Investigation on fracture models and ground pressure distribution of thick hard rock strata including weak interlayer

Dynamic disasters,such as rock burst due to the breaking of large area stiff roof strata,are known to occur in the hard rock strata of coal mines.In this paper,mechanical models of the fracturing processes of thick hard rock strata were established based on the thick plate theory and numerical simulations.The results demonstrated that,based on the fracture characteristics of the thick hard rock strata,four fracture models could be analyzed in detail,and the corresponding theoretical failure criteria were determined in detail.In addition,the influence of weak interlayer position on the fracture models and ground pressure of rock strata is deeply analyzed,and six numerical simulation schemes have been implemented.The results showed that the working face pressure caused by the independent movement of the lower layer is relatively low.The different fracture type of the thick hard rock strata had different demands on the working resistance of the hydraulic powered supports.The working resistance of the hydraulic powered supports required by the stratified movements was lower than that of the non-stratified movements.

Calculation methods of lubricant film pressure distribution of radial grooved thrust bearings

In order to calculate the pressure distribution of radial grooved thrust bearing,analytical and numerical methods were applied respectively.Grooved region and land region were linked by using the mass conservations principle at the groove/land boundary in each method.The block-weight approach was implemented to deal with the non-coincidence of mesh and radial groove pattern in numerical method.It was observed that the numerical solutions had higher precision as mesh number exceed 70×70,and the relaxation iteration of differential scheme presented the fastest convergence speed when relaxation factor was close to 1.94.

Pressure distribution of combining center cavity slipper for axial piston pump

In order to improve lubricating characteristics of slippers in an axial piston pump,the combining center cavity slipper approach was proposed based on slipper shape and moving characteristic.The cylindrical coordinate was used in the lubricant area and mesh was made.The block-weight approach was implemented to deal with non-coincidence of mesh and shallow recess border in numerical method.The finite control volume method was applied in calculating pressure distribution.The flow conservation equation and film thickness model were resolved through Gauss-Siedel relaxation iteration.The calculation and analysis results indicate that compared to the slipper1 slipper pressure distribution is improved;2 hydrodynamic pressure of the combining slipper is greatly increased;3 inclining degree is greatly reduced;4 negative pressure in lubricant film disappear.So the combining center cavity slipper is lubricated better.

An Experimental Study on the Pressure Distribution in Horizontal Gas Wells

Laboratory experiments have been carried out to study the fluid flow in the wellbore of a horizontal gas well during the production process.The related pressure distribution has been determined considering different cases(different inflow media,different perforation opening methods and different liquid holdup).It has been found that the larger the fluid flow rate,the greater the pressure changes in the wellbore under the same hole opening mode.The uniformity of the perforation opening method was also an important factor affecting the magnitude of the wellbore pressure change.The liquid holdup also affected the pressure distribution,especially when the gas volumetric flow rate exceeded 200 m3/h.Comparison of the outcomes of the present experimental study with the predictions of a theoretical model available in the literature has provided a relative error smaller than 20%.

Textile-Based Capacitive Pressure Distribution Measurement System for Human Sitting Posture Monitoring

Flexible pressure monitoring device can help correct the sitting posture and prevent health problems(e.g.,deformity of spinal column and musculoskeletal disease).Currently,most measurement systems hinder their wide applications owing to the high cost or low accuracy.In this study,a flexible sitting pressure measurement system was proposed based on a textile-based capacitive pressure sensor array in order to measure sitting pressure distribution simply and conveniently.The capacitive pressure sensor array is sandwich structure composed of a high-density sponge layer and two electrode array fabrics,which possesses high resolution(2.26 sensors/cm2),high sensitivity(0.701 kPa-1)and fast response(≤35 ms).It is worth noting that the raw materials of the sensing fabric include commercialized copper sheets and polyester yarns.The as-prepared pressure measurement system can accurately measure the pressure distribution nephogram for sitting posture analysis.The sitting pressure of 10 volunteers was measured and six types of posture were distinguished clearly.

The meshless Galerkin method for pressure distribution simulation of horizontal well reservoir

This paper provides a novel three-dimensional meshless Galerkin for horizontal well reservoir simulation.The pressure function is approached by moving least-square method which consists of weight function,basic function and coefficient.Based on Galerkin principle and use penalty function method,the paper deduces the meshless Galerkin numerical linear equations.Cut off the pressure distribution of the horizontal section from the simulation database of horizontal well reservoir.It demonstrates that meshless Galerkin is a feasible numerical method for the horizontal well reservoir simulation.It is useful to research complex reservoir.

