Showing papers on "Hydrostatic equilibrium published in 2023"

Anisotropic stars made of exotic matter within the complexity factor formalism

Abstract: Abstract Within Einstein’s General Relativity we study exotic stars made of dark energy assuming an extended Chaplygin gas equation-of-state. Taking into account the presence of anisotropies, we employ the formalism based on the complexity factor to solve the structure equations numerically, obtaining thus interior solutions describing hydrostatic equilibrium. Making use of well-established criteria we demonstrate that the solutions are well behaved and realistic. A comparison with another, more conventional approach, is made as well.

Anisotropic Quark Stars with an Interacting Quark Equation of State within the Complexity Factor Formalism

Abstract: Within the framework of Einstein’s General Relativity we study strange quark stars assuming an interacting equation-of-state. Taking into account the presence of anisotropies in a sphere made of ultra dense matter, we employ the formalism based on the complexity factor. We integrate the structure equations numerically imposing the appropriate conditions both at the center and at the surface of the stars, thus obtaining interior solutions describing hydrostatic equilibrium. Making use of well-established criteria, we demonstrate that the solutions obtained here are well behaved and realistic. A comparison with another, more conventional approach, is made as well. Our numerical results are summarized in a number of figures.

Mesoscale Convective Systems in DYAMOND Global Convection‐Permitting Simulations

Abstract: This study examines the deep convection populations and mesoscale convective systems (MCSs) simulated in the DYAMOND (DYnamics of the atmospheric general circulation modeled on non-hydrostatic domains) winter project. A storm tracking algorithm is applied to six DYAMOND simulations and a global high-resolution satellite cloud and precipitation data set for comparison. The simulated frequencies of tropical deep convection and organized convective systems vary widely among models and regions, although robust MCSs are generally underestimated. The diurnal cycles of MCS initiation and mature stages are well simulated, but the amplitudes are exaggerated over land. Most models capture the observed MCS lifetime, cloud shield area, rainfall volume and movement speed. However, cloud-top height and convective rainfall intensity are consistently overestimated, and stratiform rainfall area and amount are consistently underestimated. Possible causes for the model differences compared to observations and implications for future model developments are discussed.

Water Influence on the Determination of the Rock Matrix Bulk Modulus in Reservoir Engineering and Rock-Fluid Coupling Projects

Abstract: This research was conducted to determine how the incorporation of different poroelastic equations would affect the measured rock matrix bulk modulus in the laboratory. To do this, three experimental methods were used to measure the matrix bulk modulus, Ks, of seven sandstone specimens taken from the Świętokrzyskie mine in Poland. Those experimental methods were based on the different governing equations in poroelasticty theory. The matrix bulk modulus has a substantial impact on the rock strength against external stresses. Moreover, the rock bulk modulus depends directly on two components: the pore fluid bulk modulus and matrix bulk modulus. The second one is more important as it is much higher than the first one. In this study, the accuracy of those three methods in the measurement of the matrix bulk modulus was evaluated. For this purpose, an acoustic wave propagation apparatus was used to perform the required tests. For each method, an empirical correlation was extracted between the matrix bulk modulus and the applied hydrostatic stress. In all the experiments, an exponential correlation was observed between the matrix bulk modulus and the hydrostatic stress applied on the rock. Furthermore, it was found that the incorporation of the dry bulk modulus in the calculations led to an underestimation of the matrix bulk modulus. In addition, as the hydrostatic stress was raised, the matrix bulk modulus also increased. The applied methodology can be deployed to determine the matrix bulk modulus in coupled rock-fluid problems such as reservoir depletion, hydraulic fracturing, oil recovery enhancement, underground gas storage and land subsidence.

