bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of Non-Linear Turbulence Models on the Numerical Simulation of Cavitating Flows
Authors: Chen Ying , Chen Xin , Cao Jiayi , Lu Chuanjing
Published: October 2013

Quadratic and cubic non-linear eddy-viscosity turbulence Models (NLEVM) with low Reynolds number correction were employed to provide better treatment about the anisotropic turbulence stresses in cavitating flows, in which large density ratio and swirling structures consist. These models were carried out through a self-developed computer code, and were validated by the case of the cavity over disk cavitator. It was proven that, the nonlinear models could effectively eliminate the non-physical numerical oscillation of the cavity profile which was usually caused by linear models. It had also been experimentally proved that the computed cavity shapes and pressure inside the cavity were accurately captured by these nonlinear models. One of such nonlinear models was further applied on the simulation of the cavitating flows around submerged vehicles. The numerical results were compared with experiment data to investigate the influence of the vehicle’s head and the after-body on the characteristics of the cavity. Ultimately, the cavitating flows around an especially designed complex underwater vehicle were predicted using the cubic k–ε turbulence model. The corresponding cavitation behaviors were studied to provide a beneficial experience for the research in future.
Cruise Lane Highway Charging of Electric Vehicles
Authors: Raghav Vrishank , Komerath Narayanan
Published: October 2013

The possibility of charging electric vehicles(EV) while they are cruising on highways is explored. Such a technology would break through the ‘range anxiety’ barrier to mass adoption of EVs. Developments in emerging energy technologies for automotive radar and other applications, have made possible the implementation of wireless millimeter wave beamed power. The rapid advances in the ability to accurately beam and receive power in the 70 to 225 GHz frequency range using solid state components suggests that it will become possible in the near future to beam sufficient power to perform such charging applications. Unlike short-range wireless inductive charging, beamed cruise charging is aimed to work on vehicles traveling as fast as 100 kph on straight segments of the highway, similar to cruise toll lanes used today. Subsequent versions may use aerostats or towers to beam power, enabling power delivery on curved roads in mountainous regions. The paper will survey related prior work and set out preliminary sizing and business case calculations, followed in the final paper by trade studies to perform a first level optimization. We also discuss the architectural requirements, charging rates and perform a sustainability.
Numerical Research on Forced Response of a Compressor Rotor Row Under Inlet Distortion
Authors: Zhang Zhang , Hou Anping , Tuo Wei , Xia Aiguo , Zhou Sheng
Published: October 2013

Under inlet total pressure distortion, forced response of compressor blades poses a threat to aircraft propulsion system. Research on blade dynamic response is premise and basis for high-cycle fatigue life analysis. Blades of a compressor first rotor row are studied with three dimensional numerical simulation in fluid-structure coupling methods. The inlet distortion’s influence on blade aeroelastic dynamic response and flow field characteristics are analyzed. The results demonstrate that circumferential and radial total pressure distortion should be considered together in the phenomenon of actual inlet distortion induced blade vibration response. At the condition of low angle of attacks, radial distortion intensity is weak, the relation between vibration response level of rotor blades and circumferential distortion intensity is proportional. With the angle of attack increases, the vibratory stress under aerodynamic forces grows sufficiently. The radial total pressure distortion near hub increases dynamic response severity of rotor blades.
Fatigue Life Prediction of Microstructures
Authors: Castelluccio Gustavo M. , McDowell David L.
Published: October 2013

The formation and early growth of fatigue cracks in the high cycle fatigue regime is influenced by microstructuctural features such as grain size and morphological and crystallographic texture. However, most fatigue models do not predict the influence of the microstructure on early stages of crack formation, or they employ parameters that should be calibrated with experimental data from specimens with microstructures of interest. These post facto strategies are adequate to characterize materials, but they are not fully appropriate to aid in the design of fatigue-resistant engineering alloys. This paper presents a modeling framework that facilitates relative assessment of fatigue resistance among different microstructures. The scheme employs finite element simulations that explicitly render the microstructure and a methodology that estimates transgranular fatigue growth for microstructurally small cracks on a grain-by-grain basis, including consideration of growth within grains (embedded analytically) and stress redistribution as the cracks extend. The methodology is implemented using a crystal plasticity algorithm in ABAQUS and calibrated to study fatigue crack initiation of a bimodal grain size distribution found in RR1000 powder processed Ni-base superalloys for turbine disk applications.
Numerical Analysis to Predict the Temperature Distribution and Heat Transfer Rate From a Satellite Structure and Experimental Comparison
Authors: Schwendtner Daniel T. , Amin M. Ruhul , Klumpar David M.
Published: October 2013

Due to their small size and other attractive features, nanosatellites are becoming popular in space applications. Experimental investigation of the thermal behavior of such a satellite can be conducted in a laboratory setup using a thermal vacuum chamber to mimic the conditions of outer space. A small, cost effective thermal vacuum system was desired for performing thermal vacuum testing on nanosatellites. Numerical calculations and laboratory testing were performed as part of the design of this thermal vacuum system. A numerical method using the finite element method was employed to determine the amount of heat flux needed to be applied at the bottom plate of a satellite to achieve a certain rate of temperature increase in the plate. The numerical analysis was performed on a 40.5 kg satellite structure to predict the heat rate per unit area through its bottom surface when it was cycled in the temperature range of −40°C to +80°C with a rate of temperature change from 1°C/min to 5°C/min.

