Prediction Of Pressure Distribution Research Articles

Large Eddy Simulation of an SD7003 Airfoil: Effects of Reynolds number and Subgrid-scale modeling

This paper presents results of a series of numerical simulations in order to study aerodynamic characteristics of the low Reynolds number Selig-Donovan airfoil, SD7003. Large Eddy Simulation (LES) technique is used for all computations at chord-based Reynolds numbers 10,000, 24,000 and 60,000 and simulations have been performed to primarily investigate the role of sub-grid scale (SGS) modeling on the dynamics of flow generated over the airfoil, which has not been dealt with in great detail in the past. It is seen that simulations are increasingly getting influenced by SGS modeling with increasing the Reynolds number, and the effect is visible even at a relatively low chord-Reynolds number of 60,000. Among the tested models, the dynamic Smagorinsky gives the poorest predictions of the flow, with overprediction of lift and a larger separation on airfoils suction side. Among various models, the implicit LES offers closest pressure distribution predictions compared with literature.

Prediction of polishing pressure distribution in CMP process with airbag type wafer carrier

This paper presents a CMP process analysis considering an airbag type wafer carrier, which is used in semiconductor devices manufacturing. In the CMP process, a wafer is compressed against the polishing pad inside the wafer carrier, which consists of the retainer ring and the membrane film. Structural analysis model is developed to estimate contact pressure distribution over the wafer surface considering the airbag compression behaviour. The polishing experiment without wafer rotation indicated a unique pressure variation around the trailing edge of the wafer. The developed analysis estimated the same phenomena accurately and clarified the mechanism deteriorating the polishing pressure uniformity.

Investigation on the Influence of Gas Pressure on CO2 Arc Characteristics in High-Voltage Gas Circuit Breakers

CO<sub>2</sub> is identified as a promising alternative gas of SF<sub>6</sub>. The magnetohydrodynamics (MHD) arc model is established for a CO<sub>2</sub> circuit breaker. The influence of gas pressure is studied. The simulations are carried out for 0.5 MPa, 0.7 MPa and 0.9 MPa absolute filling pressure, allowing predictions of pressure and temperature distributions. The arc time constant θ and the power loss coefficient <em>Q</em> is extracted. The thermal interruption capability is estimated to grow with increasing filling pressure.

Bypass Flow Resistance in Prismatic Gas-Cooled Nuclear Reactors

Available computational fluid dynamics (CFD) predictions of pressure distributions in the vertical bypass flow between blocks in a prismatic gas-cooled reactor (GCR) have been analyzed to deduce apparent friction factors and loss coefficients for nuclear engineering systems and network codes. Calculations were performed for vertical gap spacings “s” of 2, 6, and 10 mm — representing 1, 3, and 5 mm in a GCR design, horizontal gaps between the blocks of 2 mm and two flow rates, giving a range of vertical gap Reynolds numbers ReDh of about 40–5300. The present focus is on the examination of the flow in the vertical gaps. Horizontal gaps are treated in CFD calculations but their flows are not examined. Laminar predictions of the fully developed friction factor ffd were about 3–10% lower than the classical infinitely wide channel. In the entry region, the local apparent friction factor was slightly higher than the classic idealized case, but the hydraulic entry length Lhy was approximately the same. The per cent reduction in flow resistance was greater than the per cent increase in flow area at the vertical corners of the blocks. The standard k–ϵ turbulence model was employed for flows expected to be turbulent. Its predictions of ffd and flow resistance were significantly higher than direct numerical simulations (DNS) for the classic case; the value of Lhy was about 30 gap spacings. Initial quantitative information for entry coefficients and loss coefficients for the expansion–contraction junctions between blocks is also presented. The present study demonstrates how CFD predictions can be employed to provide integral quantities needed in systems and network codes.

