Variation Of Pressure Distribution Research Articles

Reduction of Pressure Distribution Variation in Press Mold Based on Variable Lattice Optimization

Reduction of Pressure Distribution Variation in Press Mold Based on Variable Lattice Optimization

EFFECTS OF CROSSWINDS ON THE FLOW STRUCTURE AROUND A NEXT-GENERATION HIGH-SPEED TRAIN EXITING A TUNNEL

This study investigates the effect of crosswind on the aerodynamic behavior of the Next-Generation High-Speed Train (NG-HST) model when exiting a tunnel. Utilizing a 1/25th scale model, three distinct train exit positions and four crosswind yaw angles (15°, 30°, 45°, and 60°) were considered. Computational Fluid Dynamics (CFD) simulation with the k-ε turbulence model was used to simulate the flow structure around the train at the crosswind velocity of 25 m/s. A mesh independence study was performed to ensure that the results were not influenced by mesh sizing. Furthermore, existing wind tunnel experiment data was used to validate the mesh setup. The results showed that the crosswind angle had a significant effect on the aerodynamic flow behavior of the train as it exited the tunnel. The airflow pattern on the train surface exhibited significant changes, and variations in pressure distribution were observed on both the leeward and windward sides of the train. Moreover, the cars outside the tunnel experienced greater pressure than the cars inside the tunnel. As the last car of the train emerged from the tunnel, the strong crosswind altered the vortex structure, particularly around the head car, emphasizing its critical role in ensuring safe train operation. The results can be used to improve the design of wind barriers and other infrastructure along the railway tracks to improve the operational stability and safety of high-speed trains.

Prediction of the impact of biofouling roughness on a full-scale planing boat performance using CFD

This study investigates the crucial role of surface roughness caused by biofouling in contributing to increased drag in fast planing vessels. Through rigorous computational fluid dynamics (CFD) simulations using a full-scale reference hull, the impact of surface roughness on planing hull performance is examined. The results show that heavy slime roughness on the hull surface causes a significant increase in total resistance, ranging from 10% at low speeds to 80% at high speeds. Skin friction was identified as the most affected component of resistance, with additional changes in residual resistance. Although the change in residual resistance is relatively small, they give rise to dynamic phenomena such as variations in pressure distribution, wave elevation, and wave making formation. The study also explores the influence of surface roughness on dynamic lift forces, observing an increase in upward friction forces but ultimately concludes that overall hull performance was hampered due to the disproportionately higher increase in resistance caused by roughness (biofouling). Changes in dynamic trim, dynamic sinkage, and dynamic wetted surface area due to this roughness are also discussed.

Stability analysis of near-field acoustic levitation considering misalignment and inclination

The near-field acoustic levitation (NFAL) technique is attracting increasing attention because of its compact design and environmental friendliness. An intriguing aspect of NFAL is the restoring performance when the levitated object is misaligned with the radiator. While numerous studies have proposed models to predict this performance, they typically consider only the misalignment of the levitated object and disregard its inclination. Consequently, this paper presents a numerical model that accounts for both misalignment and inclination to investigate the stability of NFAL systems. First, the Reynolds equation, which describes the variation in pressure distribution, is introduced. Due to the misalignment, a hypothetical reflector with a groove is applied to conveniently express the film thickness. The Reynolds equation is then solved using the eight-point discrete method in conjunction with the boundary equations, and spline interpolation is used to determine the inclination angle. This approach yields the relationship between the restoring force and the eccentricity, which is validated experimentally. Furthermore, parametric studies reveal that increasing the radiator vibration amplitude or the reflector weight enhances the stability. It is also observed that air provides higher stability compared to hydrogen, and a flexible radiator exhibits higher stability compared to a rigid radiator. With decreasing film thickness (e.g., by reducing the vibration amplitude or increasing the weight of the reflector), the stability in the inclination direction is improved at the cost of increased probability of levitation failure.