A time dependent increase in temperature on the bottom wall was used as a boundary condition. The rest of the satellite walls were assumed to be insulated. Contact resistances between the components of the satellite structure were neglected. Temperature and heat flux distributions on various walls of the satellite were computed and reported in the study. From the numerical results, a maximum heat flux rate of 3,332 W/m2 was calculated on the bottom plate for a temperature increase rate of 1.5°C/min of the plate.

A similar experimental setup was tested under similar conditions as a comparison and as a method to validate the thermal system design. Experimental results indicated a heat flux rate of 17,094 W/m2 through a test satellite. The difference between the numerical and experimental results is attributed to geometric differences between the numerical satellite model and the experimental test structure.
Development and Validation of an Advanced Simulation Model for ORC-Based Systems
Authors: Ziviani Davide , Beyene Asfaw , Venturini Mauro
Published: October 2013

Low-grade heat recovery from solar or geothermal energy may be an eco-friendly resource for electric and thermal energy recovery. The Organic Rankine Cycle (ORC) is one of the main candidates to exploit low-temperature heat sources, otherwise difficult to access using conventional power generation systems.

In this paper, an advanced thermodynamic model of an ORC is developed, with the final aim to optimize ORC conversion efficiency, especially for micro-CHP applications.

First, a thorough review of issues related to ORC system modeling is presented by analyzing the state-of-the-art experience and advancements.

Subsequently, an advanced simulation model is developed, by taking advantage of all the key characteristics of the models presented in the literature. The simulation model is developed in Matlab®/AMESim® environment, which allows system modeling both for steady and transient analysis. The heat source is coupled with the system through a plate heat exchanger, which is modeled using an iterative sub-heat exchanger modeling approach. A scroll expander, modeled in detail by decomposing the behavior of the fluid stream into several steps, is used to extract the useful work.

Finally, model predictions for the evaporator and the expander are validated against both numerical and experimental data published in literature. The simulation model of the entire ORC system is also validated against literature data taken on a test bench.
Modifying the Classical 1D Catalyst Model to Include Axial Conduction and Diffusion
Authors: Loya Sudarshan , Depcik Christopher
Published: October 2013

Lean NOx Trap (LNT) catalytic aftertreatment devices are one potential option for the reduction of oxides of nitrogen (NOx) in the exhaust of Compression Ignition engines. They work through a controlled modulation between a storage phase that captures NOx over an alkali earth metal and a regeneration phase that reduces the stored nitrates on the surface using a rich pulse of injected fuel or via stoichiometric engine operation. This rich phase has an associated fuel penalty while being relatively difficult to control through temperature and chemical species. In order to improve system efficiency, a number of researchers have proposed dual leg LNT systems using two LNTs, of which one is always storing while the other is undergoing regeneration. The majority of the exhaust flows through the storage LNT while only a small fraction (low space velocity) advects across the regeneration LNT. This increases the regeneration residence time, improving effectiveness and decreasing the amount of fuel used. From an LNT simulation standpoint, most researchers utilize the classical one-dimensional (1D) aftertreatment model constructed from the Euler equations of motion that neglects axial conduction and diffusion. This paper explores the applicability of this model under low flow situations prevalent in a dual leg LNT system through a carbon monoxide light-off experiment. The authors chose this type of experiment in order to focus purely on fluid mechanics and not the choice of LNT reaction mechanism. The results suggest that a Navier-Stokes (N-S) version of the 1D aftertreatment model is preferred for the regeneration leg of a dual LNT system. Moreover, the authors provide the solution of such a model within this paper.
Air-Side Thermal and Drain Performance of Wire-Strip Fin-Tube Heat Exchanger
Authors: Kang Hie Chan , Jeong Sun An
Published: October 2013

The purpose of the present study is to investigate the characteristics of pressure drop, heat transfer rate and drainability of a wire-strip heat exchanger modified from the conventional louver fin one. Scaled-up models with the standard and four kinds of wire-strip fins were made, and their thermal and hydraulic performances tested in a wind tunnel. The drainability of the fins was evaluated by measuring the water retained after dipping the heat exchangers. The f and j factors and their ratios for the wire-strip fins are compared with those of the conventional louver fin, and empirical correlations and theoretical predictions were made. The best design for the wire-strip fins showed a better thermal performance per unit fan power than the standard louver fin by several tens of percent. It also retained about half or less of the water.
Theory of Continuously Variable Transmission With Two Degrees of Freedom: Paradox of Mechanics
Authors: Ivanov Konstantin S.
Published: October 2013

