فهرست مطالب

Maritime Technology - Volume:4 Issue: 6, Summer 2016
  • Volume:4 Issue: 6, Summer 2016
  • تاریخ انتشار: 1396/01/05
  • تعداد عناوین: 6
  • Samira Babaei, Roohollah Amirabadi, Touraj Taghikhany Page 1
    In this study, mass, stiffness and damping matrices of the Nosrat jacket; located in Persian Gulf; equipped with Semi Active Tuned Mass Damper (SATMD) system have been derived after modeling the structure in SACS software. Owing to huge number of the degrees of freedom in the model, computation of on-line control of SATMD was time consuming. For this purpose, the size of the model was reduced in the finite time and frequency intervals by programming in MATLAB software. The SATMD utilized in this study, contains a passive Tuned Mass Damper (TMD) and two Magneto Rheological (MR) dampers in order to illustrate the control effect of SATMD. The selected algorithm to control and optimize the performance of MR damper is Linear Quadratic Gaussian (LQG). Time history responses of the platform in cases with and without SATMD have been compared under three different ground motions. Results indicate that jacket equipped with SATMD can dramatically reduce the seismic-induced dynamic responses.
    Keywords: Nosrat Jacket, Persian Gul, SATMD, LQG Algorithm, Seismic, Induced Responses
  • Mr. Seyed Taleb Hosseini, Vahid Chegini, Masoud Sadrinasab, Seyed Mostafa Siadatmousavi, Sadegh Yari Page 11
    Spatial measurements of conductivity, temperature and depth were used to study salinity variations along the principal channels of the tidal hypersaline creek network in the vicinity of Bushehr Port, Persian Gulf during three 25- tidal cycles in both warm and cold months.
    Salinity variations and tidal fluctuations were out of phase throughout the short inverse estuary. The salinity values inside the creek were higher during the warm month (August 2014) than the corresponding values during the cold month (December 2014) due to the change in evaporation rates. The salinity values, also, were linearly increased longitudinally from the inlet to the head especially during warm season.
    Observed evaporation rates in August and December periods and the corresponding salinity differences between hypersaline water of the creek and the incoming seawater were used to determine the Residence Time (RT).
    The longitudinal variation of RT showed almost linear increase from the inlet to the head. The maximum temporal distribution of RT represented an increase from ~10 days in winter to ~30 days in summer due to the change in the longitudinal salinity gradient.
    Keywords: Hypersalinity, Inverse Estuary, Residence Time, Bushehr, Persian Gulf
  • Seyyed Mostafa Seyyedi, Rouzbeh Shafaghat Page 19
    Surface-Piercing Propellers (SPPs) have been widely used in high speed craft due to some desirable features such as high efficiency, omission of resistance of equipment attached to the propeller and proper functioning of cavitation. Unlike the submerged propellers, theoretical methods have no significant application on simulation of SPPsbecause of problems related to modeling of these propellers. Design of SPPs is mainly done based on empirical studies and model experiments. Water tunnel or free surface cavitation tunnel is among the most important devices to perform SPPs model testing. In this paper, the design algorithm of a free surface water tunnel to test the SPPs has been described. The design and construction stages of the free surface cavitation tunnel of Babol Noshirvani University of Technology are provided. Also,calculation of its various sectors such as elbows, nozzle, settling chamber, test section, diffuser and calculation of pressure drops, proper pump selection and dynamometer has been showed.
    Keywords: Free surface water tunnel, Surface, piercing propeller, Experimental test
  • Saeed Booshi, Mohammad Javad Ketabdari Page 31
    In this paper wave transformation in a submerged sloped breakwater and its hydraulic performance was simulated by developing a numerical model in Fortran. The code was established by combining porous flow and a two-phase model using VOF method. Modified Navier-Stokes and k-ε equations implemented to the model to simulate the flow in porous media. Cut cell method was modified to simulate fluid transformation from sloped porous media’s boundary in more accurate way and then applied in the governing equations to increase the accuracy of the model. The validity of the present program was investigated based on the comparisons with the available experimental data. The results showed that increasing of inertia coefficient and wave period and also reduction of porosity lead to some phase lags between the incident and transmitted waves. Furthermore parametric studies were performed on effect of submerged porous breakwater crest widths and heights on transmitted waves leading to useful results for design criteria.
    Keywords: Submerged Rubble Mound, Breakwater, Porous Media, Cut, Cell Porous Method, VOF Method, Transmitted Waves
  • Zahra Omrani, Rouhollah Amirabadi Page 41
    When a jack-up installed at a clay location and then leaves; it can create several meter deep footprints. In case of soft clay, the spudcan may have actually penetrated much deeper than the observed footprints. When the penetrated spudcan is pulled out, much of the soft remolded clay will flow around it and go back into the hole. This event, leaving a deep region of disturbed soil. The disturbed soil has a lower strength and stiffness in comparing to intact material around. The footprints and the associated remolded soil can potentially present significant hazards for subsequent jack-up or jacket deployments at the same location for example the events in China Sea and Pesian Gulf of Iran.
    In this research a case study and numerical simulation (using commercial software ABAQUS) was performed to analyze the effects of spudcan penetration on the adjacent foundations of offshore platforms in clayey soil. Inconsistent with other studies, it was also shown that the penetration of spudcan can affect the soil layer in an annular zone. The maximum width of the affected zone is almost two times of the spudcan diameter; therefore the safe distance for installation of new nearby structures is also affected. In this paper the consequence of deployment of jack-up units in soft to firm clay will be discussed and the safe distance from footprints territory is obtained. All of our cases are located in the Persian Gulf. A jacket location of Assaluyeh/South Pars Gas Field in Persian Gulf was modeled to verify the numerical results. The most important results were the diameter of disturbed soil is 1.5-2 times the spudcan diameter and the safe distance from the territory of footprint is 3-4 m in the Persain Gulf zone.
    These findings will help offshore geotechnical engineers to perform quick preliminary estimates on the severity of footprint-mudmat interaction problems.
    Keywords: Spudcan, Mudmat, Clayey, jack, up, instability
  • Dhara Shah, Viral Shah, Mehul Patel Patel Page 51
    Berthing force is a critical dynamic lateral force in the design of berthing structures, having equal relevance when compared to seismic forces. Besides, the construction cost of berthing structures is very high which can be optimized by calculating precise design berthing energy on fender and selecting optimum fender system. In the present study, design berthing energy of bulk carriers having size range from 5000 DWT to 250000 DWT is compared as per Indian Standard (IS) and British Standard (BS) in terms of various berthing conditions, approach velocity, different berthing coefficients and factor of safety. It is observed that British Standard gives more precise values for design berthing velocities. However, Indian standard provides constant value of berthing velocity for vessel sizes more than 250000 DWT, which is not the case with British standard. It is also perceived that for majority of berthing conditions and vessel sizes, Indian Standard gives higher design berthing energy as compared to British
    Keywords: Bulk carriers, Berthing Energy, Fender systems, berthing velocity, dead weight tonnage