scholarly journals NUMERICAL INVESTIGATION OF INTERCEPTOR EFFECT ON SEA KEEPING BEHAVIOUR OF PLANING HULL ADVANCING IN REGULAR HEAD WAVES

Brodogradnja ◽  
2021 ◽  
Vol 72 (2) ◽  
pp. 73-92
Author(s):  
Jangam Suneela ◽  
◽  
Prasanta Sahoo ◽  
Keyword(s):  
Numerical Data ◽  
Navier Stokes ◽  
Hydrodynamic Characteristics ◽  
Head Waves ◽  
Calm Water ◽  
Vessel Response ◽  
Planing Vessel ◽  
Motion Characteristics ◽  
The Impact ◽  
Regular Head Waves

In this paper an attempt has been made to assess the capability of numerical algorithm based on Reynolds Averaged Navier Stokes (RANS) for predicting the motion characteristics of the planing hull in calm water and regular waves. The focus of the present study is the impact of interceptors on the sea keeping quality of a planing vessel investigated through the application of numerical methods. The wave properties such as wavelength and wave height are taken into consideration to investigate the effect of wave steepness on vessel response. It is found that numerical data can efficiently simulate the motion attitude and the hydrodynamic characteristics of planing craft in regular head waves. The planing hull with and without interceptor fitted at the transom is simulated in numerical wave tank. The results show reduction in heave and pitch motions which gave favorable sea keeping behavior for the hull fitted with interceptor. The numerical solution is useful for the preliminary prediction of navigation safety during sailing.

The Effect of Blade Lean, Twist and Bow on the Performance of Axial Turbine at Design Point

2011 ◽  
Author(s):  
Hadi Karrabi ◽  
Mohsen Rezasoltani
Keyword(s):  
Stokes Equations ◽  
Numerical Data ◽  
Navier Stokes ◽  
Minor Effect ◽  
Complex Flow ◽  
Navier Stokes Equations ◽  
Axial Turbine ◽  
Twisted Blade ◽  
The Impact ◽  
Good Agreement

An investigation to understand the impact of twisted, leaned and bowed blades on the performance of axial turbine was undertaken. A CFD code, which solves the Reynolds-averaged Navier–Stokes equations, was used to compute the complex flow field of axial turbine. The code was validated against existing Hannover turbine experimental data. Numerical data showed good agreement with measured data. Finally, the effect of geometry changes, focusing on blade lean, twist and bow, on the Avon turbine blade performance, was analyzed. Results show that twisted blade affects performance significantly. Leaned and bowed blade has minor effect on performance.

Unsteady Numerical Simulation of the Behavior of a Ship Moving in Head Sea

2019 ◽  
Author(s):  
Adrian Lungu
Keyword(s):  
Free Surface Flow ◽  
Surface Flow ◽  
Incoming Wave ◽  
Grid Convergence ◽  
Head Waves ◽  
Calm Water ◽  
Unsteady Numerical Simulation ◽  
Resistance Coefficients ◽  
Regular Head Waves ◽  
Numerical Approaches

Abstract The paper follows a previous work of the author that dealt with ship resistance and self-propulsion numerical investigations, proposing a series of numerical simulations performed to assess the seakeeping performances of the KCS model which moves in regular head waves. Various simulations of the free-surface flow around the hull equipped with rudder moving either in calm water or in heading waves are proposed. For the calm water case, in which a series of six Fr numbers is considered, verification and validation based on the grid convergence tests are performed. Then, a series of five different simulations for various incoming wave characteristics are presented and discussed in every detail. Comparisons with the experimental data [1], [2] are provided aimed at validating the numerical approaches in terms of the total resistance coefficients as well as the heave and pitch motions characteristics. Several remarks will conclude the findings of the present work.

scholarly journals Full-Scale CFD Analysis of Double-M Craft Seakeeping Performance in Regular Head Waves

2021 ◽  
Vol 9 (5) ◽  
pp. 504
Author(s):  
Deniz Ozturk ◽  
Cihad Delen ◽  
Simone Mancini ◽  
Mehmet Ozan Serifoglu ◽  
Turgay Hizarci
Keyword(s):  
Full Scale ◽  
Stokes Wave ◽  
Added Resistance ◽  
Motion Responses ◽  
Seakeeping Performance ◽  
Head Waves ◽  
Calm Water ◽  
Maximum Improvement ◽  
Fifth Order ◽  
Regular Head Waves