On the Lubrication and Stability Behaviors of a Conical Hybrid Floating Ring Bearing with Thermal Effects

Abstract: The conical bearing can withstand both journal and axial load because of the conical-shape fluid film, and an investigation concerning the thermodynamic lubrication and stability properties is proposed for a conical hydrostatic/hydrodynamic floating ring bearing theoretically and experimentally. The finite element method is coupled with the finite difference method to solve the variable-viscosity Reynolds equations, thermal energy equations, and the corresponding boundary conditions for the inner and outer films in a floating ring equilibrium state, and the conical bearing-rotor dynamic and stability performance models are built up with the perturbation theory and Routh-Hurwitz method. The primary characteristics parameters that are obtained under different operational conditions suggested that there presents a significant temperature gradient distribution over the lubricated domain, the thermal effects decrease the load carrying capacity, friction power loss, and stiffness and damping coefficients, and the viscous dissipation influences the variation of threshold instability speed with eccentricity and reduces its maximum value. In experiments, the temperature distributions of the oil leakage flow are measured to compare with the calculated results for the validation of the mathematic model using an infrared thermal imager, and the thermal effects need to be taken into consideration for the bearing lubrication analysis and design.

Time-Dependent Pinning of Nanoblisters Confined by Two-Dimensional Sheets. Part 1: Scaling Law and Hydrostatic Pressure.

Abstract: Understanding the mechanics of blisters is important for studying two-dimensional (2D) materials, where nanoscale blisters appear frequently in their heterostructures. It also benefits the understanding of a novel partial wetting phenomenon known as elastic wetting, where droplets are confined by thin films. In this two-part work, we study the static mechanics of nanoscale blisters confined between a 2D elastic sheet and its substrate (part 1) as well as their pinning/depinning dynamics (part 2). Here, in part 1, we investigate the morphology characteristics and hydrostatic pressures of the blisters by using atomic force microscopy (AFM) measurements and theoretical analysis. The morphology characteristics of the blisters are shown to be the interplay results of the elasticity of the capping sheet, the adhesion between the capping sheet and the substrate, and the interfacial tensions. A universal scaling law is observed for the blisters in the experiments. Our analyses show that the hydrostatic pressures inside the blisters can be estimated from their morphology characteristics. The reliability of such an estimation is verified by AFM indentation measurements of the hydrostatic pressures of a variety of blisters.

Residual Stress Distribution in a Copper-Aluminum Multifilament Composite Fabricated by Rotary Swaging

Abstract: Rotary swaging is a promising technique for the fabrication of clad Cu/Al composites. Residual stresses appearing during the processing of a special arrangement of Al filaments within the Cu matrix and the influence of the bar reversal between the passes were studied by (i) neutron diffraction using a novel evaluation procedure for pseudo-strain correction and (ii) a finite element method simulation. The initial study of the stress differences in the Cu phase allowed us to infer that the stresses around the central Al filament are hydrostatic when the sample is reversed during the passes. This fact enabled the calculation of the stress-free reference and, consequently, the analysis of the hydrostatic and deviatoric components. Finally, the stresses with the von Mises relation were calculated. Hydrostatic stresses (far from the filaments) and axial deviatoric stresses are zero or compressive for both reversed and non-reversed samples. The reversal of the bar direction slightly changes the overall state within the region of high density of Al filaments, where hydrostatic stresses tend to be tensile, but it seems to be advantageous for avoiding plastification in the regions without Al wires. The finite element analysis revealed the presence of shear stresses; nevertheless, stresses calculated with the von Mises relation show similar trends in the simulation and in the neutron measurements. Microstresses are suggested as a possible reason for the large width of the neutron diffraction peak in the measurement of the radial direction.

A sequential mobile packing algorithm for micromechanical assessment of heterogeneous materials

