is that it does not require large longitudinal slip in order to provide reliable friction estimates. Simulation studies indicate that a parameter convergence rate of one second can be obtained. Experiments conducted on both dry and slippery road indicate that the algorithm can work very effectively in identifying a slippery road. Two other new approaches to real-time tire road friction identification system are also discussed in the paper.
Prediction of Oxygen Storage Capacity and Stored NOx by HEGO Sensors for Improved LNT Control Strategies
Authors: Wang Le Yi , Kim Yong-Wha , Sun Jing
Published: May 2008

In the absence of on-line emission measurements, the control of lean burn engine aftertreatment system must be implemented by using models of feedgas emissions and the aftertreatment subsystems, together with measured variables such as mass air flow rate, feedgas and tailpipe relative air-to-fuel ratios, etc. In particular, accurate estimation of stored oxygen and NOx in the LNT is of critical importance. When the ambient conditions (such as humidity, LNT brick temperature, and sulfur poisoning) change or the engine components age, oxygen storage capacity and NOx amount in the LNT vary significantly, and the performance of the control system that relies on these variables may deteriorate if the accuracy of the estimate deteriorates with the change in hardware. In this paper, we show that voltage trajectories of a tailpipe HEGO sensor can provide sufficient information to predict oxygen capacity during storage phase and stored NOx during purge phase of an lean NOx trap (LNT). This result can be used to provide accurate prediction of the termination time of purge operation, leading to improved control strategies for LNT operation. This finding also indicates that more expensive UEGO sensors can be avoided without tangible performance penalty on LNT control.
Ferrohydrodynamics in Time-Varying Magnetic Fields
Authors: Rinaldi Carlos , Lee June-Ho , Rosenthal Adam D. , Franklin Thomas , Zahn Markus
Published: May 2008

Measurements of magnetic-field-induced ferrofluid flow and torque in uniform rotating magnetic fields are presented and compared to theoretical analyses in order to understand observed paradoxical behavior. The viscous torque from this fluid flow is measured using a cylindrical Couette viscometer, as a function of magnetic field amplitude, frequency, and direction of rotation. The first set of experiments measures the torque on the outer wall of a polycarbonate spindle that is attached to a viscometer, which functions as a torque meter. The spindle is immersed in the ferrofluid, which is centered in the gap of a three-phase AC 2-pole motor stator winding. Anomalous behavior, such as negative effective viscosity, is demonstrated and discussed. The second set of experiments measures the viscous torque on the inner wall of a hollow spindle attached to the torque meter and filled completely with ferrofluid so that there is no free surface. These measurements show that magnetic fluid effects arise even in the absence of free surfaces. These observations are then shown to agree with a recently derived analysis of spin-up flow in ferrofluids.
Stability of Mushy State in Magnetic Field During Electrical Conductivity Measurements Using Rotational Technique
Authors: Bakhtiyarov Sayavur I. , Overfelt Ruel A.
Published: May 2008

The preliminary results of the mathematical modeling of the stability of a mushy state in magnetic field are presented. The problem is applied to the electrical conductivity measurements on liquid metals using rotational technique.
A Discussion of Nano-Length Scale Heat Conduction by Comparing the Ballistic-Diffusive Equation and Molecular Dynamics Simulation
Authors: Akbari Pezhman , Chui Boon-Keat , Oravecz-Simpkins Lisa , Lloyd John R.
Published: May 2008

A discussion of two methods, the Ballistic-Diffusive, Chen [1,2], and Molecular Dynamics simulation, for solving heat conduction in the nano-length regime is presented. Using data from Chen [1,2], a solution to the Ballistic Diffusive equation is rescaled and compared with the Fourier solution. Results imply that care must be taken when rescaling and comparing equations used in the different length scale regimes because physical definitions (i.e. temperature) are not identical in the two regions (nano and macro length). Analysis of the molecular dynamics simulation shows its inadequacy to describe conductive heat transfer in the nanoscale. Based on the discussion, a modified energy transport map is devised.
Vibration of Elevator Cables With Small Bending Stiffness
Authors: Zhu W. D. , Xu G. Y.
Published: May 2008

The effects of bending stiffness and boundary conditions on the lateral vibration of the stationary and moving hoist cables are investigated. The role of the trial functions in the approximate methods is examined. The optimal stiffness and damping coefficient of the suspension of the car against its guide rails are identified for the moving cable.
Spatial Discretization of Serpentine Belt Drive Dynamics Using Constrained Basis Functions
Authors: Parker Robert G. , Shah Shrenik , Kong Lingyuan
Published: May 2008

