A Piston-Type Active Absorbing Wavemaker System with Delay Compensation

Physical model tests with highly reflective structures often encounter a problem of multiple reflections between the structures and the wavemaker. This paper presents a piston-type active absorbing wavemaker system which can absorb most of the reflections. Based on the first-order wavemaker theory, a frequency domain absorption transfer function is modeled. Its time realization can be achieved by designing an IIR digital filter, which is used to control the absorbing wavemaker system. In a real system, time delays often exist in the wave making process. Thus a delay compensation term to the transfer function is proposed. Experimental results show that the system performs well for both regular and irregular waves with periods from 0.6 s to 2.0 s, and the absorption capability is larger than 96.5% at target wave fields.

Laboratory Research on Effective Test Area of Short-Crested Waves Generated by Two-Sided Segmented Wavemakers

The size and shape of the effective test area are crucial to consider when short-crested waves are created by segmented wavemakers. The range of the effective test area of short-crested waves simulated by two-sided segmented wavemakers is analyzed in this paper. The experimental investigation on the wave field distribution of short-crested waves generated by two-sided segmented wavemakers is conducted by using an array of wave gauges. Wave spectra and directional spreading function are analyzed and the results show that when the main direction is at a certain angle with the normal line of wave generators, the wave field of 3D short-crested waves generated by two-sided segmented wavemakers has good spatial uniformity within the model test area. The effective test area can provide good wave environments for seakeeping model tests of various ocean engineering structures in the deep ocean engineering basin.

Active Control of A Piston-Type Absorbing Wavemaker with Fully Reflective Structure

Multiple reflections of the waves between structure and wavemaker in hydraulic flumes could change the frequency content of the desired incident wave or result in resonance. A prominent approach to avoid multiple reflections is active control of the wavemaker. This paper proposes a simple and practical active control algorithm for piston-type wavemaker. The block diagram of the control system is presented in real time domain. It is shown that there is no need to use any transfer function or filter in the feedback and feed forward loops and the use of constant gains can yield acceptable results. In the operating frequency range(0.25-2 Hz), it is revealed that the proposed system is very effective at suppressing the excitation of resonant sloshing for regular wave. In the case of irregular waves, it is depicted that the experimental waves agree quite well with the desired wave elevation in frequency domain. In addition, comparison of the results obtained both with and without absorption discloses the good characteristics in time domain.

An iterative re-weighted least-squares algorithm for the design of active absorbing wavemaker controller

In physical model tests for highly reflective structures, one often encounters a problem of multiple reflections between the reflective structures and the wavemaker. Absorbing wavemakers can cancel the re-reflective waves by adjusting the paddle motion. In this paper, we propose a method to design the controller of the 2-D absorbing wavemaker system in the wave flume. Based on the first-order wavemaker theory, a frequency domain absorption transfer function is derived. Its time realization can be obtained by de- signing an infinite impulse response （IIR） digital filter, which is expected to approximate the absorption transfer function in the least- squares sense. A commonly used approach to determine the parameters of the IIR filter is applying the Taylor expansion to linearize the filter formulation and solving the linear least-squares problem. However, the result is not optimal because the linearization cha- nges the original objective function. To improve the approximation performance, we propose an iterative reweighted least-squares （IRLS） algorithm and demonstrate that with the filters designed by this algorithm, the approximation errors can be reduced. Physical experiments are carried out with the designed controller. The results show that the system performs well for both regular and irregu- lar waves.

FULLY NONLINEAR CALCULATION OF 2－D WATER WAVE GENERATED BY ROCKER FLAP WAVEMAKER

The BEM combined with the time-stepping scheme is employed in the fully nonlinear numerical calculation of 2-D free surface flow generated by large amplitude oscillation of rocker flap wavemaker. Special consideration is paid on the compatibility of free surface and body surface conditions at the intersection point. In the case study of weakly nonlinear regular wave, the comparison of elevations and hydrodynamic moments acting on the flap from the fully nonlinear calculation,second-order calculation in frequency domain and linear calculation in time domain is made, and the agreement indicates the feasibility of the numerical approach of the fully nonlinear calculation.

与时代共成长,与客户共成就——访Wavemaker中国首席执行官、亚太区总裁Gordon Domlija

2019年12月9日,集媒介传播、内容营销和科技革新于一身的全球新型代理公司Wavemaker,在两周年庆之际,正式宣布中文名称——"蔚迈"。蔚迈不仅是Wavemaker英文名称的近音词,这两个汉字本身也有着丰富的含义:蔚是茂盛、盛大的意思,迈包含跨步、豪迈的气势,这两个字的结合预示着这个年轻品牌的活力、朝气、勇往直前的勇气以及对美好的发展前景的预期。

超声导波检测系统在油田管道检测中的应用

超声导波检测技术以其检测距离长、可对被检管线实施100%的全面检测等区别于其它常规无损检测技术的显著优势,将为目前油田乃至全国大量存在安全隐患或出现事故可能导致严重后果的埋地占压、穿跨越管线的检测评价提供技术支持。利用中国石油化工股份有限公司胜利油田分公司某架空φ273 mm混输管线,对Wavemaker G3超声导波检测系统进行了试验应用。结果表明:管道局部腐蚀及壁厚减薄情况与检测结果完全吻合,在管线总体质量较差,对导波传播的影响较大的情况下,Wave Marker G3对被试验管线确保检出精度的单项检测距离达40m以上。

Nonlinear Capillary-Gravity Waves Produced by a Vertically Oscillating Plate

The nonlinear capillary-gravity wave produced by a vertically oscillating plate, in which the contact-angle model is considered, is studied by use of the Boundary Integral Equation Method (BIEM). The present numerical experiment shows that the code is robust and efficient for modeling the generation and propagation of capillary-gravity waves. It is found that the wave heights of stationary periodic nonlinear waves radiated away from the plate are dependent on the parameters involved in the contact-angle model. The effect of the contact-angle hysteresis and the nonlinearity of capillary-gravity waves on the wave profile is discussed in the paper.

