Sharif Digital Repository

In this paper the principles of submarine dynamics modeling have been gathered as distinguished steps. Of course, in these few pages the details cannot be discussed and the formulae cannot be proved. The interested reader has to study more detailed references to attain a better perception of the subject. The paper, in addition to gathering and editing principles, has gone through offering simplifications in each part of modeling. Such simplifications will result in a good approximation of submarine dynamic behavior, which is exactly complicated in reality. In higher levels of modeling each part can be completed and details can be processed  

Reduction in ship resistance, in order to decrease fuel consumption and also achieve higher speeds, has been the topic of major research over the last three decades. One of the most attractive ideas in this field is micro bubble drag reduction, which attempts to obtain optimum injection flow rate based on ship specifications. The model test results of a 70 cm catamaran model was used to quantify the effect of air injection rate on drag reduction, and to estimate a simple formulation for calculating an efficient injection rate by considering the main parameters of the ship, such as: length, width and speed. The test results show that excessive air injection decreases the drag reduction... 

Predicting the hydrodynamic coefficients of an autonomous underwater vehicle (AUV) is important during vehicle design. SUT-2 is an AUV. being developed by the Marine Engineering Research Center of Sharif University of Technology in Iran (MERC). Model tests are done in the marine engineering laboratory towing tank. In tins research, hydrodynamic coefficients are calculated using model test results of an autonomous underwater vehicle. Hydrodynamic forces are also analyzed. These coefficients are used for dynamic modeling and autonomous controller design  

Cavitation behavior of fully submerged propellers is an important issue in the marine engineering field. Cavitation tunnel is usually used for studying hydrodynamic performances and cavitation behavior of a propeller. In the present study, the cavitation behavior of the DTMB P4119 propeller was studied both in a uniform flow and in the wake field of a specific vessel. Considering the dimensions of the test section of K23 cavitation tunnel of Sharif University of Technology and related blockage effects, the propeller was scaled so that the model was 0.195 (m) in diameter. A wake screen was used to generate the desired wake field, which itself was primarily determined by CFD simulations around... 

We propose a component model for the scheduling of combined-cycle gas turbine (CCGT) units by mixed-integer programming (MIP) in which combustion turbines (CTs) and steam turbines (STs) are modeled as individual units. The hourly schedule of CCGT based on the component model is compared with that of the mode model. The modeling of modes, which includes a combination of CTs and STs, would require certain approximations for representing fuel input-power output curves, ramping rate limits, minimum operating time limits, etc. The approximations can result in sub-optimal schedules. Furthermore, the commitment and dispatch of CCGTs based on the mode model will require a real-time dispatch to... 

Scaled model test in towing tank is a common method to predict the ship resistance in calm water. The scale effects are dominant in these tests because the Reynolds and Froude numbers of the model and full-scale ship cannot be equal. There is a sufficient amount of knowledge about the displacement hulls which have limited speed ranges in most cases. However, scarcity of published data on high-speed crafts is noticed. The influence of the model length on ship resistance varies in different speeds, so it should be studied in more detail. The extrapolation method of model ship resistance to full scale is studied in this paper for high-speed monohulls. Resistance model tests of semi-displacement... 

This study is aimed to improve Zarnick’s (1978, A nonlinear mathematical model of motions of a planing boat in regular waves. David W. Taylor Naval Ship Research and Development Center, Bethesda, MD, USA) analytical model for motions of planing vessels. A nonlinear time domain mathematical model was developed for dynamic behaviour of longitudinal motion of high-speed planing crafts in regular waves. This model was based on two-dimensional strip theory method using expanding wedge theory and momentum. Due to the nonlinearity and complex dynamic behaviour of these vessels, the time-domain simulation was adopted. Total resistance, heave and pitch motions as well as acceleration were found very... 

This study is aimed to improve Zarnick’s (1978, A nonlinear mathematical model of motions of a planing boat in regular waves. David W. Taylor Naval Ship Research and Development Center, Bethesda, MD, USA) analytical model for motions of planing vessels. A nonlinear time domain mathematical model was developed for dynamic behaviour of longitudinal motion of high-speed planing crafts in regular waves. This model was based on two-dimensional strip theory method using expanding wedge theory and momentum. Due to the nonlinearity and complex dynamic behaviour of these vessels, the time-domain simulation was adopted. Total resistance, heave and pitch motions as well as acceleration were found very... 

The turbine control system is one of the key control loops in the dynamic performance of steam power generation units. In this paper a multivariable PID controller is designed for the governing system of steam turbine power generators. The necessary and sufficient conditions for existence of a strong robust H ∞ dynamic compensator are established in terms of linear matrix inequality (LMI) approach. This controller is designed in succeeding to the existing proportional controller in a power plant. To reach to this goal, the complete dynamic model of an actual turbine-generator including the governor, turbine and generator, are derived. Simulation results show that proposed controller has good... 

There is currently a significant focus on using boundary layer control (BLC) approach for controlling the flow around bodies, especially the foil sections. In marine engineering this is done with the hope of increasing the lift - to - drag ratio and efficiency of the hydrofoils. In this paper, effects of the method on hydrodynamic characteristics and tip vortex formation of a hydrofoil are studied. Steady water injection at the tip of the hydrofoil is simulated in different conditions by using ANSYS-CFX commercial software. Validity of the proposed simulations is verified by comparing the obtained results against available experimental data. Effects of the injection on the lift, drag, and... 

We present an efficient method to control the evolution of unsteady cloud cavitation around the CAV2003 benchmark hydrofoil using passive cavitation controllers so called cavitation-bubble generators (CGs). Cavitation control may be used in many engineering applications, particularly in the marine and turbo machinery field. We first simulated the unsteady cavitating flow around the hydrofoil without CGs using a Partially-averaged Navier–Stokes (PANS) method, and validated the acquired results against experimental data. We coupled the turbulence model with a mass transfer model and successfully implemented it in the open source toolbox OpenFOAM. Next, we studied the effect of different CGs on... 

Elongated cylindrical structures with non-uniform diameters, under cross-flow, are often encountered in marine engineering and energy harvesting devices. In this work, the vortex-induced vibrations of elastically supported circular tapered and wavy cylinders with different cross sections areas are studied numerically using a wake oscillator model. The effect of the tapering ratio on the amplitude of oscillation is particularly analyzed. For tapered cylinders it is found that the amplitude of oscillation under flow decreases strongly when a critical tapering is reached. This is consistent with experimental data. A similar effect is found in wavy cylinders. A third system, consisting of a... 

Elongated cylindrical structures with non-uniform diameters, under cross-flow, are often encountered in marine engineering and energy harvesting devices. In this work, the vortex-induced vibrations of elastically supported circular tapered and wavy cylinders with different cross sections areas are studied numerically using a wake oscillator model. The effect of the tapering ratio on the amplitude of oscillation is particularly analyzed. For tapered cylinders it is found that the amplitude of oscillation under flow decreases strongly when a critical tapering is reached. This is consistent with experimental data. A similar effect is found in wavy cylinders. A third system, consisting of a... 

A single‐cylinder marine diesel engine was modified to be operated in reactivity controlled compression ignition (RCCI) combustion mode. The engine fueling system was upgraded to a common rail fuel injection system. Natural gas (NG) was used as port fuel injection, and a die-sel/sunflower methyl ester biodiesel mixture was used for direct fuel injection. The fraction of bio-diesel in the direct fuel injection was changed from 0% (B0; 0% biodiesel and 100% diesel) to 5% (B5) and 20% (B20) while keeping the total energy input into the engine constant. The objective was to understand the impacts of the increased biodiesel fraction on the combustion characteristics and stability, emissions, and...