Numerical studies on added resistance and motions of KVLCC2 in head seas for various ship speeds

In this study, numerical simulations for the prediction of added resistance and ship motions at various ship speeds and wave steepnesses for the KVLCC2 are presented. These are calculated using URANS CFD and 3-D potential methods, both in regular head seas. Numerical analysis is focused on the added resistance and the vertical ship motions for a wide range of wave conditions at stationary, operating and design speeds. Firstly, the characteristics of the CFD and the 3-D potential method are presented. Simulations of various wave conditions at design speed are used as a validation study, and then simulations are carried out at stationary and operating speed. Secondly, unsteady wave patterns and time history results of the added resistance and the ship motions are simulated and analysed at each ship speed using the CFD tool. Finally, the relationship between the added resistance and the vertical ship motions is studied in detail and the non-linearity of the added resistance and ship motions with the varying wave steepness are investigated. Systematic studies of the numerical computations at various ship speeds are conducted as well as the grid convergence tests, to show that the numerical results have a reasonable agreement with the available EFD results

The effect of forward speed on nonlinear ship motion responses

Time-domain nonlinear vertical motion response of the S-175 containership advancing in head sea condition in large amplitude waves are analysed and compared with the experimental results provided in the literature. The boundary value problem is solved by linear 3D Rankine source panel method with sources distributed on the ship surface, free surface and control surfaces. Nonlinear fluid forces, which arise from nonlinear restoring and Froude-Kylov forces, are calculated over the instantaneous wetted portion of the ship hull. Radiation forces are kept as linear and presented in terms of impulse response functions using convolution integrals. In large amplitude waves, nonlinear motion responses are identified and presented in terms of transfer functions. The numerical results are well agreed with the experimental results and show a significant increase in non-dimensional amplitudes with the increase in the ship speed. Validation of the in-house developed code is performed and showed good agreement with the experimental results in the large amplitude waves

Estimation of added resistance and ship speed loss in a seaway

The prediction of the added resistance and attainable ship speed under actual weather conditions is essential to evaluate the true ship performance in operating conditions and assess environmental impact. In this study, a reliable methodology is proposed to estimate the ship speed loss of the S175 container ship in specific sea conditions of wind and waves. Firstly, the numerical simulations are performed to predict the added resistance and ship motions in regular head and oblique seas using three different methods; a 2-D and 3-D potential flow method and a Computational Fluid Dynamics (CFD) with an Unsteady Reynolds-Averaged Navier-Stokes (URANS) approach. Simulations of various wave conditions are compared with the available experimental data and these are used in a validation study. Secondly, following the validation study in regular waves, the ship speed loss is estimated using the developed methodology by calculating the resistance in calm water and the added resistance due to wind and irregular waves, taking into account relevant wave parameters and wind speed corresponding to the Beaufort scale, and results are compared with simulation results obtained by other researchers. Finally, the effect of the variation in ship speed and therefore the ship speed loss is investigated. This study shows the capabilities of the 2-D and 3-D potential methods and CFD to calculate the added resistance and ship motions in regular waves in various wave headings. It also demonstrates that the proposed methodology can estimate the impacts on the ship operating speed and the required sea margin in irregular seas

Three dimensional time domain simulation of ship motions and loads in large amplitude head waves