The initialization of nonlinear water waves in a numerical wave flume

This study investigates the initialization of nonlinear free-surface simulations in a numerical wave flume. Due to the mismatch between the linear input wavemaker motion and the kinematics of fully nonlinear waves, direct numerical simulations of progressive waves, generated by a sinusoidally moving wavemaker, are prone to suffering from high-frequency wave instability unless the flow is given sufficient time to adjust. A time ramp is superimposed on the wavemaker motion at the start that allows nonlinear free-surface simulations to be initialized with linear input. The duration of the ramp is adjusted to test its efficiency for short waves and long waves. Numerical results show that the time ramp scheme is effective to stabilize the wave instability at the start of the simulation in a wave flume.

Multigrid ILU Panel Method for the Calculation of Wavemaking Resistance

Panel methods for the calculation of wavemaking resistance result in a linear equation system for the unknown singularities.The coefficient matrix is full but not well conditioned.In this paper an incomplete LU decomposition (ILU) method and a combined multigrid ILU method are used to solve the linear system.Systematic computations using the ILU method have shown that the CPU time can be reduced to 30% to 40% of that using an incomplete Gaussian elimination method. In the proposed multigrid ILU method an averaged restriction and a piecewise constant prolongation are used.The construction of the coefficient matrix at coarse levels is based on geometrical considerations.It turns out that the condition of the relative consistency is fulfilled.Comparison computations have shown that nearly the same results were obtained.However,due to additional CPU time needed for the execution of the matrix vector products in the restriction and the prolongation proceses of the multigrid method,a further reduction of the total CPU time could not be reailized.

Numerical Calculation Methods for Wavemaking Response Induced by Explosion in Harbour

Using the axial symmetry results of marker and cell (MAC) method as initial value in this paper, two numerical calculating methods are presented for the late wavemaking response induced by explosion in harbour. One of the methods is the superposition method of the vibration mode based on fluid slosh in container. Another one is the joining method of the MAC results with the shallow wave theory calculation in time domain. As a practical example, it is conducted to the numerical calculation about 1000 ton TNT equivalent explosion within touch of water surface. The results show that it can be rationally described with the methods to the wavemaking progress and character. The numerical results are identical with the observed scene on the spot experiment. The methods are simple and applicable in the engineering design.

DuaISPHysics：A numerical tool to simulate real breakwaters

The open-source code DualSPHysics is used in this work to compute the wave run-up in an existing dike in the Chinese coast using realistic dimensions, bathymetry and wave conditions. The GPU computing power of the DualSPHysics allows simulating real-engineering problems that involve complex geometries with a high resolution in a reasonable computational time. The code is first validated by comparing the numerical free-surface elevation, the wave orbital velocities and the time series of the run-up with physical data in a wave flume. Those experiments include a smooth dike and an armored dike with two layers of cubic blocks. After validation,the code is applied to a real case to obtain the wave run-up under different incident wave conditions. In order to simulate the real open sea, the spurious reflections from the wavemaker are removed by using an active wave absorption technique.

STUDY OF TRIMARAN WAVEMAKING RESISTANCE WITH NUMERICAL CALCULATION AND EXPERIMENTS

Based on the potential flow assumption, this paper outlines the formulation of the boundary-value problem governing the steady free surface flow around a trimaran advancing at a constant forward. A Rankine panel method was developed for the solution of the problem. The side-hulls were treated as lifting bodies and circulation was introduced into the flow field to implement the asymmetrical flow around each side hull. The linearized free surface condition was used. The appropriate treatment for transom-stern ship was also discussed. Additionally, a test was performed to quantify the resistance and especially the interference between the main and side hulls. The numerical results are in good argeement with experimental data.

A NEW TECHNIQUE IN SOLVING UNSTEADY AND STEADY WAVEMAKING PROBLEMS

Under the' assumption of linearization of the free-surface condition, making use of Green's function method and the convolution theorem, analytic solutions of perturbation velocity potentials which correspond to three dimensional unsteady thickness problem and lifting problem caused respectively by arbitrary motions of a body and a hydrofoil beneath the water surface can be achieved in the closed form, In general, the whole perturbation velocity potential consists of three terms, namely φ=φ1+φ2+φ3 , where φ1 denotes the induced velocity potential of the surface singularity distribution in an unbounded fluid, φ2 denotes its mirror image and φ3 denotes that of wave formation which includes the memory effect of the action of the singularity distribution. Utilizing the polynomial expansion of sin[(t-τ)] , the similarity between φ2 and φ3 is discovered and thus a simpler differential relation between them is obtained. Applying this relation, the amount of work in calculation of φ3 which is the most time-consuming one will be reduced significantly. It is favorable not only for dealing with unsteady wave- making problems but also for solving the steady ones in virtue of evading a major difficulty which has to be encountered during the evaluation of an improper inte- gral containing a singularity in the Green's function. The limitation of this new technique turns out to be its slower convergence as the Froude number is lower.