نشریه مهندسی دریا
پیاپی 28 (پاییز و زمستان 1397)

The marine and ocean energies are part of renewable energy that Wave energy converters (WECs) are used to extract them. Experimental modeling will be useful in evaluating their performance. In this research, the experimental model of an attenuator WEC is built in the Sea-Based Energy Research Group of the Babol Noshirvani University of Technology, and its performance is studied and evaluated in the wave tank of the university by applying the sea waves conditions. In this evaluation, the effects of wave amplitude and wave period on the average and maximum net power of the Wavestar system are investigated. According to the results, it was observed that in larger wave amplitudes (13 to 15), at 35 and 25 rpm, the maximum net power was close to each other and was 36.7 (Watts) and 31(Watts), respectively. Due to the irregular wave and possible damage to the system at 35 rpm, the wave amplitude of 15 and the speed of 25 rpm are chosen as the optimal mode for better performance of the system.

Using spudcan as foundations for jack-up rigs is usual. Model dimensions, consolidation of clay, and spudcan penetration are the most important issues in modelling of this type of foundations in clays. Penetration of CPT cones and spudcan foundations in single- layered clayey soils was investigated in this paper. Cement stabilized clay with 5 and 10 percent cement was used to study the effect of undrained shear strength of clay on load- penetration behavior of spudcan; Also, two CPT cones with different diameters were used to estimate the undrained shear strength of clay layers. Results show that cement stabilized clays can be used for modelling of clay layers with different strengths. However, careful attention should be paid for changing of bearing capacity factors in two cases, with or without cement. Results show that cones with smaller diameters can be used in physical modelling with good accuracy as well as conventional ones.

The vortex generated around a submarine has an important influence on the uniformity of the submarine wake at the propeller and hydrodynamic noise. A suitable way to reduce the effects of this separated flow is to use vortex generators. Vortex generators have different arrangement such as counter-rotating and co-rotating. The main goal of the present study is to investigate the flow field around a standard underwater model employing the vortex generator with different arrangement by using the CFD method (OpenFOAM code) in 0°≤α≤30° angles of attack. In this study, the application of CFD simulation which can help us to precisely study the structure of vortical flow field. The results show that counter-rotating vortex generators placed along the submarine do indeed significantly reduce strength of the vortex, line separation, size of cross-flow vortices and drag force. The amount of the drag reduction for the counter-rotating vortex generator is approximately 14% in α=30° and approximately 21% in β=30°.

The energy management of ships to improve the efficiency of ships and reduce greenhouse gas emissions is among the most important issues that have been considered as a milestone in designing and constructing of vessels in recent years. The study of energy trends and attention to technological changes and the importance of more stringent environmental standards in recent years have led to a major challenge in relation to air pollution, energy management, and exposure to end-of-life sources of fossil fuels. In recent years, focus on current fuels and technologies in vehicles has led to a major challenge regarding air pollution, greenhouse gas emissions, energy security, and also exposure to exhausting sources of fossil fuels. Now days, Hybrid propulsion systems are one of the solutions that are being followed in many countries to solve this problem. In this paper, after introducing the hybrid system; conceptual design and determination of a suitable hybrid system for vessels have been investigated. Then the calculations and relations dominating the hybrid parallel system of vessel are presented. The modeling is also done using the ADVISOR software run in the Simulink platform of the MATLAB for both conventional and hybrid systems. The results show that parallel hybrid vessel has improved by 7% in total efficiency and 7.1% for consumption. In addition, HC and CO emissions have been decreased by 0.44% and 0.39%, respectively.

Instability and vibration of offshore platforms in harsh environmental force can be reduced by installing heave plates underneath of platform columns. Effect of parameters such as excitation Frequency and boundaries are investigated experimentally in this research. On the other hand, regarding to the published papers, both the added mass and damping gradually increase versus vibration amplitude for a rigid heave plate. It is predicted that using a combination of a rigid disk in center and an elastic plate around it can increase the damping.  It is generally observed from forced harmonic vibrations that frequency can decrease and increase hydrodynamic coefficients respectively near free surface and floor wall. Furthermore, frequency has considerable effect on the hydrodynamic coefficients of a rigid heave plate with large elastic part around it. This definitely depends on the excited mode shapes of the elastic edge.

