نشریه مهندسی دریا
پیاپی 35 (بهار و تابستان 1401)

One of the most important issues in the design of a vessel structure is the vibrations of the structure and its effect on the comfort of the crew and the life of the equipment. The most important factor about the comfort of the crew in a vessel is the range of free and forced vibrations under various internal and external factors in the structure of the vessel. One of the serious factors in stimulation of vibrations in the hull vessel is the propeller. Excessive vibrations as well as the being the structure in the frequency range of propeller excitation, cause fatigue, components exhaustion, and also the resonance phenomenon. Resonance and vibration of the components are the structural design challenges, so in this paper, vibrations caused by a five-bladed propeller KP505 excitation were investigated using numerical simulation on a container vessel (KCS). First, the free vibrations of the hull vessel in wet mode were investigated. Then, to investigate the forced vibrations caused by the propeller excitation, the pressure distribution on the hull in self-propulsion mode was obtained from the numerical solution of the fluid flow by computational fluid dynamics. To validate the results, the natural frequencies obtained in free vibrations were compared with empirical formulas. Comparing the values of the first, second and, third bending frequencies with the empirical values, showed that the analysis error was 5.5, 26, and 26.6, respectively, which explain the accuracy of the analysis. Comparing the results of forced vibrations with the standard allowable range, it was shown that the vibrations are within the allowable range. Also, the structure has not being within the range of the excitation frequency of the propeller. As a result, the resonance phenomenon has not occurred.

Supplying electricity to remote villages that do not have access to the electricity grid has always been a major challenge. Hybridization of renewable resources available in that rural area can be considered as a solution to this challenge.  In the present study, due to the proximity of the study area to Oman Sea and access to suitable wave power for supplying electricity, three types of Wave Energy Converters have been hybridized in Homer Software with solar systems, diesel generators, and batteries. Then, by comparing them, the superior Wave Energy Converter is selected. These Wave Energy Converters, including Pelamis, Wave Dragon, and AquaBuoy, were compared on a 4085 kW photovoltaic system, 9,000 kW diesel generator, and 197 100 kWh batteries to provide a certain amount of electrical load. Finally, the system including Wave Dragon with the energy production cost of 0.240 $ / kWh was chosen as a better economic system.

In this paper the generated eddy in the east part of the Sefidrud river, off the Kiashahr in the Guilan province is studied and discussed and also, effects of this eddy on nutrients are considered. Using a vessel-mounted ADCP and a CTD, water current profiles and, physical oceanographic parameters are measured, respectively. The results show that a small scale anticyclone eddy (warm core) is generated in the area that its core had at least 0.5 ℃ temperature difference from surrounding waters. The main current direction was westward and at location of the eddy, changes in current direction are observable. The minimum quantity of nutrients is observed at the eddy core and this means that at study area downwelling phenomenon is occurred.

The present research aimed to protect the physical space and obtain the desired land-use planning through a shoreline management plan for the Bushehr city district. To achieve objectives, considering a sea-based approach, forty-seven environmental, infrastructural, and human characteristics have been involved along with the management units (Sedimentary cell, sub-cell, and shoreline-sector). Determining the appropriateness of the development of structures and infrastructures such as ports and mooring berths, infrastructure for coastal-maritime tourism, and coastal protection structures such as dykes and coastal walls in three proportions (suitable, relatively suitable, and unsuitable) along the nine shoreline sectors with attention to the environmental and passive defense considerations were the research outcomes. The present study concluded that the construction of the coastal structure along the Abbasak Bay and Piazy estuary is inappropriate. In contrast, the coastline of Bushehr Peninsula was recognized as suitable for the establishment of the tourism infrastructure and mooring structures, commercial and fishery ports, and coastal protection structures.

Offshore wind energy is one of the main sources of renewable energy, which has led to the increasing expansion of offshore wind farms worldwide.One of the major challenges for offshore wind projects is the cost of construction of the foundation, which, depending on the location and type of wind turbine, accounts for about 16 to 34% of the total cost.Therefore, proper design of foundations is very important to ensure the performance of offshore wind turbines.The foundation proposed in this research includes a hybrid monopile-footing foundation in which CFDST sections have been used in monopile instead of conventional steel sections.Dynamic analysis of the foundation under environmental loads has been performed using finite element method by ABAQUS  software. The results show that the use of CFDST sections, in addition to being able to reduce the diameter of the monopile, add a circular footing to the monopile, creates more lateral stiffness for the monopile at mud level and also reduces its lateral displacement.Also, by comparing the natural frequencies of wind turbines based on the proposed foundation, it was found that these structures are within the allowable frequency range and do not pose a risk of resonance.

The behavior of circular surface foundations resting on sand, surrounded by peripheral skirt was studied by numerical analysis. The performance of skirted foundations was analyzed by evaluating the effect of different parameters and compared with the results of semi-deep and embedded foundations in the depths of skirt tip. The effect of lateral sand confinement on foundations behavior was evaluated by examining the parameters of foundation width, sand shear strength, skirt depth, and surface roughness. The results of numerical analysis were compared with small-scale physical modeling data. The results showed that the vertical bearing capacity of surface foundations due to lateral confinement, significantly increased and the settlement also decreased. The skirt existence causes resistance to soil lateral displacement and leads to a significant improvement in the response of the foundation. The improvement values increased with increasing skirt depth and decreasing sand shear strength. Depending on the different parameters, bearing capacity of skirted foundations increased by about 1.8 to 3.3 times, and settlement values reduced up to 54% those of surface foundations. Comparison of the results showed that the values of bearing capacity and settlement of skirted foundations are close to those of pier foundations with the same depth and width.

