bluuebunny/crossref_metadata_2025 huggingface dataset:
TEG Cold Side Heat Transfer Analysis for Harvesting the Exhaust Heat Energy
Authors: Tan Gangfeng , Ji Kangping , Guo Xuexun , Yang Mengying , Zuo Lei
Published: December 2016

Temperature differential power generation made by the thermoelectric material is an effective way to recover waste heat and enhance the internal combustion engine energy utilization efficiency. At present, single-phase coolant is applied to the thermoelectric material cold-end, but the temperature control effect is not ideal except for low power generation. In this research, a two-phase cooling system is designed to stabilize the thermoelectric material cold-end temperature. Firstly, the thermal characteristics of the diesel engine exhaust gas and the Mg2Si0.3Sn0.7 thermoelectric material are obtained through experiments. Secondly, the heat-transfer model of the heat-exchange system is established through the set system’s geometrical parameters. Finally, the characteristics of temperature between the thermoelectric material’s cold-end and hot-end besides the heat transfer rate are acquired, thus the power generation performance of the thermoelectric material would be gained. The result shows that under the engine’s experiment working conditions of 1300rpm to 2100rpm, comparing to the single-phase cooling system, the two-phase cooling system could ensure the coolant’s cold-end temperature in the range of 102 °C to 106 °C , which increases the thermoelectric material temperature difference more than 50°C. Correspondingly, the power generation increases about 122W to 2785W.
Design of Self-Supported 3D Printed Parts for Fused Deposition Modeling
Authors: Lischke Fabian , Tovar Andres
Published: December 2016

One of the primary challenges faced in Additive Manufacturing (AM) is reducing the overall cost and printing time. A critical factor in cost and time reduction is post-processing of 3D printed (3DP) parts, of which removing support structures is one of the most time consuming steps. Support is needed to prevent the collapse of the part or certain areas under its own weight during the 3D printing process. Currently, the design of self-supported 3DP parts follows a set of empirical guide lines. A trial and error process is needed to produce high quality parts by Fused Depositing Modeling (FDM). The usage of chamfer angle with a max 45° angle form the horizontal for FDM is a common example. Inclined surfaces with a smaller angle are prone to defects, however no theoretical basis has been fully defined, therefore a numerical model is needed. The model can predict the problematic areas at a print, reducing the experimental prints and providing a higher number of usable parts.

Physical-based models have not been established due to the generally unknown properties of the material during the AM process. With simulations it is possible to simulate the part at different temperatures with a variety of other parameters that have influence on the behavior of the model. In this research, analytic calculations and physical tests are carried out to determine the material properties of the thermoplastic polymer Acrylonitrile - Butadiene - Styrene (ABS) f or FDM at the time of extrusion. This means that the ABS is going to be extruded at 200°C to 245°C and is a viscous material during part construction.

Using the results from the physical and analytical models, i.e., Timoshenko’s modified beam theory for micro-structures, a numerical material model is established to simulate the filament deformation once it is deposited onto the part. Experiments were also used to find the threshold for different geometric specifications, which could then be applied to the numerical model to improve the accuracy of the simulation. The result of the finite element analysis is compared to experiments to show the correlation between the prediction of deflection in simulation and the actual deflection measured in physical experiments.

A case study was conducted using an application that optimizes topology of complex geometries. After modeling and simulating the optimized part, areas of defect and errors were determined in the simulation, then verified and and measured with actual 3D prints.
Suppression of Nonlinear Bifurcations in Flexible Structures Using Nonlinear Switching Shunt Damping Circuits
Authors: Silva Tarcisio , Tan David , De Marqui Carlos , Erturk Alper
Published: December 2016

We explore the suppression of geometrically nonlinear vibrations of a flexible structure by using nonlinear switching shunt damping circuits, namely the Synchronized Switch Damping on Short (SSDS) circuit and the Synchronized Switch Damping on Inductor (SSDI) circuit. Following the early research on linear shunt circuits, the use of nonlinear switching shunts was explored for damping of linear resonance behavior of flexible structures in the early 2000s. However, such flexible structures can easily undergo undesired bifurcations and exhibit large-amplitude nonlinear oscillations that coexist with small oscillations in their frequency response. Suppression of such nonlinear vibrations and resulting bifurcations with linear resistive-inductive circuits is impractical due to extremely large inductance requirements. In the present work, the focus is placed on a strongly nonlinear and weakly coupled flexible structure for suppressing its large-amplitude periodic response branch resulting from saddle-node bifurcations. The Duffing-like structure of interest exhibits nonlinear hardening behavior of predominantly cubic stiffness under primary resonance excitation. Purely resistive linear shunting, SSDS, and SSDI damping techniques are employed and compared with the baseline (near short-circuit) frequency response curves (up- and down-sweep) of the nonlinear structure. Specifically it is shown that the SSDI circuit can substantially reduce the large-amplitude branch, offering the possibility of entirely suppressing undesired large-amplitude bifurcations of the nonlinear system up to certain excitation levels in order to achieve low-amplitude single-valued frequency response. Coupled nonlinear modeling, numerical simulations, and experimental validations are presented.
Energy Harvesting From Arterial Blood Pressure for Embedded Brain Sensing
Authors: Nanda Aditya , Karami M. Amin
Published: December 2016