An explicit finite difference model for prediction of wellbore pressure and temperature distribution in CO2 geological sequestration

AbstractTo conveniently realize the coupling calculation between wellbore pressure and temperature and consider the friction loss in the process of wellbore flow and heat transfer, this work takes the one‐dimensional steady flow with homogeneous fluid in wellbores as the analysis object and divides the wellbore into finite micro‐segments. Then we derive the explicit finite difference model (EFDM) about pressure in a certain micro‐segment of wellbore, based on the mass and momentum equations. Next we deduce the EFDM about temperature reflecting the wellbore heat transfer in the same micro‐segment according to the energy balance equation. After that, a coupling calculation method for the EFDM about pressure and temperature is presented. Finally, a comparison of the simulation results of the EFDM, other models, and the log data from engineering is implemented, which demonstrates that the prediction results of the EFDM are more consistent with the log data than the results of other models. Therefore, the reliability of the EFDM about pressure and temperature and their coupling calculation method is verified. Discussion of the friction loss in the energy balance equation and the isobaric specific heat capacity showed that both have a great impact on wellbore temperature distribution, which means the friction loss should not be ignored and the isobaric specific heat capacity should not be assumed as a constant in applications. Generally, the prediction of wellbore pressure and temperature distribution and the comprehension of the internal essence of wellbore flow and heat transfer will be effectively promoted by this work. © 2016 Society of Chemical Industry and John Wiley & Sons, Ltd.

Viscoacoustic model for near-field ultrasonic levitation.

Ultrasonic near-field levitation allows for contactless support and transportation of an object over vibrating surface. We developed an accurate model predicting pressure distribution in the gap between the surface and levitating object. The formulation covers a wide range of the air flow regimes: from viscous squeezed flow dominating in small gap to acoustic wave propagation in larger gap. The paper explains derivation of the governing equations from the basic fluid dynamics. The nonreflective boundary conditions were developed to properly define air flow at the outlet. Comparing to direct computational fluid dynamics modeling our approach allows achieving good accuracy while keeping the computation cost low. Using the model we studied the levitation force as a function of gap distance. It was shown that there are three distinguished flow regimes: purely viscous, viscoacoustic, and acoustic. The regimes are defined by the balance of viscous and inertial forces. In the viscous regime the pressure in the gap is close to uniform while in the intermediate viscoacoustic and the acoustic regimes the pressure profile is wavy. The model was validated by a dedicated levitation experiment and compared to similar published results.

Numerical studies to propose a ghost particle removed SPH (GR-SPH) method

This paper aims to propose a new modified SPH method with novel treatments at the boundaries. Although SPH methods decrease contradictions due to grid distortions compared to traditional mesh-based methods, the penetration of particles through boundaries and the consistency problem make the simulation of problems with definite boundaries a concern. The use of ghost boundary particles and the insertion of artificial forces at the boundaries are the most popular boundary consistency treatments proposed thus far. The use of artificial forces causes the mixing of molecular and finite theories, which can violate the conservation of momentum. This paper shows how the use of ghost boundary particles can violate the continuity equation in problems with non-zero velocity divergence. This study proposes a novel ghost particle removed SPH (GR-SPH) method that discards all ghost particles and artificial forces at the boundaries. Liner layers and liner particles have been defined inside the domain instead of ghost boundary particles in such a way that the so-called violations can partially be remedied. Based on the continuity equation and kernel function unity specification, a novel truncation correction factor has been defined for density renormalization to override the consistency problem at the boundaries. In addition, a new method is proposed to detect the particles near complex wall boundaries and evaluate the normal distance from boundaries. Finally, some benchmark problems have been solved to show the capabilities of the new modified SPH method for the prediction of both particle location and pressure distribution with acceptable accuracy. The GR-SPH method facilitates programming, with fewer particles contributing to the computations. Comparison of its outcomes with published results shows that the new treatments executed at the boundaries are effective.

