bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Load Carrying Capacity of Three and Four Lobed Polygonal Shaft and Hub Connection for Constant Grinding Diameter
Authors: Bhatta Ravi , Reffeor Wendy
Published: February 2017

Polygonal shafts are used in power transmission as alternatives to keyed and splined shafts. They are designed using DIN standards. This research explores the loading strength of the standardized three lobed (P3G) and four lobed (P4C) polygonal shafts and hubs manufactured from the same stock size, subjected to torsional bending load at various fits. Due to complex conformal contact (nonlinear model) between the shaft and the hub, there is no analytical solution and, therefore, Finite Element Method had been used to determine the stresses, after validating experimentally and using the DIN standard. From the analysis, it was found that the hub experienced greater stress than the shaft in all cases and the major stress in a polygonal shaft and hub connection is the contact stress. The clearance fit was found to be the most detrimental fit and the interference fit to be the most suitable for larger power transmission. Owing to its small normal axial stress and hub displacement, the P4C clearance fit has its use in low power transmission where a sliding fit is a requirement. The maximum von Mises stress was located below the surface for P4C and P3G clearance fit, suggesting failure from pitting and fretting on these shafts. All of the stresses were found to be higher in P4C than P3G for similar loading. Therefore, for general use, the P3G profile with an interference fit is recommended.
Energy Absorption Optimization of GFRP Laminate by Considering Inner-Lamina Damage Model With Parameter Identification
Authors: Zhan Bowen , Sun Lingyu , Huang Bincheng , Shen Le
Published: February 2017

In order to improve the simulation accuracy of composite tube crush by finite element method, a nonlinear progressive damage model predicting the progressive inner-lamina damage of laminates is implemented. Each element of FEM is defined by the model. All parameters in this model were identified according to the published test data. The longitudinal crush was simulated by the solver of ABAQUS /explicit using the nonlinear progressive model. The result shows that the failure form pattern, peak force and energy absorption fit well with the published experimental ones. The robust optimization based on Six sigma technology and probability distribution of design variables is carried out to obtain an improved energy absorption property instead of deterministic optimization. This method can obtain an optimal composite tube with stable high energy absorption capability in a practical manufacture process.
A Method of Predicting Effective Interface Properties of Polymer-Metal Hybrid Structures by Molecular Dynamics
Authors: Yang Wu , Sun Lingyu , Yu Hong , Li Lijun , Shen Le , Yin Sha
Published: February 2017

The interface phase of the Polymer-Metal Hybrid (PMH) structures is formed due to the diffusion of nearby molecular, whose mechanical properties are different from pure metal or polymer, and is possibly the weakest layer. However, it is difficult to measure the interface parameters, such as the thickness and elastic modulus. When the property of PMH structure is predicted by finite element method, it would result in potential simulation errors if the interface is ignored. This study presents a new method to predict the effective interface properties of PMH Structures by Molecular Dynamics (MD) method. The interface formation process in over-molded injection of Polypropylene (PP) on the stamped steel surface was simulated by MD. The effective interface thickness between Iron (Fe) and PP is defined and calculated to be 0.63nm or so and the elastic modulus vertical to the interface is about 6.55GPa. The proposed approach is especially suitable for performance prediction of PMH structure before the physical specimen is manufactured. The predicted results could be utilized in finite element simulation at micro-scale.
Method of Fundamental Solutions in Micromechanics of Random Structure Linear Elastic Composites
Authors: Buryachenko Valeriy A.
Published: February 2017

One considers a linear elastic composite material (CM, [1]), which consists of a homogeneous matrix containing the random set of heterogeneities. An operator form of the general integral equation (GIE, [2–6]) connecting the stress and strain fields in the point being considered and the surrounding points are obtained for the random fields of inclusions in the infinite media. The new GIE is presented in a general form of perturbations introduced by the heterogeneities and defined at the inclusion interface by the unknown fields of both the displacement and traction. The method of obtaining of the GIE is based on a centering procedure of subtraction from both sides of a new initial integral equation their statistical averages obtained without any auxiliary assumptions such as the effective field hypothesis (EFH), which is implicitly exploited in the known centering methods. One proves the absolute convergence of the proposed GIEs, and some particular cases, asymptotic representations, and simplifications of proposed GIEs are presented for the particular constitutive equations of linear thermoelasticity. In particular, we use a meshfree method [7] based on fundamental solutions basis functions for a transmission problem in linear elasticity. Numerical results were obtained for 2D CMs reinforced by noncanonical inclusions.
CFD Simulation of Highway Contaminant Dispersion
Authors: Gong Liyuan , Wang Xiuling
Published: February 2017

