bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of an Integrated Photovoltaic-Thermal Option for HVAC Cooling System in UAE
Authors: Gadalla Mohamed , Al Hammadi Amani , Gadalla Dina
Published: March 2016

This paper investigates the integration of a photovoltaic-Thermal Collector (PV/T) and a Triple Effect Absorption System (TEAS) for cooling residential as well as commercial buildings. Energy and exergy analyses are conducted to examine the performance of the recommended system and to investigate the variation of different operating conditions and PV/T characteristics on the overall performance of the PV/T collector. Power and heat generated by the PV/T system are used to mainly drive mainly the TEAS by supplying power and heat to the HTG. This paper studies the effect of the of average solar radiation for different months during the year on the Coefficient of Performance (COP) and/or the overall efficiency of the (PV/T) collector integrated with TEAS to produce 10 kW of cooling capacity. This paper also investigates how the rate of energy output of the PV/T collector. It is found that energetic and exergetic efficiencies of the PV/T collector as well as the overall energetic and exergetic efficiencies of the integrated system decrease with increasing the solar irradiance. The analyses show that the maximum energetic and exergetic COPs obtained for PV/T integrated with TEAS are 2.32 and 2.06; respectively. Finally, this paper provides a new interpretation in which alternative energy is utilized in operating HVAC cooling systems and presents a new insight into one of the most sustainable integrated systems that can be applied in residential and commercial buildings in the UAE.
A Reliability Optimization Allocation Method for Multifunction System With Differentiation of Functions
Authors: Yi Xiaojian , Hou Peng , Dong Haiping , Lai Yuehua , Mu Huina
Published: March 2016

The study on the optimization of system reliability allocation rarely involved the constraints on different functions of system. Some constraints only referred to the main function or one function in system. Owing to the requirement of mission and other factors, all system functions need to have different performance and reliability respectively. For this reason, we proposed a new method for optimization of reliability allocation in this paper. The constrains in the method focus on the discrepancy of reliability of different functions of system. The reliability of system function is defined as it whether to meet the requirement of mission capacity, and the reliability of all different system functions will be calculated by universal generating function, and the objective is to minimize system cost. At last, this method is applied in reliability optimization allocation of a Power-shift Steering Transmission with the improved genetic algorithm.
Design and Optimization of the Restrictor of a Race Car
Authors: Kokkula Prithvi Raj , Bhojappa Shashank , Arslan Selin , Jawad Badih A.
Published: March 2016

Formula SAE is a student competition organized by SAE International. The team of students design, manufacture and race a car. Restrictions are imposed by the Formula SAE rules committee to restrict the air flow into the intake manifold by putting a single restrictor of 20 mm. This rule limits the maximum engine power by reducing the mass flow rate flowing to the engine. The pull is greater at higher rpms and the pressure created inside the cylinder is low. As the diameter of the flow path is reduced, the cross sectional area for flow reduces. For cars running at low rpm when the engine requires less air, the reduction in area is compensated by accelerated flow of air through the restrictor. Since this is for racing purpose cars here are designed to run at very high rpms where the flow at the throat section reach sonic velocities. Due to these restrictions the teams are challenged to come up with improved restrictor designs that allow maximum pressure drop across the restrictor’s inlet and outlet. The design considered for optimizing a flow restrictor is a venturi type having 20 mm restriction between the inlet and the outlet complying with the rules set by Formula SAE committee.

The primary objective of this work is to optimize the flow restriction device that achieves maximum mass flow and minimum pull from the engine. This implies the pressure difference created due to the cylinder pressure and the atmospheric pressure at the inlet should be minimum. An optimum flow restrictor is designed by conducting analysis on various converging and diverging angles and coming up with an optimum value.

Venturi type is a tubular pipe with varying diameter along its length, through which the fluid flows. Law of governing fluid dynamics states that the “Velocity of the fluid increases as it passes through the constriction to satisfy the principle of continuity”. An equation can be derived from the combination of Bernoulli’s equation and Continuity equation for the pressure drop due to venturi effect. [1].

A Computational Fluid Dynamics (CFD) tool is used to calculate the minimum pressure drop across the restrictor by running a series of analysis on various converging and diverging angles and calculating the pressure drop. As a result, an optimum air flow restrictor is achieved that maximizes the mass flow rate and minimizes the engine pull.
Simulation and Experiment of Mass Evacuation to a Tsunami Evacuation Tower
Authors: Kakizaki Takao , Urii Jiro , Endo Mitsuru
Published: March 2016

