bluuebunny/crossref_metadata_2025 huggingface dataset:
Natural Frequencies and Mode Shapes of Statically Deformed Inclined Risers
Authors: Alfosail Feras K. , Nayfeh Ali H. , Younis Mohammad I.
Published: February 2017

In this work, we investigate numerically the linear vibrations of inclined risers using the Galerkin approach. The riser is modeled as an Euler-Bernoulli beam accounting for the nonlinear mid-plane stretching and self-weight. After solving for the initial deflection of the riser due to self-weight, a Galerkin expansion of fifteen axially loaded beam mode shapes are used to solve the eigenvalue problem of the riser around the static equilibrium configuration. This yields the riser natural frequencies and exact mode shapes for various values of inclination angles and applied tension. The obtained results are validated against a boundary-layer analytical solution and are found in good agreement. This constructs a basis to study the nonlinear forced vibrations of inclined risers.
Effects of Stator Configurations on the Flotation Performance of Induced Gas Flotation Machine
Authors: Lee Ji-Gu , Kang Ji-Yun , Kim Youn-Jea
Published: February 2017

Induced Gas Flotation (IGF) vessel is used for water treatment of plant industries such as oil sand and chemical plants. An understanding of the interaction between the stator and rotor is essential for the design of IGF with consideration of geometric blade configuration is essential for the design of IGF. In this study, the effect of the number of stator blades on flotation performance was numerically investigated using the commercial code, ANSYS CFX ver. 16.1. The two-phase (water and air) flow characteristics in the forced-air mechanically stirred Dorr-Oliver flotation cell were considered. The flotation performance was evaluated on the basis of the correlations among the number of stator blades (8, 12, 16, 20, 24), power number and void fraction. By comparing the result of each case, the newly designed model with 12 stator blades which had the highest flotation performance was derived.
Computed Torque Control of a Two-DOF Cable-Suspended Parallel Mechanism
Authors: Xie Zexiao , Ma Ben , Ren Ping
Published: February 2017

This paper presents the design of a computed torque controller for a two-degree-of-freedom (two-dof) cable-suspended parallel mechanism. Unlike fully constrained cable-driven parallel mechanisms, cable-suspended parallel mechanisms are not redundantly actuated and usually have the same number of actuated cables as the degrees of freedom. Compared with rigid-link parallel mechanisms, the control of cabled parallel mechanisms is more challenging in that the cable tensions are unidirectional. Taking the input constraints into account, the method of computed torque control is applied to the two-dof planar cable robot. The sufficient conditions and necessary & sufficient conditions of the controller’s parameters are obtained, under which the positiveness of the tensions is always maintained during the point-to-point motion within the cable robot’s static workspace. Numerical simulations show that the controller is computationally efficient and the end-effector of the robot could converge to desired final positions with exponential stability.
Effects of Anatomical Site and Loading Rate on Tensile Behavior of Fiber Bundles Isolated From Nerve Roots
Authors: Tamura Atsutaka , Sakaya Mizuki , Koide Takao
Published: February 2017

The present study has investigated the characteristics of the tensile behavior of fiber bundles isolated from the spinal nerve roots. By conducting a series of uniaxial stretching tests at three different velocities, 0.2, 2, and 20 mm/s, we found a significant difference (P < 0.05) in failure strain (∼0.15), linear portion of elastic modulus (∼20 MPa), and tensile strength (∼2 MPa) between low (0.2 mm/s) and high (20 mm/s) loading rates. However, it was revealed that mechanical properties of fiber bundles were resultantly on the order of the same magnitude, indicating that their mechanical responses were relatively insensitive to a strain rate irrespective of a 100-fold increase in the applied stretching velocities. It was also confirmed that the “spinal level effect” does exist in the nerve roots, i.e., a fiber bundle isolated from the thoracic spinal level is the strongest in mechanical strength compared to that of the cervical and lumbar spinal levels (P < 0.01), which suggests we should pay more close attention to an anatomical site where excised samples are obtained. The mechanical data obtained here will be useful to improve a mathematical human body model and to assess the potential injury in crash simulations relevant to whiplash associated disorder.
Comparative Analysis on Traumatic Brain Injury Risk due to Primary and Secondary Impacts in a Vehicle-Pedestrian Sideswipe Accident
Authors: Tamura Atsutaka , Hasegawa Junji , Koide Takao
Published: February 2017

A series of vehicle-to-pedestrian sideswipe impacts were computationally reconstructed; a fast-walking pedestrian was collided laterally with the side of a moving vehicle at 25 or 40 km/h, which resulted in rotating the pedestrian’s body axially. Because of a limited interaction between the human body and striking vehicle, the struck pedestrian was projected transversely from the vehicle and fell to the ground close to the first impact point. Potential severity of traumatic brain injury (TBI) was assessed using linear and rotational acceleration pulses applied to the head and by measuring intracranial brain tissue deformation. We found that TBI risk due to a secondary head strike with the ground can be much greater than that due to a primary head strike with the vehicle. Further, an ‘effective’ head mass, meff, was computed based upon the impulse and velocity change involved in the secondary head strike, which mostly exceeded the mass of the adult head-form impactor (4.5 kg) commonly used for a current regulatory impact test for pedestrian safety assessment. Our results suggest that TBI risk due to a ground impact would be mitigated by actively controlling meff, because meff is closely associated with a pedestrian’s landing style in the final event of ground contact.
Dynamic Simulation of a Direct Drive Reversing Valve Based on the Hydraulic Die Forging Hammer
Authors: Zhu Muzhi , Zhao Shengdun
Published: February 2017

