Dynamic Simulation of a Warship Control Valve Based on a Mechanical-Electric-Fluid Cosimulation Model

Control valves have an important function in the warship power system. In engineering practice, the fluid oscillation inside the control valve causes the additional load to the valve actuator. When the additional load is added to the original load of the valve, it is possible that the required driving force (or driving moment) of the valve is greater than the maximum force (or moment) output by the actuator, which may cause the abnormal stop of the actuator. Conventionally, the interaction effect of the valve mechanical and electric components on the valve chamber’s flow field cannot be considered in computational fluid dynamics (CFD) simulations, so the oscillating fluid loads cannot be accurately obtained. In order to solve this problem, the mechanical-electric-fluid integrated valve model, using the FLUENT and AMESim cosimulation method, was developed to embody the interaction effect between the components of each part of the control valve and exhibit the fluid oscillation during the operating process of the control valve. Compared with the pure software simulations, the unsteady flow characteristics and dynamic response of the actuator were synchronously obtained in this study, which accurately captured the sudden fluid loads required for further compensation. At the same time, the differences in performance of different valve plugs were compared. The stability time of the valve plug and oscillation amplitude of the unstable fluid loads were distinct for control valves with different flow characteristics. The results can aid in understanding the instability mechanism of the fluid load in the control valve better, which provides the calculation basis for compensating the additional load on the valve plug and improve the reliability of the control valve.

The Effect of Draft Ratio of Side-By-Side Barges on Fluid Oscillation in Narrow Gap

In the present study, the effects of the draft ratio of the floating body on the fluid oscillation in the gap are investigated by using the viscous fluid model. Numerical simulations are implemented by coupling wave2Foam and OpenFOAM. The Volume of Fluid (VOF) model is used to capture the free surface waves. It is verified that the numerical results agree well with the experimental and other results. It is firstly found that, within the water depth range investigated in the present study, the depth of the wave tank has a significant effect on the numerical results. As the depth of the wave tank increases, the oscillation amplitude of the narrow-gap fluid largely decreases and the resonant frequency of the fluid oscillation in the narrow gap increases. The results also reveal that the draft ratio of floating bodies has a significant nonlinear influence on the resonant frequency and on the oscillation amplitude of the fluid in the narrow gap. With an increase in the draft of either the floating body on the wave side or the one on the back wave side, the resonant frequency decreases. The increase in the draft of the floating body on the wave side causes an increase in the reflection wave coefficient and leads to a drop in the fluid oscillation amplitude, and the increase in the draft of the floating body on the back wave side triggers a decrease in the reflection wave coefficient and results in an increase in the fluid oscillation amplitude. Meanwhile, the viscous dissipation induced by the fluid viscosity synchronously increases with the oscillation amplitude of the fluid in the increasing gap. Moreover, it is found that the draft ratio mainly affects the horizontal force of the floating body on the back wave side and that the highest calculated force increases with the draft ratio.

Hybrid adaptive method for finding the roots of a nonsmooth function in the problem of determining the natural frequencies of fluid vibrations in reservoirs

The article proposes a hybrid adaptive method for finding the roots of a non-smooth function of a single variable. The algorithm of adaptive root search method for non-smooth functions is presented. It assumes both adaptive reduction of a search step, and changing the search direction. It is found that the proposed approach allows us to detect the root even in the presence of a point of inflection. That is, for example, is impossible for the Newton method. The accuracy of finding the root using the proposed algorithm does not depend on the type of functions, the choice of the initial approximation; the method in any case will find the root with the given accuracy. Comparison of the results of the root calculations is performed using the dichotomy method, the "3/5" method and the proposed algorithm. It is established that the effectiveness of the developed method exceeds the efficiency of both methods - hybrids, when they have applied separately. The developed method is applied to the solution of the characteristic equation in the problem of determining the natural frequencies of oscillations of a liquid in a rigid tank having the form of a shell of revolution. The fluid in the tank is assumed to be perfect and incompressible, and its motion caused by the action of external loads is eddy. Under these assumptions, there exists a velocity potential to describe the fluid motion. The formulation of the problem is given and the method of its reducing to the solution of a nonlinear equation is given. This equation is a characteristic one for the corresponding problem of eigenvalues. The methods of integral singular equations and the boundary element method for their numerical solution are applied. The problem of fluid oscillation in a rigid cylindrical tank is considered. The results of numerical simulation of the fluid oscillation frequencies obtained by different methods for different number of nodal diameters are compared. It is noted that if the root of the characteristic equation is localized using approximate methods, then its refinement can be carried out using the proposed approach.

Analysis of Liquid Flow and Mixing in an Oscillatory Flow Reactor Provided with 2D Smooth Periodic Constrictions

In this research paper the residence time distribution (RTD) was monitored for a range of fluid oscillation, frequency, amplitude and flow rate in two oscillatory flow reactors (OFR) provided with 2D smooth periodic constrictions (2D-SPC) with different designs. It was studied the axial liquid dispersion using axial dispersion model and the mixing efficiency using tank-in-series model for continuous mode. Two cases, with and without fluid oscillation, were studied and determined the optimum conditions to ensure a close plug flow, an efficient mixing and a low axial liquid dispersion. The optimum operation conditions for the two 2D-SPC designs were found. Moreover, the effect of open cross-sectional area (a) on mixing and axial dispersion was also investigated. For low cross-sectional area values the mixing is higher. It was observed that fluid oscillation increases the mixing intensity even at lower flow rates, and the axial dispersion increases as the flow rate increases.