Papers by Keyword: Sound Radiation

Abstract: The theory of vibration resistance of blocking mass at the corner interface of L-shaped plates is put forward from the perspective of wave approach. The equation of transmission and reflection coefficients of flexure wave is deduced by the presented theory. Based on FE/SEA method, the vibration resistance performance of the hollow blocking mass at the corner interface of L-shaped plates was studied through numerical simulation. The results show that the hollow blocking mass can impede the propagation of the high frequency vibration waves, reduce the vibration and sound radiation of the latter plate, and increase the influence of the reflection waves on the former plate. However, the overall radiant energy is basically identical to the L-shaped plates without the hollow blocking mass.

Abstract: The vibration and sound radiation characteristics of laminated composite flat-panel sound radiators are studied via both theoretical and experimental approaches. In the theoretical study, a finite element model is presented to formulate the forced vibration of the sound radiators. The first Rayleigh integral is used to construct the sound pressure level curve of the sound radiators. In the experimental study, a laminated composite sound radiator was subjected to sweep sine excitation to determine the frequency response spectrum from which the natural frequencies of the sound radiator were identified. The sound radiator with salt powder distributed on its top surface was excited to generate the vibration shapes of the sound radiator at several selected frequencies. The SPL curve of the sound radiator was also measured experimentally. The experimental results are then used to verify the feasibility and accuracy of the proposed finite element model.

Abstract: This paper investigates the suppression of vibration and noise radiation in a flexible isolation system through the use of periodic layered structures. A single-stage vibration isolation model is developed first. Then, the isolation performance of the periodic structure is studied. Furthermore, the influence of the isolator location and the phase difference on the radiated sound power of the foundation is investigated. The numerical results show that the vibration and noise can be greatly attenuated in the band gaps.

Abstract: In this paper, we establish the finite element (FEM) and boundary element (BEM) models of a submarine section, and study the underwater sound radiation field of three different non-pressure shells made of steel, steel with anechoic tile, and the functionally graded materials (FGM) separately using a method combining of FEM and BEM . Research shows that the combination of FEM and BEM can address the acoustic radiation calculation problem of FGM, and in comparison with steel and anechoic tile laying submarine section, the weight of FGM non-pressure shell reduces 1600kg, and the sound radiation power decreases 4db and 2.5db respectively, thus having better performance in vibration and noise reduction.

Abstract: Based on Donnell’s thin shell theory and basic equations, the wave propagation method is discussed here in detail, which is used to investigate the vibration and sound radiation characteristics of non-uniform ring stiffened cylindrical shells under various boundary conditions. The structure damp effects of cylindrical shells are investigated and the ring ribs were considered very narrow, and the rib forces are considered in radial direction. The conclusion are drawn that with the structural loss factor changing large, the whole pressure level are changed little, but the peak of resonance are slacking down obviously; The shell’s resonance frequency can be changed with irregular ring stiffened cylindrical shell .The work will give some guidelines for noise reduction of this kind of shell.

Abstract: An approach combining FEM with BEM is adopted to calculate the structural vibration and sound radiation of an underwater cylindrical shell. By using FORTRAN codes to compute the added mass and added damping matrices, DMAP codes to add them to structural mass and damping matrices, the problem of fluid-structural interaction was solved. Through comparing the mean square normal velocity level and sound radiation power level of ring-stiffened cylindrical shell with different inertia moment of stiffeners, the results can be acquired: with the moment of inertia gets bigger, the peak frequency of the frequency-response curves increases while the peak value of vibration and sound radiation decreases. The number of strengthened stiffeners has the same effect on peak frequency as the moment of inertia, but has no effect on peak value.

Abstract: Finite cylindrical shells with stiffened ribs are major structure of cabin on the submerged or underwater vehicles. This paper aims to probe into the feasibility of sound radiation simulation of underwater structure based on ABAQUS. ABAQUS is used to compute and analysis the underwater sound radiation rule of double cylindrical shell structure. And the computation data agrees with the experimental data basically. Adopting boundary impedance technique and acoustics IEM technique to simulation infinite flow field is feasible, and adopting acoustics IEM technique has much better performance. Boundary impedance technique is promoted for the concerning of accuracy. The results indicate that ABAQUS is appropriate to solve underwater sound radiation problem and it can satisfy the requirement of project application, which provides a new analysis method.

Abstract: The relationship between the sound power and the stimulated frequency of thin plate is analyzed, and the influence from frequency is also introduced. The result presents the characteristic of thin plate sound radiation when the stimulated frequency approaches the natural frequency, while radiation difference of the square plate and the rectangular plate is also given. The analytical results present the guide for low noise design of thin plate in engineering.

Abstract: Random wave difference is, there is no continuity and no column coupled harmonic wavelet. Singapore non-coherent wave stack can be the result of linear increase. We studied a cross wall at supersonic vibration wave phase speed driving most of the radiation. While recognizing that the ultimate strength of the sound waves from the total input power source was implemented in the beginning, we point out that the first phase increase in random vibration energy stored in the random structure of sound radiation is of great significance.

Abstract: Based on Donnell’s thin shell theory and basic equations, the wave propagation method is discussed here in detail, which is used to investigate the vibration and sound radiation characteristics of thin finite length circular cylindrical shells and ring stiffened shells under various boundary conditions. The effects of boundary conditions, mode truncation, shell’s length, thickness and rings on the acoustic radiation are explored. It is shown that the wave propagation method is more effective for the long cylindrical shell, and the mode truncation can satisfy the calculation accuracy. The conclusion is drawn that the stiffeners have a great influence on the total mechanical impedance while have a slight influence on radiation impedance. The work will give some guidelines for noise reduction of this kind of shell.