Abstract: A new non-uniform sequential mobile packing (NSMP) algorithm featuring an efficient collision detection scheme was developed to rapidly generate representative volume elements (RVEs) for advanced heterogeneous and/or composite material systems with either spherical or cylindrical inclusions and a broad range of microstructural characteristics (i.e., various inclusion orientations and sizes, and agglomerations). Statistical assessment of inclusion spatial dispersion using nearest neighbor-based and pair correlation functions revealed that the NSMP algorithm generated RVEs with realistic microstructures for all cases considered. Subsequent statistical finite element micromechanical modeling was conducted to compute the effective properties for each generated microstructure. A case study for a 3D-printed nanocomposite material revealed that a combination of aligned and misoriented rod inclusions was the most representative microstructure. Contour plots of normalized effective stiffness for the 3D-printed composites and normalized average hydrostatic stress in the matrix phase enabled comparison of RVEs with different microstructures. The material system with aligned rod inclusions benefited from simultaneous high effective stiffness and effective load transfer to the inclusions (at higher inclusion volume fractions), which is indicated by low average hydrostatic stress in the matrix. The microstructures comprising spherical inclusions exhibited moderate stiffness, while those with clustered misoriented rod inclusions had the lowest effective stiffness and load transfer to the inclusions. The NSMP algorithm can be used for further microstructural optimizations and assessments of renifornced or porous heterogeneous and/or composite materials using machine learning, while the generated contours can be used as general design guidelines.

Design modification and performance evaluation of mini-hydrostatic pressure apparatus for inclined plane circular surface

Abstract: Mini-Hydrostatic Pressure Apparatus (MHSPA), of spatial size 230×210×210 mm3, was developed for individual or limited number of users to promote Covid-19 social distance protocol. A solid hemisphere with an inclined circular segment made from gypsum material (CaSO2.0.5H2 O) and coated with filler putty and oil paint, is used in place of the regular quadrants. With the solid attached to a horizontal beam mounted over a pivot, hydrostatic forces due to liquids were measured at different heights of water. The results showed that the assembly could be used to demonstrate variation of hydrostatic pressure on circular surfaces at different heights of liquid with an average difference of 4.38% against average theoretical values. Compared to other results from the use of conventional quadrants in literature, the associated error is minimal, and indicates the possibility of adopting the apparatus in school laboratories for static pressure demonstration.

Further Study on One of the Numerical Methods for Pure Loss of Stability in Stern Quartering Waves

Abstract: The International Maritime Organization (IMO) finalized the second-generation intact stability criteria in 2022. However, an accurate and practical numerical method for stability loss has yet to be established. Therefore, a 6 DOF numerical model is further improved based on the previous study. Firstly, the rolling motion is simulated using a seakeeping model instead of the previous maneuvering mathematical model. Secondly, the roll-restoring variation is calculated directly considering the instantaneous wet hull instead of the previous pre-calculated method. Thirdly, transferring frequency to time is used to obtain heave and pitch motions, further considering yaw angle and sway velocity. Fourthly, the dynamic forces for sway, roll, and yaw motions are calculated, further considering the effect of the speed variation. Fifthly, the 6 DOF motions are used to determine the instantaneous wet hull, and the FK force and the hydrostatic force are calculated by the body’s exact method. Finally, a new conclusion is obtained that the sway and yaw motions’ effect on the ship speed loss, the relative longitudinal wave profile by the speed loss, the rudder angles, and the accompanying rudder forces in the rolling direction are significant, and much more than their centrifugal force or coupled force in the rolling direction.

Comment on “Spatial changes in inclusion band spacing as an indicator of temporal changes in slow slip and tremor recurrence intervals” by Nishiyama et al.

Abstract: Abstract A recent paper by Nishiyama et al. (Earth, Planets, and Space 73:126) examined syntectonic quartz veins to constrain temporal variations in the recurrence intervals between slow slip and tremor events. The authors claim that by examining the liquid-volume fraction of syntectonic fluid inclusions in the veins, that they can accurately reconstruct pore-fluid pressures (and variations therein) that were operative during faulting at ~ 15 km depth in an exhumed subduction melange. From these observations, the authors infer that large (from lithostatic to hydrostatic) decreases in pore-fluid pressure occurred during faulting, and that these variations drove increases in supersaturation and rapid quartz precipitation over time scales consistent with the repeat times of seismologically observed slow slip and tremor events. Here, I show that Nishiyama et al.’s analysis neglects reasonable uncertainties in pore-fluid pressure reconstruction. When those uncertainties are included, the Nishiyama et al.’s results become ambiguous as to whether any variation in pore-fluid pressure during vein formation occurred at all, negating the validity of many of the subsequent conclusions. Graphical Abstract