A 3D mass evacuation simulation using precise kinematic digital human (KDH) models and an experimental study are discussed. The tidal wave associated with the large tsunami caused by the Great East Japan Earthquake was responsible for more than 90% of the disaster casualties. Unfortunately, it is expected that other huge tsunamis could occur in Japan coastal areas if an earthquake with magnitude greater than 8 occurred along the Nankai Trough. Therefore, recent disaster prevention plans should include evacuation to higher buildings, elevated ground, and construction of tsunami evacuation towers. In the evacuation simulation with 500 KDHs, the mass consists of several subgroups. It is shown that the possible evacuation path of each group should be carefully determined to minimize the evacuation time. Several properties such as evacuee motion characteristics of KDHs, number of evacuees, exit gates and, number of injured persons were carefully considered in the simulation. Evacuee motion was also experimentally investigated by building a test field that simulates the structure of an actual tsunami evacuation tower for accommodating approximately 120 evacuees. The experimental results suggest that an appropriately divided group population may effectively reduce the overall group evacuation time. The results also suggest that the fatigue due to walking during evacuation adversely affect the total evacuation time, especially the ascent of stairways. The experimental data can be used to obtain more accurate simulations of mass evacuation.
Far-Field Noise Prediction of Wind Turbines at Different Receivers and Wind Speeds: A Computational Study
Authors: Khalili Fardin , Majumdar Pradip , Zeyghami Mehdi
Published: March 2016

Far-field noise propagation from wind turbines propel development of wind farms to an issue for public acceptance. Airstream contains pressure fluctuations as a result of instability, giving a regular eddy pattern or an irregular turbulent motion which are responsible for the sound produced by wind turbine blades. Aeroacoustic noise emanated from a wind turbine is mainly generated by the interactions of tip and trailing edge of wind turbine blades with the mechanics in wake region such as inflow turbulence structures, boundary layer separation and vortex shedding. Hence, there is a strong necessity for an analytical investigation for noise reducing design and development of the technology in order to further expand wind farms. The objectives of this study are to analyze the far-field aeroacoustics of wind turbines with the purpose of predicting far-field sound pressure levels at different receivers and monitoring total acoustic power captured within wind turbine performance for various wind speeds. Blades are modeled based on NREL S825 airfoil since it has high maximum lift and low profile drag. With the purpose of predicting far-field noise, the Ffowcs Williams-Hawkings (FW-H) acoustics model is the preferred method in order to compute the far-field sound signal which is released from near-field flow. As the key attribute of the research, detached eddy simulation (DES) provides accurate results for the desired simulation since it is a hybrid modeling approach that combines features of Reynolds-averaged Navier-Stokes (RANS) simulation in boundary layers and irrotational flow regions, and large-eddy simulation (LES) in unsteady separation regions. In addition, SST K-Omega detached eddy turbulence model is used due to its good compromise between robustness, computational cost and accuracy. Aerodynamic and aeroacoustic analysis of a wind turbine is performed using a three-dimensional model and a commercial CFD Software, STAR-CCM+. In order to predict far-field sound pressure levels and acoustic powers on different locations, five point receivers are defined downstream of the wind turbine model. Receivers are placed one diameter, D, over the wind turbine rotor blades with 1D, 2D, 5D, 10D and 15D away from the wind turbine that represent receivers 1 to 5. Higher acoustic powers are delivered at closer receivers. It means that acoustic power fades out with larger distances. It is observed that there is a fractional variation of 61%, 17%, 6% and 3% as compared to the receiver 1 for receivers 2, 3, 4 and 5 respectively. Moreover, the results show that variation in total acoustic power is non-linear and higher acoustic powers will be captured for higher velocities. This comparison is done between wind speeds of 10m/s and 15m/s.
An Effective Method for Fluid Dynamics Analysis of Inflow Control Devices
Authors: Filippov Andrey , Khoriakov Vitaly
Published: March 2016

Horizontal wells are a widely applied architecture in modern field developments. However, because of the frictional pressure drop and reservoir permeability variations along the well, there is usually a non-uniform influx from the reservoir along the length and higher injection or production flow rates at the heel. Inflow control devices (ICDs) have been used for more than a decade to balance or equalize flow rates by creating additional pressure drop. To improve performance and longevity of the ICDs, their design must account for axial non-uniformity of pressure distribution and fluid flow details in the vicinity of the wellbore.

This paper discusses an effective approach to the problem and analytical solution of the pressure and flow field near the ICD section of the wellbore and prediction of the leveling of the non-uniform axial pressure distribution as a function of distance from the wellbore. The obtained analytical equations are validated through comparison with results of detailed numerical simulation using the finite difference method.
Particulate Matter: Fine and Ultrafine — How Emerging Data on Engineered Nanomaterials May Change How We Regulate Worker Exposures to Dust
Authors: Gernand Jeremy M.
Published: March 2016

Currently in the United States, agencies responsible for regulations related to worker or public exposures to dust set rules based on a few general categories determined by gross particle size categories like PM10 (particles < 10 μm) and PM2.5 (particles < 2.5 μm) and the total mass of certain specific compounds (e.g., 3.5 mg/m3 of carbon black). Environmental health researchers however, have begun to focus on a new category of ultrafine particles (PM0.1; particles < 100 nm) as being more indicative of actual health risks in people. The emerging field of nanotoxicology meanwhile is providing new insights into how and why certain particles cause damage in the lungs by investigating the effects of exposure in animals to very well characterized engineered nanomaterials.

