Pressure Disturbances Research Articles

ВЗАИМОСВЯЗЬ НЕЛИНЕЙНЫХ МАТЕМАТИЧЕСКИХ МОДЕЛЕЙ ОБРАЗОВАНИЯ ГЛИНИСТОЙ КОРКИ В РАДИАЛЬНОЙ И ЛИНЕЙНОЙ ГЕОМЕТРИИ

A quasi-stationary model for the formation of a clay filter during well drilling in depth intervals with permeable rocks is proposed, on the basis of which the physical parameters of the media, reservoir and well are established, which determine the dependence of its radial dimensions on time. It is assumed that the filtration pressure fields are described by stationary piezoconductivity equations. The dependence of pressure, mudcake thickness, radius of the zone of pressure disturbances in the permeable rock during drilling and other parameters on time is parametric. Such a dependence arises from an additional equation that relates the amount of fluid absorbed by the formation and the filtration rate at the inlet to the porous medium. The general formulation of the problem, which includes the stationary piezoconductivity equations for the mudcake and reservoir, boundary conditions, and an additional equation, is non-linear, since the boundaries of the perturbation zone in the reservoir and the mudcake are mobile. An analytical solution of the problem was constructed, on the basis of which studies were carried out on the influence of the physical parameters of the medium, wells, etc. on the process of formation of a clay cake in real conditions. Integrals of motion of a nonlinear problem are found, which represent invariant complexes of parameters that do not change during the formation of a mud cake. The presence of such integrals made it possible to establish the relationship between the solutions of problems presented in radial and linear geometries. It is shown that in the particular case of a thin mud filter, the obtained expressions for the radial geometry coincide with the known ones, when the geometric factor of the drilling fluid filtrate corresponds to a flat flow. New possibilities for estimating the physical parameters of reservoirs based on caliper logging have been identified. The solution of this problem is especially important for horizontal wells, in which the intervals of clay cake have a significant length, and its formation occurs under conditions of a wide range of reservoir properties of the formation. The considered problem is of practical importance, since the zone of penetration of the drilling fluid filtrate into the formation has a screening effect on the use of geophysical methods to determine the saturation of the formations. The obtained solutions can be used both to improve the interpretation of geophysical methods and the development of drilling technology.

Obstructive Sleep Apnea and Hypertensive Heart Disease: From Pathophysiology to Therapeutics.

Obstructive sleep apnea (OSA) is characterized by recurrent episodes of complete or partial obstruction of the upper airway that lead to intermittent hypoxemia, negative intrathoracic pressure, hypercapnia, and sleep disturbances. While OSA is recognized as a significant risk factor for cardiovascular disease, it's relationship with hypertensive heart disease (HHD) remains underappreciated. HHD is a condition characterized by the pathological hypertrophy of the left ventricle, a consequence of elevated arterial hypertension. Interestingly, both OSA and HHD share similar underlying mechanisms including hypertension, left ventricular hypertrophy, myocardial fibrosis, oxidative stress, and inflammation, which ultimately contribute to the progression of HHD. This review aims to shed light on the potential role of OSA in HHD pathogenesis, summarizing current OSA treatment options. It is hoped that this review will encourage a renewed clinical focus on HHD and underscore the need for further OSA research, particularly in the context of screening and treating HHD patients.

Partial tip air injection to extend the stall margin in an axial flow compressor with circumferential inlet distortion

As a typical non-axisymmetric inflow, circumferential pressure inlet distortion was experimentally investigated in an axial flow compressor. Based on the obvious decreasing trend of stall margin with the enhancement of distorted intensity, the stall mechanism under the condition of maximum distorted intensity, namely, 24.57 %, was studied in detailed. The casing static pressure over the rotor blade tip along the chord and circumferential direction were measured using a collection of dynamic transducers. Results show that under the circumferential inlet distortion condition, the pressure disturbance is always generated downstream from the distorted region along the rotational direction, and circumferentially propagates until it disappears in the upstream of the distorted region. With the continuous throttling, if the pressure disturbance that has not completely disappeared in the undistorted region enters the distorted region again, its energy will be enhanced, finally induces the stall. Using the above understanding as a foundation to apply partial tip air injection to suppress the disturbance caused by the circumferential inlet distortion, and resist its adverse effect on stall margin to ensure the safe operation of the compressor. It demonstrated that the tip air injection applied in the downstream of the distorted region can obtained the largest stall margin on the premise of the same injected momentum. For the strongest distortion case (DC (60) equals to 24.57 %), the injectors fixed downstream the distorted region can reduce the number and scale of the spike disturbances, suppress the local tip leakage vortex, and decrease the amplitude of the pressure disturbance energy, thus a maximum stall margin improvement of 3.18 % is obtained. However, tip air injection in the undistorted region cannot contribute the stall margin improvement that it leads to stronger tip leakage vortex and earlier stall inception. This study provides a guideline to design the non-axisymmetric tip air injection for circumferential inlet distortion with a help of injected mass flow and energy reduction.