This paper investigates energy harvesting from arterial blood pressure via the piezoelectric effect for the purpose of powering embedded micro-sensors in the brain. Blood flow is highly dynamic and arterial blood pressure varies, in the average human blood vessel, from 120 mm of Hg to 80 mm of Hg and we look at transduction of this pressure variation to electric energy via the piezoelectric effect. We propose two different geometries for this purpose. Initially, we look at the energy harvested by a cylinder, coated with PVDF (Polyvinylidene fluoride) patches, placed inside an artery acted upon by blood pressure. The arrangement is similar to that of a stent which is a cylinder placed in veins and arteries to prevent obstruction in blood flow. The governing equations of the harvester are obtained using Hamilton’s principle. Pressure acting in arteries is radially directed and this is used to simplify the governing equations. Specifically, radial pressure directed on the inner wall of the cylinder is assumed to excite only the radial breathing mode of vibration. Using this, the transfer function relating pressure to the induced voltage across the surface of the harvester is derived and the power harvested by the cylindrical harvester is obtained for different shunt resistances.

However, the natural frequency of the radial breathing mode (RBM) is found to be very high and the harvested power at the frequencies of interest (3 Hz – 20 Hz) is very low. To decrease the natural frequency, we propose a novel streaked cylinder design that involves cutting the cylinder along the length, transforming it to a curved beam with an opening angle of 360 deg.. The governing equations corresponding to a circular curved beam, with PVDF patches on top and bottom surfaces, are derived using Hamilton’s principle and modal analysis is used to obtain the transfer function relating radial pressure to induced voltage. We validate the derived transfer function by evaluating the harvested power for a beam with very large radius of curvature; in which case, the curved beam becomes a straight beam and the harvested power is compared with the same for a straight beam (which exists in the literature). Further, we conduct design analyses and obtain the power as the geometric parameters of the harvester are varied for the purpose of optimizing the dimensions of harvester for maximal power generation. The power harvested by the harvester, at lower frequencies is deemed to be satisfactory.
Towards Online Impact Force Dynamic Parameters Identification for Hydraulic Legged Robots
Authors: D’Imperio Mariapaola , Cannella Ferdinando
Published: December 2016

The design and control of legged robots capable of performing dynamic tasks, such as those involving impact in a stable manner, is of growing concern within the robotics community. Under these conditions, ground reaction force rate increase dramatically and, if the control system fails to response appropriately, the internal vibrations will damage the robotic structure. To deal with these problems, design integration between control, mechanics and electronics is required. As a means to co-develop these tasks, we present an alternative method, based on the Virtual Prototyping (VP) and cosimulation concept, to model impact phenomena for design purposes. This model has been built starting from the identification of all the parameters that affect object dynamics within the mechanical structure. Two campaigns of experimental tests have been carried out: the first one for the parameters identification, while the second one for the model validation process. The agreement between numerical results and experiments is very satisfactory, demonstrating the possibility of using the model for future mechanical and control co-development.
Analytical Solutions for Nonlinear Free Vibration of Micro-Scale Timoshenko Beams
Authors: Saadatnia Zia , Esmailzadeh Ebrahim , Younesian Davood
Published: December 2016

Nonlinear free vibration of micro-beams based on the Timoshenko beam model is studied. The governing equations of motion using the strain gradient theory, Von Kármán strain tensors and Hamiltonian principle, are developed. The Galerkin method is applied to the governing equations and the coupled nonlinear ordinary differential equations of system are obtained. The variational iteration method is utilized to determine the time responses of the micro-beam and also a close form expression for the frequency-amplitude is found. The analytical solutions obtained for different values of parameters are compared with those found from different numerical methods. The effects of geometrical and physical parameters on the dynamics of micro-beam are also examined. Moreover, the analytical formulation for frequency ratio, i.e., the ratio of nonlinear natural frequency to the linear one is obtained and the sensitivity of this ratio to the variations of various parameters is evaluated. It is proved that the proposed solution methods and the results obtained are accurate and reliable when dynamics of such micro structures are studied.
Collision Dynamics and Internal Mixing of Equal-Size Droplets of Non-Newtonian Liquids
Authors: Zhang Peng
Published: December 2016

