Hydraulic Pressure Distribution Research Articles

Water-blocking characteristics of fault zones with different structural combination of cementation degree

Recently, deep coal mining has posed a significant challenge owing to the threat of water inrush from highly pressured aquifers in the floor strata. Water inrush in the floor strata is often associated with the structural characteristics of the underlying fault zones. The permeability of these fault zones is a critical factor in determining their potential as conduits for water flow. The variation in permeability is attributed to the varying cementation degree across different locations within the fault zones. Hence, this study is based on the key stratum theory and introduces the concept of a water-blocking key stratum within fault zones. This research focuses on the engineering context of the 16th coal seam above the lower coal seam in the 10603 working face of the Yangcun Coal Mine's tenth mining area. The study investigates the activation characteristics of the 10605F5 reverse fault zone, which cuts through the working face. Various methods, including test of simulation of similar materials and numerical simulations, are employed to analyse the hydraulic pressure distribution and the impact of mining activities on the water-blocking key stratum within the 10605F5 reverse fault zone. The research findings will provide valuable insights for preventing fault activation and water inrush.

Numerical Modeling of Natural Fracture Distributions in Shale

AbstractThe production efficiency of shale gas is affected by the interaction between hydraulic and natural fractures. This study presents a simulation of natural fractures in shale reservoirs, based on a discrete fracture network (DFN) method for hydraulic fracturing engineering. Fracture properties of the model are calculated from core fracture data, according to statistical mathematical analysis. The calculation results make full use of the quantitative information of core fracture orientation, density, opening and length, which constitute the direct and extensive data of mining engineering. The reliability and applicability of the model are analyzed with regard to model size and density, a calculation method for dominant size and density being proposed. Then, finite element analysis is applied to a hydraulic fracturing numerical simulation of a shale fractured reservoir in southeastern Chongqing. The hydraulic pressure distribution, fracture propagation, acoustic emission information and in situ stress changes during fracturing are analyzed. The results show the application of fracture statistics in fracture modeling and the influence of fracture distribution on hydraulic fracturing engineering. The present analysis may provide a reference for shale gas exploitation.

Impact Response of the Tail Beam Jack Based on Bidirectional Fluid-Structure Coupling Simulation.

In top coal caving mining, the coal rock collapse will cause an irregular impact on the tail beam jack of the caving control mechanism. The severe impact will lead to jack failure. The bidirectional fluid-structure coupling model is built on Fluent and Mechanical software to study the impact response of the tail beam jack. The dynamic flow velocity streamlines, hydraulic pressure distribution, stress field, and strain field of the jack under impact load are extracted. The response characteristics of the jack in the stationary state and motion state are analyzed. The conclusions are as follows: the stress and strain of the rodless cavity are much larger than those of the rod cavity, which is more likely to be damaged. The hydraulic pressure in the jack cavity is in vertical layered distribution. The flow velocity streamlines present spiral shapes. The response degree of the hydraulic pressure signal in the rodless cavity is stronger than that in the rod cavity, and the response degree of the flow velocity signal in the rod cavity is stronger than that in the rodless cavity. The impact response of the jack in the motion state is more sensitive and stronger than that in the stationary state. The coal rock collapse situation can be most effectively identified only by comprehensively analyzing the rodless cavity's pressure signal and the rod cavity's velocity signal. This paper innovatively visualizes the flow velocity streamlines and pressure distribution together. The bidirectional fluid-structure coupling method is innovatively applied to the tail beam jack. The findings of this study can help for better understanding of the tail beam jack's structural design and failure prevention. This study provides a certain research basis for the intelligent coal rock identification technology in mining coal based on jack vibration signals.

Design and Analysis of a New Pressure Relief Valve for Oil-Immersed Electrical Equipment

Abstract Internal arcing in oil-immersed electrical equipment is inevitable and of great danger. Transient overpressure should be released by protectors quickly and controllably. Currently available pressure relief valves cannot fully protect the electrical equipment due to mismatch between insufficient relief capacity with correspondingly weak valve structure and increasing arcing energy in upgrading electrical systems. Additionally, flaming possibility of ejected high-temperature oil–gas mixture is distinct, and retained oil in an oil tank without any isolation may be ignited by the flame. Unfortunately, resealing of some existing single-outlet valves is out of control due to asymmetrical hydraulic pressure distribution on the valve plate which causes unstable valve plate movement. Therefore, a new pressure relief valve characterized by symmetrical outlets and improved pressure relief capacity was developed. The novel structure and function of the new valve was first introduced, and comprehensive analysis regarding dynamic performances, strength and fluid development during the relief process were conducted. Finally, a prototype was manufactured and tested on a specific arcing test system. The developed valve can well release the overpressure generated by a 6 MJ equivalent arcing fault without any flame during the entire relief process. Furthermore, the valve structure can withstand the pressure load, and valve plate can precisely reseal the oil tank due to optimized fluid pressure distribution. This research provides an optimized pressure relief valve and a design guide for improved pressure relief valve.

