Ship Motions From Unsteady Maneuvering in Two-Dimensional Waves: Part I—Numerical Simulations

2011 ◽  
Author(s):  
Ray-Qing Lin ◽  
Joseph T. Klamo
Keyword(s):  
Solid Body ◽  
Degrees Of Freedom ◽  
Rapid Change ◽  
Ship Motions ◽  
Two Dimensional ◽  
Wave Interactions ◽  
Challenging Tasks ◽  
Experimental Laboratory ◽  
Nonlinear Ship Motion ◽  
Dimensional Wave

Numerically simulating the six-degrees-of-freedom response motions of a ship executing an unsteady maneuver in a two-dimensional wave environment is one of the most challenging tasks in seakeeping. Mathematical difficulties may occur for several reasons. For example, the rapid change in encounter frequencies may cause a numerical dynamics imbalance. Furthermore, in order to predict the ship’s track (ship heading) accurately, the rudder forces and two-dimensional drift forces must be predicted accurately; otherwise, erroneously predicted headings can ultimately lead to obtaining entirely different ship motions. To overcome these problems, we added a well-behaved, pre-conditional iterative method into the hybrid flow-based, fully-nonlinear ship motion model, DiSSEL (Digital, Self-consistent Ship Experimental Laboratory), in a two-dimensional wave environment. DiSSEL includes two components: a ship-wave interactions model (Lin et al., 2005[1], Lin and Kuang, 2006[2]), and a solid body motions interactions model (Lin and Kuang 2010[3]). The rudder and appendage forces (Lin et al, 2010[4]) are included in the solid body motions component. This refined model is able to overcome the mathematical dynamics imbalance when the encounter frequency rapidly changes as well as accurately calculate the forces on the hull and rudders. Finally the simulations of ship response motions at various relative headings and at various forward speeds in a two-dimensional seaway will be benchmarked against experimental model data for the test cases.

Ship Motions From Unsteady Maneuvering in Two-Dimensional Waves: Part II—Analysis of Data

2011 ◽  
Author(s):  
Joseph T. Klamo ◽  
Ray-Qing Lin
Keyword(s):  
Wave Field ◽  
Degrees Of Freedom ◽  
Nonlinear Effects ◽  
Ship Motions ◽  
Two Dimensional ◽  
Linear Superposition ◽  
One Dimensional ◽  
Model Response ◽  
Experimental Laboratory ◽  
Dimensional Wave

An experimental test has been conducted to measure the six degrees-of-freedom motions of a remote-controlled model attempting to hold heading while at forward speed in a two-dimensional wave field. During testing, the two underlying components of the wave field were always orthogonal to each other but various relative headings of the model to the dominant wave were explored. Of particular interest is understanding the nonlinear effects of the two distinct underlying wave encounter frequencies on the model response and the severity to which it causes the response in the two-dimensional wave field to differ from the linear summation of responses from equivalent one-dimensional waves. Since the experimental data contains the full wave-wave and wave-ship interactions of the two-dimensional wave field, we will use numerical results from the Digital, Self-consistent Ship Experimental Laboratory (DiSSEL) to generate the necessary one-dimensional wave results. This allows us to compare the predicted ship response motions from linear superposition of two one-dimensional wave field responses to the measured motions in a two-dimensional wave field for various relative wave heading combinations. It will be shown that for waves forward of beam, the predicted pitch results from superposition are fairly accurate while the roll prediction is not. However, for waves aft of beam, the motion predictions from linear superposition of pitch and roll are both poor. In such aft of beam cases, the disagreement can be quite large due to deviations in the ship heading caused by drift forces.

scholarly journals Thermos Array: Two-Dimensional Sparse Array with Reduced Mutual Coupling

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Lei Sun ◽  
Minglei Yang ◽  
Baixiao Chen
Keyword(s):  
Closed Form ◽  
Degrees Of Freedom ◽  
Mutual Coupling ◽  
Doa Estimation ◽  
Two Dimensional ◽  
Spatial Smoothing ◽  
Planar Arrays ◽  
Half Wavelength ◽  
Planar Array ◽  
Small Spacing

Sparse planar arrays, such as the billboard array, the open box array, and the two-dimensional nested array, have drawn lots of interest owing to their ability of two-dimensional angle estimation. Unfortunately, these arrays often suffer from mutual-coupling problems due to the large number of sensor pairs with small spacing d (usually equal to a half wavelength), which will degrade the performance of direction of arrival (DOA) estimation. Recently, the two-dimensional half-open box array and the hourglass array are proposed to reduce the mutual coupling. But both of them still have many sensor pairs with small spacing d, which implies that the reduction of mutual coupling is still limited. In this paper, we propose a new sparse planar array which has fewer number of sensor pairs with small spacing d. It is named as the thermos array because its shape seems like a thermos. Although the resulting difference coarray (DCA) of the thermos array is not hole-free, a large filled rectangular part in the DCA can be facilitated to perform spatial-smoothing-based DOA estimation. Moreover, it enjoys closed-form expressions for the sensor locations and the number of available degrees of freedom. Simulations show that the thermos array can achieve better DOA estimation performance than the hourglass array in the presence of mutual coupling, which indicates that our thermos array is more robust to the mutual-coupling array.

Diffraction of a pulse by a resistive half-plane. I. Normal incidence

1960 ◽  
Vol 255 (1283) ◽  
pp. 538-549 ◽  
Keyword(s):  
Time Dependence ◽  
Half Plane ◽  
Wave Diffraction ◽  
Diffraction Problem ◽  
Normal Incidence ◽  
Step Function ◽  
Two Dimensional ◽  
Dynamic Similarity ◽  
Function Time ◽  
Dimensional Wave

The two-dimensional wave diffraction problem, acoustic or electromagnetic, in which a pulse of step-function time dependence is diffracted by a resistive half-plane is solved by assuming dynamic similarity in the solution.

A Quasi-three-dimensional Finite-volume Shallow Water Model for Green Water on Deck

2013 ◽  
Vol 57 (03) ◽  
pp. 125-140
Author(s):  
Daniel A. Liut ◽  
Kenneth M. Weems ◽  
Tin-Guen Yen
Keyword(s):  
Shallow Water ◽  
Finite Volume ◽  
Time Domain ◽  
Degrees Of Freedom ◽  
Initial Conditions ◽  
Three Dimensional ◽  
Green Water ◽  
Water Model ◽  
Ship Motions ◽  
Shallow Water Model

A quasi-three-dimensional hydrodynamic model is presented to simulate shallow water phenomena. The method is based on a finite-volume approach designed to solve shallow water equations in the time domain. The nonlinearities of the governing equations are considered. The methodology can be used to compute green water effects on a variety of platforms with six-degrees-of-freedom motions. Different boundary and initial conditions can be applied for multiple types of moving platforms, like a ship's deck, tanks, etc. Comparisons with experimental data are discussed. The shallow water model has been integrated with the Large Amplitude Motions Program to compute the effects of green water flow over decks within a time-domain simulation of ship motions in waves. Results associated to this implementation are presented.

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