The efficiency of an exterior reservoir as a Tuned Liquid Damper in controlling dynamic responses of offshore Mono-tower platforms under seismic loads has been investigated in present research. Hydrodynamic forces due to water surface movement in the reservoir act as resistant forces against structure displacement. In this research, using finite element software ANSYS utilizing transient module, a mono-tower structure having dimensions matched to the samples in the Persian Gulf climate with an exterior tank at the top, was modeled and then analyzed by transient time history method subjected to the records of three earthquake for seismic loads. The external damper tank is modeled by Solid85 and Fluid80 element employed as inside water to reflect the displacement of the fluid inside the tank. Top displacement of the mono-tower platform with and without TLD were compared and generally show that using mentioned exterior reservoir as a TLD reduced structure response more than 50 percent.

In order to optimisation of laminates including woven fibers, Present study investigated the effect of Areal density on the tensile and flexural properties of this laminates. Due to the complexity of the equations governing woven fibers, the experimental method has been used to accurately compare the properties of laminates including fibers with densities of 200, 400 and 600 gsm. The laminates studied in this research have equal thickness and overall density and their difference is in the number and Areal density of the constituent layers. In order to reduce the impact of the manufacturing process and the uniformity of the quality of the parts, the vacuum injection method has been used. Research findings show that Areal density has a significant effect on the properties of laminates and by increasing it in a certain range, the properties of laminates improve. Also, increasing the surface density of a certain value due to the creation of cavities and reducing interlayer contact, has a negative effect on the properties of the laminates. laminates including woven fibers with a density of 400 gsm have higher properties than other laminates and also fibers with a density of 600 gsm have higher properties than laminates containing fibers containing 200 gsm.

Armors are a kind of protective layer made of stone or concrete, used in breakwater constructions or coastal lines, arrayed with specific regular or irregular pattern on the breakwater or the coast. Armor damage due to wave attack is the principal failure mode to be considered when designing conventional rubble mound breakwaters. Since the cost of breakwater construction is high, the stability of this structure during its service life is important. This study includes the results of a experimental study stability of rubble mound breakwater covered with armor layers consisting of parsian national armor. In these experiments using irregular wave, the effect of significant wave height, wave period and water level changes on the stability of these concrete armor parts. The results obtained from the damage of the armor layer in the form Nod are presented that the stability of the armor decreases with increasing values of significant wave height and wave period and the armor layer of the rubble mound breakwater will be damaged. The effects of progressive damage on other breakwater components against wave interaction were also evaluated and the results of this study show the efficiency of this New Recommended Concrete Armor.

Shipping route analysis for maritime traffic management depends on equipments to collect information about ship's behavior. For this purpose, the most reliable data is the Automatic Identification System (AIS) data. The complexity and high volume of AIS data  enhances traditional surveillance operations and makes maritime traffic analysis more difficult. Therefore, an unsupervised approach is desirable for the effective conversion of raw AIS data into regular shipping route patterns. The proposed model for the shipping route analysis consists of four sections: AIS data preprocessing, structural similarity measurement, shipping route clustering and representative trajectory extraction. Experimental evaluation of the proposed model with real AIS data from the studied area shows that it has performed well visually and the expected result has been achieved. The results will contribute to better understanding of shipping route patterns and help maritime authorities in sustainable management of maritime traffic.

In this paper, the effect of scaling on the accuracy of experimental results obtained from water tunnels was investigated. Experimental tests were defined for three surface piercing propeller with similar geometry and diameters of 0.132 - 0.125 and 0.140 m. Thrust coefficients in different Immersion ratios are compatible with each other, the torque coefficient of propeller with a diameter of 0.140 does not correspond well with two propeller of 0.125 and 0.132. As the immersion ratio increases, the obstruction ratio increases, and the propeller torque with a diameter of 0.140 decreases compared to the other two propellers. Increasing the immersion ratio increases the torque and thrust in all three propellers; However, due to the effect of the obstruction ratio, the increase in torque in the immersion ratios is 0.40 to 0.70 less than the other two propellers. Also, with increasing the immersion ratio, the efficiency decreases and the highest efficiency for all three propellers is obtained in the immersion ratio of 0.40. As the immersion ratio increases in all three propellers, the critical advance coefficient decreases.

In this paper, the aim is to analyze the interaction of a commercial container vessel with irregular surface water waves by computational fluid dynamics and also to calculate the marine parameters of this structure, namely the response amplitude (RAO) operator, the kinetic response spectrum in the motion of the structure. Analysis tool in this research is STAR CCM + software based on computational fluid dynamics, which is one of the most powerful software in performing simulation and numerical analysis for the above problem. In this paper, after reviewing and analyzing the validation of the numerical model and analysis tools, the various marine and dynamic parameters for a commercial container vessel in the superficial state in different directions of irregular wave collision to the vessel are investigated.