scholarly journals Study the influence of the relative position of two vessels moving in parallel on their hydrodynamic characteristics

2020 ◽  
pp. 59-65
Author(s):  
Р. Али ◽  
Н.В. Тряскин
Keyword(s):  
Deep Water ◽  
Hydrodynamic Interaction ◽  
Turbulence Modeling ◽  
Hydrodynamic Characteristics ◽  
Rigid Boundary ◽  
Pressure Fields ◽  
Close Proximity ◽  
Calm Weather ◽  
Longitudinal Position ◽  
Good Agreement

Эксплуатация судна сопровождается ситуациями, в которых оно испытывает дополнительные нагрузки от близости твёрдых границ, таких как плавание в ограниченном фарватере, расхождение судов на малых расстояниях, погрузочные операции. Для грамотного осуществления подобных операций необходима заблаговременная оценка возможные нагрузок и учёт гидродинамического влияния между судами или судном и твёрдой поверхностью. Целью данной работы является изучение влияния взаимного положения двух судов на гидродинамическое взаимодействие между ними, а также оценка возможного взаимодействия между судами при операциях погрузки/разгрузки на глубокой воде. Гидродинамическое взаимодействие выражается в изменении полей давления и скорости при непосредственной близости нескольких судов, изменении поперечной и продольной гидродинамических сил и моментов рыскания, действующих на оба объекта. Для определения влияния относительных расстояний между судами на их гидродинамическое взаимодействие во время разгрузочных операций проведён ряд численных экспериментов. Смоделировано обтекание потоком вязкой несжимаемой жидкости двух судов типа KVLCС2, находящихся на различных относительных расстояниях друг от друга. Математическое моделирование турбулентного потока основано на решении уравнений Рейнольдса и проведено с помощью открытого программного пакета OpenFOAM. Для моделирования турбулентности использована модель турбулентности. Результаты численного моделирования обработаны и проанализированы, они находятся в хорошем соответствии с экспериментальными данными. Вычислены максимальные силы и моменты, возникающие при взаимодействии судов при их различном взаимном положении. Hydrodynamic interaction between ships continues to be a major field of research, considering that during different stages of the investment ship’s life, ship is exposed to the presence of a close rigid boundary such as sailing in restricted areas, overtaking and encountering at small distances with other ship or during investment operation such as lightering operations. In order to perform lightering operations safely, the knowledge of the interaction effects between both ships is very important. The aim of this article is to study the changes in velocity and pressure fields resulting from the presence of the two ships in close proximity, evaluating the longitudinal and transverse forces as well as yaw momentum affecting both ships, determining their relationship to the relative longitudinal position of the two ships as well as to predict the ship-to-ship interaction during lightering operations in deep water. A series of systematic computations were performed on two KVLCC2 hulls advancing in deep water and calm weather with the same constant low speed (full scale speed 4kt) in order to investigate the influence of the relative longitudinal separations on the hydrodynamic interaction forces and moments during the lightering operation. OpenFOAM, an open-source CFD packet was used for carrying out the simulations, RANS method was used for turbulence modeling and the well-known turbulent model 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. Maximum forces and moments and their relation with longitudinal position were computed.

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.

Calculation of the Hydrodynamic Interaction Between Two Encountering Bodies in Coupling Multi-Freedom Motions

2015 ◽  
Vol 157 (A4) ◽  
pp. 219-226
Keyword(s):  
Hydrodynamic Interaction ◽  
Interaction Effects ◽  
Numerical Results ◽  
Motion Equations ◽  
Flow Equations ◽  
Close Proximity ◽  
Lateral Distance ◽  
Body Sizes ◽  
Two Bodies ◽  
Good Agreement

"The sway and yaw motion will be induced additionally due to the interaction effects when two encountering bodies sail in close proximity, which may lead to the collision accident. In the present study, two ellipsoids are taken as an example. By coupling the motion equations of the two bodies and the fluid flow equations, the interaction forces and moments are calculated, and the tracks are predicted. The numerical results for the model fixed motion (only free to surge) at constant speed are compared with those published in literature for the validation of the method proposed in this paper, and good agreement is found. On this basis, more complicated multi-degree of freedom motions in surge, sway and yaw directions induced by the interaction effects are simulated. By systematically comparing and analyzing the numerical results obtained at different speeds, lateral distances and body sizes, the influences of speed and lateral distance and body size on the hydrodynamic forces are elucidated."