The efficient internal mixing of colliding non-Newtonian droplets upon coalescence is critical to various technological processes, specifically involving the initiation of the liquid-phase reaction of gelled hypergolic propellants, which are promising fuels for next-generation rocket engines. However, most previous studies on droplet collision used Newtonian fluids, and the non-Newtonian fluids that can be highly nonlinear and even trend reversing are much less understood to date. Motzigemba et al. [1] experimentally found that the deformation of colliding droplets of shear-thinning fluids is substantially larger than that of the Newtonian fluid. In a previous work [2], we numerically studied the initially stationary equal-sized droplet coalescence between a Newtonian and non-Newtonian droplet. Because of the reduced local viscosity and thereby smaller viscous dissipation for shear-thinning fluids, the flow in the non-Newtonian droplet is faster than that in the Newtonian droplet, resulting in unsymmetrical, albeit small, mixing induced by the shear-thinning effect. The above findings are encouraging since the droplet internal motion is driven solely by the surface tension of the initially stationary droplets regardless of the impact inertia. However, as the published references of Newtonian fluid characteristics, internal mixing of non-Newtonian fluid definitely can be substantially augmented because of the correspondingly substantial internal motion generated through the impact inertia. Thus, in terms of the equal-sized head-on colliding droplets, efficient mixing must require breaking the collision symmetry by varying the impact inertia and the rheological properties as well.
Study of Bubble Size and Velocity in a Vibrating Bubble Column
Authors: Mohagheghian Shahrouz , Elbing Brian R.
Published: December 2016

Bubble columns are two-phase and three-phase reactors in which a gas flow drives a liquid flow and allows transport phenomena’s to take place. With a broad application from aeration of organic organisms in bio-rectors to hydrogenation of coal slurries in the Fischer-Tropsch process and production of synthetic fuel, bubble column reactors are cheap and easy to operate. In this work bubble size was studied in a bubble column and effect of injector size and gas superficial velocity was investigated. Results showed larger bubble size as gas superficial velocity was increased. It was previously shown that vibration increases the mass transfer between phases, which one active mechanism is that vibration increases the void fraction and with more gas in contact with liquid mass transfer rate increases. To check that a shaker table setup capable of generating vibration in the range of 5–15 Hz of frequency at 5 mm of amplitude using an eccentric drive mechanism was refurbished to study the bubble velocity and void fraction under vibration. The experimental setup was first verified to check if tests are repeatable and also the results are in agreement with literature. Void fraction, bubble size and velocity was measured and comparison with previously published data showed good agreement. Bubble size measurements in a stationary column showed that over the range tested bubble size increases with increasing gas superficial velocity. Bubble velocity decreases when gas superficial velocity was increased. Vibration showed a gradual reduction in bubble velocity as vibration frequency was increased.
Multiphase Effects in Dynamic Systems Under Vibration
Authors: O’Hern Timothy J. , Torczynski John R. , Clausen Jonathan R.
Published: December 2016

Analysis, simulations, and experiments are performed for a piston in a vibrated liquid-filled cylinder, where the damping caused by forcing liquid through narrow gaps depends almost linearly on the piston position. Adding a little gas completely changes the dynamics of this spring-mass-damper system when it is subject to vibration. When no gas is present, the piston’s vibrational response is highly overdamped due to the viscous liquid being forced through the narrow gaps. When a small amount of gas is added, Bjerknes forces cause some gas to migrate below the piston. The resulting pneumatic spring enables the liquid to move with the piston so that little liquid is forced through the gaps. This “Couette mode” thus has low damping and a strong resonance near the frequency given by the pneumatic spring constant and the piston mass. Near this frequency, the piston response is large, and the nonlinearity from the varying gap length produces a net force on the piston. This “rectified” force can be many times the piston’s weight and can cause the piston to compress its supporting spring.

A surrogate system in which the gas regions are replaced by upper and lower bellows with similar compressibility is studied. A recently developed theory for the piston and bellows motions is compared to finite element simulations. The liquid obeys the unsteady incompressible Navier-Stokes equations, and the piston and the bellows obey Newton’s 2nd Law. Due to the large piston displacements near resonance, an Arbitrary Lagrangian Eulerian (ALE) technique with a sliding-mesh scheme is used to limit mesh distortion. Theory and simulation results for the piston motion are in good agreement.

Experiments are performed with liquid only, with gas present, and with upper and lower bellows replacing the gas. Liquid viscosity, bellows compressibility, vibration amplitude, and gap geometry are varied to determine their effects on the frequency at which the rectified force makes the piston move down. This critical frequency is found to depend on whether the frequency is increased or decreased with time.
Pleasingly Parallel Matrix Free Discontinuous Least-Squares Spectral Element Algorithm for Fluid Flow With Nonconformal Element Refinement
Authors: Hasbestan Jaber J. , Newman James C. , Arabshahi Abdollah
Published: December 2016