Small-Scale Modeling of Flexible Barriers. II: Interactions with Large Wood

Abstract: During strong floods, rivers often carry significant amounts of sediment and pieces of large wood (LW). When bridges and hydraulic structures are unable to allow LW to pass through, it becomes necessary to trap LW through specific wood retention structures (e.g., flexible barriers). This paper presents a comprehensive analysis of the interactions between LW and flexible barriers using small scale models. A dimensionless criterion is first proposed to compute blockage probability of single logs. It is based on experiments varying log size and shape, channel slope (2%, 4%, and 6%), water discharge, and barrier bottom clearance. Based on runs using six mixtures of hundreds of logs, an equation is secondly provided to compute flow depth at a barrier accounting for the head losses related to large numbers of logs. Conditions leading to the release of LW when the barrier is severely overwhelmed are also studied. The deformation measured on the barrier proves to be lower with LW-laden flows than under full hydrostatic loading of a barrier obstructed by a plastic sheet. Overall, we demonstrate that flexible barriers are very relevant structures to trap LW. A companion paper shows how to design and manufacture a small scale flexible barrier in mechanical similitude with the prototype scale.

Study on the Sealing Performance of O-ring under High-Pressure Environment

Abstract: The sealing properties of the O-ring of the hydraulic cylinder plunger rod under a high-pressure environment are related to a variety of factors. In this paper, we first establish a simulation model based on an O-ring reciprocating shaft seal under a high pressure-environment through finite element software and study the influence of the compression rate, static pressure, and reciprocating speed of the plunger rod on the sealing performance of O-ring through the simulation model, and then analyze the maximum stress of O-ring during installation, hydrostatic loading and reciprocating motion with the variation of structural parameters. The results indicate that the compression rate of the installation process has a significant effect on the sealing performance of the enhanced O-ring. In the hydrostatic loading process, the equivalent stress of the O-ring is increased with the increase of the compression rate, when the static pressure is low and decreases, and when the static pressure is high, and the equivalent stress shows an increasing trend and the same increase; in the reciprocating motion process, when the static pressure is low, the equivalent stress and contact stress of the O-ring does not change significantly with the compression rate, and when the static pressure is high, there is an obvious phenomenon of abrupt change. The frictional stress of the reciprocating motion is increasing, then decreases, and then increases with the change in static pressure.

Dynamical tides in Jupiter and other rotationally flattened planets and stars with stable stratification

Abstract: We develop a numerical method for directly computing the dissipative dynamical tidal response of rapidly rotating, oblate stars and gaseous planets with realistic internal structures. Applying these calculations to neutrally and stably stratified polytropes, we identify the most relevant resonances in models with rotation rates up to nearly the mass-shedding limit. We then compute the dynamical tidal response for Jupiter interior models including both stably stratified and convective regions. These calculations show that resonances involving mixed waves with both gravito-inertial and purely inertial character are capable of explaining a discrepancy between observations and hydrostatic calculations of Jupiter’s response to tidal forcing by Io. This result contrasts with recent work that excluded Jupiter’s rotational flattening, and opens the door to resonances involving a wider range of internal oscillation modes than previously considered.

Small-Scale Modeling of Flexible Barriers. I: Mechanical Similitude of the Structure

Abstract: : Flexible barriers can be used to trap woody debris or debris flows. However, their small scale modelling is challenging because of their possible deformation. This article addresses how to meet the partial mechanical similitude of manufactured flexible barriers. Relevant dimensionless parameters are defined from flow velocity, barrier geometry, and component mechanical properties. These similitude criteria are validated using numerical simulations of barriers exposed to a hydrodynamic loading at various scales. The simulations also confirm the importance of accounting for the mechanical characteristics of the barrier components when designing model barriers in view of achieving realistic deformations. Next, a real barrier with complex features is scaled to conduct flume experiments. This scaled barrier is 3D-printed with material selected to achieve the mechanical similitude criterion. Another validation of this approach is performed considering hydrostatic loading and checking that simulated and measured deformations are similar. As an application case, the deformations measured during the experiments performed with woody debris are also compared to the hydrostatic loading. DOI: 10.1061/JHEND8.HYENG-13070. This work is made available under the terms of the Creative Commons Attribution 4.0 International license, https://creativecommons.org/licenses/by/4.0/.

