Effects of Marine Growth on Hydrodynamic Coefficients of Rigid Tubular Cylinders

2014 ◽  
Vol 567 ◽  
pp. 247-252 ◽  
Author(s):  
A. M. Al-Yacouby ◽  
V. John Kurian ◽  
A.A. Sebastian ◽  
M.S. Liew ◽  
V.G. Idichandy
Keyword(s):  
Experimental Data ◽  
Water Depth ◽  
Hydrodynamic Forces ◽  
Experimental Results ◽  
Hydrodynamic Coefficients ◽  
Regular Waves ◽  
Tank Model ◽  
Rigid Cylinder ◽  
Wave Heights ◽  
Wave Induced

In this paper the wave induced hydrodynamic forces and the corresponding hydrodynamic coefficients for a 42 mm diameter model pipe subjected to regular waves was investigated experimentally and the results were compared with the responses of a similar rigid cylinder fitted with marine growth. The main objective of this study was to quantify the effects of marine growth on the hydrodynamic forces experimentally and determine the associated hydrodynamic coefficients. The experimental data were generated from a set of wave tank model tests and the results were scaled up using a scale factor of 1:55. The thickness of marine growth applied on the model pipe was varied with respect to the water depth in the ratio of 3:2:1. Regular waves were generated with wave heights ranging from 0.02 m to 0. 2 m for modal period varying from 0.6 s to 3.25 s. The tests were conducted for Keulegan-Carpenter number ranging from 3.9 to 23.3. The findings of the experimental results revealed that increasing the thickness of the full scale prototype cylinder by 110 mm due to marine growth fittings, has increased the overall wave hydrodynamic forces by 16 to 90% depending on the wave heights and the wave frequencies at which the model was tested, proving that the drag coefficients have considerably increased.

Quantification of Hydrodynamic Forces due to Torsional and Axial Vibrations in Ship Propellers

2013 ◽  
Author(s):  
B. P. M. van Esch ◽  
J. J. A. van Hooijdonk ◽  
N. W. H. Bulten
Keyword(s):  
Experimental Data ◽  
Open Water ◽  
Hydrodynamic Forces ◽  
Hydrodynamic Coefficients ◽  
Water Condition ◽  
Reduced Frequency ◽  
Vibratory Motion ◽  
Trailing Vortices ◽  
Axial Vibrations ◽  
Oscillating Plate

CFD is used to compute the hydrodynamic coefficients for torsional and axial vibrations, for one type of the Wageningen B-series of ship propellers in open-water condition. It is shown that the wakes shed from the blades have an influence on the magnitude and the phase of the damping forces. The dependency on reduced frequency of the vibratory motion is explained. This phenomenon can be related to the lift deficiency of trailing vortices in the wake of an oscillating plate, as derived by Theodorsen and Von Kármán and Sears, and is frequently overlooked by more recent investigations. Results of the calculations are compared with theoretical and experimental data from literature.

Hybrid Method for Predicting Ship Manoeuvrability in Regular Waves

2019 ◽  
Author(s):  
Tianlong Mei ◽  
Yi Liu ◽  
Manasés Tello Ruiz ◽  
Marc Vantorre ◽  
Evert Lataire ◽  
...  
Keyword(s):  
Experimental Data ◽  
Hybrid Method ◽  
Potential Flow ◽  
Flow Theory ◽  
Regular Waves ◽  
Potential Flow Theory ◽  
Hydrodynamic Derivatives ◽  
Mmg Model ◽  
Calm Water ◽  
Wave Induced

