Long-term energy supplies hinder the application of the low-power unmanned ocean devices to the deep sea. Ocean wave energy is a renewable resource with amount stores of enormous and high density. The wave energy converter (WEC) could be miniaturized so that it can be integrated into the devices to make up the power module. In this paper, a small novel heaving point absorber of energy supply for low-power unmanned ocean devices is developed based on the counter-rotating self-adaptive mechanism. The floating body as an important part of the heaving point absorber, the geometric parameters is optimized to increase the efficiency of power production. Through constructing the constitutive relation between the geometric parameters, the wave force, the motion displacement, the motion velocity, and the capture width ratio of the floating body, the energy efficiency characteristics of the multi-type floating bodies are calculated, and the optimal shape is selected. On the other hand, in the calculation process of the wave force, the Froude-Krylov method is an effective method to accurately calculate the wave excitation force. Meanwhile, nonlinear static and dynamic Froude-Krylov force effectively overcomes the inaccuracy of the linear models and reduces the time consumed to simulate. Finally, the wave force, heaving velocity, heaving displacement, and capture width ratio of the three floating bodies are compared and analyzed, and the results show that the cylindrical floater that is vertically placed on the wave surface is more suitable for the novel heaving wave energy point absorber.
Digital watermarking has been widely used in copyright protection for digital images, but most of the watermarking algorithm can't resist print-and-scan process. Print-and-scan attack is a challenging problem for most of digital watermarks. A watermarking algorithm against print-and-scan attack based on PSO (Particle Swarm Optimization) is proposed in this paper. The watermark information is embedded in a halftone process for image screening with phase modulation method. The watermark is extracted by a template, which is optimized using the PSO algorithm. Both mean filtering and median filtering are used to remove noise from the recovered watermark image. The experimental results show the halftone watermarking algorithm optimized using PSO has better performance, it is robust under smearing attack and cropping attack, and has good resistance to print-and-scan process. It can be applied in the field of anti-counterfeit printing
Visual cryptography is a cryptographic technique which allows visual information to be encrypted in such a way that the decryption can be performed by the human visual system, without the aid of computers. This paper proposes a schema of information hiding within the method of visual cryptography. The gray image is changed into two halftone images via the different dither matrixes respectively, and the secret binary pixels are encoded into shares. The secret information can be restored by stacking the different shared halftone images together. Simulation results show that the secret binary image can be decoded efficiently.
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