bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiscale Investigation of Thickness Dependent Melting Thresholds of Nickel Film Under Femtosecond Laser Heating
Authors: Ji Pengfei , He Mengzhe , Rong Yiming , Zhang Yuwen , Tang Yong
Published: January 2019

A multiscale modeling that integrates electronic scale ab initio quantum mechanical calculation, atomic scale molecular dynamics simulation, and continuum scale two-temperature model description of the femtosecond laser processing of nickel film at different thicknesses is carried out in this paper. The electron thermophysical parameters (heat capacity, thermal conductivity, and electron-phonon coupling factor) are calculated from first principles modeling, which are further substituted into molecular dynamics and two-temperature model coupled energy equations of electrons and phonons. The melting thresholds for nickel films of different thicknesses are determined from multiscale simulation. Excellent agreement between results from simulation and experiment is achieved, which demonstrates the validity of modeled multiscale framework and its promising potential to predict more complicate cases of femtosecond laser material processing. When it comes to process nickel film via femtosecond laser, the quantitatively calculated maximum thermal diffusion length provides helpful information on choosing the film thickness.
A Novel Optimization Design Method of Additive Manufacturing Oriented Porous Structures
Authors: Zhao Jiaqi , Zhang Ming , Zhu Yu , Li Xin , Wang Leijie
Published: January 2019

The advanced development of additive manufacturing (AM) has greatly promoted the research and application of variable density porous structures. Meanwhile, AM constraints highlight the significance of design for AM (DFAM). The structural performance of existing topology optimization (TO) based design methods is limited and AM constraints are little considered. In this paper, we propose a novel optimization design method of AM oriented porous structures which allows the existence of void. A novel density filter is designed to achieve multi-interval TO for better structural performance and satisfy the minimum feature size constraint. Meanwhile, another customized density filter is designed to obtained support-free porous structure for the buildability constraint of AM. FEA results demonstrate that optimized porous structure designed by proposed method has better stiffness performance and adaptability to AM constraints, compared with existing methods.
Experimental Study of the Suspension Flow Past Confined Low-Aspect-Ratio Cylinder Arranged Microchannels
Authors: Cheng Xiao , Pan Zhenhai , Wu Huiying
Published: January 2019

The recirculating wake behind the obstacle at moderate Reynolds numbers was devoid of particles, this was discovered by Haddadi et al. (J. Fluid Mech., 2014). However, only one obstacle and narrow Reynolds numbers were considered in their work. In this work, we constructed more confined environment, where the suspensions of solid fraction 0.25% with different particle diameters of 1, 5 and 10 μm flow past the critical confined low-aspect-ratio cylinder arrays (H/D = 0.3) with different arrangements were experimentally carried out. Reynolds numbers performed in the experiments ranged from 14∼550, and different flow patterns were observed. It was found that particles could flow into the region behind cylinder at low flow rate. Then, particle-depleted wake zone was formed behind the cylinder when increasing Re, which is similar with reported literature. It was interesting to find that when increasing Re further, the particles could flow into the recirculating wake zone behind cylinder. We generalized the particle behavior behind cylinder as from “entry” to “particle-free” and to “re-entry”. Additionally, the influence of different layout modes with inline and staggered cylinder arrays were also investigated. We found the particle-depleted wake zones behind the in-line cylinder array were larger than the one of the staggered cylinder array as the velocity were the same at “particle-free” stage. The in-line cylinder array possessed higher ability of allowing 1 μm particles to fill with the recirculating wake, whereas there were always existing particle-free zones in the core of recirculating wake of staggered cylinder array at “re-entry” stage. In order to understand particle-free mechanism better, microparticle image velocimetry (μPIV) technique was utilized to quantitatively measure the flow fields of in-line and staggered arranged cylinders. The obtained fluorescence pictures demonstrated that few particles flow into the zone behind cylinder at the “particle-free” stage, and fluorescence particles can flow into the wake at “re-entry” stage. That is, fluorescence particles also experienced the stages from “entry” to “particle-free” and to “re-entry”.
Photovoltaic Solar Energy: Potentials and Outlooks
Authors: Ebhota Williams S. , Jen Tien-Chien
Published: January 2019

This review focuses on modern energy attributes and to identify alternative energy source and technology that satisfy energy trilemma requirements. The results and findings of the study show that photovoltaic (PV) solar cells technologies have the potentials of satisfying the global energy quest if deployed more. This study x-rays the different PV cells technologies in terms of generation chronology, power conversion efficiencies (PCE), (EPBT), present status and outlook. This study harmonises many photovoltaic performance indexes from review as follow: PV module power conversion efficiencies (PCE) of solar cells: lab -mono-Si (26.7%), multi-Si (22.3%), CIGS (21.7%), for and CdTe (21.0%); commercial - mono-Si (17%), CdTe (16.0%); energy payback time (EPBT) in Europe, 1–1.5 years and 1.5–3.5 years for thin film and crystalline silicon PV systems, respectively, 3 months and 8 months for perovskite (PSC) and CdTe solar cells respectively. The price of PV has drastically declined from $76/W in 1997 to $0.3/W in 2015. By 2050 and 2100, PV solar technology is expected to provide 20% and over 60% of the world’s energy supply, respectively. This will account for 50% CO2 emissions reduction globally. The projections depend on further improvement on the performance indexes and lifetime, series resistance, and optical properties. CdTe technology performs better than other technologies at elevated temperature, hence, recommended for tropical regions.
Thermal Analysis of Phase Change Materials by Utilizing Nanoparticles
Authors: Nitsas M. T. , Koronaki I. P. , Beliotis A.
Published: January 2019

