bluuebunny/crossref_metadata_2025 huggingface dataset:
Automotive Powertrain Vibrations Running on Wide Open Throttle Engine Conditions
Authors: Miyasato Hugo Heidy , Simionatto Vinícius Gabriel Segala , Dias Júnior Milton
Published: April 2014

Powertrain vibrations is a great concern in the automotive industry, once they are related to many Noise, Vibration and Harshness (NVH) phenomena. These are very complex system once their dynamic behaviour, in many cases, involve the interaction between the combustion engine and the remaing components of the powertrain, such as the clutch, transmission, differential, etc. In this work a system approach is used. First, the torque generated by a four cylinder engine is obtained through the thermodynamic equations. Then, these torque curves for each cylinder are combined and used as the excitation of a simplified model of a front wheel drive powertrain. Finally, the influence of ignition angles on the combustion characteristics and on the order content of engine output torque is analyzed. Results show that significant changes may happen on the second and fourth order responses.
Waves to Drive a Direct Rotor for Unidirectional Rotation
Authors: Yang Yingchen
Published: April 2014

Ocean waves constitute a massive source of renewable energy. However, ocean wave energy is highly underutilized. In the present work, a new approach for wave energy harvesting is discussed. A direct-drive rotor is employed as a key component of a wave energy converter (WEC). The rotor absorbs wave energy and performs unidirectional rotary motion. This approach is in contrast to the overly dominant existing technologies that utilize wave-driven oscillation (either linear or angular, e.g., heave, surge or pitch) for energy conversion. It is also different from the very few existing technologies that use direct-drive rotors to realize unidirectional rotary motion. The focus of this work is on characterization of some rotor designs using numerical tools. The tools include a wave model and a drag force model. Simple circular tubes are used as blades in a basic rotor design. This basic design demonstrates strong potential for unidirectional rotary motion at a proper rotor submersion level and under various wave conditions. Two improved designs are yielded from the basic design. In one improved design, the original circular tubes are replaced with semicircular tubes as new blades. In another design, the semicircular tubes are further modified to become one-way foldable. The two improvements significantly enhance the rotors’ unidirectional rotary motion in waves, which has been verified by numerical experiments. Broad ranges of wave parameters and the submersion level have been numerically explored on the two improved rotor designs in conjunction with dimensional analysis.
Cyber-Physical Vehicle Modeling, Design, and Development
Authors: Withrow Tom , Myers Michael R. , Bapty Ted , Neema Sandeep
Published: April 2014

Vanderbilt University introduced a new course in the 2012 Fall Semester: Cyber-physical vehicle modeling, design and development. This course focused on the design, development, fabrication, verification, and validation of a scale vehicle in the virtual and the physical domains to meet a set of realistic and challenging design requirements for the Defense Advanced Research Projects Agency’s Model-Based Amphibious Racing Challenge. The students built a series of models in software and hardware to guide the design choices for the 1/5th scale amphibious vehicle. The culmination of this course was a competition against teams from other universities in January 2013 that compared the vehicle’s actual performance with student-created simulation models. This was an elective course outside the traditional capstone design curriculum and consisted of a team of juniors and seniors across the disciplines of mechanical engineering, electrical engineering, computer engineering, computer science, and physics. The students received robust training “to be an engineer” with many activities that can’t be included in a typical classroom environment: hands-on experience designing, modeling, and building a complete vehicle; simultaneously solving several open ended, rigid deadline challenges; and navigating complex team dynamics in a full end-to-end project. Additionally, the students gained experience using modern engineering modeling tools from the Defense Advanced Research Projects Agency’s META tool suite under development for the Fast, Adaptable, Next-Generation Ground Vehicle program. The META tool suite is a set of free, open source tools for compositional design synthesis at multiple levels of abstraction, design trade space exploration, metrics assessment, and probabilistic verification of system correctness. This work details the course activities and summarizes the lessons learned from a pedagogy perspective.
Insights on Centrifugal Pendulum Vibration Absorber: Part One — Dynamic Modeling and Behaviour of Eigenvalues and Eigenvectors Along Rotating Speed
Authors: Simionatto Vinícius G. S. , Miyasato Hugo H. , Dias Júnior Milton
Published: April 2014

An automotive powertrain is a system that is designed to transmit torque from the engine to the wheels of the vehicle, allowing it to move. The working principle of most of the vehicle engines is the internal combustion, which causes the torque generated by this engine to have important oscillatory components, which cause the powertrain to vibrate and generate noise, which is undesired.

In order to control this vibration, among many engineering solutions is the centrifugal pendulum vibration absorber (CPVA), whose dynamic behaviour turns it is capable of reducing the amplitude of important order components of the powertrain. It is usually installed on the flywheel of the vehicle, although it is possible to install it in other parts, such as the clutch disk.

