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We give a complete proof of the classical Benjamin and Lighthill conjecture for arbitrary two-dimensional steady water waves with vorticity. We show that the flow force constant of an arbitrary smooth solution is bounded by the flow force constants for the corresponding conjugate laminar flows. We prove these inequalities without any assumptions on the geometry of the surface profile and put no restrictions on the wave amplitude. Furthermore, we give a complete description of all cases when the equalities can occur. In particular, that excludes the existence of one-sided bores and multi-hump solitary waves. Our conclusions are new already for Stokes waves with a constant vorticity, while the case of equalities is new even in the classical setting of irrotational waves. [ABSTRACT FROM AUTHOR]

This paper deals with the experimental and numerical analysis of the flow force acting on the spool of a proportional directional valve. The flow force arises due to the fluid flow through the flow path of the proportional directional valve and significantly influences the dynamics of the valve spool. The valve under investigation is a three-position four-way proportional directional valve with zero spool lap and feedback from the spool position. The dependence of the valve spool flow force on the volumetric flow rate is measured as part of the experiment. The measurements are performed for different spool displacements. The measured data will be used to verify the numerical simulations. The proportional directional valve was modified so that a force sensor could be included on the spool axis to realize the experiment. Firstly, the flow force is measured as the fluid passes through the two flow paths of the valve (PB and AT). Subsequently, the experimental setup is modified to determine the flow force when the fluid passes through each flow path separately. The measurements are compared. Simulations of the flow through the proportional directional valve are performed using Ansys Fluent 2022 R2 software to determine the flow forces acting on the valve spool. Simulations are performed for the selected spool positions of the proportional directional valve. Finally, the results of the simulation and the experiment are compared. The contribution of this study is a CFD model of the flow paths of the proportional directional valve verified by experiment. The CFD model will allow the flow force analysis for different flow path geometries of the investigated valve. Experimental analysis of flow force is performed over the entire spool stroke at different volumetric flow rates. The flow forces are measured for each flow path separately and for both flow paths simultaneously. [ABSTRACT FROM AUTHOR]

In this article, authors investigated a DN50/80 size safety valve with computer fluid dynamics (CFD) simulation to determine the lift forces and mass flows acting on the valve disc at 3.5 to 5.5 barg inlet pressures and to observe the evolution of turbulent streamlines in the outlet side of the valve, with static disc position. The simulation results were compared with measured data. Authors studied the inner flow field of the valve with fixed 5 mm disc elevation. Lift force acting the disc and overall stream pattern were investigated with the gas vale. To eliminate backflow, authors applied a virtual streamtube on the outlet nozzle with various lengths. Differences between data of the valve measured and simulated results were investigated besides changing the length (50, 150, 250, 350 and 400 mm) of the applied tube. [ABSTRACT FROM AUTHOR]

As one of the important factors affecting the stability of slide valves, the analysis and research of flow force are of great significance. In recent years, more and more experts and scholars have conducted research in this field, attempting to find methods to reduce or utilize the flow force of hydraulic spool valves. Flow force includes steady-state flow force and transient flow force, with steady-state flow force having the most significant impact on spool valves. The influencing factors of flow force are complex and diverse, including the cavitation phenomenon, shape of the throttling groove, and jet angle. At present, the main ways to reduce flow force are to design the structure of the spool valve, the structure of the valve sleeve, and the flow channel of the valve body. This article mainly reviews the definition, calculation methods, influencing factors, and methods for reducing the flow force of slide valves. This provides a new approach to reducing the flow force in hydraulic spool valves. [ABSTRACT FROM AUTHOR]

In modeling the characteristics of a discharging valve in a hydrodynamic retarder, it is commonly required to determine the value of the flow area to calculate the force on the spool. However, the flow area often relies heavily on empirical or simulation data, which leads to increased uncertainty and computational cost, especially with the variation in the spool displacement. To overcome these shortcomings, Res-SE-U-Nets (networks that combine residual connections, squeeze-and-excitation blocks, and U-Net) are used to reconstruct the velocity field, and they have shown exceptional performance in image-to-image mapping tasks. The dataset of computational fluid dynamics (CFD) results for the velocity field is collected and verified using particle image velocimetry (PIV). The results show that Res-SE-U-Nets can capture the location information of the flow field using a training set of only 120 data points. By utilizing location information in velocity field reconstruction, the flow area can be directly obtained under different spool displacements and pressures to calculate the spool force. The valve characteristics calculated with this method show an error of less than 2% when compared with CFD results, which confirms the validity and effectiveness of this method. The proposed method, which utilizes location information extracted from flow field prediction results, is capable of calculating valve characteristics. This approach also demonstrates the feasibility of using Res-SE-U-Nets for flow field reconstruction. [ABSTRACT FROM AUTHOR]

