numerical simulation

With the development of AUVs, accurate calculation of hydrodynamic coefficients in the equations of motion of these vehicles increased significantly, and accurate calculation of hydrodynamic coefficients for predicting maneuverability, dynamic stability, and controller design is of particular importance. One of the effective parameters in the uncertainty of the results obtained from the regression methods for calculating the hydrodynamic coefficients is the clearance between the control surfaces and the body. In this article, to investigate the effect of the clearance on some linear hydrodynamic coefficients of the maneuver, a numerical analysis has been performed on the Suboff benchmark model, and the damping and added mass coefficients have been studied using static and dynamic tests. The vertical clearance of the control surfaces from the body is considered a variable and the analysis has been done at several clearance from the body. The numerical results, after validating with the model results, showed that the hydrodynamic coefficients become independent of the distance between the body and the control surfaces from the distance of 0.06 meters. Also, in the static drift test, with the increase in the clearance of the control surfaces from the body, the hydrodynamic coefficient related to the sway force and the hydrodynamic coefficient related to the yaw moment decrease. However, in the pure sway test, with the increase in the clearance, the hydrodynamic coefficient related to the sway force decreases, and the hydrodynamic coefficient related to the yaw moment first decreases and then increases.

One of the maneuvers in marine vehicles is turning maneuver. To investigate effect of sail position in submarine turning maneuver, 6 models of Suboff with different longitudinal sail positions are performed in Star CCM+. First, the simulation method, meshing, and validation are described. Validation shows that the error of calculating the resistance is less than 10%, which indicates the accuracy of numerical solution. Then, the turning maneuvers of the submarines are performed and their results are compared. The results show that by moving the sail from the nose to the aft, drift angle of the submarine decreases and the radius of turning circle decreases then increases.

Planning vessels have a special significance in the marine industry. The main and most significant aspect of designing these types of vessels is achieving high speed by having low body resistance. One of the key modifications applied to the hulls of planning vessels was the development of the chine. This research aims to analyze the impact of the chine on planning hulls using numerical analysis. After analyzing the results, improved chine can be specified in terms of the hydrodynamic performance of the hulls. The chosen method to analyze the flow around the planning hull forms is numerical simulation. This method calculates the resistance force, lift force, pitch angle, and heave amount of the intended hulls. The numerical simulations of different modifications of the C planning hulls were compared to the hydrodynamic behavior of the C-hull after verifying the results of the numerical simulations and validation of results with the laboratory results of the former reference. Based on the results obtained from the numerical simulations, the hull with 5.43% chine width to beam ratio recorded the lowest resistance. The highest trim was observed in the hull with 5.43% chine width to beam ratio, and the hull with 5.87% chine width to beam ratio registered the highest heave. Moreover, the hull with 4.57% chine width to beam ratio exhibited the highest resistance in the simulations.

Tides continuously change the water level in seas, and due to the continuity and dominance of currents caused by tides in bays, straits and estuaries, it is necessary to investigate the phenomena related to sediment transport and scouring in the surroundings of the structures located in the above areas will be illuminated more than before. In this research, by numerical simulation of the flow field and sediment transport, the scouring phenomenon under the pipelines caused by bidirectional currents has been investigated, and according to the values ​​of movement threshold speed, depth and number of tidal cycles to reach equilibrium, the characteristics of the scouring profile has been drawn. The obtained results indicate an increase in the depth and surface of the scour pit caused by the tidal current due to the alternating changes in the flow direction compared to the scour caused by the unidirectional current, and the vortex shedding process affects the final shape of the scour profile.

The Persian Gulf is an important region in the world regarding energy supply, transportation, shipping, and military missions. Therefore, studying the annual circulation of water current in the Persian Gulf is very important for marine experts. In the present study, the simulation of current circulation in the Persian Gulf has been studied using ROMS numerical model and field observations. The numerical model results are in good agreement with TMD dataset as well as field data. In addition, the circulation patterns in the summer and winter seasons are well simulated. However, the numerical simulation results showed that the modeling accuracy in summer was lower than in winter, probably due to the model's boundary data quality.