An efficient method for calculating the eigensolutions and dynamic response of a serpentine belt drive is presented. The model is a hybrid discrete-continuous one where the motions consist of rotations of the pulleys, rotation of the tensioner arm, and transverse vibrations of the continuum belt spans adjacent to the tensioner. The speed of solution results from discretization of the belt spans where the unusual feature is the use of Lagrange multipliers to enforce the geometric boundary conditions at the belt-tensioner interface. The method reduces the computational effort by several orders of magnitude compared to published methods using the same model. Also, it is not susceptible to numerical problems that binder the published methods. The sensitivities of the belt drive natural frequencies to system parameters are also studied. The model parameters under consideration include belt longitudinal stiffness, tensioner spring stiffiness, span tensions, belt transport speed, belt density, and pulley moments of inertia. Exact solutions for the eigensensitivities to these parameters are obtained using perturbation methods. The exact formulae are reduced to simple expressions related to the modal strain and kinetic energies. The eigensensitivities are readily determined, quantitatively and qualitatively, by inspection of the modal energy distributions. An example is presented to demonstrate the capabilities of the methods.
Axial and Torsional Dynamic Responses of Tubular Joints With an Annular Void
Authors: Vaziri A. , Nayeb-Hashemi H.
Published: May 2008

Dynamic responses of adhesively bonded tubular joints subjected to a harmonic axial and torsional load are investigated. Adherents are assumed elastic and the adhesive is taken to be a linear viscoelastic material. The effects of adherents and adhesive properties on the joint response as well as on the shear stress amplitude distribution along the overlap are investigated for each case of harmonic loading. Furthermore, the effects of defects such as an annular void in the bond area on the axial and torsional dynamic responses and shear stress amplitude distributions in the bond area are studied. The results indicate that for tubular joint geometries and properties investigated the axial and torsional resonant frequencies of the joint are little affected with the adhesive loss factor. These resonant frequencies initially increase rapidly with increasing adhesive shear modulus. However, the resonant frequencies asymptotically approach a constant value with further increase in adhesive shear modulus. The results further show that the resonant frequencies of the joint may not get affected with the presence of a central void in the bond area. The distribution of shear stress amplitude in the joint area is obtained. The maximum shear stress is confined to the edge of the overlap for all applied loading frequencies. For the adhesive and adherents’ properties and geometries investigated, the maximum shear stress amplitude in the joint area is little affected by the presence of a central annular void covering up to 40% of the overlap length. However, a central void larger than 40% of the overlap length may be detrimental or beneficial to the joint strength. This depends on the applied loading frequency. A central void reduces the system axial and torsional resonant frequencies. This may depart the system further away from the applied loading frequency or may bring it closer. A system excited closer or further from to its resonant frequency will develop higher or lower shear stress amplitude in the bond area.
A Method for Updating Damping of Analytical Model of Substructure Based on Frequency Response
Authors: Yu B. S. , Zheng G. T. , Du H. J.
Published: May 2008

The identification of model damping is a key for response analysis. A method is presented for updating damping of the computational model of substructure based on frequency response experiment. The proposed method directly identifies mass, stiffness and damping matrices by using the substructure error coefficient and frequency response experiment, then computational model damping is updated, finally the effectiveness of the method with simulated data gauging is studied in this paper.
Nonlinear Delay Equations With Fluctuating Delay: Application to Regenerative Chatter
Authors: Demir Ali , Sri Namachchivaya N. , Langford W. F.
Published: May 2008

The mathematical models representing machine tool chatter dynamics have been cast as differential equations with delay. The suppression of regenerative chatter by spindle speed variation is attracting increasing attention. In this paper, we study nonlinear delay differential equations with periodic delays which models the machine tool chatter with continuously modulated spindle speed. The explicit time-dependent delay terms, due to spindle speed modulation, are replaced by state dependent delay terms by augmenting the original equations. The augmented system of equations is autonomous and has two pairs of pure imaginary eigenvalues without resonance. We make use of Lyapunov-Schmidt Reduction method to determine the periodic solutions and analyze the tool motion. Analytical results show both modest increase of stability and existence of periodic solutions close to the new stability boundary.
A General Formula for Controlling Hopf Bifurcation
Authors: Yu Pei
Published: May 2008

An explicit general formula is proposed for controlling Hopf bifurcation using state feedback. This method can be used to either delay (or even eliminate) an existing Hopf bifurcation or change a subcritical Hopf bifurcation to supercritical. The Lorenz system is used to illustrate the application of the formula.
Identifying Coulomb and Viscous Friction in Forced Oscillators by Using a Harmonic Energy Balance
Authors: Liang Jin-Wei , Feeny Brian F.
Published: May 2008

