Variation Of External Pressure Research Articles

Fabrication of Highly Sensitive Porous Polydimethylsiloxane Pressure Sensor Through Control of Rheological Properties.

In order to enhance the sensitivity of elastomers, pores were integrated into their structure. These pores facilitate the adjustment of thickness in response to external pressure variations, thereby improving the sensitivity of pressure sensors. Pores were introduced by emulsifying immiscible polydimethylsiloxane (PDMS) and water with a surfactant. By controlling the water content in the PDMS and water emulsion, we controlled the size, density, uniformity, and spatial distribution (2D or 3D) of the pores within the PDMS matrix. The presence of these pores significantly improved the sensitivity of PDMS under low external pressure conditions compared to high pressures. Specifically, porous PDMS exhibited approximately 10-times greater sensitivity under low-pressure conditions than non-porous PDMS. The effectiveness of porous PDMS was demonstrated through dynamic loading and unloading detection of a small Lego toy and monitoring of human heartbeats. These results highlight the efficacy of our pressure sensor based on porous PDMS, which is fabricated through a simple and cost-effective process using a PDMS and water emulsion. This approach is highly suitable for developing the ability to detect applied pressures or contact forces.

Dynamic characteristics and prediction and control models of subsonic exhaust from a container

This study combines experimental measurements, numerical simulations, and theoretical analysis to investigate the subsonic discharge process in a container under normal temperature and pressure conditions. Experimental data captured the internal pressure dynamics during exhaust at the atmospheric environmental pressure. Numerical simulations using OpenFOAM validated the isothermal exhaust model against the experimental results. Under the assumption of ideal gas and isothermal processes, a nonlinear differential equation was derived to describe the evolution of the container's internal pressure. This equation was simplified for a specific range of pressure ratios, yielding analytical solutions for the internal pressure of the container under both constant and variable external pressures. The effectiveness of the expressions of pressure inside the container was verified by comparing them with experimental and numerical simulation data. We further developed a formula for predicting exhaust mass flow rate, with a prediction error within 9%. An improved formula was subsequently proposed to reduce the error to below 0.4%, enhancing prediction accuracy. For containers with variable external pressure, a method for controlling the exhaust mass flow rate by predicting external pressure changes was proposed, demonstrating its effectiveness in achieving precise control.

Hydrohelical ESP Gas Separator Increases Flow Range, Improves Reliability

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 214723, “New High-Performance ESP Gas Separator,” by Barry Nicholson, SPE, and Scott R. Harryman, SPE, Oxy, and Donn J. Brown, SPE, Halliburton, et al. The paper has not been peer reviewed. _ The complete paper presents research, design, and field testing of a new type of mechanical gas separator for electrical submersible pump (ESP) systems that increases operating flow range and separation efficiency while decreasing erosion problems and improving reliability. The hydrohelical separator system has been proved effective in different types of wells. Background Several methods and techniques exist for avoiding gas in ESPs, including inverted shrouds, passive separators, mechanical gas separators, and tandem gas separators. Most share the limitations of limited flow capabilities and reduced performance at higher total flow rates. The many variables associated with complex two-phase flow behavior, internal and external pressure variations, separation methods, velocity and viscosity of fluids, effect of the pump bolted above, inherent erosion issues, and single vs. tandem designs add to the challenge of basic mechanical gas-separator operation. In 2016, a program was initiated that featured investment in both experienced personnel and advanced testing technology to unravel the aforementioned challenges and improve understanding of the operation of downhole mechanical gas separation. The team investigated innovative methods of testing and created a transparent testing system that allowed visual observation of individual internal flow regimes as well as component performance. Using a combination of high-speed photography, computational fluid dynamics validation, and specialized instrumentation, every component of a mechanical separator system was enhanced for higher flow capabilities, improved separation efficiency, and higher reliability for a variety of downhole conditions. The result was the development of a new type of mechanical gas separator for ESP use. Development Most gas separators ingest multiphase fluid into a separation chamber, separate the gas and liquid phases, eject the separated gas phase into the well annulus, and provide sufficient liquid phase fluid to the pump to enable efficient pumping. Existing designs vary, but they share separation methods that result in decreased efficiency at higher flow rates and low maximum flow rates compared with the pumps they feed. The hydrohelical gas separator is the first downhole, dynamic gas-separator design improvement in more than 30 years designed to address these deficiencies (Fig. 1). The design was aimed at the following main objectives: - Increase total fluid flow rate through the separator - Maximize efficiency of every internal and external component of the system - Reduce erosion characteristics common in traditional gas-separator designs - Improve reliability The design of the hydrohelical gas separator is based on a stationary helical vortex inducer and pump stages that enable movement of large quantities of fluid while remaining immune to gas locking. The stationary helical vortex inducer design enables increased efficiency and flow rate through the separator by reducing turbulence in remixing regions within the helical inducer and separation chamber.