Vehicle emissions have been considered as a main source of air pollution contaminants. Air pollution is a severe problem which could cause many health issues, such as respiratory, infections, lung cancer, and heart disease, according to the World Health Organization (WHO). In urban area, highway transportation is the main and busy traffic that contains all types of vehicles and release multiple pollutants. Studies of highway contaminants influence have been carried out by different methods, such as field study, wind tunnel and computational fluid dynamics (CFD). Among all the methods, CFD is respectively both economical and accurate. For CFD method, in order to have a most accurate results, all the factors including terrain, wind profile, and other features in the studied area should be included. In this study, noise barrier effect is the main feature being analyzed. Different barrier heights were modelled and simulated in order to see the effect of barrier height. Situations with and without barriers were compared to get the general influence of noise barriers. Simulations were accomplished by using commercial software ANSYS 15.0. Simulated species are nitrogen oxides (NOx), including NO and NO2, carbon monoxide (CO). Double barriers configuration were modelled. A model of local high school system was built to see the difference of concentration in far wake region behind the barriers. Comparison has been made between with and without barriers. As the results of this study, a significant reduction was found in far wake area due to noise barriers. Effected flow distribution and contaminants concentration was found due to different barriers heights. Flow distribution and pollutants concentration has been depicted and analyzed. The effect has been analyzed by studying flow and wind velocity distribution.
Molecular Dynamics Study of Contact Line Dynamics of Water Droplets on PTFE Surfaces
Authors: Zhao Lei , Cheng Jiangtao
Published: February 2017

Although wetting dynamics of liquids on solid surfaces has been studied for decades, via both experimental investigation and theoretical analyses, the physical mechanism still remains obscure. One of the major difficulties is that wetting dynamics is actually dominated by interfacial reactions at the molecular level. In this study, the dynamic contact angle and contact line deformation of a water droplet on a well-confined amorphous polytetrafluoroethylene (PTFE) surface was examined by molecular dynamics (MD) simulation. The force field parameters of PTFE structures were based on the OPLSAA force field in Gromacs 5.1.2. Our MD simulation yielded a satisfactory glass transition temperature of 118.8°C. A confined-layer method was used to construct a flat PTFE surface by smoothing out the intrusion or extrusion-induced roughness. Four cases for water droplets with different diameters were simulated. The static contact angle of water droplets was found to be ∼110.6° on PTFE. An exponential relationship was verified to describe the contact area development in the wetting process. By comparing our MD results with the hydrodynamics theory and molecular kinetics (MKT) theory, the viscous and molecular friction coefficients were determined to be on the order of 10−4kg/m · s. The MKT theory demonstrates excellent agreement with our MD results in the whole range of contact line velocity, while slight deviation exists in fitting hydrodynamics theory to high contact line velocity region. For the first time, a dimensionless number Nt was proposed to quantify the relative fluctuations of contact line velocity in this study.
Effect on Sound Source Drift Caused by Angles Between Jet Flow Direction and Microphone Array or Sound Source Plane
Authors: Shen Zhe , Wang Yigang , Yang Zhigang
Published: February 2017

When sound generated in jet flow propagates to outside of flow field, direction of sound propagation changes because of wave convection and refraction of shear layer. In wind tunnel, sound source drift appears when sound source is located with out-flow microphone array based on beamforming algorithm. In some cases, angles between jet flow direction and microphone array or sound source plane are inevitable due to geometric position, which increases the number of parameters affecting sound source drift distance. Geometrical acoustics and basic beamforming algorithm were used in this paper to deduce the relation between sound source drift and the angles. Equations for drift prediction and method for error reduction were given. Experimental verification was completed in a full-scale aero-acoustic wind tunnel with 2 loudspeakers set on an auto-body surface and microphone array with 120 channels. The experimental results prove that the equations for sound drift prediction in complicated geometric position relationship have a high accuracy, could help quick locating sound sources in engineering application.
Static and Dynamic Amplification Using Strong Mechanical Coupling
Authors: Ilyas Saad , Jaber Nizar , Younis Mohammad I.
Published: February 2017

Amplifying the signal-to-noise ratio of resonant sensors is vital toward the effort to miniaturize devices into the sub-micro and nano regimes. In this work, we demonstrate theoretically and experimentally amplification through mechanically coupled microbeams. The device is composed of two identical clamped-clamped beams, made of polyimide, connected at their middle through a third beam, which acts as a mechanical coupler. Each of the clamped-clamped microbeams and the coupler are designed to be actuated separately, hence providing different possibilities of actuation and sensing. The coupled system is driven into resonance near its first resonance mode and its dynamics is explored via frequency sweeps. The results show significant amplification in the resonator’s amplitude when the signal is measured at the midpoint of the coupler, compared to the response of the individual uncoupled beams. The static pull-in characteristics of the system are also studied. It is shown that the compliant mechanical coupler can serve as a low-power RF switch actuated at low voltage loads.
Vortex Shedding Control on a Three-Dimensional Ground Vehicle With Synthetic Jets
Authors: Cui Wenshi , Yang Zhigang , Wang Guojun , Zhou Hua
Published: February 2017

