نشریه مهندسی دریا
پیاپی 27 (بهار و تابستان 1397)

Slamming loads are important in the structural design of high speed vessels. Slamming can cause global and local effects on the ship structure. Here global effect of slamming (bow flare water impact) means whipping considering hydroelasticity investigated. Considering ideal, non-viscous and non-compressible fluid, bow flare impact loads is developed after determination Bow flare impact forces, with considering of proper beam model and exerting condition due to hydroelasticity, new form of beam deflection model is derived. In deriving of the beam deflection equation, hydroelasticity is considered, thus solving beam equation leads to hydroelastic analysis of bow flare slamming. Finite difference method is used for solving this equation. In order to validate the computation of results, the third party software ANSYS is used. The ship hull girder is represented by a uniform onedimensional beam that is supported by a uniform elastic foundation. Time depending load is applied as a pressure on end beam and deflection is calculated.

The FMEA method is one of the safety and reliability management techniques, which is very effective in identifying and eliminating potential problems in the product design and production process. Despite the extensive use of the Risk Priority Number (RPN) in FMEA, it is criticized due to shortcomings such as the inability to analyze crashes with a common cause, high duplicate RPN values and the lack of direct and indirect relationships among failures and the causes. Considering the importance of safety in marine industry, this paper describes the implementation of an aggregating method of TOPSIS and DEMATEL which is able to overcome common shortcoming of traditional RPN method in a marine propulsion system. The implementation of the method in prioritizing the main root causes led to more desirable results compared to the traditional RPN and DEMATEL base methods.

Effect of aluminum interlayer and heat-input was investigated on lap joint properties of 5052 aluminum alloy to St-12 steel welded by pulsed GTAW with ER- 4047 filler metal. Direct joining of aluminum to steel without interlayer was not successful due to the formation of brittle intermetallic phases. Presence of the aluminum interlayer led to decrease in the intermetallic compounds (with the thickness

The water entry problem of spherical projectile is simulated numerically and experimentally in this study. An explicit dynamic analysis method is employed to model the fluid-structure interaction using a Coupled Eulerian-Lagrangian (CEL) formulation that is available in finite element code Abaqus. The comparison of the numerical simulation results including displacement and velocity variations of spherical projectile in water depth as a function of time, with the theoretical results, indicates a good match between these results and the precision and applicability of the numerical algorithm used. The results reveal that pinch-off time is a very weak function of projectile mass and impact velocity on free water surface; while the pinchoff depth significantly increases along with increased this parameters. Additionally, the projectile mass has a subtle effect on viscous dissipation energy, while increasing the impact velocity on free water surface leads to decrese in dissipation energy.

This paper Analyzed buckling of steel cylinders in other researches. Here by using MATLAB software, a program to buckling pressure range of steel cylindrical shell under external pressure is provided. By comparing the output results and analysis charts, the risk of buckling in the cylinders can be detected with very good accuracy. After determining the proper correlation to predict buckling, hydrostatic pressure testing system with record pressure and volume changes for online registration prepared. In order to prevent suddenly destruction, buckling test equipment with volume control method has been prepared and the hydrostatic pressure tests were carried out on specimens of steel. So from overall load which make buckling will be prevented. By this method, prediction of buckling pressure and prevention of samples destruction can be done with about 16% error.

Pile foundations provide support for structures, transferring their load to layers of soil or rock that have sufficient bearing capacity and suitable settlement characteristics. There are a very wide range of foundation types available, suitable for different applications, depending on considerations. There are various methods to estimate the axial bearing capacity of the pile such as experimental, analytical and in-situ experiments. Accurate estimation of bearing capacity is essential in geotechnical engineering due to the high cost of implementing deep foundations, that use of artificial intelligence and genetic algorithms can be helpful in this regard. In this study compressive bearing capacity for two prefabricated concrete and steel pipe evaluated under harmonic load using modeling in finite element software (Plaxis 2D), and the results were compared with the Dynamic Load Testing (PDA) data in a case study. In this research, the results of 100 numerical analyzes have been optimized using a genetic algorithm that resulted in the introduction of an estimated relationship with the accuracy of the pile bearing axial bearing capacity for concrete and metal piles. In this study, comparing different methods of assessing the bearing capacity of piles indicates the fact that most empirical methods provide a much larger load capacity compared to actual values.

Caisson breakwater is one the most common coastal protection structures which their main application is to reduce wave energies and create a calm basin for berthing of the ships in ports. A simple approach to achieve this is to build a solid wall against the waves which are know as caisson breakwater. In this paper interaction of irregular waves with normal and perforated-wall caisson breakwater using FLOW-3D is studied. In this paper, the appropriate numerical model has been selected and then the model setup is explained. After the model setup, sensitivity analysis, calibration and verification of the model results with available laboratory data are presented. When the model performance is verified, the interaction of irregular wave with the perforated-wall caisson breakwaters is evaluated. The modeling results show that the perforated caisson breakwater compared to the vertical breakwater has a better hydraulic performance. In comparison to perforated-wall caisson breakwater results and euro top 2016 results, define a new dimensionless number to consider width of chamber to be recommended.

One of the major and effectual issues in designing of floating breakwater is its geometry. In this study, effect of geometry of floating breakwater on wave transmission coefficient for the periods ranging from 0.63 to 1.26(s) will be discussed using Flow_3D software, which is mainly based on trapezoidal geometry and curvature in various sections.
First, the numerical results of the base model were verified against the experimental model and then seven various geometries are designed in two groups. For the first group, the draft was assumed to be constant and to provide this particular draft, different geometrical sections were examined, using various masses and densities. In the second group, the cross-sectional area, mass and hence density were assumed to be constant and the proposed models were evaluated at different drafts. Finally, within the range of periods stated, the geometry having the best performance and economical is suggested for the related projects.

Marine transportation industry, as the main basis of world trade, is of great importance. Here, collision and grounding are the most frequent ones, threatening the industry. To study collision accident and assessment of its occurrence risk, we need to identify ship routes, in which Automatic Identification Systems introduces the best tool. Here, based on the concept of safety domain applied on traffic, high collision concentration locations are identified. Accordingly, probability of collision occurrence in the high risk locations is examined based on the Bayesian network. This study just show sample result of implementing new approaches in accident analysis, which has no previous record in our country.

Marine vessels may cause accidental damage to the offshore platforms during uploading oil and gas production in the storm conditions or incorrect navigation by ship’s captain. This impact of sea-going vessels is source of local or global deformations in the offshore structures. In this research the reliability indexes of damaged members under vessels impact are estimated for a platform in the phase 19 of the South Pars using the first-order reliability method (FORM).Only deformation of structural members are considered as damage impact and energy dissipation during collision is not addressed in this research. The time consuming Monte Carlo simulation Method (MCS) and Important Sampling (I.S.) are used to verify the first-order reliability method because the limit state function in FORM is linear-zed by the Taylor series. At first, the wave force is applied into the safe structure, and reliability indexes are estimated for structural members. Then, in addition to the wave loads, the deformations caused by the assumed collision are also taken into account and structural reliability is estimated in the damaged state and corresponding results are compared with each other. Finally, combinations of wave and current, wave directions, and damages scenarios in chord, vertical and horizontal bracing are considered and results are compared.