Although the CPVA is an important type of passive vibration absorber, it was still not found in the literature a parametrized formulation which can be applied to any vibration absorber of this kind. For this reason, the aim of this work is to propose a formulation based on dimensionless parameters, which can be applied to any CPVA. With this formulation, the dynamic behaviour of a simple 2DOF torsional system with a CPVA, spinning at constant speed, is verified.

It is important to mention that this work is the first part of a two part work. In the second part, this formulation is applied to a more complex system with a CPVA, and results are shown to be coherent with the analyses shown here.
An Automated Approach to Developing Compact and Accurate Building Models Utilising an Inverse Heat Transfer Approach
Authors: Hillary Jason , Walsh Patrick , Walsh Edmond , Shah Amip , Escobar Sergio
Published: April 2014

This paper is focused on developing numerical modeling techniques aimed at automating and simplifying the process of generating detailed models for simulating building thermal physics. However, the methodology described can be applied in numerous application areas across the thermals sector. Automated approaches to developing energy models for buildings are of particular importance to alleviate current labor intensive practices of manual generation so that large real-estate portfolios can be analyzed within a reasonable time frame, hence providing a decision making tool that can lead to smarter renovation plans for implementation across the fleet. This process is achieved by developing custom built software code in MathWorks MATLAB® with all aspects discussed herein. The starting point in this analysis is a series of individual CAD drawings for each building in the fleet with spatial coordinates for all lines and nodes loaded into matrices within MATLAB®. A constrained Delaunay triangulation technique is then applied to automatically differentiate building fabric components such as walls, columns, windows, etc., their physical scale, and all interior zones within the building. Multiple floor plans are also automatically linked by layer information, and a series of logical steps are then followed to identify zone-to-zone interactions and exterior building fabrics. A number of generic thermal resistance/capacitance models capable of modeling the anticipated thermal responses of all building elements are defined. These are assigned to the appropriate elements of the building fabric and linked based on the aforementioned zone identification process. The overall result of this process is the automated generation of a thermal energy model for any specific building that is capable of accurately modeling its thermal physics. However, property information specifically relating to on-premise building elements is not automatically discernible from these CAD-based models. In order to address this deficit, typical material properties are assumed for each element of the building fabric in the first instance, and an inverse heat transfer approach is implemented based on a set of limited sensor data for the building in question. This process results in optimizing estimated parameters so that predicted thermal physics match that of measured sensor data. Overall, the paper describes the development of this automated procedure, presents indicative results of its application, and discusses some possible limitations as well as guidelines aimed at alleviating some of these limitations.
Comparative Analysis of Features of Task Based Conceptual Design Methods
Authors: Darbinyan H. V.
Published: April 2014

In well known conceptual design methods movement based working principles are considered to provide demanded key function of the future mechanism. Acceptable kinematical structures are searched within large number of topological diagrams generated on the base of original mechanism selected in accordance with functional demand. Further filtering of topological diagrams is leaving structures which are satisfactory for structural characteristics and additional functions.

For many cases of mechanical design those concept design methods are not providing equal synthesis conditions for all functions, discriminating the rest of functions against the key function.

The suggested novel concept design method [1] provides possibility of wide modifications of mechanism and function entities with mandatory dependence between sets of functions and mechanism’ various embodiments and implies application of identical design cycles for different stages of concept design. Some chapters of this method, as main idea, unified synthesis tools, modeling in concept design, graph and matrix based formalization of functions and mechanisms were presented in the earlier publications [2, 3]. Current study aims to formalize the concept design method itself, which facilitates presentation of the suggested design method and enables its formalized comparison with existing ones. Examples of product concept design are considered and resolved by existing methods and by the novel one, thus making obvious feature and performance efficiency evaluation.
Energy Absorption in a 1D Array of Axially Aligned Pendulums With Linear Torsional Coupling
Authors: Bernard Brian P. , Greenstein Jake E. , Mann Brian P.
Published: April 2014

This paper evaluates wave propagation and energy absorption in a 1D array of axially aligned pendulums under various forms of base excitation. In the system studied, each pair of pendulums comprising a single unit cell is connected through linear torsional coupling, and asymmetry is introduced by varying their masses. Similar to translational systems, when subjected to harmonic base excitation, band gaps are observed in this rotational system over predictable frequency ranges. It is observed that varying the uncoupled restoring force parameters (mass and gravitational strength) shifts the expected band gap regions under harmonic excitation. This asymmetry in pendulum masses can also be exploited for the purposes of energy absorption when the system is subjected to base excitation in the form of an impulse. Numerical simulations are performed to demonstrate the accuracy of analytical solutions for both types of external forcing.
Numerical Solution of Heat Transfer During Solidification of an Encapsulated Phase Change Material
Authors: Ramos Archibold Antonio , Rahman Muhammad M. , Goswami D. Yogi , Stefanakos Elias L.
Published: April 2014

