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Received Dec 5, 2017; Revised Feb 28, 2018; Accepted Mar 21, 2018
This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1. Introduction
The study of the complex echo characteristics of underwater targets is primarily based on the theory of elastic spherical shell [1, 2], infinite cylindrical shell [3–5], and finite cylindrical shell [6–8] acoustic scattering. In recent years, significant progress has been made in studies on sound scattering of finite cylindrical shells [9–11] with ring ribs and ring-ribbed plates. However, for large-scale underwater complex targets such as submarines, it is difficult to perform accurate theoretical calculation and numerical simulation because of their complex shape and structure.
Experimental research has been performed on pool and lake echo characteristics [12, 13] using models of different scales to verify theoretical research results, which has promoted the development of theoretical prediction and practice. However, because of model size limitations, it is difficult to study ribbed plates, ribs, and other small parts. The more similar the size and material of the model to the actual target are, the closer the echo characteristic to the actual target is, and a large-scale scaled model is an effective method of studying the acoustic reflection characteristics of a target object. Moreover, such a model can achieve strong controllability and provides accurate measurement of target characteristics. This is the primary direction of practice research.
In this study, a high-performance test facility was used to test large-scale underwater complex targets under single base and bistatic conditions. The azimuth and echo intensity of a strong target echo source were predicted using the planar element method. The characteristics of the target echo were studied under the bistatic condition, and the fine feature of target echo energy distribution was studied under the single base condition.
2. Theoretical Analysis and Simulation Analysis
In studies of the large-scale model transmission mechanism of the outer shell and ribbed plate of an actual target, they are approximately regarded as flat plates on two sides of water. Thus, the transmission coefficients of flat plates with different thicknesses are calculated and analyzed. Because a nonpressure shell is thin, energy is transmitted throughout a...