Research on acoustic emission monitoring of pitting corrosion on 304 stainless steel

In order to study acoustic emission （AE） characteristics of pitting corrosion on 304 stainless steel under higher than normal temperature, pitting corrosion process of 304 stainless steel in 6° ferric chloride solution at 70° was monitored by AE technology. Conventional parameter-based approach and signal-based analysis were combined to deal with recorded AE signals, and micrographic observation was performed for further verification. The results showed that AE hit and energy increased gradually with time and reached the peak at certain time, and then declined and maintained a stable condition. Signal waveform was mainly composed of low-frequency （〈 100 kHz） flexural wave with larger amplitude and energy and high-frequency （〉 100 kHz） expansion wave with lower amplitude and energy. The research results have some certain significance for AE monitoring of pitting corrosion on 304 stainless steel under higher than normal temperature.

Research on acoustic holography method for identification of sound sources

This paper presents the method named acoustic holography which can be used to identify noise sources. A new formula of holography reconstruction is obtained, based on the Kirchhoff integral formula. Some simulating tests are carried out using the new formula. The comparison with other reconstruction formulas proves that the new formula is more effective. By using acoustic holography method, some interesting results about the noise of a vehicle are shown. The results proves that acoustic holography is an effective method for the identification of the complex noise sources.

Measurement and estimation of free field to eardrumtransfer function for virtual acoustic space research

Free field to Eardrum Thansfer Function (FETF) is one of the major factors influencing the identification of the sound source direction. FETF can be employed to generate a Virtual Acoustic Space (VAS) by computer and other equlpment. In this paper the methods to improve the measurement and estimation of FETF are approached. Least-mean-squares (LMS)method is much better than empirical FFT method. This paper also gives a sample description of excitation signals for measuring the impulse response of FETF.

Acoustic design and research on the auditorium of Shanghai Grand Theatre

Shanghai Grand Theatre is a great modern theatre with the largest formula, the highest investment, the most advanced technique and excellent acoustic quality in China. This article mainly introduced Shanghai Grand Theatre's characteristics of formula, technical requirements of acoustic design of Auditorium, characteristics of figure design, reverberation control, acoustic simulation research, acoustic performance and subjective evaluation.

Researches on active structural acoustic control by radiation modes

Based on the radiation modes, an active control strategy is presented for sound radiation from elastic structures with an example of simply supported rectangular panel. The physical characteristics and mathematical meaning of the radiation modes are analyzed. The radiation efficiency of radiation mode falls off very rapidly with the increase of modes order at low frequency. A new control strategy is developed in which by canceling the adjoint coef- ficient of the first k radiation modes, the sound powers of the first k radiation modes is zero theoratically. The numerical calculation is made by using point force actuators as control forces.

Research on acoustic emission characteristics of local corrosion on Q235 steel

To solve the problem of corrosion acoustic emission （AE） source feature extraction and recognition, the AE detection validation and the amplitude-frequency characteristics were derived in theory. The amplitude of AE signal generated by bubble burst is proportional to its radius square and the liquid level, while the AE signal frequency is inversely proportional to the bubble radius. The AE signal amplitude of the steel and the steel corrosion product cracking is proportional to the local stress, and the AE signal frequency is proportional to the crack propagation velocity and inversely proportional to the crack propagation distance. Three Q235 specimens were separately immersed in the solution of 10% FeC13.6H20, 5% CuSOa.5H20 and 10% FeC13.6H20 with 0.01 mol/L HCL. The AE systems with high frequency and low frequency were used to detect the whole corrosion process AE signals. The AE signals of Q235 steel and the steel corrosion products cracking were detected as the verification experiment. The AE signals from different sources could be distinguished by AE hits count and the power spectrum. It is coincident with theoretical analysis. These conclusions have significant guidance for the corrosion detection and evaluation by on-line acoustic emission detecting.

An experimental research on the instability of ion acoustic wave with electron drift

As electron temperature Te is much higher than ion temperature Ti, and electron driftspeed Vd is larger than the critical value Vdc of Vd, the ω=KVφ mode ion acoustic wave（IAW） will be instable. Under a long wave condition （KλD【【1, where λD is Deby length,K is weve number）, the growing rate γ（K） of the IAW may be written