Pressure Field Research Articles

Diffusion-driven flows in a nonlinear stratified fluid layer

Diffusion-driven flow is a boundary layer flow arising from the interplay of gravity and diffusion in density-stratified fluids when a gravitational field is non-parallel to an impermeable solid boundary. This study investigates diffusion-driven flow within a nonlinearly density-stratified fluid confined between two tilted parallel walls. We introduce an asymptotic expansion inspired by the centre manifold theory, where quantities are expanded in terms of derivatives of the cross-sectional averaged stratified scalar (such as salinity or temperature). This technique provides accurate approximations for velocity, density and pressure fields. Furthermore, we derive an evolution equation describing the cross-sectional averaged stratified scalar. This equation takes the form of the traditional diffusion equation but replaces the constant diffusion coefficient with a positive-definite function dependent on the solution's derivative. Numerical simulations validate the accuracy of our approximations. Our investigation of the effective equation reveals that the density profile depends on a non-dimensional parameter denoted as $\gamma$ representing the flow strength. In the large $\gamma$ limit, the system is approximated by a diffusion process with an augmented diffusion coefficient of $1+\cot ^{2}\theta$ , where $\theta$ signifies the inclination angle of the channel domain. This parameter regime is where diffusion-driven flow exhibits its strongest mixing ability. Conversely, in the small $\gamma$ regime, the density field behaves like pure diffusion with distorted isopycnals. Lastly, we show that the classical thin film equation aligns with the results obtained using the proposed expansion in the small $\gamma$ regime but fails to accurately describe the dynamics of the density field for large $\gamma$ .

Localized topological states beyond Fano resonances via counter-propagating wave mode conversion in piezoelectric microelectromechanical devices

A variety of scientific fields like proteomics and spintronics have created a new demand for on-chip devices capable of sensing parameters localized within a few tens of micrometers. Nano and microelectromechanical systems (NEMS/MEMS) are extensively employed for monitoring parameters that exert uniform forces over hundreds of micrometers or more, such as acceleration, pressure, and magnetic fields. However, they can show significantly degraded sensing performance when targeting more localized parameters, like the mass of a single cell. To address this challenge, we present a MEMS device that leverages the destructive interference of two topological radiofrequency (RF) counter-propagating wave modes along a piezoelectric Aluminum Scandium Nitride (AlScN) Su-Schrieffer-Heeger (SSH) interface. The reported MEMS device opens up opportunities for further purposes, including achieving more stable frequency sources for communication and timing applications.

Strengthening by {110} and {112} edge dislocations in BCC high entropy alloys

Abstract Mechanical tests and microscopy studies on body-centered cubic (BCC) high entropy alloys reveal transitions from screw to edge dislocation slip and from {110} to {112} slip plane activity. Here, a strengthening theory for BCC edge dislocation slip on {112} planes is thus developed that parallels a recent theory for {110} slip. Using the atomistic dislocation pressure fields for four BCC elements (Nb, Ta, Mo, W) as proxies to span the range of likely alloy cores, theory predicts that the zero temperature yield strength for {112} slip is slightly lower (0%–20%) than that for {110} slip but that the associated energy barrier is slightly (0%–20%) higher. This leads to cancelling effects, and hence very similar strengths, at finite temperatures and strain rates. Full atomistic results on selected dilute binary alloys show some shifts in these trends, but with similar magnitudes and cancelling effects. The close strengths of {110} and {112} slip modes indicate that subtle aspects beyond the scope of the theory will determine which slip system controls the observed strengthening. This closeness in strength cements the use of the {110} edge theory for guiding alloy design independent of actual slip system.

Waves Generated by the Horizontal Motions of a Bottom Disturbance

Waves generated by a horizontally moving disturbance on the seabed have been studied by developing two numerical models, namely, the Navier–Stokes and the Green–Naghdi equations. Various geometries of the bottom disturbances are considered, and waves generated due to a single motion and multiple oscillatory motions of the bottom disturbances are investigated by the two models. Discussion is provided on how the motion of the disturbance on the seafloor results in the generation of surface waves. The wave-field parameters investigated include the surface elevation, velocity, pressure fields and wave celerity. A parametric study is conducted to assess the effect of the geometry of the disturbance and the kinematic characteristics on the wave generation. It is shown that both linear and nonlinear waves can be generated by a horizontally moving disturbance on the seabed. Long waves, followed by a series of dispersive waves, are produced by the single motion of the bottom disturbance. It is also found that, under appropriate conditions, there would be a balance between nonlinearity and dispersion, such that the generated waves propagate over a flat seafloor with little to no change in their form and shape.