Pressure distribution feature-oriented sampling for statistical analysis of supercritical airfoil aerodynamics

In the field of supercritical wing design, various principles and rules have been summarized through theoretical and experimental analyses. Compared with black-box relationships between geometry parameters and performances, quantitative physical laws about pressure distributions and performances are clearer and more beneficial to designers. With the advancement of computational fluid dynamics and computational intelligence, discovering new rules through statistical analysis on computers has become increasingly attractive and affordable. This paper proposes a novel sampling method for the statistical study on pressure distribution features and performances, so that new physical laws can be revealed. It utilizes an adaptive sampling algorithm, of which the criteria are developed based on Kullback–Leibler divergence and Euclidean distance.In this paper, the proposed method is employed to generate airfoil samples to study the relationships between the supercritical pressure distribution features and the drag divergence Mach number as well as the drag creep characteristic. Compared with conventional sampling methods, the proposed method can efficiently distribute samples in the pressure distribution feature space rather than directly sampling airfoil geometry parameters. The corresponding geometry parameters are searched and found under constraints, so that supercritical airfoil samples that are well distributed in the pressure distribution space are obtained. These samples allow statistical studies to obtain more reliable and universal aerodynamic rules that can be applied to supercritical airfoil designs.

Pressure Distribution of the Gaseous Flow in Microchannel:A Lattice Boltzmann Study

In this paper the pressure distribution of the gaseous flow in a microchannel is studied via a lattice Boltzmann equation(LBE)method.With effective relaxation times and a generalized second order slip boundary condition,the LBE can be used to simulate rarefied gas flows from slip to transition regimes.The Knudsen minimum phenomena of mass flow rate in the pressure driven flow is also investigated.The effects of Knudsen number(rarefaction effect),pressure ratio and aspect ratio(compression effect)on the pressure distribution are analyzed.It is found the rarefaction effect tends to the curvature of the nonlinear pressure distribution,while the compression effect tends to enhance its nonlinearity.The combined effects lead to a local minimum of the pressure deviation.Furthermore,it is also found that the relationship between the pressure deviation and the aspect ratio follows a pow-law.

Study on Pressure Coefficient Distribution of the Airship Zhiyuan-1

A wind tunnel tests with different configurations,pitch and yaw angles were performed to study the wind load characteristics of the rigid model of the airship Zhiyuan-1. The rigid model was aimed to simulate a technical demonstrating stratospheric airship named Zhiyuan-1 according to the similarity principle of geometric and Reynolds number. Based on the results of wind tunnel test,the features of pressure coefficient distributions on the surface of the airship were described. It was indicated that the fins and the gondola of airship hardly have the effect on the pressure distribution on the surface of airship,but have obviously effect on the local areas near the fins and the gondola.

Wellbore Cleaning Degree and Hydraulic Extension in Shale Oil Horizontal Wells

The efficient development and exploitation of shale oil depends on long-distance horizontal wells. As the degreeof cleaning of the wellbore plays a key role in these processes, in this study, this problem is investigated experimentallyby focusing on the dimensionless cuttings bed height. A method is proposed to calculate the horizontalwellhydraulic extension taking into account the influence of the wellbore cleaning degree on the wellborepressure distribution and assess the effect of a variety of factors such as the bottom hole pressure, the circulatingpressure drop, the drilling pump performance and the formation properties. The analysis shows that the hydraulicextension of horizontal wells decreases with an increase in the cuttings bed height, and the higher the displacementof drilling fluid, the faster the hydraulic extension declines. The annular pressure drop of the horizontalsection increases with the increase of the cuttings bed height, resulting in a higher bottom-hole pressure. Severalarguments are provided to guide the safe drilling of shale oil horizontal wells and overcome the limits of currenttechnological approaches.

A Mathematical Model and a Method for the Calculation of the Downhole Pressure in Composite-Perforation Technological Processes

Using the conservation equations for mass,momentum and energy,a model is elaborated to describe the dynamics of high-energy gases in composite-perforation technological processes.The model includes a precise representation of the gunpowder combustion and related killing fluid displacement.Through numerical solution of such equations,the pressure distribution of the high-energy gas in fractures is obtained,and used to determine crack propagation.The accuracy of the model is verified by comparing the simulation results with actual measurements.

Integration of measurement and simulation of film pressure for estimating deformation of a glass sheet on a noncontact air conveyor

Recently,large and thin glass substrates are transported by air film conveyors to reduce surface damage.On the production line,the glass substrates are desired to be transported flatly on the conveyor to ensure the quality inspection.A method by feedbacking film pressure to the theoretical model is proposed for estimation of the deformation of the glass sheet,and the validity of the method is theoretically and experimentally verified.First,a theoretical model including the flow behavior through a porous-walled gap is established,and the film pressure distribution can be predicted by solving the model.Then,an experimental setup that can simultaneously measure the film pressure and the flatness of the glass sheet is established,and,the validity of the model is verified experimentally.Next,with the pressure points at the grooves as the boundary and the pressure points at the flange area as the feedback,an algorithm is applied to shape the one-dimensional deformation at the centerlines in accordance with a quadratic curve.Furthermore,two-dimensional deformation of the glass sheet can then be estimated by an interpolation operation.Comparisons of the calculated results with the experimental data verify the effectiveness of the estimating method.

