Maximum Pressure Coefficient Research Articles

Investigating the influence of varying split injection profiles on stability of diesel engine operated under partially premixed mode with methanol

The present study explores the prospects of operational stability of dual fuel operation comprehensively, considering that; methanol and diesel are of two different kinds which exhibit different combustion processes. To this effect, investigating the stability of engine operation under such condition becomes important. In this investigation, the harshness of the operation and the non-repeatability of the combustion cycles are examined, which have been identified as the major stability indicator in many studies. Such stability indices are characterized in this study through a comprehensive set of parameters, including of maximum pressure rise rate (ROPRmax) and coefficient of variation of indicated mean effective pressure (COVIMEP); and of peak pressure (COVPP) and crank angle of 50% mass fraction burn (COVCA50). The experimental investigation is carried out under a split injection strategy by varying injection timings as well as injection mass percentages at predefined methanol injection durations. It is shown that the partially premixed mode under the split injection strategy exhibits significant potential in reducing the harshness of operation indicated by lower peak pressure rise and increasing the repeatability of the combustion cycles implied by the substantially lower scores of the considered parameters for mapping stability.

Experimental investigation of the wind loads on the solar parabolic trough collectors for structural stability

Solar parabolic trough collectors consist of reflectors that concentrate the solar radiation to the absorber tube located at its focal length. The shape accuracy of the reflectors is essential for the performance of the solar parabolic trough collectors. One of the important factors affecting the shape accuracy of the reflector is the wind load acting on the surface of the reflector. Hence, the pressure distribution study over the surface of the reflector is important, which influences the shape accuracy of the reflector. In the present study, wind tunnel tests are conducted to quantify the pressure distribution for different configurations of the solar parabolic trough. The test is conducted for the reflectors at 0°, 30°, 60°, −30° and −60° pitch angles, and 0°, 30°, 60° yaw angles for the wind speed of 5 ms−1. At 0° pitch angles, the fluctuating pressures are observed at either edge of the reflector, and 30° and 60° yaw angles result in higher pressure acting over the windward face for 5 ms−1 wind speed and the maximum pressure coefficients are observed to be located around the edges of the reflector and hence the stiffness of the reflectors must be increased at the edges.

Vibration characteristics of turbocharger rotor system considering internal thread texture parameters of semi-floating ring bearing

The internal thread texture causes changes in the dynamic characteristics of the oil film of the semi-floating ring bearing, which affects the amplitude of vibration and operating life of the turbocharger rotor system. Based on the fluid lubrication theory, the oil film governing equation of a semi-floating ring bearing with surface texture parameters is derived. The effects of the texture depth, position, and number of turns of the internal thread on the dynamic characteristics of the bearing oil film, such as the maximum pressure, load-carrying capacity and stiffness damping, are analyzed. Taking a type of turbocharger as an example, a hydrodynamic model is established to analyze the oil film lubrication in the semi-floating ring bearings, and the dynamic characteristic of the oil film is analyzed by computational fluid dynamics method. The results show that the maximum pressure, bearing capacity, and stiffness damping coefficient of oil film increase firstly and then decrease with the increase of texture depth and the number of thread turns in the range of journal rotation speed from 1000 to 20,0000 r/min. Compared with the non-texture bearings, the dynamic characteristics coefficients of the oil film such as bearing capacity and stiffness damping increase the most, when the depth of texture is 0.006 mm and the number of thread turns is 9. Secondly, the dynamic characteristic coefficient of oil film is improved when the texture is distributed in the middle than on both sides. The thread texture with appropriate parameters can suppress the rotor system vibration amplitude. The conclusion can provide a reference for the design of textual parameters of semi-floating ring bearings.