This study makes use of energy dissipation to identify damping from mechanical vibration systems. Both the viscous damping and dry friction are assumed to coexist in vibration systems. By balancing the energy loss as registered in the force-displacement relationship of the real system against that of a theoretical model, consisting of viscous damping and dry friction components, the identification algorithms are developed and the equivalent viscous-damping and dry-friction parameters are estimated. We apply the estimation equations to both numerical and experimental systems to show the effectiveness and reliability of the new identification method.
Nonlinear Effects on Coexistence Phenomenon in Parametric Excitation
Authors: Ng Leslie , Rand Richard
Published: May 2008

We investigate the effect of nonlinearites on a parametrically excited ordinary differential equation whose linearization exhibits the phenomena of coexistence. The differential equation studied governs the stability mode of vibration in an unforced conservative two degree of freedom system used to model the free vibrations of a thin elastica. Using perturbation methods, we show that at parameter values corresponding to coexistence, nonlinear terms can cause the origin to become nonlinearly unstable, even though linear stability analysis predicts the origin to be stable. We also investigate the bifurcations associated with this instability.
Control of Flexible Payloads Grasped by Actuated Grippers Undergoing Large Rigid-Body Motions: Part I — Dynamics
Authors: Park Edward J. , Mills James K.
Published: May 2008

This paper is Part I of a preliminary study to simultaneously control vibration and static shape deformation in flexible payloads. In Part I, the dynamics of a flexible payload grasped by an actuated gripper, which is attached to a rigid link robotic manipulator, is investigated using the component mode synthesis (CMS) method. Robot and actuator dynamics are also added to the system dynamic model to fully define the rigid body motion and elastic motion of the flexible payload. The CMS method is employed to explicitly model the coupling between the payload and actuators, and to reduce the system order. With the addition of fixed-interface quasi-static modes to fixed-interface vibration normal modes and actuator constraint modes an improved component mode representation is defined. Here, it is found that the inclusion of quasi-static modes in the CMS formulation results in increased ac curacy for simulation of dynamic behaviour of flexible payloads subject to both gravity and robot motion induced forces. Numerical examples are presented to demonstrate the effectiveness of the new component mode representation for the given robotics problem. In Part II [9], the two-time scale modeling (TSM) technique is used taking advantage of two-time scale behavior between the quasi-static modes and vibration modes in the dynamic model.
An Effective Algorithm for Tracking Multiple Maneuvering Targets
Authors: Li Jianxun , Jing Zhongliang , Li Feng
Published: May 2008

Multiple maneuvering target tracking in a dense clutter environment is investigated. An effective parallel processing algorithm based on state fusion and fast joint probabilistic data association (FJPDA) is proposed. State fusion and feedback of all state information are used to fit different movements of targets. The FJPDA combining cluster matrix decomposition with fast data association algorithm is built for tracking multiple targets. Two examples are simulated to prove the validity and reliability of the proposed new algorithm.
Bifurcations in a Mathieu Equation With Cubic Nonlinearities: Part II
Authors: Ng Leslie , Rand Richard
Published: May 2008

In a previous paper [6], the authors investigated the dynamics of the equation: d2xdt2+(δ+εcost)x+εAx3+Bx2dxdt+Cxdxdt2+Ddxdt3=0. We used the method of averaging in the neighborhood of the 2:1 resonance in the limit of small forcing and small nonlinearity. We found that a degenerate bifurcation point occurs in the resulting slow flow and some of the bifurcations near this point were looked at. In this work we present additional results concerning the bifurcations around this point using analytic techniques and AUTO. An analytic approximation for a heteroclinic bifurcation curve is obtained. Additional results on the bifurcations of periodic orbits in the slow flow are also presented.
Adaptive Beamforming Based on Instrumental Variable in Colored Noise
Authors: Li Jianxun , Jing Zhongliang
Published: May 2008

A method for adaptive beamforming based on model transformation is presented to overcome beam distortion with colored noise in this paper. The colored noise field is changed into the white one through the instrumental variable, further, the conventional method can be used. The proposed method is feasible for adaptive beamforming in colored noise, and numerical simulations are carried out.
Nonlinear Analysis of the Orbital Motions of Immersed Rotors Using a Spectral/Galerkin Approach
Authors: Moreira Miguel , Antunes Jose´ , Pina Heitor
Published: May 2008