The present work is aimed at simultaneously reducing the additional flow force on the cone and cavitation intensity in a poppet valve. A prediction model of flow force on the cone and cavitation was established for the poppet valve by using computational fluid dynamics method (CFD) combined with Zwart–Gerber–Belamri cavitation model. The effects of three poppet valve configurations and their parameters on the flow force and cavitation intensity in valves were investigated. The research results indicate that, compared with the poppet valve A, the poppet valve B has an excellent ability to decrease the flow force on the cone, but promotes the cavitation intensity in the valve. The poppet valve C can not only significantly decrease the flow force on the cone but also has the potential to reduce cavitation intensity in the valve. When the parameter h is 6 mm and the parameter t is 2 mm, the flow force and the relative vapor volume in the valve C can be reduced by an average of 44.2% and 100%, respectively. [ABSTRACT FROM AUTHOR]

Submarine pipelines are one of the safest ways to transport crude oil and its derivatives, and this necessitates a more careful study of the technical knowledge governing this issue. Compared to other methods of transporting petroleum products. such as the use of tankers. the use of pipelines has many advantages, including the low impact of their environmental pollution. In this study, the measurement of flow force applied to the submarine pipelines was experimentally measured using a system of load cell. This was done using a special type of flume called a knife edge flume with a length of 14 m, width of 1 m and height of 1 m. The flow force was measured directly using an electronic dynamometer (Load cell). In this study, five different pipe diameter of 5, 10, 20, 25, and 35 cm were used to model submarine pipelines at different distances as double and single pipelines. It was also tested at different depths of submergence and tested at three different buried depths. Furthermore, the results of the absorption method were compared with the results of force measurement obtained from other methods, and it was found that the force absorption method provides reliable results. Based on the experiments, it was found that methods based on energy principles do not have acceptable results except in small-diameter pipes. Also, with increasing the diameter of the pipelines and increasing the depth and increasing the depth of submergence, the amount of force applied by the flow on the pipelines increases. Furthermore, the buried depth is inversely proportional to the force applied. In dual pipelines, the taller distance between the pipelines leads to taller force applied to them. It can also be seen that the diameter of the pipes is the most effective factor in the force applied by the flow on the submarine pipelines. [ABSTRACT FROM AUTHOR]

A regulating valve is a key control element in the coal liquefaction industry, whose flow field distribution is related to the entropy production. In order to make a quantitative evaluation of the energy loss in the cavitation flow and calculate the magnitude and location of the hydraulic loss in the flow field more accurately, entropy production theory is employed to analyze the flow field in the regulating valve numerically. The entropy production under cavitation condition and its influence on steady-state flow force are also discussed. When the opening of the valve increases, the entropy production and energy loss change dramatically. The entropy production rate (EPR) is mainly distributed at the orifice and downstream of the regulating valve, the entropy production rate (EPR) reaches the maximum value at the orifice, and turbulent pulsation entropy production (TPEP) is the main part of the total entropy production for flow. When the valve's opening increases from 40% to 70%, the total entropy production (TEP) increases from 467.14 W/K to 630.04 W/K. The entropy production by cavitation (EPC) increases firstly and then decreases. The smallest value of EPC is 0.103 W/K at the 40% opening, while the maximum value is 0.119 W/K at 60% opening. Furthermore, the relationship between total entropy production (TEP) and steady-state flow force can be approximated by an exponential distribution. When the steady-state flow force increases, the total entropy production for flow also increases. Cavitation effect on the steady-state flow force is strengthened firstly and then weakened with increasing the valve's opening. Finally, a discriminant method based on the change of the steady-state flow force is proposed to detect whether cavitation occurs in the valve or not. The results in this paper could provided a directional and quantitative evaluation of energy loss in the regulating valve, which is help for the structural shape optimization and service life extension combining with external characteristics of the valve and internal flow field. [ABSTRACT FROM AUTHOR]