Numerical investigation of particles flow pattern and pressure distribution of coal bunker

Abstract The stable loading and operation of a coal bunker is critical for efficient production. In this study, the coal particle contact parameters were calibrated based on the angle of repose characteristics. The loading and discharging process of the coal bunker was simulated using the EDEM program. In addition, the flow pattern of the coal particles and the distribution characteristics of the wall pressure were investigated. The results indicate that the coal particles in the bunker can be divided into two flow patterns: mass flow and funnel flow. During discharging, the wall pressure fluctuated and exhibited a local over-pressure phenomenon, with a maximum pressure coefficient of 1.75. Finally, this study provides a reasonable explanation for the transformation of the flow pattern of coal particles and the distribution characteristics of wall pressure based on the mechanism of pressure arch influence. The findings of this study can provide theoretical guidance for designing coal bunker structures.

Three-Dimensional Analysis of Load Transfer Mechanism for Deep Cement Mixing Piled Embankment under Static and Cyclic Load

Piles have been widely used to improve the bearing capacity of the soft foundation. The existing research obtains significant findings on the load transfer mechanism for rigid piled embankments. However, limited studies have been focused on the deep cement mixing (DCM) piled embankment. To grasp the load transfer characteristics of DCM piled embankments, a three-dimensional numerical simulation was conducted in this study, which was validated by the measurements from the field case. It was found that the effect of soil arching was reduced compared with the rigid piled embankment. This induced approximately 61.5% larger vertical stress transferred to the subsoil surface and approximately 83–150% larger settlement of the embankment in DCM piled foundation system. To further understand the working mechanism of this system, the factors which influence the load transfer mechanism were investigated. It is found that the area replacement ratio is the most influential factor affecting the settlement at the top of the embankment, whereas the elastic modulus of the DCM pile influences most the vertical stress and the earth pressure coefficient. The cyclic load with vehicle speeds of 90 km/h will lead to approximately 34% growth of embankment settlement and about 11% reduction in the maximum earth pressure coefficient. Based on the numerical simulation results, the analytical equation of the normalized vertical stress acting on the subsoil surface for the DCM piled foundation was proposed and validated by two field cases, with the difference in the range of 13.8~16.7%.

Numerical investigation of the effect of blade distortion laws on the corner flow separation of the axial-flow fan

To study the effect on performance of different blade distortion laws of axial flow fans, the radial distributions of blade stagger angle were fit as Bézier curves, and five distribution laws were established. Three-dimensional numerical simulations were carried out for the fan schemes. The results show that distortion near the blade root can effectively restrain the corner separation vortex from climbing along the blade suction surface, so that the low-energy fluid accumulates in the corner region. Tip distortion rises the pressure difference between the pressure and the suction surface, and the turbulence intensity of the tip leakage is increased. Root distortion inhibits the CV diffusion, resulting the decay of tip leakage vortex, thereby improving the stall margin. Relative to a uniform distortion blade, the blade-root distortion scheme increases the radial load of the blade, while the tip distortion scheme results in a decrease of the blade load coefficient. The maximum load position of the end-zone distorted blade moves to the root area, while the maximum load position of the middle distorted blade shifts to the tip area. The end-zone distortion improves the efficiency and total pressure of the fan without changing the efficient working range, and is considered to be the optimal scheme. The maximum pressure coefficient of the end-zone distortion scheme is increased by 4.97% and the maximum efficiency is increased by 1.28%.

Direct Numerical Simulations of Turbulent Flow over Low-Pressure Turbine Blades with Aeroelastic Vibrations and Inflow Wakes

In the present work, direct numerical simulation is employed to investigate the unsteady flow characteristics and energy performance of low-pressure turbines (LPT) by considering the blades aeroelastic vibrations and inflow wakes. The effects of inflow disturbance (0 < φ < 0.91) and reduced blade vibration (0 < f < 250 Hz) on the turbulent flow behavior of LPTs are investigated for the first time. The transient governing equations on the vibrating blades are modelled by the high-order spectral/hp element method. The results revealed that by increasing the inflow disturbances, the separated bubbles tend to shrink, which has a noticeable influence on the pressure in the downstream region. The maximum wake loss value is reduced by 16.4% by increasing the φ from 0.31 to 0.91. The flow separation is majorly affected by inflow wakes and blade vibrations. The results revealed that the maximum pressure coefficient in the separated flow region of the vibrating blade has been increased by 108% by raising φ from 0 to 0.91. The blade vibration further intensifies the vortex generation process, adding more energy to the flow and the downstream vortex shedding. The vortex generation and shedding are intensified on the vibrating blade compared to the non-vibrating one that is subject to inflow wakes. The results and findings from this paper are also useful for the design and modeling of turbine blades that are prone to aeroelastic instabilities, such as large offshore wind turbine blades.