This study presents the full-scale resistance and seakeeping performance of an awarded Double-M craft designed as a 15 m next-generation Emergency Response and Rescue Vessel (ERRV). For this purpose, the Double-M craft is designed by comprising the benchmark Delft 372 catamaran with an additional center and two side hulls. First, the resistance and seakeeping analyses of Delft 372 catamaran are simulated on the model scale to verify and compare the numerical setup for Fr = 0.7. Second, the seakeeping performance of the full-scale Double-M craft is examined at Fr = 0.7 in regular head waves (λ/L = 1 to 2.5) for added resistance and 2-DOF motion responses. The turbulent flow is simulated by the unsteady RANS method with the Realizable Two-Layer k-ε scheme. The calm water is represented by the flat VOF (Volume of Fluid) wave, while the incident long waves are represented by the fifth-order Stokes wave. The residual resistance of the Double-M craft is improved by 2.45% compared to that of the Delft 372 catamaran. In the case of maximum improvement (at λ/L = 1.50), the relative added resistance of the Double-M craft is 10.34% lower than the Delft 372 catamaran; moreover, the heave and pitch motion responses were 72.5% and 35.5% less, respectively.

Analysis of Capillary Flow in Rounded Corners

Volume 1 ◽  
2004 ◽  
Author(s):  
Yongkang Chen ◽  
Mark M. Weislogel
Keyword(s):  
Numerical Solutions ◽  
Flow Problem ◽  
Capillary Flow ◽  
Outer Region ◽  
Cross Flow ◽  
Numerical Data ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Inner Region ◽  
The Impact

The problem of capillary flow in interior corners that are rounded is re-visited analytically in this work. By the appropriate geometric scaling, and through the introduction of a new parameter that features the roundedness of the corner, the Navier-Stokes equation is reduced to a convenient form for both numerical and analytical solution. The scaling and analysis of the problem is expected to significantly reduce the reliance on numerical data for such problems, and the design process can be both shortened and improved as a result. For capillary flows of perfect wetting fluids in the rounded corner with an advancing tip, a finite interfacial curvature related to the corner roundedness results at the tip. Accordingly, an outer and inner region of the flow is suggested based on the impact of the corner roundedness on the flow. In this study, asymptotic solutions of the geometrical ‘cross-flow’ problem for the outer region are sought under several constraints and are expected to narrowly bracket parallel numerical solutions. A complete understanding of the flow will be obtained only after the cross-flow problem for the inner region is solved. However, for the flow in the outer region a similarity solution is obtained and presented that reveals how roundedness retards the flow.

Study the influence of ship length ratio on ship to ship interaction on moving in parallel on their hydrodynamic characteristics

2021 ◽  
pp. 61-66
Author(s):  
Р. Али ◽  
Н.В. Тряскин
Keyword(s):  
Hydrodynamic Interaction ◽  
Turbulence Modeling ◽  
Relative Length ◽  
Velocity Fields ◽  
Length Ratio ◽  
Navier Stokes ◽  
Hydrodynamic Characteristics ◽  
Turbulent Model ◽  
Calm Water ◽  
Good Agreement

Суда в некоторых случаях эксплуатации могут двигаться в непосредственной близости друг от друга. Такой сценарий обычно связан с изменением полей давления и скорости вблизи корпуса судов, в результате чего возникают гидродинамические силы и моменты взаимодействия, которые сильно зависит от относительной длины. В этой статье была проведена серия систематических расчётов на двух корпусах KVLCC2, движущихся на большой глубине в безветренную погоду с одинаковой постоянной малой скоростью, не превышающей 4 уз., чтобы исследовать влияние отношения длин на силы и моменты гидродинамического взаимодействия. OpenFOAM, пакет CFD с открытым исходным кодом использовался для организации и проведения расчётов. Метод осреднения по Рейнольдсу уравнений Навье-Стокса (RANS) применялся для моделирования турбулентности. Хорошо известная модель турбулентности использовалась для замыкания уравнений Навье-Стокса. Числовые результаты, касающиеся поля скоростей и гидродинамического следа за судами, были обработаны, проанализированы, сопоставлены и показали хорошее согласование с экспериментальными результатами. Ships, during the lightering operations, are forced to sail in a close position to each other, such a scenario generally associates with a change in the pressure and velocity fields surrounding their hulls, as a result, interaction hydrodynamic forces and moments are generated which are strongly related to the relative length of the interacted ships. In this paper, a series of systematic computations were performed on two KVLCС2 hulls advancing in deep and calm water with the same constant low speed (full scale speed 4kt) in order to investigate the influence of the length ratio on the hydrodynamic interaction forces and moments during the lightering operation. OpenFOAM, an open-source CFD packet was used for carrying out the simulations, Reynolds Averaged Navier-Stokes (RANS) method was used for turbulence modeling and the well-known turbulent model k-ω SST was used to close RANS equations. Numerical results have been post-processed, analyzed, compared and found to be of a good agreement with the experimental results. The velocity fields and wake were presented and analyzed.