Wind pressure distribution variation law and interference effect of heliostats

The heliostat is different from the ordinary low building because of the special shape of the heliostat. The wind tunnel pressure test is carried out the model of heliostats in the range of azimuth angles are between 0° to 180° and the range of elevation angles are between 0° to 90. The wind pressure time history of each measuring point on the mirror panel are obtained. On this basis, the mean wind pressure distribution of the mirror panel under typical working conditions is obtained, and then the maximum (minimum) value of the mean wind pressure under all working conditions and corresponding working conditions and measuring points are obtained. Then 10 representative measuring points are selected to study the variation law of wind pressure with wind direction angle and pitch angle respectively, and then the variation law of the mean wind pressure of 10 measuring points under all working conditions is obtained. Finally, the interference effect of the mean wind pressure of heliostats is studied, and the variation law of the interference effect of the mean wind pressure is obtained, and the maximum value, minimum value and corresponding working conditions of the interference effect are obtained. The results show that the maximum value of the mean wind pressure of heliostats under all working conditions is appeared at the measurement point of the lower edge of the mirror panel and on working condition 15-60 (wind direction angle - elevation angle), and the minimum value is appeared at the measurement point of the upper left corner of the mirror panel and on working condition 150-20. The variation law of the mean wind pressure of 10 measuring points under all working conditions is similar, and the position of measuring points has little effect on the variation law of the mean wind pressure under all working conditions. Only the working condition of the maximum value and minimum value are affected by the position of the measuring points. The mean wind pressure distribution under the most unfavorable working condition of heliostats is obtained, the maximum (minimum) value of the interference effect and corresponding working conditions are obtained. Which can be a reference for structural design and research.

Influences of cushion contour on passenger comfort and interface pressure in high-speed train.

In this paper, eight different contoured cushions (S1-S8) in two categories (flat and wrapped) were designed to study the influence of different contoured cushions on passenger comfort in high-speed trains. Meanwhile, subjective data investigation by the comfort Likert Scale questionnaire and objective physical variables collection by the body-cushion contact pressure test was carried out. In addition, one-way ANOVA and Pearson correlation analysis were performed on the subjective survey and objective test data. The results show that the cushion contours had a significant effect on the subjective evaluation of the overall comfort of the participants, in which the overall comfort below the waist of the separated wrapped cushion S8 has the highest subjective comfort score. The overall comfort of the flat-front bulge type cushion S4 and the local comfort of the thighs and the root of the thighs were rated higher than other flat types. Under the flat cushion, the effect of stature characteristics (mainly weight and hip-width) on the overall comfort subjective ratings was insignificant, and the effect on the contact pressure distribution variables was significant, but the contact pressure distribution variables were not correlated with the comfort ratings. Under the wrapped cushion, the effect of stature characteristics on the overall comfort subjective ratings and contact pressure distribution variables was significant. There were positive and negative correlations between the average peak contact pressure and average contact pressure and comfort ratings, respectively.

Three-Dimensional Hydrodynamic Analysis of a Flexible Caudal Fin

A 3D fluid–structure coupled simulation of a square flexible flapper, the basic model of a caudal fin, is performed to visualize the flow field around the caudal fin. A plate immersed in a water tank is driven to oscillate vertically by its leading edge. A quantitative analysis of the thrust generated by the plate, which is difficult to explore experimentally, is performed over a range of non-dimensional flapping frequencies 0.93 <f*< 1.47 to explore the mechanism of thrust generation in more detail. Comparisons are made between three different flapping frequencies around the structural resonance. Numerical results at different flapping frequencies provide a reasonable estimate of the trailing edge amplitude and phase lag of the motion of the plate’s leading and trailing edges. The pressure distribution and deformation of the plate are analyzed to estimate the time evolution of the maximum and minimum thrust generation during the flapping period. Variations in pressure distribution on the plate surface are mainly due to the displacement of the trailing edge relative to the leading edge. Thrust is mainly provided by the pressure difference at the trailing edge. The maximum thrust was found to correspond to the maximum relative deformation of the trailing edge. The optimum frequency f* = 1.2 corresponding to the maximum thrust generation does not coincide with the structural resonance frequency, but remains at a frequency slightly higher than the resonance. These results indicate that the relative deformation of the plate plays an important role in the estimation of the flow field and the associated thrust generation. The numerical results may provide new guidelines for the design of robotic underwater vehicles.

