Two-dimensional Pressure Distribution Research Articles

Numerical analysis of tulip flame by dynamic mode decomposition

Inversion of a premixed flame front to the shape of a tulip flower during the last stage of its propagation in a channel or tube of aspect ratio (AR) greater than two has intrigued the scientific community for decades. In the present work, the tulip inversion of hydrogen-air premixed flame is simulated numerically in two dimensional domains of AR 7.32, and 3.66. Dynamic Mode Decomposition is carried out on the two-dimensional pressure distribution obtained from the numerical simulation to understand the reasons behind the flame inversion. A plot of real and imaginary components of the eigenvalues over a unit circle clearly showed the presence of unstable acoustic modes during the tulip inversion for the domain of AR 7.32. The tulip inversion is not observed for the domain of AR 3.66. The distribution of the power and frequency of various modes are also plotted to identify the unstable modes. The present study shows generation of additional pressure waves during the tulip inversion process, which in term creates a velocity field that facilitates the flame inversion process.

Two-dimensional sound pressure distribution: Visualization and calibration-free quantification via optical wave microphone CT scanning

In recent years, the optical wave microphone has emerged as an innovative technique, employing Fraunhofer diffraction of a laser beam, and shows promising applications in various acoustic domains where high electric and/or magnetic fields preclude the use of traditional microphones. This study utilized an optical wave microphone computed tomography (CT) scan and calibration-free quantification to ascertain sound pressure levels at multiple distances from the ultrasonic oscillator. The cornerstone of this study, which is different from the author’s previous studies, is the quantification of sound pressure distribution via a theoretical model that encompasses all physical parameters pertinent to the optical wave microphone’s experimental arrangement. This method has proven effective in visualizing and quantifying the two-dimensional sound pressure distribution emitted by an ultrasonic oscillator (40 kHz) without the necessity for calibration. The results demonstrate that the sound pressure distribution determined using the calibration-free optical wave microphone CT scan is in good agreement with the measurements obtained through a condenser microphone.

Stream-Surface Iteration-Based Flowfield Calculation Method for Pressure-Controllable Waverider Design

The performance of waveriders is greatly influenced by the wall pressure distribution. To achieve the goal of designing a waverider based on the complex two-dimensional pressure distribution, this study proposes a methodology called the stream-surface iteration-based flowfield calculation (SIFC) method. This method discretizes the three-dimensional flowfield with curved stream surfaces and approximates the flow around each point with a unique axisymmetric flow. Moreover, this method iteratively solves the shape of each stream surface and the corresponding flowfield to deal with ill-posed problems. To verify its effectiveness, the SIFC method was first applied to inversely solve the two external annular supersonic flowfields. Then, it was used for the waverider design. The computational fluid dynamics results showed that the relative error of the wall pressure was less than 2.6% for the annular supersonic flowfields. The wall pressure determines the geometric shapes and mechanical properties of waveriders. The pressure center of a waverider can be shifted by 12% of the length in the flow direction and 7.4% of the width in the crossflow direction by altering the input wall pressure. This shift will cause the waverider to produce more than 30% extra trim drag when cruising at the design Mach number.

Numerical Simulation of flow in pipe with cross jet effects

A numerical method is developed to obtain two-dimensional velocity and pressure distribution through a cylindrical pipe with cross jet flows. The method is based on solving partial differential equations for the conservation of mass and momentum by finite difference method to convert them into algebraic equations. This well-known problem is used to introduce the basic concepts of CFD including: the finite- difference mesh, the discrete nature of the numerical solution, and the dependence of the result on the mesh refinement. Staggered grid implementation of the numerical model is used. The set of algebraic equations is solved simultaneously by “SIMPLE” algorithm to obtain velocity and pressure distribution within a pipe. In order to verify the validity for present code, the flow behavior predicted by this code is compared with these of another studies and there is a good agreement is obtained

Research on tyre mechanics model for multi-axle coordinated steering of heavy vehicles