In this paper, a numerical study is performed in order to investigate the effect of the numerical diffusion on simulation of separated two-phase flow of gas-liquid. The governing equations solved by shock capturing method which can provide predicting the interface without the flow field solving. In this work, in order to calculate the numerical flux term, first-order centred scheme (Force scheme) was applied cause of its accuracy and appropriate validation. Analysis approves that the obtained stability range of this research is consistent with the classic kelvin-Helmholtz instability equation only for the long wavelength with small amplitude. Results reveal that when the wavelengths are reduced, the specified range is not consistent and wavelength affects on instability range and it is overpredicted. An algorithm for water faucet problem was developed in Fortran language. Short wavelength perturbations induce unbounded growth rates and make it impossible to achieve converging solutions. The approach taken in this article has been to adding numerical diffusion as a CFD technique is used to remedy this deficiency.

Floating breakwaters have widely been used in the past and at the present. These types of structures have some important advantages in comparison with the rubble mound breakwaters, particularly in relation to the environmental issues. In the past, most of the studies for these kinds of breakwaters have been focused on flat beds, however, in practice, uneven bed topographies, especially in shallow coastal areas, can be an effective factor in performance of these structures. For the current study, the effect of various geometries of bed forms on performance of floating breakwaters was investigated using Flow-3D software. The incident waves to the model were irregular types and the wave energy spectrum was JONSWAP. The uneven bed forms were investigated in two categories. For the first group, singular uneven bed forms were considered whereas for the second category continuous uneven forms were considered.First, to investigate the effect of different geometries of single bed forms, three common modes of these bed forms as rectangular, trapezoidal with an angle of 70 degrees and a parabolic have been considered. Also, in order to investigate the effect of bed form height on floating breakwater performance, these uneven forms have been studied at different heights. The continuous bed forms were then simulated in two forms of sinusoidal and dunes with different dimensions. Based on the results of this research, it was found that the rectangular uneven bed form of the singular forms had a great influence on improvement of efficiency of the floating breakwater and with increasing its height the performance of breakwater increased. It was also found that the continuous bed form performed better than the all singular uneven forms modes With corresponding height. Finally, the numerical results showed that among the continuous uneven forms of dune shapes,

Mixer is one of the Main components of turbofan engine, which is used to mix the cold air flow from bypass and the hot airflow form engine core. The one of the factors affecting the mixing rate is the depth of mixer lobes. Also comparing the depth of penetration of lobes and its effect on mixing flows with simulation has been investigated. In this type of turbofan engines, the Mach number range is between 0.3 and 0.8. In this study, the Navier-Stokes equations are considered as three-dimensional and steady and flow is considered as compressible and turbulence. The standard k-e model with wall function is used to simulate flow. First, the numerical simulation method is validated, then phenomenon of mixing of flows in lobed mixer is investigated under the effect of lobe depth. The results show that variations of lobe depth strongly effect the secondary flow rate, the circulation power of the flow, and pressure in the lobes. With increasing depth of lobe, the flow velocities is decreased and the lateral and span wise components of velocity increase. Finally, it can be concluded that the effectiveness of mixing in high depth mixer is 70% in the middle of the lobes and in the low depth mixer is 47% in the middle of lobe. Compared to the two types of Lobes, by quadrupling the depth of lobes in high-depth lobes, about 49% the total effect of mixing in high-depth lobes is greater. Also, it can be concluded that the effect of mixing, the rate of secondary flow and the amount of turbulent kinetic energy in the high depth lobed mixer is higher than the low depth and maximum of mixing is in middle of lobe.