The direct drive reversing valve is designed in this paper to replace the main reversing valve of the hydraulic die forging hammer system, and a new drive method based on TPMLM (tubular permanent magnet linear motor) is suggested. To verify the feasibility of the drive method, the fluid force suffered by valve core is calculated by using control volume method. After that, force analysis is carried out on the valve core. Based on FLUENT, the flow field analysis inside the valve is conducted. And then theoretical calculation and simulation on the fluid force analysis are discussed. TPMLM (tubular permanent magnet linear motor) is selected as the driving device and it is analyzed by Maxwell 2D. The simulation results of TPMLM show that the magnetic flux density, back electromotive force and output force satisfy the requirement of the reversing valve.
Droplet Oscillation After Impact on a Solid Surface
Authors: Yao Yina , Meng Shuai , Li Cong , Chen Xiantao , Yang Rui
Published: February 2017

Droplet spreading and oscillation occur when a liquid droplet impacts on the solid surfaces. This process is vital in many industrial applications, such as ink-jet printing technologies, spray coating and agricultural spray deposition. However, the researches that have been done mainly focused on the spreading process, and less attention has been paid to the droplet oscillation phenomenon, which has influence on the solidification and evaporation process. Therefore, the study on droplet oscillation phenomenon after the impact is necessary and valuable. This paper aims at analyzing the droplet oscillation phenomenon using VOF method. Since the contact angle varies dramatically in the dynamic process, a dynamic contact angle model is introduced to improve the simulation accuracy. The dynamic contact angle model has been verified by comparing the numerical results with experimental and theoretical results. In order to study the factors that may influence the droplet oscillation period, different droplet diameters and impact velocities are utilized in this simulation. The results show that the oscillation period presents a positive relationship with droplet diameter. However, the impact velocity has no apparent influence on the oscillation period, which agrees well with the theoretical analysis.
Verification Method for the Design of Remote Handling Systems Using a Reliability-Based Stochastic Petri Net Approach
Authors: Sibois Romain , Määttä Timo , Siuko Mikko
Published: February 2017

The verification of complex engineering systems from the very early phases of the design process is of primary importance as it directly influences the performance and system functionalities. Traditional design approaches aim at using simulations as a set of tools during the verification process. However, the current trend in the industry is to base the design process on the simulations as a simulation-based design. This perspective will therefore convey the design process towards a verification-driven design process. This paper reviews the definition of design process, engineering design verification process and decision making process. The objectives of the paper aim at describing an innovative verification-based design process using reliability-based stochastic Petri Net approach. The scope of the paper includes aspects of complex system designs and demonstrates a method to verify the concept design against its requirements using a quantitative approach. Finally, the method is applied on a case study and the results as well as future development are discussed in the last section.
Effects of Ambient Pressure on the Mass Burning Rate and Heat Release Rate of n-Heptane Pool Fire
Authors: Ma Qiuju , Liu Quanyi , Tian Runhe , Ye Junjian , Yang Rui , Zhang Hui
Published: February 2017

This research aims to investigate the effect of ambient pressure on the burning rate and heat release rate (HRR) of n-heptane pool fire. The experiments were performed in a large-scale altitude chamber of size 2 m×3 m×4.65 m under series of pressure, 24kpa, 38 kPa, 64 kPa and 75 kPa to 90 kPa. A round steel fuel pans of 34 cm in diameter and 15 cm in height was chosen for the pool fire tests. The fuel pan was filled with 99% pure liquid n-Heptane. Experimental results show that the burning rate increases rapidly after ignition until it reaches to the peak, and then maintains at a relatively stable stage. It decreases gradually until the flame extinguishes. The burning time is longer at lower pressure. The mean mass burning rate at the steady burning stage increases exponentially with pressure as ṁ ∼ Pα, with α = 0.68. HRR curve has a similar trend with the burning rate. The maximum HRR increases from 27kW to 62kW as the pressure rises from 24kPa to 90kPa. It is concluded that the ambient pressure has a significant effect on the fire heat release rate, and will further influent on other fire parameters.
Investigating the Effect of Al2O3/Water Nanofluid on the Efficiency of a Thermosyphon Flat-Plate Solar Collector
Authors: Negm Mohamed Nabeel A. , Abdel-Rehim Ahmed A. , Attia Ahmed A. A.
Published: February 2017

