Waves in different sea conditions are simulated by the Bretscheider double parameters spectrum using randomly chosen discrete frequencies as its parameters. Ship motion model of six degrees of freedom is established under the Ship coordinates system. As the ship system is linear, the ship motion under irregular waves can be calculated through the amplitude-frequency response function obtained by solving the model when the input is the superposition of regular waves. Finally according to the coordinate transformation between the ship coordinates system and the missile coordinates system, the motion of the shipboard missiles under excitation of sea waves can be analyzed to support the environmental analysis of its combat duty process.
In the aid of sinc sum function and matrix equation a new 2D window function is obtained. It is as simple as a 2D cosine window function. Comparison shows that the new 2D window function can provide much better 2D FIR filters than 2D Hamming window function. Maximum passband ripples are about 2.5-3.5 times smaller and maximum stopband ripples are about 1.5 times smaller with equal or very small different passband and stopband edge frequencies.
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