CALCULATION OF THE HYDRODYNAMIC INTERACTION BETWEEN TWO ENCOUNTERING BODIES IN COUPLING MULTI-FREEDOM MOTIONS

2021 ◽  
Vol 157 (A4) ◽  
Author(s):  
H M WANG ◽  
L WANG ◽  
L Q TU ◽  
C H ZHAO
Keyword(s):  
Hydrodynamic Interaction ◽  
Interaction Effects ◽  
Numerical Results ◽  
Motion Equations ◽  
Flow Equations ◽  
Close Proximity ◽  
Lateral Distance ◽  
Body Sizes ◽  
Two Bodies ◽  
Good Agreement

ellipsoids are taken as an example. By coupling the motion equations of the two bodies and the fluid flow equations, the interaction forces and moments are calculated, and the tracks are predicted. The numerical results for the model fixed motion (only free to surge) at constant speed are compared with those published in literature for the validation of the method proposed in this paper, and good agreement is found. On this basis, more complicated multi-degree of freedom motions in surge, sway and yaw directions induced by the interaction effects are simulated. By systematically comparing and analyzing the numerical results obtained at different speeds, lateral distances and body sizes, the influences of speed and lateral distance and body size The sway and yaw motion will be induced additionally due to the interaction effects when two encountering bodies sail in close proximity, which may lead to the collision accident. In the present study, two on the hydrodynamic forces are elucidated. 

Numerical evaluation of hydrodynamic characteristics of planing hulls by using a hybrid method

2021 ◽  
pp. 147509022199024
Author(s):  
Emre Kahramanoglu ◽  
Silvia Pennino ◽  
Huseyin Yilmaz
Keyword(s):  
Experimental Data ◽  
Hybrid Method ◽  
Design Stage ◽  
Hydrodynamic Characteristics ◽  
Calm Water ◽  
Preliminary Design Stage ◽  
Reduction Function ◽  
Hull Forms ◽  
Good Agreement

The hydrodynamic characteristics of the planing hulls in particular at the planing regime are completely different from the conventional hull forms and the determination of these characteristics is more complicated. In the present study, calm water hydrodynamic characteristics of planing hulls are investigated using a hybrid method. The hybrid method combines the dynamic trim and sinkage from the Zarnick approach with the Savitsky method in order to calculate the total resistance of the planing hull. Since the obtained dynamic trim and sinkage values by using the original Zarnick approach are not in good agreement with experimental data, an improvement is applied to the hybrid method using a reduction function proposed by Garme. The numerical results obtained by the hybrid and improved hybrid method are compared with each other and available experimental data. The results indicate that the improved hybrid method gives better results compared to the hybrid method, especially for the dynamic trim and resistance. Although the results have some discrepancies with experimental data in terms of resistance, trim and sinkage, the improved hybrid method becomes appealing particularly for the preliminary design stage of the planing hulls.

Effective Power and Speed Loss of Underwater Vehicles in Close Proximity to Regular Waves

2017 ◽  
Author(s):  
Stefan Daum ◽  
Martin Greve ◽  
Renato Skejic
Keyword(s):  
Free Surface ◽  
Deep Water ◽  
Water Waves ◽  
Underwater Vehicles ◽  
Total Resistance ◽  
Wave Load ◽  
Regular Waves ◽  
Effective Power ◽  
Close Proximity ◽  
Deep Water Waves