Simplified calculation of recess pressure considering the hydrodynamic effect

Abstract: The hydrostatic journal bearing's recess pressure is to be determined using a novel approach. This method treats the circumferential bearing lands on both sides of recesses as infinitely long bearings, and the axial bearing lands on both sides of recesses as infinitely short bearings. The newton-Cotes integral formula is used to solve the definite integration. By this simplification, a new analytical expression of recess pressure considering the hydrodynamic effect on bearing land is obtained. The recess pressure versus eccentricity, supply oil pressure, recess wrap angle, and attitude angle solved by the new method is compared with that calculated by the finite difference method and Liang's method from two kinds of four-recess hydrostatic journal bearing compensated by capillary restrictor. The results indicate that the new process has high accuracy and its precision isn't almost affected by the parameters change. Moreover, the new method has low time consumption.

A Novel Geometry Optimization Approach for Multi-Recess Hydrostatic Bearing Pad Operating in Static and low-Speed Conditions Using CFD Simulation

Abstract: Abstract The design of a hydrostatic bearing pad is limited to simple geometry using analytical equations or one-parameter optimization based on experimental data. This study proposes and investigates a new two-parameter method for estimating optimal hydrostatic bearing pad proportions—recess area and position, using Computational Fluid Dynamics (CFD). In this study, 3D static CFD quarter model of a multi-recess hydrostatic bearing pad assuming laminar flow is used. The CFD model was calibrated based on experimentally obtained results and the literature. The recess pressure and resulting load are evaluated for a variety of recess positions and areas. Performance factors are calculated and interpolated in the MATLAB environment. Using the proposed novel two-parameter optimization, the energetic loss was reduced by 20% compared to the classical one-parameter approach. This methodology allows versatile and effective design of optimal hydrostatic bearings operating in low-speed conditions to achieve minimum energetic loss.

Theoretical Study of Pressure-Induced Phase Transitions in Sb2S3, Bi2S3, and Sb2Se3

Abstract: We report an ab initio study of Sb2S3, Sb2Se3, and Bi2S3 sesquichalcogenides at hydrostatic pressures of up to 60 GPa. We explore the possibility that the C2/m, C2/c, the disordered Im-3m, and the I4/mmm phases observed in sesquichalcogenides with heavier cations, viz. Bi2Se3, Bi2Te3, and Sb2Te3, could also be formed in Sb2S3, Sb2Se3, and Bi2S3, as suggested from recent experiments. Our calculations show that the C2/c phase is not energetically favorable in any of the three compounds, up to 60 GPa. The C2/m system is also unfavorable for Sb2S3 and Bi2S3; however, it is energetically favorable with respect to the Pnma phase of Sb2Se3 above 10 GPa. Finally, the I4/mmm and the disordered body-centered cubic-type Im-3m structures are competitive in energy and are energetically more stable than the C2/m phase at pressures beyond 30 GPa. The dynamical stabilities of the Pnma, Im-3m, C2/m, and I4/mmm structural phases at high pressures are discussed for the three compounds.

A novel geometry optimization approach for multi-recess hydrostatic bearing pad operating in static and low-speed conditions using CFD simulation

Abstract: Abstract This study investigates a new two-parameter method for estimating optimal hydrostatic bearing pad proportions. The design of a hydrostatic bearing pad is limited to simple geometry using analytical equations or one-parameter optimization based on experimental data. In this study, 3D static CFD model results were verified using analytical results and experimental data on a hydrostatic bearing testing device. The obtained CFD results for load and pressure show a deviation within 5.2% compared to the experimentally obtained results and the literature. Using the proposed novel two-parameter optimisation, the energetic loss was reduced by 30% compared to the classical one-parameter approach. This methodology allows versatile and effective design of optimal hydrostatic bearings operating in low-speed conditions to achieve minimum energetic loss.