Recently creation continuously variable transmission (CVT) having property of the adaptation to variable technological loading develops. Traditional CVT contains the hydraulic converter and gear differential with two degrees of freedom (patents of Crockett, Volkov). The hydraulic converter imposes differential constraint on movement of links of the mechanism with two degrees of freedom. It provides definability of movement of transmission. Take place progressive CVT without use of the hydraulic converter (Harries’s patent, Ivanov’s patent). Such transmission contains only gear differential with two degrees of freedom. However the theoretical substantiation of serviceability of such transmission is not convincing for the lack of the proof of static definability of the mechanism with two degrees of freedom, having only one input. Ivanov K.S.’s theoretical researches do not contain enough convincing arguments of presence of definability of such mechanisms. Mechanisms with two degrees of freedom are considered disabled because of their contradiction to a key rule of mechanics that the number of the generalized coordinates should be equal to number of degrees of freedom of the mechanism (that is it should be equal to two, instead of to one). In Ivanov K.S.’s early works it was mentioned presence of paradox of the mechanics reflecting essence of the specified discrepancy. However in these works there was no the elementary demonstrative base of essence of the phenomenon resulting in static definability. The purpose of the present work to describe essence of the phenomenon which in certain conditions result to static definability of the mechanism with two degrees of freedom at presence only of one input, to receive the theoretical description of paradox of mechanics and its authorization using the elementary laws of theoretical mechanics. In the work the presence of paradox of mechanics is proved. The paradox of mechanics takes place in the kinematic chain having the closed contour, and it consist in the following. The structural group with two degrees of freedom having two consistently connected links is statically definable at presence only one entrance link. The paradox of mechanics is authorized by the account of additional constraint which is imposed by kinematic chain with the closed contour and two degrees of freedom on movement of links by a principle of possible works. Use of the equations of a statics and additional constraint allows to receive the equations of interrelation of parameters of transmission and to execute synthesis of transmission on the set conditions of motion. The found laws will allow creating the transfer mechanisms having property of mechanical adaptation to variable technological loading. Mechanical adaptation provides an opportunity of motion of an output link with a speed inversely force of resistance at constant input power.
The Maximum Temperature and Second Law Analysis of the Shock Tube
Authors: Bar-Meir Genick
Published: October 2013

The shock tube is a device that is used to obtain high temperatures for a very short time. The core driving force is pressured gas which is allowed to flow to a low pressure chamber, and thus achieve a high temperature. This device has been in use since the 1940s. Initially, the shock tube was used to study detonation. Later, it was used to study chemical reactions, complex flow phenomena, and several industrial applications. Several researchers suggested methods to increase the temperature. However, there is no study on the maximum potential temperature. This investigation was prompted by several industrial applications in different industries such as printing, automobile, and manufacturing.

The maximum temperature analysis is conceptually similar to the analysis of the maximum work which can be obtained when two bodies with a different temperature are brought into contact. Here, the semi–equilibrium actually creates the maximum temperature difference. This study solves for the maximum temperature and hence renders a guide on how the different parameters affect the maximum temperature. This study indicates that the typical efficiency of typical shock tube is 3–5%.
Enhanced Performance of Electric Double Layer Capacitor as Peak Power Buffer in the Hybrid Power Source Under Low Temperature
Authors: Zhang Guoyu , Yang Lin , Zhao Xiaowei , Tian Feng , Qiang Jiaxi
Published: October 2013

The performance of the hybrid power source at low temperature is experimentally analyzed. The parallel connected electric double layer capacitor (EDLC) enhances the power of Li-ion battery as it acts as a buffer in charge and discharge processes, especially at low ambient temperature. The behaviors of current and voltage of both the battery and EDLC are studied by experiments and described by a mathematical model. The EDLC can share a great part of total current load at low temperature, which effectively release the battery stress in pulse charge/discharge processes. Moreover, adding an EDLC in parallel with the battery also exhibits a considerable increase in capacity as compared to the Li-ion battery standalone in pulsed and continuous discharge processes. The performance of the hybrid power source under practical drive cycle is also studied in this article.
Experimentally-Tuned Finite Element Model of Flow-Induced Vibrations in a Square Tube Bundle Subjected to Cross-Flow
Authors: Khulief Y. A. , Said S. A.
Published: October 2013