Based on this recent research the National Institute of Occupational Safety and Health (NIOSH) has issued new recommended exposure limits (RELs) for carbon nanotubes (CNTs) and titanium dioxide nanoparticles that are 2–3 orders of magnitude more stringent than RELs for larger particles of the same or similar substance. It remains unclear at present how stringent future regulations may be for engineered and inadvertently created nanoparticles or ultrafine dusts. Nor is it clear whether verification methods to demonstrate compliance with these rules could or should be devised to differentiate between engineered and inadvertently created nanoparticles.

This study presents a review of the history of dust regulation in the United States, how emerging data on the health risks of ultrafine particles and engineered nanoparticles is changing our understanding of the risks of inhaled dust, and how future rulemaking in regards to these and similar particulate materials may unfold.

This review shows the extent to which rules on dust have become more stringent over time specifically in the case of diesel emissions and silica exposure, and indicates that new rules on worker exposure to ultrafine dusts or engineered nanomaterials may be expected in the United States within 5–10 years based on past experience on the time delay in connecting research on new hazards to regulatory intervention. Current research suggests there will be several challenges to compliance with these rules depending on the structure of the final rule and the development of detection technologies. Although the research on ultrafine dust control technologies appears to indicate that once rulemaking begins there may be no serious feasibility limits to controlling these exposures. Based on ongoing exposure studies, those industries likely to be most affected by a new rule on ultrafine dusts not specific to engineered nanomaterials will include transportation, mining, paper and wood products, construction, and manufacturing.
Highly Sensitive Pressure Sensor Using Two-Dimensionally Aligned Carbon Nanotube Bundles
Authors: Nozaki Takuya , Suzuki Ken , Miura Hideo
Published: March 2016

A highly sensitive two-dimensional tactile sensor has been developed by applying the stain-induced change of the electronic resistance of MWCNTs (Multi-Wall Carbon Nano-Tubes). The elastic deformation of a bundle of MWCNTs was confirmed under the axial compressive strain from 0% to 60%, and the sensitivity of compressive force was 1 mN. The maximum gauge factor of the bundle under the compressive strain was about 100, and it was obtained from the buckling deformation of the bundle. Since the effective elastic constant of the bundle was about 140 kPa, it was important to use a very soft dielectric material for electrical isolation among area-arrayed fine bundles in the tactile sensor. The application of polydimethylsiloxane (PDMS) was found to be effective for assuring the flexible deformation of each bundle in the sensor under the application of a distributed load.
A Revisit of Material and Structural Failures
Authors: Wang Sheldon
Published: March 2016

In this paper, we revisit the issues related to material and structural failures. In particular, we employ a similar bridging function between the typical structural failure, the so-called column buckling, and the typical material failure under compression, to link the low stress high cycle and the high stress low cycle fatigue. A part of the intention of this paper is to come up with simple formulas as guidelines in engineering practice for both material and structural failures in both static and dynamic situations.
Control for Robots With Braking Actuators in a Uniform Force Field
Authors: Framstad Erlend , Bedillion Mark D.
Published: March 2016

This paper concerns the control strategy of a robot with controllable brakes placed in a uniform force field. Without loss of generality this force field is assumed to be gravity, and the robot to be an object resting on an inclined plane. The controller’s objective is then to use the brakes to lead the robot into a desired position and orientation.

The system’s dynamics were derived from Newton’s second law with a Coulomb friction model. The controller was derived from geometric properties and the energy equation. The controller was then tested using Matlab and Simulink on the dynamics that were derived. The results of the simulation shows high accuracy even with some disturbances, and uncalibrated parameters.
Study of the Fluid Dynamics of Thin Liquid Films Flowing Down a Vertical String With Counterflow of Gas
Authors: Zeng Zezhi , Warrier Gopinath , Ju Y. Sungtaek
Published: March 2016

