Prediction of Added Resistance in Irregular Waves by Using a Time-Domain Approach

2010 ◽  
Author(s):  
K H Kim ◽  
◽  
Y Kim ◽  
Keyword(s):  
Time Domain ◽  
Irregular Waves ◽  
Added Resistance

Time-Domain Hydroelasticity Theory of Ships Responding to Waves

1997 ◽  
Vol 41 (04) ◽  
pp. 286-300
Author(s):  
Jinzhu Xia ◽  
Zhaohui Wang
Keyword(s):  
Time Domain ◽  
Separation Of Variables ◽  
Mathematical Formulation ◽  
Rigid Motion ◽  
Surface Flow ◽  
Slender Body ◽  
Irregular Waves ◽  
Restoring Force ◽  
Slender Body Theory ◽  
Body Theory

A time-domain linear theory of fluid-structure interaction between floating structures and the incident waves is presented. The structure is assumed to be elastic and represented by general separation of variables, whereas the fluid is described as an initial boundary value problem of potential free surface flow. The general interface boundary condition is used in the mathematical formulation of the fluid motion around the flexible structure. The general time-domain theory is simplified to a slender-body theory for the analysis of wave-induced global responses of monohull ships. The structure is represented by a nonuniform beam, while the generalized hydrodynamic coefficients can be obtained from two-dimensional potential flow theory. The linear slender body theory is generalized to treat the nonlinear loading effects of rigid motion and structural response of ships traveling in rough seas. The nonlinear hydrostatic restoring force and hydrodynamic momentum action are considered. A numerical solution is presented for the slender body theory. Numerical examples are given for two ship cases with different geometry features, a warship hull and the S175 containership with two different bow flare forms. The predicted results include linear and nonlinear rigid motions and structural responses of ships advancing in regular and irregular waves. The results clearly demonstrate the importance and the magnitude of nonlinear effects in ship motions and internal forces. Numerical calculations are compared with experimental results of rigid and elastic material ship model tests. Good agreement is obtained.

scholarly journals A time-domain method for separating incident and reflected irregular waves

1995 ◽  
Vol 24 (3-4) ◽  
pp. 205-215 ◽  
Author(s):  
Peter Frigaard ◽  
Michael Brorsen
Keyword(s):  
Time Domain ◽  
Time Domain Method ◽  
Irregular Waves ◽  
Domain Method

Numerical Analysis of a Surface Ship in Waves

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Shawn Aram
Keyword(s):  
Stokes Equations ◽  
Body Motion ◽  
Irregular Waves ◽  
Design Stage ◽  
Fluid Viscosity ◽  
Sea Waves ◽  
Added Resistance ◽  
Physical Mechanisms ◽  
Strip Theory ◽  
Seakeeping Analysis

Abstract Ship's resistance and engine power to sustain ship's speed in seaways are augmented due to complex non-linear interactions between the ship and the ambient sea (waves). Ship designers, in early design stage, use an ad hoc "sea margin" to account for the effects of seaways in selecting propeller and engine. A numerical tool capable of accurately predicting added resistance and power of a ship cruising in waves would greatly help select its powering (margin) requirement and determine the optimal operating point that can maximize the energy efficiency. For seakeeping analysis, strip theory-based methods have long been used. More recently, nonlinear time-domain three-dimensional (3D) panel methods have started being used widely. A more physics-based avenue to seakeeping analysis is offered by coupled solutions of two-phase unsteady Reynolds-Averaged Navier-Stokes equations and six degrees-of-freedom rigid-body motion (RBM) equations. The URANS approach also avails itself of including the effects of propulsors, either explicitly or approximately. By accounting for all the nonlinear effects in hydrodynamic forces and moments and the resulting ship motions, and the effects of fluid viscosity and turbulence, the coupled URANS-RBM method is believed not only able to predict added resistance and speed loss more accurately, but also to provide valuable insights into the physical mechanisms underlying added resistance and power. The objectives of this study are: (1) to validate a coupled URANS-RBM solver developed for high-fidelity prediction of added resistance, speed loss and added power on ships cruising in regular head sea and irregular waves, and (2) to conduct a detailed analysis of the interactions among ship hull, propeller and waves for a 1/49 scaled model of the ONR Tumblehome (ONRT) (Model 5613) in order to shed light on the physical mechanisms leading to added resistance, speed loss and added power. Figure 1 depicts the ONRT self-propellers with two 4-bladed propellers in regular waves. The main flow features such as the free surface, the hub vortices and blade-tip vortices from the propeller, as well as vortices generated by the sonar dome, shafts, shaft brackets and bilge keels are captured.