Deformation rule and mechanical characteristic analysis of subsea tunnel crossing weathered trough

It is difficult to comprehend the deformation rule and mechanical characteristics in the construction process of subsea tunnel crossing weathered trough owing to the complex tunnel structure and unfavorable geological conditions. In this study, a geomechanical model test and a numerical model system for the excavation of subsea tunnel were developed based on Haicang Subsea Tunnel to investigate the characteristics of the tunnel displacement, stress, and seepage. After subsea tunnel excavation, the displacement, stress, and hydraulic pressure distribution of surrounding rocks were similar, with the release of stress and lower hydraulic pressure often accompanied with the growth of its displacement. Generally, multiple-physical monitoring information was interactional. In addition, the influence of seawater on the weathering trough was mainly concentrated in an area approximately twice the diameter of the hole, and the influence of water on the vault was greater than that of the sidewall. These results could serve as reference for the construction of subsea tunnel crossings and warning mechanisms of weathered trough.

One-dimensional finite element limit analysis for hydraulic pile extraction

This paper presents a numerical method to efficiently calculate the required overpressure for hydraulic pile extraction. The method uses a one-dimensional (1D) model involving two steps: (1) the steady state hydraulic pressure distribution is calculated for a unit pressure using a finite element model and (2) the required overpressure is calculated using finite element limit analysis. This combined model leads to an efficient calculation tool for estimating the required hydraulic overpressure to extract the pile. The model can also capture other failure mechanisms, such as failure of the pile plug, and the 1D approach allows for alternative soil resistance formulations to be incorporated easily. This allows the method to be used for preliminary analysis as well as detailed extraction assessments for an entire wind farm site. The proposed method is applied to study a pile in sand, clay and layered soil profiles. The analyses in sand show a significant increase in the plug shaft resistance due to the hydraulic gradient, resulting in a super-linear increase of break-out pressure with embedment depth. In clay soils, the break-out pressure increases linearly, but plug failure may occur at large embedment depths. Furthermore, soil layering can have a significant effect on the break-out pressure.

On the Efficacy of Water Transport in Leaves. A Coupled Xylem-Phloem Model of Water and Solute Transport

In this paper, we present and use a coupled xylem/phloem mathematical model of passive water and solute transport through a reticulated vascular system of an angiosperm leaf. We evaluate the effect of leaf width-to-length proportion and orientation of second-order veins on the indexes of water transport into the leaves and sucrose transport from the leaves. We found that the most important factor affecting the steady-state pattern of hydraulic pressure distribution in the xylem and solute concentration in the phloem was leaf shape: narrower/longer leaves are less efficient in convecting xylem water and phloem solutes than wider/shorter leaves under all conditions studied. The degree of efficiency of transport is greatly influenced by the orientation of second-order veins relative to the main vein for all leaf proportions considered; the dependence is non-monotonic with efficiency maximized when the angle is approximately 45° to the main vein, although the angle of peak efficiency depends on other conditions. The sensitivity of transport efficiency to vein orientation increases with increasing vein conductivity. The vein angle at which efficiency is maximum tended to be smaller (relative to the main vein direction) in narrower leaves. The results may help to explain, or at least contribute to our understanding of, the evolution of parallel vein systems in monocot leaves.

Modeling of the roller pressing of fibrous materials

The work is devoted to modeling the regularities of hydraulic pressure distribution and fluid removal from the fibrous material in the contact zone. It was found that the hydraulic pressure in the compression zone increases from zero at the initial point of contact to a maximum at the point of maximum compression of the fibrous material. The patterns of distribution of hydraulic pressure in the recovery zone depend on the length of the section, where the fluid moves from the layer of material to the elastic coatings. It was revealed that the amount of liquid removed at the beginning of the compression zone grows faster, then the growth rate is much lower, and at the end of the compression zone, the removed liquid is stabilized. The patterns of change in the removed fluid in the recovery zone depend on the angle, which determines the position of the point where the fluid changes direction.