Numerical Analysis of Turbocharger’s Bearing using Dynamic Mesh

Journal bearings are widely used in different machineries. Reynolds equation is the governing equation to predict pressure distribution and load bearing capacity in journal bearings. There are many analytical and numerical methods for solving this equation. The main disadvantage of these methods is their inability to analyze complex geometries. In this paper, a comprehensive method based on dynamic mesh method is developed to solve the conservation equations of mass, momentum and energy. This method has smaller error compared to other techniques. To verify the accuracy of this method, the bearings with different length to diameter ratios are analytically and numerically analyzed under different loads and compared with each other. In continue, the turbocharger’s bearing is numerically simulated and the effects of rotational speed change are studied. Finally, the turbocharger’s bearing with four axial grooves are simulated. The simulations results show that adding grooves to the turbocharger’s bearing causes the bearing eccentricity ratio and lubricant flow rate to increase and the attitude angle, rate of temperature rise and frictional torque to decrease.

Evaluation of fiber-based tools for glass polishing using experimental and computational approaches.

Polymeric pad or pitch-based tools combined with loose abrasive slurries are typically used in the polishing of optical materials. In this paper, the potential of fiber-based tools to both remove material and provide high quality surface finishes on BK7 glass is explored. The potential advantage of fiber-based tools over traditional tools is their inherent compliance, which could accommodate varying workpiece surface curvatures as found in aspheres and freeforms. To evaluate the new tools, both experimental and finite element (FE) modeling approaches were taken. A FE model consisting of a single fiber engaged with the workpiece surface was used to estimate the shape and magnitude of the pressure distribution exerted by the fiber on the workpiece surface. Two different tool configurations, yielding two different Fes, predicted pressure distributions, were used to polish BK7 samples, and the material removal profiles were interferometrically measured. The resulting profiles and the predicted pressure distributions share the same v-shape. While differences in scale exist between the experimental and FE-predicted profiles, the tool generating higher material removal had the greater predicted pressure distribution, thus demonstrating the ability of the FE model to provide insights into tool design. Additional testing was conducted to determine if the tool's removal rate can be predicted by Preston's equation. Initial results indicate the equation is valid within the range of parameters tested. The surface roughness of BK7 samples processed by this tool was measured and some deterioration on the Sq value was noted; the surface roughness increased from 1.89 to 3.66 nm Sq. Over several hours of continuous use, the load applied by the fibers decays in a repeatable manner, and little wear was observed on the fibers after 5.33 h of polishing.

Numerical Approach for the Assessment of Pressure Generated by Elastic Compression Bandage.

Compression of the lower leg by bandages is a common treatment for the advanced stages of some venous or lymphatic pathologies. The outcomes of this treatment directly result from the pressure generated onto the limb. Various bandage configurations are proposed by manufacturers: the study of these configurations requires the development of reliable methods to predict pressure distribution applied by compression bandages. Currently, clinicians and manufacturers have no dedicated tools to predict bandage pressure generation. A numerical simulation approach is presented in this work, which includes patient-specific leg geometry and bandage. This model provides the complete pressure distribution over the leg. The results were compared to experimental pressure measurements and pressure values computed with Laplace's law. Using an appropriate surrogate model, this study demonstrated that such simulation is appropriate to account for phenomena which are neglected in Laplace's law, like geometry changes due to bandage application.

Predicting pressure distribution between transfemoral prosthetic socket and residual limb using finite element analysis

A static implicit nonlinear finite element model (FEM) was created and analysed to determine the pressure distribution between the residual limb and the prosthetic socket of a transfemoral amputee. This analysis was performed in an attempt to develop a process allowing healthcare providers and engineers to simulate the fit and comfort of transfemoral prosthetics to reduce the number of re-fittings. The FEM considered the effects of donning and body weight and included geometric nonlinearity due to large deflections, nonlinear contacts due to friction, and nonlinear hyper-elastic material properties for the residual limb's soft tissue. The results attained can provide prosthetic fitting clinicians customised information on where the prosthetic fits too tight, and how stress concentrations would change as a result of geometric modifications to the prosthetic. This knowledge can improve patients' comfort levels by providing well targeted and more accurate modifications to the prosthetic, minimising the need for numerous refittings.