Macro encapsulation techniques have gained considerable attention in latent heat storage systems for solar energy applications in order to improve the overall energy conversion efficiency in solar thermal power plants. However the heat transfer mechanisms that govern the charging and discharging processes at high operating temperatures are still under development and represent an important aspect in the thermal energy storage design process. This study presents a numerical solution of the heat transfer and phase change that occurs during the solidification process of a phase change material (PCM) encapsulated in a spherical container. A transient two-dimensional axisymmetric mathematical model was solved using the control volume discretization approach along with the enthalpy-porosity method to track the melting front. A spherical shell of thickness t, under the gravitational field is completely filled with liquid PCM. For time t>0, a constant temperature boundary condition Tw, which is lower than the phase change temperature of the PCM, is imposed at the outer surface of the shell. A comprehensive analysis is presented in order to assess the role of the capsule size, buoyancy-driven flow in the liquid phase, and shell outer surface temperature on the thermal performance of the system. Results show that with the increase of Stefan number the solidification rate is enhanced. A reduction of 39.25% in total solidification time is predicted when the Stefan number changed from 0.095 to 0.143. Finally a generalized correlation for the solid mass fraction during solidification is obtained based on a combination of Fourier and Stefan numbers and a dimensionless material parameter.
Shape Optimization of Engine Mounts for Enhanced Vibration Isolation
Authors: Alkhatib Fadi , Dhingra Anoop K.
Published: April 2014

In this article, a parametric approach is used to determine the optimum geometric shape of an engine mount in order to minimize the vibrations transmitted to and from the engine. The engine mount used is an elastomeric mount which is made of rubber. For proper vibration isolation, elastomeric mounts are designed such that they have the necessary elastic stiffness rate characteristics in all directions. An optimization problem is first solved to determine the optimum values of stiffness, orientation and location of the mount system such that vibrations transmitted are minimal. Besides determining the optimum mount stiffness values, knowing the optimum shape of the rubber mount is also vital. The shape of the mount is determined such that it meets the required stiffness of the mounting system obtained from the dynamic analysis. A nonlinear finite element analysis is used to determine the final optimum shape and stiffness of the mount.
Vibration Control for Parallel Manipulator Based on the Feed Forward Control Strategy
Authors: Li Ming , Wu Huapeng , Handroos Heikki , Ceccarelli Marco , Carbone Giuseppe
Published: April 2014

Due to the high stiffness, high dynamic performance, the parallel manipulator presents great advantages in the industrial manufacture. However in the machining process, the external low frequency disturbance, e.g. the varying cutting force, has a significant effect on the control system of parallel manipulator, which presents a chatter phenomenon on the end-effector of manipulator.

In this paper, a feed forward control strategy is proposed to eliminate the effect of the random external disturbance on the control system of parallel manipulator. By applying the external disturbance force on the inverse dynamic model, the compensation torque is calculated and fed forward into the manipulator driving joints to cancel out the effect of the disturbance acting on the manipulator end-effector. The key issue herein is to be able to establish the accurate dynamic model for the parallel manipulator.

Furthermore, in order to guarantee the position precision of the manipulator, a feed forward model-based control strategy combined with the feedback loop PV (position and velocity) control has been developed based on the reference trajectory, which could relatively simplify the highly nonlinear control system of the parallel manipulator and obtain a stable tracking error model.

The whole research has been carried out on a parallel manipulator named CaPaMan which has been built in the laboratory of robotics and mechatronics in university of Cassino and South Latium. The results show that the chatter phenomenon could be utterly depressed by the force compensation from the feed forward path of the external disturbance; meanwhile the model-based controller can guarantee the trajectory tracking accuracy within a stable error by choosing the suitable PV gains.
Real-Time 3D Model Reconstruction and Interaction Using Kinect for a Game-Based Virtual Laboratory
Authors: Zhang Zhou , Zhang Mingshao , Chang Yizhe , Aziz El-Sayed , Esche Sven K. , Chassapis Constantin
Published: April 2014

Over the last few years, academic institutions have started to explore the potential of using computer game engines for developing virtual laboratory environments. Recent studies have shown that developing a realistic visualization of a physical laboratory space poses a number of challenges. A significant number of modifications are required for adding customized interactions that are not built into the game engine itself. For example, a major challenge in creating a realistic virtual environment using a computer game engine is the process of preparing and converting custom models for integration into the environment, which is too complicated to be performed by untrained users.