This PhD thesis presents the development of a practical computational tool named Large Amplitude RESponse (LARes), based on 3D quasi-non-linear time-domain technique, to predict ship motions and loads in large amplitude waves which can be accessible to ship designers. Firstly, a linear 3-D Green source panel code (LARes L1) was developed to perform linear time-domain analysis ship motion and internal load simulations based on the frequency-domain hydrodynamic coefficients which were calculated in the linear PRECAL software. Linear simulations are validated with the linear time-domain PRETTI software results using rectangular barge geometry. The motions, internal loads, global and sectional hydrodynamic forces were agreed well with the linear PRETTI model results in zero and forward speed simulations. Then, non-linear time-domain panel code (LARes L2) was developed in order to predict ship motions and loads in large amplitude waves using the Froude-Krylov nonlinearity level. At each time step, the exact wetted area of the ship surface under the wave profile was calculated and fed in the time-domain motion and load equations while the diffraction and radiation forces were kept as linear. The present program achieved good agreement with the non-linear PRETTI model results both for the barge and S175 container geometries at zero and forward speed conditions in small amplitude waves. Moreover, the S175 container ship results are compared with the available experimental data and agreed well with the experimental results in forward speed case. It has been observed that PRETTI code is over-estimating motion and load responses especially around the resonant frequency due to the surge motion influence in the memory forces evaluations. In the Froude-Krylov nonlinear level predictions, it has been observed that PRETTI diverges from the experimental results when the wave steepness is higher than 0.08 due to the linear radiation and diffraction forces. Based on the same framework, a more advanced nonlinear time-domain panel code (LARes L3) was developed in order to investigate the effects of quasi-non-linear diffraction and radiation forces in large amplitude ship simulations. A new mesh generator was introduced in order to cut and correct the original panels under the still water level in the updated position of the ship after displacements and rotations. The quasi-non-linear diffraction and radiation forces were calculated at the pre-defined position cases and stored in a database. In order to lower the computational cost multi-dimensional integration and interpolation codes were generated. The S-175 containership was tested in 120 different position cases and resulting hydrodynamic coefficients and forces were stored in the database. The results of the LARes L3 model were compared with the available experimental data using the S-175 containership in forward speed. The computed motion responses showed a good agreement with the experimental data. Moreover, three of the developed models are compared with the experiments and their performances were investigated with respect to the increasing wave slope. In addition to that, the effect of the wave length and ship speed in large amplitude waves are investigated in detail. Non-linear behaviors of the codes were compared with the experimental results which showed a good agreement. Finally, the Vertical Shear Force (VSF) and Vertical Bending Moment (VBM) responses were investigated in large amplitude motions. It was observed that, in the validation section, numerical model peak amplitudes showed well agreement with the experimental results, but they were observed to be shifted to the higher frequencies compared to the experimental results. The reason for that was attributed to the longitudinal mass distribution on the ship in the experimental setup which had not been provided in detail in the published experimental results.This PhD thesis presents the development of a practical computational tool named Large Amplitude RESponse (LARes), based on 3D quasi-non-linear time-domain technique, to predict ship motions and loads in large amplitude waves which can be accessible to ship designers. Firstly, a linear 3-D Green source panel code (LARes L1) was developed to perform linear time-domain analysis ship motion and internal load simulations based on the frequency-domain hydrodynamic coefficients which were calculated in the linear PRECAL software. Linear simulations are validated with the linear time-domain PRETTI software results using rectangular barge geometry. The motions, internal loads, global and sectional hydrodynamic forces were agreed well with the linear PRETTI model results in zero and forward speed simulations. Then, non-linear time-domain panel code (LARes L2) was developed in order to predict ship motions and loads in large amplitude waves using the Froude-Krylov nonlinearity level. At each time step, the exact wetted area of the ship surface under the wave profile was calculated and fed in the time-domain motion and load equations while the diffraction and radiation forces were kept as linear. The present program achieved good agreement with the non-linear PRETTI model results both for the barge and S175 container geometries at zero and forward speed conditions in small amplitude waves. Moreover, the S175 container ship results are compared with the available experimental data and agreed well with the experimental results in forward speed case. It has been observed that PRETTI code is over-estimating motion and load responses especially around the resonant frequency due to the surge motion influence in the memory forces evaluations. In the Froude-Krylov nonlinear level predictions, it has been observed that PRETTI diverges from the experimental results when the wave steepness is higher than 0.08 due to the linear radiation and diffraction forces. Based on the same framework, a more advanced nonlinear time-domain panel code (LARes L3) was developed in order to investigate the effects of quasi-non-linear diffraction and radiation forces in large amplitude ship simulations. A new mesh generator was introduced in order to cut and correct the original panels under the still water level in the updated position of the ship after displacements and rotations. The quasi-non-linear diffraction and radiation forces were calculated at the pre-defined position cases and stored in a database. In order to lower the computational cost multi-dimensional integration and interpolation codes were generated. The S-175 containership was tested in 120 different position cases and resulting hydrodynamic coefficients and forces were stored in the database. The results of the LARes L3 model were compared with the available experimental data using the S-175 containership in forward speed. The computed motion responses showed a good agreement with the experimental data. Moreover, three of the developed models are compared with the experiments and their performances were investigated with respect to the increasing wave slope. In addition to that, the effect of the wave length and ship speed in large amplitude waves are investigated in detail. Non-linear behaviors of the codes were compared with the experimental results which showed a good agreement. Finally, the Vertical Shear Force (VSF) and Vertical Bending Moment (VBM) responses were investigated in large amplitude motions. It was observed that, in the validation section, numerical model peak amplitudes showed well agreement with the experimental results, but they were observed to be shifted to the higher frequencies compared to the experimental results. The reason for that was attributed to the longitudinal mass distribution on the ship in the experimental setup which had not been provided in detail in the published experimental results