Abstract The ship’s manoeuvring behaviour in waves is significantly different from that in calm water. In this context, the present work uses a hybrid method combining potential flow theory and Computational Fluid Dynamics (CFD) techniques for the prediction of ship manoeuvrability in regular waves. The mean wave-induced drift forces are calculated by adopting a time domain 3D higher-order Rankine panel method, which includes the effect of the lateral speed and forward speed. The hull-related hydrodynamic derivatives are determined based on a RANS solver using the double body flow model. The two-time scale method is applied to integrate the improved seakeeping model in a 3-DOF modular type Manoeuvring Modelling Group (MMG model) to investigate the ship’s manoeuvrability in regular waves. Numerical simulations are carried out to predict the turning circle in regular waves for the S175 container carrier. The turning circle’s main characteristics as well as the wave-induced motions are evaluated. A good agreement is obtained by comparing the numerical results with experimental data obtained from existing literature. This demonstrates that combining potential flow theory with CFD techniques can be used efficiently for predicting the manoeuvring behaviour in waves. This is even more true when the manoeuvring derivatives cannot be obtained from model tests when there is lack of such experimental data.

Numerical Investigation of Hydrodynamic Performance of a Light Buoy with Different Mooring Configurations in Regular Waves

2021 ◽  
pp. 1-26
Author(s):  
Xin Li ◽  
Yimei Chen ◽  
Lilei Mao ◽  
Huiyu Xia
Keyword(s):  
Experimental Data ◽  
Yangtze River ◽  
Coupled Model ◽  
Coupling Model ◽  
Numerical Approach ◽  
Hydrodynamic Performance ◽  
Irregular Waves ◽  
Regular Waves ◽  
Induced Motion ◽  
Wave Induced

Abstract The single-moored light buoys employed in the lower reaches of the Yangtze River play an important role in indicating ship navigation and ensuring safety. To clarify the interaction between waves and floating buoys moored to the riverbed, this paper develops a numerical approach to investigate the wave-induced motion performance of a light buoy and reveal the effects of different mooring configurations to extend its service life. A new open-source SPH based numerical model named DualSPHysics coupled with MoorDyn is implemented. This coupled model is validated by simulating the motion of a moored rectangle buoy in regular waves, and compared with experimental data and the numerical results of REEF3D code, a new mesh-based CFD model. The validation results show that the coupled model reproduces experimental data well and has a smaller deviation in comparison with REEF3D. Then the coupling model is applied to simulate the hydrodynamic performance of the real-size light buoy employed in Yangtze River and investigate effects of encounter angle between wave propagation direction and mooring chain. The results demonstrate the capability of this coupled mooring model to simulate the motion of a moored buoy in regular waves, and this numerical approach will be extended to simulate the light buoy in more complex environments such as irregular waves, flow or extreme weather in further work.

Drift of an articulated cylinder in regular waves

1984 ◽  
Vol 394 (1807) ◽  
pp. 363-385 ◽  
Keyword(s):  
Near Field ◽  
Second Order ◽  
Regular Waves ◽  
Floating Bodies ◽  
Wave Heights ◽  
Tilt Mode ◽  
The Mean ◽  
Wave Induced ◽  
Theoretical Results ◽  
Drift Forces

Potential flow theory is used to investigate the wave induced harmonic response and the mean drift of an articulated column in regular waves. The mean drift horizontal force is evaluated by means of the Stokes expansion to second order in wave steepness. Analyses based on both near field and far field formulations are shown to give identical expressions, provided that the second-order forces at the intersection between column and seabed are included in the near field approach. The latter have not been considered in previous studies concerned with drift forces on floating bodies. It is shown that the drift forces on a column, although of second order, can excite piech responses of first order: this is because articulated columns are designed to have a low natural frequency in the tilt mode, relative to wave frequencies. Comparison of the theoretical results with experimental data, from a model tested in regular waves, suggests reasonable agreement for the drift forces over a range of frequencies and two wave heights.

