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Existing mathematical models for deflector jet hydraulic amplifiers cannot accurately describe the influence of the deflector motion on the receiver jet, which results in calculation differences for the receiver pressure. To deeply investigate this problem, the momentum transfer model considering secondary jet velocity distribution was used to develop an improved model that is more aligned with the actual state of the flow field. In this model, the receiver jet velocity is calculated, for the first time, with a maximum error of 18% when compared with existing models. To verify the improved model, the recovery pressures in the receivers were verified by numerical simulations and experiments. The verification results show that the model can accurately predict the recovery pressures in the receivers within an 8.1% maximum error. This model fills the gaps in the theoretical research and lays a foundation for the structural design of deflector jet pressure servo valves. [ABSTRACT FROM AUTHOR]

The C4F7N/CO2 mixture is considered one of the most promising alternatives to sulfur SF6. Recent studies have shown that the addition of O2 to the C4F7N/CO2 mixture can suppress carbon precipitation following electric arc discharges. This paper conducts arc-burning experimental research on SF6, 10%C4F7N/90%CO2, and 10%C4F7N/85%CO2/5%O2 mixtures. Measurements were taken of the arc voltage and arc current under a 10 kA breaking current for these three gases. Additionally, the pressure at the nozzle throat during arc and cold flow conditions, as well as the pressure in the storage chamber, were measured. The post-arc current and Rate of Rise of Recovery Voltage (RRRV) for the three gases were calculated. The study also compared the solid precipitates in the gas medium after multiple arc-burning experiments. The results indicate that adding O2 to the C4F7N/CO2 mixture can increase the pressure at the nozzle throat during the arc phase, and the inclusion of O2 has minimal impact on the peak arc-extinguishing voltage and critical RRRV. It is hypothesized that a small amount of oxygen has a negligible effect on the thermal recovery properties of the C4F7N/CO2 mixture, while also inhibiting the precipitation of carbon following electric arc discharges. This research could provide a reference for developing and optimizing eco-friendly high-voltage circuit breakers. [ABSTRACT FROM AUTHOR]

Aerodynamic pressure is one of the important elements impacting the degradation of service performance of high-speed railways. Aerodynamic characteristics produced by high-speed train associated with tunnel length are studied using numerical method. The input parameters, which are adopted in simulation, are verified with the on-site monitoring obtained by other researchers. The characteristics of aerodynamic pressure and micro pressure wave associated with tunnel length are systematically explored. It can be found that, when tunnel length is increases from 200 to 1,000 m, the maximum peaks related to positive and negative pressure are respectively shifted from the position nearby tunnel exit and entrance to that of tunnel middle section. Before train tail leaves tunnel exit, the maximum peak-to-peak values increase and then decrease with the increase of tunnel length. After train tail leaves, the maximum peak-to-peak values decrease and then increase. The characteristics of the maximum positive peak of initial micro pressure wave at identical location associated with different tunnel lengths are negligible. And the relationships between maximum positive peak and the distance away from tunnel exit are similar for different tunnel lengths, which can be fitted by a power function. [ABSTRACT FROM AUTHOR]

In recent years, the C4F7N mixed gas has attracted considerable attention for its outstanding insulation and arc-extinguishing capabilities, positioning it as a potential substitute for sulfur hexafluoride, SF6. However, there remains a limited understanding of the arc-extinguishing and insulation performance of C4F7N/CO2 mixed gas. In addition, there is limited research on high-current breaking in circuit breakers. Therefore, this study aims to investigate the arc characteristics and breaking behavior of 10%C4F7N/90%CO2 and 15%C4F7N/85%CO2 mixed gases using a magnetohydrodynamic model based on the 252kV air pressure circuit breaker. The dynamic characteristics of this mixed gas are compared with pure SF6 under short-circuit current breaking conditions, while analyzing different parameters of the C4F7N configuration. The results indicate that the mixed gas exhibits lower levels in terms of arc temperature, axial diffusion distance and pressure difference at the moment of arc initiation compared to pure SF6. Furthermore, increasing the inflating pressure can effectively enhance the breaking performance of the circuit breaker with 0.6 MPa, making it more suitable. Additionally, increasing the proportion of C4F7N in the mixed gases will cause the arc temperature to rise slightly at the initial arc and current crossing zero, but decrease at the peak current. The core pressure also rises significantly, with a greater pressure difference established in the compressor at moment of arc initiation. This study provides a reference for the design of an environmentally friendly circuit breaker and the selection of the mixed gas ratio. [ABSTRACT FROM AUTHOR]