A smart system to determine sensor locations for structural health monitoring of ship structures

Utilizing the strain data collected from on-board strain sensors in order to solve the inverse problem of real time reconstruction of full-field structural displacements, strains, and stresses is known as displacement and stress monitoring. Displacement and stress monitoring is the vital feature for performing Structural Health Monitoring (SHM). An efficient algorithm called inverse Finite Element Method (iFEM) was recently developed for displacement and stress monitoring of engineering structures. Obtaining the surface strain measurements from the sensors placed on the optimum locations of structure is crucial in terms of the iFEM methodology. Therefore, the main goal of this work is to develop a smart system that determines the most appropriate and practical locations of the on-board strain sensors for SHM of ship structures. The system is developed by combining three different in-house software, hydrodynamic software, finite element software, and iFEM software. The following execution sequence is used. First, the hydrodynamic analysis is performed in order to find hydrodynamic ship loading and rigid body motion of the ship. Then, finite element analysis is performed to obtain structural response and simulated sensor-strain data. Finally, iFEM analysis is performed to reconstruct the three-dimensional global structural response by using the simulated strain data obtained from different number of strain sensors located at various locations of the structure as input. By utilizing the developed system, a long barge is analyzed and the optimum locations for placing on-board sensors are determined and discussed

Numerical studies on non-linearity of added resistance and ship motions of KVLCC2 in short and long waves

In this study, numerical simulations for the prediction of added resistance for KVLCC2 with varying wave steepness are performed using a Computational Fluid Dynamics (CFD) method and a 3-D linear potential method, and then the non-linearities of added resistance and ship motions are investigated in regular short and long waves. Firstly, grid convergence tests in short and long waves are carried out to establish an optimal mesh system for CFD simulations. Secondly, numerical simulations are performed to predict ship added resistance and vertical motion responses in short and long waves and the results are verified using the available experimental data. Finally, the non-linearities of added resistance and ship motions with unsteady wave patterns in the time domain are investigated with the increase in wave steepness in both short and long waves. The present systematic study demonstrates that the numerical results have a reasonable agreement with the experimental data and emphasizes the non-linearity in the prediction of the added resistance and the ship motions with the increasing wave steepness in short and long waves. Keywords: Added resistance, Wave steepness, Short waves, Potential flow, CFD, KVLCC

Management of Priapism: Results of a Nationwide Survey and Comparison with International Guidelines

Objective: The aim of this study is to evaluate current urologic practice regarding the management of priapism in Turkey and compare with international guidelines. Methods: Urologists and urology residents were invited to an online survey consisting of 30 multiple-choice questions on priapism-related clinical practices that were considered most important and relevant to practices by using Google Forms. Results: Total number of responses was 340. Respondents reported that they recorded a detailed patient’s medical history and physical examination findings (n = 340, 100%) and laboratory testing, which includes corporal blood gas analysis (n = 323, 95%). Participants announced that they performed Doppler ultrasound for 1/4 cases (n = 106, 31%), but 22% of the participants (n = 75) replied that they performed in >75% of cases. Participants (n = 311, 91%) responded that the first-line treatment of ischemic priapism is decompression of the corpus cavernosum. Moreover, most respondents (n = 320, 94%) stated that sympathomimetic injection drugs should be applied as the second step. About three-quarters of respondents (n = 247, 73%) indicated adrenaline as their drug of choice. Phosphodiesterase type 5 inhibitors seems to be the most preferred drug for stuttering priapism (n = 141, 41%). Participants (n = 284, 84%) replied that corpora-glanular shunts should be preferred as the first. A large number of participants (n = 239, 70%) declared that magnetic resonance imaging can be performed in cases with delayed (>24 hours) priapism to diagnose corporal necrosis. Most of the participants (84%) responded that penile prosthesis should be preferred to shunts in cases with delayed (>48 hours) priapism. Conclusion: It would be appropriate to improve the training offered by professional associations and to give more training time to the management of priapism during residency