The study is mainly focused on the influence of the vortex shedding control of a three-dimensional ground vehicle by using synthetic jet actuators based on Large-eddy simulation. Excitation parameters for synthetic jet actuators, such as the excitation frequency, momentum coefficient and jet location, have an influence on vortex shedding control process, which lead to different unsteady flow phenomenon, vortex shedding frequency value and space distribution in the wake. Vortex shedding suppression and vortex-synchronization phenomenon have an influence on the pressure. Under present momentum coefficient, the excitation frequency plays an important role in the occurrence of vortex-synchronization phenomenon behind vertical base. As the momentum coefficient increase, the vortex-synchronization zone expands.
Effects of Elastic Deformation and Corrugation Potential on Friction of Suspended Graphene
Authors: Dong Yun , Duan Zaoqi , Gueye Birahima , Cai Shuang , Zhang Yan , Chen Yunfei
Published: February 2017

In this paper, based on molecular dynamics simulation method, the authors construct a graphene flake sliding on a suspended graphene layer which is anchored on a bed of springs. This graphene-spring system provides an ideal model to replace the multilayer graphene under the top layer. We firstly mimic different layers of suspended graphene through changing the stiffness of spring bed; then the contributions of Van der Waals force of the tip and elastic deformation of the top layer supported by spring bed to friction force are analyzed; finally, an energy dissipation mechanism based on the amount of corrugation potential energy and sample deformation elastic energy is proposed. It is demonstrated that the effects of energy barrier and surface compliance are directly related to the observed friction force. It is helpful to achieve a theoretical basis for the design of graphene-based nano electromechanical systems (NEMS) devices.
Development of IKVAV Modified PLLA Guide Tube Having Unidirectional Fibers on Inner Surface to Enhance Axonal Extension
Authors: Akizawa Y. , Morita Y. , Hsu Y. , Yamaoka T. , Nakamachi E.
Published: February 2017

The bi-layer poly-L-lactic acid (PLLA) guide tube for peripheral nerve regeneration was developed by electrospinning method to enhance axonal extension. The inner layer of the guide tube had unidirectional nanofiber and Ile-Lys-Val-Ala-Val (IKVAV) modified surface. IKVAV modified unidirectional fiber sheets which had different fiber diameters from 400 to 1200 nm were fabricated to optimize fiber diameter of the guide tube for axonal extension. Fiber sheets without the IKVAV were prepared as the control group. PC12 cells seeded on the fiber sheets were cultured for 6 days. Axons were most extended in fiber diameter of 1090 nm with IKVAV and 1160 nm without IKVAV. Maximum axon length increased by about 25% due to IKVAV modification. The bi-layer guide tube which had fiber diameter about 1133 nm was fabricated. It was confirmed that the inner layer had unidirectional fibers and the outer layer had random fibers in the guide tube. CS, which corresponds to radial compressive stiffness, of the guide tube and the sciatic nerve were 230 N/mm2 and 1.64 N/mm2 respectively. Since radial compressive stiffness of the guide tube was higher than that of the sciatic nerve, the developed guide tube was expected to enhance axonal extension without narrowing.
Nonlinear Stability Analysis of a Macroscopic Traffic Flow Model for Adaptive Cruise Control Systems
Authors: Porfyri Kallirroi N. , Nikolos Ioannis K. , Delis Anargiros I. , Papageorgiou Markos
Published: February 2017

The occurrence of perturbations in traffic flow may lead to the formation of stop-and-go waves traveling upstream, or to traffic jams. Therefore, traffic flow stability analysis is considered to be one of the fundamental problems in traffic flow theory, and a lot of effort has been spent to analyze the formation and evolution of such traffic flow instabilities. Recent advances in the field of Vehicle Automation and Communication Systems (VACS), including the most widespread Adaptive Cruise Control (ACC) systems, may consist a possible solution in reducing the magnitude or even eradicating the development of such traffic flow instabilities. This paper aims to perform a nonlinear stability analysis of a second-order macroscopic traffic flow model, which was recently developed by the authors for the simulation of the traffic flow of ACC-equipped vehicles, and identify the ways that ACC systems affect the stability of the flow, in relation with large traffic disturbances around the equilibrium state. Numerical simulations are additionally conducted, to validate the derived stability conditions.
A MoS2 Field-Effect Transistor With a Liquid Back Gate
Authors: Lin Kabin , Yuan Zhishan , Yu Yu , Li Kun , Yang Haojie , He Pinyao , Ma Jian , Sha Jingjie , Chen Yunfei
Published: February 2017

The two-dimensional layer of Molybdenum disulfide (MoS2) has attracted much interest due to its direct-gap property and potential applications in the field of catalysis, nanotribology, microelectronics, lithium batteries, hydrogen storage, medical, high-performance flexible electronics and optoelectronics. In this paper, based on few-layer MoS2 acquired by mechanical exfoliation method, a MoS2 liquid-gated field effect transistor (L-FET) is fabricated. Simultaneously, the few-layer MoS2 is characterized by Raman spectral. Then, the performance of MoS2-based L-FET devices is investigated by a source meter instrument in the different back gate voltage of 0.1mol/L NaCl solution. The result reveals that the Schottky barriers is formed between platinum and few-layer MoS2 and the back gate voltage has a great control effect with the drain-to-source current of MoS2 field effect transistor.
Research on Function Reliability of Gear Door Lock System With Correlated Failure Models Based on Mixed Copula
Authors: Shen Linjie , Zhang Yugang , Zhuang Xinchen
Published: February 2017