Validation Exercises for a Free Falling Wedge Into Calm Water

2018 ◽  
Author(s):  
João Muralha ◽  
Luís Eça ◽  
António Maximiano ◽  
Guilherme Vaz
Keyword(s):  
Mathematical Model ◽  
Deep Water ◽  
Navier Stokes ◽  
Main Challenge ◽  
Calm Water ◽  
Pressure Peak ◽  
Peak Pressures ◽  
Free Falling ◽  
The Impact ◽  
The Mathematical Model

This paper presents the assessment of the modelling error (Validation) of a Navier-Stokes solver using Volume of Fluid (VOF) and moving grid techniques in the simulation of a free falling wedge into calm water. This problem has been studied experimentally to determine the time histories of six pressure probes located on the wedge surface and the acceleration of the wedge. The simulation is restricted to the first 100ms after the impact of the wedge on the water (t = 0 at the impact) and the mathematical model uses the following assumptions: incompressible fluid; two-dimensional, laminar flow, negligible shear-stress at the surface of the wedge and deep water. The selected quantities of interest are the peak pressures at the six sensors, time intervals between peak pressures at the sensors, sensors pressures and acceleration of the wedge at six different time instants and integrated pressure signals for 80ms after the pressure peak at the first sensor. The application of the ASME V&V 20 standard to local quantities is presented, including the estimation of experimental and numerical uncertainties. Furthermore, a multivariate metric is used to evaluate quantitatively the overall performance of the mathematical model. The results show significant comparison errors (mismatches between simulations and measurements) for the accelerations, which may be a consequence of the assumptions of a deep water boundary condition at the bottom. However, such conclusion is hampered by some doubts about the accuracy of the experimental data. On the other hand, modeling errors are significantly smaller for the pressure measurements at the six sensors for which the main challenge is to reduce the validation uncertainty Uval. In many of the selected flow quantities, Uval is dominated by the experimental uncertainty.

Numerical Prediction of the Propulsion Characteristics of Ships in Waves

2016 ◽  
Author(s):  
Sebastian Sigmund ◽  
Ould el Moctar
Keyword(s):  
Equations Of Motion ◽  
Open Water ◽  
Computational Effort ◽  
The Self ◽  
Experimental Results ◽  
Characteristic Change ◽  
Flow Solver ◽  
Head Waves ◽  
Calm Water ◽  
Regular Head Waves

The influence of regular head waves on the propulsion characteristics of a twin screw cruise ship is investigated using RANS based flow-solver. Propeller open water characteristics are determined at first by computing the propeller forces in homogeneous inflow. Then, computations of the towed model without propeller and of the self-propelled model in calm water are performed to obtain the propulsion characteristics in calm water. Afterwards, the total resistance as well as the forces of the self-propelled model in regular head waves are computed. All computations are performed using a RANS based flow-solver coupled with the six-degrees-of-freedom equations of motion. The sliding interface method is used to allow the rotation of the geometrically modelled propeller, when needed. Computations are performed using the same numerical grids to keep errors originating on different spatial and temporal discretization as small as possible. Grid studies are performed to evaluate discretization errors of each mesh region, namely the hull region and the rotating propeller region, separately. The numerical results are compared with experimental results obtained from physical tests. It is shown, that RANS is capable of investigating the propulsion behavior of a ship in regular head waves, but to the cost of high computational effort. Fair agreement between numerical and experimental results is obtained. All results show that the propulsion characteristic change in waves. It is also found, that this is mainly caused by the change of the propeller efficiency due to a different propulsion point as a consequence of the added resistance in waves.

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