Uneven Pressure Distribution Research Articles

Pressure distribution study in cone slot gap drives of electric power systems

The distribution of pressure in the conical slotted gaps of drives of electric power systems has been studied. A general expression is found to determine the pattern of pressure change along the flow of a viscous fluid in the gaps of non-contact seals, and special cases are also considered. For a narrowing gap, the maximum pressure will be in the section with the smallest gap. In this case, the plunger will tend to take a coaxial position. In the expanding gap, the maximum pressure will be in the section with a larger gap, so the plunger will be pressed against the wall of the sleeve by the forces of unbalanced pressure. With an eccentric location of the plunger in the sleeve, the pressure in the gap will change. Moreover, the uneven distribution of pressure increases as the eccentricity increases. With a larger taper of the slotted channel and with a constant inlet gap, the nature of the pressure change along the slot differs significantly from the linear one. If the flow and the plunger move in the direction of the increasing gap (expanding gap), then the plunger is pressed against the wall of the sleeve by the forces of unbalanced pressure. In this case, the contact surface of the plunger pair is destroyed, which leads to scuffing and failure of the units.

Flow mechanism and axial force distribution characteristics of multistage pump cavity.

The gap leakage between the impeller ring leads to the change of the pump cavity flow characteristics, resulting in the uneven pressure distribution of shroud, which causes the axial force of the cavity to change. In this paper, the flow in the front and the rear cavity of the multistage centrifugal pump was taken as the research object. Through the numerical method, the radial flow velocity, the leakage flow size and its direction, the core zone rotation factor of the front and the rear cavity of the multistage pump impeller at all stages and the axial force of pump cavity were studied. The results show that the leakage in the front cavity of multistage pump impeller at all stages flows inward along radial direction (i.e. it flows from the inlet of pump cavity to the front ring clearance). The rotation factor in core zone is higher than 0.5, and with the increase of rotation factor, the axial force of the front pump cavity increased. The leakage in the rear pump cavity flows outward along radial direction (i.e. it flows from the rear ring to the inlet of pump cavity). The rotation factor in core zone is less than 0.5, and with the increase of rotation factor, the axial force decreased gradually. Besides, the radial velocity and rotation factor in the front and the rear multistage pump of impellers were obviously along the axial direction at three regions, the regions are pump case boundary layer, core zone and impeller boundary layer. The flow in the core zone is dominated by circumferential circular motion, and the radial velocity in the core zone is 0. It is shown that the direction of the leakage in the pump cavity and the rotation effect of the flow micelle in the mainstream core zone are the main factors affecting the axial force of the pump cavity, and the research results can provide theoretical guidance for the calculation and suppression of axial force of multistage pumps.

An analytical model for gas leakage through contact interface in proton exchange membrane fuel cells

Sealing performance between two contacting surfaces is of significant importance to stable operation of proton exchange membrane (PEM) fuel cells. In this work, an analytical micro-scale approach is first established to predict the gas leakage in fuel cells. Gas pressure and uneven pressure distribution at the interface are also included in the model. At first, the micro tortuous leakage path at the interface is constructed by introducing contact modelling and fractal porous structure theory. In order to obtain the leakage at the entire surface, contact pressure distribution is predicted based on bonded elastic layer model. The gas leakage through the discontinuous interface can be obtained with consideration of convection and diffusion. Then, experiments are conducted to validate the numerical model, and good agreement is obtained between them. Finally, influences of surface topology, gasket compression and gasket width on leakage are studied based on the model. The results show that gas leakage would be greatly amplified when the asperity standard deviation of surface roughness exceeds 1.0 μm. Gaskets with larger width and smaller thickness are beneficial to sealing performance. The model is helpful to understand the gas leakage behavior at the interface and guide the gasket design of fuel cells.