Direct-contact heat transfer between a falling liquid film and a gas stream yield high heat transfer rates and as such it is routinely used in several industrial applications. This concept has been incorporated by us into the proposed design of a novel heat exchanger for indirect cooling of steam in power plants. The DILSHE (Direct-contact Liquid-on-String Heat Exchangers) module consists of an array of small diameter (∼ 1 mm) vertical strings with hot liquid coolant flowing down them due to gravity. A low- or near-zero vapor pressure liquid coolant is essential to minimize/eliminate coolant loss. Consequently, liquids such as Ionic Liquids and Silicone oils are ideal candidates for the coolant. The liquid film thickness is of the order of 1 mm. Gas (ambient air) flowing upwards cools the hot liquid coolant. Onset of fluid instabilities (Rayleigh-Plateau and/or Kapitza instabilities) result in the formation of a liquid beads, which enhance heat transfer due to additional mixing. The key to successfully designing and operating DILSHE is understanding the fundamentals of the liquid film fluid dynamics and heat transfer and developing an operational performance map. As a first step towards achieving these goals, we have undertaken a parametric experimental and numerical study to investigate the fluid dynamics of thin liquid films flowing down small diameter strings. Silicone oil and air are the working fluids in the experiments. The experiments were performed with a single nylon sting (fishing line) of diameter = 0.61 mm and height = 1.6 m. The inlet temperature of both liquid and air were constant (∼ 20 °C). In the present set of experiments the variables that were parametrically varied were: (i) liquid mass flow rate (0.05 to 0.23 g/s) and (ii) average air velocity (0 to 2.7 m/s). Visualization of the liquid flow was performed using a high-speed camera. Parameters such as base liquid film thickness, liquid bead shape and size, velocity (and hence frequency) of beads were measured from the high-speed video recordings. The effect of gas velocity on the dynamics of the liquid beads was compared to data available in the open literature. Within the range of gas velocities used in the experiments, the occurrence of liquid hold up and/or liquid blow over, if any, were also identified. Numerical simulations of the two-phase flow are currently being performed. The experimental results will be invaluable in validation/refinement of the numerical simulations and development of the operational map.
A Hybrid RANS-LES Modeling Methodology Sensitized to Transitional and Curvature/Rotation Effects
Authors: Chitta Varun , Walters D. Keith
Published: March 2016

This paper presents a new hybrid model that seeks to combine the strengths of Reynolds–averaged Navier-Stokes (RANS) and large eddy simulation (LES) methods. The new model is based on a recently proposed version of a dynamic hybrid RANS-LES (DHRL) framework that addresses several deficiencies inherent in most current hybrid models, including explicit grid dependence, boundary layer model stress depletion, and delayed shear layer breakdown. The DHRL framework is highly generalized, allowing coupling of any desired LES model with any given RANS model. In this study, a recently proposed four-equation eddy-viscosity model (EVM) capable of predicting both flow transition from laminar-to-turbulent (T) and rotation and/or streamline curvature (RC) effects is used for the RANS component, and a monotonically-integrated LES (MILES) scheme is used for the LES component. The new model (DHRL with T-RC effects) is implemented into a commercial computational fluid dynamics (CFD) code and investigated against three different flow configurations. The test cases include nonrotating and rotating channel flow, zero-pressure-gradient (ZPG) boundary layer flow over a flat plate, and flow over a circular cylinder. Results obtained from the numerical simulations indicate that the new hybrid model produces significant levels of turbulent fluctuations in the flowfield and successfully resolves T-RC effects. The results show improved accuracy compared to RANS models and are obtained at a significant reduction of computational cost compared to full LES models. Further investigation on complex test cases is warranted before commenting on the accuracy and potential usage of the model as a practical tool.
Numerical Investigation on the Effect of Aluminum Foam in a Latent Thermal Energy Storage
Authors: Buonomo Bernardo , Ercole Davide , Manca Oronzio , Celik Hasan , Mobedi Moghtada
Published: March 2016

In this paper, a numerical investigation on Latent Heat Thermal Energy Storage System (LHTESS) based on a phase change material (PCM) is accomplished. The geometry of the system under investigation is a vertical shell and tube LHTES made with two concentric aluminum tubes. The internal surface of the hollow cylinder is assumed at a constant temperature above the melting temperature of the PCM to simulate the heat transfer from a hot fluid. The other external surfaces are assumed adiabatic. The phase change of the PCM is modeled with the enthalpy porosity theory while the metal foam is considered as a porous media that obeys to the Darcy-Forchheimer law. The momentum equations are modified by adding of suitable source term which it allows to model the solid phase of PCM and natural convection in the liquid phase of PCM. Both local thermal equilibrium (LTE) and local thermal non-equilibrium (LTNE) models are examined. Results as a function of time for the charging phase are carried out for different porosities and assigned pore per inch (PPI).

The results show that at high porosity the LTE and LTNE models have the same melting time while at low porosity the LTNE has a larger melting time. Moreover, the presence of metal foam improves significantly the heat transfer in the LHTES giving a very faster phase change process with respect to pure PCM, reducing the melting time more than one order of magnitude.
Shaped Magnetic Field in Resonance Technology and its Application to Transportation System
Authors: Cho Dong-Ho , Suh Nam Pyo , Yoon Uooyeol , Jung Guho
Published: March 2016

KAIST has developed the Shaped Magnetic Field in Resonance (SMFIR) technology that transfers a large amount of energy to electric vehicles when they are running or stationary. The wireless charging SMFIR technology provides a solution to the commercialization barriers of electric vehicles such as the problems of batteries and charging infrastructure.

Using 20-kHz wireless power transfer system based on the SMFIR technology, our eco-friendly On Line Electric Vehicle (OLEV) bus was wirelessly powered by 100 kW through a power grid embedded under the road. On the other hand, using high-capacity, high-efficiency and low-cost 60kHz power supply and pickup systems based on the SMFIR technology, tram and high speed train were wirelessly powered by 180 kW and 1 MW through a power grid built in rail roads, respectively.