In this research, a numerical study is conducted to simulate a separated two-phase flow of gas-liquid with the conservative two-fluid model. Also, the stability district of equations was investigated. The governing equations solved by the shock-capturing method. This technique can provide predicting the interface without using the flow field solving and the interface is obtained from the solution of the two-phase flow’s governing equations. Obtaining the well-posed criteria of the model as one of the results of this study is another novelty of this paper. Water faucet problem which is a famous and basic case study in fluid dynamics is implemented and results are compared to the analytical solution and finally, the strengths and weaknesses of the simulation are provided.

The purpose of this paper is to investigate the behavior of positive buoyancy jets of urban wastewater in stationary and non-stratified water bodies using the investigation of the laboratory data acquired by a 3D-LIF laser 3D scanning system and numerical modeling results from the simulation by FLOW-3D software. Laboratory simulation was performed for three discharge jets with Froude numbers 10, 15, and 20, and compared with the results of the numerical model and the previous numerical results. The trajectory of the jet, concentration variations, the position of the impact point, and the rate of dilution at the impact point was determined. In the numerical model, both K-Ɛ and RNG turbulence models were used to evaluate the accuracy of the numerical simulation where the K-Ɛ results were closer to laboratory results and are capable of accurately modeling the jet trajectory than the RNG model. By different Froud numbers, the results at Fr = 20 are almost the same for all experimental and numerical states and indicating that by increasing the discharge and Froud number, the accuracy of the results in the numerical model increases and present closer results to the experimental model.

Seasonal circulation of coastal currents of the Persian Gulf with a horizontal resolution of 2-minutes of latitude and longitude was simulated using COHERENS numerical model. The currents of the Iranian coasts flew northwestward from January to April, reaching the highest level from June to August, when surface inflow currents through the Strait of Hormuz gradually became stronger with establishment of the seasonal thermocline. The simulation results indicated thermocline expansion with the onset of the heating season. Under the mentioned conditions, stronger coastal currents were generated in summer. The simulation results showed the presence of coastal jet with a speed of approximately 30 cm/s from May to October. The coastal jet near the Iranian coasts is only confined to the surface, moves toward southeast; however, the coastal jet in the vicinity of Saudi Arabia is entirely present at all columns of water from surface to the seabed and moves toward southeast.

A three dimensional numeric oceanic model sensitive to wind tension based on primitive equations in the earth’s spherical coordinates modified by array of sigma vertical coordinate is designed to simulate the Sound velocity structures in the Northwest Indian Ocean.Wind speed data from the ECMWF database in 2018 as well as measuring of temperature salinity data, are extracted from WOA18 database. To predict temperature and salinity, after applying the wind stress and initial data on temperature and salinity, the model will be used in each of the months of winter (December 2017, January and February 2018) and summer season (June, July And August 2018). In order to compare vertical sound velocity, seasonal mean of measured and predicted temperature and salinity are used in Mackenzie equation. The results of this comparison show good compatibility between the sound velocity structure obtained from measurements and predictions. The results of the numerical model and also the measurements show that the sound channel is formed under the thermocline layer and is not affected by seasonal changes.

In this paper, lifting line theory(LLT) and finite volume method (FVM) have been used for numerical simulation of hydrodynamic performance of marine propeller. The LLT is based on the potential flow and vortex theory to quickly design and analyze the marine propeller. On the other hand, the FVM is based on the discretization of the Navier-stocks equations. In this paper, the accuracy and efficiency of these two methods have been investigated for analyzing the performance of the submerged propeller. In order to validate the methods, the geometry and experimental results of the VP1304 and DTMB4119 propellers have been used. For studying the hydrodynamic performance of marine propeller,the torque and thrust coefficients versus advance ratio were computed by FVM and LLT. For all of the advance ratios, the FVM provides acceptable thrust and torque coefficients. Wheras its preprocessing and processing times are high. In return, the LLT in low advance ratios did not calculate the satisfactory results. Wheras it needs short cpu time to process.Therefore it is suitable for parametric studies.