Latent TES systems utilize phase change materials (PCMs) which at a suitable temperature range can be melted and thus store thermal energy. The stored energy is removed during the reverse process which solidifies the PCM. Due to the superiority of high latent heat compared to sensible heat, PCMs can contribute to the reduction of the storage systems’ size offering a promising solution especially when coupled with solar collectors. Despite the aforementioned advantages, the relatively low thermal conductivity of PCM hinders their wide utilization. In the present study, a thermal analysis of phase change materials is carried out. Different types of phase change materials (PCMs) are analyzed at various temperature ranges. The energy equation for the PCM is solved by implementing a 1D explicit finite difference scheme in Matlab and the results are compared with corresponding results deriving from Comsol. The properties of the utilized PCMs are altered accordingly so as to take into account their variation during phase change. In this analysis, only the thermal behavior of a PCM is investigated while the gravitational effect is neglected. The results of the analysis regard the temperature variations within the phase change material, the stored energy in the PCM per volume unit, the process speed and the effect of thermal conductivity on phase change, especially on the melting front displacement. Primary results have shown that the stored energy depends on the heat source and on the utilized PCM. In order to tackle the problem of PCM low conductivity, nanoparticles are added so as to enhance the stored energy due to the higher thermal conductivity. Upon the addition of two types of nanoparticles, the enhancement of melting fraction and stored heat are determined.
Heat Transfer Analyses of a 3D Graphene-Carbon Nanotube Pillared Structure
Authors: Zhao Weihuan , Almahmoud Khaled
Published: January 2019

This work is aimed towards studying and analyzing the heat transfer performance in a novel 3D graphene-carbon nanotube (CNT) pillared structure. Although both graphene and CNT are known to have high thermal conductivity in in-plane and along the axis, respectively, they have low thermal conductivities in the other directions. Hence, the 3D graphene-CNT structure will have high thermal conductivities in both in-plane and out-of-plane directions due to the pillared architecture. It can be applied to small-scale electronic devices for high efficient heat dissipation and/or exchange. The pillared structure consists of few-layer graphene (FLG) and bundles of CNTs. CNT bundles connect between two sheets of FLG. The heat transfer performance of the structure was investigated through a continuum model by COMSOL Multiphysics. Parameter studies were conducted to determine the optimum graphene-CNT configuration, including number of CNTs in each bundle, number of bundles in the structure, distance between bundles (a.k.a. inter-pillar distance “IPD”), length of CNT, and the arrangement of CNT bundles. Results of the simulations concluded that (1) the reduced IPD could prevent the in-plane heat spreading, (2) the increased number of CNTs could enhance the axial-direction thermal transport, and (3) the arrangement of CNT bundles between FLG sheets (e.g. shifting one row of CNT bundles) has minor impacts on the overall heat transfer performance of the structure.
Effect of Size Distribution on Optical Absorption During Intense Pulsed Light Sintering of Metal Nanoparticles
Authors: Devaraj Harish , Hwang Hyun-Jun , Malhotra Rajiv
Published: January 2019

Intense pulsed light sintering (IPL) of nanoparticles on rigid or flexible substrates enables rapid fabrication of thin films and patterns over large areas. In IPL, visible light from a high energy xenon lamp is absorbed by the nanoparticles for rapid sintering of metallic and non-metallic nanoparticles. This plasmonic optical absorption during the process for metal nanoparticles has been shown to depend on individual nanoparticle size. However, but there is little understanding of how this absorption depends on nanoparticle size distribution during IPL. This work incorporates a fully three-dimensional packing model along with an electromagnetic model of plasmonic absorption in silver nanoparticles to bridge this gap. It is shown that smaller standard deviation in a unimodal distribution and smaller size ratios in a bimodal distribution demonstrate relatively higher optical absorption in IPL.
A Whole Operation Life Cycle Model of Gas Turbine Blades Under Multi-Physics Based on Variation of Blade Profile Parameters
Authors: Zhou Dengji , Wei Tingting , Ma Shixi , Zhang Huisheng , Lu Zhenhua , Weng Shilie
Published: January 2019