The commercial OLEV tram has been operated commercially from July 2011 in Seoul National Grand Park. Also, the OLEV shuttle bus has been operated for convenience of students and faculty members at KAIST campus since Oct. 2012. In addition, the world’s first intra-city OLEV bus with 100 KW pickup capacity has been operated commercially at Gumi city from March 2014. Then, airgap is about 20 cm and maximum power transfer efficiency is 85 %.
Long-Term Archiving of Exact 3D-CAD Geometry With JT
Authors: Trinkel T. , Anderl R. , Zocholl M. , Eichhorn H.
Published: March 2016

The technology of Computer Aided Design (CAD) has been in use for 3D design for more than 30 years. Still today, the result of the 3D design process is usually a 2D engineering drawing. Thus, many downstream processes in the industry are dependent on engineering drawings. Nowadays, many companies are replacing their engineering drawings with 3D-CAD models and transforming their drawing-based processes into model-based processes. Consequently, these 3D-CAD models have to be archived and new methods to do so have to be implemented. The standardization of the Jupiter Tessellation (JT) file format specification as ISO 14306 could be an opportunity to use a single data format for both purposes: downstream processes and long-term archiving of exact 3D-CAD geometries.

This paper describes an approach for long-term archiving of exact 3D-CAD geometries. Initially the state of the art in long-term archiving methodology and archiving systems is analyzed. In order to enable an investigation from a technological point of view, the ISO JT data format is examined subsequently. The formal and technological requirements for a JT-based approach are then derived from these analyses. The next step is to introduce a conceptual process for long-term archiving of exact 3D-CAD geometries with the JT data. As a proof of concept, this approach is implemented prototypically. Through a comparison of the representation of exact 3D-CAD geometries in the JT and STEP data formats, the conditions for responsible long-term archiving using JT are defined.

As a conclusion, this paper provides an overview of the advantages and the associated risks of long-term archiving with the ISO JT data format for exact 3D-CAD geometries.
Modeling Phase Change Heat Transfer of Liquid/Vapor Systems in Free and Porous Media
Authors: Wilson James A. , Wehking Jonathan D. , Trautman Mark , Blue Mark E. , Kumar Ranganathan
Published: March 2016

Effective Solvent Extraction Incorporating Electromagnetic Heating (ESEIEH) is a relatively new concept that relies on Radio Frequency (RF) heating and solvents to replace steam in current thermal processes for the purpose of extracting bitumen from oil rich sands. The work presented here will further the understanding of the near wellbore flow and phase behavior of the ESEIEH process in order to better predict solvent vaporization dynamics and heat rates delivered to the pay zone. This numerical study details the aspects of phase change of liquid/vapor systems confined in porous media heated by electromagnetic radiation, and approximated by a volumetric heat source term in the energy equation. The objective of this work is to utilize the numerical methodology presented herein to predict liquid penetration depth in a heated isotropic porous matrix to avoid the over-saturation of liquid solvent in the pay zone. Results demonstrate the sensitivity of the liquid solvent penetration depth to the solvent delivery rate and the resulting temperature.
A Parametric Study of the Modeling of Orthogonal Machining Using the Smoothed Particle Hydrodynamics Method
Authors: Avachat Chinmay S. , Cherukuri Harish P.
Published: March 2016

Modeling machining processes with conventional finite element methods (FEM) is challenging due to the severe deformations that occur during machining, complex frictional conditions that exist between the cutting tool and the workpiece, and the possibility of self contact due to chip curling. Recently, the Smoothed Particle Hydrodynamics (SPH) method has emerged as a potential alternative for modeling machining processes due to its ability to handle severe deformations while avoiding mass and energy losses encountered by traditional FEM. The method has been implemented in several commercial finite element packages such as ABAQUS and LS-DYNA for solving problems involving localized severe deformations.

Numerous control parameters are present in a typical SPH formulation. The purpose of this work is to evaluate the effect of the three most important parameters, namely, the smoothing length, particle density, and the type of SPH formulation. The effects of these parameters on the chip morphology and stress distribution in the context of orthogonal machining of AISI 1045 steel are investigated. The LS-DYNA finite element package along with Johnson-Cook material model is used for this purpose. Results from the parametric study are presented and compared with the previously reported results in the literature. In addition, the sensitivity of chip morphology and stresses to Johnson-Cook parameters for AISI 1045 steel is also investigated by considering five different sets of values reported in the literature for this steel.
A Study on the Corrosion Behaviour of Aluminium Alloy 2014 T-651 Friction Stir Welds Using Stress Corrosion Cracking
Authors: Kollapuri Thamilarasan , Manoharan Madhanagopal , Sadayan Rajendra Boopathy , Sajja Rama Koteswara Rao
Published: March 2016