Least squares spectral element methods formulate the partial differential equation (PDE) as an optimization problem. One of the advantages of this method is that the boundary conditions can be implemented by adding a penalty equation to the cost function and hence be imposed in a weak sense with little effort. In this study a discontinuous methodology is utilized; that is, each element has its own set of degrees-of-freedom. This formulation possesses a greater sparsity pattern in the Jacobian matrix, and has a smaller bandwidth when compare to the continuous counterpart. However, these attributes come at the expense of an increased number of degrees-of-freedom on a given discretization. In the current work, the conventional discontinuous approach is modified to convert the equations to a matrix free system where there is no need for assembling the global system. The continuity in the formulation between two neighboring elements is imposed in a weak sense with a penalty equation added to the original PDE in each element. This penalty term minimizes the integral of the square root of the difference between the unknown state-vectors on each edge for neighboring elements. The conventional discontinuous approach evaluates this integral at the current time iterate. Using the aforementioned approach, assembly of the system is required and is not matrix free. It is shown in this study that by modifying this equation it is possible to obtain a matrix free system. Additionally each element becomes independent from other elements, and the direct solution for each element possible. The system matrix obtained by this least squares method is symmetric positive definite and can be effectively solved by Cholesky decomposition. This solution procedure is well suited for parallelization using Pthreads and CUDA. This is due to the fact that there is now no need for any communication, and each element only reads the data from the neighboring elements, while solving for its own unknowns. Another advantage of the matrix free approach is that adaptation is easily implemented by only introducing the new state-vectors into the data structures and updating the neighbor connectivity. The value of the cost function in the formulation may be used to select the elements to be refined. Each tagged element is then divided by h-refinement. This results in a nonconformal mesh. Utilization of a nonconformal mesh alleviates the need for increasing the resolution in unnecessary locations. To require conformality of the mesh, the extent of refinement and the number of degrees-of-freedom are increased. In the current work, quintic quadrilateral elements are used in the simulations, and a C++ vector class is used for updating mesh refinement data structures.
Active Flow Control Schemes for Bluff Body Drag Reduction
Authors: Whiteman Jacob T. , Zhuang Mei
Published: December 2016

Numerical simulation experiments on vortex shedding and corresponding drag coefficients from a two-dimensional bluff body are performed over a range of Reynolds numbers from one to four million. Active control is implemented on the body via velocity boundary conditions in the form of blowing and suction jets. These controls range in velocity from half to double the free-stream inlet velocity. An overall drag coefficient reduction in excess of 75% is observed for maximum power input to the actuators. In addition, a trend of increasing Strouhal number for each successive increase in actuator power (and corresponding reduction in drag) is noted. Important physical mechanisms involving near-body wake flow are analyzed to determine optimal wake flow pattern and corresponding control schemes.
Motion of Active Fluids: Diffusion Dynamics of Cyanobacteria
Authors: Vourc’h Thomas , Léopoldès Julien , Méjean Annick , Peerhossaini Hassan
Published: December 2016

Cyanobacteria are photosynthetic micro-organisms colonizing all aquatic and terrestrial environments. The motility of such living micro-organisms should make their diffusion distinct from typical Brownian motion. This diffusion can be investigated in terms of global behavior (Fickian or not) and in terms of displacement probabilities, which provide more detail about the motility process. Using cyanobacterium Synechocystis sp. PCC 6803 as the model micro-organism, we carry out time-lapse video microscopy to track and analyze the bacteria’s trajectories, from which we compute the mean-squared displacement (MSD) and the distribution function of displacement probabilities.

We find that the motility of Synechocystis sp. PCC 6803 is intermittent: high-motility “run” phases are separated by low-motility “tumble” phases corresponding to trapped states. However, this intermittent motility leads to a Fickian diffusive behavior, as shown by the evolution of the MSD with time.
Numerical Analysis of SDBD-Plasma Based Separation Control on the Blades of a Rotating Impeller
Authors: Aram Shawn , Lee Yu-Tai , Shan Hua
Published: December 2016

A numerical study is conducted to explore the performance and efficiency of Single Dielectric Barrier Discharge (SDBD) plasma actuators for controlling the turbulent boundary layer separation that occurs on the blades of a centrifugal fan. The numerical approach is based on the computational method developed previously to couple a DBD Electro Hydro-Dynamic (EHD) body force model with a RANS/LES flow model. The EHD body force model is based on solving the electrostatic equations for the electric potential due to applied voltage and the net charge density due to ionized air. The efficiency of the actuator at four different alternative current (AC) waveforms including sine, pulse, square, and pulse-amplitude-modulated sine is investigated in this study. The effect of applied voltage on the performance of the plasma actuator is also examined for all waveforms.
Numerical Investigations on Intake Tube Design of Micro Kaplan Hydro-Turbine System
Authors: ElGammal Tarek , Yen Yi-Hsin , Amano Ryoichi S. , Millevolte Joseph , Mueller Randal J. , Lequesne Bruno
Published: December 2016

In this context, a numerical study was conducted to predict the performance of a small axial Kaplan hydro-turbine of 30 cm diameter that can be manufactured and installed vertically on a low head water level of less than 3 m. As a CFD simulation scheme, Large Eddy Simulation was selected to solve for the variables of turbulent flow due to its high fidelity performance for capturing time-variable turbulence wakes and eddies.