For long-term operation, blades start to show some defects with increasing operating hours, such as fouling, erosion, corrosion, damage and tip clearance. As the basic unit components of gas turbines, the health conditions of blades directly affect the energy conversation efficiency and service life of the whole equipment. The process from first installation to scrap is blades’ whole operation life cycle. It is an effective way to establish the whole operation life cycle model of blades for real-time monitoring, troubleshooting and prevention, so as to improve the management of equipment. The current research on the whole operation life cycle model is mostly limited to a single subject, such as thermal effects or stress effects. It lacks a profound analysis of this issue from the multi-disciplinary perspective. Meanwhile, the deterioration of blades influence on geometry variation of the blade surface is not taken into consideration in detail. Therefore, the current blade life model is not accurate enough to represent the actual situation. In this paper, the typical gas path deterioration is characterized by blade profile parameters, including the increment of the blade leading edge thickness, the increment of the blade trailing edge, and the change of the blade surface roughness in the whole operation life cycle model of blades. The influencing factors of aerodynamics and strain are synthetically characterized through the study of their multi-disciplinary influence mechanism. And the relationship between the corresponding influencing factors and the variation of blade profile parameters is established. Thus, the numerical simulation model under multi-physics is built to reveal its distribution and trends of the flow field and stress in the gas path. The result shows that it can protect the blades, ensure safe and stable operation, and reduce the deterioration rate.
Performance Analysis of Multi-Pass Cross-Flow Heat Exchangers
Authors: Lankalapalli Kiran , ElSawy Ahmed , Idem Stephen
Published: January 2019

A steady state sensible performance analysis of multi-pass cross-flow finned-tube heat exchangers is reported. The investigation considers various flow circuiting, such as counter cross-flow, parallel cross-flow, and cross-flow where the tube-side flow is in parallel. A previously developed matrix approach is used to evaluate the heat exchanger performance in each tube pass. The equations required to model the thermal performance of these configurations are presented, and the thermal performance is compared for each type of flow circuiting. Thereafter a parametric study on cross-flow heat exchanger performance is performed by varying physically significant parameters such as number of transfer units (NTU) and capacity rate ratios, and the graphical results for each type of flow circuiting are presented both for both two-pass and three-pass arrangements. A consistent criterion is proposed for each case, wherein increasing the NTU beyond a certain threshold value does not significantly improve heat exchanger thermal performance.
Probabilistic Properties of Steel for Nuclear Piping
Authors: Avrithi Kleio
Published: January 2019

For the development of design rules for nuclear piping using the Load and Resistance Factor Design (LRFD) method, the probabilistic properties of steel, namely, the mean value, bias, coefficient of variation, and probability distribution are needed. The paper presents background information for the existing material tables in the ASME Boiler and Pressure Vessel Code, Section II. Then it investigates the probabilistic properties for the most representative materials used for nuclear piping such as a carbon, stainless austenitic, and low alloy steels. Properties up to temperature 700°F are examined through a review of studies for the mechanical behavior of these materials. The paper discusses approaches for grouping materials in broader categories than the consideration of each type of steel separately. The impact of the steel probabilistic properties on the development of LRFD equations and the associated target reliability index is provided.
Optimal Reaction Wrench Measuring Platform
Authors: Kumar Rajesh , Jain Aditya , Khatait Jitendra P.
Published: January 2019

Measurement of the reaction forces and moments (general wrench) are instrumental in the development stage of a product. Currently available measurement setups have varying ranges in different directions. The range of the device is limited to least stiff direction. The optimal use of load cell for predicted force/moment bounds is based on utilizing the system efficiently in different directions. We have presented a methodology to optimize the measurement setup based on directional stiffness behavior. The technique is coupled to design of load cell based on the characteristic structure of “Stewart platform”. The optimization function proposed allows the designer to design a measurement setup for a bound of the reaction force/moment. Additionally, the nonlinearities like friction and issue of loose joints due to relative motion at the passive joints are avoided. The improvement comes from replacement of the mechanical joints by kinematically constrained flexures.
CFD Model of the Turboprop Engine Hot Part: Bay Cooling
Authors: Simeunovic Goran , Popelka Lukáš , Hatschbach Petr
Published: January 2019

The bay cooling of a specific new turboprop engine is investigated in this paper. The new ATP turboprop engine has additional jets with hot air stream close to the PT. This considerably increases the temperature inside the first nacelle compartment in the hot engine part around the engine combustion chamber. In order to achieve the optimal temperature conditions for engine parts inside the nacelle in the critical operating regime (triple red line), a new bay cooling system is proposed. Using the existing standard (National Advisory Committee for Aeronautics) NACA inlet at the front of the nacelle, two additional groups of ribs on rear part of front nacelle compartment and standard nacelle gaps (around exhausts), the temperature in the front part of the nacelle is decreased bellow the critical temperature for installed devices and engine parts (gear box etc.) in this compartments. Using a 3D CFD model of the first compartment of the nacelle is analyzed using the software ANSYS. The boundary conditions for this CFD simulation are obtained from ground testing of the turboprop engine.
Design and Testing of a Solar-Driven Wastewater Treatment Unit for Off-Grid Applications
Authors: Lakeh Reza Baghaei , Andrade Daniel , Miller Kyle , Modabernia Mohammad Masoud , Nguyen Thuan John , Nguyen Justine , Flanagan Elbon , Jacobo David , Lopez Laura , Phun Binh , Kest John , Baradii Johnny , Delagah Saied , Sharbatmaleki Mohamadali
Published: January 2019

