نشریه مهندسی دریا
پیاپی 15 (بهار و تابستان 1391)

Beam-to-column connections have been found to be of great significance in influencing structural behavior at ambient and elevated temperatures. Observations from full-scale fire tests and damaged structures confirm that connections have a considerable effect on the stability time of structural components in fire. Due to the high cost of elevated temperature tests, adequate experimental data about a broad range of connections is not available. One type of such connections is the connections between I-shape beam and pipe shape columns in oil platform decks. Considering the high probability of fire in oil platforms, study of the behavior of these connections at elevated temperatures is of great importance. Therefore, 11 experimental tests were conducted on this connection type to investigate their fire-resistance capacity. The failure modes and deformation patterns of these specimens were studied. The results showed that the main failure mode of the connection is the tensile failure of top star plate.

Chloride ion ingress is one of the major problems that affect the durability of reinforced concrete structures such as bridge decks, concrete pavements, and other structures exposed to harsh saline environments. Therefore, durability based design of concrete structures in marine areas has gained great significance in recent decades and various mathematical models for estimating the service life of reinforced concrete have been proposed. In spite of comprehensive researches on the corrosion of reinforced concrete, there are still various controversial concepts. Effect of environmental conditions on durability of concrete structures is one of the most important issues. Hence, regional investigations are necessary for durability-based design and evaluation of the models proposed for service-life prediction. The Persian Gulf is one of the most aggressive regions of the world because of elevated temperature and humidity as well as high content of chloride ions in seawater. In this work, two probabilistic service-life prediction models and two other service-life models proposed by local research centers are studied and compared using chloride profiles obtained from marine RC structures located in the Persian Gulf region. The results show the various uncertainties in model predictions and incompatibility of non-local models with Persian Gulf region.

In this article, a numerical meshless method called Weakly Compressible Smoothed Particle Hydrodynamic (WCSPH) is used to simulate the solitary wave breaking process on the beach. The present model is a two dimensional model that considers the fluid weakly compressibility. This model solves the viscous fluid equations to obtain velocity field and density and solves the equation of state to obtain the pressure field. This leads to computational efficiency of the model in comparison with basic SPH model. To simulate the fluid turbulence in wave breaking process, the Sub Particle Scale (SPS) model that is obtained from Large Eddy Simulation (LES) theory of turbulence is used. In this research to consider the accuracy of free surface simulation, first a dam break test is performed to compare the model results with experimental data of Martin and Moyce (1952). Afterwards to verify the turbulence model, a comparison between model results of dam break phenomenon and experimental results of Issa (2005) is carried out. These comparisons showed that the developed model is a powerful tool for simulation of the turbulent flow behavior. Finally, the transform of a breaking solitary wave on the sloping beach is modeled and the results were discussed.

This paper deals with a free vibration analysis of functionally graded elliptical plates with different classical boundary conditions on the basis of polynomial-Ritz method and classical plate theory. The proposed admissible function is capable to obtain accurate natural frequencies of various classical boundary conditions namely, clamped, free and simply supported edges. The mechanical properties of the FG plate are assumed to vary continuously through the thickness of the plate and obey a power law distribution of the volume fraction of the constituents. The convergency of applied polynomial-Ritz method is investigated. In order to verify the accuracy of the present solution, a comprehensive comparison study is performed with the available results in the literature for homogeneous elliptical plate and FG circular plate. Also, the numerical results of the present solution for FG elliptical plate are compared with those of the finite element method (FEM). Finally, the effects of the plate geometry and inhomogeneity on the natural frequencies are investigated and some vibrational mode shapes related to symmetric-symmetric, symmetric-antisymmetric, antisymmetric- symmetric and antisymmetric- antisymmetric states are presented.

For stabilization of zero speed ships active anti roll tanks and gyro stabilizers are used. Because of anti roll tank limitations on working frequencies gyro stabilizers are proposed. A nonlinear model for ship is used to simulate hydrodynamic forces. Wave’s disturbances are considered as non-parametric uncertainty. A sliding mode controller is used for roll stabilizing. A nonlinear h infinity controller is designed to reduce the disturbance effects on the ship. The designed sliding mode controller uses more control energy from h infinity controller. Instead roll reduction of the sliding mode controller is grater from the other one. The main concept of the used model in this article was taken from an authority that ship model data estimated from real ship with Halcyon gyro actuator. Roll reduction increases by applying designed controllers in wide range of sea states. In addition nonlinear effects intended in this article. Simulation results based on Jonswap wave spectrum demonstrates the performance of robust system in confrontation with wave perturbations.

Analysis of wedge water entry as a basic problem has wide application. Model testing is a powerful means to deal with the said problem. In this study, a set of water entry tests on wedges of 20, 30 and 40 degrees deadrise angles has been conducted and the pressure distributions are recorded. Free falling method in symmetry conditions are considered in this research. A parametric study on pressure coefficients due to velocity and deadrise angles has been carried out on the wedge. Furthermore, Z-parameter as a non-dimensional factor defined for two individual parameters, time and depth of entry, has been evaluated. Finally, some comparison with numerical methods is presented. The kind of parametric study by means of model test may be regarded as the outcome of this study.

The predominant principle included in the design of reshaping berm breakwaters is the supply of a wide berm at or nearby the water level with less armor stone size than that used in conventional design, which are allowed to reshape until an equilibrium slope is attained. In the present study, the recession of the berm due to wave and structure parameters has been investigated based on two dimensional experimental modeling in a wave flume. A series of 156 tests have beencarried out with irregular waves with JONSWAP spectrum to observe the behavior of the structure.To cover the effects of initial berm width and stone sizes on berm recession, several wave parameters such as wave height, wave period and storm duration have been considered. To analyze the results, the experimental data are presented together, leading to a formula for prediction of the berm recession considering foregoing parameters, i.e. wave and structural parameters.

Evaluation of seismic behavior of offshore platforms is one of the important design steps in seismic regions. Nevertheless, because of complication and time cost of these methods, engineers usually do not study them deeply. Endurance Time (ET) method is a good solution for this problem. In this method, with acceptance of a reasonable region of errors, the time of analysis can be reduced considerably. Besides with one ET analysis, the behavior of structure can be evaluated in different seismic levels. In this paper, the ET and other usual methods in standards are introduced and then the seismic behavior of three platforms is compared with ET and response spectrum method. In this comparison, the acceleration function which is generated base on Iranian cod (2800 standard), is used and the differences are considered in relation to spectral analysis of 2800 standard. The results show appropriate conformity between two methods.