Abstract This work considers the flow field as two-dimensional turbulent flow and studies the steady-state properties of heat transfer and the pressure of the suspension nozzle. An adiabatic wall parallel to the moving wall and two slit entrances at either end of the adiabatic wall make up the rectangular flow field. The SST $$k - \omega$$ k - ω turbulence model is used in the turbulence computation. Both qualitative and quantitative analyses are conducted on the distribution of the flow field, temperature field, local Nusselt number, local pressure coefficient, average Nusselt number, and average pressure coefficient under various combination conditions. The findings indicate that when the suspension nozzle's flow field varies greatly, wall-jet velocity ratio is 0.1. A rise in Jet inclination angle is not helpful for the wall's suspension, and it has minimal effect on the flow field. The flow field is greatly influenced by separation space-slit width ratio. Larger separation space-slit width ratio values are advantageous for the wall's heat transmission but unfavorable for the wall's suspension. The flow field is most influenced by wall-jet velocity ratio. The wall's ability to convey heat is stronger the higher the wall-jet velocity ratio, but its ability to support weight falls.

This work considers the flow field as two-dimensional turbulent flow and studies the steady-state properties of heat transfer and the pressure of the suspension nozzle. An adiabatic wall parallel to the moving wall and two slit entrances at either end of the adiabatic wall make up the rectangular flow field. The SST k - ω turbulence model is used in the turbulence computation. Both qualitative and quantitative analyses are conducted on the distribution of the flow field, temperature field, local Nusselt number, local pressure coefficient, average Nusselt number, and average pressure coefficient under various combination conditions. The findings indicate that when the suspension nozzle's flow field varies greatly, wall-jet velocity ratio is 0.1. A rise in Jet inclination angle is not helpful for the wall's suspension, and it has minimal effect on the flow field. The flow field is greatly influenced by separation space-slit width ratio. Larger separation space-slit width ratio values are advantageous for the wall's heat transmission but unfavorable for the wall's suspension. The flow field is most influenced by wall-jet velocity ratio. The wall's ability to convey heat is stronger the higher the wall-jet velocity ratio, but its ability to support weight falls. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Zhejiang University: Science A is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Machine Tool & Hydraulics is the property of Guangzhou Mechanical Engineering Research Institute (GMERI) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Radial borehole fracturing that combines radial boreholes with hydraulic fracturing is anticipated to improve the output of tight oil and gas reservoirs. This paper aims to investigate fracture propagation and pressure characteristics of radial borehole fracturing in multiple layers. A series of laboratory experiments with artificial rock samples (395 mm × 395 mm × 395 mm) was conducted using a true triaxial fracturing device. Three crucial factors corresponding to the vertical distance of adjacent radial borehole layers (vertical distance), the azimuth and diameter of the radial borehole are examined. Experimental results show that radial borehole fracturing in multiple layers generates diverse fracture geometries. Four types of fractures are identified based on the connectivity between hydraulic fractures and radial boreholes. The vertical distance significantly influences fracture propagation perpendicular to the radial borehole axis. An increase in the vertical distance impedes fracture connection across multiple radial borehole layers and reduces the fracture propagation distance along the radial borehole axis. The azimuth also influences fracture propagation along the radial borehole axis. Increasing the azimuth reduces the guiding ability of radial boreholes, which makes the fracture quickly curve to the maximum horizontal stress direction. The breakdown pressure correlates with diverse fracture geometries observed. When the fractures connect multi-layer radial boreholes, increasing the vertical distance decreases the breakdown pressure. Decreasing the azimuth and increasing the diameter also decrease the breakdown pressure. The extrusion force exists between the adjacent fractures generated in radial boreholes in multiple rows, which plays a crucial role in enhancing the guiding ability of radial boreholes and results in higher breakdown pressure. The research provides valuable theoretical insights for the field application of radial borehole fracturing technology in tight oil and gas reservoirs. [ABSTRACT FROM AUTHOR]