Compared with passenger cars, heavy vehicles have larger loads, longer bodies, more steering modes, and are more likely to cause improper steering angle relationships among the wheels, resulting in uncoordinated steering. This uncoordinated steering makes the tyres roll and drag, which results in abnormal lateral and longitudinal slips, changing the lateral and longitudinal mechanical characteristics of tyres and leading to low path tracking accuracy and poor steering performance of vehicles. Therefore, a tyre model containing lateral and longitudinal mechanical characteristics under heavy load is the key to solving the problem of uncoordinated steering in heavy vehicles. Firstly, with the physical tyre model, the lateral and longitudinal slip is described as carcass deflections. With the carcass deflections and contact pressure distribution of heavy load, the tyre forces under uncoordinated steering conditions are derived. Then, the tyre imprint parameters are obtained with a test bench, and a two-dimensional contact pressure distribution model is established to reproduce the contact pressure distribution of tyre under heavy loads and dynamic slips. The comparison results with Magic Formula (MF) and Trucksim are generally consistent, proving the effectiveness of the model. Finally, a lateral and longitudinal tyre force distribution control of vehicles is carried out based on the established model. The results of the Trucksim-Simulink co-simulation show that the path tracking accuracy of vehicles is significantly improved, which demonstrates that the tyre model incorporating lateral and longitudinal mechanical characteristics under heavy loads can provide a theoretical basis for solving the problem of uncoordinated steering in heavy vehicles.

Numerical Simulation Analysis on Hydraulic Optimization of the Integrated Pump Gate

Based on the Reynolds time mean N-S equation and standard k-ε turbulence model and using Computational Fluid Dynamics technology, this study aims to integrate the brake pump to carry out numerical simulation. Through the adoption of different arrangements of impending height and spacing, the hydraulic characteristics of the full tubular pump unit are analyzed. The two-dimensional streamline, velocity and pressure distribution, and three-dimensional streamline, axial velocity and vorticity distribution of the front pool of each scheme are displayed. The results show that the recommended pump installation height is 0.8 Dd, the maximum limit value of the pump station design specification; in the dual-pump mode, the recommended pump spacing is 2.00 Ds.

Method for Calculating Plastic Deformation of High Resolution and Large Contact Area

AbstractIn a rolling contact, the tribological properties in terms of friction, wear, and fatigue are significantly influenced by the surface roughness. Due to solid contact of the surfaces in the contact area, the roughness and thus also the tribological properties change during the service life of the contact. The initial load leads to major changes of the tribological properties figured out by Brecher et al. (2019, “Influence of the Metalworking Fluid on the Micropitting Wear of Gears,” Wear, 61(434–435), p. 202996). Prediction of the initial changes in topography in the contact area is necessary for specific optimization of rolling contacts. Especially for dry rolling–sliding contact, the roughness of the surfaces is crucial for the lifetime, which is part of the investigations within the DFG priority program 2074 (357505886). In this work, an elastic-plastic contact algorithm for calculating plastic deformation for dry contact of rough surfaces with large contact area and high resolution is presented. Due to the nonlinearity behavior associated with plastic deformation, the plastic contact algorithm is based on an iterative approach. An optimized meshing strategy is implemented to calculate the elastic pressure distribution on the surface. Corresponding to the two-dimensional pressure distribution, the three-dimensional stress distribution allows the consideration of residual stresses and interactions of the microscopic peaks of the rough surface. Furthermore, the three-dimensional plastic strain distribution allows the application of an analytical approach to represent the plastic deformation of the surface. Finally, the solution of a plastic contact calculation with an exemplary topography measured on a real rough surface is presented.

Study on tangential stiffness nonlinear softening of bolted joint in friction-sliding process

This paper proposed a new friction mechanical model of joint interface to better describe the tangential stiffness softening. A new probability density function is obtained by analyzing the actual two-dimensional pressure distribution of bolted joint. Then, an improved tangential stiffness model and the corresponding extraction method of the model parameters based on FEA method was introduced, and the effectiveness of the model was verified by the designed slip test. Finally, this paper discussed the influence of various parameters on tangential stiffness, and explained the stiffness nonlinear softening from the evolution of sliding area. Compared with the existing model, the calculation accuracy is improved by 18.2%. The research content has a better application prospect in dynamic analysis of connection structures.

