نشریه مهندسی دریا
پیاپی 11 (بهار و تابستان 1389)

A pipeline is considered as shell structure so its design is based on stability concepts; dueto the exerted high pressure, local instability is probable to occur and so prevention of itsoccurrence and propagation are important subjects in its design. In this paper, dynamic buckle propagation has been modeled by 3D finite element method, results are verified with experimental tests and velocity of dynamic buckle propagation is calculated for pipes with different diameter to thickness ratios. Due to the effect of velocity in designing of marine pipelines, separate relations based on the initiation pressure are derived for the velocity of propagation and the influence of diameter to thickness ratio on the propagation velocity is studied.

The estimation of wave loads on very large flouting structure is usually done by an empirical or a computational approach. The computational approach usually assumes two types. Some use the Laplace equation or potential flow and some take the Navier-Stokes equation or viscous flow analysis. In this study, the interaction between wave and elastic plate is investigated by using viscous flow assumption. It is coupled with the elastic plate equation. Numerical solution is carried out with finite difference method in form of upwind scheme. The displacement of elastic plate is simulated numerically. Numerical results are compared with the numerical results of Basirat Tabrizi and Kouchaki Motlaq for potential flow and with the numerical results of Ohkusu and Namba and experimental results of Kashiwagi for viscous flow. The results show that viscous flows have more damping effect on displacement of elastic plate than nonviscous flows.

The objective of this paper is to introduce a new method for coastlines delineation fromhigh-resolution satellite images automatically. The proposed approach integrates the colorhistogram analysis for estimating the number of clusters, fuzzy c-partition, and geneticalgorithms for optimizing fuzzy c-partition matrix. The imagery is classified into homogenous areas using the proposed fuzzy logic segmentation approach. Morphological filtering is then used to remove noises from the segmented image. The coastlines are finally extracted from the filtered image by a delineation algorithm. Thedeveloped approach is evaluated based on a 1 m resolution IKONOS pansharpened imagery of Konarak region in Chabahar, Iran. It is demonstrated that 95% of the extracted lines remain within the three-pixels buffer areas around the coastlines. This presents the effectiveness of the proposed algorithm.

Nowadays oil spill are one of the most important problem in the humans life. Usuallyadvection and dispersion occur because of chemicals, physicals and biological processes that related by properties of oil and other things. These processes are evaporation, dispersion and so on. When oil spills on the sea, it is extended and made oil slick. Increasing these kinds of events cause developing many kind of oil spill model.In this paper a numerical model for simulating drifting and spreading of oil slick thicknessincluding dissipative processes such as advection and diffusion of averaged oil concentration in the water column and evaporation, with Eulerian approach and multi phase model has been developed. Equations were discrete using finite volume method. Available hydrodynamic model can solve two-dimensional depth-averaged unsteady Navier-Stokes equations. Alternating Direction Implicit method (ADI) is used for numerical solution of flow. In order to verify the accuracy of hydrodynamic, advection and diffusion model of oil slick thickness and oil average concentration, numerical results compared with experimental measurements and analytical model. Comparison shows the model can satisfactory simulate the problem.

Asaluyeh Fishery Port is an old fishery port located in the south-east of the BushehrProvince. The rapid shoreline advancement of the updrift fillet of the main breakwater during past few years and the sedimentation at the port entrance has resulted to substantial difficulties in using the port. The relatively large amount of sedimentation finally affected the navigation at the entrance of the port. Using field observations, sedimentology analyses of the obtained sediment samples and comparisons of hydrographic maps in order to get the rate and direction of the updrift sedimentation, the cause of rapid sedimentation and the source of this sediment have been studied in current paper. Statistical parameters of sediment samples have been calculated and minerology, morphoscopy and morphometery investigations were conductedusing a binocular microscope. The results show that while there is not a clear clue of coralsource among the sediment samples of the west coast of the sampled site, a large portion of coral segments are observed in the vicinity of the port. The investigation of sediment samples confirms the larger percentage of terrigenous sediments in the past as well as the increase of carbonate sediments in recent years. The field observations and analyses of sediment samples reveal the increase of sediment stress, as one of the most profoundly deleterious impacts on corals, which has resulted to the considerable decrease of patch reefs and the related marine organisms. It is apparent that the reclamations and large construction works have caused the excess of sediment load. This is the cause of considerable increase of carbonate sediment and huge sedimentation at the port. The investigations suggest that construction of a groin and dredging of the harbor is the most suitable option for solving the sedimentation problem in longterm.