円筒状突起に対する二層式マットレスの変形測定とウレタンフォームの圧縮特性に基づく圧力分布の予測

円筒状突起に対する二層式マットレスの変形測定とウレタンフォームの圧縮特性に基づく圧力分布の予測

Study of Pressure Distribution in Compliant Contact Wheels for Robotic Surface Finishing

This paper investigates the compliance characteristics of contact wheels in robotic finishing process, especially pressure distribution – a key parameter for material removal. The current study tackles this problem by developing finite element models of compliant contact wheels to predict pressure distribution with respect to various tool-workpiece scenarios. These models are further verified using pressure film sensors with flat and serrated contact wheels mounted on a robot.

Oil-based critical mud weight window analyses in HTHP fractured tight formation

Abstract There are plenty of tight oil and gas reserves in western China. The depths of the target reservoirs are usually as deep as 6000–7000 m, which are featured by: HTHP drilling environments, low matrix permeability, well-developed natural fracture systems, and anisotropic in-situ stresses. Even using highly inhibitive oil-based fluids during drilling operation, mud losses and wellbore collapses still occurred frequently. Moreover, in many wells when the mud weight is added, borehole conditions become worse. Contrary to the traditional field experiences, collapse pressure itself has a window. The purpose of this work is to investigate the features of fractured tight formation and correspondingly build a model to explain the unusual drilling complexities. In this approach, the formation is divided into a tight member and a fractured member. 1. In the tight member, a model for pore pressure and stress distribution prediction around a borehole is used based on the poroelasticity theory. The calculation results show that in the near borehole region, instantaneously after the borehole is opened, an abnormal high pore pressure is induced due to the poro-mechanical coupling effect under anisotropic in-situ stress field. The induced pressure is harmful to borehole stability, and a mud weight lower bound is necessary to overcome it. 2. In fractured member, a 3D weak plane model is established considering natural fracture׳s (weak plane) orientation and mud invasion. The calculation results show that muds with hight weight will infiltrate into the aperture of fractures and decrease the normal stress on it, which may induce shear slip failure along the weak plane. Thus an upper bound of mud weight is derived. 3. The time dependent temperature drop at the bottom of a wellbore is also simulated and its impact on borehole stability of tight and fractured section is studied respectively, which helps constrain the mud weight auxilarily. By integrating the above-mentioned factors, a comprehensive critical mud weight window is obtained, which can serve as the theoretical basis for wellbore stability analyses in the fractured tight formation drilled with oil-based fluid.

Modeling of human model for static pressure distribution prediction

Vehicle comfort, the key factor that influences the purchase of automobile products, is becoming increasingly important. However, the processes of traditional empirical and experimental approaches to design a new, more comfortable seat is complicated, time consuming and costly. The finite element method could facilitate, accelerate and economize this process. In the present work, a complete human FE model is established based on the Hybrid III dummy, the appropriate element size of 10 mm was ascertained. The body segment mass was verified by comparing segment mass percentages obtained from this model with previous data. The further validation study of the human model was achieved via the human pressure distribution experiments over human-rigid seat interaction under three postures, the validation reveals that the simulation results agree well with the experimental data. On this basis, the human model was applied to predict the interactions between human body and an automobile seat, then the contact pressure distribution, additional information about the contact shear stresses distribution and stress distribution within the soft tissue were obtained through simulation. The human model presented in this paper can reflect the interaction between human body and automobile seat precisely. Relevance to industryThe results deduced that the model is capable of realistically predicting pressure distribution, the present model allows the evaluation of seating comforts in a virtual phase of seat development, and the study can be taken as reference for vehicle seat design and biomechanical evaluation.

