Homogeneous near-perfect invisible ground and free space cloak

2017 ◽  
Vol 31 (09) ◽  
pp. 1750059 ◽  
Author(s):  
Mohamad Fazeli ◽  
Seyyed Hassan Sedighy ◽  
Hamid Reza Hassani
Keyword(s):  
Incident Wave ◽  
Free Space ◽  
Single Step ◽  
Wave Direction ◽  
Transformation Theory ◽  
Design Flexibility ◽  
Mapping Process ◽  
Optical Transformation ◽  
Constitutive Parameters ◽  
Incident Wave Direction

A general approach to design near perfect invisible ground and free space cloaks is introduced in this paper. The proposed method which is based on the optical transformation theory, leads to homogeneous constitutive parameters for the cloaks without any singularities. Moreover, the single-step mapping process with linear relations achieves an uncomplicated designing process. Invisibility performance obtained by using this approach does not depend on the incident wave direction, also. The simplicity and design flexibility of the introduced approach with the homogeneity of extracted parameters greatly facilitate the design and fabrication processes of the both proposed ground and free space invisible cloaks. The numerical simulations prove the capability and universality of the proposed design approach.

Design of a Wave Shifter with the Exit Direction Controllable Based on Coordinate Transformation Theory

2013 ◽  
Vol 798-799 ◽  
pp. 590-593
Author(s):  
Wen Yan Yan ◽  
You Gang Ke
Keyword(s):  
Numerical Simulations ◽  
Coordinate Transformation ◽  
Longitudinal Axis ◽  
The Other ◽  
Wave Direction ◽  
Transformation Theory ◽  
Transformation Medium ◽  
Theoretical Design ◽  
Constitutive Parameters

We propose a wave shifter with the exit wave direction controllable by using a transformation-medium slab. The coordinate transformation takes two steps. One is along the longitudinal axis to realize shift and the other is on the transversal axis to adjust the exit directon. By using coordinate transformation theory, the constitutive parameters of the slab are obtained. Numerical simulations are further given to validate the performance of the theoretical design.

Hydrodynamic Analysis of Oil Storage Vessels for National Strategic Petroleum Reserve

2011 ◽  
Vol 291-294 ◽  
pp. 2541-2551
Author(s):  
Gang Jun Zhai ◽  
Yong Cheng ◽  
Wen Hua Wang ◽  
Yi Huang
Keyword(s):  
Incident Wave ◽  
Vertical Direction ◽  
Time History ◽  
Wave Force ◽  
Mooring System ◽  
Wave Direction ◽  
Storage Vessel ◽  
Oil Storage ◽  
Motion Responses ◽  
Incident Wave Direction

This paper expatiates hydrodynamic time-domain analysis on strategic oil storage vessels in free floating condition or with dolphin-fender mooring system by means of AQWA numerical software. The results indicate that motion responses of the oil storage vessel with dolphin-fender mooring have improved significantly. The time-history of wave diffraction forces in incident wave direction are basically consistent between the free floating and moored condition. However, in vertical direction of incident wave, the diffraction wave force of the oil storage vessel in free floating condition is obviously different from that with mooring system, which is the result of the coupling interaction between dolphin and vessels. Mooring forces include fender reaction and cable tension, as for which dominate, it depend on evocable motion responses about incident wave direction.

Numerical Study of Wave Diffraction with Four Cylinders

2014 ◽  
Vol 638-640 ◽  
pp. 1758-1762
Author(s):  
Bao Lei Geng ◽  
Ci Heng Zhang
Keyword(s):  
Mathematical Model ◽  
Incident Wave ◽  
Numerical Study ◽  
Wave Force ◽  
Wave Direction ◽  
Linear Waves ◽  
The Given ◽  
Four Cylinders ◽  
Incident Wave Direction ◽  
Origin Point