Slip Backflow of Polymers in Elastic Fractures for Subsurface Heat Recovery

This research delves into the complexities of backflow phenomena in finite-length and flat-walled fractures with elastic walls, specifically focusing on power-law fluids, whose shear-thinning behavior distinguishes them from Newtonian fluids. We model the backflow process under the lubrication approximation and by incorporating the linear Navier slip law. We numerically examine the influence of parameters such as slip length, fluid rheology, and external pressure on the backflow propagation of the carrier fluid. Our findings underscore the significant role played by the rheological index in determining the fracture closure rate. Additionally, our investigations highlight the marked effect of external pressure variations on pressure distribution within the fracture. Notably, the friction coefficient at the fracture walls, as denoted by a dimensionless slip number, exhibits limited influence on the fundamental dynamics of the problem. These insights advance our understanding of power-law fluid backflow and have wide-ranging applications across various engineering disciplines.

Torsion of Rods Made of Hardening Material Subjected to the Influence of Variable External Pressure under a Linearized Plastic Flow Rule

Torsion of Rods Made of Hardening Material Subjected to the Influence of Variable External Pressure under a Linearized Plastic Flow Rule

Torsion of Rods Made of Hardening Material Subjected to the Influence of Variable External Pressure under a Linearized Plastic Flow Rule

The article deals with the torsion of rods made of an anisotropically hardening rigid-plastic material under the linearized plastic flow rule. It is assumed that the rod is subject to external pressure, which varies linearly along the generatrix. The components of the stress and strain tensors that describe the limiting state of the rod are determined.

Financial Statement Fraud, Audit Committee and Audit Quality: Insight into Fraud Diamond Theory

Based on the Fraud diamond theory, the study investigates whether the audit and quality committee can strengthen or weaken financial statement fraud. this study aims to prove the influence of diamond fraud on the potential for financial statement fraud and that the audit and quality committee can strengthen or weaken the effect of diamond fraud on the potential for financial statement fraud. This study sample was selected using the purposive sampling method and obtained 850 observations from 214 companies’ sector non-financial listed on Indonesia Stock Exchange from 2016-2019. Furthermore, this study uses secondary data obtained from www.idx.co.id and each company's website. Data analysis in this study using logistic regression. The result of this study indicates that variable financial stability, board change, and financial target positively affect the detection of fraudulent financial statements. In contrast, variable external pressure, ineffective monitoring, and auditor change do not affect the detection of fraudulent financial statements. As the first variable moderating in this study, the audit committee does not affect weakening the relationship between fraud diamonds and fraudulent financial statements. On the other hand, audit quality, as the second moderating variable in this study, weakens the relationship between external pressure and ineffective monitoring of fraudulent financial statements. But, audit quality does not weaken the relationship between financial stability, financial target, audit change, and board change on the fraudulent financial statement.