Application of engineered compressible inclusions to mitigating soilstructure interaction issues in integral bridge abutments

The thermally induced cyclic loading on integral bridge abutments causes soil deformation and lateral stress ratcheting behind the abutment wall due to the expansion and contraction of the bridge deck.The forward and backward movements of the abutment in response to the expansion/contraction of the bridge deck lead to the formation of settlement trough and surface heaving,frequently creating a bump at the bridge approach and increasing the lateral earth pressure behind the abutment.Measures to reduce the bump at the bridge approach,including several treatment methods,such as compaction of selected backfill materials,grout injection,installation of approach slab,and using a layer of compressible inclusion material behind the abutment were proposed.However,these guidelines still lack sufficient design details and there are limited experimental findings to validate design assumptions.In this paper,the use of engineered compressible materials to alleviate the lateral earth pressure ratcheting and settlement at the bridge approach is investigated.The comparative study is presented for the soil-inclusion,material-structure and soil-structure interactions for an integral bridge under three different backfill conditions,i.e.(a)sand,(b)sand and EPS geofoam,and(c)sand and Infinergy®.The study was conducted in a special large-scale test chamber with a semi-scale abutment to gain better insights into the soil-structure interaction(SSI).The kinematics and rearrangement of the soil during the cyclic loading have been investigated to identify the mitigating effects of compressible inclusions.The comparative study indicates that both compressible inclusions perform comparatively well,however,Infinergy®is a better alternative than the medium-density EPS geofoam,as it works more effectively to reduce the backfill settlement and heaving as well as soil ratcheting effects under cyclic translational movement.

HYBRID AIRFOIL DESIGN FOR FULL-SCALE ICE ACCRETION TEST

A hybrid airfoil inverse design method according to the target pressure distribution and the impingement efficiency is presented.The method is developed to design hybrid airfoils that simulate the droplet impingement and ice accretion of full-scale airfoil.Flow field and droplet impingement around the full-scale airfoil are calculated to obtain pressure distribution and impingement efficiency firstly.The Navier-Strokes(N-S)solver is used in flow field calculation to improve calculation precision.The droplet impingement and ice accretion on the airfoil are performed by FENSAP-ICE.Once the target chord or original airfoil is given,the hybrid airfoil geometries can be computed.The designed hybrid airfoil consists of full-scale leading edges and redesigned aft-section.The hybrid airfoil can be tested under full-scale conditions to produce full-scale ice accretion in the exiting icing tunnels which are too small to perform ice accretion testing of full-scale airfoils.Moreover,the ice shapes formed on the full-scale and hybrid airfoils are compared at various attack angles.The results demonstrate that ice shapes between hybrid and full-scale airfoils match well and the developed method is effective.

Incremental Static Analysis of 2D Flow by Inter-Colliding Point-Particles and Use of Incompressible Rhombic Element

A simple method is proposed, for incremental static analysis of a set of inter-colliding particles, simulating 2D flow. Within each step of proposed algorithm, the particles perform small displacements, proportional to the out-of-balance forces, acting on them. Numerical experiments show that if the liquid is confined within boundaries of a set of inter-communicating vessels, then the proposed method converges to a final equilibrium state. This incremental static analysis approximates dynamic behavior with strong damping and can provide information, as a first approximation to 2D movement of a liquid. In the initial arrangement of particles, a rhombic element is proposed, which assures satisfactory incompressibility of the fluid. Based on the proposed algorithm, a simple and short computer program (a “pocket” program) has been developed, with only about 120 Fortran instructions. This program is first applied to an amount of liquid, contained in a single vessel. A coarse and refined discretization is tried. In final equilibrium state of liquid, the distribution on hydro-static pressure on vessel boundaries, obtained by proposed computational model, is found in satisfactory approximation with corresponding theoretical data. Then, an opening is formed, at the bottom of a vertical boundary of initial vessel, and the liquid is allowed to flow gradually to an adjacent vessel. Almost whole amount of liquid is transferred, from first to second vessel, except of few drops-particles, which remain, in equilibrium, at the bottom of initial vessel. In the final equilibrium state of liquid, in the second vessel, the free surface level of the liquid confirms that the proposed rhombing element assures a satisfactory incompressibility of the fluid.