The gear door lock system (GDLS) is a mechanism with multi-failure modes. It often leads to a large error when ignoring the correlation between failure modes. Copula theory in this work is applied to research the correlation between two failure modes. A dynamic simulation model is constructed to acquire the joint statistics characteristics of the two failure modes. Gumbel and Clayton Copula functions are chosen to establish the reliability model respectively, which shows that the single Copula model cannot fully capture the tail dependence. To solve the problem, a mixed Copula function is constructed. The minimum squared Euclidean distance is adopted to estimate the parameters of the reliability models. It shows that the result of mixed Copula model is the closest to that of the Monte Carlo simulation, and it presents the relative error is at least 46% lower than the single Copula.
RELAP5 Code Analysis of LSTF Small Break LOCA Tests With Steam Generator Intentional Depressurization and its Uncertainty Quantification by Monte Carlo Method and Wilks Formula Approach
Authors: Kinoshita Ikuo , Murase Michio
Published: February 2017

The Best Estimate Plus Uncertainty (BEPU) method has been applied by the authors to analysis of the “intentional depressurization of steam generator secondary side” which is an accident management procedure in a small break loss-of-coolant accident with high pressure injection system failure. In the present study, experimental analyses using the RELAP5/MOD3.2 code were carried out for the ROSA/Large Scale Test Facility (LSTF) secondary-side depressurization tests. The two test cases were selected with different break sizes and different depressurization conditions to ensure the reliability for the accident scenario analyses. The uncertainty propagation analyses were performed through the random variations of input parameters whose uncertainty ranges and distributions were determined previously by the PIRT and the separate effects tests. One thousand random calculations were conducted to get the 95% upper limit values of the peak cladding temperature (PCT) by the Monte Carlo method. Furthermore, the 95%/95% tolerance limits for the PCT were obtained according to Wilks formula. It was confirmed that the code predicted well the major event progressions such as rod surface temperature and the 95% uncertainty bands included the measured values. Furthermore, the 95% upper limit values of the PCT are below the 95%/95% tolerance limit values. However, the statistical fluctuation of the tolerance limit values by Wilks first order formula is as large as the uncertainty value itself. The statistical fluctuation decreases with increasing order of Wilk formula. It is desirable to increase the order of Wilks formula to more than the second order to get the reliable safety margin.
Dropwise Condensation on Carbon Steel Surface
Authors: Cao Fangyu , Hoenig Sean , Chen Chien-hua
Published: February 2017

The increasing demand of heat dissipation in power plants has pushed the limits of current two-phase thermal technologies such as heat pipes and vapor chambers. One of the most obvious areas for thermal improvement is centered on the high heat flux condensers including improved evaporators, thermal interfaces, etc, with low cost materials and surface treatment. Dropwise condensation has shown the ability to increase condensation heat transfer coefficient by an order of magnitude over conventional filmwise condensation. Current dropwise condensation research is focused on Cu and other special metals, the cost of which limits its application in the scale of commercial power plants. Presented here is a general use of self-assembled monolayer coatings to promote dropwise condensation on low-cost steel-based surfaces. Together with inhibitors in the working fluid, the surface of condenser is protected by hydrophobic coating, and the condensation heat transfer is promoted on carbon steel surfaces.
Behavior Evaluation of Deformation, Damage and Fracture of Biological Soft Tissue by Using Indentation Test
Authors: Sakuma Atsushi , Igarashi Katsuya
Published: February 2017

In this study, two types of indentation tests were used for the observation of deformation behavior of biological soft tissue, because indentation testing is an easy method to manage observation and control of the condition of complex tissue specimens. First, a fundamental indentation test was used to evaluate quasi-static deformation behavior of soft tissue. In the evaluation of the quasi-static behavior, elasticity, damage, and fracture of the tissue were analyzed from the profile of reaction force during the indentation. Ball-impact testing with subsonic indentation velocity was used for the evaluation of dynamic behaviors of soft tissue. In the impact test, the viscoelastic characteristics of specimens were evaluated by analyzing stress response, using extended Hertzian contact theory and wave equations, at the moment when a simple ball bullet shot from an airsoft gun strikes the specimen. In the experimental results of the test, an obvious relationship between quasi-static and impact responses of the specimen were observed subjectively. The results are evaluated to analyze the damage and the fracture of the soft tissue for the objective formulation of tissue mechanics. The plateau behavior of reaction force in relation to stress response was also reviewed, in order to quantify the beginning of tissue fracture.
Heat Transfer and Hydraulic Characteristics of Cooling Water in a Flat Plate Heat Sink for High Heat Flux IGBT
Authors: Chen Chang-Nian , Han Ji-Tian , Gong Wei-Ping , Jen Tien-Chien
Published: February 2017