Tank Model Testing on the Fish Cage Installed in Variable Depths in Current and Waves

2013 ◽  
Author(s):  
Daisuke Kitazawa ◽  
Hiroki Shimizu ◽  
Yoichi Mizukami
Keyword(s):  
Experimental Data ◽  
Numerical Model ◽  
Current Velocity ◽  
Angle Of Attack ◽  
Hydrodynamic Forces ◽  
Water Current ◽  
Mooring System ◽  
Water Tank ◽  
Tank Model ◽  
Water Current Velocity

A fish cage should be submerged to reduce hydrodynamic forces from high waves if the fish cage is installed in an exposed sea area. Usually, the submergible fish cage is suspended from the framework at a fixed depth. The framework is set by floats and anchors at the middle position between water surface and the top surface of the submergible fish cage. The submergible fish cage will be used not only for reduction of hydrodynamic forces but for the other purposes such as choosing the best environment for cultured fishes in the vertical direction, and escaping from the flood with high-level nitrogen or turbidity, harmful algal blooming, and floating ices. In such cases, it is useful for the fish cage to be installed in variable depths. The purpose of the present study is to examine the safety of the fish cage installed in variable depths in current and waves by means of tank model testing. The mooring system consists of a fish cage and four floats. The vertical position of the fish cage is variable by adjusting the buoyancy of these floats. First, the drag of the fish cage was examined by towing test, and the results were compared with the drag estimated by the existing studies. The effects of interaction among twines, the angle of attack, wake, and the top and bottom nets were discussed. Then the fish cage was moored in the water tank, which has the length of 50 m and the width of 10 m. The tank model has a scale of 1/100 of the full-scale model of the fish cage used for tuna farming. The model was made according to Tauti’s similarity law. The water depth was set at 0.68 m by adjusting the position of the variable floor. The motion of the fish cage and four floats, and the tension of the mooring lines between the fish cage, floats, and anchors were measured by the underwater video camera and load cells, respectively. As a result, the drag of the fish cage could be estimated from the experimental results of the drag of a plane net since the results include the effect of interaction among twines. The effects of the angle of attack and the reduction in water current velocity inside the cage were also taken into account. The drag of the fish cage could be estimated well by the above method, while it was underestimated by 10% in comparison with the experimental data. In the water tank testing of the mooring system, the tension of the mooring line increased rapidly with the increase in water current velocity since the drag of the fish cage was proportional to the 1.8th power of water current velocity and increased due to the inclination of the fish cage. The increase in the tension due to wave-induced forces to the fish cage could be negligible when the fish cage was submerged. The safety and the design guideline of the mooring system should be assessed by the simulations using a numerical model, which is being developed by the authors. The experimental data obtained in the present study will be useful for the validation of the numerical model.

scholarly journals TRANSMISSION OF REGULAR WAVES PAST FLOATING PLATES

1974 ◽  
Vol 1 (14) ◽  
pp. 112
Author(s):  
Uygur Sendil ◽  
W.H. Graf
Keyword(s):  
Water Depth ◽  
Wave Length ◽  
Wave Theory ◽  
Finite Amplitude ◽  
Linear Wave ◽  
Regular Waves ◽  
Transmission Coefficients ◽  
Wave Flume ◽  
Wave Heights ◽  
Incident Waves

Theoretical solutions for the transmission beyond and reflection of waves from fixed and floating plates are based upon linear wave theory, as put forth by John (1949), and Stoker (1957), according to which the flow is irrotational, the fluid is incompressible and frictionless, and the waves are of small amplitude. The resulting theoretical relations are rather complicated, and furthermore, it is assumed that the water depth is very small in comparison to the wave length. Wave transmissions beyond floating horizontal plates are studied in a laboratory wave flume. Regular (harmonic) waves of different heights and periods are generated. The experiments are carried out over a range of wave heights from 0.21 to 8.17 cm (0.007 to 0.268 ft), and wave periods from 0.60 to 4.00 seconds in water depth of 15.2, 30.5, and 45.7 cm (0.5, 1.0 and 1.5 ft). Floating plates of 61, 91 and 122 cm (2, 3 and 4 ft) long were used. From the analyses of regular waves it was found that: (1) the transmission coefficients, H /H , obtained from the experiments are usually less than those obtained from the theory. This is due to the energy dissipation by the plate, which is not considered in the theory. (2) John's (1949) theory predicts the transmission coefficients, H /H , reasonably well for a floating plywood plate, moored to the bottom and under the action of non-breaking incident waves of finite amplitude. (3) a floating plate is less effective in damping the incident waves than a fixed plate of the same length.

