A shallow water tomography scheme based on the modal wave number inversion technique is considered in this paper. The scheme is based on the assumption that modal wave number for trapped modes can be measured in a sui...A shallow water tomography scheme based on the modal wave number inversion technique is considered in this paper. The scheme is based on the assumption that modal wave number for trapped modes can be measured in a suitable way. The tomographic inversion is accomplished in two steps: firstly, the bottom parameters are inverted by using the bottom reflection phase shift with the known sound speed profile; secondly, the variation of sound speed profile at different time is inverted provided the bottom parameters are known. A numerical simulation shows that the proposed scheme works well, and the sensitivity analysis of sound speed profile inversion is performed for shallow water environmental parameters: sound speed, density and attenuation coefficient of the bottom.展开更多
The propagation of multipole modal waves along the well-axis in a fluid-filled borehole surrounded by elastic and nonelastic, infinite and finite formation is analysed by using the wave equations. The phase velocity d...The propagation of multipole modal waves along the well-axis in a fluid-filled borehole surrounded by elastic and nonelastic, infinite and finite formation is analysed by using the wave equations. The phase velocity dispersion and the excitation curves are numerically calculated. The waveforms excited by attenuating bursts are also calculated. The measurements with long-spaced dipole transducers made of PZT thin disks vibrating in bending mode are carried out in a concrete model well and the experimental results are compared with the theoretical results.展开更多
On the basis of a nonhydrostatic numerical model, the interaction of internal solitary wave with slope - shelf was studied. The breaking and polarity transformation were analyzed. A ＂kink＂ structure, due to shoaling...On the basis of a nonhydrostatic numerical model, the interaction of internal solitary wave with slope - shelf was studied. The breaking and polarity transformation were analyzed. A ＂kink＂ structure, due to shoaling topography and higher nonlinear effect, was found to be generated by the leading wave before breaking. Coherent vortex shedding behind the leading wave was presented. The evolution characteristics of the modal structure were analyzed based on the empirical orthogonal function method. The modal structure was complicated due to the effect of the variable topography, especially when breaking occurred. In the performed experiments, the contributions to the total variance from higher mode jumped from no more than 20% to over 40%.展开更多
Oscillating water column wave energy converter is a power generation device in which ocean waves excite the oscillation of the water surface in an air chamber, which generates fluctuations in air pressure and rotate a...Oscillating water column wave energy converter is a power generation device in which ocean waves excite the oscillation of the water surface in an air chamber, which generates fluctuations in air pressure and rotate air turbine generator(s). The oscillation of the fluid in the air chamber is a fluid oscillation phenomenon with a natural period, similar to fluid oscillation in a container such as sloshing. Previous research has shown that for an oscillating water column with a single air chamber submerged in water, the oscillation characteristics can be modeled as a one-degree-of-freedom oscillation system that takes only a single oscillation mode into account. However, a double-slit breakwater integrated oscillating water column wave energy converter using two water columns of the breakwater separated by slit walls, has been verified to have two resonance periods. In this study, the free oscillating motion of the oscillating water column wave energy converter using the double-slit breakwater is modeled by modal superposition method including the first-order and second-order modes of vertical motion of the two water surfaces. The result from the simulation is similar to the result of the free vibration experiment.展开更多
Based on the standard spaces of the physical presentation, both the quasi-static mechanical approximation and the quasi-static electromagnetic approximation of piezoelectric solids are studied here. The complete set o...Based on the standard spaces of the physical presentation, both the quasi-static mechanical approximation and the quasi-static electromagnetic approximation of piezoelectric solids are studied here. The complete set of uncoupled elastic wave and electromagnetic wave equations are deduced. The results show that the number and propagation speed of elastic waves and electromagnetic waves in anisotropic piezoelectric solids are determined by both the subspaces of electromagnetically anisotropic media and ones of mechanically anisotropic media. Based on these laws, we discuss the propagation behaviour of elastic waves and electromagnetic waves in the piezoelectric material of class 6 mm.展开更多