The flow field structure in the pilot stage of the electro-hydraulic servo valve is small and complex, and the extreme temperature environment will aggravate the self-excited oscillation, resulting in a decrease in the control accuracy of the servo valve. With the increase in temperature, the size of the orifice, the temperature characteristics of the fluid and the pressure loss in the flow pipe will influence the characteristics of the pilot stage. Considering the influence of temperature and pressure loss, a theoretical mathematical model is established to describe the flow force in the pilot stage. To verify the accuracy of the theoretical model, CFD simulations of the flow force at different inlet pressures and deflection positions and temperatures are analyzed in this paper. As the temperature rises, the oil viscosity rapidly decreases, which results in the flow force acting on the flapper increasing with the temperature. When the temperature exceeds 50 °C, the effect of oil viscosity is small, and the flow force tends to decrease slightly with the combined effect. As the supply oil pressure increases and the flapper moves toward the nozzle, the flow force acting on the flapper increases, and the trend is consistent with the CFD simulation results. An experimental device is designed, including establishing the experimental conditions and measuring the flow force to validate the theoretical model and to observe the cavitation phenomenon of the pilot stage. [ABSTRACT FROM AUTHOR]

The hydraulic sliding-spool valve is a key component to control the flow rates and thus pressures in different hydraulic volumes. The lateral force on the spool is one of the important effects resulting from moving resistance. This paper presents research aimed at understanding the effects of radial flow force and static pressure upon the lateral force. The radial flow force is calculated from three types of control surfaces labelled with square land, 45° conical, and round curved surfaces, for discovering the effects of control profile, combined with inlet and outlet control conditions. The pressure difference effect is analyzed along with six cases under the same orifice opening, and the radial flow force is found to vary linearly with the pressure difference. The results also indicate that the radial force for the inlet control mode is less than that of the outlet control mode. The jet angle is discovered to not only be related to the annular orifice opening and gap clearance, but is also influenced by the flow direction and control surface profile. The static pressure is the predominant factor in the lateral force compared to the radial flow force. The results indicate that the static pressure variation on the surface of the cylindrical spool shoulder increased linearly with the inlet pressure; and two stagnation points can be observed in the case of the valve cavity with oil passages on the same section, and square land control edge profile. The lateral force on the spool increases with the pressure, and could reach to the maximum of 300 N, implying that this force should be taken into account in the selection of an actuator, especially in high pressure applications.

We are concerned here with an analysis of the nonlinear irrotational gravity water wave problem with a free surface over a water flow bounded below by a flat bed. We employ a new formulation involving an expression (called flow force) which contains pressure terms, thus having the potential to handle intricate surface dynamic boundary conditions. The proposed formulation neither requires the graph assumption of the free surface nor does require the absence of stagnation points. By way of this alternative approach we prove the existence of a local curve of solutions to the water wave problem with fixed flow force and more relaxed assumptions. [ABSTRACT FROM AUTHOR]

A regulating valve is a key control element in the coal liquefaction industry, whose flow field distribution is related to the entropy production. In order to make a quantitative evaluation of the energy loss in the cavitation flow and calculate the magnitude and location of the hydraulic loss in the flow field more accurately, entropy production theory is employed to analyze the flow field in the regulating valve numerically. The entropy production under cavitation condition and its influence on steady-state flow force are also discussed. When the opening of the valve increases, the entropy production and energy loss change dramatically. The entropy production rate (EPR) is mainly distributed at the orifice and downstream of the regulating valve, the entropy production rate (EPR) reaches the maximum value at the orifice, and turbulent pulsation entropy production (TPEP) is the main part of the total entropy production for flow. When the valve’s opening increases from 40% to 70%, the total entropy production (TEP) increases from 467.14 W/K to 630.04 W/K. The entropy production by cavitation (EPC) increases firstly and then decreases. The smallest value of EPC is 0.103 W/K at the 40% opening, while the maximum value is 0.119 W/K at 60% opening. Furthermore, the relationship between total entropy production (TEP) and steady-state flow force can be approximated by an exponential distribution. When the steady-state flow force increases, the total entropy production for flow also increases. Cavitation effect on the steady-state flow force is strengthened firstly and then weakened with increasing the valve’s opening. Finally, a discriminant method based on the change of the steady-state flow force is proposed to detect whether cavitation occurs in the valve or not. The results in this paper could provided a directional and quantitative evaluation of energy loss in the regulating valve, which is help for the structural shape optimization and service life extension combining with external characteristics of the valve and internal flow field.