Overpressure characteristics and geological origin of the paleogene in Baiyun Sag, Pearl River Mouth Basin

The accurate understanding of the origin of overpressure is the basis of formation pressure research and the core work of determining the distribution of formation pore pressure in drilling design. The deep water area of Baiyun Sag in the Pearl River Mouth Basin in the northern margin of the South China Sea has been proved to be a hydrocarbon rich depression. In recent years, overpressure has been encountered in the middle and deep layers, but the geological origin of the overpressure in the deep water area are still unclear. Therefore, the pore pressure profile of the Baiyun Sag was evaluated using the data of drilling and seismic velocity, and the relationship between overpressure and the generation mechanism was established. Most of the surrounding and shallow strata of Baiyun Sag show normal pressure, while the middle and deep strata generally show overpressure, with the maximum pressure coefficient up to 1.55. The overpressure zone mainly develops from the middle of Zhujiang Formation to the upper member of Enping Formation. The mudstone resistivity and density values of the two typical Wells deviated from the normal trend. The density showed a constant trend with the increase of depth, while the resistivity showed a certain degree of reversal. The upper layer of the overpressure zone showed abnormally high resistivity values, corresponding to the overgland and transition zone formed by high carbonate content. There is no obvious increase of porosity in the overpressured sandstone strata of Baiyun sag, which does not have the characteristics of undercompaction. The velocity in the overpressure section of the two Wells varies greatly, and the density is basically unchanged or slightly decreased. It is concluded that the overpressure is caused by fluid expansion from hydrocarbon-generation. The large-scale and long-term fluid expansion caused by hydrocarbon generation and expulsion of source rocks provides the power source for the formation of overpressure in Baiyun sag. The distribution of effective source rocks has a controlling effect on the distribution range of overpressure. The tight sandstone strata in the Zhuhai, Wenchang and Enping formations become the cover layer of the overpressure system in the longitudinal direction.

Effects of Interference of Hill on Wind Flow around Tall Buildings Situated in Hilly Region Using CFD

Abstract: The location of tall building in complex region, wind is the powerful factor exerted on tall buildings. This pressure has a direct affected on the drag force. The drag force has a significant impact on the building's surface. All the faces of a tall building's drag force or maximum pressure coefficient have generally been measured through wind tunnel experiments. It's difficult and costly, but it's the best option. Computational Fluid Dynamics (CFD) has been used in this study to determine the external pressure coefficient on the front and back sides of a tall building in the presence of hill interference in complex region. In addition, the current research investigates the behaviour of wind flow around tall buildings at different location of hill first scenario the top of a hill, second scenario the front and third scenario back zones of a hill, and the interactions between tall buildings and the hill itself

Aerodynamic characteristics of a train on a long-span bridge with steel truss section under crosswinds

An experimental-numerical methodology was performed to investigate the aerodynamic characteristics of train vehicles on a truss bridge under crosswinds and the flow field around. Taking a long-span cable-stayed bridge with three main trusses as the engineering background, a wind tunnel test was carried out on a 1:80 scale model under different deck cross-section shapes, vehicle positions, and wind-attack angles. A three-dimensional CFD model was further established to explore the distribution of the flow speed inside the complex truss structure. The results show that when the train moves from the box deck to the truss deck, both the mean and RMS values of the pressure coefficients on the vehicle surface are greatly reduced. The maximum surface pressure coefficient occur when the vehicle is located at the track just behind the middle truss plane. The flow field inside the three-main-truss structure is notably uneven. The average equivalent wind speed is much lower than the oncoming crosswind speed. However, the maximum crosswind reduction coefficient reaches 0.92 occurring near the triangle center of the leeward truss panel. In addition, higher winds occur at 0.25 times the truss height above each track, which is consistent with the height of the center of the vehicle body.