The mechanical balance process is the key process to eliminate the quadrature error and improve the performance of the cupped wave gyro. The conventional mechanical balance method for cupped wave gyro based on cup-wal...The mechanical balance process is the key process to eliminate the quadrature error and improve the performance of the cupped wave gyro. The conventional mechanical balance method for cupped wave gyro based on cup-wall trimming requires high control accuracy of trimming quantity, which increases the production cost and decreases the fabrication efficiency in large extent. However, it is hard to reach the high balance accuracy with the natural frequency split of mHz grade by using the conventional method. In this paper, the lumped mass dynamic model of the cupped wave gyro is built by discretization method, and the effects of different position trimming on the natural frequency are analyzed. It is pointed out that trimming off a tiny quantity of material from cup-wall causes large variation of the natural frequency is the main reason for the low accuracy of the conventional mechanical balance method. Then, a precision balance method for cupped wave gyro based on cup-bottom trimming is presented and the entire procedures of this method are given. The static balance process and dynamic balance process of the precision balance method are simulated by the finite element software. The simulation result shows that the precision balance method based on cup-bottom trimming brings less additional natural frequency split in the static balance process, minimizes the natural frequency split to mHz grade and rectify the angle of mode offset to 0.1° grade in the dynamic balance process, furthermore, the method decreases the requirement for control accuracy of trimming quantity evidently. The research work provides references for structure optimization design and balance process plan of the cupped wave gyro.展开更多
The equilibrium equations of anisotropic media, coupled to the heat conduction equations, are studied here based on the standard spaces of the physical presentation, in which an new thermo-elastic model based on the s...The equilibrium equations of anisotropic media, coupled to the heat conduction equations, are studied here based on the standard spaces of the physical presentation, in which an new thermo-elastic model based on the second law of thermodynamics is induced. The uncoupled heat wave equation for anisotropic media is deduced. The results show that the equation of heat wave is of the properties of dissipative waves. In final part of this paper, we discuss the propagation behaviour of heat waves for transversely isotropic media.展开更多
This study explores the influence of rotor blade angle on stall inception in an axial fan by means of numerical simulations grounded in the Reynolds-Averaged Navier-Stokes(RANS)equations and the Realizable k-εturbule...This study explores the influence of rotor blade angle on stall inception in an axial fan by means of numerical simulations grounded in the Reynolds-Averaged Navier-Stokes(RANS)equations and the Realizable k-εturbulence model.By analyzing the temporal behavior of the outlet static pressure,along with the propagation velocity of stall inception,the research identifies distinct patterns in the development of stall.The results reveal that stall inception originates in the second rotor impeller.At a blade angle of 27°,the stall inception follows a modal wave pattern,while in all other cases,it assumes the form of spike-type stall.The flow field associated with spike stall inception demonstrates a relatively uniform gradient in the radial direction,whereas the modal wave stall case displays a distinctive“L”-shaped propagation feature.At blade angles of multiple stall inceptions are observed.-9°and-18°,These phenomena initiate at the blade’s leading edge,propagate along both axial and radial directions,and transition dynamically between single and multiple inception states.展开更多
文摘A shallow water tomography scheme based on the modal wave number inversion technique is considered in this paper. The scheme is based on the assumption that modal wave number for trapped modes can be measured in a suitable way. The tomographic inversion is accomplished in two steps: firstly, the bottom parameters are inverted by using the bottom reflection phase shift with the known sound speed profile; secondly, the variation of sound speed profile at different time is inverted provided the bottom parameters are known. A numerical simulation shows that the proposed scheme works well, and the sensitivity analysis of sound speed profile inversion is performed for shallow water environmental parameters: sound speed, density and attenuation coefficient of the bottom.
基金The Project is supported by:Science and Technology Committee of Jiangsu Province,the Oil and Research Center of Nanjing Universitya and the Fundation of the National Education Commission
文摘The propagation of multipole modal waves along the well-axis in a fluid-filled borehole surrounded by elastic and nonelastic, infinite and finite formation is analysed by using the wave equations. The phase velocity dispersion and the excitation curves are numerically calculated. The waveforms excited by attenuating bursts are also calculated. The measurements with long-spaced dipole transducers made of PZT thin disks vibrating in bending mode are carried out in a concrete model well and the experimental results are compared with the theoretical results.
基金This project was supported by the National Natural Science Foundation of China under contract No. 40576010.
文摘On the basis of a nonhydrostatic numerical model, the interaction of internal solitary wave with slope - shelf was studied. The breaking and polarity transformation were analyzed. A ＂kink＂ structure, due to shoaling topography and higher nonlinear effect, was found to be generated by the leading wave before breaking. Coherent vortex shedding behind the leading wave was presented. The evolution characteristics of the modal structure were analyzed based on the empirical orthogonal function method. The modal structure was complicated due to the effect of the variable topography, especially when breaking occurred. In the performed experiments, the contributions to the total variance from higher mode jumped from no more than 20% to over 40%.