We recently developed a symbolic-numerical formulation for the nonlinear planar motion of rotors under fluid confinement, based on a spectral/Galerkin approach, for gap geometries of about δ = H/R ≈ 0.1 — where H is the average annular gap and R is the rotor radius. Results showed a quite good agreement between the class of approximate models generated, the corresponding analytical exact planar model and experiments. This methodology can be almost entirely automated on a symbolic computing environment. In the present paper this symbolic-numerical spectral/Galerkin procedure is extended in order to deal with nonlinear orbital motions — X (t) and Y (t) taking place in orthogonal directions. Numerical simulations performed over a centered rotor configuration maintained by non-isotropic supports (Kyst/Kxst = 0.4, where kxst and kyst stand for the structural stiffnesses), which exhibit an interesting dynamics, show a quite good agreement between this type of approximate models and the corresponding analytical exact (but quite involved) model, developed in the past by the authors. With the proposed symbolic-numerical approach one can obtain accurate nonlinear dynamical formulations enabling the study, understanding and prediction of nonlinear orbital rotor-dynamics.
Simulation of the Oscillation Regimes of Bowed Bars: A Nonlinear Modal Approach
Authors: Ina´cio Octa´vio , Henrique Lui´s , Antunes Jose´
Published: May 2008

It is still a challenge to properly simulate the complex stick-slip behavior of multi-degree-of-freedom systems. In the present paper we investigate the self-excited nonlinear responses of bowed bars, using a time-domain modal approach, coupled with an explicit model for the frictional forces, which is able to emulate stick-slip behavior. This computational approach can provide very detailed simulations and is well suited to deal with systems presenting a dispersive behavior. The effects of the bar supporting fixture are included in the model, as well as a velocity-dependent friction coefficient. We present the results of numerical simulations, for representative ranges of the bowing velocity and normal force. Computations have been performed for constant-section aluminum bars, as well as for real vibraphone bars, which display a central undercutting, intended to help tuning the first modes. Our results show limiting values for the normal force FN and bowing velocity y˙bow, for which the “musical” self-sustained solutions exist. Beyond this “playability space”, double period and even chaotic regimes were found for specific ranges of the input parameters FN and y˙bow. As also displayed by bowed strings, the vibration amplitudes of bowed bars also increase with the bow velocity. However, in contrast to string instruments, bowed bars “slip” during most of the motion cycle. Another important difference is that, in bowed bars, the self-excited motions are dominated by the system first mode. Our numerical results are qualitatively supported by preliminary experimental results.
The Periodic Impact Responses of Human-Body in a Vehicle Traveling on the Rough Terrain
Authors: Yu Ke , Luo Albert C. J.
Published: May 2008

The human-body in a vehicle traveling on the rough terrain is modeled through the lumped mass approach and its periodic impact motions and stability are investigated through a linear model of vehicle and passenger systems. The linear model assumes the motion response of vehicle is very small compared to passenger’s rotational motion since the vehicle chassis has a very large mass and moment of inertia. The period-1 impact motion for two impacts respectively on two walls for a specific number of periods is predicted analytically and numerically. The stability and bifurcation of such a period-1 impact motion are developed analytically. The phase planes of the periodic impact motions are illustrated for a better understanding of the human-body impacting motion in the vehicle.
Exact Solution of Heat Conduction in a Two-Domain Parallelepiped With an Orthotropic Layer and Its Application to the Estimation of the Three-Dimensional Thermal Conductivity Tensor and Volumetric Heat Capacity of the Orthotropic Layer
Authors: Aviles-Ramos Cuauhtemoc
Published: May 2008

The three-dimensional exact solution of heat conduction in a two-layer composite is found applying the method of separation of variables. One layer is orthotropic and the other layer is isotropic. This solution is used to calculate sensitivity coefficients with respect to the thermophysical properties of the orthotropic layer at fourteen thermocouple locations. Numerical experiments are carried out to solve a parameter estimation problem that involves the estimation of the thermal conductivities in the x-, y-, and z-directions, the volumetric heat capacity of the orthotropic layer, the effective thermal conductivity of the isotropic layer, and the heat flux input. The exact solution is used to generate temperature readings at fourteen thermocouple locations. First, the parameter estimation problem is solved using the exact temperatures and a hybrid algorithm to estimate the thermal properties and the heat flux. Second, random noise is added to the exact temperatures and the thermal properties and heat flux are estimated using the same hybrid algorithm. It is found that when using the exact temperatures, the minimized quadratic functional has a value of 2.4×10−16 (°C)2 and the estimated properties agree to the ninth decimal place with the “exact” properties.