Influence of pressure disturbance wave on dynamic response characteristics of liquid film seal for multiphase pump

Slug flow or high GVF (Gas Volume Fraction) conditions can cause pressure disturbance waves and alternating loads at the boundary of mechanical seals for multiphase pumps, endangering the safety of multiphase pump units. The mechanical seal model is simplified by using periodic boundary conditions and numerical calculations are carried out based on the Zwart-Gerber-Belamri cavitation model. UDF (User Define Function) programs such as structural dynamics equations, alternating load equations, and pressure disturbance equations are embedded in numerical calculations, and the dynamic response characteristics of mechanical seal are studied using layered dynamic mesh technology. The results show that when the pressure disturbance occurs at the inlet, as the amplitude and period of the disturbance increase, the film thickness gradually decreases. And the fundamental reason for the hysteresis of the film thickness change is that the pressure in the high-pressure area cannot be restored in a timely manner. The maximum value of leakage and the minimum value of axial velocity are independent of the disturbance period and determined by the disturbance amplitude. The mutual interference between enhanced waves does not have a significant impact on the film thickness, while the front wave in the attenuated wave has a promoting effect on the subsequent film thickness changes, and the fluctuation of the liquid film cavitation rate and axial velocity under the attenuated wave condition deviates from the initial values. Compared with pressure disturbance conditions, alternating load conditions have a more significant impact on film thickness and leakage. During actual operation, it is necessary to avoid alternating load conditions in multiphase pump mechanical seals.

Numerical Analysis of Unsteady Characteristics of the Second Throat of a Transonic Wind Tunnel

The unsteady characteristics of the second throat of a transonic wind tunnel have an important influence on the design and test of the wind tunnel. Therefore, the forced oscillation characteristics were studied by a numerical simulation method. The governing equation was the viscous compressible unsteady Navier–Stokes equation. Under the sinusoidal pressure disturbance of the computational domain exit, the shock wave presents a clear forced oscillation state, and the shock wave periodically changes its position. Under a pressure disturbance of 1%, the shock wave displacement reaches 150 mm. Additionally, overshoot occurs when the shock moves upstream or downstream. The shock-boundary layer interference is very sensitive to the motion characteristics of the shock wave, resulting in a transformation of the flow field symmetry. The flow field downstream of the shock wave exhibits periodic structural changes. Compared with the pressure change at the outlet, the pressure change near the shock wave has a phase delay. The increasing disturbance near the shock wave shows a clear amplification effect. The pressure disturbance near the shock wave had an obvious amplification effect, and its fluctuation amount reached 16% under the pressure disturbance of 1%. The variation trend of the second throat wall force, wavefront Mach number, and Mach number in the test section with time is similar to that of the downstream disturbance, but it does not have a complete follow-up effect, which indicates that the pressure disturbance can propagate into the test section through the boundary layer or the shock gap. Nevertheless, the second throat choking can still control the Mach number stability of the test section. The dynamic characteristics of shock oscillation are related to the amplitude and frequency of the applied pressure disturbance. The shock displacement decreases with the increase in the excitation frequency. When the excitation frequency is higher than 125 Hz, the flow field basically does not change.

