Seismometer self-noise levels were determined using Sleeman’s three-sensor method in combination with the Welch method for different parameter combinations. The self-noise levels decreased with the increasing segment...Seismometer self-noise levels were determined using Sleeman’s three-sensor method in combination with the Welch method for different parameter combinations. The self-noise levels decreased with the increasing segment window length, which is equivalent to the subwindow length, and with the increasing segment overlap rate for different frequency points at a fixed band. After the statistical examination of 9800 different parameter combinations, a zone of reasonable self-noise calculation parameter combinations was identified. Reasons for the unsuitability of certain parameter combinations were explored with respect to their distortion of the seismometer’s self-noise levels.展开更多
Airfoil self-noise is a common phenomenon for many engineering applications. Aiming to study the underlying mechanism of airfoil self-noise at low Mach number and moderate Reynolds number flow, a numerical investigati...Airfoil self-noise is a common phenomenon for many engineering applications. Aiming to study the underlying mechanism of airfoil self-noise at low Mach number and moderate Reynolds number flow, a numerical investigation is presented on noise generation by flow past NACA0018 airfoil. Based on a high-order accurate numerical method, both the near-field hydrodynamics and the far-field acoustics are computed simultaneously by performing direct numerical simulation. The mean flow properties agree well with the experimental measurements. The characteristics of aerodynamic noise are investigated at various angles of attack. The obtained results show that inclining the airfoil could enlarge turbulent intensity and produce larger scale of vortices. The sound radiation is mainly towards the upper and lower directions of the airfoil surface. At higher angle of attack, the tonal noise tends to disappear and the noise spectrum displays broad-band features.展开更多
The self-noise in cavity is tested in the circling tank, prediction method of cavity＇s self-noise induced by turbulent boundary layer is established. The window＇s vibration is using the simply supported boundary con...The self-noise in cavity is tested in the circling tank, prediction method of cavity＇s self-noise induced by turbulent boundary layer is established. The window＇s vibration is using the simply supported boundary condition, the sound wave in the cavity is expanded using the rigid wall boundary condition, the modal coupling vibration equation between them is established using the radiation boundary condition. The turbulent boundary layer pulsating pressure is random, the self-noise power spectrum in the cavity is solved. Test of self-noise and turbulent pressure is carried out in the circling tank when the flow velocity is 5 m/s and 8 m/s, the result verifies that the theoretical method can predict the real cavity＇s hydrodynamic noise approximately, the trends are similar, this provides one analytical method for sonar dome＇s material selection and noise control.展开更多
基金supported by Study on Seismograph Calibration and Preparation of Draft International Standard (201408005)the Earthquake Science and technology Program of Hebei Province (201303)Special Program for Earthquake monitoring (20130203)
文摘Seismometer self-noise levels were determined using Sleeman’s three-sensor method in combination with the Welch method for different parameter combinations. The self-noise levels decreased with the increasing segment window length, which is equivalent to the subwindow length, and with the increasing segment overlap rate for different frequency points at a fixed band. After the statistical examination of 9800 different parameter combinations, a zone of reasonable self-noise calculation parameter combinations was identified. Reasons for the unsuitability of certain parameter combinations were explored with respect to their distortion of the seismometer’s self-noise levels.
基金supported by the National Natural Science Foundation of China(10972022)the Specialized Research Fund for the Doctoral Program of Higher Education of China(20091102110011)the 111 Projects B07009 of China
文摘Airfoil self-noise is a common phenomenon for many engineering applications. Aiming to study the underlying mechanism of airfoil self-noise at low Mach number and moderate Reynolds number flow, a numerical investigation is presented on noise generation by flow past NACA0018 airfoil. Based on a high-order accurate numerical method, both the near-field hydrodynamics and the far-field acoustics are computed simultaneously by performing direct numerical simulation. The mean flow properties agree well with the experimental measurements. The characteristics of aerodynamic noise are investigated at various angles of attack. The obtained results show that inclining the airfoil could enlarge turbulent intensity and produce larger scale of vortices. The sound radiation is mainly towards the upper and lower directions of the airfoil surface. At higher angle of attack, the tonal noise tends to disappear and the noise spectrum displays broad-band features.
文摘The self-noise in cavity is tested in the circling tank, prediction method of cavity＇s self-noise induced by turbulent boundary layer is established. The window＇s vibration is using the simply supported boundary condition, the sound wave in the cavity is expanded using the rigid wall boundary condition, the modal coupling vibration equation between them is established using the radiation boundary condition. The turbulent boundary layer pulsating pressure is random, the self-noise power spectrum in the cavity is solved. Test of self-noise and turbulent pressure is carried out in the circling tank when the flow velocity is 5 m/s and 8 m/s, the result verifies that the theoretical method can predict the real cavity＇s hydrodynamic noise approximately, the trends are similar, this provides one analytical method for sonar dome＇s material selection and noise control.