Blast furnace ironmaking is one of the most serious carbon dioxide emission processes. To reduce energy consumption and CO2 emissions, fluidized bed ironmaking technology with hydrogen as a reducing agent has attracted more and more attention. An inclined agitator was added to the fluidized bed reactor to address the sticking issue in the conventional fluidized bed ironmaking process. In this research, numerical simulation was used to examine the impacts of reducing gas composition and agitation speed on the gas-solid fluidization quality in the cold fluidization of iron ore powder in the fluidized bed with an inclined agitator. The results indicate that the fluidization effect of iron ore powder is better when the volume ratios of H2 to CO and H2 to N2 are 1:1. Under the intensive shear action of the agitator, the standard deviation of pressure drop constantly decreases with the increase in agitation speed, and the decreasing range is smaller and smaller. The fluidization state of the iron ore powder particles in the bed stabilized when the agitation speed reached 160 rpm. [ABSTRACT FROM AUTHOR]

In the mining of close coal seam, the stress concentration under the residual coal pillar in the upper coal seam leads to serious deformation to roadway surrounding rock in the lower coal seam. Hence, it poses a huge challenge to the maintenance of entry surrounding rock. Based on this, an approach of entry surrounding rock control technology, directional pre-splitting, and roof-cutting pressure relief, was applied. The stress and deformation of entry surrounding rock utilizing directional pre-splitting and roof-cutting pressure relief were studied by numerical simulation and field test The results indicated that the depth of stress concentration under the residual coal pillar achieve 44 m. With the application of the roof presplitting, the vertical stress of the entry roof decreased. Utilizing the roof presplitting with a height of 7 m and an angle of 15°, the gangue filled the goaf and supported the overlying strata. Meanwhile, the surrounding rock of entry was controlled with a constant resistance anchor cable (9 m length) and gangue prevention support structure. Through field test monitoring, the roof pressure and the deformation of surrounding rock increases rapidly at 30 ∼ 110 m behind the working face. From 110 ∼ 160 m, the increased rate of roof pressure and surrounding rock deformation gradually slows down and tends to be stable at 160 m behind the working face. The maximum displacement of the roof to the floor is 511 mm, and the maximum displacement of the gangue rock wall to coal wall is 421 mm. The remaining roadway meets the demand of the adjacent working face. [ABSTRACT FROM AUTHOR]

In order to study the dynamic characteristics of the three-dimensional bow impact in water, a series of a bow flare water entry drop tests were carried out in water tank, and the snapshots of water entry were meticulously reported. The scale ratio of the bow model is 1:30. Findings reveal that second slamming can yield a higher slamming pressure coefficient and even surpass the pressure generated by the initial slamming. The temporal evolution of dimensionless pressure time histories exhibits remarkable similarity among points at the same height, with differences primarily attributed to peak values dependent on deadrise. Additionally, the study investigates the impact of velocity on slamming load. Results indicate that pressure coefficient near the bow is more responsive to impact velocity than elsewhere. Notably, experimental peak pressure is at least 3% lower than direct calculations using Wagner's formula or DNV rules away from the bow. However, due to the effective impact angle, experimental peak pressure can be up to 9 times higher than theoretical results in the flow separation area, underscoring the need for enhanced scrutiny in pressure direct calculation. • Slamming characteristics of a larger bow flare (1:30) are investigated. • The temporal and spatial distribution characteristics of slamming pressure are studied. • Dimensionless slamming pressure is proposed to analyze the evolution of pressure. • The slamming pressure coefficient of the second slamming may exceed the first. • The characteristics of slamming pressure coefficient on 3D bow flare is analyzed quantitatively. [ABSTRACT FROM AUTHOR]