Spatiotemporal flow evolution in a rocket-based combined-cycle inlet during ejector-to-ramjet mode transition

The spatiotemporal distribution characteristics and flow stability of a rocket-based combined-cycle (RBCC) inlet during the ejector-to-ramjet mode transition are investigated numerically. The operational pressure of the embedded rocket is adjusted to three different levels, and the time-sequences of the rocket and back pressure regulation are varied. The pressure in feature sections is monitored to reveal the coupling relationship and stability of the internal flowfield. The inlet is more adaptable to severe disturbances under the “throttle-maintaining” regulation and is susceptible under the “direct-shutdown” regulation. The severe fluctuation period is relatively short within “medium throttle-maintaining,” while is lengthy within the “high throttle-maintaining.” The severe fluctuation under the direct-shutdown develops with the propagation of the regulation and decays with its establishment. The ultimate flowfields driven by different time-sequences reach unanimity with the same adjustable parameters of embedded rocket and back pressure; however, the dynamic evolutions show distinct characteristics. During the mode transition, pressure “valleys” are formed in any selected sections with the rocket regulations, and “peaks” are developed in many sections due to the propagation of back pressure or the instability of the rocket jet. For the medium throttle-maintaining regulation, the effect of time-sequence on the flowfield is relatively weak. For the high throttle-maintaining regulation, the pressure disturbance rises abruptly under the rocket priority regulation, with a most severe amplitude of 100.7%. For the direct-shutdown regulation, the maximum pressure disturbance of 125% is observed within the rocket priority regulation, and the minimum disturbance occurs within the back pressure priority regulation.

Scattering of moving atmospheric pressure induced tsunamis by bathymetry and coastline

Tsunamis can be generated by a moving atmospheric pressure disturbance. The 2022 Tonga volcanic eruption and tsunami demonstrated the global relevance of such a tsunami generation mechanism. The generated locked and free waves are often scattered by bathymetric variations and coastlines, generating more free waves and resulting in a complex wave field. The physical processes involved can be described by the forced linear shallow water equations. Analytical solutions are sought after for simplified bathymetric variations and coastline configurations. In this paper, a moving atmospheric pressure front, which is uniform in the direction normal to its propagation direction, is considered. The water wave motion is assumed to start from the quiescent condition, so that the incident locked and free waves are related. However, since the wave scattering processes are linear, the solutions obtained in this paper can be used for analyzing scattering of the incident locked and free waves with uncorrelated amplitudes. For one-dimensional horizontal (1DH) problems, the water depth is either a constant or has a sudden change (i.e., a step) with or without a vertically walled coastline and the atmospheric pressure front always moves in the direction normal to the depth contours. In the case where a coastline is considered, the atmospheric pressure front can either move from the land to the sea or from the sea to the land. In the 2DH (two-dimensional horizontal) example, the wave field generated by a moving atmospheric pressure front, sweeping over the a circular island surrounded by a circular shelf, is investigated and discussed. For all the cases considered, analytical solutions in the integral form are obtained using the Fourier transform method. For the 1DH cases, analytical solutions are also presented in the form of infinite series, summing over infinite number of scattered and reflected waves from the bathymetric variations and coastlines. The new solutions reveal both the complexity of the wave scattering process and the significant differences between locked and free waves.

Numerical investigation of the self-induced unsteadiness phenomenon in the impeller of a high-loading centrifugal compressor

Unsteady flow phenomena are common in turbomachinery and have serious impacts on its stable operation. This paper reports a self-induced unsteady phenomenon inside a centrifugal impeller due to strong secondary flow that has not been previously reported. A high-loading centrifugal impeller is selected as the research object, an accurate three-dimensional model is established, and exhaustive numerical simulations are performed based on unsteady compressible Navier–Stokes equations. The unsteady performance of the compressor is measured in detail during the experiment, and the experimental results are compared with the numerical simulation results to verify the reliability of the numerical simulation method. The results of the unsteady pressure signal show the existence of unsteady phenomenon when the operating point is far away from the choke boundary. The power spectrum results of the unsteady pressure distribution at the impeller blade tip are analyzed, and two different modes of this unsteady phenomenon are confirmed. Higher-order frequency characteristics are not observed near the stall boundary. The detailed analysis of the flow field inside the impeller clarifies that the instability of the interface formed between the secondary flow and the main flow induces this unsteady phenomenon. This unsteady pressure disturbance propagates inside the blade passage through pressure waves, which contributes to the instability of the interface and the existence of this self-induced unsteady phenomenon.

