JOURNAL OF MARINE ENGINEERING
Year:2009 | Volume:5 | Issue:9|Papers Count:8

Suction caisson foundation systems have been successfully used in the past two decades in numerous occasions on a variety of offshore structures in a wide range of environments. The pull-out capacity of suction caissons remains a critical issue in their applications, and reliable methods of predicting the capacity are required in order to produce effective designs. In the current study a numerical approach has been chosen to investigate the behavior of suction caissons under pull-out loads. The model has first been calibrated against available experimental data and also been verified against other test data. The verified model has then been used to study the influence of a number of parameters on the pull-out behavior of suction caissons. Variations in the soil type, soil cohesion, internal friction angle, dilatancy angle, Poisson's ratio and the aspect ratio of the caisson have been studied. Soil nonlinearities, soil/caisson interactions, drainage conditions and suction effects have also been taken into consideration. Simple approximations have been put forward to express the effects from above mentioned different parameters on the pull-out capacity. These approximations have also been compared with some analytical and simplified relationships proposed by other researchers.

In this paper, the behavior of a typical jack-up platform under accidental loading of ship collision was investigated. The studied platform was modeled using ANSYS software and analyzed dynamically under ship impact. The platform was also analyzed dynamically under secondary ship impact. The initial collision results showed that the main energy absorption mechanism in impact to jack-up platform is overall deformation of platform; it also shown that environmental preloading in some cases causes yielding or fracture of impacted member. The subsequent collision analysis showed that leg chords can resist to a subsequent impact and the platform in both first and second impacts has local damage such as indentation of the chord wall but the rest of the structure remains almost intact. Finally, the platform was modeled in damaged condition and analyzed dynamically under one-year environmental loads and the value of maximum stress and probability of platform failure was investigated. In addition, the value of stress and displacement in the intact and damaged platform has been compared and the results are analyzed.

Providing an illustration of sound propagation in the Hormoz Strait ,this paper is about acoustic wave propagation in shallow water for a harmonic point source with low frequency, less than 1000Hz and solution of a homogenous Helmholtz equation using parabolic equation. C++ programming is used to solve Helmholtz equation [9] and MATLAB software is used to illustrate figures and animate them [6], [7]. The input parameters are water characteristics such as, salinity, temperature, corresponding depth of the surface and of the bottom, in the software, as well as the number of frames. One can view animation of frames and see how salinity and temperature can effect on the sound propagation and how grazing angle come closer to the normal (vertical line) with respect to decrease of temperature and increase of salinity and depth in water column and therefore decrease of sound velocity, corresponding to Snell's law, increase of refraction index and specially at the Hormoz Strait. The convergence zone distances at the surface are more than two kilometers although it lowers at the bottom.

In this paper, first a sample Autonomous Underwater Vehicle called NEROV from the University of Trondheim of Norway has been selected with its equations of motion and by using dynamic programming approach; optimal paths for consuming energy have been designed. There are moving obstacles in the environment wherein the robot moves. It is seen that the planned paths is smooth and the energy used for the robot is minimized. After planning the path, a control system has been designed for by using Slotine & Li algorithm. In this paper, the interaction between the robot dynamics and environmental effects due to the obstacles dynamics is ignored. In the final stage of the path planning, using an Intelligent Converted Solution (ICS), an optimal path is designed for the vehicle and employing the same control system, the optimal path is tracked.

The berm recession of a reshaping berm breakwater has a very important role in the stability and reshaping of this structure. In this research, the recession of the berm due to wave parameters has been studied based on 2D experimental modeling method in a wave flume. Irregular waves with JONSWAP spectrum were used. A total of 60 tests have been performed to cover the impact of wave parameters such as significant wave height, mean wave period and storm duration on berm recession. A new dimensionless parameter is introduced to evaluate the simultaneous influence of wave height and wave period. Then, a new formula that includes the wave parameters is derived using the new dimensionless parameter for estimating the berm recession. A comparison is made between the estimated berm recession by this new formula and formulae given by other researchers. The results of this new formula in comparison with the other investigators formula show a proper correlation with the present experimental data and other experimental results.

According to the high demand of fiberglass/polyester composites in marine applications, this paper has studied the properties of these composites. It has also been shown that isophthalic polyester has better properties than orthophthalic polyester, in marine applications. This paper has also investigated the vinyl ester and phenolic resin stability especially in the sea water and has shown that vinyl ester resin in comparison with polyester resin has better physical stability and chemical resistance in the sea water. Note that depend on nonflammable properties of phenolic resin, its application in each part of ship which has the highest probability of conflagration is almost inevitable. In addition, we have discussed the use of carbon fiber instead of glass fiber because the intrinsic problems of glass fiber such as heaviness and having low modulus could be solved with using carbon fiber.

Prediction of wave parameters is necessary for many applications in coastal and offshore engineering. In the literature, several approaches have been proposed to wave predictions classified as empirical based, soft-computing based and numerical based approaches. Recently, soft computing techniques such as Artificial Neural Networks (ANNs) have been used to develop wave prediction models. In this work, the performance of regression trees for prediction of wave parameters was investigated. The data set used in this study comprises of wind and wave data gathered in Caspian Sea. Results of regression trees were compared with those of artificial neural networks. Results indicate that error statistics of regression trees and artificial neural networks were nearly similar. In addition, regression trees need lower run-time.