Near-Optimal Time-Domain Control of Small Buoys in Irregular Waves

2014 ◽  
Author(s):  
Umesh A. Korde ◽  
R. Cengiz Ertekin
Keyword(s):  
Optimal Control ◽  
Impulse Response ◽  
Time Domain ◽  
The Body ◽  
Irregular Waves ◽  
Single Frequency ◽  
Impulse Response Functions ◽  
Control Force ◽  
Response Functions ◽  
Absorbed Power

Within the linear theory framework, smooth optimal control for maximum energy conversion in irregular waves requires independent synthesis of two non-causal impulse response functions operating on the body oscillations near the free surface, and one non-causal impulse response function relating the exciting force to the incident wave profile at the body. Full cancellation of reactive forces and matching of radiation damping thus requires knowledge or estimation of device velocity into the future. As suggested in the literature, the control force can be synthesized in long-crested waves by suitably combining the ‘full’ impulse response functions with wave surface elevation information at an appropriately determined distance up-wave of the device. This paper applies the near-optimal control approach investigated earlier by one of the authors (Korde, UA, Applied Ocean Research, to appear) to small floating cylindrical buoys. Absorbed power performance is compared with two other cases, (i) when single-frequency tuning is used based on non-real time adjustment of the reactive and resistive loads to maximize conversion at the spectral peak frequency, and (ii) when no control is applied with damping set to a constant value. Time domain absorbed power results are discussed.

Multi-floater-mooring coupled time-domain hydro-elastic analysis in regular and irregular waves

2020 ◽  
Vol 101 ◽  
pp. 102276 ◽  
Author(s):  
Chungkuk Jin ◽  
Farid P Bakti ◽  
MooHyun Kim
Keyword(s):  
Time Domain ◽  
Irregular Waves ◽  
Elastic Analysis

scholarly journals Predictions of Ship Extreme Hydroelastic Load Responses in Harsh Irregular Waves and Hull Girder Ultimate Strength Assessment

2019 ◽  
Vol 9 (2) ◽  
pp. 240 ◽  
Author(s):  
Jialong Jiao ◽  
Yong Jiang ◽  
Hao Zhang ◽  
Chengjun Li ◽  
Chaohe Chen
Keyword(s):  
Ultimate Strength ◽  
Time Domain ◽  
Three Dimensional ◽  
Direct Calculation ◽  
Wave Force ◽  
Irregular Waves ◽  
Restoring Force ◽  
Strength Assessment ◽  
Hull Girder ◽  
Rule Approach

In this paper, the hydroelastic motion and load responses of a large flexible ship sailing in irregular seaways are predicted and the hull girder ultimate strength is subsequently evaluated. A three-dimensional time-domain nonlinear hydroelasticity theory is developed where the included nonlinearities are those arising from incident wave force, hydrostatic restoring force and slamming loads. The hull girder structure is simplified as a slender Timoshenko beam and fully coupled with the hydrodynamic model in a time domain. Segmented model towing-tank tests are then conducted to validate the proposed hydroelasticity theory. In addition, short-term and long-term predictions of ship responses in irregular seaways are conducted with the help of the developed hydroelastic code in order to determine the extreme design loads. Finally, a simplified strength-check equation is proposed, which will provide significant reference and convenience for ship design and evaluation. The hull girder ultimate strength is assessed by both the improved Rule approach and direct calculation.

scholarly journals TIME DOMAIN COMPARISONS OF MEASURED AND SPECTRALLY SIMULATED BREAKING WAVES

2017 ◽  
pp. 12
Author(s):  
Mustafa Kemal Ozalp ◽  
Serdar Beji
Keyword(s):  
Time Domain ◽  
Surf Zone ◽  
Field Measurements ◽  
Wave Model ◽  
Breaking Waves ◽  
Irregular Waves ◽  
Dissipative Effects ◽  
Spectral Components ◽  
Breaking Mechanism ◽  
Acceptable Agreement

For realistic wave simulations in the nearshore zone besides nonlinear interactions, the dissipative effects of wave breaking must also be taken into account. This paper presents the applications of a spectral nonlinear wave model with a dissipative breaking mechanism introduced by Beji and Nadaoka (1997). Results obtained for spectral components are converted to the time series and compared with Beji and Battjes' (1993) laboratory measurements and the field measurements of Nakamura and Katoh (1992) in the surf zone. While the model predicts the spilling-type breaking of irregular waves in acceptable agreement with the measurements in time domain, the agreement is unsatisfactory for plunging-type breakers.

scholarly journals Time domain simulation of riser VIV in current and irregular waves

2018 ◽  
Vol 60 ◽  
pp. 241-260 ◽  
Author(s):  
J.V. Ulveseter ◽  
M.J. Thorsen ◽  
S. Sævik ◽  
C.M. Larsen
Keyword(s):  
Time Domain ◽  
Irregular Waves ◽  
Time Domain Simulation
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