Cavitating Venturi as a Mass Flow Controller in a Deep Throttling Liquid Rocket Engine

Abstract The most common solutions for rocket engines are the single operation point (thrust level) units. Oxidiser and fuel mass flow rates and the oxidiser-to-fuel mass flow rate ratio (OFR) are some of the determinants of the thrust level. Based on these, planetary ascent and descent; space rendezvous; orbital manoeuvring, including orientation and stabilisation in space; hovering, hazard avoidance during planetary landing; and ballistic missile trajectory control propulsion systems could use throttleable liquid engines. Several engine throttling methods, such as supply pressure variation and variable injector area, can be applied. Among others, a cavitating venturi propellant regulatory valve is one of the most promising throttling method. This type of valve can provide steady mass flow, despite the downstream pressure disturbance (i.e. from the combustion chamber), which sustains a stable engine thrust as the mass flow is kept. The article presents the valve sizing method, design and prototype test results of the cavitating venturi valve that has potential for utilisation in a deep throttling rocket engine. Mass flow stability and repeatability are presented for valve operating points in the 10%–110% nominal mass flow range. Valve design optimisation, based on CFD, to sustain cavitation for a higher downstream-to-upstream pressure ratio is shown.

Impact of continuous-flow mechanical circulatory support on cerebrospinal fluid motility.

Mechanical circulatory support (MCS), including ventricular assist devices (VADs), have emerged as promising therapeutic alternatives for end-stage congestive heart failure (CHF). The latest generation of these devices are continuous flow (CF) blood pumps. While there have been demonstrated benefits to patient outcomes due to CF-MCS, there continue to be significant clinical challenges. Research to-date has concentrated on mitigating thromboembolic risk (stroke), while the downstream impact of CF-MCS on the cerebrospinal fluid (CSF) flow has not been well investigated. Disturbances in the CSF pressure and flow patterns are known to be associated with neurologic impairment and diseased states. Thus, here we seek to develop an understanding of the pathophysiologic consequences of CF-MCS on CSF dynamics. We built and validated a computational framework using lumped parameter modeling of cardiovascular, cerebrovascular physics, CSF dynamics, and autoregulation. A sensitivity analysis was performed to confirm robustness of the modeling framework. Then, we characterized the impact of CF-MCS on the CSF and investigated cardiovascular conditions of healthy and end-stage heart failure. Modeling results demonstrated appropriate hemodynamics and indicated that CSF pressure depends on blood flow pulsatility more than CSF flow. An acute equilibrium between CSF production and absorption was observed in the CF-MCS case, characterized by CSF pressure remaining elevated, and CSF flow rates remaining below healthy, but higher than CHF states. This research has advanced our understanding of the impact of CF-MCS on CSF dynamics and cerebral hemodynamics.

CROSS FLOW IN THE WELL

The article considers the problem of pressure fields in a system consisting of two perforated reservoirs penetrated by one well, providing a hydrodynamic connection between them. One-dimensional equations of piezoconductivity in radial geometry are used to describe the pressure fields in the reservoirs. The hydrodynamic connection between the layers through the well is given by an integro-differential equation obtained on the basis of mass balance and Darcy's law.It is assumed that there are no pressure disturbances at the initial moment of time and in the parts of the reservoirs remote from the well. At the boundaries between the well and the reservoirs for the time t>0, the conditions for equal pressures are set. Exact analytical solutions describing pressure fields in reservoirs and wells are constructed in the Laplace–Carson image space. Computational experiments for modeling pressure fields and flows were carried out using the Stehfestand den Iseger algorithms, which made it possible to eliminate the time-consuming procedure of transition to the original space. The joint use of these algorithms made it possible to increase the reliability and accuracy of the results of field calculations, since direct control based on analytical formulas in the originals is difficult.
 The purpose of computational experiments is to determine the conditions for the existence of interlayer cross flows and their temporal dynamics in the absence of production from the well. Calculations are made for the case when reservoir characteristics of reservoirs are the same. For definiteness, it is assumed that the reservoir, which occurs at a shallower depth, is high-pressure. It is shown that in the absence of production from the well, after some time, an equilibrium pressure that changes slightly with time is established in the wellbore, equal to the average hydrostatic pressure of the lower and upper reservoirs. At the same time, in the region of short times, the flow rate of each reservoir depends on the value of the initial hydrostatic pressure in the well, and in the region of long times, this pressure does not affect the dynamics of interlayer flows. It has been established that the total flow rate of reservoirs is equal to zero only for times longer than the relaxation time. It is noted that the pressure relaxation time in the well increases with a decrease in reservoir permeability.