This paper describes the usage of the Microsoft Kinect for rapidly creating a 3D model of an object for implementation in a virtual environment by retrieving the object’s depth and RGB information. A laboratory experiment was selected to demonstrate how real experimental components are reconstructed and embedded into a game-based virtual laboratory by using the Kinect. The users are then able to interact with the experimental components. This paper presents both the technical details of the implementation and some initial results of the system validation.
Simplified Modeling Technique for Damping Materials on Light Structures: Experimental Analysis and Numerical Tuning
Authors: Splendi Luca , D’Agostino Luca , Baldini Andrea , Castignani Luca , Pellicano Francesco , Pinelli Marco
Published: April 2014

Specific polymeric and asphaltic materials are widely used for NVH automotive applications. If patches of such materials are properly collocated on vehicle’s panels, they are able to improve significantly noise and vibration performance by modulating damping and stiffness.

This work presents a methodology for tuning a FE composite model, using optimization techniques to improve the correlation with the experimental modal tests performed.

In particular, plain and ribbed aluminum plates have been considered for several covering ratios of three damping materials.

The correlation between numerical and experimental data is achieved by monitoring dynamic parameters such as natural frequencies, mode shapes, and frequency response functions (FRFs). The optimization strategy consists of two steps and makes use of evolutionary and gradient-based algorithms. LMS Virtual.Lab® is used in this part of the work as an environment for correlation and optimization.

In order to verify the reliability of the correlation, modal tests are performed on a particular vehicle’s panel.
Optimization of the Thermodynamics Cycles of Generation IV Gas-Cooled Fast Reactors
Authors: Polanský Jiří , Gášpár Roman
Published: April 2014

This paper deals with the thermo-hydraulic properties of Generation IV Gas Cooled Fast Reactors. The paper is focused on the comparison of direct and indirect thermodynamic cycles of helium cooled reactors from a thermodynamic point of view. The calculation includes pressure losses at all major parts of the equipment — reactor, heat exchangers, pipe lines, etc. The compressor and the gas turbine efficiencies are included in calculation as well. The working fluid used in the primary circuit is helium. In the secondary circuit a mixture of helium and nitrogen is used. The cycle characteristic point and efficiency calculation reflects mixture properties of the real gas — especially for N2.

Calculations point out the influence of the mixture composition on the basic structural parameters of the turbines, compressors and heat exchangers. Thermodynamic cycle efficiency, specific heat input/output, heat flux and cycle work will be presented as characteristic parameters.
Wilsak-Thodos Equation of State for Refrigerants
Authors: Rogdakis E. D. , Koronaki I. P. , Gorgoraptis E.
Published: April 2014

In recent years different equations of state for environmentally friendly refrigerants have been developed from different sources of experimental data which, in many cases, use a very large number of auxiliary functions and coefficients. A rather interesting equation that has not been recollected lately, proposed by Wilsak and Thodos in 1985, appears to have a convenient form for effective and significantly accurate calculations of the thermophysical properties of substances.

Wilsak-Thodos equation of state presents a relatively simple form as it correlates experimental data with the corresponding ones at saturation and contains only three density dependent functions. For this reason, this study attempts to identify the coefficients of the equation approximating accurately the experimental data and attributing in an integrated manner with auxiliary equations for some of the most common of the environmental friendly refrigerants.
Factors That Can Influence Mentorship Relationships in Advanced Education: Critical Insight
Authors: Ferreira Ana C. , Leão Celina P.
Published: April 2014

“Mentoring is a brain to pick, provide an ear to listen, and give a push in the right direction” John C. Crosby. Mentoring, by definition, is a relationship between a more experienced or more knowledgeable person and a less one. This relationship improves the personal and professional growth for the mentee. However, mentoring brings benefits for both individuals involved in such relationship. The mentoring process must be regarded not only from the mentee point of view, but also from the mentor perspective. In effect, both sides work together in order to achieve the best outcome considering the initial defined objectives. Mentoring is a growing phenomenon that has demonstrated positive results. This reality is due to the increase number of students applying for postgraduate training and search for guidance. To verify how this process on advanced studies is conducted, several semi-structured interviews were carried out under the postgraduate engineering programme of a Portuguese university. The focus of these interviews was the identification of the parameters that influence the mentoring process. Topics such educational background, age, previous experiences, gender and longevity of mentoring relationship were queried in this study. This paper aims to understand the perceptions of the mentorship relationship from a group of engineering students in advanced education and connect their point of views with some aspects of the mentoring literature.
Flow Structures and Losses in the Exhaust Port of an Internal Combustion Engine
Authors: Wang Yue , Semlitsch Bernhard , Mihaescu Mihai , Fuchs Laszlo
Published: April 2014

A numerical study of the flow in the exhaust port geometry of a Scania heavy-duty Diesel engine is carried out mainly by using the Large Eddy Simulation (LES) approach. Unsteady Reynolds Averaged Navier-Stokes (URANS) simulation results are included for comparison purposes. The calculations are performed with fixed valve and stationary boundary conditions for which experimental data are available. The simulations include a verification study of the solver using different grid resolutions and different valve lift states. The calculated numerical data are compared to existent measured pressure loss data. The results show that even global parameters like total pressure losses are predicted better by LES than by URANS. The complex three-dimensional flow structures generated in the flow field are qualitatively assessed through visualization and analyzed by statistical means.