Turbine intake tube dimensioning was primarily studied as an affecting element to maximize energy extraction with the set of initial design parameters. The intake tube was tested at six angles (3, 6, 9, 12, 15, 18 degrees) and four lengths (50, 60, 75, 90 cm). The simulations were performed on a pre-determined water height, one diffuser design, and one set of stator-rotor having a rotational speed of 750 rpm. Maximizing the efficiency of a system with less material cost was the primary goal of the comparative study. After that, bellmouth profile was adopted to find out its influence on the system performance. Outcomes have proven the merit of higher slope per side length in enhancing output power with an average of 2.7 percent by full expansion from minimum to the maximum angle. Moreover, a corresponding marginal efficiency raise was observed by increasing intake slope, while it was found that the system acts poorly with longer intake tubes as both power and efficiency go down. Bellmouth profiles, based on the guidelines of the best straight design, significantly improved system output to reach 81 percent efficiency.
Numerical Optimization of Micro Kaplan Hydro Turbine System
Authors: Yen Yi-Hsin , ElGammal Tarek , Amano Ryoichi S. , Millevolte Joseph , Lequesne Bruno , Mueller Randal J.
Published: December 2016

Micro hydro turbines with capacity ranging from 5–100 kW can provide a source of renewable energy which has high potential to grow due to the sheer number of available sites with a relatively small head difference and flow rate. Such systems would complement existing conventional large-scale hydro installations.

The paper presents a study of a 30 cm diameter Kaplan hydroturbine geometry with performance optimization through Computational Fluid Dynamics (CFD) method based on Large Eddy Simulation (LES) of transient turbulence modeling. The work under this study include: selection of horizontal or vertical setup, tail water head test, draft tube length test, draft tube angle test, intake tube geometry test and blade geometry combination test. All of these geometric parameters will be tested and compared based on power output, mass flow rate and efficiency. The optimized geometry was selected for system manufacturing and experimenting by Cadens LLC in a project site in Sullivan, WI.
Numerical and Experimental Study of Wave Over Coastal Levee Structures
Authors: Pei Yuyi , Zhang Ning , Dermisis Dimitrios
Published: December 2016

Louisiana coast experiences significant erosion due to wave actions. The loss of beaches in some coastal areas in Louisiana is severe. There are wetlands and marshes located in the coastal areas. Wetland loss is a major threat to the coast areas. 3D numerical simulations of wave-levee interactions were conducted, and the results were analyzed to determine the flow characteristics and surface shear distributions. The simulation setup is exactly the same as an experiment conducted in a wave tank facility. The velocity histories on different locations near the test levee surface were compared, and the agreement is very good, therefore the simulation is validated. A test levee system was also constructed on a test Gulf beach site, approximately 4.6 miles west of Holly Beach in Cameron Parish, Louisiana. Long term observation of erosion was conducted, and survey data showing the change of the test levee were produced. From the observations, the loss of this portion of Gulf beach is significant during the 2-year research period. Real-time images were recorded to show this significant change in topography. The losses of the levee materials during the entire project period were quantified based on the survey data. The history of the loss was plotted. It indicates some major storm event contributed to significant losses and erosion of the test structure. It can be seen from the results that the real-time erosion pattern on the test site agrees reasonably with the surface shear patterns from the simulations. In the numerical simulation, commercial package ANSYS-FLUENT was used. A free-surface flow model is adopted with open channel wave boundary conditions. A grid-independence study was performed to determine to appropriate grid resolution to be used in the simulation. Parallel computing was conducted due to the expensive cost of this 3D simulation with relatively fine grid resolutions.
Coupled 3-D CFD-DDPM Numerical Simulation of Turbulent Swirling Gas-Particle Flow Within Cyclone Suspension Preheater of Cement Kilns
Authors: Cristea Eugen-Dan , Conti Pierangelo
Published: December 2016

The paper presents a three-dimensional (3-D), time-dependent Euler-Lagrange multiphase approach for high-fidelity numerical simulation of strongly swirling, turbulent, heavy dust-laden flows within large-sized cyclone separators, as components of the state-of-art suspension preheaters (SPH) of cement kilns.

The case study evaluates the predictive performance of the coupled hybrid 3-D computational fluid dynamics–dense discrete phase model (CFD-DDPM) approach implemented into the commercial general purpose code ANSYS-Fluent R16.2, when applied to industrial cyclone collectors used to separate particles from gaseous streams. The gas (flue gases) flow is addressed numerically by using the traditional CFD methods to solve finite volume unsteady Reynolds-averaged Navier-Stokes (FV-URANS) equations. The multiphase turbulence is modeled by using an option of Reynolds stress model (RSM), namely dispersed turbulence model. The motion of the discrete (granular) phase is captured by DDPM methodology.

The twin cyclones of SPH top-most stage have been analyzed extensively both for the overall pressure drop and global collection efficiency, and for the very complex multiphase flow patterns established inside this equipment. The numerical simulation results have been verified and partially validated against an available set of typical industrial measurements collected during a heat and mass balance (H&MB) of the cement kiln.
Optimization of Anastomotic Geometry for Vascular Access Fistula
Authors: Bao Guangyu , Chen Xiaomin , Agarwal Ramesh K.
Published: December 2016

Arteriovenous fistula (AVF) is one type of vascular access which is a surgically created vein used to remove and return blood during hemodialysis [1]. It is a long-term treatment for kidney failure. Although clinical treatment and technology have both achieved great improvements in recent years, the vascular access for hemodialysis still has significant early failure rates after the insertion of AVF in patients [2]. Studies have shown that stenosis in the vascular access circuit is the single major cause for access morbidity. Majority of efforts to understand the mechanisms of stenosis formation, and its prevention and management have largely focused on understanding and managing this complication based on the pathophysiology, tissue histology and molecular biology; however these efforts have not resulted in significant progress to date. We believe that the major impact in this area will come from continued and accurate understanding of the hemodynamics, and by development of techniques of intervention to modulate factors such as flow rates, pressures and compliance of the circuit.