High heat flux is very dangerous for electronic heat transfer, such as IGBT (Insulated Gate Bipolar Transistor) cooling. In order to explore and master the heat transfer and hydraulic characteristics for IGBT cooling, experiments have been carried out to study the situation mentioned above in a flat plate heat sink, which was designed for high heat flux IGBT cooling. The geometrical parameters of the test section are as follows: outline dimension 229 mm × 124 mm × 30 mm; flow channels of 229 mm × 3 mm × 4 mm in total of 20. The experiments performed at atmospheric pressure and with inlet temperatures of 25–35°C, heat fluxes of 3.5–18.9 kW/m2. The influence of temperatures, heat fluxes on IGBT surface temperature and the cooling effect of the liquid cold plate have been investigated under a range of flow rates of 280–2300 kg/m2s. It was found that the heat transfer enhancement was very obvious using this kind of small sized channel for IGBT cooling, which was tens of times of the effect than air cooling or triple of the effect than that in normal sized channels. And the heat transfer enhancement increases with increasing heat fluxes and flow rates, while it decreases with increasing inlet temperatures. Most of the experimental results show good cooling effect as expected. However, it is dangerous for the cooling system under high heat fluxes when the system starts or stops suddenly, when the Respond Time (RT) is less than 5 seconds to cut off heated power. Also, the cooling performance is bad when the heat fluxes increased greatly, which is considered as abnormal situation in operating. The effect on IGBT surface temperature of heat flux is more obvious when the average Nusselt Number is smaller. For hydraulic characteristics observed, it was found that the flow friction increased with flow rates increasing, but the pressure drops of heated flow channels ahead were slightly larger than those back, especially under large flow rates conditions. That is because the temperatures of flow heated in channels ahead are lower than those back, which causes the fluid viscosity to be higher. At last, this paper suggested a series of method for enhancing heat transfer in flat plate heat sink, and also gave some ways to avoid heat transfer dangerous situations for IGBT cooling, which can provide a basis for thermodynamic and hydraulic calculation of flat plate heat sink design and lectotype.
Boom Lift Operator Protection From Stored Energy Hazards
Authors: Pierce William H. , Railsback Ben T.
Published: February 2017

Boom lifts are useful throughout a variety of industries, such as manufacturing, maintenance service, real estate management, and construction. Boom lifts are designed to allow operator mobility at high elevations and are often used as a substitute for traditional ladders, man-baskets on lift trucks and scaffolding. Although boom lifts are very practical and efficient in allowing personnel to work at high elevations and in areas with limited access, several known hazards exist with boom lifts such as falls, machine tipping, crushes, collapse of machine and electrocution.

Although boom lift operator manuals and safety literature discuss the aforementioned hazards, they do not or incompletely discuss the hazard of suddenly released stored energy when stored energy is rapidly converted from potential energy to kinetic energy through the boom to the operator platform.

One example of rapid conversion of potential energy to kinetic energy involves the boom lift driven over a sudden drop off such as a curb. A relatively low drop off can be amplified substantially by the lever arm of the boom, and as a result, the operator platform and operator(s) within, rapidly accelerate. A second example is when the operator platform is snagged on an external structure and continued hydraulic movement builds up potential energy within the boom. The buildup of potential energy can suddenly and unexpectedly release if the platform springs free from entanglement with the structure. Such release results in the boom, the platform, and the operator(s) rapidly accelerating.

During the rapid acceleration experienced in both examples, operators can potentially be and have historically been violently thrown against the railing of the platform, ejected from the platform, and/or crushed by any nearby overhead obstacles.

The purpose of this paper is to address, analytically quantify, and propose engineering solutions to guard against the sudden conversion of potential energy to kinetic energy on boom lifts. This hazard is currently not discussed or incompletely discussed in boom lift operator manuals and safety literature.

Analytical techniques are used to quantify the rapid acceleration experienced by operator platforms and operators upon the sudden conversion of potential to kinetic energy in various scenarios. Further, the principles of safety engineering are utilized to determine methods to eliminate or reduce the frequency and severity of injuries associated with the sudden conversion of potential to kinetic energy on boom lifts.

This engineering and safety engineering analysis demonstrates that the sudden conversion of energy on boom lifts can rapidly accelerate the operator platform and operator(s) within. Further, there are technologically feasible designs that protect operators against the sudden conversion of potential energy to kinetic energy on boom lifts. Such improved, safer designs are more effective at eliminating or reducing the frequency and severity of injuries than simply warning against the hazards.
Experimental Identification of the Constitutive Model of Viscoelastic Non-Standard Materials
Authors: Amadori Stefano , Catania Giuseppe
Published: February 2017