Human mobility is of importance in supporting smart cities, urban planning and constructions of resilient environments. Previous studies on dominant mobility models (i.e., gravity and radiation models) rarely describe the refined spatiotemporal process of human mobility flow forces especially within city. To address this gap, this paper proposes a spatiotemporal flow force model (FFM) of sink/source human mobilities within city, which is derived from Navier-Stokes equation in the field of fluid mechanics. The FFM model outperforms the gravity and radiation models in modeling the refined spatiotemporal flow force process of source/sink human mobilities, in the aspect of intensity and direction of mobility flow force. Comparison results show that the gravity and radiation models in the source mobility scenario can give a rough force estimation about the total outflow from source mobility areas while without the capability of explaining the specific directions of mobility flow from source mobility areas. Pearson correlation coefficient between the intensity results of the two models and those of FFM range from 0.65 to 0.90 and direction differences between the results of the two models and FFM respectively show no clear regularity. In the sink mobility scenario, the direction of mobility flows can be estimated well by the gravity and radiation models while the intensity of mobility flow between small-scale areas within cities is susceptible to inaccuracies. Pearson correlation coefficient ranges from 0.13 to 0.59 and direction differences follow a stepped distribution from high to low within the range of 0° to 180°. In addition, the potential field of human mobility flow force provides a powerful tool for visually analyzing mobility flows within cities. This proposed model enriches human mobility models and is generalizable in supporting smart cities, urban planning, and constructions of resilient environments in terms of the refined spatiotemporal process of mobility flow force. • A spatiotemporal flow force model (FFM) of sink/source human mobilities within city is proposed. • Gravity and radiation models fail to explain specific directions of mobility flow from source mobility areas within city. • Mobility flow intensity between small-scale areas modeled by gravity and radiation models is susceptible to inaccuracies. • FFM model outperforms the gravity and radiation models in intensity and direction of mobility flow force. • The proposed model is generalizable in supporting smart cities, urban planning, and resilient environments. [ABSTRACT FROM AUTHOR]

Nozzle-flapper servo valves are widely used in modern electro-hydraulic control systems of many engineering applications. Flow cavitation in the nozzle-flapper pilot stage could produce noise and cavitation erosion, reducing the performance stability and reliability of the servo valves. In this paper, diamond nozzles are proposed to replace the traditional circular nozzles to reduce the flow cavitation in the nozzle-flapper stage. Numerical simulations using CFD software ANSYS/FLUENT were conducted to explore the flow characteristics of the nozzle-flapper pilot stage. Mass flow rate and image measurements were performed to verify the simulation results. Vapor fraction, lateral velocity, pressure distribution, and flow force are compared in detail between the pilot stage with the traditional nozzles and with the diamond nozzles. It is found that the vapor fraction is greatly reduced under the effect of the diamond nozzles. Finally, to explore the effect of the diamond nozzles on the performance of the nozzle-flapper servo valve, the pressure-flow characteristics and time step response of the load flow rate are examined using the software AMESim. The simulation results show that the pressure-flow characteristics and time step response of the load flow rate almost remain the same. This suggests that the diamond nozzles could suppress the cavitation in the nozzle-flapper servo valve without varying its performance.