The goal of this paper is to study anastomotic models of AV access using Computational Fluid Dynamics (CFD) and optimize them to minimize the wall shear stress (WSS). In order to achieve this goal, the commercial CFD software FLUENT [3] is employed in conjunction with a single objective genetic algorithm [4].

Computations for two types of AVF currently in use in clinical practice are performed. AVF with 25° angle/3–4mm diameter and 90° angle/3–5mm diameter are selected to conduct the optimization. A single-objective genetic algorithm is employed in the optimization process and a k-kl-ω turbulence model is employed in CFD simulations; this model can accurately compute transitional/turbulent flows. In order to optimize for the same flow conditions, a fixed boundary condition is used during the optimization process. Computations for 16 to 20 generations of the selected AVFs are obtained from the genetic algorithm solver. The maximum WSS in the two AVFs considered are 6997.8 and 7750 dynes/cm2; however, the maximum WSS in the shape-optimized AVFs are reduced to 3511.2 and 4293.9 dynes/cm2 respectively, which have decreased by 49.82% and 44.59% respectively. Thus, the probability of the formation of stenosis in AVFs and early failure rates of vascular access are reduced by using the optimized AVFs.
Study on Flow Around a Rectangular Cylinder With an Asymmetric Slot for Synthetic Jets
Authors: Kobayashi Nobuhiro , Nishibe Koichi , Watabe Yusuke , Sato Kotaro , Yokota Kazuhiko
Published: December 2016

Several recent studies have examined the fundamental behavior of synthetic jets as substitutes for continuous jets [1–4]. In addition, attempts to control fluid machines with synthetic jets have also begun [5, 6]. However, little attention has been given to the effects of an asymmetric flow field on the behavior of synthetic jets [7, 8]. There have been few reports on the influence of a large-scale asymmetric boundary on the motion of synthetic jets [7]. In this study, an attempt was made to describe the flow around a rectangular cylinder with an asymmetric slot for synthetic jets. The main results are as follows: (1) the continuous jets proceed toward the nearest rigid wall by the Coanda effect independently of the slot geometry (with/without beak), (2) when the nondimensional stroke of the synthetic jets is large, the flow patterns are similar to those of continuous jets, (3) when the nondimensional stroke is small and the rectangular cylinder is placed near the wall opposite the side of the beak, the synthetic jets turn to the upstream direction under the present range of conditions, and (4) the flow rate in the duct depends on the non-dimensional stroke length when the rectangular cylinder is placed near the wall opposite the side of the beak.
Experiments and CFD Analysis on Safe-Return-to-Port of a Damaged Ship in Head and Following Seas
Authors: Seo Jeonghwa , Rhee Shin Hyung
Published: December 2016

In the present study, model tests in a towing tank and computational fluid dynamics (CFD) analysis on damaged stability of a passenger ship in waves were conducted. An autopilot system that controlled the rudder angle was introduced to the test model, for course-keeping maneuverability of the test model in asymmetric damaged condition. Following the regulations of the safe-return-to-port (SRTP) of passenger ships, the ship speed in the test corresponded to 8 knots in the full scale. In the damaged condition, a compartment at midship was flooded and the stability of the model degraded. Tests were conducted in head and following seas. Wave conditions correspond to Sea states 4 to 6. The six-degrees-of-freedom (6DOF) motion response of the test model was measured by a wireless inertial measurement unit and gyro sensors to achieve fully untethered model tests. Thrust and torque on the propulsive system and free-surface height in the damaged compartment were also measured. CFD analysis was performed in the same condition as the experiments. 6DOF motion, the propulsion, and flooding behavior were analyzed. CFD analysis results were compared with the experimental results. In addition, some physical features that could not be measured by experiments were identified and investigated. With the results of the experiments and CFD analysis, the effects of incoming waves and flooding behavior on the propulsion and seakeeping performance of the damaged ship model could be identified.
Sand Flow Regimes in Slightly Upward Inclined Gas-Liquid Stratified Flow
Authors: Dabirian Ramin , Mohan Ram S. , Shoham Ovadia , Kouba Gene
Published: December 2016

Sand particles are produced from the reservoir with low formation strength. A sand management system is required to be designed to keep the sand particles moving so as to prevent them from accumulating in the pipeline. Operating under unnecessarily high fluid velocities is not cost effective, moreover, it can lead to equipment failure; therefore, it is required to find the minimum velocity, known as critical sand deposition velocity, to keep the particles constantly moving.