Study on Wind Load Characteristics and Wind-Induced Response of Supertall Buildings with Single-Sided Large-Span Straight Platforms

The presence of large-span straight platforms can complicate the airflow around buildings and alter surface wind pressure, gas bypass and wind response in supertall buildings. The article uses the Reynolds-averaged Navier–Stokes (RANS) method in Computational Fluid Dynamics (CFD) to investigate the differences in surface mean wind pressure, gas bypass, wind coefficients, displacement and acceleration responses between the models with and without platforms, and the wind load on the platforms themselves at different wind directions. The results show that: the presence of platforms generally reduces the maximum negative pressure coefficient on the building surface, reaching a maximum reduction of 31.56% at 30°, and causes a small increase in the maximum positive pressure coefficient, reaching a maximum increase of 5.30% at 0°. The mean wind pressure on the lower surface of the platform is greater than the upper surface. The target building has a lower frequency of vortex shedding than the reference model, with a maximum reduction of 5.68%. The presence of platforms increases the vertex displacement of the building by up to 22.85% and decreases the vertex acceleration by up to 9.14%. These results can be used as references for the ventilation, comfort and safety assessment of similar supertall buildings.

Experimental Investigation of Wind Loads on Roof-Mounted Solar Arrays

An experimental study was conducted to investigate the aerodynamic loads on roof-mounted solar arrays. Four different parapet heights of 0 m, 0.9 m, 1.2 m, 1.5 m, and two tilt angles of 5° and 10°, are set to examine their effects on wind pressure coefficients. The statistics (means, standard deviations, skewness, kurtosis, maximum and minimum peaks) of wind pressure coefficients in different wind directions are exhibited and discussed in the current study. The results show that the oblique wind directions are critical for most measured locations, as the extreme of maximum and minimum peak pressure coefficients occur. The parapet can decrease wind loads on solar arrays, as expected. However, as the parapet is within a limited height in practice, it is not quite efficient to decrease wind loads despite the increasing of the parapet height. When the solar arrays are installed on the roof almost horizontally (tilt angle is less than 10°), the statistics of the aerodynamic load change a little with the decreasing of the tilt angle.

Multi-Objective Optimization for the Radial Bending and Twisting Law of Axial Fan Blades

The performance of low-pressure axial flow fans is directly affected by the three-dimensional bending and twisting of the blades. A new blade design method is adopted in this work, where the radial distribution of blade angle and blade bending angle is composed of standard-form rational quadratic Bézier curves. Dendrite Net is then trained to predict the pneumatic performance of the fan. A non dominated sorting genetic algorithm is employed to solve the global optimization problem of the total pressure coefficient and efficiency. The simulation results show that the optimal blade load distribution along the radial direction becomes uniform, and the suction surface separation vortex and passage vortex are restrained. On the other hand, the tip leakage vortex is enhanced and moves toward the blade leading edge. According to the experimental results, the maximum efficiency increases by 5.44%, and the maximum total pressure coefficient increases by 2.47% after optimization.

A Numerical Study of a Submerged Water Jet Impinging on a Stationary Wall

The impinging jet is a classical flow model with relatively simple geometric boundary conditions, and it is widely used in marine engineering. In recent years, scholars have conducted more and more fundamental studies on impact jets, but most of the classical turbulence models are used in numerical simulations, and the accuracy of their calculation results is still a problem in regions with large changes in velocity gradients such as the impact zone. In order to study the complex flow characteristics of the water flow under the condition of a submerged jet impacting a stationary wall, the Wray–Agarwal turbulence model was chosen for the Computational Fluid Dynamics (CFD) numerical simulation study of the impacting jet. Continuous jets with different Reynolds numbers and different impact heights H/D were used to impact the stationary wall, and the results show that the jet flow structure depends on the impact height and is relatively independent of the Reynolds number. With the increase in the impact height, the diffusion of the jet reaching the impact area gradually increases, and its velocity gradually decreases. As the impact height increases, the maximum pressure coefficient decreases and the rate of decrease increases gradually, and the dimensionless pressure distribution is almost constant. In this paper, the flow field structure and pressure characteristics of a continuous submerged jet impacting a stationary wall are explored in depth, which is of great guidance to engineering practice.