Drying of granular medium by hot air and microwaves. Modeling and prediction of internal gas pressure and binder distribution

With the aim of enhancing the industrial drying (hot air and microwaves) of inserts made of agglomerated sand and to assess product quality, a comprehensive internal heat and mass transfer model has been proposed. In this model, liquid and vapor transfer by filtration, liquid expulsion at the surface and binder transfer by advection were directly accounted for. This model was validated on the basis of the experimental average water and binder content and core temperature curves for drying trials at different operating conditions. Then, it was used for comparing the drying time, the internal pressure and the binder content calculated for several test processes. It was demonstrated that the simultaneous application of hot air and micro-waves provided a real possibility to dry faster and to maintain quite the same internal overpressure and overall binder content as for the reference (damage free) process. The heating power should be increased gradually during the process. The decrease of the drying time was around 30% with regard to the reference mild process.

A Panel Method with a Full Wake Alignment Model for the Prediction of the Performance of Ducted Propellers

An improved perturbation potential‐based panel method is applied to model the flow around ducted propellers. One significant development in this method is the application of full wake alignment scheme in which the trailing vortex wake sheets of the blades are aligned with the local flow velocity by also considering the effects of duct and duct wake. A process of repaneling the duct is simultaneously introduced to improve the accuracy of the method. The results from the improved wake model are compared with those from a simplified wake alignment scheme. At the same time, full-blown Reynolds-averaged Navier‐Stokes (RANS) simulations are conducted via commercial solvers. The forces, i.e., thrust and torque, on the propeller predicted by this panel method under the improved wake alignment model show good agreement both with experimental measurements, a hybrid method developed by the Ocean Engineering Group of University of Texas at Austin, and the full-blown RANS simulations. Moreover, predicted pressure distribution on the blades and duct are compared among the various methods.

A Panel Method with a Full Wake Alignment Model for the Prediction of the Performance of Ducted Propellers

An improved perturbation potential-based panel method is applied to model the flow around ducted propellers. One significant development in this method is the application of full wake alignment scheme in which the trailing vortex wake sheets of the blades are aligned with the local flow velocity by also considering the effects of duct and duct wake. A process of repaneling the duct is simultaneously introduced to improve the accuracy of the method. The results from the improved wake model are compared with those from a simplified wake alignment scheme. At the same time, full-blown Reynolds-averaged Navier-Stokes (RANS) simulations are conducted via commercial solvers. The forces, i.e., thrust and torque, on the propeller predicted by this panel method under the improved wake alignment model show good agreement both with experimental measurements, a hybrid method developed by the Ocean Engineering Group of University of Texas at Austin, and the full-blown RANS simulations. Moreover, predicted pressure distribution on the blades and duct are compared among the various methods.

A Solution Adaptive Cartesian Grid Based Euler Solution for Compressible Flow Around BOEING TR-1322 Multi-element Airfoil

Cartesian grids constitute a special branch in unstructured grid technology. They use specially designed algorithms to generate automatic grids for complex geometries and to simulate flows around such geometries regardless of the body shape and number of bodies. Cartesian grids are generated by constructing a quadtree based data structure for the purpose of connecting the Cartesian cells to each other. A “hands-off”, Cartesian grid generator based Euler solution called GeULER is implemented in object-oriented FORTRAN programming language. In this study, implementations of generated two-dimensional adaptive refinement/coarsening scheme codesare appended to the developed compressible flow solver by using special Cartesian-based algorithms, namely cut-cell adaptation and curvature adaptation around BOEING TR-1322 multi-element airfoil. A subsonic flow at free stream Mach number of 0.11 around the airfoil is tested to predict pressure distributions around it and Mach contours of the flow are depicted by using the developed GeULER code.

Numerical Analysis of Flow Over the NASA Common Research Model Using the Academic Computational Fluid Dynamics Code Galatea

A recently developed academic computational fluid dynamics (CFD) code, named Galatea, is used for the computational study of fully turbulent flow over the NASA common research model (CRM) in a wing-body configuration with and without horizontal tail. A brief description of code's methodology is included, while attention is mainly directed toward the accurate and efficient prediction of pressure distribution on wings' surfaces as well as of computation of lift and drag forces against different angles of attack, using an h-refinement approach and a parallel agglomeration multigrid scheme. The obtained numerical results compare close with both the experimental wind tunnel data and those of reference solvers.