By taking the 3D Laplace equation as the basic governing equation, a mathematical model with respect to the interaction between linear waves and arbitrary 3D structures was founded. With an example of wave action with four cylinders, numerical results show that when incident wave direction is 22.5°, wave force Fx on 1# cylinder and 2# cylinder is the biggest and when incident wave direction is 0°, wave force Fx on 3# cylinder and 4# cylinder is the biggest; wave force Fy and the wave height on origin point increases with incident wave direction increasing for the given layout and incident wave conditions.

scholarly journals Near Trapping Effect on Wave-Power Extraction by Linear Periodic Arrays

2019 ◽  
Vol 12 (1) ◽  
pp. 29
Author(s):  
Dezhi Ning ◽  
Zechen He ◽  
Ying Gou ◽  
Malin Göteman
Keyword(s):  
Incident Wave ◽  
Wave Energy ◽  
Hydrodynamic Interaction ◽  
Wave Power ◽  
Wave Direction ◽  
Power Extraction ◽  
Periodic Arrays ◽  
Wave Energy Converters ◽  
Incident Wave Direction ◽  
Energy Converters

Near trapping is a kind of strong hydrodynamic interaction phenomenon in a regular array under specific incident wave conditions, which causes the excitation force on the structures in the array to change suddenly. In this paper, based on linear potential flow theory, the effects of near trapping on the hydrodynamic interaction and wave-power extraction characteristics of linear periodic arrays composed of the oscillating float type wave energy converters are studied by using the higher-order boundary element method in a frequency domain. The parameters considered include the separation spacing, number of devices, and incident wave direction. It is found that the near trapping significantly reduces the overall wave-power extraction, especially for the cases with a large number of devices, and changes the trend of the power distribution. The occurrence of the near trapping phenomenon depends on the ratio of the separation spacing to the wavelength and the incident wave direction. The results highlight the effective layout of linear arrays under the influence of near trapping, which not only ensures the total production power, but also reduces the power difference among wave energy converters.

scholarly journals PREDICTION OF DEVELOPMENT OF SAND SPITS AND CUSPATE FORELANDS WITH RHYTHMIC SHAPES CAUSED BY SHORELINE INSTABILITY USING BG MODEL

2012 ◽  
Vol 1 (33) ◽  
pp. 35 ◽  
Author(s):  
Masumi Serizawa ◽  
Takaaki Uda ◽  
Shiho Miyahara
Keyword(s):  
Probability Distribution ◽  
Incident Wave ◽  
Three Dimensional ◽  
High Angle ◽  
Dimensional Model ◽  
Wave Direction ◽  
Three Dimensional Model ◽  
Wave Instability ◽  
Shoreline Evolution ◽  
Incident Wave Direction

The BG model (a three-dimensional model for predicting beach changes based on Bagnold’s concept) was used to simulate the shoreline evolution caused by the high-angle wave instability discussed by Ashton et al. Three calculations were carried out: the wave direction was assumed to be obliquely incident from 60˚ counterclockwise (Case 1) or from the directions of ±60˚ with probabilities of 0.5:0.5 (Case 2) and 0.65:0.35 (Case 3), while determining the incident wave direction from the probability distribution at each step. The three-dimensional development of multiple sand spits and cuspate forelands with rhythmic shapes was successfully explained using the BG model. The results of the previous study conducted by Ashton et al. were reconfirmed and reinforced.

scholarly journals Simulation and analysis on low-frequency scattering characteristics of the finite cylindrical shell in shallow water

2019 ◽  
Vol 283 ◽  
pp. 03007
Author(s):  
Jinyu Li ◽  
Dejiang Shang ◽  
Yan Xiao
Keyword(s):  
Cylindrical Shell ◽  
Free Space ◽  
Acoustic Scattering ◽  
Low Frequency ◽  
Target Strength ◽  
Wave Direction ◽  
Scattering Field ◽  
Simulation Results ◽  
Finite Cylindrical Shell ◽  
Target Locations