FRAUD DIAMOND DAN KECURANGAN PELAPORAN KEUANGAN PADA SAAT SEBELUM DAN SAAT COVID-19 DENGAN GOOD CORPORATE GOVERNANCE SEBAGAI VARIABEL MODERATING

The phenomenon that is currently happening is covid-19, in this research the researcher wanted to know before and during covid-19 whether there was fraud in financial reporting by using fraud diamonds to detect the fraud. The sample used is a manufacturing company with a period of 2018 - 2020.This study uses the independent variable external pressure for DAR proxy, financial target for ROA proxy, nature of industry for Inventory proxy, change in auditor and change in director. Good corporate governance is also used in this study as a moderating variable. The data processing used by the researcher is SPSS version 20.0. The results of this study indicate that the independent variable external pressure has an influence on fraudulent financial reporting either before or during covid-19 and also when using moderating variables.

A triangular wavy substrate-integrated wearable and flexible piezoelectric sensor for a linear pressure measurement and application in human health monitoring

In this article, we present a triangular-wavy-substrate pressure sensor (TWSPS) consisting a microstructural substrate, a polyvinylidene fluoride (PVDF) film, an elastic layer, and a flexible measuring circuit for real-time monitoring of external pressure variation. A force-electric coupling model is computed to clarify the physical mechanism of strain and response charge amplification with four types of substrate structures in the proposed sensor system. The simulation results show that the response charge initially increases, and then decreases when the contact angle (α) increases. The maximum value of the response charge is about 1.21e−10C at α of 54°. Moreover, the experimental results show that the TWSPS can measure low pressures within 500 Pa with linear response and high sensitivity (19 mV/kPa). More importantly, the design strategy of substrate stain amplification introduced in this work can be fitted with any piezoelectric or piezoresistive material to form a high-performance pressure sensor.

Estimation of Wind Load on Stepped Tall Building Using CFD Simulation

The behavior of wind around stepped tall building is quite different comparing with the symmetric plan shape tall building. Setback roof of stepped buildings is widely responsible for the turbulence around the building. The purpose of this work is to understand the behavior of wind load on stepped tall building model. Four different models having the same dimensions and same aspect ratios but different setback distances, namely Models A, B, C and D, are considered. The setback distances are 0.2L, 0.3L, 0.4L and 0.5L (L = length) and are located at H/2 level (H = height) from the base of domain. Computational fluid dynamics simulations are taken out of terrain category 2 with the model scale 1:300. The foreground of this study is the external pressure and force variation around the building face and roof at 0° and 90° wind incidence angles. Maximum positive pressure coefficient develops at 90% of building height from the base of all models and for setback case it goes to 80%. Negative pressure develops at the building roof top, whereas positive pressure develops in the setback roof for the same model and wind angle. This type of pressure variable will be considered in roof design of stepped building.

Guest Removal and External Pressure Variation Induce Spin Crossover in Halogen-Functionalized 2-D Hofmann Frameworks.

The effect of halogen functionalization on the spin crossover (SCO) properties of a family of 2-D Hofmann framework materials, [FeIIPd(CN)4(thioX)2]·2H2O (X = Cl and Br; thioCl = (E)-1-(5-chlorothiophen-2-yl)-N-(4H-1,2,4-triazol-4-yl)methanimine) and thioBr = (E)-1-(5-bromothiophen-2-yl)-N-(4H-1,2,4-triazol-4-yl)methanimine)), is reported. Inclusion of both the chloro- and bromo-functionalized ligands into the Hofmann-type frameworks (1Cl·2H2O and 2Br·2H2O) results in a blocking of spin-state transitions due to internal chemical pressure effects derived by the collective steric bulk of the halogen atoms and guest molecules. Cooperative one-step SCO transitions are revealed by either guest removal or the application of external physical pressure. Notably, removal of solvent water reveals a robust framework scaffold with only marginal variation between the solvated and desolvated structures (as investigated by powder and single crystal X-ray diffraction). Yet, one-step complete SCO transitions are revealed in 1Cl and 2Br with a transition temperature shift between the analogues due to various steric, structural, and electronic considerations. SCO can also be induced in the solvated species, 1Cl·2H2O and 2Br·2H2O, with the application of physical pressure, revealing a complete one-step SCO transition above 0.62 GPa (as investigated by magnetic susceptibility and single crystal X-ray diffraction measurements).