It has been recognized that modeling of the complex dynamics of fluidelastic forces, that give rise to vibrations of tube bundles, requires a comprehensive dynamic model of high fidelity based on experimental insight. Accordingly, the prediction of the flow-induced vibration due to unsteady cross-flow can be greatly aided by semi-analytical models, in which some coefficients are determined experimentally. In this paper, the elastodynamic model of the tube array is formulated using the finite element approach, wherein each tube is modeled by a set of finite tube-elements. The interaction between tubes in the bundle is represented by fluidelastic coupling forces, which are defined in terms of the multi-degree-of-freedom elastodynamic behavior of each tube in the bundle. A laboratory test rig with an instrumented square bundle is constructed to measure the fluidelastic coefficients used to tune the developed dynamic model. The test rig admits two different test bundles; namely the inline-square and 45° rotated-square tube arrays. Measurements were conducted to identify the flow-induced dynamic coefficients. The developed scheme was utilized in predicting the onset of flow-induced vibrations, and results were examined in the light of TEMA predictions. The comparison demonstrated that TEMA guidelines are more conservative in the two configurations considered.
Investigation of the System Parameters Affecting the Runtime of a Freezer Compartment
Authors: Kerpicci Husnu , Poyraz Onur , Aynur Tolga N. , Teke Ismail
Published: October 2013

In this study, an experimental setup was built to evaluate the energy consumption of a freezer compartment by varying the runtime (i.e. the ratio of the compressor ON time to the total cycle time) of the system with the evaporation temperature and the airflow rate. Evaporation temperature and the normalized airflow rate were varied from −25°C to −28°C and from 0.8 to 1.4, respectively, thus the effects of these parameters on the runtime of the freezer were evaluated in a wide range of operating conditions. In addition, an empirical model that estimates the runtime within ± 4% compared to the experimental data was presented. By using the empirical model, optimum operating conditions (i.e. evaporation temperature and airflow rate) for the freezer were found with an energy saving of %13.8.
Nonlinear Vibration Response Analysis on a Composite Plate Reinforced With Carbon Nanotubes
Authors: Guo Xiang-Ying , Zhang Wei , Wang Qian
Published: October 2013

In order to compare nonlinear vibration response of the different enabled materials in the matrix of composites, the nonlinear vibrations of a composite plate reinforced with carbon nanotubes (CNT) are studied. In this paper, the carbon nanotubes are supposed to be long fibers. The nonlinear governing partial differential equations of motion for the composite rectangular thin plate are derived by using the Reddy’s third-order shear deformation plate theory, the von Karman type equation and the Hamilton’s principle. Then, the governing equations get reduced to ordinary differential equations in thickness direction with variable coefficients and these are solved by the Galerkin method. The case of 1:1 internal resonance is considered. The asymptotic perturbation method is employed to obtain the four-dimensional averaged equations. The numerical method is used to investigate the periodic and chaotic motions of the composite rectangular thin plate reinforced with carbon nanotubes. The results of numerical simulation demonstrate that there exist different kinds of periodic and chaotic motions of the composite plate under certain conditions. At last, the nonlinear vibration responses of the plate are compared with the same responses of angle-ply composite laminated plates.
Energy Efficient Two-Phase Micro-Cooler Design for a Concentrated Photovoltaic Triple Junction Cell
Authors: Reeser A. , Wang P. , Bar-Cohen A. , Hetsroni G.
Published: October 2013

This paper investigates the potential application of an R134a-cooled two-phase micro/mini-cooler for thermal management of a triple junction solar cell under 2000 suns concentration. An analytical model for the triple-junction solar cell temperature based on prediction of two-phase flow boiling in mini/microchannel coolers is developed and exercised with empirical correlations from the open literature for the heat transfer coefficient, pressure drop, and critical heat flux. The thermofluid analysis is augmented by detailed energy modeling, using two uniquely defined coefficient of performance metrics — COP relating the solar energy harvest to pumping power consumption and COPT relating the solar energy harvest to the “parasitic” work expended to provide the requisite cooling, including pumping power and the energy consumed in the formation and fabrication of the microcooler itself. Three constant fin thicknesses of 100μm, 300μm and 500μm are examined for a range of R134a flow rates and geometries to determine the energy efficient design for a 10mm×10mm triple junction CPV cell. The results reveal that two-phase cooling of CPV’s can achieve very high COPT values, substantially exceeding 104 for much of the design space of interest, though the energy efficiency is dependent on microcooler geometry and the number or pitch of the microcooler channels.
Micro Solar Thermal Collector Glazing for Enhanced Thermal Energy Harvesting
Authors: Ogbonnaya E. , Weiss L.
Published: October 2013

Increasing focus on alternative energy sources has produced significant progress across a wide variety of research areas. One particular area of interest has been solar energy. This has been true on both large and small-scale applications. Research in this paper presents investigations into a small-scale solar thermal collector. This approach is divergent from traditional micro solar photovoltaic devices, relying on transforming incoming solar energy to heat for use by devices like thermoelectrics.

The Solar Thermal Collector (STC) is constructed using a copper collector plate with electroplated tin-nickel selective coating atop the collector surface. Further, a unique top piece is added to trap thermal energy and reduce convective, conductive, and radiative losses to the surrounding environment. Results show a capture efficiency of 92% for a collector plate alone when exposed to a 1000 W/m2 simulated solar source. The addition of the top “glazing” piece improves capture efficiency to 97%.