There is an increasing interest towards the use of non-conventional material such as Functionally Graded Materials (FGM) for aerospace and automotive mechanical applications. Classical material models, e.g. Kelvin or Zener, can show some limitations in describing the viscoelastic behavior of these materials. A numerical and experimental approach to identify the optimal model order and the parameters of the constitutive material relationship in the frequency domain is proposed. The constitutive equation is modeled by means of a generalized Kelvin model and expressed in the form of a rational function. To describe the complex material behavior, high order polynomials are needed for the rational function and the problem of finding the function coefficients can be ill-conditioned. Different approaches for the rational function parameters identification are compared. A least square error identification technique adopting Forsythe orthogonal polynomials is proposed. The selected procedure is first applied on numerically estimated measurements with noise, and then on real measurement data obtained by forced vibration testing of Polytetrafluoroethylene specimens.
Impact of Particle Selection on Nanoparticle Self-Assembly in Evaporating Colloidal Droplets
Authors: Greyson Marcette , Maki Kara L. , Schertzer Michael J.
Published: February 2017

Colloidal droplets often leave behind ring-shaped depositions of material after they evaporate called “coffee ring” patterns that are undesirable in many medical diagnostic and printing applications. By applying electric fields to a droplet, additional electrowetting and electrophoretic forces can be applied on the droplet’s contact line and particles, respectively, to suppress this phenomenon. Better understanding of the effects of electrowetting and electrophoresis may lead to novel techniques for nanoparticle self-assembly in evaporating colloidal droplets that are subjected to electric fields.

This work experimentally examines the effect of particle selection on nanoparticle deposition in evaporating droplets. Droplets consist of deionized water seeded with polystyrene or titanium oxide nanoparticles on the order of 20 nm. Colloidal droplets are evaporated on substrates coated with an SU-8 photoresist. Before fundamentally understanding the effects of an applied electric field, the evaporative dynamics and resultant colloidal transport in similar unactuated systems must first be understood. Current trials involve studying these unactuated control cases, but future trials will involve droplets actuated on the same material with applied AC or DC electric fields. Droplet interface shapes during evaporation are recorded and compared between trials. Final deposition patterns and their particle distributions are also qualitatively examined. Polystyrene droplets pinned for approximately the first 30% of the total evaporation time and then receded at a constant contact angle and produced ring depositions. Titanium oxide droplets pinned for approximately the first 60% of the total evaporation time and then receded in a slip-stick pattern. These produced more uniform depositions with a less-distinct outer ring, despite pinning for more of the evaporation time. The variations in transient behavior suggest that differences in particle characteristics may be impacting the contact line dynamics and resulting in different final deposition pattern.
Mesh-Independent Design of Phononic Crystals Using an Advanced Finite Element Formulation
Authors: van den Boom Sanne J. , Aragón Alejandro M. , van Keulen Fred
Published: February 2017

The numerical modeling of phononic crystals using the finite element method requires a mesh that accurately describes the geometric features. In an optimization setting, involving shape and/or topological changes, this implies that a new matching mesh needs to be generated in every design iteration. In this paper a mesh-independent description for both the interior and exterior boundaries of the periodic unit cell is proposed. A method is developed to apply Bloch-Floquet periodic boundary conditions to edges that are non-matching to the mesh. The proposed method is applied to a one-dimensional phononic crystal and is demonstrated to exhibit improved performance over the commonly used interface material averaging. We show that this method provides an accurate mesh-independent model.
Temperature Chamber for Adhesive Bonding Properties From Mode Specific Testing Specimens
Authors: Meraz Jesus , Aerne Nick , Rawlings Taylor , Parmigiani John P.
Published: February 2017

Adhesive use in fastening is increasing in many industries. Modeling the behavior of adhesives allows joints to be optimized, decreasing costs from over-design and validation testing. Unfortunately, available adhesive material properties provided by manufactures are often insufficient to accurately model and predict behavior under real-world conditions. An adhesive joint in service is often subjected to a combination of mode I (tensile) and mode II (shear) loading. Also, when used in outdoor environments, ambient temperatures can vary from below freezing to over 40°C. This paper describes a project to measure the relevant adhesive material properties at the environmental conditions of interest for two specific adhesives and to use them in subsequent modeling. The needed material properties have been found to be mode I cohesive strength, mode I cohesive toughness, mode II cohesive strength, and mode II cohesive toughness. These properties are measured individually using four tests that isolate each of the material properties by using specimens with distinct geometries and loading conditions. These geometries allow the process zone of the adhesives to be controlled. A large process zone will relate to the cohesive strength, and a small process zone will relate to the cohesive toughness, in either mode I or mode II loading. Since the values of cohesive strength and toughness of the adhesives included in this study are unknown before testing, iterations of each specimen are varied by changing the process zone size to ensure valid properties are measured. Testing is conducted at −30°C, 20°C, and 45°C. In order to conduct this testing a temperature chamber was designed, fabricated, and validated. Commercially available temperature chambers were either too small or prohibitively expensive. The temperature chamber this project created was constructed of laser cut and bent stainless steel sheets with an insulated double-wall construction. Two seals were used at every entry point to maintain an air-tight chamber. A heating and cooling circulator and heat exchanger were used for temperature control. The chamber can heat to 45°C in approximately 15 minutes, and cool to −30°C in approximately 30 minutes.
Effect of Vibrations on the Performance of a Centrifugal Pump-Impeller When Using a Variable Frequency Drive
Authors: Lara-Rodriguez G. , Begovich O. , Naredo J. L.
Published: February 2017