Analysis and design of the gas generator multifunctional bulkhead considering the thermal and structural loads

The operation of gas generators brings relatively high thermo-mechanical loads on the gas generator structure. The objective of this article is to determine the operating conditions, in terms of mechanical loads at extremely high temperatures in very limited and narrow space, of a multifunctional bulkhead for application on specific kinds of gas generators with back-to-back rotor concept. The paper contains numerical analysis and experimental investigation for determining the loads and behavior of the structure. Numerical analysis indicates that there is significant influence of the Tesla turbine effect on flow parameters. Also, uneven pressure distribution and significant thermal loads are identified. With experimental investigation and subsequent exploitation tests, it was concluded that the presented methodology identifies the operating conditions, truthfully simulates the bulkhead stress state and deformations and that the presented design solution satisfied all demands. Regarding results obtained by these numerical simulations, the innovative design solution for the multifunctional bulkhead was proposed.

CFD Simulation and Experiments of Pneumatic Centralized Cylinder Metering Device Cavity and Airflow Distributor

The distribution of airflow field in the pneumatic centralized cylinder metering device cavity, airstream distributor and different angle seed feeding tubes was investigated based on the pneumatic centralized cylinder direct-seeding metering device to study the effect on the movement law of rice seed. In total, three suction hole sizes (1.5 mm, 2 mm and 2.0 mm 45° wedge) were used for CFD simulation. The results showed that under the same inlet vacuum, the pressure at the 1.5 mm hole is higher than the other two types of holes, and the five measurement points of the 2 mm hole are more stable than the other two types of holes. At the positive pressure seed feeding area, the inlet pressure was set as 1.5 kPa, and the outlet pressure was set as 0 Pa. The pressure distribution at different measuring points showed that the 2 mm 45° wedge had the most uneven positive pressure distribution, and the 1.5 mm hole had higher positive pressure distribution than the 2 mm hole in general. Three different structured airflow distributors were designed. CFD simulation experiments showed that the arc transition type presented better uniformity than the other two types. The uniformity experiments at the ends of the seed-feeding tubes indicated that the airflow velocity had the trend of large in the middle and small at two sides. Finally, the movement law of the rice seeds in seed feeding tubes at different angles was obtained by using high-speed photography. The results showed that the rice seeds in tube C (maximum angle) presented a movement posture of falling sector a and kept falling after colliding in sector b; the rice seeds in tube B (the second angle) presented a movement posture of falling in sector a and kept falling after colliding in sector b. The above research provides a reference for the optimal design of a pneumatic centralized cylinder metering device.

Research on Water Pressure Distribution Characteristics and Lining Safety Evaluation of Deep Shaft in Water-Rich, Large, Fractured Granite Stratum

Building deep shafts in water-rich granite formations with large fissures has difficulties, such as high-water pressure and high construction risks, and is prone to water inrush and shaft flooding. This paper relies on the No. 1 vertical auxiliary shaft project of Gaoligongshan tunnel and obtains the uneven distribution of water pressure on the outside of the lining in the horizontal direction through on-site monitoring data. In order to explain this phenomenon, based on the statistical parameters of actual fractures in the field and the Monte Carlo method, the DFN built in FLAC3D6.0 is used to generate a discrete fracture network, and a dual medium model, considering the distribution of large fractures, is established. The reason for the uneven distribution of water pressure is obtained through research: the large fissures in the surrounding rock make the hydraulic conductivity of each part of the stone body formed after grouting of the surrounding rock different. This results in different osmotic pressures from the hydrostatic pressure outside the grouting ring to the outside of the lining through the grouting ring. Based on the distribution characteristics of water pressure outside the lining, the safety of the lining under non-uniform pressure is studied. The lining safety factor is defined as the ratio of the lining’s normal service limit state load to the actual load. The normal service limit state load is the load when the RFPA software is used to establish a load-structure model to simulate the load when the lining has obvious cracks under the action of external load; the actual load is the monitoring load. The new method and mine design code method are used to evaluate the lining safety and make a comparative analysis. The results show that the new method can effectively calculate the lining safety factor and has a larger safety reserve.

Experimental Study on Propagation Characteristics of Kerosene/Air RDE with Different Diameters

A series of experimental tests were carried out in order to study the propagation characteristics of a liquid kerosene rotating detonation engine (RDE) with different diameters. Distinguished characteristics of spatial and temporal instability were found in the large-scale RDE due to the uneven circumferential distribution of kerosene supply pressure. As for the two counter-waves detonation system, the 500 mm-diameter RDE maintains a higher detonation wave velocity due to its longer injection recovery time. However, the 220 mm-diameter RDE can obtain a larger equivalence ratio operation range, higher specific thrust, and higher specific impulse. In addition, compared with the deflagration combustion, the detonation combustion has higher chamber pressure and thrust under the same operational conditions.