Future work will integrate these unique devices with thermoelectric generators for electric power production. This will yield a fully autonomous system, capable of powering small sensors or other devices in remote locations or supplementing existing devices with renewable energy.
Fabrication and Characterization of a Metal-Based Micro-Heat Exchanger by Electrodeposition Technique
Authors: Ogbonnaya E. , Weiss L.
Published: October 2013

The investigation of a small-scale, MEMS-based heat exchanger is reported in this work. The Exchanger is based on capillary action and is designed for use in low-temperature thermal energy scavenging applications. The device is a microfabricated design, employing unique nickel channels for capillary effect.

Fabrication of the nickel channels is based on processes that pattern and develop SU-8 negative photoresist on the substrate. Electroplating is then used to form metal channels between the bounding SU-8 structures. The removal of the SU-8 leaves only the metallic channels behind. Channels are fabricated to heights of 115 μm using these methods. The operation of this micro heat exchanger (MHE) is compared to other exchangers fabricated with SU-8 channels.

Working fluid mass transfer rate from the heated MHE is utilized as a basic metric of operation. The mass transfer rate recorded from the nickel-based MHE is 2.51 mg/s. By contrast, an MHE fabricated with 150 μm tall SU-8 channels is shown to evaporate up to 3.01 mg/s. This translates into an effective thermal power consumption rate of 1.92 kW/m2 and 2.28 kW/m2 for the nickel and SU-8 based MHE respectively. Investigations of working fluid contact angle with the electroplated nickel surface are also presented. The surface is found to be a porous structure stemming from the electroplating process.
The Influence of Transmission Ratios Selection on Electric Vehicle Motor Performance
Authors: Zhou X. X. , Walker P. D. , Zhang N. , Zhu B. , Ding F.
Published: October 2013

Increasingly electric vehicle design is looking forward the application of multiple ratio transmissions in place of traditional single ratio gearboxes. The choice of gear ratio has significant influence on vehicle performance, including range, acceleration, and gradeability. To study the impact of different transmissions on EV’s dynamic and economic performance, mathematical models of an EV is presented which is applicable to both single and multiple ratio transmissions. These transmission variants are then studied under different operating conditions to investigate how operating conditions in the motor work efficiency change with different transmissions. Here comparisons are made between 2-speed and single speed transmission. Then the reasons for the results are analysed.
Minimum Pumping Energy of Tree-Shaped Water Supply Networks for Probabilistic Demands in Built Environment
Authors: Wong L. T. , Mui K. W. , Cheung C. T.
Published: October 2013

Minimization of pumping energy is a major concern for designing sustainable water supply in buildings. Modular designs of tree-shaped water supply piping system, such as 2 by N array include water cisterns of water closet in public toilets, washbasin taps in schools are commonly found in building complexes. Potable water demands in water systems serving built environment are unsteady, random and intermittent. However, the existing statistical Hunter-based probabilistic approaches to pipe sizing, however, do not consider the minimization of pumping energy for water distribution through proper selection of pipe radii.

This paper demonstrates a pipe sizing method with probabilistic demands for optimizing pipe friction energy loss constrained by the fixed pipeline volume. A mathematical model for pumping energy optimization in infinite tree-shape water supply piping networks for probabilistic demands is proposed. Compared with the Hunter’s based probabilistic approach in sizing an 8-section tree-shape water supply network for demand of probabilities 0.1 and 0.2, the proposed method offers reduction potentials of pipe friction energy loss of 12% and 43% respectively. With piping systems of pipe radius ratios, the optimal tree-shape networks are also determined.
Effects of Bubble Growth and Solidification Rate on Pore Formation in Solid
Authors: Wei P. S. , Hsiao S. Y.
Published: October 2013

The shapes of a pore in solid resulted from entrapment of a tiny bubble by a solidification front are predicted in this work. Pore formation and its shape in solid are one of the most critical factors affecting properties and microstructure, in materials. For simplicity without loss of generality, the tiny bubble is considered to have a spherical cap. From a geometrical analysis, the contact angle of the bubble cap on the solidification front or the pore shape in solid is found to be governed by the Abel equation of the first kind. The pore becomes closed by imposing a finite bubble growth rate-to-solidification rate ratio which can produce a minimal bubble radius at the contact angle of 90 degrees. Closure of a pore resulted from a greater solidification rate than bubble growth rate, as accepted in the literature, is incorrect.
Friction Characteristics in Light Weight Design Focusing Bolted Joints
Authors: Kopfer H. , Friedrich C. , De Agostinis M. , Croccolo D.
Published: October 2013

Today more and more light weight structures are used for moved components in automotive, aviation and general industry. Often assemblies of these structures are realized by friction-based connections. Therefore precise information about the friction coefficients are necessary, because in light weight design no simple approximation of the loading capacity with significant over-dimensioning is possible. Furthermore, the short-time tribology of mechanical contacts plays an important role during tightening of bolted joints, especially when using light metals and coated surfaces.