The impact of piston and sloshing motions on added resistance from moonpool configurations

Moonpools are vertical watertight openings employed in the decks and lower structures of marine vessels and offshore platforms to allow drilling pipes and risers to be lowered into the sea. In the present work, the resistance performance of a drillship with varied moonpool configurations under calm water and regular wave conditions is investigated using a shear-stress transport (SST) k-ω model based on OpenFOAM. It is confirmed by comparing experimental and numerical results that this method can accurately predict the resistance of a ship with a moonpool. The numerical results suggest that the added resistance caused by a moonpool can be effectively reduced by optimally arranging the notch on the recess. A significant variation in the local flow field of the moonpool accounts for this. The implementation of the notch affects the development of vortices structures, thus transforms the free surface evolutions as well as the fluid resonance. Finally, the variation in pressure distribution contributes to a decline in the added resistance associated with the moonpool.

Accurate modeling and simulation of seepage in 3D heterogeneous fractured porous media with complex structures

The past decades have witnessed an increasing interest in numerical simulation for flow in fractured porous media. To date, most studies have focused on 2D or pseudo-3D computational models, where the impact of 3D complex structures on seepage has not been fully addressed. This work presents a method for modeling seepage in 3D heterogeneous porous media. The complex structures, typically the stochastic discrete fractures and inclusions, are able to be simulated. A mesh strategy is proposed to discretize the complex domain. In particular, a treatment on the intersected elements is developed to ensure a conforming mesh. Then, numerical discretization is provided, in which the flux interactions of fractures, inclusions and surrounding rock matrix are included. Numerical tests are performed to analyze the hydraulic characteristics of 3D fractured media. First, the developed framework is validated by comparing numerical solutions with the results of embedded discrete fracture model. Next, the effects of orientation, aperture and radius of fractures on fluid flow and equivalent permeability tensor are analyzed. The variations of pressure distribution are studied in heterogeneous and homogeneous media. Finally, the hydraulic properties of a medium with complex structures are investigated to show the difference of hydraulic feature between fractures and inclusions.

Numerical Study of Wind Loads on Y Plan-Shaped Tall Building Using CFD

The increase in the population is at an exponential rate, and the available land is in the form of irregular shapes. That is why irregular shapes are very commonly built. Wind load increases with respect to height, so wind load evolution is necessary for such high-rise structures. Wind forces majorly depend on the plan's cross-sectional shape. Therefore, for an irregular shape, an investigation is needed for tall buildings. This paper demonstrates a detailed study on velocity stream line, external pressure coefficients, pressure distribution on the surfaces of the building and the turbulence kinetic energy for the Y-shaped plan for tall buildings under wind excitation for wind incidence angles of 0o to 180o. k- turbulence model is utilized to solve the problem using computational fluid dynamics techniques in ANSYS for terrain category II as per IS: 875 (Part3), 2015. Wind ward faces in all building models show positive pressure distribution, while the leeward faces are under the effect of negative pressure distribution. Wind load can be reduced on building models by modifying the corners, such as chamfering, rounding, and double recessed. The variation of pressure distribution on different faces of a "Y" plan shaped tall building for 0° and 180° is investigated using ANSYS CFX, and the pressure contours are plotted for all the faces of different "Y" shaped buildings to compute the effect of corner modification on pressure distribution. In this research, it was found that building models with rounded corners are highly efficient in resisting the wind load. Doi: 10.28991/CEJ-2022-08-02-06 Full Text: PDF

Aero-structural Characteristics of Membrane Aeroshell at Transonic Speed

Inflatable membrane aeroshell has the potential ability to deliver higher payload in planetary exploration missions. Receiving in-flight aerodynamic force, the membrane surface undergoes large deformation affecting the flow. To investigate the behavior, a coupled aero-structural interactions analysis is required. This paper aims to present a model based on fluid solver SU2, structural solver CalculiX, and coupling library preCICE in a partitioned-coupled manner. The computed results demonstrated that the membrane surface elastically deformed due to the substantial variation in pressure distribution around the aeroshell. Transient behavior has been observed in the aerodynamic coefficients as a result of the small amplitude oscillation of the capsule. This oscillation was induced by the large wake formed behind the vehicle. Wrinkling of the surface caused by the high aerodynamic force shows circumferential movement tendency with time. This study indicated that the analysis model can sufficiently reproduce the coupled aero-structural interaction, which provides insight for developing a flexible structure reentry vehicle.