The near valve region is a major source of losses. Due to the presence of the valve, an annular, jet-like flow structure is formed where the high-velocity flow follows the valve stem into the port. Flow separation occurs immediately downstream of the valve seat on the walls of the port and also on the surface of the valve body. Strong longitudinal, non-stationary secondary flow structures (i.e. in the plane normal to the main flow direction) are observed in the exhaust manifold. Such structures can degrade the efficiency of a possible turbine of a turbocharger located downstream on the exhaust manifold.
A Modified Step-Wise Transient Method for Measuring the Thermal Conductivity of Anisotropic Materials
Authors: Li Xiao-Fei , Yue Kai , Zhang Xin-Xin
Published: April 2014

Acquiring the thermal conductivity of anisotropic insulating materials accurately has important implications for applications of insulation materials. In this study, a modified step-wise transient method with special considerations of heat-loss effect occurring at the edge of measured samples, finite geometry of the sample and orthotropic thermal conductivity was proposed. A three-dimensional model in a rectangular coordinate system was established to describe the heat transfer process correctly. A general analytical solution of the temperature rises of the measured sample was derived by applying Laplace-transform technique and the separation of variables method. It is indicated that the temperatures calculated by the analytical solution agree well with the results of numerical calculation. The sensitivity analysis of crucial parameters was performed to select appropriate measuring points of the measured sample. Based on the above analysis, the orthotropic thermal conductivities of the measured anisotropic materials were achieved by measuring the temperature rises at two points of the measured sample. The simulation results demonstrate the reliability and validity of the proposed model taking orthotropic thermal parameters, heat-loss effect and finite geometry of the sample into account.
The Effect of Perfusion Rate on the Radiofrequency Ablation of Liver Tumors
Authors: Ulucakli M. Erol , Lavery Christopher S.
Published: April 2014

Radiofrequency ablation is a medical procedure used to treat a variety of illnesses including liver carcinomas that cannot be treated by resection or radiological procedures. A multi-physics code was used to solve the Bio-heat Equation by a finite element methodology. The volume of coagulation necrosis caused by the heating of the tumor tissue as a function of perfusion rate was determined. A multi-needle probe deposited the RF energy into the tissue. Once the tissue was heated to greater than 50°C it was considered irreversibly damaged. Increasing perfusion rates reduced the size of the lesion. In order to heat a volume to a required temperature the time elapsed did increase.
Modeling of a Microhollow Cathode Discharge Reactor for Carbon Dioxide Dissociation
Authors: Taylan Onur , Berberoglu Halil
Published: April 2014

This paper reports a numerical study on carbon dioxide dissociation using a microhollow cathode discharge (MHCD) plasma reactor. These reactors can produce non-equilibrium plasmas and can be a promising technology for converting carbon dioxide into valuable chemicals and renewable fuels. However, these applications are currently in their early stages. In order to understand the effects of major design and operational parameters on the reactor performance a MHCD system was modeled and simulated. In this study, different types of dielectrics including mica, alumina, acrylic and quartz were used, and applied DC voltage was varied from 250 to 10,000 V. First the operating voltage regions of this reactor were determined based on the breakdown thresholds of the dielectric and gas phase. Then, the effects of applied voltage on the discharge volume and power requirement of operation were determined. Results showed that the reactor with mica as the dielectric material showed the largest operating voltage range, as well as the highest power requirement. In addition, the discharge volume increased with applied voltage and it was possible to discharge about 96% of the gas in the MHCD reactor with mica at 10 kV.
Light-Driven and Control of Paraboloidal Thin Shell Using Photodeformable Materials
Authors: Wang X. J. , Huang J. H. , Wang J. , Cheng W. X.
Published: April 2014

Photodeformable materials can transform light energy into mechanical energy without electromagnetic noise. Lanthanum modified lead zirconate titanate (PLZT) ceramics are one kind of photodeformable materials. Since light is an environment-friendly, remotely controllable stimulus, the actuation based on PLZT ceramics is green driven and non-contact driven, which has many advantages in micro-driven and structure vibration control. In this paper, light-driven and active control of paraboloidal thin shells laminated with PLZT actuators is studied. Based on the new photostrictive mathematical model of PLZT and mode shape functions obtained using membrane theory, the control equations of photostrictive laminated paraboloidal thin shells are deduced. Active control scheme for the photostrictive laminated thin shell structure is obtained through combining the illumination scheme and the control algorithm. Active vibration control simulation analysis for the two modes of the paraboloidal shell with two actuator configurations is carried out using Newmark-β method. Simulation results show that the control scheme is suitable and effective for the photostrictive laminated paraboloidal thin shell, and the control effect is affected by the actuator configuration.
An Experimental Study of the Effect of Drag Reducing Additive on the Structure of Turbulence in Concentric Annular Pipe Flow Using Particle Image Velocimetry Technique
Authors: Rodriguez Corredor Fabio Ernesto , Bizhani Majid , Kuru Ergun
Published: April 2014

The effect of drag reducing additive on the structure of turbulence in concentric annular pipe flow was investigated using Particle Image Velocimetry (PIV) technique. Experiments were conducted using a 9m long horizontal flow loop with concentric annular geometry (inner to outer pipe radius ratio = 0.4). The drag reducing additive was a commercially available partially hydrolyzed polyacrylamide (PHPA). The experiments were conducted using 0.1% V/V polymer concentration, giving a drag reduction of 26% at a solvent Reynolds number equal to 56400.