Stress Corrosion Cracking (SCC) is the initiation and slow growth of cracks under the influence of tensile stresses and aggressive corrosion environment. Al alloy 2014 T 651 was solution heat treated and stress-relieved. In the present work, Stress Corrosion Cracking (SCC) experimental arrangement has been used to test the severity of aluminium alloys under particular environmental conditions. Sound welds were obtained with Friction Stir Welding at rotational speed of 800 rpm and welding speed of 200 mm/min. Friction Stir Welds were cut into standard tensile specimens as per ASTM E8 standards. Time to failure of the welds were obtained using 3.5 wt% NaCl solution at pH 10 in 0.7 and 1.1 yields by Stress Corrosion Cracking. Vickers micro-hardness was taken along various regions of the weld. Optical micro-graphs and scanning electron fractographs were taken to analyse the fracture behavior and fracture morphology of Friction Stir Welded aluminium alloy specimens, subjected to Stress Corrosion Cracking.
Testing and Modeling the Effect of Strain-Rate on Plastic Anisotropy for a Traditional High Strength Steel
Authors: Li Wei , Zhu Juner , Xia Yong , Zhou Qing
Published: March 2016

The effect of strain-rate on plastic anisotropy of an HSLA340 steel sheet is investigated in the present paper. Uniaxial tension tests in seven different directions are performed under three strain-rates (one in quasi-static range and two in intermediate range). Flow stress and Lankford r-value are obtained from the test data to describe the plastic anisotropy of the material. Results show that the anisotropy varies with the increase in strain-rate. To model this rate-dependent anisotropic behavior, three associated flow rule based yield functions, Hill48, Yld96, and Yld2000_2d, are employed first for each strain-rate. Though the result cannot match the test data perfectly, it still seems acceptable considering the complexity of the trend of anisotropy. Accordingly, the coefficients of these models are studied, and it turns out that all of them change with the stain-rate in a similar trend. Based on this result, a rate-effect term is introduced to the coefficients of the models to characterize the rate-effect on plastic anisotropy. Finally, two issues about the modeling work are discussed. One is calibrating the Yld96 and Yld200_2d model with the non-associated flow rule, which means the coefficients of the functions are determined by flow stress only or r-value only separately. It is found that the accuracy of the characterization is largely improved because of the increase in model coefficients. The other issue that is discussed is the modeling of strain-rate effect on the plastic anisotropy. A new strategy is considered, in which the strain-rate effects in different directions are characterized first, followed by the anisotropy description. The results of the two strategies are compared and good agreement is achieved.
Immersed Boundary Method for CFD Analysis of Moving Boundary Problems in OpenFOAM
Authors: Singh Krishna M. , Nonaka Norihiko , Oh U.
Published: March 2016

CFD simulation of hydraulic equipments involving moving boundary components is really challenging due to difficulty in maintaining a good quality mesh essential for obtaining accurate numerical solutions. To deal with these problems, commercial codes such as Ansys CFX provide the option of mesh morphing which must be used in conjunction with pre-defined multiple grid configurations to account for changing flow domain. In contrast to this approach, immersed boundary method (IBM) provides an attractive alternative in which the complex moving surface is immersed in a fixed Cartesian (or polyhedral) grid. We have developed an immersed boundary simulation tool-kit for moving boundary problems based on OpenFOAM. It requires the user to provide the definition of the immersed surfaces in STL (stereolithography) format, type of flow (internal/external) and motion (stationary, pre-defined or flow-induced) of the surface. Numerical simulations have been performed for selected test cases to assess the computational performance of the immersed boundary too-kit. Numerical results of flow over stationary as well as vibrating cylinders agree very well with available experimental and numerical results, and show that the immersed boundary simulations accurately capture the vortex shedding frequency and vortical structures for moving boundary problems.
Energy Savings for Sustainability of Machining Process
Authors: Bharambe Ganesh , Dabeer Prakash , Sapate Kumar Digambar , Sawant Suresh M.
Published: March 2016

Processing of metals in industries is lifeline of economy of country, which helps to shape the country. Energy saving in this process is attributed to both the parts ie process of machining and energy consumed in machine tools itself. The process of material removal had experienced lot of improvements in last few decades. This consists of developments in pre-machining processes, metal cutting methods and developments in cutting theories and cutting tools. Cutting fluid is one of challenging field to yield more favourable results. Manufacturing practices beyond its existing limits, process and machine automations, using the previous data for improving machinabilities, optimizing through relative benchmarks (a market driven schemes) shall lead the manufacturing speed to a new high. Adaptibility of manufacturing set up to absorb new requirement will also be a controlling factor for acceleration of manufacturing processes. This paper discusses the efforts to reduce the energy to produce a product. Various methods are discussed to minimize the energy consumed for driving the machine components such as spindle, feeding device, lubricating system, cutting fluid system, indexing and tooling management, speed and feed controlling devices etc. Different requirements such as friction energy in braking action, speed reducing or cushioning will also consume certain amount of energy during its operations. Therefore one has to understand the various types of energy flows and classification of energy forms used from place to place. Study of constructional features of machines brings a lot of opportunities for savings in energy. The concepts of material handling, fluid handling like hydraulic and pneumatic circuits, lubrication system, shall also provide the opportunities for savings in energy consumption. Energy used for working of accessories whether they are required at that particular moments needs to be considered from time to time. There are few more methods for locating the chances for arresting the energy wastages and reducing specific energy consumption referring a particular process or function. Previous data generated for similar functions can be referred for comparison and efforts can be added to reduce the requirement of energy. Efficient and effective utilization of equipment shall open a fresh path for finding the energy reductions. Sustainability of machining processes can be ensured for future using the lean energy utilizations for productions. Authors have explained the live cases to demonstrate reduction in energy consumption. Few potential guidelines are also narrated in this line. Further few cases are discussed from literature survey which support and will help to pursue the target.
PIV Measurements of Turbulent Flows Over Single and Dual Rectangular Cavities
Authors: Hammad Khaled J. , Saucier Kyle W. , Koblick Nicholas C.
Published: March 2016