Static and dynamic stability of pendant drops

Despite the widespread occurrence of pendant drops in nature, there is still a lack of combined studies on their dynamic and static stability. This study focuses on the dynamic and static stability of elongated drops with either a free or pinned contact line on a plane. We first examine static stability for both axisymmetric and non-axisymmetric perturbations subject to volume or pressure constraints. The stability limits for volume and pressure disturbances (axisymmetric) correspond to the maximum volume and pressure of the drops, respectively. Drops with free contact lines are marginally stable to non-axisymmetric perturbations because of their horizontal translational invariance, whereas pinned drops are stable. The linear dynamic stability is then investigated numerically through a boundary element model, restricted to volume disturbances. Results show that when the stability limit is reached, the first zonal mode has a zero frequency, suggesting that the thresholds for static and dynamic stability are essentially equivalent. Furthermore, natural frequencies experience sharp changes as the stability limit is approached. Another zero frequency mode associated with the horizontal motion of the centre of mass is also revealed by the numerical results, reflecting the horizontal translational invariance of drops with free contact lines. Finally, the frequency spectrum modified by gravity is explored, resulting in the identification of five gravity-induced frequency shift patterns. The frequency shifts break the spectral degeneracy for hemispherical drops with free contact lines, leading to various spectral orderings according to polar and azimuthal wavenumbers.

Assessment of Endothelial Cell Count Changes Post-Yttrium Aluminium Garnet Laser for Posterior Capsular Opacification

Objective: The study aimed to assess the effect of Neodymium : Yttrium Aluminium Garnet laser (ND:YAG laser) on endothelial cell count loss and anterior segment elements. Study Design: Quasi-experimental. Place and Duration Of Study: Armed Forces Institute of Ophthalmology, Rawalpindi from Jul 2021 to Feb 2022. Methodology: A total of 60 patients with a history of posterior capsular opacities planned for Neodymium: Yttrium Aluminium Garnet laser posterior capsulotomy were included. Specular microscopy was done pre and post-laser to study and parameters such as central corneal thickness, endothelial cell count, intra-ocular pressure was noted. Data were analyzed by using the Statistical Package for the Social Sciences version 23 software Result: After four weeks of Neodymium : Yttrium Aluminium Garnet laser, there was no significant change in the intraocular pressure (p=0.334), however, the visual acuity improved from 0.6±0.3-0.05±0.1 (p<0.001) along with a decrease in endothelial cell count 2101±485-1919±427 (p<0.001) and central corneal thickness 0.504±0.03-0.502± 0.03 (p=0.010). A similar trend of changes in the parameters was observed for lower (1.0-1.2MJ) and higher energy (2.1-2.5MJ) in the sample for posterior capsulotomy. Conclusion: Our study concluded that the corneal structural changes occur post-Neodymium: Yttrium Aluminium Garnet posterior capsulotomy, including changes in endothelial cell count. However, there is no significant disturbance in the intraocular pressure after the procedure.

Stable Gastric Pentadecapeptide BPC 157-Possible Novel Therapy of Glaucoma and Other Ocular Conditions.

Recently, stable gastric pentadecapeptide BPC 157 therapy by activation of collateral pathways counteracted various occlusion/occlusion-like syndromes, vascular, and multiorgan failure, and blood pressure disturbances in rats with permanent major vessel occlusion and similar procedures disabling endothelium function. Thereby, we revealed BPC 157 cytoprotective therapy with strong vascular rescuing capabilities in glaucoma therapy. With these capabilities, BPC 157 therapy can recover glaucomatous rats, normalize intraocular pressure, maintain retinal integrity, recover pupil function, recover retinal ischemia, and corneal injuries (i.e., maintained transparency after complete corneal abrasion, corneal ulceration, and counteracted dry eye after lacrimal gland removal or corneal insensitivity). The most important point is that in glaucomatous rats (three of four episcleral veins cauterized) with high intraocular pressure, all BPC 157 regimens immediately normalized intraocular pressure. BPC 157-treated rats exhibited normal pupil diameter, microscopically well-preserved ganglion cells and optic nerve presentation, normal fundus presentation, nor- mal retinal and choroidal blood vessel presentation, and normal optic nerve presentation. The one episcleral vein rapidly upgraded to accomplish all functions in glaucomatous rats may correspond with occlusion/occlusion-like syndromes of the activated rescuing collateral pathway (azygos vein direct blood flow delivery). Normalized intraocular pressure in glaucomatous rats corresponded to the counteracted intra-cranial (superior sagittal sinus), portal, and caval hypertension, and aortal hypotension in occlusion/occlusion-like syndromes, were all attenuated/eliminated by BPC 157 therapy. Furthermore, given in other eye disturbances (i.e., retinal ischemia), BPC 157 instantly breaks a noxious chain of events, both at an early stage and an already advanced stage. Thus, we further advocate BPC 157 as a therapeutic agent in ocular disease.

