دریامانی

Nowadays, comprehensive research is done on the hydrodynamic analysis of oil tankers to reduce their resistance. Most of these studies have focused on drag reduction in calm water and design conditions, and have rarely evaluated the ship's behavior under real operational conditions at sea. For this reason, in the current paper, using a practical and effective method, the dynamic behavior of an oil tanker has been studied in real conditions. To this accomplishment, the KVLCC2 tanker was selected, its resistance in calm water, dynamic behavior, and added resistance in the wavy condition were measured and the results obtained were compared with the experimental database. The numerical simulation shows the acceptable accuracy of the present method compared to the experimental results. After ensuring the accuracy of the results, a wide range of ship working conditions and exposure to waves, as well as different loading conditions have been studied. Based on the obtained results, it can be seen that the strip theory method is more accurate in estimating the added resistance of such a vessel compared to predicting its dynamic behavior. Also, the angle of impact of the waves on the vessel does not have a significant effect on the maximum range of the vertical displacement. In addition, the maximum added resistance at all wave impact angles is directly proportional to the ship draft.

Nowadays, the need to access high speeds and durability in bad sea conditions for vessels has provided a wide and extensive field of research. Reducing Ship motions from an economic aspect leads to a reduction in the power required to move the ship and thus reducing fuel consumption and cost and increases the operational capacity of employees. One of the major problems of sea transportation is seasickness caused by Pitch motions of vessels for passengers and ship crew. When the vessels are subjected to Pitch motions by the wave, the acceleration of the heave and pitch motions will intensify. The geometric form of the underwater ship hull and the design form of its hydrofoils have a significant effect on the dynamic performance of this vessel. High-speed hydrofoil vessel has attracted the attention of ship designers and architects due to their special capabilities, and extensive research is being done on them. In this paper, the initial design of the model was done in the Rhino software. The ship hull mold and front and rear hydrofoils were made by CNC milling machine. Then model of ship was tested in the towing tank at different speeds and frequencies, and the heave and pitch motions RAO were extracted. The results showed that by increasing the frequency or decreasing the wave length, the motions of the ship are greatly reduced. At high speeds and after passing the maximum point, the ship reaches a stable state.

This article presents a new innovative method to reduce the motions and stabilizing the ships using the ordinary fishing net. The study of ship motions in the waves has been the main concerns of ship designers. Some methods have been used to stabilize the ship in the waves, such as stabilizing tanks, gyro stabilizers and fin stabilizer, which these have their own advantages and disadvantages. In this paper, the study of the net element to reduce the amplitude of Pitch motion in the regular waves in the static state has been done by experiments in a towing tank. The model experiments were performed in the towing tank of National Iranian Marine Laboratory (NIMALA) using two kinds of net with different meshes to compare the effects. The innovative idea of using the fishing net element to reduce the ship motions in the waves was presented for the first time in this research. The findings of this study for the planing craft show a reduction in Pitch motion of up to 20% in regular waves. The length of the model is 2.5 meters and the requirements of the test method are based on the ITTC marine testing instructions.

Nowadays, the optimal use of energy, speed increase, fuel consumption reduction and environmental pollution prevention are essential in the ship design and manufacturing discussion. So it is critical to be able to estimate ship's response to waves, since the resulting added resistance and increasing fuel consumption also increasing environmental pollution. In this study, the numerical solution of the Iran-Bushehr container ship model was determined to simulate the free surface flow around the hull and estimate the total resistance and investigate ship motions in 2 degree-of-freedom (heave and pitch) in regular head waves. Finally, the results of simulation in different conditions are presented and compared. KCS container ship used for validation. CFD codes in Star-CCM+ used to calculate three dimensional, incompressible, unsteady RANS equations.

This paper investigates the heave and pitch motion responses of an inverted bow hull. The experimental data were obtained from seakeeping tests with two scaled models of reference fishing vessel NA8-14 BSRA. The bow shape of the models is redesigned by inverted shape in two angles of 45 and 60 degrees. Several tests were conducted on the models at different speeds of 0.6, 0.9, and 1.2.m/s. Generated waves in the towing tank are of the regular type with the wavelength changing from 0.6L to 1.6L by an increment of 0.2L m. The amplitude of the waves was equal to either 35 mm. The heave and pitch response amplitude operator (RAO) versus no dimensional frequencies are presented. The investigations demonstrated that by decreasing inversion angle of bow to 45 degrees motions of the model improved. The results also showed that the interactions between the motions responses leads to the frequent appearance of “Kinks” in a coupled form with the responses of other motions.

Trimaran is a multi-hull ship that consisting of a main slender hull and two smaller outriggers. These outriggers are connected by a transverse cross deck to the main hull. The position and geometry form of the outriggers have a significant effect on the stability, dynamic motions and wave loads on this modern ship. In this paper, the effect of the outriggers geometry on heave and pitch motions of a trimaran ship, considering the inboard and outboard asymmetric geometry hull form are investigated. A model of ship has been tested in a towing tank at different speeds and different frequencies in forward sea. The results showed that due to the proper interaction between the main hull and the outriggers in terms of using the side body with the outboard asymmetric form, the responses are less than those of the inboard asymmetric hull. Also, there are local maximum and minimum points on ship responses in zero speed conditions due to the heave and pitch coupling in their respective frequencies.

Sea environmental conditions including wave and wind, influence the ship performance parameters like speed, safety, dynamics loads acting on ship srtucture and etc. ship motion prediction for proper vessel operational planning and utilization is considered by ship designers. In this article, motions of a trimaran ship in design speed are predicted by maxsurf software, 3D panel method. Besides, motions of trimaran ship are simulated by computational fluid dynamic (CFD) using Flow-3D software. In order to modeling the irregular waves in sea state 5, Bert schnider spectrum is used. 3D panel method calculations are implemented in frequency domain and CFD software calculations are implemented in time domain; then results are transformed from time domain to frequency domain by Fourier transform. for validation of calculations we used results of a reference tested model. according to achieved results the panel method is quiet well for investigation of trimaran motions and we can use it for complex hull forms and multihulls and in various maritime cases like wave encounter angle, ship speed and wave conditions

Among different offshore platform concepts; FPSOs (Floating Production, Storage and Offloading units) have been more attractive these days. Stability and seakeeping are two effective hull design parameters and overall efficiency assessment of FPSOs. This study has focused on some performance factors such as, stability both intact and damage condition, hull position, displacement and acceleration due to environmental loads. The aim of this study is to achieve a systematic procedure to evaluate the quality of performance for three type of FPSO hull forms including: ship-shaped, rectangular box and oval. The procedure is done by an MCDM model with an AHP method. Models are done in Finite Element Method (FEM) and diffraction analysis have been performed. Oval type FPSO has better performance in stability and rectangular box has better performance in seakeeping assessment. Better seakeeping performance of rectangular box FPSO leads to have greater score in overall efficiency assessment among three case studies. In this study, spread mooring type with steep-s flexible riser are used for all case studies.

In this article we have discussed seakeeping different body types. As we know seakeeping ability of a vessel or offshore structure to the desired buoyancy is such that if a vessel or floating structures، seakeeping good، bad sea conditions can also have acceptable performance. Numerical Investigation movements with heave and pitch of three type hull of Wigley، Series 60 and DDG 51 floating in front of the regular wave and validation of numerical results are compared with experimental results to predict seakeeping floating ship in effect Maxsurf Ratios software deals have. It should be noted that the shape and size of ship movements of the body، but the results of this study cannot be used in similar cases.

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.