The flow field structure in the pilot stage of the electro-hydraulic servo valve is small and complex, and the extreme temperature environment will aggravate the self-excited oscillation, resulting in a decrease in the control accuracy of the servo valve. With the increase in temperature, the size of the orifice, the temperature characteristics of the fluid and the pressure loss in the flow pipe will influence the characteristics of the pilot stage. Considering the influence of temperature and pressure loss, a theoretical mathematical model is established to describe the flow force in the pilot stage. To verify the accuracy of the theoretical model, CFD simulations of the flow force at different inlet pressures and deflection positions and temperatures are analyzed in this paper. As the temperature rises, the oil viscosity rapidly decreases, which results in the flow force acting on the flapper increasing with the temperature. When the temperature exceeds 50 °C, the effect of oil viscosity is small, and the flow force tends to decrease slightly with the combined effect. As the supply oil pressure increases and the flapper moves toward the nozzle, the flow force acting on the flapper increases, and the trend is consistent with the CFD simulation results. An experimental device is designed, including establishing the experimental conditions and measuring the flow force to validate the theoretical model and to observe the cavitation phenomenon of the pilot stage.

Safety valves are the most important safety devices of the pressure system. For safety valves in the vast majority of cases in industrial environment, direct spring-loaded safety valves are used. The most important parameter of the equation of motion is the flow force. The main goal of the analysis was to compare the simulated flow forces with the measured results and validating the computational fluid dynamics model. Simulations were made in ANSYS 2019 R1 code for numerous fixed valve disk positions on different pressures. Results are in good agreement with the measured data. [ABSTRACT FROM AUTHOR]

The classical irrotational capillary-gravity water wave problem described by the Euler equations with a nonlinear free surface boundary condition over a flat bed is considered. A modified flow force has been defined and a new formulation of capillary-gravity waves in the framework of the modified flow force function has been developed. Using bifurcation theory, the local existence of waves of small amplitude is proved. [ABSTRACT FROM AUTHOR]

In modeling the characteristics of a cartridge valve with traditional methods, it is commonly required to determine the value of flow area and other coefficients such as discharge coefficient and jet angle, etc. However, these parameters often rely heavily on empirical or experimental data and often involve some uncertainties, especially with the variation of the spool displacement (valve opening). To avoid these uncertainties, this paper proposes a modeling method which calculates spool force and flow rate directly through the distribution of fluid field. Transient 3D flow field simulation with dynamic mesh technique is conducted using commercial code FLUENT, and Proper Orthogonal Decomposition (POD) method is introduced to simplify fluid field data. The results showed that the POD method can capture the main features of the fluid field while significantly reducing the amount of data. With reconstructed pressure field and velocity field, spool force and flow rate can be calculated directly without using traditional formulas which contain uncertain coefficients. Valve characteristics calculated with this method agree with Computational Fluid Dynamics (CFD) and experimental data well, which confirms the validity and effectiveness of this method.

The classical irrotational water wave problem described by Euler equations with a nonlinear free surface boundary condition and influenced by gravity over a flat bed is considered. Exploiting the monotonicity property of the flow force lines with depth, the unknown boundary problem is transformed into a problem with fixed domain. A flow force function formulation of the irrotational water wave problem is developed. Variational approach is used to prove the existence of small amplitude irrotational traveling wave solutions. Local bifurcation results have been proved relying on Crandall-Rabinowitz bifurcation theorem. [ABSTRACT FROM AUTHOR]

East and west artificial islands are used to realize the transition from bridge to tunnel for Hong Kong-Zhuhai- Macao Cross-sea Tunnel. Immersed tunneling method is applied in sea tunnel and the total length of the sinking section is 5 664 m. The tube sections of El—E33 are arranged from west artificial island. The standard pipe section is 180 m long, 37.95 m wide, 11.4 m high and weighs about 80 000 tons. The connection area of the island and tunnel is affected by the deflecting flow1 and the sudden change of the water depth during the foundation trough excavation, and the flow pattern is complicated. Moreover, the flow pattern will be changed when the sinking joint is subsided. It is necessary to obtain the magnitude of water flow force to guarantee the safe sinking and accurate docking of the immersed tube. By using the undistorted model in a wide flume with the geometric scale of 1: 100, the experimental study on the flow distribution and water flow force during the sinking process of the island tunnel is carried out. The results indicate that, when there is no protective measure at the head of the island, the deflecting flow would affect the middle part of tube El and the flow velocities on the surface and at the bottom layers are larger than that of the middle layer. When sinking tube EI, the maximum longitudinal flow force can reach 4 601 kN, and the averaged longitudinal flow force of tube E2 is 5 149 kN. After sheltering tube El, the flow velocity at tube El decreases significantly. The middle part of tube E2 is mostly affected by the sheltering body, the maximum increment in the flow velocity reaches to 40%, and the flow velocity of the middle layer is larger than those on the surface and at the bottom layers. The average longitudinal flow force of tube E2 is 5 240 kN. When the sinking tube is completely immersed into the water, the flow velocity in the foundation trench is relatively small, and the water flow force during the sinking process decreases gradually. The vertical distribution of water flow in the connection area of island and tunnel is not exponential one, and the velocity distribution along the length of the pipe section is not uniform due to the influence of deflecting flow on the island head wall. The formula of floating water flow force at the pipe section is not suitable for calculating the magnitude of the water flow force during the sinking process of immersed pipe. [ABSTRACT FROM AUTHOR]

