Abstract
A sound radiation calculation method by using dominant modes is proposed to predict the sound radiation from a cylindrical shell. This method can provide an effective way to quickly predict the sound radiation of the structure by using as few displacement monitoring points as possible on the structure surface. In this paper, modal analyses of a submerged cylindrical shell are carried out by taking the vibration mode of a cylindrical shell in a vacuum, as a set of orthogonal bases. The modal sound radiation efficiency and modal contributions to sound radiation power are presented, and comparison results show that a few modes dominantly contribute to the sound radiation power at low frequencies. These modes, called dominantly radiated structural modes in this paper, are applied to predict the sound radiation power of submerged cylindrical shells by obtaining the modal participant coefficients and sound radiation efficiency of these dominant modes. Aside from the orthogonal decomposition method, a method of solving displacement modal superposition equations is proposed to extract the modal participant coefficients, because few modes contribute to the vibration displacement near the resonant frequencies. Some simulations of cylindrical shells with different boundaries are conducted, and the number of measuring points required are examined. Results show that this method, based on dominant modes, can well predict the low-frequency sound radiation power of submerged cylindrical shells. In addition, compared with the boundary element method, this method can better reduce the number of required measuring points significantly. The data of these important modes can be saved, which can help to predict the low-frequency sound radiation of the same structure faster in the future.
Highlights
At present, underwater vehicles such as submarines and unmanned underwater vehicles (UUVs) are being widely used in national defense, marine development, and other fields
The p order modal displacement can be represented as φp, where p is from 1 to P, and the actual displacement of the vibrating structure can be represented as Φ, and the location of the measurement points can be represented as xq, where q is from 1 to Q(Q≥P), and p order modal participant coefficients will be expressed as Wp
The previous analysis shows that the key problem of the sound radiation prediction method based on the dominantly radiated structural mode (DRSM) is to identify the DRSMs and obtain their modal participant coefficients
Summary
Underwater vehicles such as submarines and unmanned underwater vehicles (UUVs) are being widely used in national defense, marine development, and other fields. The above methods are all based on establishing the integral relationship between the surface vibration velocity and the sound field to predict the radiated sound They all require a large number of measuring points on the structure surface. To simplify the procedure of predicting the radiated sound field and efficiently obtain the radiated sound power of the structure, a new method based on the main radiation structural modes is proposed in this paper, and this method is developed from the modal contribution idea in the ARM method. On the basis of this characteristic, DRSM is used to efficiently predict the radiated sound power of underwater cylindrical shells This method is efficient because it inherits the idea of efficient ARM and obtains the radiated sound power by superposition of several DRSMs. In addition, in most frequency bands, the DRSMs contribute significantly to the vibration displacement. Structural modal information of the underwater structure can be precomputed and saved in the database for the forecast and calculation, which makes it easier to meet the real-time requirements of online prediction
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