Research on Improvement of the End Cover of Intra-vane Type Pump Based on ANSYS

The flow distribution side plate (FDSP) of the intra-vane pump is loaded to the hydraulic thrust of the oil film of the distribution pair and the hydraulic pressing force of the kidney-shaped cavity on the end cover of the pump core. The kidney-shaped cavity structure in the end cover has a certain effect on the deformation of the FDSP, and then affects the oil film thickness, leakage power loss and friction power loss of the distribution pair. In this paper, the hydraulic pressure distribution of oil film in the distribution pair is studied. Using the principle of redundant squeezing force, the calculation formula for the kidney-shaped cavity area on the end cover is deduced. Through simulation, the contour of the deformation of the FDSP is obtained, and it is found that the deformation of the discharge area and the oil suction area is not uniform. By improving the design of the kidney-shaped cavity structure in the end cover, the uniformity of the FDSP deformation can be achieved. The research conclusion has certain guiding significance for improving the volume efficiency and mechanical efficiency of the intra-vane type pump.

Failure Mode of the Water-filled Fractures under Hydraulic Pressure in Karst Tunnels

AbstractWater-filled fractures continue to grow after the excavation of karst tunnels, and the hydraulic pressure in these fractures changes along with such growth. This paper simplifies the fractures in the surrounding rock as flat ellipses and then identifies the critical hydraulic pressure values required for the occurrence of tensile-shear and compression-shear failures in water-filled fractures in the case of plane stress. The occurrence of tensile-shear fracture requires a larger critical hydraulic pressure than compression-shear failure in the same fracture. This paper examines the effects of fracture strike and lateral pressure coefficient on critical hydraulic pressure, and identifies compression-shear failure as the main failure mode of water-filled fractures. This paper also analyses the hydraulic pressure distribution in fractures with different extensions, and reveals that hydraulic pressure decreases along with the continuous growth of fractures and cannot completely fill a newly formed fracture with water. Fracture growth may be interrupted under the effect of hydraulic tensile shear.

Effect of Outflow Volume of Pressure Medium on Fluid-Lubrication Effect during Sheet Hydroforming

The effect of the outflow volume of the pressure medium on the fluid-lubrication effect during the sheet hydroforming was investigated experimentally. The hydraulic pressures in the flange area obtained for the sheet hydroforming during which the hydraulic pressure was pressurized using pump were higher than those of the sheet hydroforming during which the pump was not utilized. This might be owing to the difference in the outflow volume of the pressure medium. On the other hand, the drawability of the sheet was almost independent of with or without using pump. Examining the so-called effective punch force, we found that the effect of the difference in the outflow volume of the pressure medium on the fluid-lubrication effect was negligible. We concluded from these results that the fluid-lubrication effect was affected significantly by the existence or non-existence of the outflow of the pressure medium, i.e. the lubricant oil, but it was almost independent of the outflow volume of the pressure medium. Furthermore we also found that the hydraulic pressure distribution in the flange area would not affect the fluid-lubrication effect.

Outflow Characteristics of a Pressure Medium during Sheet Hydroforming

The outflow characteristics of a pressure medium during a sheet hydroforming process have been studied experimentally by directly measuring the hydraulic pressure distribution. Initial measurements of the outflow of the pressure medium though the gap between two clamped dies were carried out in order to verify the method for measuring the hydraulic pressure distribution employed in this study and to investigate the basic properties of the outflow. The upward forces were calculated by integrating the measured hydraulic pressure during the outflow and found to be in satisfactory balance with the clamping forces, which demonstrates the validity of this measurement method. Furthermore, we suggest that the critical outflow pressure can be predicted by considering the force equilibrium. An experimental investigation of a square-cup sheet-hydroforming process was then carried out. The upward forces were calculated by integrating the measured hydraulic pressure and again found to be in satisfactory balance with the forming forces at the beginning of the process, which shows that the critical outflow pressure can also be predicted for square-cup deep-drawing processes. The hydraulic pressure distributions in the flange area and the chamber change significantly as the sheet conforms to the die shoulder, and the friction loss of hydraulic pressure at the die shoulder becomes large. These results indicate that the magnitude of the fluid-lubrication effect on the drawability of the sheet can vary with the stage of sheet deformation.

Analysis and prediction of fouling layer structure in microfiltration

A dynamic analysis procedure has been adopted based on mass and force balances for particle deposition on the membrane surface to analysis and predict the particle fouling layer structure in microfiltration. The local properties in a fouling layer, say porosity distribution, resistance to fluid flow and hydraulic pressure distribution can be estimated by the proposed dynamic analysis with a preliminary request of a set of filtration data and the surface porosity of fouling layer only. A prototype software for the analysis of the fouling layer properties in microfiltration has been devised and can be used both for design of a membrane filtration system and later to predict or monitor its performance during plant operation.