Still today, the tightening method of torque controlled screw assembly is the most used. For this tightening method the friction coefficients have to be well-known for an efficient design of the bolted joint. Up to now analytical calculations do not consider any local deviation of friction behavior in component systems, only average values are taken. This is the reason why in modern engineering processes extended friction laws are necessary. A suitable formulation should take contact pressure and sliding velocity into account.

Based on this, the contribution shows experimental examples for main uncertainties of frictional behavior during tightening with different material combinations (results from assembly test stand).
The Effect of the Contact Model on the Design of Mechanical Systems
Authors: Brake M. R. , Aragon D. S. , VanGoethem D. J. , Sumali H.
Published: October 2013

Impact is a wide-spread phenomenon in mechanical systems that can have a significant effect on the system’s dynamics, stability, wear, and damage. The simulation of impact in complex, mechanical systems, however, is often too computationally intensive for high fidelity finite element analyses to be useful as design tools. As a result, rigid body dynamics and reduced order model simulations are often used, with the impact events modeled by ad hoc methods such as a constant coefficient of restitution or a penalty stiffness. The consequences of the choice of contact model are studied in this paper for a representative multiple-degrees of freedom mechanical system. Four contact models are considered in the analysis: a constant coefficient of restitution model, two similar elastic-plastic constitutive models, and one dissimilar elastic-plastic constitutive model. The predictions of wear, mechanical failure, and stability are assessed for each of the contact models, and the subsequent effect on the system design is investigated. These results emphasize the importance of choosing a realistic contact model when simulations are being used to drive the design of a system.
Robust Control Design for a Nanosat Launch Vehicle
Authors: Iriarte Estuardo , Lu Bei , Besnard Eric
Published: October 2013

The attitude control of a launch vehicle is a challenging task due to the dramatically varied vehicle dynamics along a flight path. The objective of this paper is to design robust controllers for a nanosat launch vehicle developed by California Launch Vehicle Education Initiative at California State University Long Beach. In order to control the rocket along a trajectory ascending through the earth’s atmosphere, a set of operating points at different times along the flight path are selected, the corresponding dynamics models of the rocket are obtained via linearization, and a robust H∞ controller is designed for each operating point. Simulations are conducted in Matlab/Simulink to verify if the proposed control law stabilizes the inherent, unstable pitching motions of the vehicle at different times.
Drag Reduction With Superhydrophobic Riblets
Authors: Barbier Charlotte , Jenner Elliot , D’Urso Brian
Published: October 2013

Samples combining riblets and superhydrophobic surfaces are fabricated at University of Pittsburgh and their drag reduction properties are studied at the Center for Nanophase Materials Sciences (CNMS) in Oak Ridge National Laboratory with a commercial cone-and-plate rheometer. In parallel to the experiments, numerical simulations are performed in order to estimate the slip length at high rotational speed. For each sample, a drag reduction of at least 5% is observed in both laminar and turbulent regime. At low rotational speed, drag reduction up to 30% is observed with a 1 mm deep grooved sample. As the rotational speed increases, a secondary flow develops causing a slight decrease in drag reductions. However, drag reduction above 15% is still observed for the large grooved samples. In the turbulent regime, the 100 μm grooved sample becomes more efficient than the other samples in drag reduction and manages to sustain a drag reduction above 15%. Using the simulations, the slip length of the 100 μm grooved sample is estimated to be slightly above 100 μm in the turbulent regime.
Parameter Identification in Ecological Systems via Discontinuous and Singular Control Regimes
Authors: McDonald Dale B. , Falade Joseph O.
Published: October 2013

Policy decisions regarding commercial harvesting of aquatic species by (typically governmental) regulatory agencies are often based in part upon field data, simulation results, and mathematical models. Regulatory agencies may limit or expand seasons, determine total harvest allowed, increase or decrease licensure fees, and raise or lower taxation rates in response to the state of the ecological system. Ultimately, the regulatory agency uses such measures to ensure viable populations in an attempt to balance ecosystem health and benefits for society. Such decisions impact commercial fishing ventures affecting the nature of harvesting efforts and their intensity. Conclusions drawn from mathematical models of ecological systems, and derived simulation results which affect this reality are highly dependent upon the validity of information available. Knowledge or estimates of critical parameters such as intrinsic growth rate, carrying capacity, etc. and dynamic variables such as biomass levels dictate the usefulness of analytical and numerical analyses. The purpose of this treatment is to illustrate that control laws applied to mathematical models of species dynamics may be used to discern estimates of parameters that inherently exist in such models in an effort to provide more valuable information upon which to base policy decisions. Dynamic models of both single-species evolution and predator-prey interactions are examined.
2-DOF Planar Motion Control System Using Model Reference Adaptive Control (MRAC) Algorithm
Authors: Luk Andrew M. Y. , Fung Eric H. K. , Gan W. C.
Published: October 2013