Production Engineering of Parts by Cold Stamping

In the scientific article presents the results of the finite element modeling of cold extrusion of carbon steel, the stress-strain state of massive dies at high cyclic stresses characteristic of the cold extrusion of steel are presented. The possibility of significant amplification of dies in their working area by creating a variable external pressure from the rims of a special design is shown. Dies banding with variable external pressure, proportional to the internal pressure in the die, is aimed at increasing the technical resource of the tool.

Modeling of Tool for Cold Extrusion of Steel and Tooling with Proportional Bandaging

In the article the results of the finite element modeling of cold extrusion of carbon steel, the stress-strain state of massive dies at high cyclic stresses characteristic of the cold extrusion of steel are presented. The possibility of significant amplification of dies in their working area by creating a variable external pressure from the rims of a special design is shown. Dies banding with variable external pressure, proportional to the internal pressure in the die, is aimed at increasing the technical resource of the tool.

High-sensitivity hydraulic pressure sensor based on Fabry-Perot interferometer filled with polydimethylsiloxane film.

A high-sensitivity hydraulic pressure sensor is proposed, which consists of a Fabry-Perot interferometer (FPI) filled with a polymer film of polydimethylsiloxane (PDMS). The FPI structure is fabricated by splicing a section of hollow core fiber (HCF) to the end-face of a lead-in single mode fiber (SMF). Then, the PDMS is filled into the HCF which acts as a light reflector and a diaphragm to detect external pressure variation. As a result, the length of the FPI cavity and the thickness of the PDMS are 137.8 µm and 33.8 µm, respectively. Experimental results indicate that the sensor's wavelength exhibits a linear response to the hydraulic pressure, which function is described as y = -7.35 × 10-3x + 1536.395. Here, x and y represent the hydraulic pressure and the wavelength, respectively. The pressure sensitivity is up to -7.35 nm/kPa. Besides, a temperature compensation method based on a fiber Bragg grating is proposed to eliminate the influence of temperature. Experiments show that the scheme can effectively eliminate the influence of temperature and achieve accurate measurement of hydraulic pressure.

Analysis of elastic velocities behavior and porosity in carbonates submitted to external pressure variation

Carbonate rocks usually present a complex porous system that exhibits different behavior of porosity and elastic velocities when submitted to external pressure variation. This work aims to study compressional- and shear-wave velocity variation and porosity in carbonate rock samples submitted to external pressure variation. By analyzing the data set, it is intended to characterize carbonate rocks samples porous system. Experimental tests were carried out at the Rock Physics Laboratory of UENF/LENEP on a set of carbonate rocks. Those tests consisted of measurements of petrophysical properties, mineral composition and optical microscopy images that aid to characterize the pore system of such rocks. The Differential Effective Medium (DEM) theory was used to estimate the microporosity aspect ratio supposing a dual porosity scenario,macro-meso pores captured by optical microscopy and micropores that are out of the resolution of the image analysis. The influence of pressure variation in the aspect ratio was also studied as well as its impact on the behavior of porosity and elastic velocities for different rock textures.

Unraveling the Environment Influence in Bistable Spin-Crossover Particles Using Magnetometric and Calorimetric First-Order Reverse Curves

A first-order reversal curve (FORC) method is used here to analyze the unexpected change of memory characteristic of spin-crossover microparticles embedded in glass-forming or semicrystalline matrices, reflected in the larger hysteresis loop compared to the bulk. The huge reversibility shown by the reversal curves was attributed to the effect of the matrix, implying a variable external pressure and a cutoff–switch on mechanism of particle–matrix interactions. The FORC analysis indicates that heating and cooling processes in the case of matrix-embedded spin-crossover systems are driven by different mechanisms. In complement of standard magnetometry measurements, a calorimetry method, which demands an alternative method to extract FORC distributions, is introduced for tracking the signature of the composite transformation to understand and control the role of embedding matrices.