Effect of Slurry Hydraulic Pressure in Slip Casting.

Effect of the slurry depth on slurry hydraulic pressure and cake growth rate during slip casting was examined for zirconia aqueous slurry of 50-75mass% solid. Buoyancy, which acted on three sorts of stainless steel sinkers in the zirconia slurries, was measured. Buoyancy in slurry increased linearly with the slurry density and the volume of the sinker. Buoyancy is generated by the slurry hydraulic pressure distribution. It is found that slurry hydraulic pressure increases proportionally to the slurry depth. The cake growth rate became higher at a higher head of the slurry.

Dewatering of Gels by Constant Pressure Expression.

The dewatering process of constant pressure expression was experimentally investigated with three kinds of bulk gels (agar-agar gel, a heavy oil gel and a salad oil gel). While the structure of a gel is different from that of a solid liquid mixture, hydraulic pressure distribution in the gel approximately coincides with that calculated from the conventional theory of filtration during the first term of the process. This first term is able to be reasonably analysed as the filtration period. The subsequent process can be analysed as the consolidation period. Some of the liquid in the gel is mechanically inseparable, so as a rule it is essential to account for this liquid in analysis of the expression process for gelatinous materials. Results of electrical conductivity measurement of the gel indicate that the net free water almost corresponds with the water mechanically separable. The experimental results of agar-agar gel coincide favourably with the calculated results based on the conventional theory of expression and the compression permeability test data

Mechanism of cake formation in constant pressure filtrations

The concept of the critical friction angle between particles is adopted to study cake formation for constant pressure filtrations. By taking a force balance for a depositing particle, the value of the critical friction angle is determined, and the structure of cake is simulated numerically. A numerical program is also designed to evaluate the growth of cake, hydraulic pressure distribution, local cake porosity, and local specific filtration resistance from the experimental data of filtration rate versus time. The calculated results agree very well with the available data.

Drainage of supported excavations

The paper provides the approximate closed-form expressions for the estimation of the amount of ground water infiltration, the seepage exit gradient and the hydraulic pressure distribution on the cutoff elements in the case of sheeted excavations below the water table. The expressions are obtained by a multiple regression-type fitting of the results of an extensive parametric finite-element analysis for the two-dimensional steady-state flow in the soil around a sheeted excavation. In addition to the problem geometry, the effects of an impermeable base and a thin low permeability layer penetrated by the sheeting are also studied. The predictions of the approximate expressions deviate from the corresponding finite-element results by less than 15%, for a wide range of geometries and soil characteristics. It is shown how shape factors might be used to adapt the semi-empirical formulae for the case of excavations with limited length (circular and rectangular).

Leachate Collection System Performance Analysis

The sensitivity of a waste disposal impoundment's leachate collection system performance to a range of design parameter values is investigated based on a computer modeling study. The piezometric head distribution in a vertical cross section of the impoundment is simulated using the finite element method to solve the combined equation of motion and continuity for two‐dimensional flow through a saturated anisotropic porous media. The design parameters studied include saturated waste depth; ground slope; underdrain spacing; and the hydraulic conductivities of the waste, clay liner, drainage blanket, and drain filter. The emphasis in this investigation is on the effect of the design parameters on the hydraulic pressure distribution directly above the clay liner which underlies the waste. The results of the study indicate that the three key parameters controlling the hydraulic pressure on the liner are the underdrain spacing and the hydraulic conductivities of the underdrain filter and the drainage blanket between the waste and clay liner.

Hydraulic deliquoring of compressible filter cakes. Part 1: Reverse flow in filter presses

AbstractRemoval of liquid from filter cakes can be accomplished by mechanical or hydraulic methods after cake formation is complete. This paper deals with the latter procedure. The local porosity in porous beds (Tiller and Cooper, 1962) is a function of hydraulic pressure distribution and cake compressibility. Calculation of average porosity requires an integration of local values as determined by liquid flow patterns. As most compressions of filter cakes are irreversible, the local porosity is a function of the maximum effective pressure (frictional pressure loss) reached during cyclical operations. Reversal of flow through a cake develops radically changed pressure distributions which can be utilized to reduce local porosities. Analytical expressions are presented for reduction of average porosity brought about by reversing flow of liquid in plate‐and‐frame and recessed plate filter presses.