In order to assess the critical sand deposition condition, a unique test facility was designed and constructed with 4-in ID PVC pipeline, which enables the pipe to be inclined 1.5° upward. Experiments were conducted with air-water-glass beads at low sand concentrations (< 10,000 ppm), and the air and water flow rates were selected to ensure stratified flow regime along the pipe. At constant superficial liquid velocity the gas velocity was reduced to find the critical sand deposition velocity.

The experimental results reveal that air-water flow regime plays an important role in particle transport; slug flow has high capability to transport particles at the pipe bottom, while the stratified flow has high risk of sand deposition. As long as the sand dunes are observed at the pipe bottom, the critical sand deposition velocities slightly increase with concentrations, while for stationary bed, the critical velocity increases exponentially with concentration.
Fluid Dynamics of Hydrophilous Pollination in Ruppia (Widgeon Grass)
Authors: Musunuri Naga , Fischer Ian , Singh Pushpendra , Bunker Daniel E. , Pell Susan
Published: December 2016

The aim of this work is to understand the physics underlying the mechanisms of two-dimensional aquatic pollen dispersal, known as hydrophily, that have evolved in several genera of aquatic plants, including Halodule, Halophila, Lepilaena, and Ruppia. We selected Ruppia maritima, which is native to salt and brackish waters circumglobally, for this study. We observed two mechanisms by which the pollen released from male inflorescences of Ruppia is adsorbed on a water surface: 1) inflorescences rise above the water surface and after they mature their pollen mass falls onto the surface as clumps and disperses as it comes in contact with the surface; 2) inflorescences remain below the surface and produce air bubbles which carry pollen mass to the surface where it disperses. In both cases dispersed pollen masses combined with others under the action of lateral capillary forces to form pollen rafts. The formation of porous pollen rafts increases the probability of pollination since the attractive capillary force on a pollen raft toward a stigma is much larger than on a single pollen grain. The presence of a trace amount of surfactant can disrupt the pollination process as the pollen is not captured or transported on the water surface.
Modeling Separation and Cavitation Behind a Blunt Body
Authors: Ma Jingsen , Hsiao Chao-Tsung , Wu Xiongjun , Chahine Georges L.
Published: December 2016

Cavitation flow behind a blunt body is modeled using a physics-based numerical model of cavitation initiation and transition to larger cavities. The calculations initiate from the dynamics of nuclei, then tracks the dispersed bubble phase with a two-phase viscous model. This solver includes a level set method to model coalescence of the nuclei into large cavities and to track the dynamics of the resulting free surfaces. A transition scheme enables collection of the bubbles into a large cavity and also enables breakup of a large cavity into a bubble cloud.

Using this model, simulations are conducted for different flow velocities and corresponding cavitation regimes. When the velocity is relatively small (i.e., large cavitation number), flow separation behind the body results in the shedding of vortices, which capture nuclei in their cores to form elongated vortical cavities. As the flow velocity increases (or as the ambient pressure decreases) the flow evolves into a separated flow with a large cavity behind the body. A reentrant jet may form and move upstream into the cavity towards the body. This jet periodically shears off portions of the cavity volume, resulting in large amounts of bubble clouds. These results are in good qualitative agreements with experimental observations.
A Study of the Effect of Various Recess Shapes on Hybrid Journal Bearing Using CFD and Response Surface Method
Authors: Fu Gen , Untaroiu Alexandrina
Published: December 2016

Hybrid bearings are mostly used in high speed and load situations due to their better stability and loading capacity. They are typically designed with recess grooves to enhance both static and dynamic performance of the bearing. Previous theoretical studies on the influence of the recess geometrical shapes often utilize the Reynolds equation method and most of the research focuses on thrust bearings. The aims of this paper is to analytically study the influence of various recess geometrical shapes on hybrid journal bearings.

A 3-D CFD model of a hybrid journal bearing is built and a new method of response surface model is employed to determine the equilibrium position of the rotor. Based the response surface model, an optimization scheme is used to search around the equilibrium position to get a more accurate solution. The current analysis includes the recess geometry of rectangular, circular, triangular, elliptical and annular shapes. All these different shapes are studied assuming the same operating and loading conditions and bearing static properties are used as the indices of the bearing performance.

