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Propagation of AE Wave in the Air that was Occurred in a Window Frame
Kunihisa KATSUYAMA, Masahiro SETO
National Institute for Resources and Environment
16-3 Onogawa, Tsukuba, Ibaraki, Japan 305-8569
Yoshidahonmachi, Sakyo, Kyoto, Japan
Window frames of an excellent hotel were warmed up by sunshine in the summer. The window frames were stressed by the thermal stress, and frames squeaked because of the sudden changes in temperature. This phenomenon is called one of Acoustic Emission (AE). Many guests could hear those squeaks, but they could not find out the hypocenters. So, the acoustic emissions and the squeaks were measured by an AE instrument and by sound-level meters.
The hypocenters which were occurred in the window frames were decided by the AE instrument. But it was very difficult to decide them by the sound-level meters because of the difference of the propagation velocity of P-wave in the window frames and in the air.
The occurrence of various kinds of phenomena in materials gives rise to the emission of elastic waves. These waves are called acoustic emission (AE) or stress wave emission (SWE). AE technique is used very well for material science, non-destructive test of facilities in industry and predicting fracture.
At the excellent hotel, a lot of complain that squeaking noise could be heard around windows frame came out from many guests. Employees of the hotel listened carefully and investigated where the squeaking noise happened. They could find out rooms where the squeaking noise could be heard, but they could not decide the window frames where they happened. Therefore, AE sensors were set up on the window frames to obtain hypocenters of AE. In this paper, propagation phenomena that AE waves which generated in the window frames propagate in the frames and they went out into the air as sound were discussed.
SIMULATION OF AE PROPAGATION AND SOUND PROPAGATION
The computer used for analysis is IBM·RS6000·SP. Program is ANSYS which is made for a wide use of structural analysis by FEM.
Fig 8: A force given at mark in Fig. 9 and Fig.11.
Fig. 8 shows a force given at one point which is assumed to be a hypocenter of AE. Fig. 9 shows the simulation result in the case of sound propagation in the air of the room. The size of the area calculated by FEM is 100 cm×100 cm, and one mesh size is 1cm×1cm. At the center of the left hand side of the air, the force as shown in Fig.8 was given to the air. The sound propagates concentrically. And the sound wave forms at points 1~9 are shown in Fig.10. The amplitudes of the wave forms become smaller with distance from the hypocenter. The coordinates of these points are as follows.
1( 20, 0), 2(10,-20), 3(20,20) , 4(40,10), 5(40,-20), 6(10,15), 7(0,-24), 8(6,7), 9(13,-20)
Fig.11 shows the simulation result in case of with window frame. AE hypocenter happened in the aluminum frame, and AE propagates in the frame at first with the velocity of 6420m/s, then it propagates in the air with the velocity of 340m/s. So, the sound does not propagate concentrically. Fig. 12 shows the sound wave forms at point 1~9. The amplitude of sound wave forms near the hypocenter is not always big.
The coordinates of these points are as follows;
1(20,30), 2(10,10), 3(20,10), 4(40,40), 5(40,10), 6(10,10), 7(0,6), 8(6,37), 9(13,10)
Fig 9: The simulation result of the concentric sound propagation in case of without window frame
Fig 10: Amplitudes of the sound at points 1~9 in case of without window frame
Fig 11: The simulation result of the sound propagation in case of with the window frame
Fig 12: Amplitude of the sound at point 1~9 in case of with window frame