文摘Oscillating water column wave energy converter is a power generation device in which ocean waves excite the oscillation of the water surface in an air chamber, which generates fluctuations in air pressure and rotate air turbine generator(s). The oscillation of the fluid in the air chamber is a fluid oscillation phenomenon with a natural period, similar to fluid oscillation in a container such as sloshing. Previous research has shown that for an oscillating water column with a single air chamber submerged in water, the oscillation characteristics can be modeled as a one-degree-of-freedom oscillation system that takes only a single oscillation mode into account. However, a double-slit breakwater integrated oscillating water column wave energy converter using two water columns of the breakwater separated by slit walls, has been verified to have two resonance periods. In this study, the free oscillating motion of the oscillating water column wave energy converter using the double-slit breakwater is modeled by modal superposition method including the first-order and second-order modes of vertical motion of the two water surfaces. The result from the simulation is similar to the result of the free vibration experiment.
文摘Based on the standard spaces of the physical presentation, both the quasi-static mechanical approximation and the quasi-static electromagnetic approximation of piezoelectric solids are studied here. The complete set of uncoupled elastic wave and electromagnetic wave equations are deduced. The results show that the number and propagation speed of elastic waves and electromagnetic waves in anisotropic piezoelectric solids are determined by both the subspaces of electromagnetically anisotropic media and ones of mechanically anisotropic media. Based on these laws, we discuss the propagation behaviour of elastic waves and electromagnetic waves in the piezoelectric material of class 6 mm.
基金supported by National Natural Science Foundation of China (Grant No. 51005239)
文摘The mechanical balance process is the key process to eliminate the quadrature error and improve the performance of the cupped wave gyro. The conventional mechanical balance method for cupped wave gyro based on cup-wall trimming requires high control accuracy of trimming quantity, which increases the production cost and decreases the fabrication efficiency in large extent. However, it is hard to reach the high balance accuracy with the natural frequency split of mHz grade by using the conventional method. In this paper, the lumped mass dynamic model of the cupped wave gyro is built by discretization method, and the effects of different position trimming on the natural frequency are analyzed. It is pointed out that trimming off a tiny quantity of material from cup-wall causes large variation of the natural frequency is the main reason for the low accuracy of the conventional mechanical balance method. Then, a precision balance method for cupped wave gyro based on cup-bottom trimming is presented and the entire procedures of this method are given. The static balance process and dynamic balance process of the precision balance method are simulated by the finite element software. The simulation result shows that the precision balance method based on cup-bottom trimming brings less additional natural frequency split in the static balance process, minimizes the natural frequency split to mHz grade and rectify the angle of mode offset to 0.1° grade in the dynamic balance process, furthermore, the method decreases the requirement for control accuracy of trimming quantity evidently. The research work provides references for structure optimization design and balance process plan of the cupped wave gyro.
文摘The equilibrium equations of anisotropic media, coupled to the heat conduction equations, are studied here based on the standard spaces of the physical presentation, in which an new thermo-elastic model based on the second law of thermodynamics is induced. The uncoupled heat wave equation for anisotropic media is deduced. The results show that the equation of heat wave is of the properties of dissipative waves. In final part of this paper, we discuss the propagation behaviour of heat waves for transversely isotropic media.
基金the Natural Science Foundation of Hebei Province,China(Grant No.E2022502052)Fundamental Research Funds for the Central Universities,China(Grant No.2022MS081)Fundamental Research Funds for the Central Universities,China(Grant No.2023MS121).
文摘This study explores the influence of rotor blade angle on stall inception in an axial fan by means of numerical simulations grounded in the Reynolds-Averaged Navier-Stokes(RANS)equations and the Realizable k-εturbulence model.By analyzing the temporal behavior of the outlet static pressure,along with the propagation velocity of stall inception,the research identifies distinct patterns in the development of stall.The results reveal that stall inception originates in the second rotor impeller.At a blade angle of 27°,the stall inception follows a modal wave pattern,while in all other cases,it assumes the form of spike-type stall.The flow field associated with spike stall inception demonstrates a relatively uniform gradient in the radial direction,whereas the modal wave stall case displays a distinctive“L”-shaped propagation feature.At blade angles of multiple stall inceptions are observed.-9°and-18°,These phenomena initiate at the blade’s leading edge,propagate along both axial and radial directions,and transition dynamically between single and multiple inception states.