This paper reports the application of Model Reference Adaptive Control (MRAC) to an X-Y planar motion mechanism. A flexure-based 2-DOF planar motion platform is first developed for the wafer probing purpose and a planar Voice Coil Motor (VCM) is used for driving the mechanism and the flexural bearings. The dynamics of the motion platform is governed by a set of differential equations using the mass-spring-damper model and the Kirchhoff’s circuit laws. Due to the non-linearity of the force constant and the coupling effect of the VCM, a MRAC algorithm is proposed to implement on the motion control system so as to improve the system transient response. In order to guarantee the stability of the Model Reference Adaptive System (MRAS), Lyapunov Theory is adopted in the controller design. The control system performance is simulated using MATLAB /SIMULINK with the considerations of the motor non-linearity and the assembly variation of the flexural mechanism. On the other hand, a conventional PID controller is also constructed for control experiments to compare the transient responses between MRAC and PID control systems. Simulation results revealed that the proposed MRAS outperforms the PID controller for the 2 DOF planar motion system in the presence of sensor noise, disturbing force and parameter variation effects.
H
∞ Based Adaptive Fuzzy Control of a Tower Crane System
Authors: Karkoub Mansour , Wu Tzu Sung , Chen Chien Ting
Published: October 2013

Tower cranes are very complex mechanical systems and have been the subject of research investigations for several decades. Research on tower cranes has focused on the development of dynamical models (linear and nonlinear) as well as control techniques to reduce the swaying of the payload. Inherently, the dynamical model of the tower crane is highly nonlinear and classified as under-actuated. The crane system has potentially six degrees of freedom but only three actuators. Also, the actuators are far from the payload which makes the system non-colocated. The dynamic model describing the motion of the payload from point to point is affected by uncertainties, time delays and external disturbances which may lead to inaccurate positioning, reduce safety and efficacy of the overall system. It is proposed here to use an H∞ based adaptive fuzzy control technique to control the swaying motion of a tower crane. This technique will overcome modeling inaccuracies, such as drag and friction losses, effect of time delayed disturbances, as well as parameter uncertainties. The proposed control law for payload positioning is based on indirect adaptive fuzzy control. A fuzzy model is used to approximate the dynamics of the tower crane; then, an indirect adaptive fuzzy scheme is developed for overriding the nonlinearities and time delays. The advantage of employing an adaptive fuzzy system is the use of linear analytical results instead of estimating nonlinear system functions with an online update law. The adaptive fuzzy scheme fuses a Variable Structure (VS) scheme to resolve the system uncertainties, and the external disturbances such that H∞ tracking performance is achieved. A control law is derived based on a Lyapunov criterion and the Riccati-inequality to compensate for the effect of the external disturbances on tracking error so that all states of the system are uniformly ultimately bounded (UUB). Therefore, the effect can be reduced to any prescribed level to achieve H∞ tracking performance. Simulations are presented here to illustrate the performance of the proposed control design.
Analysis for Stress Singular Fields Near a Wedge Corner in 2D Joints Considering Interface Stress and Interface Elasticity
Authors: Koguchi Hideo , Kato Osamu
Published: October 2013

Surface stress and surface elasticity are related to an organization of surface morphology, surface pattern and surface atomic structures. As a size of structure reduces to a nanometer level, a ratio of its surface to volume increases. Generally, surface energy in deformable solids depends on surface strain. Surface stress and elasticity influence on the distribution of bulk stress near the surface. Interface stress and elasticity also exist in an interface of materials and characterize interface properties. In this study, singular stress at a wedge corner in an anisotropic 2D joint under a tensile loading is analyzed using molecular dynamic (MD) method and the anisotropic elasticity theory using the boundary condition with interface stress and interface elasticity. Interface stress and interface elasticity are obtained through the MD analysis. In the case of 2D joint. the obtained interface stress and elasticity depend on the distance from the wedge corner. The stress field around the wedge corner obtained by the MD analysis had a larger value of order of singularity than a value predicted from the ordinary boundary condition at the interface. In the analysis of anisotropic elasticity, eigenequation for determining the order of stress singularity is newly derived using the boundary condition with interface stress and interface elasticity. The order of stress singularity varies with the distance from the wedge corner. The stress distribution near the wedge corner can be approximated using the relation between the order of stress singularity and the distance from the wedge corner.
On Free Vibration of Functionally Graded Euler-Bernoulli Beam Models Based on the Non-Local Theory
Authors: Moheimani Reza , Ahmadian M. T.
Published: October 2013

In this paper, the governing equations and boundary conditions of a functionally graded Euler-Bernoulli beam are developed based on the non-local theory of elasticity. Afterward, the free vibration is investigated and the effects of the axial load, the non-local parameter and the power index on the natural frequency of a hinged-hinged beam is assessed. The results indicate that the non-local parameter has a decreasing effect on the frequency while the power index has an increasing effect. It is also noted that the effect of the axial load is increasing too.
Opto-Mechanical Actuation of Carbon Nanotube/Polymer Composite Membranes for Microfluidic Pumping Applications
Authors: LaPrade Bennie , Panchapakesan Balaji , Williams Stuart J.
Published: October 2013