Substantiating arched support made of composite materials (carbon fiber-reinforced plastic) for mine workings in coal mines

This paper studies a new composite materials based on carbon fiber-reinforced plastic, which is planned to be used for supporting the preparatory workings when mining the coal at depths of more than 1000 meters. The composite material made of carbon fiber-reinforced plastic has sufficient lt high physical-mechanical properties, which are even higher than that of low-alloy steel used as the main material for supporting in coal mines. The purpose of the research is to substantiate the model of support (arched three-link) and determine its rational parameters. The calculation of the stress-strain state around mine working, using the support made of composite materials, has been perfomed based on the method of finished elements in the Solid Works software product. In addition, a model of the support for coal mines has been developed on a 3D-printer. This made it possible to conduct additional research on the interaction of the support with the rock mass. Using the Solid Works software, a detailed modeling of the composite supporting system has become possible. The stress-strain state of the rock mass has revealed that support can be used to improve the strength characteristics and prevent uneven pressure distribution around mine workings. A support made of composite materials contributes to the introduction of resource-saving technologies in the mining industry.

Elastic deformation of liquid spiral groove face seals operating at high speeds and low pressure

The uneven distribution of fluid pressure in the spiral groove area leads to the elastic deformation of the seal faces, which not only affects the sealing performance but also affects the running stability. In this paper, a numerical model of a high-speed spiral groove liquid face seal is proposed with the consideration of elastic deformation and cavitation medium compressibility. The novelty of this study is that the pressure of the cavitation region is modeled as an uneven distribution rather than as a constant. This uneven pressure distribution of sealing surfaces is generally regarded to have an influence on face deformation. Based on the assumption that the fluid exists at a complete gas state in the cavitation, the elastic deformation and pressure distribution of sealing surfaces are calculated. The influence of elastic deformation on sealing performance is further investigated. Results show that the elastic deformation of sealing surfaces and cavitation effect has a significant influence on the stability of sealing clearance, which may produce a negative effect on the sealing performance of liquid face seals. The face deformation causes a divergent gap between two seal faces. With the increase of rotational speed, the elastic deformation of sealing surfaces reduces at low seal pressure but increases at higher seal pressure, which may influence the cavitation behavior and pressure distribution of surfaces. Furthermore, the sealing performance of spiral groove liquid face seal becomes more complicated because of the coupling effect of cavitation effect and elastic deformation. The changing trend of sealing performance is different under various seal clearance and seal pressure. The obtained results may provide guidance for the future design of liquid face seals in engineering applications under high-speed conditions.

Transient Flow and Heat Transfer in a Horizontal Rectangular Channel Considering Thermal–Fluid–Structure Interaction

Abstract For the supercritical n-decane horizontally flowing in a rectangular channel of an active regenerative cooling system, a transient thermal–fluid–structure coupling method is employed to investigate the unsteady thermal-hydraulic characteristics and the wall deformation at a starting stage. The temperature distributions of the fluid domain and solid domain along the flow direction are investigated at fixed times as well as at a certain cross section. Streamlines in cross sections are employed to explain the temperature distribution. The velocity and pressure at a fixed point versus time are also given. Besides, the solid deformation is presented according to the uneven pressure distribution and temperature distribution. It is found that the response time is less than 30 s when the heat flux is less than 3.0 MW/m2. A larger heat flux contributes to promoting the steady state. The high-temperature part of the solid domain is close to the heated wall, but the situation is reversed for the fluid domain. This is because a bunch of dead-zone vortices appears in the vicinity of the upper wall of the channel. The maximum deformation is 0.132 mm for the condition of heat flux 3.0 MW/m2 and it is exacerbated by the uneven temperature and pressure distributions on the solid domain.