The flow rate, fluid film thickness and recess flow pattern are analyzed for various recess shapes. The CFD model for the baseline bearing is validated against experimental data. The results show that the response surface model method is fast and robust in determining the rotor equilibrium position even though a 3-D CFD model is utilized. The results suggest that recess shape is a dominant factor in hybrid bearing design. This study proposed a new design process for a 3-D CFD bearing model with the ability of calculating equilibrium position and is expected to be useful to bearing designers.
The Effect of the Thickness and Angle of the Inlet and Outlet Guide Vane on the Performance of Axial-Flow Pump
Authors: Kim Sang-Won , Kim Youn-Jea
Published: December 2016

An axial-flow pump has a relatively high discharge flow rate and specific speed at a relatively low head and it consists of an inlet guide vane, impeller, and outlet guide vane. The interaction of the flow through the inlet guide vane, impeller, and outlet guide vane of the axial-flow pump has a significant effect on its performance. Of those components, the guide vanes especially can improve the head and efficiency of the pump by transforming the kinetic energy of the rotating flow, which has a tangential velocity component, into pressure energy. Accordingly, the geometric configurations of the guide vanes such as blade thickness and angle are crucial design factors for determining the performance of the axial-flow pump. As the reliability of Computational Fluid Dynamics (CFD) has been elevated together with the advance in computer technology, numerical analysis using CFD has recently become an alternative to empirical experiment due to its high reliability to measure the flow field. Thus, in this study, 1,200mm axial-flow pump having an inlet guide vane and impeller with 4 blades and an outlet guide vane with 6 blades was numerically investigated. Numerical study was conducted using the commercial CFD code, ANSYS CFX ver. 16.1, in order to elucidate the effect of the thickness and angle of the guide vanes on the performance of 1,200mm axial-flow pump. The stage condition, which averages the fluxes between interfaces and is accordingly appropriate for the evaluation of pump performance, was adopted as the interface condition between the guide vanes and the impeller. The rotational periodicity condition was used in order to enable a simplified geometry to be used since the guide vanes feature multiple identical regions. The shear stress transport (SST) k-ω model, predicting the turbulence within the flow in good agreement, was also employed in the CFD calculation. With regard to the numerical simulation results, the characteristics of the pressure distribution were discussed in detail. The pump performance, which will determine how well an axial-flow pump will work in terms of its efficiency and head, was also discussed in detail, leading to the conclusion on the optimal blade thickness and angle for the improvement of the performance. In addition, the total pressure loss coefficient was considered in order to investigate the loss within the flow paths depending on the thickness and angle variations. The results presented in this study may give guidelines to the numerical analysis of the axial-flow pump and the investigation of the performance for further optimal design of the axial-flow pump.
Ultrasonography as an integrated tool in clinical decision-making in the Emergency Department
Authors: Golea Adela C. , Mureșan Eugenia G.P. , Lăcan Sorin S. , Pasc Mihaela Gh. , Bolboacă Sorana D.
Published: December 2016

The aim of this retrospective study was to identify the role of ultrasonography as a decision-making and screening tool in emergency patients with pathological changes. Material and method: The study was carried out for 28 months in the Emergency Department of the County Emergency University Hospital, Cluj-Napoca. An ultrasound examination was performed as part of the clinical algorithm within the first hour of treating non-critical patients after they had been triaged. The diagnostic decision based on the results of the ultrasound examination was compared with the final diagnosis on discharge from the Emergency Department. Results: In study were included 1565 patients with a mean age of 50.61±19.21 years. Ultrasound changes were detected in a statistically significant number of patients from all the examined subgroups (p≤0.002). The concordance between clinical and ultrasound findings was of 54.06%. Of all the examined patients, 20.63% were referred to surgery department based on the results of the ultrasound examination. Surgery was the final therapeutic decision in 5.06% of all the patients with normal ultrasound findings. Conclusions: Ultrasonography as an integrated tool in the clinical examination algorithm allowed the identification of non-critical patients who required emergency surgery (20.63%). The integration of point-of-care ultrasound into the clinical examination allows the management of emergency patients through the ranking of decisions: hospital admission for surgery and medical treatment, other diagnostic investigations, referral to outpatient care and family physician.
Diagnosis of endometriotic lesions by sonovaginography with ultrasound gel
Authors: Brătilă Elvira , Comandaşu Diana Elena , Coroleucă Ciprian , Cîrstoiu Monica Mihaela , Berceanu Costin , Mehedintu Claudia , Bratila Petre , Vladareanu Simona
Published: December 2016

Aims: The aim of the study was to evaluate the diagnostic ability of sonovaginography (SVG) with ultrasound gel in patients with endometriosis. Material and methods: We conducted a multicentre prospective study, which included 193 patients with symptoms highly suggestive for endometriosis. All patients were investigated by transvaginal sonography and SVG with gel and afterwards underwent laparoscopic surgery. For each category of endometriotic lesions investigated, we calculated and compared the sensitivity, specificity,  positive predictive value and negative predictive value of the imagisticinvestigations used. Results: In the case of endometriotic lesions of the uterosacral ligaments, SVG with gel had a sensitivity of 78.5% and a specificity of 96% (p=ns). The lesions of the vagina and rectovaginal septum were diagnosed with a sensitivity of 79%, respectively 94% (p=ns), obtaining a specificity of 99%, respectively of 97% (p=0.007). The lesions of the Douglas pouch were identified with a sensitivity of 81% (p=0.015), and those of the rectosigmoid with a 94% sensitivity (p=0.010). We obtained lower sensitivity (67%) in detecting the lesions of the urinary bladder (p=ns). Conclusions: SGV with ultrasound gel represents a useful investigation tool for the evaluation of endometriotic lesions in the posterior pelvic compartment.