Blast furnace ironmaking is one of the most serious carbon dioxide emission processes. To reduce energy consumption and CO2 emissions, fluidized bed ironmaking technology with hydrogen as a reducing agent has attracted more and more attention. An inclined agitator was added to the fluidized bed reactor to address the sticking issue in the conventional fluidized bed ironmaking process. In this research, numerical simulation was used to examine the impacts of reducing gas composition and agitation speed on the gas-solid fluidization quality in the cold fluidization of iron ore powder in the fluidized bed with an inclined agitator. The results indicate that the fluidization effect of iron ore powder is better when the volume ratios of H2 to CO and H2 to N2 are 1:1. Under the intensive shear action of the agitator, the standard deviation of pressure drop constantly decreases with the increase in agitation speed, and the decreasing range is smaller and smaller. The fluidization state of the iron ore powder particles in the bed stabilized when the agitation speed reached 160 rpm.

3• A 3D model of an oil-injected twin-screw compressor was simulated with CFX. 3• The CFD model accounted well for the pressure in both time and frequency domains. 3• The highest pressure pulsation acted on the inner surface of the rotor housing. 3• The fluid hammer effect was found at the oil injection outlets. The internal pressure characteristics of an oil-injected twin-screw refrigeration compressor was studied using a full 3D CFX model, and the hexahedral moveable meshes of the twin-screw domain were generated by the professional mesh tool SCORG. The gas pressure throughout the whole working process was investigated to disclose its distribution feature. The working pressure at different locations, such as the inner surface of the screw rotor housing, the oil injection paths, the male screw groove, the internal suction and discharge flowing paths, were all captured and analyzed. The simulated pressure inside the screw working chamber agreed well with the experimental results in both time and frequency domains. The pressure pulsations in the compression section acting on the inner surface of the screw rotor housing presented higher levels than the data in the other domains. The highest pulsation level occurred on the location where could record the whole discharge process of the internal ports. Under the high oil flowrate conditions, due to the different influences of the fluid hammer effect, the pressure pulsation increment of the axial oil injection outlet was much larger than that of the radial oil injection outlet. The orifice on the oil path could help reduce the influence of the fluid hammer. Finally, several suggestions were given based on the simulation findings. [ABSTRACT FROM AUTHOR]

Copyright of Journal of South China University of Technology (Natural Science Edition) is the property of South China University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A vehicle model with variable stiffness elastic trailing edge is designed to analyze the influence of elastic trailing edge on the hydrodynamic characteristics of supercavitating vehicles. The cavity shape and the pressure characteristics at different differential pressures and ventilation rates are studied through water tunnel experiment. In the experiment, an industrial camera is used to observe the shape of elastic trailing edge and the flow field, and a dynamic measurement system is used to measure the pressure fluctuation about the feature points. The influence of elastic trailing edge on the hydrodynamic characteristics of supercavitating vehicle is analyzed by comparing the changes of cavity shape and pressure fluctuation. The results show that the deformation of elastic trailing edge increases with the increase in the differential pressure coefficient. When the diameter ratio of the elastic trailing edge to the main body of vehicle is 1.35, the elastic trailing edge has an obvious effect on the cavity shape, and the cavity is closed in front of the trailing edge. Behind the trailing edge, the surface pressure of the model increases with the surface contacting water. With the continuing increase in diameter ratio, a tail cavity appears and fluctuates wildly, which causes the reduction in the wetted area downstream the elastic trailing edge and the drop in surface pressure. [ABSTRACT FROM AUTHOR]