Retracted: “Characterization of the stability indices of a methanol induced partially premixed diesel dual fuel operation under varying split injection profiles: An experimental endeavour”

Abstract The present investigation attempts to explore the prospects of the engine operational stability of a methanol induced partially premixed dual fuel operation under split injection strategy operating on a conventional single cylinder diesel engine coupled with a dedicated CRDI. The operation of such LTC regimes often deals with the stability concerns which are primarily characterized as the harshness of the operations and the non-repeatability of the combustion cycles. These two markers of operational stability have been mapped in this study through a comprehensive set of metrics of maximum pressure rise rate (ROPRmax) and Coefficient of Variation of Indicated Mean Effective Pressure (COVIMEP), Peak Pressure (COVPP) and Crank Angle of 50% mass fraction burn (COVCA50). The parametric investigation has been carried out at three different injection timings and pilot mass percentages at predefined methanol injection durations. The results have shown tremendous reductions in the non-repeatability of the combustion cycles and the harshness of the engine operation under split injection strategy, indicated by the lower scores of the stability indicators in comparison to the baseline single injection operation. Subsequently, the lowest scores of the maximum pressure rise rate and the Coefficient of Variation of indicated mean effective pressure, peak pressure and CA50 for the entire scope of investigation were registered as 0.62bar/CA, 0.75%, 0.48% and 1%, which were apparently observed as 65.5%, 86.36%, 94% and 53% lower than the corresponding scores registered in the baseline single injection operation.

ANALYSIS OF THE WATER IMPACT OF SYMMETRIC WEDGES WITH A MULTI- MATERIAL EULERIAN FORMULATION


 
 
 The two-dimensional hydrodynamic problem of a symmetric wedge vertically impacting in calm water is analysed by using an explicit finite element method based on a multi-material Eulerian formulation. The slam-induced loads on wedges with different deadrise angle at a constant velocity are calculated, including pressure distribution, maximum pressure coefficient, force coefficient and time history of vertical force, which are compared with available theoretical and analytical results. The time evolution of pressure distribution and free surface elevation are presented. Furthermore, the effects of impact velocity are investigated. It shows that this method is capable of predicting the local slamming loads, and as well assessing the effects of the deadrise angle and the impact velocity on the slamming pressure for the wedge-shape section.
 
 

Large deformation characteristics and controlling measures of steeply inclined and layered soft rock of tunnels in plate suture zones

To clarify the inducing factors and mechanisms of geological disasters, such as large deformation and tunnel collapse, tunnels with layered and soft rock in the Luang Prabang suture zone were examined in this paper. Based on an investigation and summary of the disaster characteristics of tunnel deformation, the excavation loosening zone and geo-stress conditions were field-tested by using a sonic detector and a hollow inclusion strain gauge to analyse the correlation between the surrounding rock deformation and the extent of the excavation loosening zone and geostress distribution. The results show that, influenced by the Luang Prabang geological suture zone, underground water and the mechanical characteristics and occurrence of the rock mass, the surrounding rock mass deformation presents obvious asymmetric features. A large deformation of the rock mass more easily occurs at the tunnel crown and right spandrel (waist), and the main deformation phenomena are the spalling and cracking of shotcrete, buckling and bending of the steel arch and large horizontal convergent deformation. According to the sonic velocity monitoring of the rock mass, the scope of the excavation loosening zone of the rock mass is approximately 5.5 m to 7 m, which is beyond 60% of the tunnel width. Based on the field geostress test, the tunnels in plate suture zones bear intensively horizontal tectonic action, and the maximum lateral pressure coefficient of three tunnels is more than 1.5 (σ1/σ3). Thus, the horizontal convergence deformation and supporting structure failure of the tunnel are serious. Some controlling measures were adopted to release and control rock mass deformation, such as improving the advance support structure, enhancing the steel arch strength and increasing the allowed deformation of the rock mass. Moreover, asymmetric support design, such as local borehole grouting and temporary horizontal support structures, also be implemented. Additionally, the optimal design of rock bolt installation and grouting reinforcement depth should be given more attention during tunnelling.