Chuprov invariant for vector-scalar fields of multipole sources in a shallow sea

A computational and theoretical study of the properties of the well-known waveguide invariant S.D. Chuprova (IC) was carried out in a plane-parallel Pekeris waveguide. Unlike earlier works, in which predominantly non-directional (monopole) sources were used as a source, and sound pressure fields (scalar fields) were studied, in this work not only scalar, but also vector fields formed in the waveguide by directional - combined multipole sources with directivity in both horizontal and vertical planes. A differential equation has been obtained that makes it possible to fairly accurately calculate the IC values under different conditions of signal propagation and different depths of sources and receivers. This makes it possible, in a simpler way than “full computer modeling,” to predict the invariance (stability) of the IC when varying both the hydrophysical conditions in the waveguide and the geometry of the experiment. It is shown that the directionality of sources in the horizontal plane has virtually no effect on the properties of the IC, and the directionality in the vertical plane leads to a shift in the fan structure of the signal amplitude fields, but has little effect on the IC values. The properties of the fan structure change in a similar way when using vertical projections of the oscillatory velocity vector - despite the fact that another analytical relation, different from scalar fields, is used to calculate the IC, the IC value is close to (+1) at all frequencies and distances, except those at which new modes or dislocations arise. At these frequencies and in these zones, alternating emissions with different signs and magnitudes occur. It is concluded that the stability of IC allows the application of signal processing algorithms developed for scalar fields and non-directional sources to vector-scalar fields generated, including using directional sources.

Course control in a self-consistent model of cuttlefish movement

We developed a simulation model to mimic cuttlefish movement. We developed a simulation model to mimic cuttlefish movement, representing an elongated body with two undulatory fins that generate propulsive forces for underwater movement. Our mathematical model concurrently solved equations for both body mechanics and fluid dynamics, using the Navier–Stokes equations to describe the latter. To implement this self-consistent model, we utilized deformable mesh techniques. This enabled us to compute both the apparatus’s movement performance characteristics and hydrodynamic flow parameters, such as vorticity and pressure fields. Our study focused on examining how oscillations of the left and right fins, each with different parameters, impact the apparatus’s maneuverability. We found that differences in frequencies between the left and right fins resulted in a peak turning angle velocity. We also explored how the interplay between hydrodynamic forces influences the apparatus’s course control.

Experimental synthesis of random pressure fields based on Transfer-Matrix analysis on 1D arrays

Synthesizing random pressure fields with loudspeaker arrays in a laboratory setting requires acquiring a global transfer matrix of all channels between the loudspeaker array and the microphone array. This inevitably involves measuring a large and unwieldy number of transfer functions. Therefore, we propose a prediction method for the transfer matrix under free-field conditions, combining a substantially reduced number of measurements with specific predictions based on segmented acoustic centers. In free-field conditions, if only three sets of transfer functions are measured for each loudspeaker and the remaining entries in the global transfer matrix are predicted using analytical expressions, the results show that the normalized error between the predicted and measured transfer matrices can be less than -13 dB. The experimental results indicate that, based on a one-dimensional loudspeaker array in a standard anechoic chamber, this prediction method shows promise for accurately reproducing random pressure fields, such as a diffuse acoustic field and the pressure field in the spanwise direction of a turbulent boundary layer. Additionally, the prediction method demonstrates the potential for extension to two-dimensional synthesis.

A comparative study of multi-tentacled underwater robot with different self-steering behaviors: Maneuvering and cruising modes

Based on the concept of same structure but different laws, we propose two driving modes, maneuvering and cruising, using multiple tentacles of cephalopods as biomimetic prototypes. These two modes are distinguished by transient or continuous kinematic laws and can achieve self-steering behaviors with different features. The computational evolution process between this underwater robot and the flow field is solved on the OpenFOAM platform. We nest the secondary developed solver with dynamic overlapping mesh technology and integrate multiple functional modules. The numerical results show that for the maneuvering mode, the robot achieves rapid turning by collectively generating high-intensity pressure and vorticity fields during the upstroke of tentacles. This mode is suitable for application scenarios that require real-time direction adjustment, such as obstacle avoidance and emergency response. For the cruising mode, the robot relies on continuous asymmetric swing of their tentacles to generate stable yaw moment, and the navigation trajectory presents a fan-shaped pattern with serrated edges. This mode is suitable for purposeful application scenarios such as anti-interference stability and advance prediction.