The incorporation of pressure levels and pressure gradients in the design of compression stockings offers excellent potential to enhance function in the sport science, clinical research and rehabilitation fields. Yet, the connection of processing parameters and structure accompanying the pressure characteristic of current graduated compression stockings (GCS) is not well quantitatively studied. To bridge this knowledge gap, this study aims to analyze the effects of processing parameters, such as elastane yarn count, loop length and elastane feeding tension, on the structure and pressure behavior of GCS in our work. In addition, to investigate the mechanism of the pressure characteristic, two numerical models, the cylinder model and the conical model, are employed to predict the pressure value and the pressure gradient of stockings. The experimental results of the statistical analysis indicate that the loop length is a key factor to control the wale density, length of stockings and final pressure values. Moreover, the elastane feeding tension could affect the course density, girth of stockings and pressure gradient. On the other hand, the numerical results reveal that the conical model is suited for predicting the pressure values because of the change in radius of the limb in the model. The entire experimental and numerical work provide the mechanism for the study basis of processing, structure and pressure characteristics of GCS. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering Geology / Gongcheng Dizhi Xuebao is the property of Journal of Engineering Geology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The flow of viscous liquid in highly efficient commercial axial pumps is hydrodynamically analyzed. Design recommendations are made regarding the flow sections of the pump, so as to ensure a pressure characteristic with no descending section and efficient coolant circulation in a fast-neutron reactor. [ABSTRACT FROM AUTHOR]

The propagations of blast waves on Floating, Production, Storage, and Off-loading unit (FPSO) are influenced by the shapes, dimensions and arrangements of obstacles. In this paper, the effects of cylindrical obstacles on the characteristics of explosion pressures in the process modules of FPSO are studied by using computational fluid dynamic (CFD) method. Defining an effect coefficient η to express the changes of explosion pressures due to the existence of obstacles. It indicates that only the explosion pressures in the limited region adjacent obstacles can be affected by cylindrical obstacles. The increase of obstacle diameter only improve the η values front of the obstacles while increasing obstacle height can significant decrease the explosion pressures behind obstacle. When blast waves propagate multiple obstacles, the explosion pressures adjacent front obstacle are not affected by the rear obstacle, however, the explosion pressures in the gap of two obstacles are relieve due to the existence of front obstacle. The comparisons of effect of cubical and cylindrical obstacles reveal that cubical obstacles have more excellent pressure reduction ability as cylindrical obstacles can provide a larger pressure reduction region. • The pressure characteristics around cylindrical obstacles in normal or oblique blast waves are summarized. • The effect of obstacle dimensions and arrangements on pressure distribution are analyzed. • Comparisons of the effect of two shaped obstacles are given. [ABSTRACT FROM AUTHOR]

Aiming at the request of miniaturization and integration of microfluidic chip, a pneumatic microfluidic chip system driven by a stepper motor was presented. A controller signal was sent to the stepper motor, and the valve opening was changed by deforming the PDMS channel. The simulation model was built by using Simulink nonlinear module after analyzing the flow rate of the micro valve and the pressure of the gas container. The pressure dynamic response characteristics of the pneumatic microfluidic chip system on different step signal of the stepper motor were given based on simulation. The pressure characteristic test curves of the gas container were obtained and compared with the simulation results by building a test platform. The results indicate that pressure characteristics of pneumatic microfluidic chip system through experiment are basically the same with the simulation results. The response of systemis quick to the pressure cavity. When the valve opening is larger, the pressure of the gas container rises more quickly and higher. [ABSTRACT FROM AUTHOR]

The accurate model of the jet-type valve, as the pilot control stage of a jet-pipe/deflector-jet servovalve, is of great significance to analyze and design a servovalve. However, the flow field in the jet-type valve is too complex to build an accurate mathematical model. In this paper, the collision between the liquid and the jet is supposed as the impact of jet on a moving piston, which makes a complex the fluid mechanical problem become simple. Based on this assumption, a model of the jet-type valve is developed in this paper. Unlike the previous models, the structural parameters, the distance between the jet-nozzle exit and receiving surface, the included angle between two receiver holes as well as the distance between two receiver holes, all can be considered in this model. To test and verify the theoretical model, the pressure and flow characteristic curves of a jet-type valve are given by the methods of flow filed numerical simulation and experiment.As shown by the verification results, the theoretical pressure characteristic curve is very approximate with the experimental data and numerical simulation, while the flow characteristic curves need to be modified and the modified model is valid. [ABSTRACT FROM AUTHOR]

