The effect of diffraction on the ultrasonic velocity measured by the pulse interference method has been investigated in VHF range theoretically and experimentally. Two silicate glasses are taken as the specimens, thei...The effect of diffraction on the ultrasonic velocity measured by the pulse interference method has been investigated in VHF range theoretically and experimentally. Two silicate glasses are taken as the specimens, their frequency dependences of longitudinal velocities are measured in the frequency range of 50-350 MHz, and the phase advances of ultrasonic signals caused by diffraction effect are calculated using A. O. Williams’ theoretical expression. For the velocity error due to diffraction effect, the experimental results are in good agreement with the theoretical prediction. It has been shown that the velocity error due to diffraction effect is directly proportional to dθ21 (f)/df, whereθ21 (f) is the phase advances difference between the two partial reflection signals used in velocity measurement and f is the ultrasonic frequency.展开更多
Offshore structures are generally classified as small-scale structures or large-scale structures.Their wave forces are then estimated by Morison equation and diffraction/radiation theories,respectively.However,the cla...Offshore structures are generally classified as small-scale structures or large-scale structures.Their wave forces are then estimated by Morison equation and diffraction/radiation theories,respectively.However,the classification criterion is not well quantified.In the present paper,a numerical wave flume is established to simulate the wave forces acting on a fixed and vertical surface-piercing circular cylinder under linear waves.By solving Navier–Stokes equation and Euler equation with free surface involved,respectively,the viscous force and inertia force are separated accurately.The variation of viscous force and inertia force with the cylinder diameter to wave length ratio is discussed in detail.The scale intervals for significant viscous and diffraction effects are given.The error caused by neglecting viscous and diffraction forces is quantitatively analyzed.Based on these analysis,the concept of medium-scale structure is proposed and the classification criteria for small-,medium-and large-scale structures are given.In the meantime,the estimation methods of wave forces for different scales of structures are suggested.展开更多
文摘The effect of diffraction on the ultrasonic velocity measured by the pulse interference method has been investigated in VHF range theoretically and experimentally. Two silicate glasses are taken as the specimens, their frequency dependences of longitudinal velocities are measured in the frequency range of 50-350 MHz, and the phase advances of ultrasonic signals caused by diffraction effect are calculated using A. O. Williams’ theoretical expression. For the velocity error due to diffraction effect, the experimental results are in good agreement with the theoretical prediction. It has been shown that the velocity error due to diffraction effect is directly proportional to dθ21 (f)/df, whereθ21 (f) is the phase advances difference between the two partial reflection signals used in velocity measurement and f is the ultrasonic frequency.
基金This work was supported by the National Key R&D Program of China(Grant 2017yfc1404200)the National Natural Science Foundation of China(Grant 11572332)and the Strategic Priority Research Program of the Chinese Academy of Sciences(Grants xdb22040203 and xda22OOOOOO).
文摘Offshore structures are generally classified as small-scale structures or large-scale structures.Their wave forces are then estimated by Morison equation and diffraction/radiation theories,respectively.However,the classification criterion is not well quantified.In the present paper,a numerical wave flume is established to simulate the wave forces acting on a fixed and vertical surface-piercing circular cylinder under linear waves.By solving Navier–Stokes equation and Euler equation with free surface involved,respectively,the viscous force and inertia force are separated accurately.The variation of viscous force and inertia force with the cylinder diameter to wave length ratio is discussed in detail.The scale intervals for significant viscous and diffraction effects are given.The error caused by neglecting viscous and diffraction forces is quantitatively analyzed.Based on these analysis,the concept of medium-scale structure is proposed and the classification criteria for small-,medium-and large-scale structures are given.In the meantime,the estimation methods of wave forces for different scales of structures are suggested.