The world is still dependent on fossil fuels as a continuous and stable energy source, but rising concerns for depletion of these fuels and the steady increase in demand for clean “green” energy have led to the rapid growth of the renewable energy field. As one of the most available energy sources with high energy conversion efficiency, solar energy is the most prominent of these energies as it also has the least effect on the environment. Flat plate collectors are the most common solar collectors, while their efficiency is limited by their absorber’s effectiveness in energy absorption and the transfer of this energy to the working fluid. The efficiency of flat plate solar collectors can be increased by using nanofluids as the working fluid. Nanofluids are a relatively recent development which can greatly enhance the thermophysical properties of working fluids. In the present study, the effect of using Al2O3/Water nanofluid as the working fluid on the efficiency of a thermosyphon flat-plate solar collector was experimentally investigated. The results of this experiment show an increase in efficiency when using nanofluids as the working fluid compared to distilled water. It was found that Al2O3/water nanofluids are a viable enhancement for the efficiency of flat-plate solar collectors.
Contact Stiffness Calculation and Effects on Rotordynamic of Rod Fastened Rotor
Authors: Zhuo M. , Yang L. H. , Yu L.
Published: February 2017

Rod fastened rotor is widely used as one kind of structures of gas turbine rotors. Due to its discontinuity, the stiffness of the combined rotor is different from integral rotor. In order to obtain the dynamic of rod fastened rotor, the stiffness of contact needs to be calculated. There are two main methods to calculate the stiffness of contact. One is focus on the microscopic spots in contact based on the fact that maching surface is full of asperities. Hertz contact theory and Greenwood model are used to calculate the contact stiffness under both moment and preload. The other method is finite element method and assumes the contact surfaces are absolutely smooth which is from macroscopic aspect. Contact stiffness is calculated using the two methods and their influencing factors are discussed. Also the contact stiffness from the two methods is used to build a finite element model of a rod fastened rotor and their influences on dynamics of combined rotor are investigated and compared. Results show that the effect of preload of rods on contact stiffness is due to the roughness of contact surfaces. When no separation appears in contact, the bending stiffness is independent of bending moment in both methods. However, it shows a contrary variation when separation appears. Although there is big difference of bending stiffness from both methods, it shows little influence on the rotordynamic of the rod-fastened rotor.
Effect of Halogen-Free Ionic Liquids as Additives of Biolubricants for Room Temperature Titanium-Steel Contact
Authors: Bossung Kyle , DeRosa Matthew , Salas Jose , Iglesias Patricia
Published: February 2017

The surface interactions and tribological behavior of titanium-steel contact have been previously studied under the application of several commercial Ionic Liquids (ILs). In certain cases, superior anti-wear characteristics have been experienced when lubricating using ILs. This is often attributed to the development of a protective tribolayer that forms during application. One anion in particular amide, [Tf2N], has exhibited these characteristics with particularly positive results. However, amide is an anion that contains halogens, which are toxic and can cause harm if not handled properly. Due to the toxicity of most lubricants there has been a growing need to transition to bio-lubricants due to their low impact to the environment. This particular work will investigate the use of Trihexyltetradecylphosphonium, [P6,6,6,14]-+, cation with anion decanoate [Deca] as a non-toxic alternative to amide [Tf2N]. [P6,6,6,14]-+[Deca] and [P6,6,6,14]-+[Tf2N] will be compared as additives (1.0 and 2.5 wt. %) in Coffee Bean oil (CB) for lubrication of titanium-steel contact at room temperature.

In this work, tests are conducted using a ball-on-flat reciprocating tribometer as per ASTM G133 with lubricated titanium-steel contact. An AISI 420C stainless steel ball is used on a Grade 5 6Al-4V titanium alloy disk specimen. Friction and wear volume are measured, examined, and discussed.
Sensor-Fusion Approach for the Characterization of Human Walking
Authors: Felipe Martínez , Antonio Cardenas , Maya Mauro , Bortoletto Roberto , Blum Lillian A. , Piovesan Davide
Published: February 2017

The need to understand the control strategies utilized by humans in their everyday activity requires the measurement of several variables, which pertain to different aspects of the interaction with the environment. This work focuses on validation and uncertainty quantification of a sensor-fusion suite for the acquisition of biometric information that can be used for the estimation of the control strategy in a variety of everyday tasks. Specifically, the acquisition of biomechanical parameters such as those involving estimations of human ankle mechanical impedance is addressed. The sensor fusion suite that we devised consists of a centralized program that can synchronize and integrate the information coming from several transducers. In this work the system combines a set of two computer vision cameras. The cameras utilize a stereovision algorithm that transforms the markers acquired in Cartesian space with a model in the camera space. Furthermore, a biomechanical model of the human is integrated in the system for the reconstruction of the tracked movements in the joint space. The architecture of the systems allows for the integration of transducers beyond those implemented to date, including inertial measurement units, electromyography and pressure sensors. The system was able to capture the dynamics of an inverted pendulum on a cart mimicking human walking on a treadmill there the mechanical parameters of the ankles where estimated simulating a single stand phase.
Decision-Making and Group Behaviors in a Building Evacuation Experiments Considering Occupancy Social Network
Authors: Li Lihua , Ma Yaping , Jin Hua , Zhang Hui , Liu Yi
Published: February 2017

