Showing 6 results for Irregular Waves
Mohammad Javad Ketabdari, Amir Yazdanpour,
Volume 4, Issue 8 (3-2009)
Abstract
Guyed tower is a compliant offshore platform used for drilling and extraction of oil in deep water. This platform has a flexible body and needs proper mooring system to control the deck movements. In present study this platform is analyzed in frequency domain due to irregular waves. The exiting force extracted from Pierson Moskovits spectrum using Morrison Equation. Modeling of moorings is difficult due to their variable stiffness and non linear interaction with main structure. Therefore first using static analysis data the diagram for mooring force–excursion was obtained and fitted to a polynomial of order 5. Then using this equation the spring force of moorings was linearized. Furthermore the drag term was linearized and both of these two linearized terms used in dynamic equation of motion. The results of analysis showed that errors due to these linearization on final results is negligible. Results of this research can be used for optimum design of guyed towers in deep water and its special application in Caspian Sea can be considered.
Mohammad Navid Moghim, Mehdi Shafiefar, Vahid Chegini, Peyman Aghtouman,
Volume 5, Issue 9 (9-2009)
Abstract
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 recessions 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.
Hamid Matin Nikoo, Mostafa Zeinoddini, Homayoon Estekanchi, ,
Volume 8, Issue 16 (3-2013)
Abstract
based assessment of offshore jacket type platforms against wave loading. This approach can be employed to obtain a more realistic estimate for the ultimate capacity of offshore platforms, in comparison to the commonly used push-over analysis. On the other hand, ocean and sea waves are both random they are irregular in shape, height, speed, period and directions. Therefore, one of the most important uncertainties in the offshore field loading is the stochastic nature of the waves. In this paper a probabilistic method has been proposed in order to estimate the ultimate capacity of offshore platforms subjected to random waves using IWA. To this end, a sufficient number of long-term simulations (3hours) and constrained simulations (using Constrained NewWave methodology) have been carried out.
Amir Arsalan Karami Matin, Mehdi Shafieefar, Hassan Akbari,
Volume 14, Issue 28 (1-2019)
Abstract
Berm breakwater is a type of reshaping rubble mound breakwaters that its seaside profile can be reshaped under severe wave attack. The final berm recession is an important criterion to check the berm width as well as the stability of these breakwaters. Berm recession due to a design wave is usually determined by means of empirical equations derived from experiments. Initial sections with no recession have been assumed in most of these experiments. However, in a real condition, a berm breakwater may experience many of waves before experiencing a design wave condition. The wave history and possible recessions before a stormy condition may affect the final reshaped profile. This subject is therefore investigated in the present study by means of performing 2D tests in the hydraulics laboratory at Tarbiat Modares University. In addition, the effects of wave parameters on the hydrodynamic response of berm breakwaters are evaluated performing 30 tests in the wave flume. In all experiments, irregular waves have been generated based on JONSWAP spectrum wave with γ factor of 3.3 and the median stone diameter and gradation are selected as 2 cm & 1.6 respectively. Based on the measurements, the berm recession (in both statically and dynamically stable berm breakwaters) increases by increasing the wave height and wave period. In addition, once the design wave height rises and exceeds a threshold level, the impact of previous waves on the final reshaped profile will be decreased.
Moein Bozorg Zadeh, Mohammad Reza Zareei,
Volume 18, Issue 36 (12-2022)
Abstract
The main purpose of this paper is to investigate the stochastic roll motion of a ship in irregular waves. To achieve this goal, the differential equation of ship roll motion roll in longitudinal waves with respect to nonlinear damping and restoring arm has been created. Due to the stochastic nature of sea waves, the wave excitation force is generated through stochastic excitation using effective wave theory. To achieve the ship roll motion response, the stochastic differential equation of the roll is converted to the Ito’s stochastic differential equation form. The generated equation is solved several times using the Monte Carlo process to statistically evaluate the roll motion response. Finally, the probability distribution function of the ship's roll motion at irregular waves is calculated for the C11 container ship as a sample ship. Using these results, a better approximation of the maximum angle of roll motion of a ship in irregular waves can be obtained.
Hassan Karimi Baseri, Jalil Fereidooni, Mohammad Moonesun, Mehdi Adjami,
Volume 19, Issue 38 (4-2023)
Abstract
In this article, the most important specifications of hydrofoil floats, i.e. their seakeeping under regular and irregular waves under different encounter angles of wave, has been investigated. Numerical simulation has been done using STAR CCM+ software. Surge, heave, roll and pitch motions are kept free at the same time and their effects on each other are taken into account. USV01 model, whose laboratory test results are available, was used to validate the simulation. The results show that the increase and change in the regular wave components and speed of the craft, cause less changes in the movements of the hydrofoil craft compared to the planing craft, except in the following sea, where planing craft performs better overall. Therefore, it should be said that the most dangerous situation for a hydrofoil craft is encounter angles less than 90 degrees, especially zero-degree encounter angle, i.e. following sea.
