Stereo Measurement Of 3d Wave Surface Of Wave Diffraction Around Circular Cylinder

Wave surface measurement is one of the fundamental task in the experimental fluid mechanics.Comparing with traditional intrusive wave gauges,stereo vision measurement has many advantages,such as no disturbance to wave field,large area of measurement field and low cost,which has been a promising experimental technique in different circumstances.Due to the refraction and inflection of light across the air-water interface,the stereo vision measurement has not been widely applied in the field of experimental fluid mechanics.A mid-scale 3D free surface measurement system(3DFSM)has been proposed in the present thesis.Based on ideal camera model and multiple view geometry,a numerical algorithm for the proposed 3DFSM has been developed.Based on the projection of a laser-beam matrix onto air-water interface,the free surface can be captured by the stereo vision algorithm.In order to verify the robustness and accuracy of the algorithm,the proposed method has been applied to reconstruct the free surface elevation for a 3D printed model designed from wave diffraction around cylinder.Comparisons between the reconstructed surface profile and the 3D printed model indicate that the algorithm performs accurately and stably,with absolute error below 2mm,and relative error less than 1%For practical applications,the proposed 3DFSM has been applied to measure the free surface elevation for periodic wave diffraction around a surface piercing circular cylinder in wave flume.The measured wave period and height are in good agreement with the experimental data obtained by capacitance wave gauges,with a maximum relative error around 5%,which demonstrates that the proposed 3DFSM can be used to measure the complex three-dimensioned wave efficiently and precisely in laboratory.