A local synergy angle of velocity, temperature and pressure fields for enhancement of comprehensive heat transfer performance

A local synergy angle of velocity, temperature and pressure fields for enhancement of comprehensive heat transfer performance

Comparative analysis of Zero Pressure Geometry and prestress methods in cardiovascular Fluid-Structure Interaction

Background and Objective:Modelling patient-specific aortic biomechanics with advanced computational techniques, such as Fluid–Structure Interaction (FSI), can be crucial to provide effective decision-making indices to enhance current clinical practices. To effectively simulate Ascending Thoracic Aortic Aneurysms (ATAA), the stress-free configuration must be defined. The Zero Pressure Geometry (ZPG) and the Prestress Tensor (PT) are two of the main approaches to tackle this issue. However, their impact on the numerical results is yet to be analysed. Computed Tomography Angiography (CTA) and Magnetic Resonance Imaging (MRI) data were used to develop patient-specific 2-way FSI frameworks. Methods:Three models were developed considering different tissue prestressing approaches to account for the reference configuration and their numerical results were compared. The selected approaches were: (i) ZPG, (ii) PT and (iii) a combination of the PT approach with a regional mapping of material properties (PTCAL). Results:The pressure fields estimated by all models were equivalent. The estimation of Wall Shear Stress (WSS) based metrics revealed good correspondence between all models except the Relative Residence Time (RRT). Regarding ATAA wall mechanics, the proposed extension to the PT approach presented a closer agreement with the ZPG model than its counterpart. Additionally, the PT and PTCAL approaches required around 60% fewer iterations to achieve cycle-to-cycle convergence than the ZPG algorithm. Conclusion:Using a regional mapping of material properties in combination with the PT method presented a better correspondence with the ZPG approach. The outcomes of this study can pave the way for advancing the accuracy and convergence of ATAA numerical models using the PT methodology.

Characterizing surface pressure and wind fields of typhoons approaching Hong Kong

In this paper, 17 severe typhoons that have affected Hong Kong are simulated using an advanced numerical atmospheric simulation system - Weather Research and Forecasting model (WRF). The simulated surface pressure and wind fields of these typhoons are validated against a wide range of field observations. Then azimuth-dependent models for the radius of maximum winds and the Holland parameter are established statistically at the surface level. It is observed that the shape parameter of the Holland pressure model is smaller at the surface than that at the gradient level. And the Holland wind field model cannot well reproduce the simulated radial wind profiles due to the complexities of nonuniform surface conditions and typhoon dynamics. It is found that the modified Rankine model provides satisfactory estimates of typhoon wind speeds in Hong Kong. Additionally, wind field asymmetries of typhoons approaching Hong Kong are highly correlated with the typhoon track velocity, vertical wind shear and the angle between them. The proposed statistical models and identified characteristics of wind field asymmetries of typhoons will provide useful information for rapidly assessing typhoon wind hazards.

Mesh topology-based spurious pressure stabilization in 3D finite elasticity using Voronoi tessellations

AbstractIn this paper, we present a mesh topology-based stabilization approach to suppress spurious pressure modes in 3D nearly-incompressible finite elasticity. The focus lies on a mixed formulation with lowest-order approximation for the displacement and pressure fields. Motivated by the fact that the popular H1/P0 element does not fulfill the inf-sup condition, all possible local spurious pressure modes are derived on a patch of elements. The nullspace method is used to determine all spurious pressure solutions. From this, the topological requirements of the finite element mesh are established. We conclude that no more than four elements are allowed to intersect in the same vertex to overcome local checkerboarding. To fulfill this requirement, we employ non-degenerate 3D Voronoi diagrams with several different site distributions. These result in random, centroidal, and honeycomb Voronoi meshes. The resulting convex polyhedral elements are discretized by a polyhedral mixed finite element based on the lowest possible interpolation pair. The numerical examples illustrate that spurious pressure modes do not occur for any degree of mesh refinement as long as the topological mesh requirements are met. Furthermore, it is shown that the numerical inf-sup test is passed. By violating the topological requirements, it is shown that a stable pressure field cannot be guaranteed and the checkerboard phenomenon is provoked.