Investigation of the flow pattern around bridge piers is of utmost importance because of its great effect on destruction of the piers. Despite the hydrodynamical and structural values of designing sections causing minimum turbulence against the flow passing the bridge pier, a review of the literature shows that investigation of the flow pattern around bridge piers with varying section has not been studied by the researchers. In this research study, a threedimensional numerical model has been used to study the flow field around a cylindrical and four conical piers of different slopes. The computational domains were first discretized using GAMBIT and then analyzed by FLUENT. Finally, the flow pattern and bed shear stress around the piers have been investigated and the relevant comparisons have been made. Numerical model results show that increment of the pier’s slope has a great effect on reducing turbulence of the passing flow and thus lessening the bed shear stress around the pier.

In the present paper optimum height of skirt of Skirt Pontoon Floating Breakwater arereported by physical model. 54 tests on 3 types (skirt heights: 8,16 and 24 cm) of skirt pontoon floating breakwater is conducted in the wave flume of Soil Conservative and Watershed Research Center. Hydrodynamical and geometrical parameters were analysised. In this research optimum height of skirt to water depth ratio is determined.

The important characteristic of sea waves is their high energy density, which is the highest among renewable energy sources. Having up to 2700 km. of shoreline, Iran has a great potential in construction of offshore wave buoys (hereafter called OWB). In this article a OWB model with the possibility of assembling different buoy configurations is introduced. The system is exposed to regular and irregular waves which are generated using wave maker in a 2D wave tank. Wave energy can be extracted from vertical oscillation of its floating buoy. The device is so designed as to operate in rotational (pitch) mode in addition to vertical (heave) motion. Some experiments are also conducted to demonstrate system performance. Experimental results in different conditions are presented and the effect of different buoy configurations on the system efficiency is studied. Numerical simulations that obtain the hydrodynamic coefficients and dynamic response (the Response Amplitude Operator or simply RAO) of each buoy in waves validate test results that the buoy with highest transfer function obtained in simulationshas highest efficiency in power extraction. It is finally shown that the horizontal buoy is the most efficient configuration among other constructed buoys for extracting wave energy. The non-dimensional groups are studied and the output power of a full scale OWB is obtained based on similarity laws.

The effects of wave direction, frequency and the waterline shape of floating structures on the wave mean drift force formula have been considered separately by several authors but there isnt a general formula to take into account all of these effects. In this regard, Faltinsen’s wave drift force formula has been modified by adding finite draft coefficient. The results obtained from this formula which is dependent on wave frequencies, has been compared with Helvacioglu’s experiments favorably in high wave frequencies. Moreover, the influence of the current on the wave mean drift force has been taken into account by considering the current coefficient derived from the ship added resistance formula. In addition, the formula for the calculation of the wave drift damping has been extended to cover high wave frequencies as well as low wave frequencies. The results compared with asymptotic formula showed good agreement in the high frequency band.

Wave diffraction is a very important phenomenon in marine engineering and several models have been developed for its simulation. The new version of SWAN, a third generation spectral model, includes an approximation to wave diffraction. The approximation is based on the mildslope equation for refraction and diffraction, omitting phase information. The objective this paper is to evaluate the performance of a numerical model. To do so, the propagation of unidirectional and multi-directional irregular waves through a breakwater gap is simulated to validate the model. It is desired to evaluate the dependence of the diffraction coefficient (Kd) and incident wave parameters. Wave parameters are directional spreading parameter (S) and peak enhancement factor (γ) of JONSWAP wave spectrum and direction of incident wave. The model is also tested using two different lengths of breakwater gap. A laboratory data set is used for the evaluation of SWAN. The comparison shows a good agreement between the model outputs and the experimental data. The average scatter index is about 5% for Kd and Th average of Bias parameter is about -0.05. This shows that the model, in most cases slightly under estimates the diffracted wave height. It is also found that the wave directional spreading parameter is more effective compared to the peak enhancement factor on the wave diffraction.The calculated results indicate that, this numerical model is applicable to the real engineering problems.