The decline of surface water sources along with periodic droughts has introduced new challenges for the state of California. In order to keep up with the increasing demand for water, the state is heavily relying on imported water from the north to Southern California as well as importing water from the Colorado River. The imported water has a large carbon footprint due to using grid power for water transport. Water reuse (reclaimed) is considered as one of the solutions to reduce the dependency of state on imported water. The research team at Cal Poly Pomona, is developing an off-grid solar-powered greywater treatment system for non-potable use in single households. Greywater is the drained water from bathroom sinks, showers, tubs, and washing machines; not including wastewater from toilets or kitchen sinks. Treating greywater on-site can provide significant water savings, and can reduce the carbon footprint of desalination using solar panels. The developed system is comprised of a three-stage treatment train: micro-filtration, solar-driven reverse osmosis, and ultraviolet disinfection. The end product of the project is capable of reclaiming 90–100 gallons of water per day which is about 60% of residential greywater waste. The system removes large suspended particles (particles of dirt, food, etc.) as well as organic and inorganic dissolved contaminants. It is demonstrated that the system can provide a permeate quality that agrees with recommended guidelines for reclaimed water. The system has a recovery rate of up to 62%.
Effects of Harmonic Vibration on Cycloidal Rotor Performance
Authors: Monteiro Jakson Augusto Leger , Páscoa J.
Published: January 2019

Cycloidal rotors have the inherent ability to provide vectorized thrust with fast reaction times. However, their present efficiency levels restricts their routinely use as propulsion elements for air-vehicles. Efforts have been made to improve the performance of cycloidal rotors through the optimal combination of its geometric parameters. In the present work the performance improvement of cycloidal rotors is demonstrated using a different approach, namely by imposing an unsteady change on the dynamics and structure of the vortices developed around the blades. This required change on the flow field, around the blades, was applied by adding an harmonic vibration to the traditional cycloidal movement of the blades, thus causing the blades to vibrate as they describe their oscillating pitch movement. This research on the effect of harmonic vibration, on lift and drag coefficients, was done first for a single blade profile, and later for a full cycloidal rotor, and is based on the Takens reconstruction theorem and Poincaré map. Therefore, diverse test cases and conditions were considered: a single static airfoil, an oscillating blade profile, and a complete cycloidal rotor. We concluded that the optimal combination of harmonic vibration parameters, specifically; amplitude, phase angle and vibration frequency, under adequately tuned design conditions, can have a beneficial effect on cycloidal rotor performance.
Viscoplastic Fluid Flow Between Parallel Plates With Triangular Obstacles
Authors: Ashrafi Nariman , Sadeghi Ali , Chegini Armin
Published: January 2019

In the present research, the flow of visco-plastic fluid is investigated in a duct with triangular obstacles on the bottom plate. The effect of different inlet velocities on the flow behavior is observed specially around the obstacles. The viscosity as the function of velocity gradient and hence the Reynolds numbers, are obtained on certain lines for different values of fluid characteristics and flow indexes. Herschel-Bulkley model as a generalized model of visco-plastic fluids is used to simulate the fluid motion along the channel. Reverse flows and vortexes are shown before and past the obstacles.
Analysis of Two-Phase Flow Slug Regime With Engineering Approach
Authors: Ashrafi Nariman , Chegini Armin , Sadeghi Ali
Published: January 2019

In this research, the two-phase slug regime is investigated analytically with an engineering approach. due to the velocity gradient in the layers of the two-phase flow, numbers of waves form and grow in the liquid phase and may block the duct which in this case is called slug. Blocking the flow, it causes higher pressure accumulation which is the main reason of slug’s momentum through the duct. Simplifying the slug’s geometry and using basic physics laws yielded an equation between the slug’s back pressure and its length.
Influence of Blade Shape Geometry on Very Low Specific Speed Centrifugal Pump Performance
Authors: Al-badawi Muhamed , Adam I. G. , Haddara Sherif , El Sherif Ahmed H. M.
Published: January 2019

Direct or inverse design methods for centrifugal pumps play an important role in investigating their performance. In this paper, a very low specific speed centrifugal pump impeller of ns = 9.5 (metric), three blades and 222° wrap angle. This pump was investigated using the direct design method to achieve the blade shape geometry and examine the blade angle distribution. As the blade angle progression affects the pump performance, four models with different blade angle distribution were used to perform the hydrodynamic and suction performance of the pump. The linear and non-linear derived correlation models were designed firstly using ANSYS-BladeGen module then studied numerically using ANSYS-CFX module to solve the three-dimensional Navier-Stokes equations. Validation of the numerical simulation of the investigated centrifugal pump was done using experimental data. Numerical results show that the change in the blade angle distribution has an influence on the blade wrap angle. Consequently, the variation in the blade wrap angle affects the pump head and the relative velocity distribution. The pressure gradient varies in the pump with changing the blade length. Using the velocity streamline and the velocity vector, the eddies existence and distribution in the blade suction side affect the relative velocity distribution and the pump performance. It was found that the blade with the smallest length decreases the pump head and have best velocity distribution.
Natural Convection in a Square Cavity Utilizing Different Nanofluids in Presence of Constant Magnetic Field With Brownian Motion Effect
Authors: Abdelaziz Misarah , El-Maghlany Wael , Ismail Ashraf S.
Published: January 2019