Particle Image Velocimetry (PIV) was used to measure the turbulent flow fields over single and dual rectangular cavities. Four sets of PIV measurements were acquired, corresponding to two Reynolds numbers per each cavity configuration. The cavity depth based Reynolds number was varied between 21,000 and 42,000, while the cavity length-to-depth ratio was fixed at four. Galilean decomposition is used to present instantaneous velocity fields. Turbulent velocity fields are presented using Reynolds decomposition into mean and fluctuating components. Characteristics of the instantaneous and time-averaged velocity fields corresponding to a single cavity configuration are in agreement with the observations from previous studies. All mean flow field results display a large vortical structure spanning the entire length and height of each cavity. In the case of a dual cavity configuration, the free shear layer and trailing edge regions of the second cavity were found to always display higher streamwise and crosswise flow fluctuations in comparison with the first cavity. Furthermore, a wider free shear layer region is observed in the second cavity, in comparison with the first cavity.
Characterization of the Electronic Properties and Strain Sensitivity of Graphene Formed by C2H2 Chemical Vapor Deposition
Authors: Yang Meng , Ohnishi Masato , Suzuki Ken , Miura Hideo
Published: March 2016

We succeed in synthesizing large-area single-layer graphene sheets with different grain size using C2H2 chemical vapor deposition process. Our graphene shows high uniformity and low sheet resistance to 1080Ω/□. By fabricating graphene-based field effect transistors (FETs), the relation between the nucleation density and the electronic properties of CVD grpahene are investigated. We found that the nucleation density can severely affect the defects formation in graphene, leading to the change in the electronic properties of graphene. We also check the strain sensitivity of CVD graphene. The as-grown graphene/Cu film was fixed onto the SiO2/Si substrate with a double-sided tape. The strain device is fabricated directly on the graphene-coated Cu foils by using the standard photolithography and reactive ion etching (RIE) process. Then the device is transferred onto a stretchable and flexible polydimethysiloxane (PDMS) substrate. By using a motorized stage, the tensile test is performed to investigate the piezoresistive properties of graphene-based strain sensors. The one-dimensional tensile test is performed to investigate the piezoresistive properties. A gauge factor 3.4 was achieved under the tensile deformation.
Stiffness Update Procedure in Iterative Global-Local Analysis of Columns
Authors: Erkmen R. Emre , Afnani Ashkan , Niki Vida
Published: March 2016

The purpose of this study is to develop a stiffness update technique to be used in a computationally efficient finite element solution for the analysis of columns undergoing local deformations, within the procedure of iterative global-local analysis. The computational problem that arises is that the stiffness matrix is formulated according to the global model, and as a result, considerably large number of iterations is required when the local deformations are significant. To overcome this difficulty, a stiffness update technique is presented in which the displacement field of the global model is altered at each step to consider the locally induced softening behaviour in order to accelerate the convergence. This goal is achieved by introducing embedded discontinuities in the beam element.
Unsteady Two-Phase Flow Analysis on Water Retarder Performance Using Sliding Mesh Technique and VOF Method
Authors: Lee Wonju , Hur Nahmkeon
Published: March 2016

Hydraulic retarders are used as auxiliary brake system in heavy vehicles and high speed trains. A hydraulic retarder is composed of two parts, a rotor and a stator. When the system is activated, the working fluid is injected into the wheel and circulates between the rotor and stator vanes using the resisting torque of the stator to slow down the vehicle. The purpose of this research is to investigate a water retarder system and the details of flow characteristics of the water, and to investigate the device performance as well. The water retarder is basically composed of a rotor and a stator. In the present research, the rotor rotating speed is fixed at 2000 rpm. Since the performance characteristic of the water retarder is dependent upon the water volume ratio, different volume ratios have been investigated. In this paper water retarder simulations are carried out using CFD using sliding mesh technique. To capture the unsteady effects, the cases have been solved as transient simulations using standard k-ε turbulence model. The simulations have been solved as two phase flow, water and air. The results are compared for different water volume ratios. The result show that the air particles are accumulated in the center of the wheels forming a tube shape (doughnut shape) and water particles are at the outside, wrapping the air particles. In addition, torque values are sensitively dependent upon water volume fraction.
Methane Steam Reforming and Metallic Membranes to Capture Carbon Dioxide in Gas Turbine Power Plants
Authors: Carapellucci Roberto , Favre Eric , Giordano Lorena , Roizard Denis
Published: March 2016

Pre-combustion CO2 capture is regarded as a promising option to manage greenhouse gas emissions from power generation sector. In this regard, metallic membranes can provide a significant boost in power plants energy performances, due to their infinite hydrogen perm-selectivity and their ability to operate at high pressure and temperature. However, the properly integration of these devices still requires a deep investigation of power plant behavior, in order to detect the mutual interaction between system components, which may impose constraints on their operating conditions.

