M. Hasanat Zaman

Spurious Waves During Generation of Multi-Chromatic Waves in the Wave Tank in Shallow Water

Accurate generation of the primary waves and the reproduction of the group-induced second-order low and high frequency waves have been considered essential for physical i.e. model test in the laboratory. In the laboratory when multi-chromatic primary waves are generated the required bounded waves will be generated naturally at the difference frequencies. In addition to that several unwanted free waves are also generated. The free waves, having the same frequencies of the bounded waves are reproduced due to mismatch of the boundary conditions at the wave paddle. The other two types of free waves are due to the wave paddle displacement and the local disturbances. We carried out physical experiments to identify the second order spurious waves in shallow water in the Offshore Engineering Basin (OEB) at the Institute for Ocean Technology (IOT) of National Research Council (NRC) Canada. In the basin water depths in the range of 0.4m to 0.6m are used for the experiments. The peak wave periods also have varied from 1.133s to 2.145s. In the experiments multi-chromatic waves are used. The drive signals of the wave-makers are generated using first-order and second-order wave generation techniques. Total 14 wave probes are used to capture the data in the wave tank. A NRC-IOT code is used to isolate the primary waves, the bounded waves and the unwanted free waves from the measured data at each wave probe. The measured data are analyzed in this paper to illustrate the differences in the waves generated by two different generation techniques.Copyright

Behavior of the Residual Wave Components in a 3D Wave Basin After the Termination of the Wave Maker

After the termination of the wave making, the characteristics of the existing wave components in a 3D large scale Offshore Engineering wave Basin (OEB) at the National Research Council of Canada have been investigated experimentally. In the generation of any wave in the tank we get the relevant primary wave components along with bounded wave components if the incident primary wave has more than one frequency. Inevitably we also get interacted wave components, natural frequency components of the tank and other free waves. In this paper the tank’s natural frequency components, bounded wave components and other free waves after the termination of wave making were investigated using several cases of mono- and bi-chromatic waves. These component energies were then compared with the total energy of the measured primary waves. The magnitudes of the residual undulations are also investigated for mono-, bi- and multi-chromatic waves over different time segments. Several sets of wave data are analysed to perceive the energy due to natural frequency of the basin, energy transferred to the side bands and the damping rate of the residual waves in the tank with respect to the chosen incident wave conditions. In the analysis it is observed that the energy damping rate varies with the incident wave condition but seems much faster than that of 20 minutes traditional waiting time in between two runs in the OEB. The energies for tank’s natural frequency components and other free waves were found to be very small compare to the incident primary wave energies.Copyright

A 3D wave model to simulate the interaction of wave field in the presence of multi-structures

A 3D dispersive numerical model has been developed and utilized to study the interacted wave field in the Offshore Engineering Basin (OEB) of National Research Council Canada in the presence of array of structures. The basic physics of the numerical model follows the concept of the depth averaged velocity distribution along with an enhanced dispersion relation. The Alternating Direction Implicit (ADI) algorithm has been employed for the solution of the governing equations. As an application, the model has been used to study the wave propagation in the presence of different combinations of structures where the effects due to the reflection and diffraction are also incorporated. Relevant experiments are carried out in the OEB. Total 10 wave probes are deployed to measure the data at different locations in the Basin. Later the numerical results are compared with the experimental results in the OEB at different probe locations for different wave and structure conditions. The comparisons of the numerical results show great agreement with the experimental results. In this paper the results for regular waves will only be presented and discussed.

Identifications of Spurious Waves in the Wave Tank With Shallow Water

Accurate generation of the primary waves and the reproduction of the group-induced second-order low and high frequency waves have been considered essential for physical model test in the laboratory. In the laboratory when bi-chromatic primary waves are generated the required bounded waves will be generated naturally at the difference frequency. In addition to that several unwanted free waves are also generated. The free waves, having the same frequency of the bounded wave are reproduced due to mismatch of the boundary conditions at the wave paddle. The other two types of free waves are due to the wave paddle displacement and the local disturbances. We carried out an extensive experimental program to identify the second order spurious waves in shallow water in the Offshore Engineering Basin (OEB) at the Institute for Ocean Technology (IOT) of National Research Council (NRC) Canada. In the experiments water depths are used in the range of 0.3m to 0.8m. The wave periods also have varied from 0.9s to 2.22s. In the experiments mono- and bi-chromatic waves are used. The drive signals of the wave-maker are generated using first-order and second-order wave generation techniques. Total 14 wave probes are used to capture the data in the wave tank. A NRC-IOT code is used to isolate the primary waves, the bounded waves and the unwanted free waves from the measured data at each wave probe. The measured data are analyzed in this paper to illustrate the differences in the waves generated by two different generation techniques.Copyright

Transformation of Mono- and Multi-Chromatic Water Waves Propagating From a Quasi-Deepwater to a Shallow Water Region

A vertically integrated 3D numerical model that uses the concept of depth average velocity distribution with enhanced dispersion characteristics investigates the propagation and transformation of mono- and multi-chromatic waves from a quasi-deep region to shallow water region. A finite difference method has been employed for the numerical computation that follows ADI (Alternating Direction Implicit) algorithm. The local sea bottom is uneven and turns into a moderately shallow water due to presence of a ridge-like bottom near the coast. The bottom configuration is from a location off Nova Scotia coast in Canada. Detail results and discussions are presented.Copyright

Generation and Propagation of Long-Crested Finite-Depth Surface Waves: Comparison Between the Corresponding Results From Numerical Models and a Wave Tank

The evolution of long-crested surface waves subject to side-band perturbations is investigated with two different numerical models: a direct solver for the Euler equations using a non-orthogonal boundary-fitted curvilinear coordinate system and an FFT-accelerated boundary integral method. The numerical solutions are then validated with laboratory experiments performed in the NRC-IOT Ocean Engineering Basin with a segmented wave-maker operating in piston mode. The numerical models are forced by a point measurement of the free surface elevation at a wave probe close to the wave-maker and the numerical solutions are compared with the measured time-series of the surface elevation at a few wave probe locations downstream.Copyright

Suppression of Ocean Waves by Uniform Forced Currents

Ocean current might be a useful tool to suppress ocean waves that approach a particular region of interest. A reliable short term sheltering approach might be enough in some areas where a heavy and/or permanent protection system is impractical, considering its usage, duration of deployment and money involved. This study is carried out using a 3D finite difference numerical model. The model is presently developed for long crested waves and uniform current by the vertical integration of the continuity equation and the equations of motion. A semi-implicit finite difference technique is employed for the discretization of the governing equations in time and space. Results are shown in terms of wave height distributions, reflection and transmission coefficients for varying currents, incident wave and current angles.Copyright