Field study on train-induced aerodynamic pressure near the entrance of fully enclosed sound barriers

A systematic field test was conducted for aerodynamic pressure near the entrance of the double-track fully enclosed sound barriers (FESBs). The generating mechanism of pressure was revealed by referring to the slipstream distribution around the moving train and considering the influence of marshalling length, speed and streamline of trains. Results show that near the entrance, the compression wave caused by the head car is predominant and determined by the maximum, minimum and peak-to-peak pressure, while near the exit, the negative and positive peak pressure are, respectively, triggered by the head car and tail car. Uneven pressure distribution along the circumference of the FESB wall and the greater pressure is on the wall near the running train. The head car of double-connection electric multiple units (EMUs) generates greater pressure near the entrance than that of common EMUs, and the tail car of double-connection EMUs causes weaker pressure transient, while near the exit, the head car of double-connection EMU induces weaker pressure. Even if the train speed increases in a small range, the pressure near the entrance/exit of the FESB increases, and the blunter the train is, the greater and the more evenly distributed pressure on the FESB will be.

Modeling and free vibration analysis for bolted composite plate under inconsistent pre-tightening condition

During the service process of bolted composite structures, the local bolt pre-tightening force may decrease, that is, the bolts are inconsistently pre-tightening, which will affect the integrity of the whole system. Here, a semi-analytical modeling method for bolted composite plates with inconsistent pre-tightening conditions is studied. To simulate the uneven pressure distribution on the bolted joint surface, a variable stiffness spring surface model is proposed and a method to obtain the parameters of the model is also described. For a specific connection structure, each joint is simplified into a spring surface model and modeling of inconsistent bolt preload in the connection structure could be realized by assigning different parameters to each spring surface model. Based on the classical laminate plate theory, the strain and kinetic energy of the composite plate are calculated and the motion equation of the structures is deduced by the Rayleigh-Ritz method. Finally, a modal test is applied for a multi-bolted fiber-reinforced composite plate. The accuracy of the model is verified by both test and 3D finite element analysis results. The influence of loosening degree, position and quantity of loosening bolts on natural frequencies of bolted composite plates is further analyzed.

ORGANIZATIONAL SUPPORT OF STATE MANAGEMENT OF WATER RESOURCES ACCORDING TO THE BASIN PRINCIPLE

Water resources are an integral part of nature management, which in terms of market relations is considered a commodity. Uneven territorial distribution of water resources and significant anthropogenic pressure lead to acute water shortages. At present, Ukraine's water management has a significant number of problems, including: deepening the trend of irrational water use; unsatisfactory water quality in natural water bodies; significant increase in material damage from the negative impact due to floods, flooding of groundwater, waterlogging, secondary salinization of land, water erosion, reduced investment in water management. The realities of water use, especially in the field of water resources management, have led to the need to improve existing scientific approaches that will allow more efficient allocation of resources and will be based on the principles of sustainable development. For a long time there was a notion of unlimited water resources and, accordingly, of free access to them. However, with the development of the country's productive forces and especially water-intensive enterprises, pollution of water sources, disputes between water users over the use of water resources, and, finally, water scarcity in some large river basins, society's costs of increasing water resources and bringing them to quality standards have risen sharply. It has become clear that water is a limited and rather expensive resource for society. The main essence, features and main advantages of the basin principle of water resources management are considered in the work; the functions, types and features of the water resources management system based on the basin principle were studied and researched, the structure was analyzed, the main problems of implementation were identified and measures for the effective operation of the water resources management system were proposed. It is noted that the development of the basin system of water resources management in Ukraine should be carried out with maximum use and significant expansion of the functions provided by the water sector of the State Water Management. This approach makes it possible to predict the consequences of human activities, for early prevention of environmental and man-made disasters.