Effects of viscoelasticity on the onset of vortex shedding and forces applied on a cylinder in unsteady flow regime

The present paper aims to investigate the effect of viscoelasticity on the onset of vortex shedding of a high concentration polymer solution over a cylinder using the finite volume method for the first time. To describe the behavior of the viscoelastic fluid, mathematically, the Phan–Thien–Tanner (PTT) model is employed. The convergence problems are resolved using the rheoFoam solver developed by previous researchers based on the log-conformation method. The exact critical Reynolds number (Recr), which corresponds to the onset of vortex shedding, is estimated by implementing numerous unsteady simulations at each elasticity number (El). The Recr is also calculated at every retardation ratio (β) and elongational viscosity. The results revealed a significant impact of viscoelasticity on Recr so that the flow of a high viscosity ratio PTT becomes unstable at higher Re (at very low El) or lower Re (at higher El), compared to a Newtonian fluid. In addition, Recr decreases linearly with β according to Recr=−34.5β+46.525 and increases with extensional viscosity. It is also found that β plays a vital role in the effect of viscoelasticity on the flow parameters. The averaged drag coefficient (CD¯) and the amplitude of lift coefficient (CLmax) do not have similar behaviors for low and high β. Moreover, viscoelasticity enlarges the vortices and increases the shedding frequency. A comprehensive physical analysis of flow structures is carried out using the distribution of time-averaged stress components and pressure over the cylinder. The numerical results demonstrated the three regimes of drag reduction at El < 0.015, drag enhancement at 0.015 < E1 < 1, and a Newtonian behavior at El > 1 that is an opposite trend compared to a steady regime. The variations of CLmax with El are also similar to CD¯, but at different critical elasticity numbers (El = 0.005 and 2). It is found that the normal stress changes the drag force by the variation of pressure distribution over the cylinder, while the shear stress directly affects the drag and lift forces. In addition, the viscoelasticity decreases the size of the vortices behind the cylinder and increases their vorticity, and changes the position of maximum normal stress, which leads to drag variations. It was also concluded that the higher the elongational viscosities, the lower the shedding frequency.

CFD modelling and grid uncertainty analysis of the free-falling water entry of 2D rigid bodies

The open source Computational Fluid Dynamics (CFD) library, OpenFOAM, is utilized to simulate the water impact of two-dimensional wedges and ship bow sections. For the free falling cases, the predicted results are validated against existing experimental data, and the parameter study is performed regarding the number of cells, time step, and width of the water domain applied in the numerical models. Grid uncertainty analysis for the CFD results is performed with a constant Courant–Friedrichs–Lewy number, to assess the consistency and accuracy of the CFD solver in solving the present problem. Three uncertainty estimation methods are compared on the peak slamming forces and pressures: Correction Factor (Cf), Factor of Safety (Fs), and Least-squares Fit (Lf) based approaches. All three of them can provide reliable uncertainty estimation for CFD simulations, as long as the right mesh configuration has been used. The variations of pressure distribution on wedge sections with various deadrise angles and initial entry velocities are analyzed. To examine the capability of the tool to predict the slamming loads for a section with roll motions two cases are simulated: one considering a free roll motion and another with constant roll angles. The predicted slamming loads are compared with the available experimental data and other numerical results.

Simulation of Turbulent Flow with High Reynolds Number over an Elliptical Cylinder

A complex turbulent flow with high Reynolds number (Re= 5 × 105, 1 × 106, 2 × 106 and 3.6 × 106) over an elliptical cylinder, is investigated using 2D URANS equations with a standard k-ε turbulence model. The present study compares the effect of various upstream velocity profiles on the variations in flow characteristics along the surface of an elliptical cylinder having variable axis ratios. The comparison of results with the published data for a circular cylinder in cross flow shows the importance of axis ratio and other velocity profiles to reduce the drag force and variation in pressure distribution. Drag force over an elliptical cylinder is found to be lower than that of a circular cylinder. The drag force is seen to increase with increasing slenderness ratio. The drag coefficient of an elliptical cylinder with an axis ratio 0.6 is found to reduce by half as compared to that of a circular cylinder. The influence of slenderness ratio and velocity profile over back pressure recovery, flow separation and shear stress distribution is observed for an elliptical cylinder.