Near wall local fluctuating velocity values were determined by analysing the PIV data. The root mean square (RMS) values of radial velocity fluctuations showed a significant decrease with the use of drag reducing additive. The RMS values of axial velocity fluctuations near the wall (Y+<10) were similar for both water and polymer fluid flow; though, higher peaks were obtained during the polymer fluid flow.

As compared to water flow, a strong reduction in vorticity was observed during polymer fluid flow. The degree of vorticity reduction on the inner wall was higher than that of the outer wall.

Results of the viscous dissipation and the shear production terms in the kinetic energy budget showed that less energy was produced and dissipated by the route of turbulence when using polymer fluid.
Application of DQM Method to the Steady State Analysis of Thermo-Tunneling Electrodes
Authors: Enikov Eniko T. , Ganji Mahdi
Published: April 2014

Thermo-tunneling of hot electrons across a few nanometer gap has application to vacuum electronics, flat panel displays, and holds great potential in thermo-electric cooling and energy generation. However development of such applications requires formation of dynamically balanced gap separating the two surfaces. One such approach is the use of Lorentz (repulsive) and Coulomb (attractive) forces to obtain an equilibrium gap between two elastic electrodes. The present paper describes the application of the Differential Quadrature Method (DQM) to the solution of a clamped-clamped Euler-Bernouli beam subject to the combined action of Lorentz and Coulomb forces. The results show that due to non-local action of the Lorentz force, the shape of the tunneling electrode is inherently non-uniform with Coulomb forces acting primarily at one end of the beam while the Lorentz force distributed along the remaining part. DQM method also allows analysis of the stability of the tunneling current as a function of the applied external potential and magnetic field. In addition to the classical electrostatic pull-in instability with no-tunneling, a second regime with non-zero tunneling current is also identified. To the best of our knowledge this is the first attempt to analyze this phenomenon under the effect of both Electrostatic and Lorenz forces in this particular case. Linear stability analysis of the tunneling regime indicates the appearance of a saddle-saddle bifurcation indicating unstable tunneling regime.
Designing Phononic Crystals With Convex Optimization
Authors: Men Han , Freund Robert M. , Nguyen Ngoc C. , Saa-Seoane Joel , Peraire Jaime
Published: April 2014

Designing phononic crystals by creating frequency bandgaps is of particular interest in the engineering of elastic and acoustic microstructured materials. Mathematically, the problem of optimizing the frequency bandgaps is often nonconvex, as it requires the maximization of the higher indexed eigenfrequency and the minimization of the lower indexed eigenfrequency. A novel algorithm [1] has been previously developed to reformulate the original nonlinear, nonconvex optimization problem to an iteration-specific semidefinite program (SDP). This algorithm separates two consecutive eigenvalues — effectively maximizing bandgap (or bandwidth) — by separating the gap between two orthogonal subspaces, which are comprised columnwise of “important” eigenvectors associated with the eigenvalues being bounded. By doing so, we avoid the need of computation of eigenvalue gradient by computing the gradient of affine matrices with respect to the decision variables. In this work, we propose an even more efficient algorithm based on linear programming (LP). The new formulation is obtained via approximation of the semidefinite cones by judiciously chosen linear bases, coupled with “delayed constraint generation”. We apply the two convex conic formulations, namely, the semidefinite program and the linear program, to solve the bandgap optimization problems. By comparing the two methods, we demonstrate the efficacy and efficiency of the LP-based algorithm in solving the category of eigenvalue bandgap optimization problems.
Flexural Modulus of Lasersintered PA 2200
Authors: Coy Johannes A. , Kuball Clara-Maria , Roppenecker Daniel B. , Lueth Tim C.
Published: April 2014

With the evolving of rapid manufacturing methods, new fields of application become feasible. Selective Laser Sintering (SLS), an additive process, allows the production of medical devices made out of PA 2200, a biocompatible plastic powder. Due to the fast production cycle, medical robots or devices can be highly customised. However, those new production methods force the engineer to design robots and mechanisms adapted for this process. In particular the use of compliant structures is necessary if small mechanisms are to be created.