The knowledge of transient flow in pressure pipelines is very important for the designing and describing of pressure networks. The water hammer is the most common example of transient flow in pressure pipelines. During this phenomenon, the transformation of kinetic energy into pressure energy causes significant changes in pressure, which can lead to serious problems in the management of pressure networks. The phenomenon is very complex, and a large number of different factors influence its course. In the case of a water hammer caused by valve closing, the characteristic of gate closure is one of the most important factors. However, this factor is rarely investigated. In this paper, the results of physical experiments with water hammer in steel and PE pipelines are described and analyzed. For each water hammer, characteristics of pressure change and valve closing were recorded. The measurements were compared with the results of calculations perfomed by common methods used by engineers - Michaud's equation and Wood and Jones's method. The comparison revealed very significant differences between the results of calculations and the results of experiments. In addition, it was shown that, the characteristic of butterfly valve closure has a significant influence on water hammer, which should be taken into account in analyzing this phenomenon. Comparison of the results of experiments with the results of calculations? may lead to new, improved calculation methods and to new methods to describe transient flow. [ABSTRACT FROM AUTHOR]

• The effects of piston offset on compressor performance are studied. • The pressure and mass flow characteristics are compared with different active offset. • The existence of offset deteriorates the compressor efficiency and increases the power consumption. Piston offset in the helium valved linear compressor (VLC) deteriorates the cooling performance and operating life of Joule-Thomson (JT) refrigerators, especially in aerospace applications. To clarify the influence of piston offset on the VLC performance, an experimental investigation was carried out. Based on a laboratory developed VLC, the effects of piston offset on the suction and discharge pressure, pressure ratio, mass flow rate, motor efficiency, volume efficiency and adiabatic efficiency are systematically studied under two piston motion states (fixed piston displacements and full strokes). The results show that when the piston stroke is constant, the offset will increase the discharge pressure and mass flow rate, and decrease suction pressure. When the piston moves at full stroke, the offset will reduce the discharge pressure and mass flow rate, and increase suction pressure. Regardless of the working conditions, the existence of offset will affect the efficiency of the compressor, hence increasing the power consumption. [ABSTRACT FROM AUTHOR]

In this study we characterized various screw elements of a co-rotating twin-screw extruder used for pharmaceutical hot melt extrusion (HME) and measured the pressure characteristic, i.e., the correlation between the axial pressure gradient and the material throughput in a completely filled screw section at different screw speeds. A typical HME matrix material, Soluplus, was used for the experiments and its required rheological properties were determined. A three-parameter model based on a dimensionless formulation of the measured quantities was used. These parameters could not be determined uniquely by fitting to experimental data. Therefore we developed an approach to approximate one empirical parameter based on the mechanistic consideration of a pressure-driven channel flow. The model was extended to account for the variable melt temperature. The results confirmed the expected tendencies and established an essential input parameter set for one-dimensional simulations of co-rotating twin-screw extruders. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4440-4450, 2013 [ABSTRACT FROM AUTHOR]

The most complicated component in cavitating flow and pressure distribution is the flow in the cavity closure line. The cavitating flow and pressure distribution provide critical aspects of flow field details in the region. The integral of pressure results of the hydrodynamic forces, indicate domination in the design of a supercavitating vehicle. An experiment was performed in a water tunnel to investigate the pressure characteristics of the cavity closure region. Ventilation methods were employed to generate artificial cavity, and the ventilation rate was adjusted accordingly to obtain the desired cavity length. An array of pressure transducers was laid down the cavity closure line to capture pressure distribution in this region. The experimental results show that there is a pressure peak in the cavity closure region, and the rise rate of pressure in space tends to be higher in the upwind side when the flow is non-axisymmetric. The transient pressure variations during the cavity formation procedure were also present. The method of measurement in this paper can be referenced by engineers. The result helps to study the flow pattern of cavity closure region, and it can also be used to analyze the formation of supercavitating vehicle hydrodynamics. [ABSTRACT FROM AUTHOR]