Effect of cavitation and spallation on ribbon morphology of Fe73.5Si13.5B9Cu1Nb3 alloy in planar flow melt spinning process

An experimental and analytical study concerns the effect of cavitation and spallation during the puddle solidification in planar flow melt spinning rapid solidification process. An instantaneous change in solidification temperature, dynamic variation in pressure distribution, density and motion of the liquid puddle leads to defect formation on ribbon surface. The initiation of nucleation and kinetic crystal growth at weak zone where pressure is relatively low may leads to inception of cavitation in the puddle province. The liquid puddle behaves like elastic membrane due imbalanced force between the liquid and entrapped air molecules caused to irregular contact on wheel substrate. Spallation of cavitate nuclei causes to grow equiaxed cellular shapes at boundary layer of the liquid puddle which leads formation of micro dimple on ribbon surface. The shear bands are affected to nucleus in the puddle due to dynamic fluctuation at the weak zones, which controls the solidification process of puddle.

Glide Time Relates to Mediolateral Plantar Pressure Distribution Rather Than Ski Edging in Ski Skating.

The purpose of this study was (i) to assess the differences in relative glide time and both ski edging angle and plantar pressure mediolateral distribution in skiers of different levels and (ii) to further investigate the relationships between the aforementioned variables. Twelve male cross-country skiers (6 national and 6 regional level) skied at 4.2 m s−1 on a 2.5° uphill snow track using the V2 technique. The relative glide time (in percentage of contact time) and mediolateral plantar pressure distribution variables (asymmetry index, ASI) were derived from pressure insole measurements. Ski edging angle variables were calculated from an Inertial Measurement Unit placed on the ski. Minimum, maximum, mean, and range of both ASI and ski edging angle were computed over the gliding phase, giving information about the beginning, end, and throughout the gliding phase. Relative glide time was significantly higher, and minimum and mean ASI were significantly lower in the national- than in the regional-level skiers. Relative glide time was strongly negatively correlated to minimum ASI (i.e., plantar pressure mostly on the foot lateral side at the beginning of gliding phase) and strongly positively correlated to ASI range. These results may reflect a larger body mass transfer above the ski from the beginning of the gliding phase to increase gliding, especially in the national-level skiers. Ski edging angle seems less relevant to discriminate skiers' level of performance. These results have direct consequences on how technique must be taught to young cross-country skiers.

Evaluation of Normal Pressures during Filling in Steel Hoppers with Eccentric Outlet

Filling pressures are a necessary starting point in the design of silos and hoppers. The hoppers with complicated geometries are common in industrial applications due to physical space constraints and the need to interface with other processing equipment. The current paper deals with the effect of outlet eccentricity on normal pressures formed in steel hoppers during distributed filling process. Using finite element method, progressive filling process in hoppers was simulated and by changing the percentage of outlet eccentricity, the variation of pressure distribution was fully studied. The results showed an increase in the normal pressures of shallow side compared with the steep side of eccentric hopper. To quantify the pressure asymmetry, two parameters were introduced and they were evaluated for practical range of material parameters and steel hoppers dimensions. The results obtained are of interest since they facilitate the design of silos and hoppers with eccentric outlet.

