Identification Of The Propeller-Induced Fluctuating Pressure

Propeller-induced fluctuating pressure is the important case of the stern vibration which would interference the equipment onboard and lowdown the efficient of the crew. The method to identify the propeller-induced fluctuating pressure would be very important.The identification of propeller-induced fluctuating pressure belong to the second inverse problem of dynamics. This paper explore the fitting technique of distributed load by Chebyshev orthogonal polynomial form the aspect of finite element modeling technology and load identification method.In finite element modeling technology, first, according to the Timoshenko beam theory, two2-nodes beam elements are presented by used the trigonometric function and exponential function as assumed shear strains interpolating shape function. These element can avoid the shear locked phenomena. Numerical results demonstrate that the elements have good accuracy in a large range of span ratio. And their formulation is relatively simple and easy to use. Later, according to the concept of generalized conforming method, two rectangle membrane element with vertex rotations is presented. The contribution of the vertex rotations to the line displacement field is expressed as a high order formula. Numerical results demonstrate that this element, with relatively simple formulation, don’t need extra constraints to overcome the redundant zero energy mode. This new element is easy to apply in the real construction calculation.In load identification method, used the Chebyshev orthogonal polynomial to fitting the unknown distributed load. Transformed the calculation of the complex distributed load into the more easier calculation of the coefficients of orthogonal polynomial. Numerical results demonstrate that this method have high precision with the accurate displacement response. The discuss of the method’s calculation accuracy under the displacement response with certain proportion errors show that the even distribution measuring points and the less points with certain orders of orthogonal polynomial would let the calculation more accurate.