The calculation model of the flow force is the basis of modeling and dynamic analysis of a hydraulic valve. However, the flow passage of the directional valve used on the hydraulic roof support is complex, so the calculation method of the flow force is different from that of the conventional valves, and it is difficult to verify the flow force model through the direct test of flow force under such conditions. In order to solve this problem, the complex flow passage model was established, and two control volumes were used to divide the model into two parts. The combination of theoretical calculation and flow simulation was used to study the flow force at the valve port and that at the turning channel. The flow force calculation formula was modified according to the distribution characteristics of the flow field and the corresponding modified factors were obtained. On the verification method of the flow force, the indirect method which tests the dynamic characteristics of the valve was used instead of the conventional direct method which focuses on the direct test of flow forces. When the 1000 L/min directional valve of the hydraulic roof support was designed, the modified formula and the unmodified model of the flow force were applied to its mathematical model. The effects of the modified model and the unmodified model on the valve dynamic characteristics were compared through the combination of simulations and experiments so as to verify the accuracy of the modified model. The new method avoids the shortcomings of the direct method in dealing with complex flow passage model. The comparison between the simulations and the experiments in the two cases shows that the simulation dynamic characteristics of the valve using the modified formula are close to the experimental results while there is great difference in the other cases. Results illustrates the accuracy of the modified flow force model, and verifies the rationality of the calculation and tests methods of the flow force for the valve with complex flow passages. The methods of theoretical analysis and experimental verification are all different from others, and they are verified in the practical engineering application. It provides solutions for the flow force of hydraulic valve with complex passages. [ABSTRACT FROM AUTHOR]

In modeling the characteristics of a cartridge valve with traditional methods, it is commonly required to determine the value of flow area and other coefficients such as discharge coefficient and jet angle, etc. However, these parameters often rely heavily on empirical or experimental data and often involve some uncertainties, especially with the variation of the spool displacement (valve opening). To avoid these uncertainties, this paper proposes a modeling method which calculates spool force and flow rate directly through the distribution of fluid field. Transient 3D flow field simulation with dynamic mesh technique is conducted using commercial code FLUENT, and Proper Orthogonal Decomposition (POD) method is introduced to simplify fluid field data. The results showed that the POD method can capture the main features of the fluid field while significantly reducing the amount of data. With reconstructed pressure field and velocity field, spool force and flow rate can be calculated directly without using traditional formulas which contain uncertain coefficients. Valve characteristics calculated with this method agree with Computational Fluid Dynamics (CFD) and experimental data well, which confirms the validity and effectiveness of this method. [ABSTRACT FROM AUTHOR]

In the pilot stage of nozzle-flapper servo valve, the flow force on the flapper is the key reason that leads to forced vibration of the armature assembly, which may result in the fatigue of the flexure tube in torque motor. To master the principles and features of the flow force and the source of the forced vibration of the armature assembly, mathematical models of flow force and the forced vibration are deduced in this paper. For validating the model, a three-dimensional model is built and a finite element analysis of the flow force with different inlet pressure and deflections is presented and an innovative and experimental rig for measuring the steady and dynamic frequency of flow force is also designed. The characteristic of the main flow force, minor flow force and total flow force are analyzed contrastively, and the experimental results agree well with the CFD results and mathematical model analysis. To find the source of forced vibration of the armature assembly, a knocking method is proposed to measure the natural frequency of armature assembly. By comparing the spectrum of the pressure and vibration movement through experiments, a conclusion can be drawn that the inlet pressure fluctuation near the natural frequency of armature assembly and the asymmetric structure of pilot stage are the necessary and sufficient conditions to make the armature assembly yield forced vibration. In the end, some suggestions have been made to decrease the intensity of forced vibration of the pilot stage according to the findings. [ABSTRACT FROM AUTHOR]