Numerical Simulation on the Impact of A Liquid Square on Rigid Plate and Liquid Layer

Fluids and structures impact is one of the common phenomena in nature, and it widely exists in engineering practice,including ship hydrodynamic slamming, wave impact on offshore platforms, plunging wave on coastal structures,emergency landing of aircrafts at sea as well as impact of ultra-cold droplets and ice lumps under aviation conditions.In this paper, a two dimensional (2-D) solver for Navier-Stokes equations is developed and applied in the numerical simulation of the impact on a rigid plate by a liquid square. The computational domain is discretized by Finite Volume Method (FVM). The Volume of Fluid (VOF) technique is used to track the free surface and the PiecewiseLinear Interface Construction (PLIC) is used for reconstruction. The Continuum Surface Force (CSF) model is used to account for the surface tension. The convective term and the diffusive term are upwind and centrally differenced respectively. The Inner Doubly Iterative Efficient Algorithm for Linked Equations (IDEAL) is used to decouple the pressure and velocity. Based on the proposed techniques, collapse of water column is simulated and convergence study is performed for the validation of the numerical solver. Then the impact of a free falling liquid body is simulated, and the effect of volume and initial height of the liquid body is analyzed. In addition, the impact on a plate with a liquid layer is also simulated to study the effect of falling height on a liquid floor.

A Numerical Investigation on the Characteristics of the Radial Force in a Cycloid Gerotor Pump

In order to improve the performances of a cycloid gerotor pump,the variations of the radial force induced by different rotating speeds and outlet pressures are analyzed numerically.Using the numerical simulations as a basis,an improved oil inlet and outlet groove structure is proposed.The results show that the radial force decreases with the decrease of the outlet pressure and of the rotor speed.Compared with the original model,the large-end oil inlet line and pressure line of the new oil groove are claw-shaped.This configuration can effectively weaken the pressure changes inside the gerotor pump and reduce accordingly the radial force on the inner rotor.

Spatial distribution model of the filling and diffusion pressure of synchronous grouting in a quasi-rectangular shield and its experimental verification

Considering that the particular geometric shape of a quasi-rectangular shield,the grout flowing law and its motion process are more complicated than those of a conventional circular shield.To interpret the grouting mechanical ehaviour in the special-shape shield tail void,the filling and diffusion mechanism of synchronous grouting was analysed.The grout flowing is separated into two independent motion processes,which contains a circumferential filling and a longitudinal diffusion.The theoretical model of the grout pressure spatial distribution was derived based on the principle of fluid mechanics.Then,the pressure distributions in the two directions were obtained using a case study and compared with the field measured data to verify the validation of the model.Although the overall spatial pattern of grout pressure distribution on the tunnel profile show a change trend dominated by the self-weight effect mostly,its local fluctuation characteristics is very abnormal relative to that of a circular shield tunnel.Moreover,the important factors in the model were analysed,including the grout material parameters,the grouting construction parameters,and some geometry parameters.The results show that the pressure loss along this way is positively correlated with the grout flow velocity and is sensitive to the shear yield stress of the grout.The pressure loss along the circumferential direction is the most sensitive to the thickness of the ring cake,and the value range suitable for the model should be 0.02-0.03 m.The pressure loss along the longitudinal diffusion direction is the most sensitive to the size of the tail void.The research results can provide a theoretical basis for the control of special-shape shield construction.

Research on the comfort degradation mechanism of high-speed railway passengers:a field study using dynamic interface pressure

Discomfort caused by long-term sitting decreases the passenger experience and may lead to musculoskeletal diseases, and this hasbecome one of the main problems for passengers of high-speed railways. However, the comfort degradation mechanism during longtermsitting in high-speed railways is still unknown. This study aimed to reveal passengers’ sitting comfort degradation mechanismin high-speed railways. By carrying out long-term sitting tests on high-speed trains running on the Shanghai-Kunming line, the dynamicinterface pressure and subjective comfort including overall and regional comfort of seven participants were obtained.Machinelearning models and statistical analysis methods were combined for data analysis to reveal the effect of regional comfort and thecontribution of sitting duration during the process of sitting comfort degradation. The results show that overall comfort is most significantlyinfluenced by the comfort of the shoulders, waist and buttocks. The seats play different roles before and after 20 minutesduring long-term sitting and there is a lag between the fatigue occurring and being offset. Therefore, the structure of seats affectsoverall comfort by affecting important regional comfort, and a long-term sitting test is necessary for accurate seat assessment. Thecomfort degradation mechanism can be used to define standards for long-term sitting comfort or provide guidance for seat evaluation,and the design and evaluation plan mentioned in this article for second-class seats can be applied to other cases with limitedaccommodating space.