Creating laparoscopic grippers out of flexible hinges revealed that there are properties unknown for the particular material used. Lasersintered PA 2200 parts seem to have a flexural modulus, which varies with their thickness and build orientation during the production process. This paper investigates those phenomenons with three-point loading tests. A dependency could be found and has been characterised for five orientations allowing the engineer to estimate the flexural modulus of lasersintered PA 2200 parts according to their thickness.
Receding Horizon Real-Time Energy Management Strategy for Hybrid Vehicles
Authors: de Jager Bram , van Keulen Thijs
Published: April 2014

Indirect optimal control and dynamic programming are combined in a receding horizon controller to obtain an energy management strategy for hybrid vehicles. This combination permits the use of inaccurate predictions of the future, instead of requiring exact knowledge, and allows the use of mixed state-control constraints, like voltage constraints for batteries. The controller can run in real-time on commodity hardware and, using a prediction of the future based on geographic information only, obtains a fuel use within 0.2% of the optimal fuel use computed with the exact speed and power trajectory of the vehicle known in advance. All this for a planned distance of more than 500 [km].
Nonlinear Reduced-Order Models for the Structural Dynamics of Combustor Systems With Pre-Stress and Friction
Authors: Jung Chulwoo , Epureanu Bogdan I. , Baik Sanghum , Huffman Marcus B.
Published: April 2014

An efficient methodology to capture the nonlinear responses of combustor systems with pre-stress and Coulomb friction is developed. The combustor systems experience wear at the interfaces between components due to flow-induced vibrations. In particular, wear has been observed at the interface between the transition piece and the hula seal, and at the interface between the hula seal and the liner. These interfaces are pre-stressed, and their vibratory response has a softening nonlinearity caused by Coulomb friction combined with micro-slip. In addition, the contact between the hula seal and the transition piece is that between a convex surface and a concave surface. Hence, geometric nonlinearity of the contact stiffness in the normal direction is present also. These phenomena are hard to capture by full order finite element approaches because they require time marching or harmonic balancing of very large models. To address this issue, we develop reduced order models (ROMs) which are specifically designed to capture Coulomb friction (combined with micro-slip and macro-slip). To demonstrate the proposed approach, a simplified hula seal is placed between two very rigid plates (which relate to the transition piece and the liner). For validation, contact elements are used to model the interface between the plates and the hula seal. Transient dynamic analysis (TDA) in ANSYS is applied to the full order model. The model is shown to exhibit softening nonlinearity and micro-slip at all levels of pre-stress. To show that ROMs for this system are possible (i.e., they exist), we use proper orthogonal decomposition to show that the dynamics is dominated by a low number of spatial coherences. For a variety of frequency ranges and pre-stress levels, we show that a single such coherence is dominant. Next, low order models are proposed and their parameters are identified. A systematic method to identify these parameters is developed. Particular attention is paid to the amount of calculations needed for obtaining these parameters. Finally, the ROMs are validated by comparing their predictions with results from TDA for the full-order model. We show that these ROMs can accurately predict the nonlinear response of the system.
Distribution of Bacteria in Simplified Surrogate Extremities Shot With Small Caliber Projectiles
Authors: Hinz Brandon J. , Muci-Küchler Karim H. , Smith Pauline M.
Published: April 2014

Experiments were conducted to determine bacteria distribution trends in wound cavities of simplified surrogate extremities shot using small caliber projectiles. Two different shapes of targets, cylindrical and square, were used in this study. Cylindrical targets are more representative of an extremity but create difficulties while conducting tests due to inconsistent cavity lengths and optical distortions. Square targets, which are not as susceptible to the problems mentioned above, could be used in place of cylindrical ones if their shape does not significantly affect the distribution of bacteria within the wound cavity. Surface contamination of the targets in the experiments was represented using a circular piece of filter paper moistened with a solution with a known amount of Escherichia coli strain K-12. The projectiles used were 11.43-mm (0.45-in) caliber round nose projectiles shot from a commercially available air rifle. The permanent cavities were extracted from the targets and sliced into small, evenly spaced segments and the area surrounding the permanent cavities was removed with a biopsy punch. The radial tears that were made by the formation of the temporary cavity and surround the permanent cavity were removed using a scalpel. The permanent cavity and radial tears for each section were processed and plated on agar plates. Commercial software was used to count the number of colony forming units on each plate and the percentage of the total bacterial colony count per segment was determined. High speed video and motion analysis software was used to qualitatively and quantitatively compare the temporary cavities in the cylindrical and square targets. The data from the experiments showed that the bacteria distribution trends for the cylindrical and square targets were similar even though the maximum openings of the temporary cavity at the entrance and exit locations were higher for the cylindrical ones. For both target shapes, the bacterium was evenly distributed between the permanent cavity and the radial tears in the middle sections of the “wound tracks.” In addition, significantly higher amounts of bacterium were found in the entrance and exit segments compared with the rest of the segments in the “wound tracks”.
Errors and Uncertainties: What Hath the GUM Wrought?
Authors: Emery A. F. , Vosk T.
Published: April 2014

Traditional error analysis to estimate the uncertainties in experimental measurements and predictions has given way during the last two decades to uncertainty analysis. The current methodology is described in the GUM (Guide to the Expression of Uncertainty in Measurement) issued by ISO. The reasoning behind the change was the recognition that one could never know the true value of a measurement and thus the error could not be determined.