In this paper, social network analysis method is applied to verify that daily life social relation is an important factor affecting individual and group behaviors and evacuation efficiency. Evacuation experiments are conducted by carrying out 15 multi-mode collaborative evacuation drills including 6 in 2014 and 9 in 2015.The same group of 30 evacuees from a undergraduate class has been tracked for two years. Social network method is used to study following behavior, leading behavior and decision-making behavior in evacuation experiments. Through the questionnaires before and after all the evacuation drills, by defining the mutual trust degree (MTD) and being followed degree (BFD), the MTD relation matrix on daily life and the BFD relation matrix in evacuation can be constructed. Then normal social relation network graph and following relation network graph in emergency are drawn. Results show that small groups and leaders will be formed automatically during group evacuation, and the leaders in emergency demonstrate some certain stability, which has some relevance with gender and relations in normal situation. When two emergency exits are available during evacuation including stair and elevator, evacuation efficiency is best when the elevator and stair are located at the same side.
The Influence of Sensors Arrangement and Quantity on MCMC Inversion Model Based on Bayesian Inference
Authors: Li Cong , Meng Shuai , Yao Yina , He Yuanhua , Yang Rui
Published: February 2017

In this paper, Markov chain Monte Carlo(MCMC) inversion method based on the Bayesian inference is used to invert parameters of leak source in two-dimensional space. Sensors are divided into three groups with different arrangements: linear-array perpendicular to the wind direction, linear-array parallel to the wind direction and cross-array. Then the source probability distributions of different arrangements and quantities on the accuracy and efficiency were analyzed and compared. It is shown that in one direction, more measurement information from different sensors result in more accurate inversion parameters. In the case with the same quantity of sensors, inversion parameters considering information of two directions are more accurate than which only considering one direction. It means that the combination of information in two directions can improve the inversion accuracy. The ventilation will enlarge the possible convergence region and increase the instability of inversion results in wind direction because of its migration and dilution effect. The inversion time consumed presents a positive relationship with the quantity of sensors. However, too much sensors may lead to the growth of consumption time, which are not conducive to practical application.
Fabrication of Bulk Skinless Polyetherimide (PEI) Nanofoams
Authors: Jose David , Gutierrez Christopher , Srinivas Sundarram Sriharsha
Published: February 2017

Polymer nanofoams are classified as foams having pore size less than hundred nanometers. Several techniques to fabricate nano porous polymer morphologies have been developed. However, majority of them result in foams with a thin layer of un-foamed polymer on the surface. The un-foamed polymer region called the skin layer is typically around 10 microns thick which restricts the use of these foams for many applications such as filtration. Skinless open-celled nanofoams are a unique category of foams that have pore size on the order of tens to hundreds of nanometers and do not have any unfoamed solid polymer layer on the surface post processing. Potential applications for skinless nanofoams include filtration, catalysts, dielectronics and biological scaffolds. It has also been suggested that these nanofoams will have improved thermal and electric properties due to the open celled porous morphology and the absence of skin layer. In this study bulk skinless polyetherimide (PEI) nanofoams were fabricated using a novel two stage technique consisting of combined solid state and laser foaming. Initially, PEI samples embedded in a sacrificial polymer layer were saturated with supercritical carbon dioxide (CO2) as the blowing agent. The sacrificial layer ensures uniform gas concentration gradient at the surface during subsequent desorption step. A hot press and heated bath technique were used independently to foam the samples. Solid state foaming parameters — foaming time and number of sacrificial layers were varied to study their effect on the skin thickness of the nanofoams. The thickness of the sacrificial polymer layer had a direct effect on the skin thickness of the PEI nanofoams after foaming. It was observed that the skin thickness reduced by nearly 60% on an average due to the sacrificial layer. The solid state foaming process was followed by laser foaming using a CO2 laser with a wavelength of 10.6 μm to generate pores in the thin skin layer. The power intensity of the laser beam, the travel speed and the working distance had a direct effect on the laser pore formation process. It was found that a power intensity of 0.09 W, laser head travel speed of 50 mm/s and working distance of 4.5 cm were the most ideal conditions to form pores in a skin layer of approximately 10 micron thickness. The cross sections were observed using a scanning electron microscope to study the cell morphologies, pore size and the skin layer. This technique was found to produce skinless nanofoams with average porosity 78 % and smallest pore-size of 250 nm. To summarize, optimal parameters and processing conditions for bulk production of skinless PEI nanofoams are presented in this study.
Investigation of Heat Transfer and Fluid Flow Over Pocket Cavity in the Rear Part of Gas Turbine
Authors: Liu Jian , Wang Chenglong , Wang Lei , Xie Gongnan , Andersson Martin , Sundén Bengt , Abrahamsson Hans , Arroyo Carlos
Published: February 2017