The present study is focused on performance issues of underwater vehicles near the free surface and gives insight into the analysis of a speed loss in regular deep water waves. Predictions of the speed loss are based on the evaluation of the total resistance and effective power in calm water and preselected regular wave fields w.r.t. the non-dimensional wave to body length ratio. It has been assumed that the water is sufficiently deep and that the vehicle is operating in a range of small to moderate Froude numbers by moving forward on a straight-line course with a defined encounter angle of incident regular waves. A modified version of the Doctors & Days [1] method as presented in Skejic and Jullumstrø [2] is used for the determination of the total resistance and consequently the effective power. In particular, the wave-making resistance is estimated by using different approaches covering simplified methods, i.e. Michell’s thin ship theory with the inclusion of viscosity effects Tuck [3] and Lazauskas [4] as well as boundary element methods, i.e. 3D Rankine source calculations according to Hess and Smith [5]. These methods are based on the linear potential fluid flow and are compared to fully viscous finite volume methods for selected geometries. The wave resistance models are verified and validated by published data of a prolate spheroid and one appropriate axisymmetric submarine model. Added resistance in regular deep water waves is obtained through evaluation of the surge mean second-order wave load. For this purpose, two different theoretical models based on potential flow theory are used: Loukakis and Sclavounos [6] and Salvesen et. al. [7]. The considered theories cover the whole range of important wavelengths for an underwater vehicle advancing in close proximity to the free surface. Comparisons between the outlined wave load theories and available theoretical and experimental data were carried out for a submerged submarine and a horizontal cylinder. Finally, the effective power and speed loss are discussed from a submarine operational point of view where the mentioned parameters directly influence mission requirements in a seaway. All presented results are carried out from the perspective of accuracy and efficiency within common engineering practice. By concluding current investigations in regular waves an outlook will be drawn to the application of advancing underwater vehicles in more realistic sea conditions.

scholarly journals A Depth-Bistatic Bottom Reverberation Model and Comparison with Data from an Active Triplet Towed Array Experiment

2020 ◽  
Vol 10 (9) ◽  
pp. 3080
Author(s):  
Youngcheol Jung ◽  
Woojae Seong ◽  
Keunhwa Lee ◽  
Seongil Kim
Keyword(s):  
Time Series ◽  
Deep Water ◽  
Water Environment ◽  
Ray Theory ◽  
Reverberation Time ◽  
Environment Model ◽  
Line Array ◽  
Model Predictions ◽  
Towed Array ◽  
Good Agreement

In this paper, a depth-bistatic bottom reverberation model that employs the ray theory is presented. The model can be applied to an active towed array in the ocean. The reverberation time series are modeled under the depth-bistatic assumption and their Doppler shift is calculated based on the actual source–receiver geometry. This model can handle N × 2D range-dependent bathymetry, the geometry of a triplet array, and the Doppler motion of the source, targets, and receiver. The model predictions are compared with the mid-frequency reverberation data measured by an active triplet towed array during August 2015 in the East Sea, Korea. These data are collected with a variable depth source at mid-frequency and the triplet line array in a deep-water environment. Model predictions of the beam time series and its spectrogram are in good agreement with the measurement. In particular, we discuss the effects of the source and receiver depths on the reverberation in deep water observed in both the measured and modeled results.

Numerical Modeling of Flow Over a Dam Spillway

2006 ◽  
Author(s):  
Iraj Saeedpanah ◽  
M. Shayanfar ◽  
E. Jabbari ◽  
Mohammad Haji Mohammadi
Keyword(s):  
Free Surface ◽  
Stokes Equations ◽  
Iterative Solution ◽  
Free Surface Flows ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Continuity Equations ◽  
Water Jets ◽  
Pressure Fields ◽  
Good Agreement

Free surface flows are frequently encountered in hydraulic engineering problems including water jets, weirs and around gates. An iterative solution to the incompressible two-dimensional vertical steady Navier-Stokes equations, comprising momentum and continuity equations, is used to solve for the priori unknown free surface, the velocity and the pressure fields. The entire water body is covered by a unstructured finite element grid which is locally refined. The dynamic boundary condition is imposed for the free surface where the pressure vanishes. This procedure is done continuously until the normal velocities components vanish. To overcome numerical errors and oscillations encountering in convection terms, the SUPG (streamline upwinding Petrov-Galerkin) method is applied. The solution method is tested for different discharges onto a standard spillway geometries. The results shows good agreement with available experimental data.