Two-dimensional pressure field and backflow in the annular skirt of vortex gripper

The vortex gripper is a kind of pneumatic noncontact gripper that does not produce a magnetic field and heat. It can grip a workpiece without physical contact, which avoids any unintentional damage such as mechanical scratches, local stress concentrations, frictional static electricity, and surface stains. This study focused on the two-dimensional pressure distribution field on a workpiece surface under the vortex gripper. Theoretical, experimental, and computational fluid dynamics results were combined to study the backflow phenomenon in the annular skirt, which can decrease the gripper’s suction force after the maximum value is reached. First, the pressure distribution in the annular skirt was theoretically modeled. A comparison with the experimental results showed that increasing the gap height between the gripper and workpiece generates a circumferentially asymmetrical flow field in the skirt. Based on this, it was hypothesized that an airflow in the circumferential direction may exist. The experimental data and simulation results were analyzed under large gap height conditions to observe the backflow in detail and it was found that an uneven pressure distribution with positive and negative pressure regions generated by the uneven flow is the root cause of the backflow. Finally, the effect of the backflow on the flow field in two different flow regions (in the annular skirt and inside the vortex chamber) was analyzed and the reason why the suction force of the vortex gripper has a maximum value was determined.

Numerical and analytical predictions of nuclear steam generator secondary side flow field during blowdown due to a feedwater line break

For the structural integrity evaluation of pressurized water reactor (PWR) steam generator (SG) tubes subjected to transient hydraulic loading, determination of the tube-to-tube gap velocity and static pressure distributions along the tubes is prerequisite. This paper addresses both computational fluid dynamics (CFD) and analytical approaches for predicting the tube-to-tube gap velocity and static pressure distributions during blowdown following a feedwater line break (FWLB) accident at a PWR SG. First of all, a comparative study on CFD calculations of the transient velocity and pressure distributions in the SG secondary sides for two different models having 30 or no tubes is performed. The result shows that the velocities of sub-cooled water flowing between any adjacent two tubes of a tubed SG model during blowdown can be roughly estimated by applying the specified SG secondary side porosity to those of the no-tubed SG model. Secondly, simplified analytical approximate solutions for the steady two-dimensional SG secondary flow velocity and pressure distributions under a given discharge flowrate are derived using a line sink model. The simplified analytical solutions are validated by comparing them to the CFD calculations.

Two-Dimensional Pore Pressure Distribution Model to Evaluate Effects of Shale Semipermeable Membrane Characteristics

During the drilling of shale formations, drilling fluids can intrude into the wellbore, raise the pore pressure, and lead to wellbore instability. Based on the thermodynamic theory, a new model was established to calculate pore pressure. The model considers the effects of solute diffusion and solution convection and conducts sensitivity analyses. The results show that the drilling fluid activity significantly affects the pore pressure distribution. The pore pressure under high drilling fluid activity will increase rapidly in the early stage. Low drilling fluid activity can effectively suppress the growth of pore pressure. And a low effective diffusion coefficient of solute and a high membrane efficiency also help to reduce pore pressure. Therefore, reducing drilling fluid activity should be conducted in priority in drilling fluid design. Lowering its solute effective diffusion coefficient and increasing its viscosity can also be considered as auxiliary methods.

Achieving high-resolution pressure mapping via flexible GaN/ ZnO nanowire LEDs array by piezo-phototronic effect

Simulating human tactile sensing through high-resolution electronics is a significant and challenging topic in artificial intelligence. A flexible p-GaN film/n-ZnO nanowire light-emitting diode (LED)-based pressure sensor array, with the merits of flexibility, high resolution, good transparency, fast response, stability, and lightweight, is fabricated through laser lift-off (LLO) process and hydrothermal growth of ZnO nanowires directly on a flexible GaN film, which is used for acquiring the two-dimensional (2D) pressure distribution mapping by reading the illumination intensities from all LED pixels parallelly. The intensity of each pixel composed by a GaN/ZnO nanowire heterostructure LED can be enhanced by the local compressive strain based on piezo-phototronic effect. A high spatial resolution of 2.6 μm and a fast response time of 180 ms were obtained, and also the sensor arrays can still function well after 4000 bending circles. The promising flexible LEDs-based pressure sensor array gains some technological innovations in the field of tactile sensing, with potential applications in smart skin, biomedicine, optical MEMS, and touchpad technology.

