نشریه مهندسی دریا
پیاپی 12 (پاییز و زمستان 1389)

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.

In this paper, a concept is presented for decreasing the response amplitude of fixed offshore platforms using a movable submerged tank. The idea is based on utilization of the tank’s buoyancy and inertia forces to reduce the responses of the platform. In this concept, a four-legged platform is investigated in which braces are removed in lower levels, and the movable submerged tank including substantial amount of buoyancy force is added. As a result of the tank oscillation, the upward buoyancy force causes a reversible moment which depends on the tank position and time. Actually, tank movement changes the internal forces distribution pattern that could produce time dependent stiffness. The non-linear and large displacement effects are considered in the static analyses using a program developed by employing MATLAB software. Results of static analyses indicate the tank efficacy in decreasing the displacement amplitude of the platform. The performance of the concept can be improved by taking an appropriate volume and oscillation amplitude for the tank. It is noteworthy that the tank should be placed in enough proper depth for preventing any uncontrolable wave loads; additionally, results show that the tank usage in less stiffened platform could be more efficient, in other word, the tank efficiency will be increased by depth magnification.