Hydrodynamic Interaction Forces on Ship Hulls Equipped With Propulsors

2012 ◽  
Author(s):  
Serge Sutulo ◽  
C. Guedes Soares
Keyword(s):  
Pressure Distribution ◽  
Hydrodynamic Interaction ◽  
Potential Interaction ◽  
Interaction Forces ◽  
Ship Hulls ◽  
Actuator Disk ◽  
Close Proximity ◽  
Body Potential ◽  
Yaw Moment ◽  
Accelerating Motion

Typically, study of hydrodynamic interaction between vessels navigating in close proximity to each other is limited to hydrodynamics of bare hulls. Meanwhile, ship propulsors, especially heavily loaded, which may happen in accelerating motion, can alter substantially the flow and distribution of pressure on the hulls which can be viewed as generalization of the thrust deduction phenomenon. The 3D doubled body potential interaction code based on the source panel method developed earlier by the authors has been enhanced to include the effect of a propeller on each of the interacting ships under the assumption that the propeller jets (slipstreams) are not involved into the interaction. Each propeller is simulated by a disk of sinks further approximated with a polygon composed of identical triangular panels with identical constant sink density linked to the thrust of the propulsor according to the actuator disk theory. Comparative computations were carried out for two identical tanker vessels in the close-proximity overtaking manoeuvre at various values of the loading coefficient of each propeller. The loading coefficient is not supposed to be necessarily defined by the steady propulsion point. Numerical results demonstrate that a heavily loaded propeller substantially modifies the pressure distribution on both hulls resulting in alteration of the hydrodynamic interaction loads, especially of the surge force and yaw moment.

HYDRODYNAMIC CALCULATION OF ROTATING WEIS-FOGH-TYPE WATER TURBINE WITH THE ADVANCED VORTEX METHOD

2015 ◽  
Vol 39 (2) ◽  
pp. 337-355
Author(s):  
Ki-Deok Ro
Keyword(s):  
Velocity Ratio ◽  
Vortex Method ◽  
Maximum Efficiency ◽  
Hydrodynamic Characteristics ◽  
Opening Angle ◽  
Pressure Fields ◽  
Hydrodynamic Calculation ◽  
Water Turbine ◽  
Type Water ◽  
Maximum Opening

In this study, a rotating-type water turbine model applying the principle of the Weis-Fogh mechanism is proposed, and its hydrodynamic characteristics calculated by an advanced vortex method. The unsteady flow and pressure fields around the wing for two revolutions were calculated by changing the uniform flow and maximum opening angle of the wing. The maximum efficiency for one wing of the water turbine was 45.3% at the maximum opening angle of the wing 36° and velocity ratio 2.0. The flow field of the water turbine is very complex because the wing rotates and moves unsteadily in the channel. However, using the advanced vortex method, accurate calculations were possible.

scholarly journals Heat Transfer Enhancement and Hydrodynamic Characteristics of Nanofluid in Turbulent Flow Regime

2015 ◽  
Vol 2015 ◽  
pp. 1-6 ◽  
Author(s):  
Mohammad Nasiri-lohesara
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Pure Water ◽  
Reynolds Numbers ◽  
Hydrodynamic Characteristics ◽  
Two Phase ◽  
Tube Heat Exchanger ◽  
Turbulent Flow Regime ◽  
Lower Slope ◽  
Good Agreement

Turbulent forced convection ofγ-Al2O3/water nanofluid in a concentric double tube heat exchanger has been investigated numerically using mixture two-phase model. Nanofluids are used as coolants flowing in the inner tube while hot pure water flows in outer tube. The studies are conducted for Reynolds numbers ranging from 20,000 to 50,000 and nanoparticle volume fractions of 2, 3, 4, and 6 percent. Results showed that nanofluid has no effects on fully developed length and average heat transfer coefficient enhances with lower slope than wall shear stress. Comparisons with experimental correlation in literature are conducted and good agreement with present numerical study is achieved.

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