This paper presents the regulation methods of flow forces acting on the main poppet in a large flow load control valve. The negative flow forces working on the originally designed main poppet, which is as high as 10% of the control force, act as a big disturbance to the main poppet position control, resulting in poor lowering speed control performance of the load control valve or even instability of the main poppet. Firstly, by introducing a damping tail structure to the main poppet, the direction of the flow forces can be regulated to positive and best stability of the main poppet can be achieved with the calculated best parameter combination. Secondly, by introducing a damping tail with holes to the main poppet, the positive flow forces of all main poppet positions can be reduced to minimum, which results in minimum disturbance for the control of main poppet. Computational fluid dynamics calculations were conducted to analyze how the damping tail parameters affect the flow forces and obtain the best parameter combinations. A test rig was set up to validate the effect of above methods. Good agreement of the computational fluid dynamics calculations and experiment results indicates that the proposed methods can provide guidance for the flow force regulation of other valve poppets. [ABSTRACT FROM AUTHOR]

Compared with the oil hydraulic systems, cavitation is more serious in water hydraulic systems due to the higher saturated vapor pressure of water. Poppet valve is one of important hydraulic components and cavitation is easy to happen due to the sharp pressure drop caused by throttling. This paper presents a numerical investigation into the flow force and cavitation characteristics inside water hydraulic poppet valves. Three kinds of typical structures of poppet valves are selected in the research. The effects of geometric parameters and backpressure of the poppet valves on flow characteristics, cavitation and flow force have been analyzed. Considering the axisymmetric structure of the valves, a half of 2D mixture model is selected and a two-phase mixture model is adopted in the calculation. The accuracy of the numerical models has been validated by comparing the simulation results with the experiment data. The results reveal that two-stage throttle valve (TS valve) can effectively suppress the occurrence of cavitation while the flow force of TS valve is much bigger than that of other valves. By comparing the simulation results under two different boundary conditions (including with backpressure and without backpressure), it seems that cavitation could slightly decrease the flow force. [ABSTRACT FROM AUTHOR]

The environment management system of an aircraft requires regulated air at nearly constant temperature and pressure, despite their wide variations at the system inlet. A pressure regulation valve is an important part of that system. In response to the variation of inlet pressure, a change in the motive flow force on a spool causes a change in the steady-state opening of an orifice in the main flow path, thereby providing the pressure regulation. The change in the flow force is contributed both by the main flow and a pilot flow through a fixed orifice and a relief valve. Simple models for the pilot flow and the pressure dynamics of a pilot chamber at the head side of the spool have been developed here for capturing the spool dynamics. The transient flow through the fixed valve body and the moving spool chamber has been solved by finite-volume method with dynamic meshing. The numerical results of the pressure drop in the main flow path for the fully open spool valve have shown good agreement with the corresponding experimental results with the pilot-line flow put off by the closed relief valve. Detailed analysis of the transient main flow leading to useful design conclusions has been provided in terms of different contour plots. For a given specification of the spool valve, a parametric study has provided the appropriate length of the pilot chamber, the stiffness of the spring in the relief valve, and the size of the fixed orifice in the pilot line. [ABSTRACT FROM AUTHOR]

Perturbation methods up to first order with respect to motion or wave amplitude are common in seakeeping predictions. For higher than first order, lengthy theoretical analyses are required. They result in complicated formulae requiring high programming effort, and often the well-established numerical methods for first-order quantities fail when applied to second-order flow quantities. Both the derivation of the required expressions and their programming are simplified by using mathematical entities called perturbators. The concept of perturbators is described, and their application is demonstrated, for a two-dimensional test problem: A cylinder with horizontal axis partly immersed into an ideal fluid. The cylinder performs sinusoidal heave, sway, and roll motions. Stationary and double-frequency second-order forces are determined. For a heaving semicircle, vertical forces are determined numerically and compared to published results. [ABSTRACT FROM AUTHOR]