JOURNAL OF MARINE ENGINEERING
Year:2011 | Volume:6 | Issue:12|Papers Count:8

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, lengthand location. Results obtained through numerical modeling experiments showed that around 30 percent reduction in harbor siltation could be achieved.

This research is concerned with the nonlinear elastic-plastic analysis of ship curved bilge plate, located at the junction between ship's side and its bottom. After derivation of average stress-average strain relationships by finite element analyses of the models with varying dimensional and mechanical characteristics, the effects of any of parameters on the trends of such relationships is studied and interpreted. A commercial finite element code is used in such analyses. The boundary and loading conditions are tried to be adopted according to real practice.It is finally observed that the behaviour of such curved plates is entirely different from elasticperfectly plastic behaviour and there is a reduction in their load carrying capacity after ultimate strength level. Finally, based on the obtained results, a set of empirical formulations areintroduced in order to simulate the average stress-average strain relationship of such plate sections of the ship. These formulations have the capability of being used in the progressive collapse analysis of ship's hull girder.

Seakeeping recording of a vessel, so called seakeeping trial, is an important issue which is performed for some vessels. The goal of this research is to develop principles of seakeeping trial of planing vessel in sea waves. For this purpose it is initiated with the principles of ship seakeeping in sea trial. The main feature of a planing vessel is dynamic trim, high slamming accelerations and impact nature of slamming acceleration. This behavior makes its seakeeping more complicated. In this study, for the first time, an attempt has been made to extract boat six motions in hydrodynamic coordinate system from measured accelerations and rate of angular motions in body coordinate system. To realize the goal, the three coordinate system and transformations are defined. An instruction for seakeeping trial of planing vessel is introduced.A set of seakeeping trial on boat is done and the results of measurement are analyzed according to above principles. Validation and conclusions are also presented.

The visco-elastic properties of asphaltic layers make it appropriate for application in coastal protection in embankments. In this research, an experimental set up of a coastal embankment is developed to investigate the characteristics of lean stone asphalt layer on coastal embankments.More than 100 laboratory tests were carried out considering various loading conditions on the asphalt protective layer. The main variables in the tests are the incident wave height and period, front slope angle of embankment, still water depth, and the wave cycles incoming to the structure. The main measurements and observations in the experiments are the mechanical strength and damage pattern in the asphaltic protection, erosion pattern on the movable bed adjacent to the asphaltic heel, and wave-structure interaction such as wave run-up and overtopping.

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 fourlegged 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 tankposition 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.

The goal of this study was to simulate the wave characteristics in the south of Persian Gulf over a 60 year period. Wind data from the study area including offshore measurement, satellite observation and numerical atmospheric models were collated and analyzed. The modified NCEP/NCAR wind field was chosen as input to the SWAN model which has the longest duration among wind data sources. SWAN model was run in stationary mode for different cases of wind speed and direction and lookup tables were made for each wave parameters in each point of interest. A 60 year time series of wave characteristics were made using these lookup tables. Having such long time series enables us to calculate the wave characteristics with larger return periods. Execution time was drastically decreased using this method.

Simultaneous effects of mooring characteristics and waves heading on mooring forces of a multi-rows floating pier which is composed of pontoons have been investigated in this paper.The investigated variable parameters include the moorings array, number of mooring lines and their pretensions. A floating structure consisting of 12 pontoons connected together with rigid connectors and is located under irregular sea waves. Hydrodynamic analyses have been carriedout for various conditions. Results show that even though pre-tensioning of mooring lines results in increasing of the structure stiffness and better force distributions between mooring lines, however, increasing the pre-tensioning from critical values has no considerable effect on the structure responses. Using the results of present work and requirements from multipontoons, it is possible to suggest a proper mooring system and direction of floating structure in the conceptual design of such structures.

In recent years, unmanned vehicles have intensively been developed to reduce risk on human life for marine applications. Predicting the dynamics behavior of an autonomous underwater vehicle is important during the vehicle’s design phase. In other words to design an AUV, one must clarify its maneuverability and controllability based on a mathematical model. The mathematical model contains various hydrodynamics forces and moments expressed collectively in terms of dynamics equations. Therefore, to optimize the AUV design it is necessary to predict maneuvering ability and dynamics behavior of AUV. This can be done by computational simulation.SUT-2 is an AUV system, being developed by Marine Engineering Research Center, Sharif University of Technology in Iran. Primary dynamics test have been developed in marine engineering laboratory. In this paper dynamics behavior of this AUV is investigated by using experimental test and computational simulation. Results can be used to optimize the dynamics behavior and designing the autonomous controller of AUV.