Physical modeling of deformation of a steel bushing under axial compression of an elastic-plastic vibration-damping element of a milling mandrel

To reduce vibrations when milling thin-walled steel sleeves, compression is applied from the inside by uniformly distributed forces created by axial compression of an elastoplastic element made of polyurethane or rubber. It was hypothesized that the pressure at the point of application of the axial compressive force of the elastoplastic element will be higher than at the opposite end, which will lead to uneven elastic deformations of the fixed sleeve and, accordingly, to additional processing errors. When the base-push bush is pressed, the initial force builds up pressure in the first ring. In this case, the initial length of the set of washers will be reduced to a value at which the washers begin to deform and reach contact with the steel sleeve. Then, when you try to move the first ring virtually, the force of its pressing on the second will decrease by the friction force between the first ring and the steel sleeve. The theoretical dependences of the pressure distribution between sequentially located compressible elastoplastic elements are derived as functions of the friction coefficient and geometric parameters of the vibration damping sleeve system. The calculation examples show that in cases where rubber or polypropylene inserts are used as elastoplastic elements, the pressure already on the first element should be completely, and even in excess, blocked by the friction force of the elastoplastic element on the steel sleeve. To resolve this contradiction, physical modeling of the process under study was carried out. 3 rubber washers were inserted inside the steel sleeve. The set of washers was acted upon by two plungers extending into the sleeve by 2 mm. Experimental data show that the central part of the sleeve is most susceptible to deformations, the diameters of the ends also increase, but to a much lesser extent, and approximately the same, which refutes the hypothesis of uneven distribution of pressure and deformation along the length of the sleeve.The reported study was conducted under fi nancial support of RFBR within the framework of the scientific and research project «Postgraduates” No. 20-38-90248.

DefectTR: End-to-end defect detection for sewage networks using a transformer

The sanitary sewer is a crucial underground infrastructure of any country that collects wastewater and carries it to the treatment plant. The damage triggered by various factors, such as external interference, long-term corrosion, and uneven distribution of pressure, could lead to various types of defects inside the sewer pipe. Previous studies primarily relied on human visual perception to evaluate the sewage system, which was tedious, time-consuming, and costly. As a result, an efficient and robust sewer defect localization framework was proposed in this manuscript. The main contributions include (1) a novel sewer defect detection system motivated by the state-of-the-art detection transformer (DETR) architecture, which views object localization as a set prediction topic; (2) a defect severity analysis approach based on the transformer’s self-attention operation to analyze defect zone of influence and defect grade; and (3) a manually validated sewer defect localization dataset that contains 10 types of commonly appeared sewer defects. The experimental results suggested that the proposed system outperformed the previous standard object detection approaches with the highest mean Average Precision (mAP) of 60.2% on the collected dataset.

Об одной из причин нарушения надежной и безопасной работы рудничной водоотливной установки

The Russian Federation is one of the world leaders in diamond mining. Currently, the predominant part (about 95 %) of all the Russian diamonds is mined at the ore (kimberlite) and alluvial deposits located on the territory of Yakutia. Practice shows that the underground development of kimberlite deposits in the territory of Western Yakutia is associated with an abundant flow of mine water into the mine workings. Without the use of a sufficient amount of pumping equipment, mine waters make the process of mining diamond-bearing ores more difficult, and most importantly, unsafe for the operating personnel. Currently, electric pump units of sectional type are used to combat the mine waterways at the kimberlite mines. In order to ensure safe mining of deposits of the solid minerals by the underground method, and to avoid flooding of the mine workings, the pumping equipment of the main drainage plant must always be in the working order, which is ensured by increasing its operational reliability. One of the probable reasons for a significant deterioration in the performance and reliability of sectional pumps is considered. As a material for analysis, practical data on the operation of the main drainage plant of the Udachny underground mine were taken. It is established that the reason for a significant deterioration in the performance of sectional pumps can be an increase in the cylindrical gap of the hydraulic heel assembly. It is shown that the increase in the gap is associated with a decrease in the outer diameter of the cylinder of the unloading disk. A significant reduction in the size of the cylinder can occur as a result of the total impact of such negative factors: an increase in the concentration of mechanical impurities in the mine water passing through the cylindrical gap of the hydraulic heel assembly; uneven distribution of pressure in the gap due to unskilled repair of the discharge cover.