Natural convection in a square cavity filled with water-Al2 O3 nanofluid is studied numerically. Upper, lower, and left surfaces are insulated. Right wall is at low temperature, while two heat sources are kept at high temperature. The sources are vertically attached to the horizontal walls of a cavity . A uniform magnetic field is applied in a horizontal direction. Effective thermal conductivity and viscosity of nanofluids are obtained using Koo-Kleinstreuer model which implements the Brownian motion of nanoparticles effect. Steady state laminar regime is assumed. The conservation of mass, momentum, and energy equations are solved using finite volume method. The numerical results are reported for the effect of Rayleigh number, solid volume fraction, and Hartmann number on the streamlines as well as the isotherms. In addition, the results for average Nusselt number are presented for various parametric conditions. This study is presented in the following ranges, Rayleigh number from 103 to 105, Hartmann number from 0 to 60, and solid volume fraction from 0 to 0.06, while the Prandtl number which represents water is kept constant at 6.2. The results showed that heat transfer rate decreases with the rise of Hartmann number and increases with the rise of Rayleigh number, and volume fraction. Moreover, results showed that heat sources positions, lengths and intensities have crucial effect on heat transfer rate. Additionally, the effect of nanofluids type was studied, it was found that water-Cu nanofluid enhances the heat transfer better than water-Al2O3, water-CuO and water-TiO2 nanofluids.
A Comparative Study of Rapid Quadrupedal Sprinting and Turning Dynamics on Different Terrains and Conditions: Racing Greyhounds Galloping Dynamics
Authors: Hayati Hasti , Walker Paul , Mahdavi Fatemeh , Stephenson Robert , Brown Terry , Eager David
Published: January 2019

Identifying optimum athletic race track surfacing for greyhounds to reduce risk of injuries is a challenging practice as there are several single and coupled variables that should be considered as risk factors. To study the impact of bend and straight sections, surface type and camber, on biomechanics of galloping quadrupeds, an inertial measurement unit (IMU).

has been used to measure the associated galloping accelerations. The IMU was sewn into a pocket located on the back of the greyhounds racing jacket positioned between the two forelegs. Simultaneous kinematics were performed using high frame rate (HFR) videos for calibrating IMU data. The results showed that there were lower G-forces on galloping on grass than wet sand which is consistent with the mechanical behavior of grass (grass is softer than wet sand). Moreover, galloping around the bend had higher G-forces than galloping along the straight section suggesting an excessive force is applied on the greyhound’s limbs due to centrifugal force. A cambered bend assisted the greyhounds in having a smoother gait and lower G-forces when compared to a flat bend. The results reported in this paper will not only be beneficial for the welfare of racing greyhounds, but will also contribute in the simulation of legged locomotion for bio-inspired engineering and robotics.
Understanding Mathematical Definitions of Circularity/Roundness in ASME GD&T Y14.5 As Related to Part Functionality
Authors: Ghosh Suhash , Sahay Chittaranjan
Published: January 2019

With the advent and development of precision machining and manufacturing, the necessity to ensure quality of the produced parts for their longevity has grown as fast the advances in technology. One of the ways of achieving higher product lives has been through tighter tolerances on size and form characteristics. Thus, it is imperative that designers, manufacturers and quality inspectors understand the mathematical principles guiding these dimensional and form characteristics, and further utilize them, to the greatest degree possible, in the inspection equipment and tooling. One of the greatest benefits to mankind was the invention of wheel. It is inarguably evident how much of our lives depend on machines with rotating parts. From power stations to power tools, from the smallest watch to the largest car, all contain round components. In precision machining of cylindrical parts, the measurement and evaluation of roundness (also called circularity in ASME Geometric Dimensioning & Tolerancing, GD&T Y14.5) is an indispensable component to quantify form tolerance. Based on reference circles, this paper focuses on the four modeling methods of roundness. These are (1) Least Squares Circle (LSC), (2) Maximum Inscribed Circle (MICI), (3) Minimum Circumscribed Circle (MCCI) and (4) Minimum Zone or Minimum Radial Separation Circles. These methods have been explained in the context of their implications on design applications, advantages and disadvantages. This article also explores how these multitudes of parameters are to be understood and be incorporated into undergraduate engineering curriculum, and be taught as an improved toolkit to the aspiring engineers, process engineers and quality control professionals.
Characterization of Model-Based Uncertainties in Incompressible Turbulent Flows by Machine Learning
Authors: Usta Mustafa , Tosyali Ali
Published: January 2019