Assessment on jet direction effect on drag and heat reduction efficiency for hypersonic vehicles

Introducing jet for drag reduction and thermal protection in hypersonic flows has attained worldwide attentions due to its giant potential, and this paper focused on the drag and heat reduction efficiency of unit mass flow rate for different jet directions in hypersonic flows. The developed code employed conjugate heat transfer approach to solve unsteady Reynolds-averaged Navier-Stokes equations and Fourier's heat conduction equation simultaneously, and then it was thoroughly validated by two classical experiments. Based on that, the flow field characteristics induced by different jet directions under the constant mass flow rate of jet were numerically investigated. Besides, two parameters were introduced to quantitatively evaluate the drag and heat reduction efficiency of different jet directions. The obtained results show that though the total mass flow rate of jet is constant, jet direction still has a decisive influence in manipulating the flow structures, and the rear jet would result in more complicated shock waves due to the interaction between the rear jet flow and spike. The force produced by the jet is the key role in determining the total drag, and the variation of pressure distribution along the blunt body is not the direct presentation of drag reduction performance. The opposing jet has the highest drag reduction efficiency, and lateral jet has the highest heat flux reduction. However, compared with the lateral and rear jets, the opposing jet has better thermal protection performance from the overall perspective as it can also protect the aerodome head from severe aerodynamic heating.

Simulation research on water-entry impact force of an autonomous underwater helicopter

Autonomous Underwater Helicopter (AUH) is a novel dish-shaped multi-functional submersible vehicle in the autonomous underwater vehicle (AUV) family. Numerical study of launch and recovery system for AUVs from a research vessel is significant in the overall design. Single-arm crane and air-launch way are the important ways of launching AUVs with the high expertise and security. However, AUVs are still easily subject to a huge impact load which can cause the body damage, malfunction of electronic components, and other serious accidents when AUVs are launching into water. In this paper, unsteady, incompressible, two-phase flow with identified boundary conditions was modeled in the computational domain using Volume of Fluid (VOF) technology, and different overset-grid sizes were set and analyzed to ascertain the accuracy of computational fluid dynamics (CFD) simulation first due to the setting of the grid which will directly affect the accuracy of the calculation results, especially the overset-grid convergence validation. Then, the change of water-entry impact force and velocity of AUH with different water-entry velocities and angles were calculated by CFD analysis software STAR-CCM + solver. The proper immersion angle of the AUH should be 75° under comprehensive analysis and comparison. Besides, the variations of pressure distribution of the AUH in the whole water-entry process were also obtained, which provides reference for the shape optimization in the future work.

Numerical simulation of intranasal airflow in nasal numerical models with nasal septum perforations of different locations and sizes

Objective: To investigate the effect of nasal septum perforation (SP) with different locations and sizes on nasal airflow by means of numerical simulation. Methods: Two healthy persons with normal nasal anatomy were enrolled in this study, including a 45 years old male (case 1) and a 36 years old female (case 2). Nasal CT data was used as the basis to create nasal airway numerical models of nasal SP with different locations (anterior caudal, central caudal, posterior caudal and anterior cranial) and sizes (diameter of 10 mm and 5 mm respectively). The inspiratory airflow characteristics (nasal cavity volume, nasal cavity wall area, pressure, nasal resistance, temperature, airflow velocity, wall shear stress, airflow-rate partitioning and vortex) of these nasal airway numerical models were simulated and analyzed. Pearson correlation analysis was performed between nasal resistances, airflow temperature and nasal cavity wall area. Results: In terms of pressure and nose resistance, the anterior caudal and larger size SP lead to more obvious variation of pressure distribution, and increased nasal resistance was especially found in the nasal cavity with anterior and medium caudal SP. In terms of temperature, the anterior (caudal and cranial) and larger size SP had significant effect on local temperature gradient as same as the anterior cranial and smaller size SP. Nasal heating efficiency was lower in nasal model with the anterior and larger size SP than that in the normal model. The temperature difference from the nostril to the end of nasal septum had positive correlation with nasal cavity wall area (R(2) value of case 1 and case 2 was 0.69, 0.41, respectively, all P<0.01). In terms of airflow velocity, the anterior caudal and cranial SP had more significant effect on the average airflow velocity in the nasal cavity. The anterior and medium caudal SP could make the airflow distribution in the asymmetric bilateral nasal cavity more unbalanced compared to the bilateral symmetrical nasal models. The anterior and medium SP resulted in a more pronounced vortex distribution than the posterior SP. Conclusions: The effect of SP on nasal cavity is related to its location and size. The anterior and larger size SP shows more negative influence on intranasal pressure, nasal resistance, heat transmission efficiency, airflow-rate partitioning than the posterior and smaller size SP.