Current Issue : April - June Volume : 2018 Issue Number : 2 Articles : 5 Articles
This paper proposes a method based on simulation techniques for fluctuation characterizations of unmanned surface vehicle (USV)\noperations under Sea State 3. In order to simulate the operations of a USV in Sea State 3, we generated the data of sea surfaces using\nlinear wave theory and utilized the motion equation. Fluctuation analysis results by the proposed simulation method could provide\ncrucial information for designing the stabilization system for the critical equipment on a USV.Through these works, it was verified\nthat the design specifications such as range of motion, maximum speed, and acceleration could be estimated using the simulation\ndata....
Wave slamming loads on a circular cylinder during water entry and the subsequence submergence process are predicted based\non a numerical wave load model. The wave impact problems are analyzed by solving Reynolds-Averaged Navier-Stokes (RANS)\nequations andVOF equations.Afinite volume approach (FV) is employed to implement the discretization of the RANS equations.A\ntwo-dimensional numerical wave tank is established to simulate regular ocean waves.Thewave slamming problems are investigated\nby deploying a circular cylinder into waves with a constant vertical velocity.The present numerical method is validated using other\nnumerical or theoretical results in accordance with varying free surface profiles when a circular cylinder sinks in calm water. A\nnumerical example is given to show the submergence process of the circular cylinder in waves, and both free surface profiles and\nthe pressure distributions on the cylinder of different time instants are obtained. Time histories of hydrodynamic load on the\ncylinder during the submergence process for different wave impact angles, wave heights, and wave periods are obtained, and results\nare analyzed in detail...
Qualitative simulation is a well-known reasoning technique that involves the use of simulation technologies. Reasoning is made to\ndetermine qualitative values and change directions of system variables, and it is done for each time point and time interval following\nthe time point. Qualitative variables possess continuous qualitative value sets that are discretized by landmark points. Qualitative\nsimulation uses qualitative time representation and its quantitative value is of no interest. The main purpose of this study was to\ndevelop a technique to determine time steps for a quantitative simulation under guidance of qualitative information. The proposed\ntechnique determined time advances using qualitative and quantitative information together to obtain a robust time step as wide as\npossible for simulation time advances. For this purpose, sign algebraic properties and derivation roots of quantitative equations and\nqualitative variable values with their change directions were used to compute time advances. In the approach, qualitative simulation\ndetermined landmark points to be advanced, and quantitative simulation calculated the duration required. Using the proposed\nalgorithm, the simulation is advanced instead of iterating simulation time for a predefined time step and checking whether or not\nthere is any activity in the interval, directly to the time points that are qualitatively different....
To solve problems of leakage, vibration, and noise caused by disorders of flow field distribution and working pulsation in the\nrotating-sleeve distributing-flow system, governing equations of plunger and rotating sleeve and computational fluid dynamics\n(CFD) model are developed through sliding mesh and dynamic mesh technology to simulate flow field and working pulsation.\nSimulation results show that the following issues exist: obviously periodic fluctuation and sharp corner in flow pulsation, backward\nflow when fluid is transformed between discharge and suction, and serious turbulence and large loss in kinetic energy around\nthe damping groove in transitional movements. Pressure in the pump chamber rapidly rises to 2.2MPa involving over 10% more\nthan nominal pressure when the plunger is at the Top Dead Center (TDC) considering changes about damping grooveââ?¬â?¢s position\nand flow area in two transitional movements. Shortly pressure overshoot gradually decreases to a normal condition with increasing\nflow area. Similarly, pressure in the pump chamber instantaneously drops to a saturated vapor pressure âË?â??98.9 KPa when the plunger\nis at the Bottom Dead Center (BDC). With increasing flow area the overshoot gradually increases to the normal condition. This\nresearch provides foundations for investigating flow field characteristic and structure optimization of rotating-sleeve distributingflow\nsystem....
The paper considers the possibility of using different approaches to modeling turbulence under conditions of highly developed\nconvection at high Rayleigh numbers. A number of industrially oriented problems with experimental data have been chosen for\nthe study. It is shown that, at Rayleigh numbers from 109 to 1017, the application of the eddy-resolving LES model makes it possible\nto substantially increase the accuracy of modeling natural convection in comparison with the linear vortex viscosity model SST.\nThis advantage is most pronounced for cases of a vertical temperature difference with the formation of a large zone of convection\nof strong intensity. The use of the Reynolds stress model EARSM is shown for cases of natural convective flow in domains with\ndihedral angles in the simulated region and the predominance of secondary currents. When simulating a less intense convective\nflow, when the temperature difference is reached at one boundary, the differences in the approaches used to model turbulence\nare less significant. It is shown that, with increasing values of Rayleigh numbers, errors in the determination of thermohydraulic\ncharacteristics increase and, for more accurate determination of them, it is expedient to use eddy-resolving approaches to the\nmodeling of turbulence....
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