This work determines the inaccuracy of using Reynolds averaged Navier Stokes (RANS) turbulence models in transition to turbulent flow regimes by predicting the model-based discrepancies between RANS and large eddy simulation (LES) models. Then, it incorporates the capabilities of machine learning algorithms to characterize the discrepancies which are defined as a function of mean flow properties of RANS simulations. First, three-dimensional CFD simulations using k-omega Shear Stress Transport (SST) and dynamic one-equation subgrid-scale models are conducted in a wall-bounded channel containing a cylinder for RANS and LES, respectively, to identify the turbulent kinetic energy discrepancy. Second, several flow features such as viscosity ratio, wall-distance based Reynolds number, and vortex stretching are calculated from the mean flow properties of RANS. Then the discrepancy is regressed on these flow features using the Random Forests regression algorithm. Finally, the discrepancy of the test flow is predicted using the trained algorithm. The results reveal that a significant discrepancy exists between RANS and LES simulations, and ML algorithm successfully predicts the increased model uncertainties caused by the employment of k-omega SST turbulence model for transitional fluid flows.
Interfacial Heat Transfer Between Erythritol and Xylitol Crystals As a Mixture Heat Storage Material
Authors: Feng Biao , Fan Li-Wu
Published: January 2019

The binary eutectic mixtures of sugar alcohols, which can maintain their high latent heat of fusion while extending the range of melting points for more flexible utilizations, have attracted increased attention. The eutectic mixture of erythritol and xylitol, with a melting point of 82 °C and a latent heat of fusion of 270 kJ/kg, has been identified as a promising latent heat storage material at the temperature range around 80 °C. In comparison to the pure components, the changes in thermal conductivity of mixture sugar alcohols are of great interest, which are investigated in this work with emphasis on the interfacial heat transfer across erythritol and xylitol molecules. Molecular dynamics simulations were performed to study the nanoscale heat transfer over an artificial interface between two crystal layers of erythritol and xylitol in contact with each other. Based on the non-equilibrium molecular dynamics method and eHEX algorithm, a constant heat flux was imposed over the simulated box. The dependence of the erythritol-xylitol interfacial thermal resistance on the system length was studied by adapting different system lengths. With increasing the length from 26 to 78 Å, the interfacial thermal resistance was predicted to decrease from 5.5 × 10−10 to 3.8 × 10−10 m2·K/W, which then becomes nearly unvaried while further increasing the system length to over 100 nm. The knowledge on the interfacial thermal resistance will help understand the changes in thermal conductivity of bulk mixtures of sugar alcohols.
A Phase Spectrum Method for the Measurement of Liquid-Layer Thickness
Authors: Li Quanchang , Ding Junkai , Huang Wenbin
Published: January 2019

Ultrasonic technology has been widely used to measure the thickness of lubricant film. The time delay between multiple reflections reflects the thickness of the liquid layer. As the thickness of liquid layer decreases, the measurement becomes more difficult owing to the overlapping of waveforms. Unlike the mainstream methods focusing on the characteristics of amplitude, a phase spectrum method is proposed in this paper to determine the thickness, which is much easier to operate and doesn’t need any extra noise reduction. It provides another point of view to solve the problem of film thickness measurement. This algorithm has been verified to test the liquid layer thickness ranging of 10–200 μm in a self-made experimental platform. Experimental results show that the thickness can be obtained accurately and the error is within the allowable range.
Analyzing the Flow in Annular Gap With a Restrictor Mounted on Outer Cylinder
Authors: Luo Guohu , Wang Shengde , Shen Hong , Yao Zhenqiang
Published: January 2019

The flow in annular gap with a restrictor mounted on outer cylinder is numerically simulated based on the hybrid Reynolds Averaged Navier-Stokes (RANS)/Large eddy simulation (LES) model. In stationary inner cylinder case, the pressure drop, mean axial velocity profiles and characteristic length scale of the recirculation zones are analyzed. Then the effects of rotating inner cylinder on the axial pressure distributions and the size of recirculation regions are examined. With the increase of rotating Reynolds number, the pressure loss of flow past the forward-backward step pair is greatly increased. Meanwhile, the transient pressure difference between the upstream inlet and downstream outlet gradually becomes fluctuating periodically due to the vortex shielding at the edge of backward step regularly. And the amplitude of the fluctuating pressure difference is comparable to its mean value. Moreover, the size of recirculation regions is reduced with the rising azimuthal Reynolds number, resulting from the interacting with enhanced Taylor vortices.
Experimental Analysis and Testing of the Hemming Process Types Utilized in the Automotive Industry
Authors: Limon-Leyva Pablo Alberto , García-Zugasti Pedro de Jesús , Balvantín-García Antonio de J. , de la Peña José A. Diosdado , Sanchez-Arce Isidro de Jesus , Govea-Valladares Eder Hazael
Published: January 2019

A comparative experimental analysis of three common hemming processes used in the automotive industry is presented. These processes are die hemming, table hemming, and roll hemming. We aim to determine which one of the three processes provides the better quality hemming.