The pocket cavity is generated at the transition part between the low pressure turbine (LPT) and outlet guide vane (OGV) in a gas turbine engine. Because the important connection with OGV, the heat transfer and fluid flow need to be investigated and analyzed. In the present work, a simplified triangular pocket cavity is built and heat transfer and fluid flow are investigated experimentally and numerically. Liquid Crystal Thermography (LCT) is employed to measure the heat transfer over the pocket surface with Reynolds number ranging from 54,054 to 135,135. In addition, two fillets with different radii are designed to investigate the flow structures over the pocket surface. The turbulent flow details are provided by numerically calculations based on the commercial software Fluent 15.0 with a validated turbulence model. Based on the results, the highest heat transfer value is located in the downstream boundary of the pocket cavity where the strongest flow impingement happens. The smaller fillet radius presents a higher heat transfer peak value and also induces stronger recirculating flow inside the pocket cavity. Considering the design requirement in the rear part of a gas turbine, i.e., to decrease the heat transfer peak value, a larger fillet radius is recommended for practical design. The heat transfer and flow details also provide a reliable reference for gas turbine engine design.
Dynamic Model of a Membrane Pump Powered by a Scroll Pump in an Absorption Refrigeration Cycle
Authors: Costa Tiago F. , Santos Carlos A. C. dos
Published: February 2017

This paper presents the dynamic modelling of a pumping system used in an absorption refrigeration cycle using water-ammonia as cooling fluid. This system consists in a membrane pump (with a membrane made of PTFE - Polytetrafluoroethylene), powered by a scroll pump, in which two spring-loaded check valves control the flow direction. By having a system of nonlinear differential equations, using numerical methods, it was possible to find solutions and obtain time dependent functions of flow rate (making possible the analysis of the flow pulsation and its behaviors), valves openings, membrane position, in order to better understand the system. In addition, it was possible to generate functions and graphics that shown the relations between changes in variables such as membrane radius and thickness and excitation frequency and amplitude. It was also possible to generate double variable prediction graphics, that could lead to a user-friendly software on future works, which can help on faster and precise design optimization techniques.
Modelling and Simulation of Al/SiCp MMCs During Hot Machining
Authors: Jadhav Mahesh R. , Dabade Uday A.
Published: February 2017

Metal Matrix Composites (MMCs) give higher strength and stiffness, greater wear resistance over a wide range of conditions, making them an option in replacing conventional materials for many engineering applications. These materials are difficult-to-machine due to high hardness and abrasive nature of reinforcing elements like silicon carbide, aluminum oxide, and boron carbide particles. High tool wear and pits, cavities on machined surface due to fracturing of reinforcements puts certain constraints on MMCs for experimentation. Similarly, the experimental or analytical approaches are not able to explore the behavior of MMCs during machining due to the complex deformation and interactions with particles, matrix and tool. The numerical approach is very important tool to simulate the machining process of MMCs in which plastic deformations, modelling the plasticity are involved. FEM analysis eliminates the restrictions of experimental approach such as control of large process parameters, the exhaustive material characterization and the trial-and-error approach which is expensive and time consuming procedure to determine the mechanical responses. These advantages of finite element method make this approach more popular. It has come up as the main tool of simulation of metal cutting processes to calculate stress, strain, strain-rate, temperature distributions, tool wear, cutting forces and chip formation. In this paper, an attempt is made to present a 3D oblique finite element modelling using Deform software. In Deform, FEM analysis carried out by using steps are preprocessing, simulation and post-processing of data for the established machining process. Deform 3D is a robust simulation tool that uses the finite element model to complex machining process in three dimensions. It has been used in simulations of two types of Al/SiCp/220 MMCs with 10 and 30% of SiC reinforcement particles. These materials are considered as perfectly plastic and its shape was taken as a curved model by means of coated carbide insert as a rigid body. A simulation scheme involves size and weight fraction of reinforcement, speed, feed rate, depth of cut and preheating temperature. Four levels of speed, feed rate, depth of cut and preheating temperature are chosen. Designs of experiments are done by Taguchi’s design of experiments (DOE). For four level four parameters, suitable L16 orthogonal arrays are selected. Based on design of experiments, a machining simulation and analysis are carried out using Deform 3D, software. Obtained finite element simulation results are found to be closely match within 10 to 15% variation with the experimental results during hot machining of Al/SiCp/220 metal matrix composites (MMCs).
The Impact of the Interaction Between Impeller and Spiral Casing on the Performance of Radial Fans
Authors: Epple Philipp , Fritsche Manuel , Rußwurm Hans
Published: February 2017

In thermal recycling plants high performance fans are needed to transport gas through the process. For this application, the fans have to fulfill very special requirements. The pyrolysis and gasification processes transform different kinds of waste, e. g. biomass and municipal scrap waste, electronic or industrial waste, into highly clean efficient synthetic gas, i.e. usable energy. Therefore, the thermal operating range of these fans lies between ambient temperatures of about 20°C and 530°C. Due to the requirements and design space of the recycling facility, new radial fans were developed according to these particular specifications.