The constraint of deep rock stresses in H underground gas storage based on a modified stress polygon and focal mechanism solution

H underground gas storage (H-UGS), located in the junction of the southern margin of the Junggar Basin and the eastern part of the northern Tianshan Mountains, is one of the large natural gas storage in China. It is of significance to study the deep rock stresses in H-UGS for fault slip tendency, safe storage of energy and other research. Most of the regional stress information in H-UGS data from in-suit measurements lacks deep in-suit stress data in this region. This research proposes a hybrid constrain stress magnitudes present in deep rock masses. First, the fault friction strength, an essential parameter of lateral pressure coefficient polygon, is established by the stress accumulation index method and apparent friction strength evaluation method. Second, we inverse the stress factor R from the focal mechanism solutions in this area, and the lateral pressure coefficient polygon is qualified quadratic to narrow down the range of results by this parameter. Finally, the complete stress profile of H-UGS is obtained by using the simple transition relationship between lateral pressure coefficient and in-situ stress. The result shows that the principal compressive stress of the H-UGS region is determined by the N22°E, the maximum lateral pressure coefficient K max (or S H) at three depths (3.0km, 6.5km, and 12.0km ) are 1.2 (80.22 MPa), 1.22 (202.72 MPa), 1.28 (421.34 MPa) respectively, and the minimum lateral pressure coefficient K min (or S h) are 0.87 (58.21 MPa), 0.86 (142.12 MPa), 0.86 (282.61 MPa) respectively. The result is primarily consistent with in-situ measurement from the depth of 3.0km to 3.7km. The maximum horizontal principal stress and the minimum coincidence ratio are 54% and 69%. The result of estimating deep rock stresses established in this research provides sufficient regional stress field data in H-UGS.

Wind tunnel test on mean wind forces and peak pressure acting on ellipsoidal nacelles of wind turbine

Mean wind forces and peak pressures acting on ellipsoidal nacelles are investigated by wind tunnel tests. The wind force coefficients of the ellipsoidal nacelles for the wind turbine design and the peak pressure coefficients for the nacelle cover design are proposed based on the experimental data. The wind force coefficients are expressed as functions of yaw angles. The proposed formulas are compared with Eurocode, Germanischer Lloyd and ASCE7-16. It is found that the mean wind force coefficients for the wind turbine nacelles are slightly underestimated in Eurocode. The equivalent maximum and minimum mean pressure coefficients are proposed for use in Design Load Case 6.1 and Design Load Case 6.2 of IEC 61400-1. The peak pressure coefficients are derived using a quasi-steady theory. The proposed equivalent maximum and minimum mean pressure coefficients are much larger than those specified in Germanischer Lloyd.

Multipoint Synchronous Monitoring of Cladding Pressures on a 600-m-High Skyscraper during Super Typhoon Mangkhut 2018

This paper analyzes the wind pressures on the claddings of a 600-m-high skyscraper in Shenzhen, China, during Super Typhoon Mangkhut on September 16, 2018. A synchronous monitoring system that included 48 pressure transducers was implemented to measure the cladding pressures of the skyscraper during the typhoon event. Based on field measurements, the mean, root-mean-square fluctuating, peak (maximum and minimum) pressure coefficients are presented and discussed. Then the mean and peak pressure coefficients are used to validate the design values stipulated in the design code of China. Comparative study finds that the design values of the peak pressure coefficients on the windward and leeward faces of the skyscraper are conservative, while those on the side faces are nonconservative. As for the mean pressure coefficients, the design values are conservative for all faces. Moreover, the non-Gaussian characteristics, power spectral densities, coherences, and correlations of the measured cladding pressures are analyzed to explore the mechanisms of pressure fluctuations on the four sides of the skyscraper. This paper aims to enhance understanding of cladding pressures of high-rise buildings under extreme wind conditions and, therefore, to provide useful information for future designs of wind-resistant skyscrapers in tropical cyclone–prone regions.