This paper deals with turbomachinery, such as pumps or turbines, which are very sensitive to changes in fluid speed over the contours of the blades when the volumetric flow is varied. These changes modify the fluid incidence angle, causing a rapid decline in pump performance. Our research focuses on an analysis of the performance or efficiency of a centrifugal pump with a variable frequency drive, where losses in efficiency are caused by turbulence generating harmful vibrations in the installation. The methodology consists of measuring the magnitude of the vibrations. The data obtained are compared to the performance reached when the change in velocity has been produced with the regulation of the volumetric flow to a partial load of the pump. This suggests an analysis to attempt to resolve the issue of density variation that occurs when pumping liquefied petroleum gas (LPG) under regular operating conditions.
Uncertainty Quantification for Cantilever Based MEMS Switches Considering Bouncing Dynamics
Authors: Bognash Mohamed , Asokanthan Samuel
Published: February 2017

Design methods of MEMS switches are typically based on deterministic approaches, where the parameters such as geometrical and physical properties as well as the operating conditions that characterize the behavior of systems are assumed to be known precisely. However, in practice, due to the batch-production processes used in MEMS fabrication as well as the micron-scale dimensions of the structural elements, consideration of uncertainties in system parameters and an understanding of their effects are warranted and should be investigated in order to improve the switch performance and reliability. The primary purpose of the present paper is to perform uncertainty quantification predictions for MEMS switches based on the transient dynamic response, in particular, the bouncing behavior. A suitable mathematical model that captures the bouncing dynamics and previously validated via experiments is employed for this purpose. In particular, quantification of performance in terms of second order statistics is performed to predict propagation of uncertainties in Young’s modulus, beam width, beam thickness as well as actuation voltage. The influence of these uncertainties on significant switch performance parameters such as initial bounce time as well as maximum bounce height have been quantified.
Dynamic Impact Simulation Study of Tubeless Pneumatic Tires
Authors: Linayao Floyd , Yee Raymond K.
Published: February 2017

Traditionally speaking, prototype tires are designed, and then tested on an experimental basis to evaluate performance. Using finite element analysis instead allows tire design parameters to be modified at will and underperforming architectures to be ruled out. This paper characterizes the dynamic response of a tubeless pneumatic vehicle tire as it is exposed to sudden impact and determines conditions under which failure would occur. Three cases were studied using a 175SR14 passenger tire, since passenger tires are most commonly used and impacts are more substantial on smaller tires. ABAQUS finite element program was used to perform nonlinear transient dynamic three-dimensional finite element analyses for three commonly tire encountered conditions. The first case, direct curb impact, determined that a safe inflation pressure range for tire velocities exists between 10 and 60 km per hour (kph). The second case, angled curb impact, found a smaller range of 10 to 40kph. The third case, impact with a pothole, found that at low inflation pressures, less stress is produced at higher velocities; increasing inflation pressure results in a transition point, causing larger stresses to be produced at higher velocities. From these analyses, several conclusions are drawn: inflation pressures below 100KPa do not produce a useful relationship between tire velocity and stress; thicker sidewalls help shield the tire from impact failure; and it is better for the tire to accelerate past a pothole in the 30 to 70kph range.
Numerical Investigation of Various Approaches to Avoid Natural Convection Instabilities Inside the Channels of Horizontal Plate Fin Heat Sinks
Authors: Tari Ilker , Ozet Mehmet Erdem
Published: February 2017

In case of natural heat convection from a horizontal plate fin heat sink, heat transfer rates highly depend on the geometric parameters. It is observed that if the fin height is very low, fresh cooler air may not be able to reach middle parts of the heat sink causing an ineffective use of the extended heat transfer area. Using a validated numerical model of an underperforming heat sink, various ways of improving heat sink geometry has been investigated. The tried approaches include leaving gaps in the length of the fins in different patterns, adding two different shape pin fins in the channels between the plate fins and raising the height of the fins on the edges. The last approach is shown to be effective in improving heat transfer by blocking the side flows over the heat sink. By numerical simulations, causes of the unwanted in-channel longitudinal vortices were also investigated in detail with the help of powerful flow visualization capability of Computational Fluid Dynamics.
An Eulerian Approach for Characterization of Solid Suspension in Multiphase Flow Systems and its Application in Hole Cleaning During Drilling
Authors: Zhang Feifei , Miska Stefan , Yu Mengjiao , Ozbayoglu Evren , Takach Nicholas
Published: February 2017

Solids suspension has broad applications in the oil and gas industry (i.e., sand production, cuttings transportation during drilling, and barite sag in drilling fluids). The conventional modeling approaches for solids suspension and transportation include mechanics models (i.e., layer models) and computational fluid dynamics (CFD) based Eulerian-Lagrangian models. One of the most important assumptions for these approaches is that the solid particles have uniform size, which is not true in the actual applications. The computational fluid dynamics/discrete element method (CFD-DEM) approach can track each single particle in the system; however, the computational time is not practical for industrial applications.