This paper aims to investigate a chemically recuperated gas turbine (CRGT) with pre-combustion CO2 recovery based on hydrogen separation through a metallic membrane. At first, the steam reforming and membrane separation processes are investigated, in order to assess their sensitivity to the variation of the main operating parameters. Then, the CRGT power plant with CO2 capture is analyzed, highlighting the effect of system components interaction on energy and environmental performances. In addition, the study accomplishes a preliminary investigation of the system capability to produce an excess of hydrogen to be used as an energy carrier.
Time-Dependent Reliability Analysis for Bivariate Responses
Authors: Hu Zhen , Zhu Zhifu , Du Xiaoping
Published: March 2016

Time-dependent system reliability is measured by the probability that the responses of a system do not exceed prescribed failure thresholds over a period of time. In this work, an efficient time-dependent reliability analysis method is developed for bivariate responses that are general functions of random variables and stochastic processes. The proposed method is based on single and joint upcrossing rates, which are calculated by the First Order Reliability Method (FORM). The method can efficiently produce accurate upcrossing rates for the systems with two responses. The upcrossing rates can then be used for system reliability predictions with two responses. As the general system reliability may be approximated with the results from reliability analyses for individual responses and bivariate responses, the proposed method can be extended to reliability analysis for general systems with more than two responses. Two examples, including a parallel system and a series system, are presented.
Performance Analysis of a Silica Gel-Water Adsorption Cooler: Impact of Nanofluids on Cooler Performance and Size
Authors: Koronaki I. P. , Nitsas M. T. , Papoutsis E. G. , Papaefthimiou V. D.
Published: March 2016

Thermally driven chillers also known as sorption heat pumps have drawn considerable attention in recent years. They can be divided into two main categories: absorption (liquid-vapor) and adsorption (solid-vapor) systems. Even though adsorption cycles have relatively lower coefficient of performance compared to absorption cycles, however they prevail in terms of heat source, electric consumption for moving parts, crystallization etc. In order to overcome the drawback of low COP and specific cooling capacity, nanofluids, i.e. mixtures of nanometer size particles well-dispersed in a base fluid, can be used as heat transfer fluids as recent experimental and theoretical research has proved that nanofluids can exhibit a significant increase on heat transfer.

In this study a two bed, single-stage adsorption chiller which utilizes the silica gel-water pair as adsorbent-refrigerant is simulated. The cooling capacity and the COP of the chiller are calculated for various cycle times. The usage of nanofluids as heat transfer fluids in the chiller evaporator and condenser and their effect on chiller performance and size is investigated. It is proved that the presence of nanofluids at different volume concentrations will enhance the cooling capacity and the COP of the adsorption chiller and therefore will lead to smaller, in terms of size, heat exchangers.
Modeling, System Identification and Linearization of Underwater Turbine Power Plant Dynamics
Authors: Tzelepis Vasileios , VanZwieten James H. , Xiros Nikolaos I. , Sultan Cornel
Published: March 2016

A suite of nonlinear dynamical simulations of in-stream hydrokinetic devices has been developed and this paper discussed the linearization of these models for control system development. One of these numerical simulations represents a small 3 meter rotor diameter, 35 kW turbine with fixed pitch blades, and the other a 20 meter, 700 kW turbine with variable pitch blades. Each turbine simulation can be operated to represent a bottom mounted tidal turbine or a moored ocean current turbine. These nonlinear dynamical models can serve as stepping stones toward control system design using linear or nonlinear, time or frequency-domain methodologies. A common step further toward controller synthesis is to obtain linearized models of the system dynamics. Towards this end, two linearization techniques are presented. The first is based straightforward analytical and numerical linearization of the full nonlinear state-space equations of the plant; this method has been applied for the underwater flight dynamics of the 700 kW plant. The second is a phenomenological system identification approach consisting of data analysis performed on time series obtained through simulations; it has been used to model the system of systems in the case of the 35 kW plant. In the first approach, the linearized model is valid for specific operating conditions around equilibrium values of the state variables. In the second approach, the plant dynamical model is used as a black-box in order to obtain the simulated response of the system to a variety of test input signals, like e.g. sinusoids of relatively small amplitudes and various frequencies superimposed to steady-state offsets; in effect, a phenomenological model is derived describing the plant dynamics. The outcomes of both approaches are assessed and several conclusions are drawn from the analysis.