As promulgated, the uncertainties are represented in statistical terms based upon sampling (classical statistics) and upon subjective reasoning (Bayesian). The approach combines these uncertainties in the usual error analysis approach of summing the variances (now labeled the ‘Law of Propagation of Uncertainties’) and then using the student-t distribution to attach some meaning to the result.

The correct procedure is to apply the Bayesian approach throughout, but many investigators have heard only that Bayesian inference is computationally expensive and question the idea of subjective probability and resort to using the Law of Propagation of Uncertainties.

This short note treats the common problem of the uncertainty of a measurement using a calibrated device. It compares the two methods, reminding the reader of what the GUM calls for and assumes, and showing that with our current computing power there is no good reason to avoid Bayesian inference to provide more exact and informative understandings of measurement uncertainties.
Finite Element Analysis for Reliable Replication of Alignment Structures in Micro Hot Embossing
Authors: Gomez Juan A. , Conner Glenn , Song In-Hyouk , Kim Yoo-Jae , You Byoung Hee , Chun Du-Hwan
Published: April 2014

Numerical analysis to predict the flow behavior of polymers was conducted using commercial finite element software, DEFORM-2D. An alignment structure, a hemisphere-tipped post with an annular ring, was modeled to demonstrate the flow front of the polymer during molding. The cavity filling process was evaluated by measuring the heights of the molded posts and confirmed and validated by experimental data. Estimated and measured heights showed better replication accuracy with the increase of molding temperature and embossing force. Results exposed complete cavity filling at embossing forces of 600 and 900 N at a molding temperature of 137.5°C. The FEM prediction tool can be used to select the adequate process parameters for a high fidelity replication of polymer microstructures.
Steepest Entropy Ascent Models of the Boltzmann Equation: Comparisons With Hard-Sphere Dynamics and Relaxation-Time Models for Homogeneous Relaxation From Highly Non-Equilibrium States
Authors: Beretta Gian Paolo , Hadjiconstantinou Nicolas G.
Published: April 2014

We present a family of steepest entropy ascent (SEA) models of the Boltzmann equation. The models preserve the usual collision invariants (mass, momentum, energy), as well as the non-negativity of the phase-space distribution, and have a strong built-in thermodynamic consistency, i.e., they entail a general H-theorem valid even very far from equilibrium. This family of models features a molecular-speed-dependent collision frequency; each variant can be shown to approach a corresponding BGK model with the same variable collision frequency in the limit of small deviation from equilibrium. This includes power-law dependence on the molecular speed for which the BGK model is known to have a Prandtl number that can be adjusted via the power-law exponent.

We compare numerical solutions of the constant and velocity-dependent collision frequency variants of the SEA model with the standard relaxation-time model and a Monte Carlo simulation of the original Boltzmann collision operator for hard spheres for homogeneous relaxation from near-equilibrium and highly non-equilibrium states. Good agreement is found between all models in the near-equilibrium regime. However, for initial states that are far from equilibrium, large differences are found; this suggests that the maximum entropy production statistical ansatz is not equivalent to Boltzmann collisional dynamics and needs to be modified or augmented via additional constraints or structure.
Probabilistic Fatigue Crack Growth Analysis for Life Prediction of Automotive Components
Authors: Yazdanipour Mahboubeh , Pourgol-Mohammad Mohammad , Choupani Naghd-Ali , Yazdani Mojtaba
Published: April 2014

This research focuses on investigating the probabilistic fatigue crack growth models on W319 aluminum alloy which has vast applications in automotive parts products. The aim of this study is to determine the crack growth rate probabilistically and quantification of uncertainty of probabilistic models on estimation of damages (crack length) versus life (number of cycles) under fatigue loading in automotive parts. The models used in this paper include Walker and Forman correlations. The deterministic forms of these models are verified with AFGROW code and validated experimentally with fatigue data of W319 aluminum. After verifying the accuracy of deterministic models, the models are treated probabilistically by considering the models’ parameters stochastic. Monte Carlo simulation is devised to investigate the models under stochastic conditions by drawing samples from these random variables. Finally the propagation of uncertainty is quantified by calculating standard deviations of crack lengths through propagation of the uncertainties via cycles. The results are useful for selecting a proper probabilistic fatigue crack growth model in specific applications and can be used in future studies in automotive industry to obtain more accurate and reliable conclusions.