In this work, we characterize the laser induced, opto-mechanical actuation of carbon nanotube (CNT)/polymer composite membranes for use in microfluidic pumping applications. Until recently, the use of opto-mechanical actuation in the field of microfluidics had not been realized [1]. This novel form of actuation offers distinct advantages over conventional external and integrated microfluidic pump actuators. Of particular interest are the abilities to decouple the pump and actuation mechanisms and wirelessly actuate microfluidic pumps. This research utilizes previously demonstrated fabrication methods to produce and test CNT/Polydimethylsiloxane (PDMS) polymer pump membranes [1]. By varying the thickness of the CNT film layer within composite pump membranes, and by adjusting the laser intensity used to actuate the membranes, the deflection of microfluidic pump membranes can be tuned to achieve precise volume displacement and pumping volumes.
Bridge Dynamics for Capillary-Based Liquid Deposition
Authors: Lutfurakhmanov Artur , Wang Yechun , Schulz Douglas L.
Published: October 2013

A new capillary-based lithography technique of liquid droplet deposition is further developed. Main advantage of this method in comparison with others techniques is that it is non-invasive both to the substrate and to the writing tip. The method is studied both theoretically and experimentally. To adequately describe bridge dynamics between the capillary and the substrate, proper boundary conditions must be set in the model for the liquid-surface interface. Based on literature review, two laws of contact line motion are identified: Tanner’s law and Blake’s equation. These two approaches are tested in multiple experiments with different retraction speeds from 3 microns/s to 300 microns/s. Analysis of the experimental data show that both Tanner’s and Blake’s equation can describe the correlation between the contact line velocity and the dynamic contact angle. In addition, both laws are employed in the direct numerical simulation of the bridge dynamics using 3D spectral boundary element method. Modeling results are compared with experimental data and show good agreement.
Combustion Characteristics of Small Isolated Methanol Droplets
Authors: Awasthi Inkant , Gogos George , Sundararajan Thirumalachari
Published: October 2013

The paper presents a transient, axisymmetric numerical simulation of combustion of methanol droplets in a nearly quiescent environment (with ambient temperature of 1200 K, ambient pressure of 1 atm., and Reynolds number of 10−2). The focus is on the combustion process of droplet sizes applicable in a practical spray. A gradual transition from kinetically controlled combustion to diffusion controlled combustion is found with the increase in droplet sizes. Droplets smaller than ≈ 60 μm are influenced more by chemical kinetics due to the reaction zone broadening and a concomitant reduction in flame temperatures. In this kinetically controlled regime, the burning rate of an individual droplet first increases to a maximum, and then decreases. In this regime, the average of droplet burning rate over its life time is bounded by an upper bound of thin flame-sheet burning rate (large Damköhler number limit), and a lower bound of pure evaporation rate (small Damköhler number limit). The actual average burning rate lies between the two values, determined by the droplet size. For droplets smaller than ≈ 60 μm, the flame stand-off ratio varies throughout their lifetime. The analysis underlines the importance of accurate chemical kinetics modelling for small droplets.
Evaluation of Droplet Sizing Methods for Aerosols
Authors: Brizio P. J. , Protheroe M. D. , Al-Jumaily A. M.
Published: October 2013

Three methods of determining the droplet size distribution in aerosols are investigated. These are based on using photography, impact/capture and optics, respectively, to determine the droplet size distribution in an air-water aerosol produced from an ultrasonic atomization device. Comparison is made between these methods based on the required procedure, equipment used and results obtained. An optical method, based on laser diffraction, stands out in terms of accuracy and ease of use although it requires relatively expensive equipment.
Computational Modeling of a Novel Mitral Valve Stent
Authors: Kumar Gideon Praveen , Fangsen Cui , Danpinid Asawinee , Wei Chan Zhi , Boyang Su , Liang Leo Hwa , Hon Jimmy Kim Fatt
Published: October 2013

Although percutaneous heart valve replacement is getting known amongst cardiovascular surgical procedures, as it was recently introduced, and reports of early clinical experience been published, this technique is limited to the replacement of pulmonary and aortic valves in old patients who cannot undergo open heart surgery. One of the reasons is the uphill challenges in the generation of an ideal design that would address anchorage and leakage issues. Stent anchorage and paravalvular leaks prove to the greatest challenge posed to biomedical design engineers. This paper describes a novel Nitinol based mitral valve stent that addresses migration and paravalvular leaks associated with the bioprosthetic mitral valve. The geometry-based model presented here specifically addresses issues of valve migration and paravalvular leaks This is of great interest to designers of new prosthetic heart valve models, as well as to surgeons involved in valve sparing surgery. Simulation results show that the studied stent design seemed to be good by virtue of its acceptable maximum crimping strain.