Two different impellers were designed with an extended analytical method, as described in Epple et al. [1] and [2]. The first one was designed with a parallel flat shroud and the second one with a conical shroud. In order to fulfill the manufacturer requirements of ease of manufacturing, the impellers were designed with circular arc blades. With these two impellers and at a temperature of 530 °C, as it is needed in the recycling plants, a first Bommes spiral casing was optimized adjusting the spiral casing opening angle and the Bommes parameter, i.e. the ratio of the spiral casing width to the impeller exit width, BSC/b2 (Epple et al. [3]). The results show that the predictions of Bommes work well with impellers with conical shrouds, but for impellers with parallel shrouds the Bommes prediction does not work properly.
Analytical and Numerical Design of a High Performance Double–Throated Supersonic Blowdown Windtunnel
Authors: Epple Philipp , Steppert Michael , Steber Michael
Published: February 2017

In this publication the focus lies on the design process of the full supersonic double throated wind tunnel. Starting with the fundamental equations of gas dynamics in combination with an analytical model of the pressure reservoir, the area of the throat at the nozzle and the runtime of the blowdown wind tunnel were computed. Based on these results, the shape of a shock free nozzle was calculated by the method of characteristics. For this purpose, a nozzle design program was developed using Python. In order to validate the results of the method of characteristics program, these results were compared with the area-Mach number relation, which is the exact analytical solution of the isentropic flow through supersonic nozzles.

The convergent part of the nozzle, which initially accelerates the flow to sonic speed, cannot be calculated by the method of characteristics, since it applies to supersonic flows only. Hence the subsonic convergent section of the nozzle was designed directly with 2D CFD using CD Adapco Star-CCM+ v. 10.06. A parametric model of the convergent nozzle section was used to find the optimum nozzle shape, i.e. a nozzle which results in a maximum mass flow rate in order to have an undisturbed flow field and Mach number in the following test section.

In order to decelerate the flow again from supersonic to subsonic flow after the test section and minimize the total pressure losses, an oblique shock diffuser was used [1]. As for the convergent subsonic nozzle, the optimum shape of a diffusor was found by 2D CFD analysis.

Putting all these elements together, i.e. nozzle, test section and diffuser the optimum supersonic wind tunnel shape was found. Finally, a full 3D simulation of the supersonic wind tunnel was performed in order to validate the complete design procedure and computations and also to include the viscous effect of the side walls. These results and the whole design process are presented and analyzed in the paper.
Ring Specimen Geometry for Determining the Ductility of Tubulars
Authors: Al Khaled M. A. , Barsoum I.
Published: February 2017

Pressure vessels designed in accordance with the ASME BPVC code are protected against local ductile failure. Recent work has shown that local ductile failure highly depends on the stress state characterized by both stress triaxiality (T) and the Lode parameter (L). In this paper, the effect of stress state on the ductility of a tubular steel is studied. Two ring specimen configurations were optimized to allow the determination of the ductile failure locus of both tensile and plane strain loadings. The geometry of both ring specimen configurations was optimized to achieve a plane strain (L = 0) condition and a generalized tension (L = −1) condition. Notches with different radii were machined on both types to achieve a wide range of stress triaxiality. Specimens were manufactured from SA-106 carbon tubular steel and were tested to determine the ductile failure loci as a function of T and L. Failure locus of SA-106 steel was constructed based on the failure instants and was found to be independent of the variation in the Lode parameter. The ASME-BPVC local failure criterion showed close agreement with experimental results.
Study on Leakage Rate of Rubber Sealing Structures Based on Percolation Theory
Authors: Huang Xiaoming , Xu Guoliang
Published: February 2017

To enhance the containment integration for nuclear safety, sealing performance of those numerous penetrations has to be concerned. Surface roughness of the sealing pairs contact ends has great influence on the leakage characteristics. Following the essence of leakage phenomena, a theoretical mechanism model of leakage rate for rubber sealing structure was built based on percolation theory, where rough contact interface was treated as an aperture region. Deformation behavior of the roughness was solved by using Hertz contact theory. The mechanism model can realize the conversion of leakage rate between different operating conditions, which is important to leakage rate prediction. And the model can be easily combined with macro mechanical analysis of the sealing structure, which is helpful for their optimum design. Validation and convenience of this model is verified through two concrete examples.
Effect of Gradient Anode on Mass Transfer Performance for Anode-Supported Planar Solid Oxide Fuel Cells
Authors: Fu Pei , Zeng Min , Wang Qiuwang
Published: February 2017

For anode-supported planar solid oxide fuel cells (SOFCs), the thick anode support layer (ASL) prevents the supply of fuel gas to the anode functional layer (AFL) where the electrochemical reactions take place. Shortage of the fuel gas at the active region results in concentration polarization. SOFC designs with porosity gradient anode may improve the cell performance. In order to investigate the effect of the porosity distributions on mass transfer characteristics of SOFC, a three dimensional half-cell model is developed based on the computational fluid dynamics (CFD) method. The numerical model solves continuity equation, conservation of momentum, multi-component mass transfer and electrochemical reaction. According to the numerical results, a SOFC design with a higher porosity gradient anode could effectively enhance mass transport of the fuel gas in the AFLs, which would lead to the reduction of polarization loss. It is also found that high porosity gradient among the anode layers could improve the H2 concentration gradient in the porous anode, which is beneficial to facilitate diffusion of the fuel gas in the porous anode. Concentration overpotentials of the SOFC decrease with the increase of the porosity gradient, especially for the low inlet H2 molar fraction. These findings indicate that the comprehensive performance of SOFC can be effectively improved by employing a high porosity gradient anode.
Synthesis of Variable-Diameter Helical Extension Springs
Authors: Mohammed Riyaz , Zhou Hong
Published: February 2017

