Research Of Wave Action On Large-scale Bridge Foundation Based On Potential Theory

Bottom-mounted cylindrical structures are frequently employed as the support component of the cross-strait bridge.The phenomenon of diffraction wave can be observed as wave acting on such structures.To ensure the safety of cross-strait bridge in the period of construction and operation,wave load prediction for the structure in its life cycle becomes an important topic in bridge engineering and offshore engineering.In the 1950 s,researchers established a theoretical method for the interaction between linear wave and circular cylinders.The following studies mainly focused on the cylinders with circular or elliptical cross-sections.However,with the requirements from engineering,other cross-sections are preferred rather than a circular section,for instance,the caisson of cross-strait bridges with a quasi-ellipsoid section.As there is no theoretical solution for such kind of cross-section right now,building an adequate theoretical solution to this problem can not only provide a new method for solving the wave action around the bridge foundation but also afford a deeper understanding of the mechanism of wave interaction with such structure.In this thesis,a theoretical method basing on the potential theory is established for the wave diffraction around the cylinder with an arbitrary cross-section.The main content is:(1)Based on the theoretical framework of potential flow,an analytical method for solving the wave diffraction around a bottom-mounted cylinder with non-circular smooth cross-section is established.In this method,the radius function of cross-section,Bessel function,Hankel function,and other related functions are expanded into Fourier series with a finite term.By substituting them into the velocity potential function of diffraction wave and boundary conditions,the total velocity potential function of the fluid domain can be solved with the determined parameter.Then,the wave action on each structure,such as wave force,base bending moment and wave run-up can be obtained sequentially.The wave action on the cylinder with a cosine-disturbed section is discussed.The variables including cross-section disturbance value,wave number and wave exposure are considered.(2)To obtain the wave action on the quasi-ellipsoid bridge foundation array with different sea states,an analytical method for diffraction wave around cylinder array with non-circular smooth cross-section is established.The wave actions on the arrays with two and four cylinders are discussed.The near-trapping phenomenon for the multi-body and the corresponding scatter-frequency distribution are analyzed.(3)For the problem of wave diffraction around a truncated cylinder,an analytical method for the cylinder with a non-circular smooth cross-section is established.It can be used to analyze the diffraction wave action on a quasi-ellipsoid caisson,which is floating in a balance between buoyancy and gravity.Convergence analysis is performed for each Fourier expansion function in the process of calculation to ensure that its truncation order satisfies the final convergence.The feasibility and accuracy of the proposed method for the mentioned problems are verified by comparison with numerical methods.Wave action on the truncated cylinder with different drafts are analyzed.(4)Based on the potential flow theory and the data of free surface elevation,a method for calculating wave action on the cylindrical structure is established.It builds the indirect relationship between the time history data of free surface and the pressure around the structure.The real-time wave load on the structure can be obtained by integrating the pressure around the structure.At the same time,flume tests on a circular cylinder were carried out.Compared with the measured wave load data,the accuracy of the presented method was verified in both the stationary process and the non-stationary process of wave action.The spectral error caused by the simplification of the theoretical model is discussed.(5)Mathematics model for perforated structures with different cross-sections is built to investigate the interaction mechanism between waves and structures with different porosity.The relationship between free surface fluctuation amplitude and incident wave parameters are obtained.Furthermore,wave action on the inner structure with the protection of perforated wall is investigated.Experimental tests were carried out to verify the accuracy of present method.The effect of wave steepness on the wave action and the predicted error of the presented method are investigated.Finally,simplified design formulae of wave load are provided.