Field test measurement of the dynamic tightness performance of high-speed trains and study on its influencing factors

During the actual operation of a high-speed train, the airtight performance of the carriages will change significantly. Based on a series of field tests, the external and interior pressure variations of train carriages are measured and then the dynamic pressure tightness coefficient are analysed quantitatively for investigating the airtight performance of a train passing at various speeds through tunnels of different lengths. It is found that the amplitude of the external pressure variations is proportional to the square of the train speed, while the amplitude inside the vehicle is approximately proportional to the speed to the 0.7th power due to the airtight effect. The dynamic pressure tightness coefficient increases with increasing tunnel length and decreases with increasing train speed. Regarding the effect of the carriage location, the coefficient shows an overall increasing trend from the train head to tail.

Structure and dynamic properties of stretched water in graphene nanochannels by molecular dynamics simulation: effects of stretching extent.

Water confined in nanochannels can be stretched with variation of the external pressure, leading to unusual properties compared with bulk water. In order to unravel the impacts of stretching extent on the structural and dynamic properties of water confined in hydrophobic graphene nanochannels with various channel widths (L = 1 nm, 2 nm and 3 nm), molecular dynamics (MD) simulations were performed in this work. It was found that an ultrahigh negative pressure was present in the confined space with the increase of stretching extent before cavitation. The interfacial density peak and tetrahedral arrangement were reduced with the increasing hydrogen bond length, indicating the more disordered structural organization, especially in channels with small channel widths. On the other hand, the hydrogen bond lifetime was increased due to the prolonged stability of the hydrogen bond under stretching. The remarkably increased diffusion coefficients of confined water with the increasing stretching coefficient result from the faster diffusion of interfacial water along the channel surface regardless of channel width. At last, the oscillating tangential pressure profile inside the nanochannels demonstrated that the confined water under stretching consists of multiple layers exhibiting alternate positive and negative pressures, which is reduced with the increase of stretching coefficient, corresponding to the enhanced diffusion.

Correction for stress-induced optical path length changes in a refractometer cell at variable external pressure

In the field of interferometry for high-precision length measurements the influence of the refractive index of air can either be eliminated by completely measuring in a vacuum or by the application of a refractometer cell which enables the precise in situ determination of the refractivity. In the latter case, systematic effects can occur in connection with the operation of the refractometer cell due to mechanical stress induced at different pressures. Operation at a pressure range beyond the usual atmospheric pressure variation is needed when, for instance, the compressibility of a material measure is investigated or the pressure dependence of the refractive index of gases is aimed at. In this work an approach is shown for the correction of pressure-induced effects for the type of interference refractometer being used at PTB when starting from a reference state in vacuum. The required correction of the refractivity’s value was found to be of the order of for a refractometer cell of 420 mm length which corresponds to a relative contribution of when determining the air refractivity at standard laboratory conditions. For instance, in the application of high-precision length measurements (up to 1000 mm) the effect amounts to a length correction of several nanometers.

A Review of Models for Bubble Clusters in Cavitating Flows

This paper reviews the various modeling strategies adopted in the literature to capture the response of bubble clusters to pressure changes. The first part is focused on the strategies adopted to model and simulate the response of individual bubbles to external pressure variations discussing the relevance of the various mechanisms triggered by the appearance and later collapse of bubbles. In the second part we review available models proposed for large scale bubbly flows used in different contexts including hydrodynamic cavitation, sound propagation, ultrasonic devices and shockwave induced cavitation processes. Finally we discuss the main challenges of cavitation models.