The die hemming and table hemming used in this study were performed with custom made tooling and a 35 tonne hydraulic press. Similarly, roll hemming was performed using a custom made workbench with a three-degree of freedom system of rolls.

The material used for testing was aluminum sheet (6011); three rolling directions were taken in account: 0°, 45°, and 90° for the manufacture of the samples.

Hemming quality was determined from the geometric variables such as: lip high, pre-hemming angle, tool position, roll radius (roll hemming only). As a result, the comparison of roll in/out and wrinkle defects are reported and compared.
Investigations on the Structure and Properties of the Hot Extruded AA2014-Nano SiCp Composite
Authors: Karibeeran Shanmuga Sundaram , Sathishkumar Dhanalakshmi , Ramaiyan Sankar , Subban Rajamanickam
Published: January 2019

Aluminium based metal matrix composites with nano particle reinforcement are currently finding wide spread applications in automobile, aerospace and space structures because of their high strength, fatigue life, excellent wear resistance, low thermal coefficient value. However, in order to use these materials for critical automotive applications, extensive study in terms of manufacturing feasibility of the composites have to be carried out. Based on the objectives, the present investigation focuses on the development of Aluminium-SiC nano composite for structural applications. The aim of this research work is to arrive at an optimum weight faction of nano particle which gives the highest properties of the nano composite. The composites were produced by stir casting route. The base alloy and the composites were extruded and subsequently subjected to age hardening treatment. Microstructural evaluation, hardness studies were carried out on both the base alloy and the composites in the as-cast and extruded conditions. The effect of extrusion on the microstructure and properties of the AA2014-0.8 wt.%SiC composites have been discussed in detail.
Novel Approach for Tension Testing Micro Tubes
Authors: Wagner Scott W. , Emblom William J. , Johnson Kevin M. , Shah Kahaan P. , Handa Navrose , Kapare Nihal
Published: January 2019

Due to the miniaturization of products, new or modified processes are required to create small components. With the development of these new processes, it is also important to establish methods to evaluate the mechanical properties of the materials used in these components. These properties are necessary for accurately creating representative predictive models and simulations. At the same time, this evaluation can be challenging as sampling specimens become smaller the securing and handling of these smaller specimens becomes very difficult.

Recently, researchers made studies to develop and model the micro tube hydroforming (MTHF) process. In many of these studies, the mechanical properties used were either traditional book values or were values obtained directly from the manufacturers. The question then becomes, how do the manufacturers determine their provided mechanical properties?

The research in this study focuses on the development and testing of a new process to determine the mechanical properties of stainless steel micro tubes. Specifically, a set of clamps for securing a micro tube in a standard tension-testing machine were developed. A method for localizing the stress within the middle of a specimen was developed and the findings are presented in this paper.
Degradation of the Strength of a Grain and a Grain Boundary due to the Accumulation of the Structural Defects of Crystal
Authors: Zheng Guoxiong , Luo Yifan , Miura Hideo
Published: January 2019

Various brittle fractures have been found to occur at grain boundaries in polycrystalline materials. In thin film interconnections used for semiconductor devices, open failures caused by electro- and strain-induced migrations have been found to be dominated by porous random grain boundaries that consist of a lot of defects. Therefore, it is very important to explicate the dominant factors of the strength of a grain boundary in polycrystalline materials for assuring the safe and reliable operation of various products.

In this study, both electron back-scatter diffraction (EBSD) analysis and a micro tensile test in a scanning electron microscope was applied to copper thin film which is used for interconnection of semiconductor devices in order to clarify the relationship between the strength and the crystallinity of a grain and a grain boundary quantitatively. Image quality (IQ) value obtained from the EBSD analysis, which indicates the average sharpness of the diffraction pattern (Kikuchi pattern) was applied to the crystallinity analysis. This IQ value indicates the total density of defects such as vacancies, dislocations, impurities, and local strain, in other words, the order of atom arrangement in the observed area in nano-scale. In the micro tensile test system, stress-strain curves of a single crystal specimen and a bicrystal specimen was measured quantitatively. Both transgranular and intergranular fracture modes were observed in the tested specimens with different IQ values.