Helical extension springs store energy and provide resistance to tensile loads that are applied through appropriate spring ends. Typical spring ends include different types of hooks or loops. Both ends of a helical extension spring are attached to other components. When the two components move apart and their distance is increased, the helical extension spring exerts a tensile force between the two components and tries to decrease their distance. There are various applications for helical extension springs that include automobiles, toys, hand tools, agriculture machines, textile machines, and medical devices. The common configuration of helical extension springs uses straight cylindrical shape that has constant coil diameter and pitch. Unlike regular helical extension springs, variable-diameter helical extension springs do not employ constant coil diameter. Their variable coil diameter enables them to produce desired force deformation relationships and reduce stress concentration. The distinctive features of variable-diameter helical extension springs also raise their synthesis challenges. To surmount these challenges, a method is introduced in this paper to model and design variable-diameter helical extension springs. The configuration of a synthesized spring is described by a composite parametric curve. The entire spring is defined by its control parameters. Synthesizing the spring is systematized as optimizing its control parameters. Examples on modeling, analyzing and designing springs are presented in the paper to demonstrate the procedure and verify the effectiveness of the introduced synthesis method.
Aerodynamic Load Mapping of Bluff Bodies: An Update and Summary
Authors: Motahari Nicholas , Shukla Dhwanil , Hiremath Nandeesh , Komerath Narayanan
Published: February 2017

Measurements of 6-DOF aerodynamic loads on bluff bodies using the continuous rotation method are summarized. New results are presented on two rectangular prisms and on three practical shapes — an Engine Canister model, a Ribbon Bridge model, and a model of a standardized aerodynamic container to carry automobiles. Efforts are described, to relate the aerodynamic loads on the practical shapes, to weighted combinations of aerodynamic loads on interpolated canonical shapes. The Engine Canister aerodynamic loads are obtained to good approximation from those on an interpolated cylinder of aspect ratio 1.9. Likewise, the Ribbon Bridge aerodynamic loads are approximated from loads on rectangular prisms and circular cylinders. An attempt is made to predict the load variation on a rectangular prism, from those measured on a prism 1/3 as long using topological arguments; this attempt shows the large interaction effects on such a shape.
Numerical Simulations of Turbulent Natural Convection in Laterally-Heated Cylindrical Enclosures With Baffles for Crystal Growth
Authors: Enayati Hooman , Chandy Abhilash J. , Braun Minel J.
Published: February 2017

Ammonothermal crystal growth technique is one of the most effective methods used for growing Gallium Nitride (GaN) crystals. GaN crystals have wide applications in light emitting diodes (LEDs) or UV lasers. Three-dimensional large eddy simulations (LES) of natural convection in a laterally heated cylindrical reactor, using the commercial computational fluid dynamics (CFD) software ANSYS FLUENT, are presented for a Rayleigh number of Ra = 8.8 × 106. The objective of the current calculations is to understand the effect(s) of opening area of the baffle on the flow pattern and temperature distribution inside the reactor. The baffles considered in this study are annular hollow discs with different opening areas. Three cases with total opening areas of 40%, 25% and 100% (baffle-less) are considered. Velocity and temperature distributions across the different planes and lines, are analyzed in order to obtain information on the flow and heat transfer processes (temperature maps) resulting from various baffle openings.
Numerical Investigation of Turbulent Flow Over a Windscreen Wiper Blade
Authors: Cadirci Sertac , Ozsipahi Mustafa , Coskun Umut C. , Ak Suleyman E. , Gunes Hasan , Selenbas Bugra
Published: February 2017

Windshield wipers were developed to improve visibility during inclement weather and belong to standard safety equipment. A conventional wiping system of a vehicle consists of three components; namely, motor and mechanism, wiper arm and wiper blade. The wiper arm transfers the movement to the wiper blade and cleaning is achieved by wiping water and dirt from the windscreen by a blade rubber. In order to wipe water and dirt from the windscreen, the wiper blade should be forced onto the windscreen with a specified force. The necessary force is obtained by the spring mechanism within the arm. In this study the effect of free-stream velocity, turbulence models on the drag and lifting forces acting on the windshield wiper and spoiler geometry are investigated numerically. The spoiler geometry is modified to reduce the lifting force.
A Multiphase Flow Simulation for a Cells-on-a-Chip Device
Authors: Zhang Meihua , Zheng Amy , Zheng Z. Charlie , Wang Zhuo Michael
Published: February 2017