Non-Hydrostatic Numerical Model of Bragg Resonance on Periodically Submerged Breakwater

Abstract: The Bragg resonance (BR) of a reflection coefficient resulting from the propagation of monochronic waves over periodically submerged breakwater was studied using the non-hydrostatic numerical model SWASH (Simulating WAves till SHore). Bragg resonance occurs when the incident wavelength is approximately twice the structural length of a periodic structural breakwater according to Bragg’s law and conditions. This study aimed to investigate the dynamics of Bragg resonance at water depths of 0.2, 0.3, and 0.4 m as the number of periodically submerged breakwater and their wavelengths changed. Specifically, this study focused on the Bragg resonance point of occurrence at a ratio of two structural wavelengths to the incoming wavelengths (2S/L). Regular waves were propagated over two periodically submerged breakwaters, with increasing structural wavelengths from 1 to 2 m at 0.2 m intervals. The results showed that Bragg resonances rapidly increase in value as the water depth decreases, but do not shift in their point of occurrence as the number of periodically submerged breakwaters increases. However, the Bragg resonance shifts leftward in 2S/L as the structural wavelength increases, with a slight increase in value at shallower water depths. More incident wave energy is reflected when the number of periodically submerged breakwater increases compared with when the structural wavelength of the periodically submerged breakwater increases. The differences in the Bragg resonance values are associated with the changes in the number of periodically submerged breakwater. Additionally, the shift in the point of occurrence was influenced by both water depth and structural length. This causes the Resulted Bragg resonance to deviate from the Expected Bragg resonance, which could be the reason why Bragg resonance does not mainly occur at 2S/L=1, as stated by Bragg’s law.

A nonhydrostatic oceanic regional model, ORCTM v1, for internal solitary wave simulation

Abstract: Abstract. The Oceanic Regional Circulation and Tide Model (ORCTM), including a nonhydrostatic dynamics module which can numerically reproduce internal solitary wave (ISW) dynamics, is presented in this paper. The performance of a baroclinic tidal simulation is also examined in regional modeling with open boundary conditions. The model control equations are characterized by three-dimensional and fully nonlinear forms considering incompressible Boussinesq fluid in Z coordinates. The pressure field is decomposed into the surface, hydrostatic, and nonhydrostatic components on the orthogonal curvilinear Arakawa-C grid. The nonhydrostatic pressure determined by the intermediate velocity divergence field is obtained via solving a three-dimensional Poisson equation based on a pressure correction method. Model validation experiments for ISW simulations with the topographic change in the two-layer and continuously stratified ocean demonstrate that ORCTM has a considerable capacity for reproducing the life cycle of internal solitary wave evolution and tide–topography interactions.

Lubrication characteristics and thermal deformation of hydrostatic thrust bearing based on conjugate heat transfer

Abstract: Purpose The purpose of this paper is to analyze the variation of temperature field, pressure field and deformation of hydrostatic thrust bearing under different working conditions, so as to provide a theoretical basis for improving accuracy and reliability. Design/methodology/approach In this study, the double rectangular hydrostatic bearing of type Q1-224 was selected as the research object, and the simulation was carried out according to different working conditions, and the obtained data were summarized regularly. Findings It is found that the overall temperature of hydrostatic bearing increases with the increase of speed and load, and the increase in load will result in a larger pressure distribution which first increases and then decreases with the speed. The deformation trend of the deformation field is found, and it is found that the force deformation is larger than the thermal deformation at low rotational speed, and the thermal deformation is larger than the force deformation at high rotational speed. Originality/value In this study, the fluid-structure coupling method of conjugate heat transfer is applied to study the whole hydrostatic bearing. Most of the previous studies only studied the oil film and considered the influence of the convective heat transfer between the hydrostatic bearing and the air in heat transfer, which is rarely seen in the previous research literature.