Time Domain Simulation of the Maneuvering of a Vessel in a Seaway

2009 ◽  
Author(s):  
Elin Marita Hermundstad ◽  
Jan R. Hoff
Keyword(s):  
Time Domain ◽  
Transfer Functions ◽  
Experimental Results ◽  
Numerical Code ◽  
Ship Motions ◽  
Time Domain Simulation ◽  
Regular Waves ◽  
Simulation Code ◽  
Wigley Hull ◽  
Wave Induced

This paper presents a new unified seakeeping-maneuvering simulation model valid for surface ships and underwater vessels. If the total ship motions are derived from the traditional formulations for the hydrodynamic and maneuvering models, considering them as two separate problems, the results will be inconsistent. It has therefore been necessary to develop a unified formulation which calculates the total ship motions including both the maneuvering aspects and the wave induced motions. Focus in this study has been on submarines. Examples of application of the developed time domain simulation code are given. These are simulations of the response and corresponding control plane forces of a submarine in straight line motions in regular waves at given headings. The developed code can also be used to e.g. simulate turning circles. This has been conducted for the same submarine, and the results are compared to experimental results. Additionally, simulations of the response of a surface vessel (Wigley hull) with forward speed in regular waves at given headings are presented. In this case only the potential forces are considered. The results from the simulations are used to establish motion transfer functions, which are compared to other numerical and experimental results. There are some limitations in the developed method which affects the application area of the numerical code. This refers particularly to underwater vessels. This will be addressed, and further possible development of the method will be discussed.

Hydrodynamic Coefficients of a Mooring Tower

1984 ◽  
Vol 106 (2) ◽  
pp. 183-190 ◽  
Author(s):  
S. Chakrabarti ◽  
D. Cotter
Keyword(s):  
Hydrodynamic Coefficients ◽  
Regular Waves ◽  
Morison Equation ◽  
Wave Tank ◽  
Rigid Cylinder ◽  
Load Sensing ◽  
Small Load ◽  
Uniform Diameter

Wave tank tests have been performed on an articulated tower in order to determine the hydrodynamic coefficients associated with the tower. The tower was a uniform diameter rigid cylinder and incorporated a localized load sensing device. It was tested in three different phases: 1) fixed in regular waves, 2) mechanically oscillated in still water, and 3) free to move in the direction of regular waves. Thus, different forms of the Morison equation could be compared. The forces on the small load sensing segment were measured and the coefficients were correlated with local values of KC and Re. It is found that the data for the hydrodynamic coefficients for fixed cylinders in waves and mechanically oscillated cylinders in still water are reasonably applicable to articulated cylinders in waves.

scholarly journals Hydrodynamic and Dynamic Analysis to Determine the Longitudinal Hydrodynamic Coefficients of an Autonomous Underwater Vehicle

2020 ◽  
Vol 30 (7) ◽  
pp. 43-48
Author(s):  
Quang Le ◽  
Anh Tuan Phan ◽  
Thi Thanh Huong Pham
Keyword(s):  
Dynamic Analysis ◽  
Dynamic Stability ◽  
Dynamic Simulation ◽  
Autonomous Underwater Vehicle ◽  
Underwater Vehicle ◽  
Hydrodynamic Forces ◽  
Experimental Results ◽  
Hydrodynamic Coefficients ◽  
Underwater Environment

A useful tool for understanding the performance of an Autonomous Underwater Vehicle (AUV) is a dynamic simulation of the motions of the vehicle. To perform the simulation, the hydrodynamic coefficients of the vehicle must be first provided. These coefficients are specific to the vehicle and provide the description of hydrodynamic forces and moments acting on the vehicle in an underwater environment. This paper provides a method for the calculation and evaluation of the hydrodynamic coefficients of an AUV. The presence methodology is therefore one useful tool for determining an underwater vehicle’s dynamic stability. The calculated values have been compared with experimental results of a torpedo shape. It was concluded that the methods could calculate accurate values of the hydrodynamic coefficients for a specific AUV shape with its elliptical nose

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