The biomimetic and hydrodynamic study of aquatic animals is one of the most challenging computational fluid dynamics topics in recent studies due to the complexity of body geometry and the type of flow field. The movement of the aquatic body, and particularly the tail section and the corresponding movement of fluid around the body, causes an unsteady flow and requires a comprehensive study of the interaction of fluid and aquatic body which makes the analysis more complicated. In this research, the main purpose is to investigate the numerical simulation of hydrodynamic flow around the aquatic body regarding dolphin swimming condition. Specifically, considering the precise 2D geometry of a dolphin body, the studied parameters include the drag and lift coefficients, body movement and its effect on vorticity, pressure and velocity fields immediately around the body. According to the results it can be claimed that the body movement frequency and the length of tail motion highly affect the mentioned parameters.

Greenhouse gas emissions and atmospheric pollutants, economic savings, as well as alignment with the new rules of the shipping industry's leading is a new concern. In order to meet and achieve these goals, many efforts have been made. In this paper, some methods for reducing fuel consumption, including optimization of floating trim, have been considered in design draught. In this regard, the body resistance of model of the KCS container ship is calculated in design draught; This analysis was performed by numerical solution and experimental test for -0.1 to +0.1 trim range. And the results of ship model analysis was generalized to the main body. In this regard, the mathematical model of ship propulsion system is implemented in the MATLAB-Simulink software; and by using this model for different trims, rates of ship specific fuel consumption presented. According to the results of modeling and simulation of the floating body, a reduction of 1.5% of fuel consumption has been achieved due to optimization of the trim.

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.

Security is one of the most important problems facing the wider use of hydrogen and the increased risk of release into the closed environments. The existence of hydrogen gas in submarine's battery well is also accidental. One way to reduce this risk is to identify the behavior of hydrogen in different situations. For this reason, In this paper, transient behavior of the hydrogen gas in leakage and diffusion in a closed cylinder chamber is simulated numerically. Hydrogen Volume Fraction (HVF) extracted during 60 s leakage and up to 100 minutes after stopping the leak and compared with experimental data of the Shebeko work , in 2 , 50 and 100 minutes after stopping the leak. Moreover, location of the leakage parameter, investigated numerically. Studies have shown that high-risk regions of flammability are formed in top of the room, quickly and with an increase in height of release hole, hazard regions has become broader and becomes more lasting.

In maneuvering analysis of high speed planning craft, developing the use of numerical methods, could provide a good insight into the hull maneuvering performances. In this paper, based on 4DOF system of equations for surge, sway, yaw and roll motions, the hydrodynamic coefficients related to lateral speed and drift angle are evaluated for a typical mono-hull planning craft by numerical simulations. For this purpose, the restrained test of the scaled model of the proposed craft is modeled through computational fluid dynamic by Ansys CFX and the results of simulations of its motion on straight line are extracted at two different forward speeds for different drift and roll angles. Some of these results are compared to the values obtained by available semi empirical formulas proposed by Lewandowski which showed some discrepancies. The results also show that forward speed is a main influencing factor on the hydrodynamic coefficients of maneuvering of a planning craft. Meanwhile maneuvering forces and moments tend to vary linearly with respect to lateral speed, but variation of sway force and yaw moment with respect to roll angle, tend to nonlinearity by increasing the forward speed. At lower forward speed, these relations could be well predicted by linear regressions.

One of the major and effectual issues in designing of floating breakwater is its geometry. In this study, effect of geometry of floating breakwater on wave transmission coefficient for the periods ranging from 0.63 to 1.26(s) will be discussed using Flow_3D software, which is mainly based on trapezoidal geometry and curvature in various sections.
First, the numerical results of the base model were verified against the experimental model and then seven various geometries are designed in two groups. For the first group, the draft was assumed to be constant and to provide this particular draft, different geometrical sections were examined, using various masses and densities. In the second group, the cross-sectional area, mass and hence density were assumed to be constant and the proposed models were evaluated at different drafts. Finally, within the range of periods stated, the geometry having the best performance and economical is suggested for the related projects.