Steps located in the non-aerated flow region of a chute are prone to cavitation damage. Two models operated with various Froude numbers and bottom slopes were employed to measure the pressure on the steps. The minimum and maximum pressures on the horizontal step surfaces occurred at the chute beginning and at the chute end, respectively. These characteristics were also found in the fully-developed flow region. The time-averaged pressure on the horizontal step surfaces is negative at the chute start, and then becomes positive along the flow direction in the non-uniform flow region. On the vertical step surfaces, the pressure is always negative at the top and remains negative along the entire vertical surface if the unit discharges are high enough in the non-uniform flow region. These results differ from the pressure characteristics in the uniform aerated flow region. [ABSTRACT FROM PUBLISHER]

Slamming load during water impact is one of the main concerns for the design of marine structures. However, accurate prediction of impact pressure largely relies on two-dimensional or simplified three-dimensional structures due to the difficulty in modeling complicated fluid forms such as flow separation and air cavity. In order to improve the prediction of slamming loads in complex three-dimensional models, a truncated stern model impacting water was investigated experimentally through a series of free drop tests. The falling kinemics (water entry depth and acceleration) and slamming loads (pressure and vertical force) were measured through arranging the sensors. Details of impact characteristic including falling kinemics and slamming pressure were presented. In order to clarify the 3D effects, the 2D CFD numerical results were compared with experimental results, showing that the numerical results are larger than the experimental ones with an average of 21%. Finally, influence of water entry velocity on the non-dimensional pressure was further discussed to improve the application. Some factors related to impact velocity such as air pocket and jet flow can influence the pressure which should be paid attention. • A series of drop-test experiments was performed to investigate the hydrodynamic characteristics of 3D stern model. • Complete experimental data set including falling kinematics and slamming loads were provided to clarify the impact characteristics. • Air effect was clarified through the free surface evolution based on a 2D CFD method. • The influence of 3D effects and impact velocity on the slamming loads had been discussed. [ABSTRACT FROM AUTHOR]

Gas explosion accidents may result in catastrophic damage to structures and humans. Generally, the gas explosion pressures on Floating, Production, Storage, and Off-loading unit (FPSO) are affected by the obstacles. In this paper, the numerical simulation method is applied to study the blast wave propagation in the modules of FPSO. The types of the blast wave, dimensions of the obstacle, and combinations of multiple obstacles are regarded as the variables to study the change of explosion pressure fields. An effect coefficient η is defined to represent the effect of the obstacles on explosion pressures. Results show the obstacles can only affect the finite areas in the surrounding. The explosion pressures on the front or side of the obstacle only depend on the intensities of incident waves. However, the pressures at the back of the obstacle are determined by the path difference of the diffraction waves, which is sensitive to obstacle dimensions. Extending the width and height significantly reduces the explosion pressures behind the obstacle. Analyzing the effect coefficients in the multi-obstacle combinations, reveals the medium spacing distance can reduce the explosion pressure. Based on the analysis results, some suggestions are recommended for escape and refuge. • Cause for the different features of blast wave propagation on the two floors of FPSO are analyzed. • Effect of the reflection wave and diffraction wave on the tendency and peak feature of pressure curves is summarized. • Effect of obstacle dimensions on the pressure reduction result behind obstacle are analyzed. • Analyzing the effect of obstacle spacing on the blast wave propagation in three multiple obstacle combinations. • Giving the pressure enhancement and reduction region in the obstacle combinations to provide the recommendation of escape and refuge. [ABSTRACT FROM AUTHOR]