Microfluidics-based microscale cell culture (cells-on-a-chip) provides a well-controlled system with physiological realistic parameters that emulates the organ-to-organ network of the human body. In the microenvironment, the in vivo situation can be resembled closely by controlling the chip geometry, medium flow behavior, medium-to-cell ratio, and other fluid dynamic parameters. This study is to develop a multiphase model to simulate the flow in such a device. The cell deposition rate influenced by the flow shear is discussed. The physics of fluid dynamics for each of the above mentioned parameters is investigated.
Modeling and Measurement of Temperature Distributions in Bone Drilling
Authors: Lee JuEun , Ozdoganlar Burak , Rabin Yoed
Published: February 2017

The heat generated during bone drilling can cause significant thermal damage to the tissue. Hence, prediction of the developing temperature field as a function of the drilling parameters is of high clinical value. However, no experimentally validated model has been reported yet. Furthermore, prior theoretical studies are limited to the drilling process, while extending the analysis beyond drill-bit retraction may be of equal interest. Therefore, the current study aims at experimental validation of a recently published thermal model for temperature distributions both during bone drilling, which is now expanded beyond drill-bit retraction. For validation of the model, a set of experiments was conducted on bovine cortical bone, following the new procedures suggested in the previous study in order to ensure a high degree of accuracy and repeatability. This study is based on thermal data collected at a distance range of 0.15 mm to 0.5 mm from the drilled hole, using thermocouples. Measuring temperatures closer to the drilled hole enabled better understanding of temperature distributions in the tissue in bone drilling. Comparison of experimental data and theoretical simulation results validate the model used. Additionally, about 57°C of difference of the maximum temperatures measured at the radii locations between 0.15 mm and 0.5 mm was observed.
Numerical Investigation of Slip Flows Through 2-D U-Shaped Microchannels
Authors: Shojaeian Mostafa , Koşar Ali
Published: February 2017

Micro-electro-mechanical systems (MEMS) offer vast applications and those involving fluid flow/gas flows typically operate in the slip flow regime, where the normal non-slip condition assumptions for boundary conditions are not valid. In this study, two-dimensional numerical simulations of continuum and slip flows for U-shaped microchannels were performed to evaluate flow characteristics by means of the ANSYS-FLUENT software. In order to model slip condition existing at the solid-liquid interface of microchannels, a user defined subroutine was linked to the software. The effect of Reynolds number and geometric parameters such as the bend shape and the distance between legs on fluid flow and heat transfer characteristics were examined in detail. The computational results showed that increasing either the slip length or Reynolds number decreased the average friction factor, while the distance between legs does not have any effect on it. Moreover, it was found that the averaged Nusselt number would increase with Reynolds number and the slip length, but increasing the distance between legs decreased the averaged Nu for square bend compared to its negligible increase for circular bend.
Modeling of Transport During Droplet Deposition and Spreading on Smooth and Microstructured Superhydrophilic Surfaces
Authors: Mizerak Jordan P. , Carey Van P.
Published: February 2017

The dynamic behavior of impinging water droplets is studied in the context of varying surface morphologies on smooth and microstructured superhydrophilic surfaces. The goal of this study is to evaluate the capability of contact angle wall adhesion models to accurately produce spreading phenomena seen on a variety of surface types. We analyze macroscale droplet behavior, specifically spreading extent and impinging regime, in situations of varying microscale wetting character and surface morphology. Axisymmetric, volume of fluid (VOF) simulations with static contact angle wall adhesion are conducted in ANSYS Fluent. Simulations are performed on water for low Weber numbers (We<20) on surfaces with features of length scale 5–10μm. Advanced microstructured surfaces consisting of unique wetting characteristics and lengths on each face are also tested. Results show that while the contact angle wall adhesion model shows fair agreement for conventional surfaces, the model underestimates spreading by over 60% for surfaces exhibiting estimated contact angles below approximately 0.5°. Microstructured surfaces adapt the wetting behavior of smooth surfaces with higher effective contact angles based on contact line pinning on morphology features. The propensity of the model to produce Wenzel and Cassie-Baxter states is linked to the spreading radius, introducing an interdependency of microscale wetting and macroscale spreading behavior. Conclusions describing the impact of results on evaporative cooling are also discussed.
Annular Shear-Thinning Flow Over an Axisymmetric Sudden Expansion
Authors: Hammad Khaled J.
Published: February 2017

Suddenly expanding annular pipe flows of a shear-thinning non-Newtonian fluid were numerically investigated within the steady laminar flow regime. The power-law constitutive equation is used to model the rheology of interest. A parametric study is performed to reveal the influence of annular diameter ratio, k, and power-law index, n, over the following range of parameters: k = {0, 0.5, 0.7} and n = {1, 0.8, 0.6}. Flow separation and entrainment, downstream of the expansion plane, creates two recirculation regions. The first is a central recirculation region between the expansion plane and the flow stagnation point along the centerline. A second, corner recirculation region forms between the expansion plane and the flow reattachment point along the wall. The results demonstrate impact of the investigated geometrical and rheological parameters on the extent and intensity of both flow recirculation regions, the wall shear stress distribution, and the evolution and redevelopment characteristics of the flow downstream the expansion plane.