Visualization of Contact-Pressure Distribution between Material and Backing Plate in Friction Stir Processing

In this study, the authors evaluated pressure distribution on a backing plate in friction-stir processing (FSP) utilizing an embedded pressure pin connected to a load sensor. They conducted FSP on aluminum alloy plates repeatedly offsetting the path-lines from the center of the pin and recorded change of forming pressure with tool position, which was compiled from the bearing load of the pin. The authors mapped the results to visualize the two-dimensional contact pressure distribution on a backing plate during FSP. They then compared the height distribution of the wall fabricated by friction-stir forming (FSF) utilizing a die having a groove with the observed distribution of pressure. Consequently, maximum pressure was observed beneath the rim of the tool probe at the retreating side (RS), and the highest points of the wall were observed at the RS.

Oxygen-assisted preparation of mechanoluminescent ZnS:Mn for dynamic pressure mapping

Mechanoluminescent materials that convert mechanical stimuli to light emission have attracted extensive attention for potential applications in human-machine interactions. Here, we report a simple and available novel approach for the oxygen-assisted preparation of ZnS:Mn particles by solid-state reaction at atmospheric pressure without the formation of the corresponding oxides. The existence of O2 has a positive impact on the formation of S vacancies in wurtzite-phase ZnS, leading to the introduction of Mn2+ ion luminescent centers and shallow donor levels, which can improve the electron-hole recombination rate. The O2 ratio and Mn2+ ion doping concentration have significant effects on the luminous efficiency, which is optimal at 1%–20% and 1 at.%–2 at.% respectively. In addition, a device based on the piezo-photonic effect with excellent pressure sensitivity of 0.032 MPa−1 was fabricated, which can map the two-dimensional pressure distribution ranging from 2.2 to 40.6 MPa in situ. This device can be applied to real-time pressure mapping, smart sensor networks, high-level security systems, human-machine interfaces, and artificial skins.

Compressibility effects on flat-plates with serrated leading-edges at a low Reynolds number

This study evaluates the influence of a serrated leading edge on flat-plate aerodynamics at low-Reynolds-number and subsonic high-Mach-number conditions. Forces are measured for a Mach number ranging from 0.2 to 0.64 at aReynolds number of (12,000 ± 1000). Pressure distributions are obtained under the same conditions using pressure sensitive paint (PSP) measurement. Three models are tested: a flat plate without serrations used as the baseline case and two flat plates with serrated leading edges of different wavelength-to-amplitude ratios. Results show that the aerodynamic performance of flat plates with serrations is slightly changed from the baseline case. The plate with short-wavelength serrations underperforms in terms of the lift-to-drag ratio under all the conditions compared to the baseline case while the plate with large-wavelength serrations slightly outperforms it at around the stall angle. The Mach number has little effect on the attached flow while the lift increases with the Mach number under deep stall conditions. Serrations maintain the lift even under high angle of attack conditions when Mach number varies. The twodimensional pressure distributions and the analyses of local chordwise pressure coefficient distributions at different spanwise locations and of periodicity of spanwise pressure coefficients allow categorisation of the complex flow structures into three types. These configurations feature different types of low pressure regions downstream of troughs. The periodicity of the pattern depends not only on the angle of attack but also on the Mach number.

Numerical and Experimental Investigations on Preload Effects in Air Foil Journal Bearings

A detailed elastogasdynamic model of a preloaded three-pad air foil journal bearing is presented. Bump and top foil deflections are herein calculated with a nonlinear beamshell theory according to Reissner. The two-dimensional pressure distribution in each bearing pad is described by the Reynolds equation for compressible fluids. The assembly preload is calculated by simulating the assembly process of top foil, bump foil, and shaft. Most advantageously, there is no need for the definition of an initial radial clearance in the presented model. With this model, the influence of the assembly preload on the static bearing hysteresis as well as on the aerodynamic bearing performance is investigated. For the purpose of model validation, the predicted hysteresis curves are compared with measured curves. The numerically predicted and the measured hysteresis curves show a good agreement. The numerical predictions exhibit that the assembly preload increases the elastic foil structural stiffness (in particular for moderate shaft displacements) and the bearing damping. It is observed that the effect of the fluid film on the overall bearing stiffness depends on the assembly preload: For lightly preloaded bearings, the fluid film affects the overall bearing stiffness considerably, while for heavily preloaded bearings the effect is rather small for a wide range of reaction forces. Furthermore, it is shown that the assembly preload increases the friction torque significantly.