Experimental investigation on weak shock wave mitigation characteristics of flexible polyurethane foam and polyurea

In recent years, explosion shock wave has been considered as a signature injury of the current military conflicts. Although strong shock wave is lethal to the human body, weak shock wave can cause many more lasting consequences. To investigate the protection ability and characteristics of flexible materials and structures under weak shock wave loading, the blast wave produced by TNT explosive is loaded on the polyurethane foam with the density of 200.0 kg/m3 (F-200) and 400.0 kg/m3 (F-400), polyurea with the density of 1100.0 kg/m3 (P-1100) and structures composed of the two materials, which are intended for individual protection. Experimental results indicate that the shock wave is attenuated to weak pressure disturbance after interacting with the flexible materials which are not damaged. The shock wave protective capability of single-layer materials is dependent on their thickness, density and microscopic characteristics. The overpressure, maximum pressure rise rate and impulse of transmitted wave decrease exponentially with increase in sample thickness. For the same thickness, F-400 provides better protective capability than F-200 while P-1100 shows the best protective capability among the three materials. In this study, as the materials are not destroyed, F-200 with a thickness more than 10.0 mm, F-400 with a thickness more than 4.0 mm, and P-1100 with a thickness more than 1.0 mm can attenuate the overpressure amplitude more than 90.0%. Further, multi-layer flexible composites are designed. Different layer layouts of designed structures and layer thickness of the single-layer materials can affect the protective performance. Within the research range, the structure in which polyurea is placed on the impact side shows the optimal shock wave protective performance, and the thicknesses of polyurea and polyurethane foam are 1.0 mm and 4.0 mm respectively. The overpressure attenuation rate reached maximum value of 93.3% and impulse attenuation capacity of this structure are better than those of single-layer polyurea and polyurethane foam with higher areal density.

Transonic buffet alleviation via virtual control surfaces

In this work, computational fluid dynamics simulations are carried out to assess the ability of control surfaces to alleviate or suppress transonic buffet. Among the available control surfaces, upper trailing edge flaps were considered since they modify the aerofoil pressure distribution and fix the shock at an upstream position. Spoilers were also studied as they produce a similar effect by interfering with the pressure disturbance propagation in the boundary layer and prevent buffet. For both devices, the sensitivities to geometric parameters are studied. The effectiveness of these buffet control methods is first assessed for 2D computations around different wing sections. As spoilers were considered more effective, results on a 3D configuration are provided to discuss the influence of finite-span devices on aerodynamic performance. In addition, a simple model accounting for changes in the flight Mach number together with the spoiler is presented to simulate a simple flight scenario and provide an effective strategy for buffet suppression. In the framework of numerical investigations, the adoption of virtual control surfaces allows for avoiding difficulties associated with the modelling of slotted and deployable devices.

Dynamic Response Analysis of the Bi-Tandem Axial Piston Pump with Dual-Loop Positive Flow Control under Pressure Disturbance

The bi-tandem axial piston pump is an indispensable powerhouse in high-pressure and high-power engineering hydraulic systems, with its output flow response characteristics under pressure disturbance exerting a significant influence on the working process of double pumps. Unfortunately, the stability of the original single-loop mechanical–hydraulic servo control system is sensitive to unpredictable interference. To alleviate this quandary, this paper proposes a dual-loop positive flow control method for the flow control of the bi-tandem axial piston pump, establishes a mathematical model of the bi-tandem axial piston pump with dual-loop positive flow control, and establishes a simulation model based on Simulink. The validity of the model is verified by experiments. The performance advantages of the dual-loop positive flow control method relative to the single-loop positive flow control method are analyzed. The results show a faster response speed and smaller steady-state error with the dual-loop method, which performs better than the original single-loop positive flow control. Furthermore, the study examines the influence of different forms, degrees, and directions of pressure disturbance on the dynamic response characteristics of the bi-tandem axial piston pump. Symmetric pressure disturbance results in an increase in the maximum relative error of the output flow proportional to its degree. Notably, the influence of asymmetric pressure disturbance on the output flow of the double pumps possesses characteristics of a superimposable nature, and the steady-state value of the output flow is highly dependent on superimposed pressure disturbance and less affected by the action time point of asymmetric pressure disturbance. Further, the unloading pressure disturbance exerts less influence on the system compared to the loading pressure disturbance. This paper provides valuable insights into improving the response speed and control accuracy of bi-tandem axial piston pumps equipped with positive flow control.