Research on Wellbore Integrity Evaluation Model of CO2 Enhanced Composite Fracturing

CO2 injection composite fracturing is an effective method for shale oil and gas well development. The downhole casing is prone to uniform corrosion, pitting, perforation, and even corrosion fracture in the CO2 environment. Therefore, it is particularly important to reveal the physical characteristics of CO2 under actual geological conditions and the impact of CO2 corrosion on the performance of casing. A mathematical model for the temperature and pressure field of CO2 in the wellbore under fracturing conditions is established in this paper, and the temperature and pressure distribution along the depth of the well is calculated. By optimizing the CO2 state equation and using the S-W equation, Lee model, and RK model to calculate the CO2 density, viscosity and compression factor, respectively, the phase distribution pattern of CO2 along the actual wellbore is obtained. Through CO2 corrosion tests on the casing, the influence of temperature and CO2 concentration on the corrosion rate of the casing is clarified. The peak corrosion rate of Q125 steel corresponds to 80 °C, and the corrosion rate increases with the increase in CO2 concentration. Finally, a prediction model for the uniform corrosion rate of casing under different temperatures and CO2 concentration conditions is obtained, which can provide technical support for the design of CO2-enhanced fracturing technology.

Research on leakage characteristics of working clearances of hydrogen circulation pump

The volumetric efficiency of the hydrogen circulation pump (HCP) is mainly affected by the amount of leakage in working clearances. Studying the leakage characteristics of working clearances is of great significance for optimizing the performance of the HCP. Therefore, this paper developed a three-blade elliptical conjugate rotor HCP, and compared the results of experiments and simulations for different working conditions. On this basis, the flow rate, pressure, and internal flow field changes of radial clearance models and axial clearance models with four different scales of 0.1mm, 0.14mm, 0.18mm, and 0.22 mm were studied. The results indicate that: under four different pressure ratios and rotational speeds, the simulation results using the overlapping grid method showed a maximum difference of 4.17% compared to the experimental results, verifying the reliability of the simulation calculation method; the average flow rate of the HCP is linearly inversely proportional to both the radial clearance and the axial clearance, with a decrease rate of 11.6 Nm3/h and 5.8 Nm3/h as the clearance size increases by 0.04 mm; the radial clearance leakage of the same size is higher than the axial clearance, the leakage value in the radial clearance between the rotors is higher than that between the rotor and the pump casing, and the internal leakage of axial clearance is not evenly distributed, with higher leakage value in the middle area than that in the left and right areas.

Recent Advances in the Health Benefits of Phenolic Acids in Whole Grains and the Impact of Processing Techniques on Phenolic Acids: A Comprehensive Review.

Phenolic acids, essential compounds in whole grains, are renowned for their health-enhancing antioxidant and anti-inflammatory properties. Variations in concentration, particularly of hydroxybenzoic and hydroxycinnamic acids, are observed among grain types. Their antiobesity and antidiabetes effects are linked to their modulation of key signaling pathways like AMPK and PI3K, crucial for metabolic regulation and the body's response to inflammation and oxidative stress. Processing methods significantly influence phenolic acid content and bioavailability in whole grains. Thermal techniques like boiling, baking, or roasting can degrade these compounds, with loss influenced by processing conditions. Nonthermal methods such as germination, fermentation, or their combination, can protect or enhance phenolic acid content under ideal conditions. Novel nonthermal approaches like ultrahigh pressure (UHP), irradiation, and pulsed electric fields (PEF) show promise in preserving these compounds. Further research is needed to fully comprehend the impact mechanisms of these innovative methods on the nutritional and sensory attributes of cereals.

Experimental exploration of methane-coal dust explosion suppression by expandable graphite: From the point of view of pressure, flame, spectrum, and flow field

Expandable graphite (EG) has been proposed as a more efficient material for suppressing methane-coal dust explosions. The suppression effect was evaluated based on pressure, flame, spectrum, and flow field. The influence of particle size, expansion ratio, and suppressant concentration on the suppression effect was considered, and the suppression mechanism was analyzed. The explosion characteristics and OH* emission spectrum indicated that EG effectively suppressed methane-coal dust explosions. Higher concentrations, smaller particle sizes, and higher expansion ratios resulted in a stronger suppression effect. The influence of EG parameters on suppression effectiveness was ranked from highest to lowest in terms of the concentration, particle size, and expansion ratio. Schlieren imaging showed that EG can partially suppress the initial flame. However, the significant suppression effect occurs during the pressure-increase stage. The flow field was also analyzed using proper orthogonal decomposition. The results showed that EG suppressed flow-field fluctuations, with the mode coefficient trends aligned closely with the pressure-change curve.

