جستجوی مقالات مرتبط با کلیدواژه "هیدرودینامیک" در نشریات گروه "مهندسی دریا"

The use of step at the bottom of the hull is one of the effective factors in reducing the resistance and increasing the stability of the Planning hull. The presence of step at the bottom of this type of hulls creates a separation in the flow, which reduces the wet surface on the hull, thus reducing the drag on the body, as well as reducing the dynamic trim. In this study, a design space was created by making changes to the three input parameters. Input parameters include the linear speed of the hull, the distance from the step from the transom and the change in the step height across the hull. The present study was carried out using the Computational Fluid Dynamics (CFD) coupled with Response Surface Method (RSM). The Computational Fluid Dynamics simulation was done by StarCCM+ software. The design of experiments and the Box–Behnken design method were used to select samples and the Kriging model for the Response Surface Method was used. Genetic Algorithm and screening method were also used to find optimal points. Output parameters include Drag and Lift force on the hull, the total hull trim. The results of the sensitivity analysis on the input parameters show that the hulling speed is the most influential parameter on the value of the output parameter.

For most vessels, the frictional resistance of the hull in the water has the largest share in the total resistance of the ship, so in the past few decades much research have been done on reducing the frictional resistance of ships. Among these, stepped vessels with a significant reduction in the amount of wetted surface have a special place. In this study, the effect of a single transverse-step on a flat plate is investigated in calm water with computational fluid dynamics methods. First, the vessel is modeled as a planing flat plate in a fixed trim and draft. By adding a transverse step to the geometry of the model, the proportion of frictional drag to the lift is calculated and compared with the other results. Also, changing the amount of frictional drag and wetted surface due to the changing of the longitudinal position and height of the step are investigated.

Utilizing transverse steps for high-speed planning hulls is one of the methods for reducing of their resistance and thereafter increasing of their speed. Similar to regular planning hulls, the stepped hulls also have a hump in their resistance-speed curves during the transition from displacement to planning stage. Overcome to the hump usually follows with a heavy load on propulsion systems. In this paper, hydrodynamic characteristics of two planning boat model, a regular V-bottom hull and a hull with one transverse step, are investigated experimentally using towing tank tests. After that the tests for the stepped hull are repeated while a ventilation system is also added behind the transverse step. The results show in preplanning stage, resistance of the stepped hull increased about 30 to 40 percent whereas at the planning stage their resistance reduced about 5 percent respect to the regular planning hull. Using a natural ventilated system for stepped planning hulls reduced both the hump resistance (about 21 percent) and preplanning resistance respect to non-ventilated stepped hull. So, it can be used as a low cost system for practical issues.

Siltation is a serious problem occurred in riverine harbors and estuaries. To overcome this problem and navigation control, continuous dredging is needed. To date, many approaches have been developed to reducing siltation in harbors.The objective of the current research study is to intoduce an cost effective structural method to control the siltation in riverine and tidal harbors. This method which is based on the flow pattern control at the entance of the harbor, is implementation of a current deflecting wall (CDW) at the harbor entrance. In the current study, the efficiency of the CDW was investigated for reducing sedimentation in reverine harbours and also the influence of geometrical specification of CDW on the hydrodynamic condition inside the harbor have been investigated. In the first step of the study, the hydrodynamic model was calibrated against experimental measurements cited in the literature. Then the model was applied to various alternatives of CDW shape, apex angle, length and location. Results obtained through numerical modeling experiments showed that around 30 percent reduction in harbor siltation could be achieved.

Among compliant offshore platforms, tension leg platforms (TLP) are referred to, as hybrid structures. This kind of platforms resemble to ordinary semi submersibles when their serge, sway and yaw motions are considered, since they are compliant whereas with respect to pith, roll and heave motions they respond more like a fixed platform rather than a floating body. This paper presents a method to analyze and evaluation of hydrodynamic forces of a regular simple wave on a TLP and a general solution to expand the method to be applied for a randomly changed water surface with a known spectrum e.g. pierson-Moskowitz. This analysis was made, using a 3D model with 6 coupled degree of freedoms. Stiffness of mooring system and drag force are assumed to non-linear and the effect of diffraction and radiation are neglected. Hydrodynamic forces and response were modeled, using modified Morison equation. The dynamic behavior of mooring lines and hydrodynamic forces on tensioners were neglected. The resulting equation was solved in time domain by Newmark-Beta algorithm.