Cylindrical shell structures are widely utilized in aircraft and underwater vehicles. In these applications, the structure-borne low-frequency noise is an outstanding issue for passenger comfort (interior noise) and vulnerable to be detected by hostile sensors (radiated noise).
So CAO Yin, SUN Hongling, AN Fengyan, LI Xiaodong from the Key Laboratory of Noise and Vibration Research, Institute of Acoustics, Chinese Academy of Sciences did a research to propose and theoretically analyze a novel approach of active radiated sound control of cylindrical shell under axial excitations by using a pair of piezoelectric stack force actuators to reduce both the vibration and the sound radiation of the cylindrical shell structures.
This sound control approach was based on a pair of piezoelectric stack force actuators as shown below installed on the shell and parallel to the axial direction.
The actuators were driven in phase and acted at x1 and x2 points on the shell generating the same forces to control the vibration and the sound radiation of the cylindrical shell. The contribution to sound radiation of the cylindrical shell structure could be divided into two parts: rigid body motion of the end-caps in the axial direction and the cylindrical shell in the radial direction.
The model used in this article was a fluid-loaded finite stiffened cylindrical shell with two rigid end-caps and only low-frequency axial vibration modes were involved.The whole model was divided into two parts of cylindrical shell and end plates which were independent from each other, and the sound radiation was dominated by the axial motion of the end plates in low frequency range.
To calculate the sound pressure of the finite cylindrical shell analytically, the cylinder was extended by two semi-infinite rigid cylindrical baffles shown below. The analysis showed that the baffles had minor effects on the sound radiation of the finite cylindrical shell, and could make the solution of the pressure field more conveniently.
Active vibration control (AVC) and active structural acoustic control (ASAC) were two different control strategies, using vibration and sound radiation as objective function, respectively. In practical applications, vibration signal was much easier to pick up than the sound pressure signal. In this article, both AVC and ASAC of a cylindrical shell were analyzed based on the model, focusing on the required control force and the feasibility of taking the vibration response as objective function to control the sound radiation.
In the following, numerical simulations were performed firstly to analyze the advantages and disadvantages of the Pan's method, and then the control effects of the vibration and the sound radiations of the cylindrical shell using piezoelectric stack force actuator were analyzed numerically in detail.
The results showed that the piezoelectric stack force actuator could control the sound radiation of the axial modes of cylindrical shell effectively. However, the center of the actuator could not be located at the anti-nodal line of the corresponding controlling mode. Sine when the displacement of multiple points or the radiated sound pressure was chosen as cost functions, the proposed method could also control the radiated sound at the non-modal frequencies. The proposed actuator did not need base structures or large mass blocks to generate reaction forces as well as had little effect on original physical properties of the structure. It was easy to design and install and had great potential in some practical applications.
This research result was published on the recently issued Journal of Sound and Vibration (Volume 331, Issue 11, 21 May 2012, Pages 2471–2484).