Use of wide-element one-dimensional receiving arrays to measure two-dimensional lateral pressure distribution of ultrasound beams

Measurement of acoustic fields is an important aspect of ultrasound research and development. The corresponding data is usually collected by a raster scan using a single point receiver moved by a computer-controlled positioning system. A faster approach could be based on the use of a 1D linear multi-element array with several tens or hundreds of small elements, which is moved in a direction perpendicular to the beam axis. The drawback of such an approach is difficulty in making small, closely-positioned receiving elements that provide sufficient signal-to-noise ratio. The current paper presents an alternative design for a 1D linear array: instead of using small elements, here it is suggested to use narrow but long elements, with a width on the order of a half wavelength or less and a length larger than the extent of the ultrasound beam being studied. The drawback of the proposed long-element arrays is absence of resolution in the direction along the element. This problem is solved by incrementally rotating the array either around the axis parallel to the array surface and perpendicular to the elements or around the axis perpendicular to the array surface. [Work supported by RSF 14-15-00665, NIH R01 EB007643, and NIH R21 EB016118.]

Flexible Light Emission Diode Arrays Made of Transferred Si Microwires-ZnO Nanofilm with Piezo-Phototronic Effect Enhanced Lighting

Due to the fragility and the poor optoelectronic performances of Si, it is challenging and exciting to fabricate the Si-based flexible light-emitting diode (LED) array devices. Here, a flexible LED array device made of Si microwires-ZnO nanofilm, with the advantages of flexibility, stability, lightweight, and energy savings, is fabricated and can be used as a strain sensor to demonstrate the two-dimensional pressure distribution. Based on piezo-phototronic effect, the intensity of the flexible LED array can be increased more than 3 times (under 60 MPa compressive strains). Additionally, the device is stable and energy saving. The flexible device can still work well after 1000 bending cycles or 6 months placed in the atmosphere, and the power supplied to the flexible LED array is only 8% of the power of the surface-contact LED. The promising Si-based flexible device has wide range application and may revolutionize the technologies of flexible screens, touchpad technology, and smart skin.

A prediction model for two-dimensional pressure distribution from underwater shock wave focusing by an ellipsoidal reflector.

Underwater shock wave focusing by ellipsoidal reflector is an important method for medical treatment, detection, and acoustic warfare. However, its pressure field is difficult to predict due to complicated physics. In this study, the pressure by focusing is modeled based on theories of shock wave propagation, nonlinear reflection, and nonlinear focusing, and the calculation domain is determined by approximate equations of wave fronts and lines. The pressure field during the whole process is described by combining direct and focusing pressures in the time and space domains. On this basis, the focusing behavior is simulated, and obtained pressure profiles are compared with experimental results, and the influence of reflector length on focusing performance is also discussed. The results indicate that although there are some rough assumptions, this model can simulate the underwater focusing in some detail and does a good job of predicting the pressure distribution, especially for the positive peak pressure, with an error below 10%; as the reflector length increases, the dynamic focus tends to move linearly forward to the other geometric focus, and the pressure gain increases continuously but the growth rate decreases.

Mechanically Induced Light Emission and Infrared-Laser-Induced Upconversion in the Er-Doped CaZnOS Multifunctional Piezoelectric Semiconductor for Optical Pressure and Temperature Sensing

In this study, we report an Er-doped quaternary piezoelectric semiconductor CaZnOS:Er3+ which shows both mechanoluminescence and upconversion luminescence properties. Under mechanical stimulation, green light emission can be observed by the naked eye from a flexible film fabricated by encapsulating CaZnOS:Er3+ particles between two polyethylene glycol terephthalate substrates. The integral emission intensity is proportional to applied pressure, making CaZnOS:Er3+ suitable for dynamic pressure sensing applications. Moreover, the doped sample also shows bright visible emission with near-infrared (980 nm) excitation. The fluorescence intensity ratio between two upconversion emission bands corresponding to 2H11/2, 4S3/2 → 4I15/2 transitions of Er3+ is sensitive to the variation of temperature. As a multifunctional optical material, CaZnOS:Er3+ could be used to not only visualize two-dimensional pressure distribution, through mechanically induced emission, but also sense temperature via the upconversion (UC) l...