Study on Aerodynamic Interference of Tilt-rotor Aircraft at Different Rotor Deflection Angles

This paper presents a numerical simulation of a tiltrotor aircraft developed in the United States, examining the aerodynamic interference between the rotors, wings, and fuselage in three flight conditions: forward flight, transition mode, and hover. The study investigates the distribution of the velocity field, pressure field, vorticity field, and streamlines around the aircraft at different rotor tilt angles.

Predictive Model for Cell Positioning during Periodic Lateral Migration in Spiral Microchannels.

The periodic lateral migration of submicrometer cells is the primary factor leading to low precision in a spiral microchannel during cell isolation. In this study, a mathematical predictive model (PM) is derived for the lateral position of cells during the periodic lateral migration process. We analyze the relationship of migration period, migration width, and starting point of lateral migration with microchannel structure and flow conditions and determine the empirical coefficients in PM. Results indicate that the aspect ratio of the microchannel and the Reynolds number (Re) are key factors that influence the periodicity of the cell lateral migration. The lateral migration width is jointly affected by Re, the cell blockage ratio, and the microchannel curvature radius. The inlet structure of the microchannel and the ratio of the cell sample to the sheath flow rate are critical parameters for regulating the initial position. Moreover, the structure of the pressure field at the inlet constrains the distribution range of the starting point of the lateral migration. Regardless of whether the particles/cells undergo 0.5, 1, or multiple lateral migration cycles, the lateral positions predicted by PM align well with the experimental observations, thus verifying the accuracy of PM. This research helps to elucidate the characteristics of periodic lateral migration of cells in spiral microchannels and can provide practical guidance for the development and optimization of miniature spiral microchannel chips for precise cell isolation.

An explicit incompressible scheme based on the MPS method to simulate slump flow

AbstractIn this study, an explicit incompressible scheme based on the Moving Particle Semi-implicit method (MPS) is applied to simulate slump flow. In the numerical method, the pressure Poisson equation is explicitly solved to obtain the pressure field. In simulating slump flow caused by fresh concrete, the fluid is treated to be non-Newtonian fluid and a regularized Bingham model is employed to calculate the viscosity. Flow characteristics in the slump flow are reproduced by the numerical method, and in good agreement with experimental measurements. The parameters including the rheological regularized parameter, yield stress, plastic viscosity, and particle distance, are examined in the simulations. It is found that the explicit incompressible scheme can well reproduce the concrete spreading. The yield stress in the rheology model affects the spreading distance significantly while the plastic viscosity plays an important role in the acceleration stage of the material spreading.

Experimental analysis of pressure deviation-induced film cooling effectiveness deviation in pressure sensitive paint measurement

The use of the Pressure Sensitive Paint (PSP) measurement method allows for obtaining dense, completely adiabatic film cooling effectiveness (η) results. In order to adapt to the increasing trend of high-speed and complexity in the application scenarios of film cooling, the pressure deviation-induced film cooling effectiveness deviation in PSP measurements needs to be quantified and corrected. Initially, two different jets of specific materials were injected into a dual-hole flat plate test piece. The pressure difference at corresponding positions of the two jet flows was measured to demonstrate that, compared to air, a ternary oxygen mixed gas better simulated the pressure field of the foreign gas. This illustrates the feasibility of the Test3-OM correction method. Building upon this, the influence of pressure deviation on the accuracy of measurement results was quantitatively evaluated in various scenarios, including a flat circular hole, film holes with a compound angle, a converging slot hole, and film holes at three positions on the blade. The results indicate that the pressure deviation-induced η deviation is non-negligible under conditions of high blowing ratios in most positions. Particularly in the low η region, there is a higher sensitivity to pressure deviation. Generally, there is a negative deviation region near the hole downstream, and a positive deviation region slightly downstream. The generation of deviations stems from variations in density, resulting in different flow patterns of the jet near the wall surface.