Combined Experimental and Numerical Investigation of a Hypersonic Turbulent Boundary Layer by Means of FLDI and Large-Eddy Simulations

This work investigates a hypersonic turbulent boundary layer over a 7° half angle cone at a wall-to-total temperature ratio of 0.1, M∞=7.4 and Re∞m=4.2×106 m−1, in terms of density fluctuations and the convection velocity of density disturbances. Experimental shock tunnel data are collected using a multi-foci Focused Laser Differential Interferometer (FLDI) to probe the boundary layer at several heights. In addition, a high-fidelity, time-resolved Large-Eddy Simulation (LES) of the conical flowfield under the experimentally observed free stream conditions is conducted. The experimentally measured convection velocity of density disturbances is found to follow literature data of pressure disturbances. The spectral distributions evidence the presence of regions with well-defined power laws that are present in pressure spectra. A framework to combine numerical and experimental observations without requiring complex FLDI post-processing strategies is explored using a computational FLDI (cFLDI) on the numerical solution for direct comparisons. Frequency bounds of 160 kHz <f<1 MHz are evaluated in consideration of the constraining conditions of both experimental and numerical data. Within these limits, the direct comparisons yield good agreement. Furthermore, it is verified that in the present case, the cFLDI algorithm may be replaced with a simple line integral on the numerical solution.

Evaluation of Control Effect of Confined Water Hazard in Taiyuan Formation Coal Seam Mining in Huanghebei Coalfield

The shallow-layer resources in the Huanghebei Coalfield have been depleted, and the deep coal seam of the Taiyuan Formation (lower coal group) is the main continuous resource in mining at this stage. With the annual increase in mining depth, the exploitation of lower coal groups is being met with the influence of high ground stress, high water pressure, high temperature, and strong mining disturbances, as a result of which the threat of water inrush is particularly serious. Based on the grouting data of the coalface floor aquifer, this paper proposes an evaluation method for the control of water rushing into the coalface floor. By comparing the test data with mine electrical exploration data through ArcGIS, the results show that the water pressure threshold based on ArcGIS is twice the water pressure of the grouting reconstruction layer as the optimal solution. The research results can provide a reference for the prevention and control of water inrush in the lower coal group of Huanghebei Coalfield.

A flexible pressure sensor with interference immunity capability

PurposeFlexible pressure sensor arrays have promising applications in analog haptics, reconfiguration of sensory functions, artificial intelligence, wearable devices and human-computer interaction. The force disturbance generated by the connecting material between the sensor array units will reduce the detection accuracy of the unit. The purpose of this paper is to propose a flexible pressure sensor with interference immunity capability. A C-type bridge flexible piezoelectric structure is used to improve the pressure perturbation. The interference immunity capability of the sensor has been improved.Design/methodology/approachIn this paper, a C-type pressure sensor array structure by rapid injection moulding is manufactured through the positive piezoelectric effect of a piezoelectric material. The feasibility of C-type interference immunity structure in a flexible sensor array is verified by further analysis and experiment. A flexible pressure sensor array with C-type interference immunity structure has been proposed.FindingsIn this paper, we present the results of the perturbation experiment results of the C-type pressure sensor array, showing that the perturbation error is less than 8%. The test of the flexible sensor array show that the sensor can identify the curved angle of up to 120 °, and the output sensitivity of the sensor in the horizontal state reaches 0.12 V/N, and the sensor can withstand the pressure of 80 N. The flexible sensor can work stably in the stretch rate range of 0–8.6% and the stretch length range of 0–6 mm.Originality/valueIn this paper, C-type pressure sensor array structure is fabricated by rapid injection moulding for the first time. The research in this paper can effectively reduce the disturbance of input pressure on the sensor’s internal array and improve the output accuracy. The sensor can intuitively reflect the number of fingers sliding on the sensor by the order in which the maximum voltage appears. Due to the strong interference immunity capability and flexibility of the flexible sensor array mechanism, it has a broad application prospect in the practical fields of haptic simulation, perceptual function reconstruction, artificial intelligence, wearable devices and human–computer interaction.