Based to the results of these experiments, it was found that there is the critical IQ value at which the fracture mode of the bicrystal specimen changes from brittle intergranular fracture at a grain boundary to ductile transgranular fracture in a grain. The strength of a grain boundary increases monotonically with IQ value because of the increase in the total number of rigid atomic bonding. On the other hand, the strength of a grain decreases monotonically with the increase of IQ value because the increase in the order of atom arrangement accelerates the movement of dislocations. Finally, it was clarified that the strength of a grain boundary and a grain changes drastically as a strong function of their crystallinity.
Evaluation of Heat Transfer Kinetics on Layers of Air-Rich Soft Materials in Their Natural State
Authors: Kaneko Hiroki , Sakuma Atsushi
Published: January 2019

Air-rich soft materials are widely used in textile products, such as clothes and towels, because they exhibit good heat-retaining properties. Quantification of the heat-retaining properties of materials is necessary for product design engineering. Here, the behavior of heat transfer in the layer structure of the material is evaluated to formulate its kinetics. Such evaluation can address the barriers to appropriate design. The heat transfer kinetics of the multilayered structure of the materials are evaluated by assessing the surface temperature of the outer layers. The evaluation equation for kinetics is formulated by applying the fundamental relationship of heat transfer, which is represented by thermal conductivity and the heat transfer coefficient. In the experimental evaluation, a simple wind tunnel was developed using a blower, hot plate, and digital radiation temperature sensor. The temperature of the hot plate was set at three levels. In the evaluation of surface temperature, the quantity of infrared ray was measured using the digital radiation temperature sensor, because it could be used without mechanically influencing the specimen. The surface temperature of the materials was measured by changing the number of layers from one to eight. In the evaluation of heat transfer kinetics, some properties of the conductivity and the transfer were identified by the formulated relationship for the kinetics of the layered structure and the numerical technique of inverse analysis. It was found that the heat conductivity of the material and heat conductivities between the layers can be identified by the examination of surface temperature variation caused by the change in the number of layers. Then, the crush effect of air-rich structures can be assessed by compressing the material and then analyzing the behavior change in heat transfer caused by the crush. The difference between the observed results and those obtained without the crush of air-rich structure was significant. Thus, we concluded that the physical properties of heat transfer in a multilayered structure of air-rich soft materials can be identified using the surface temperature change in the material resulting from the number of layers. Therefore, it is important to measure its behavior without the crush of the air-rich structure to evaluate the most natural state of the material appropriately.
Numerical Modeling of a Pure Water Jet Machining of Ti-6Al-4V and Al 6061-T6 Using ABAQUS and Smoothed Particle Hydrodynamics
Authors: Pasken Gregory , Ma J. , McQuilling M. , Jahan Muhammad P.
Published: January 2019

Pure water jets are not as effective as abrasive water jets for cutting hard materials at large scales. However, for nano-scale cutting, water jet cutting with abrasives is not possible because the abrasive particles are typically in the micron range which is three orders of magnitude larger than sizes to be cut. A pure water jet at the nano-scale might be a viable option. To ensure that it is possible to cut metals using a pure water jet, simulations at millimeter scale are conducted before downscaling to nano-scale. These simulations, using the smooth particle hydrodynamics (SPH) feature of ABAQUS, are conducted using two plate materials, Al 6061 and Ti-6Al-4V, with identical plate dimensions. The water jet is simulated via SPH, while the plate is modeled using standard FE methods. The water velocity and nozzle diameter are chosen to match those commonly used by companies employing water jets. Both the Al 6061 and Ti-6Al-4V simulations achieve convergence. Simulation results for both materials show damage on the surface and material removal. The top layer is removed in both cases as well as damage initiation is observed on the next layer of elements. These numerical results suggest that it is possible to use a pure water jet to cut two different metals. This research lays the foundation to use a pure water jet to conduct nanomachining of hard materials.
FEM Investigation of Phase Transformation in Vibration Assisted Nano Impact Machining by Loose Abrasives (VANILA)
Authors: Duong Nick H. , Ma J. , Jahan Muhammad P. , Lei Shuting , Sundaram Murali
Published: January 2019

In this paper, a numerical study of a nanomachining process, Vibration Assisted Nano Impact machining by Loose Abrasives (VANILA), has been conducted. In the VANILA process, an atomic force microscope (AFM) is used as a platform and the nano abrasives (diamond particles) are injected in slurry between the silicon workpiece and the vibrating AFM probe. The vibration of the AFM probe generates kinetic energy for the abrasives to impact the silicon workpiece and result in nanoscale material removal. In addition, silicon usually experiences phase transformation when subject to high pressure at nano-scale. The commercial Finite Element Method (FEM) software package Abaqus is employed to simulate the phase transformation experienced by the silicon workpiece in this VANILA process under different machining parameters such as impact speed, impact angle and coefficient of friction between the nano-abrasive and silicon workpiece. It is found that the machining parameters (impact speed, impact angle, and coefficient of friction) have substantial influence on the phase transformation of silicon workpiece in the nanomachining VANILA. Phase volumes for Si-VII, Si-VIII, and Si-X increase as the impact speed increases from 100 m/s to 200 m/s. Phase volume of Si-X increases as the friction coefficient increases. For Si-VII and Si-VIII, the phase volumes decrease as friction coefficient increases from 0.05, 0.3 and 0.5. In addition, the phase volumes for Si-VII, Si-VIII, and Si-X usually increase as the impact angles increases from 20° to 90°. However, for impact speed of 150 m/s and frictional coefficient of 0.05, the Si-VII phase volume increases first as impact angle increases from 20° to 70° and then decreases as the impact angle increases from 70° to 90°.