Low-frequency acoustic scatterings from a finite cylindrical shell are numerically analyzed by FEM. The simulation results show that the acoustic-scattering field in waveguide has lots of frequency-related sidelobes, while no sidelobes exist in free space at low frequencies. The simulation also indicates that the module value in waveguide can be almost 20 dB larger than that in free space at low frequency, which is caused by the ocean boundaries. We also demonstrate that when the incident wave direction is normal to the target at low frequency, the target strength will be maximum and the distribution of the acoustic-scattering field is axisymmetric about the incident waving direction. Meanwhile, the acoustic-scattering field is also related to the impedance of the seabed, and the change of the impedance makes just a little contribution to the scattering field. Finally, the influence of different target locations is analyzed, including the targets near the sea surface, seabed and the middle region of the ocean waveguide, respectively. From simulation results, it is evident that the distribution of the acoustic-scattering field at low frequency has a little difference, which is smaller than 0.5 dB with various target locations, and the change is frequency and boundary-related.

RESEARCH ON THE WAVE-INDUCED SHIP MOTIONS IN FRONT OF DIFFERENT TYPES OF WHARF

2005 ◽  
Vol 19 (28n29) ◽  
pp. 1731-1734
Author(s):  
YAN BAO LI ◽  
XUE LIAN JIANG
Keyword(s):  
Wave Height ◽  
Incident Wave ◽  
Ship Motions ◽  
Design Codes ◽  
Wave Direction ◽  
Green Function Method ◽  
Frequency Wave ◽  
Different Types ◽  
Current Design ◽  
Wave Induced

One important function of the port is to protect ship or some other facilities from wave attack so as to stably handle cargoes. In current design codes, there are mainly two expressions of the tranquility standard of harbor basin: one is the acceptable wave height in front of wharf; the other is the tolerable amplitude of ship motion. However, ship motions are affected by some more factors simultaneously, such as wave frequency, wave height, incident wave direction, ship properties and wharf type. This paper presents some computed results of the wave-induced ship motions on the basis of a port case in China. First, the Simple Green Function method is employed to solve and compare the 2-dimension hydrodynamic coefficients in front of open or bulkhead wharf. The results show a great difference between them. Then, this paper computes and discusses the ship motions in front of open wharf at different wave frequencies and incident wave directions.

scholarly journals The CFS-PML for 2D Auxiliary Differential Equation FDTD Method Using Associated Hermite Orthogonal Functions

2017 ◽  
Vol 2017 ◽  
pp. 1-6 ◽  
Author(s):  
Feng Jiang ◽  
Xiao-Ping Miao ◽  
Feng Lu ◽  
Li-Yuan Su ◽  
Yao Ma
Keyword(s):  
Differential Equation ◽  
Free Space ◽  
Fdtd Method ◽  
Absorbing Boundary Conditions ◽  
Complex Frequency ◽  
Two Dimensional ◽  
Orthogonal Functions ◽  
Absorbing Boundary ◽  
The Matrix ◽  
Constitutive Parameters

The complex frequency shifted (CFS) perfectly matched layer (PML) is proposed for the two-dimensional auxiliary differential equation (ADE) finite-difference time-domain (FDTD) method combined with Associated Hermite (AH) orthogonal functions. According to the property of constitutive parameters of CFS-PML (CPML) absorbing boundary conditions (ABCs), the auxiliary differential variables are introduced. And one relationship between field components and auxiliary differential variables is derived. Substituting auxiliary differential variables into CPML ABCs, the other relationship between field components and auxiliary differential variables is derived. Then the matrix equations are obtained, which can be unified with Berenger’s PML (BPML) and free space. The electric field expansion coefficients can thus be obtained, respectively. In order to validate the efficiency of the proposed method, one example of wave propagation in two-dimensional free space is calculated using BPML, UPML, and CPML. Moreover, the absorbing effectiveness of the BPML, UPML, and CPML is discussed in a two-dimensional (2D) case, and the numerical simulations verify the accuracy and efficiency of the proposed method.

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