This paper presents a relatively simple Eulerian approach for characterizing solids suspension in multiphase flow systems. The multiphase flow equations are derived by using a proper averaging procedure without considering interphase mass transfer. A proposed new solids suspension model, which is based on the fluid-solid interaction and kinetic theory, account for multiple solids sizes in the flow. The suspension characterizations for particles with different sizes are considered by introducing a particle size distribution function, which also captures detailed particle distribution and fluid/particle and particle/particle interactions. Therefore, a more realistic solids transportation prediction can be achieved. A simulation package is developed by solving the model using the finite difference method. The boundary-fitted coordinate system is applied to integrate the irregular geometry caused by drillpipe eccentricity and a packed solids bed. The influence of the solid phase on the carrier fluid is considered, and solid-liquid two-way coupling is implemented.

The simulation package has been used for transient hole cleaning simulations during drilling. Simulation results show that cuttings’ backsliding makes the hole cleaning process in intermediate inclined wells different from that in horizontal and highly inclined wells. The cuttings movement in this part of the well follows the two-steps-forward, one-step-back routine. Well packoff is also captured by the program for improper hole cleaning operations in an intermediated inclined position. Transient hole cleaning tests were conducted on a 90 ft long, 8 × 4.5 in. flow loop. Experimental data are compared with the simulation results, and good matching is obtained. This method can also be used as a general tool for solids suspension and transportation simulation in multiphase systems.
Experimental Investigation of Temperature Dependent Thermal Conductivity of Aluminum Oxide and CNT Heat Transfer Fluids
Authors: Calamas David , Willis John , Wilkes Zachary , Rahman Mosfequr , Dannelley Daniel
Published: February 2017

Nanofluids often exhibit superior heat transfer characteristics when compared with conventional heat transfer fluids. The increase in thermal conductivity due to the presence of various nanoparticles was experimentally examined using commercially available equipment that utilizes the two thickness method. The thermal conductivity of 10 and 30 nm aluminum oxide nanoparticles suspended in distilled water at concentrations of 2% and 5% was measured for a temperature range of 15°C to 70°C in increments of 5°C. For a 2% concentration of 10 nm aluminum oxide the experimentally derived thermal conductivity deviated from the theoretical thermal conductivity predicted by Maxwell by an average of 1.55%. The average percent increase in the thermal conductivity of the base fluid due to the presence of 10 nm aluminum oxide nanoparticles was found to be 4.17 and 4.90% for concentrations of 2 and 5% respectively. The presence of 30 nm nanoparticles resulted in a greater discrepancy with the theoretical model developed by Maxwell, regardless of concentration. In addition, the presence of 10 nm aluminum oxide nanoparticles resulted in a greater increase in thermal conductivity when compared with 30 nm aluminum oxide nanoparticles. In addition, the thermal conductivity of a base fluid dispersed with multi-walled carbon nanotubes (MWNTs) with an outer diameter ranging from 13–18 nm and a length ranging from 3–30 micrometers (μm) was examined. The presence of a 0.2% concentration of MWNTs resulted in an average increase in thermal conductivity of 0.31%. Unfortunately, there was a large standard deviation in the results for the MWNTs and significant fluctuations with temperature. While this experimental methodology may be sufficient for metal based nanofluid particles it may be undesirable for fluids enhanced by MWNTs.
Pool Boiling Heat Transfer of Water on Hydrophilic Surfaces With Different Wettability
Authors: Girard Adam R. , Kim Jinsub , You Seung M.
Published: February 2017

The effect of wettability on boiling heat transfer (BHT) coefficient and critical heat flux (CHF) in pool boiling of water on hydrophilic surfaces having different contact angles was investigated. Hot alkali solutions were utilized to promote cupric and cuprous oxide growth which exhibited micro and nanoscale structures on copper surfaces, with thicknesses on the order of a couple of micrometers. These structure and surface energy variations result in different levels of wettability and roughness while maintaining the effusivity of the bare copper surface. The study showed that the BHT coefficient has an inverse relationship to wettability; the BHT coefficient decreases as wettability increases. Furthermore, it was shown that this dependency between BHT coefficient and wettability is more significant than the relationship between BHT coefficient and surface roughness. The CHF was also found to increase with increases in wettability and roughness. For the most hydrophilic surface tested in this study, CHF values were recorded near the 2,000 kW/m2 mark. This value is compared with maximum values reported in literature for water on non-structured flat surfaces without area enhancements. Based on these results it is postulated that there exists a true hydrodynamic CHF limit for pool boiling with water on flat surfaces, very near 2,000 kW/m2, independent of heater material, representing an 80% increase in the limit suggested by Zuber [1].