As the cost of maintaining and repairing floating wind turbines is high compared with conventional turbines, one way to reduce these costs is to investigate the defects in these structures before any practical work. The importance of the stability and structural safety of wind turbines becomes more important with water depth growth and one of the most important factors for the stability of floating wind turbines is the system of mooring cables. In this paper, the effects of broken mooring cables on the dynamic response of a TLP type wind turbine is investigated. For this purpose, the floating wind turbine is modeled accurately with non-linear equations so that this modeling is responsive to large rotation angles that may be caused due to the cutting-off of the mooring cables. After concluding turbine modeling and applying forces, by cutting various mooring cables, the dynamic response changes of the structure are investigated. Studying the results shows that unlike other platforms, breaking of the mooring lines in a TLP-type turbine does not cause extreme oscillations and drifts in the structure.

The wave pattern generated by motion of autonomous underwater vehicle (AUV) near the water free surface is one of the significant factors in order to identify the AUV. In this research, firstly simulating the flow with constant velocity around the Wigley hull body by using Flow 3D computational fluid dynamics software has been carried out. In this stage, the numerical simulation results were compared with experimental datasets. The validity of Flow 3D software in estimating of wave pattern generated by the rigid obstacle which sets in the flow path was investigated. Then, the wave pattern due to the motion of Suboff 5470 AUV at different depths, moreover, the lift and drag forces applied on the AUV body were investigated. The results reveal that in constant depth of AUV motion, when the speed of AUV is increasing from 1.3 to 6.5 m/s, the drag and lift forces are increasing up to 57.17 and 48.97 percent respectively. Also the wave pattern generated by motion of autonomous underwater vehicle (AUV) near the water free surface is kelvin wave pattern with divergent and transverse waves system.

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.

In order to numerically simulate transmission of oil spilled in Caspian Sea from Turkmenistan oil fields, wind induced currents in the sea were simulated using an unstructured grid Finite Volume Community Ocean Model (FVCOM) in the summer and spring of 2012. The results of the model in the fall season were then compared to the measured data for surface currents in three stations of Astara, Roudsar, and Amirabad. Comparison of the measured data and the current model output revealed that implementing turbulence closure module produces more accurate results than when the module was excluded. Later on, in order to determine the destination for the oil spilled from Turkmenistan oil fields, the output of flow model was imported into the GNOME computer application along with 6-hourly wind time series. Turkmenistan’s oil wells on the eastern shores of the southern fields of the Caspian Sea in front of the Cheleken Peninsula were considered as the location of oil pouring. The type of pouring was momentary and the volume of oil pouring in each well was 100 barrels. Simulation of trajectory of spilled oil was conducted based on different pouring time and the location of the oil spill hitting the shore were acquired. Comparing the results from simulation and location of collecting oil spills in August 2012 demonstrates acceptable accuracy; thus, it could be said that, it is quite feasible that oil spills from Turkmenistan oil fields could reach the shores of Iran in the summer.

renewable resources deployment and their dependence on the weather conditions makes them non-dispatchable. Therefore, they need appropriate storage devices in the energy systems. Vessels' energy system has different energy carriers like electricity, heat, cooling, etc. and they are usually operated individually. Hence, this paper presents an integrated model based on energy hub concept for optimal design and operation of a vessel energy system containing electrical, heat and cooling loads that will be satisfied by wind and solar renewable energies, fuel cell, electrolyzer, hydrogen storage tank and battery packs. The proposed method has been validated through GAMS software.

An important point in design of coastal structures is their structural response to design waves. In this study, wave interaction with a caisson breakwater is studied numerically by means of a modified SPH method. An efficient method is introduced to take into account the static and dynamic sliding forces at the interface boundary beneath the caisson. After a validation test, a time history analysis is done to investigate the structural response of a caisson breakwater against waves. The results are compared with experimental data as well as with similar numerical outcomes.  There are good compatibilities between the experiments and the predicted values regarding both caisson movements and applied wave forces. In addition, three different solid boundary conditions are applied and it is concluded that utilizing a dynamic boundary condition is computationally efficient and numerically appropriate for modeling the problems involve with solid-fluid interactions.