Parametric study of the influence of location and extension height of the rod interceptor on jet engine nozzle characteristics

Modern aircraft need increased maneuverability to maintain a competitive position. One way to improve this characteristic is to use methods to adjust the thrust vectors of a jet engine nozzle. One method of controlling nozzle thrust is the use of nozzle interceptors devices of various shapes that extend into the nozzle channel and cause an uneven distribution of pressure along the walls of the channel. The extension of the rod interceptor near the critical section of the nozzle creates a greater lateral force than the extension of the rod near the exit section. The dependence of the lateral force on the extension height is nonlinear. The article presents a description of a nozzle interceptor of a cylindrical shape extended from the channel wall. Numerical simulation of gas flow in the nozzle with a cylindrical interceptor was carried out. The patterns of gas flow in the channel and in the environment outside the nozzle are presented. The plots of the lateral and axial components of the thrust force against the interceptor rod length are also presented for both cases of the rod location. Rod interceptors can be used in combination with other correcting devices.

Evolution law of comet-shaped defects in magnetorheological finishing.

Ultraprecision optical systems such as high-energy laser systems have very strict requirements for surface defects of optical components. Comet-shaped defects are common in magnetorheological finishing, which is one of the main ultraprecision manufacturing technologies. Computational fluid dynamics is used to simulate the pressure and velocity of the magnetorheological fluid in pits during magnetorheological finishing for the first time, to the best of our knowledge. The simulation model analyzes the distribution of velocity and pressure in the process of the formation of comet-shaped defects. After the simulation, magnetorheological polishing experiments were carried out on the fused quartz silica glass. The polishing experiments use the rotation speed and immersion depth of the polishing wheel to verify the velocity and pressure distribution in the simulation experiment. The polishing experiment results are consistent with the simulation results, which show that the high polishing speed will increase the depth of the defect, and the uneven velocity and pressure distribution at the pits make the pits evolve into comet-shaped defects. We explain the cause of comet-shaped defects from the perspective of material removal and provide an optimization method of process parameters for high-efficiency removal of comet-shaped defects.

Hydrofracture plugging mechanisms and evaluation methods during temporary plugging and diverting fracturing

AbstractTemporary plugging and diverting fracturing (TPDF) technique shows great advantages in stimulating unconventional oil and gas reserves. Revealing the fracture plugging mechanism and establishing the evaluation method are beneficial for revealing the mechanism of forming multiple fractures during TPDF. This work revealed the processes of plugging the fractures based on the typical injection pressure curve of hydraulic fracturing operation and then applied the stress cage model, the fracture closure stress model, and the fracture propagation resistance model to reveal the fracture plugging mechanisms. Moreover, this paper establishes a 2D XFEM model to evaluate the fracture plugging effect, and the reliability of the model is verified against the finite element model. Based on the XFEM model, this work investigates the fracture plugging effects influenced by the uneven distribution of net pressure within the fracture. The results prove that fracture mouth plugging of TPF mainly enhances the wellbore circumferential stress, in‐fracture plugging mainly enhances fracture closure pressure, fracture tip plugging mainly hinders fracturing fluids flowing toward fracture tips, all of them aim at enhancing the reopen pressure of the existing fractures and prevent the propagation of the existing fracture. Diverter bridging and plugging can change the distribution of fracture net pressure and dramatically reduce the fracture tip stress factor, and thus, the existing fracture propagation can be efficiently stopped.

Micro-spall damage and subsequent re-compaction of release melted lead under shock loading

Micro-spall is a large-area of liquid cavitation debris cloud formed near the free surface when metal melts during shocking or releasing process. We performed a molecular dynamics simulation to investigate the evolution of micro-spall and the related physical mechanism during the re-compaction process of a single crystal Pb by the second shock wave loading. The temperature and pressure obviously increase during re-compaction process. The ultra-high temperature-rise and local high pressure in the damage area is due to the collision between atoms and the collapse of voids. There is also one more pressure-rise and temperature-rise in the damage region, which is originated from the formation of high-speed internal micro jet and its striking on the back wall of large voids. Due to the uneven distribution of pressure and temperature after the 2nd shock wave passing through the micro spall damage region, the microstructures are also unevenly distributed. Besides, the damage region will swell due to the high temperature-rise during re-compaction process. Therefore, the micro-spall damaged region closed to the free surface is difficult to be compacted to dense state. Because that the voids in the damage region near the free surface are larger for the longer time interval, the temperature-rise originated from the collapse of voids is more severe. The wavefront plane is gradually broadened in the process of re-compaction.