5. Case studies

As shown in Figure 8, the sound insulation test was performed in an anechoic room. The control target is a stiffened CFRP plate and the dimension parameter is 840 mm 840 mm 1 mm. The plate is mounted on an aluminum cavity, with a thickness of 16 mm. A loudspeaker is placed inside the cavity, which generates acoustic excitation the stiffened plate. The CFRP plate is clamped to the aluminum cavity using screws. The edges between the CFRP plate and aluminum box are sealed to prohibit air leakage.

According to the sound insulation mass law, because the box's thickness is much larger than the CFRP plate, the sound transmission path from the internal cavity to

<sup>z</sup> <sup>¼</sup> <sup>1</sup> <sup>þ</sup> Ts=<sup>2</sup>

Effective Low Frequency Noise Insulation Adopting Active Damping Approaches

The components of the control system is shown in Figure 10. Band-limited noise (20–500 Hz) is sent to the loudspeaker, which can excite multiple vibration modes of the CFRP panel. Besides, the 1-1 mode is a global vibration mode, which needs more control effort. In view of the above circumstances, a hybrid control law is

In the hybrid scheme, the NAF control puts control authority to the plate's 1-1

mode and FVF control puts control authority to multiple modes of the plate.

where T is the sampling time.

DOI: http://dx.doi.org/10.5772/intechopen.85427

proposed to solve the problem.

Figure 10.

Figure 11.

91

Schematic diagram of the hybrid control system.

Components of the control system.

<sup>1</sup> � Ts=<sup>2</sup> (9)

Figure 8. Schematic diagram for the active sound insulation test.

Figure 9. Photograph of the test structure.

the outside is the latter. To evaluate the control law's performance, in front of the CFRP plate, a microphone sensor (G.R.A.S 40 ph) is used to monitor the sound pressure level (SPL) value. The distance between the microphone sensor and CFRP plate is 1 m.

For the control system implementation, three independent control channels are adopted. Correspondingly, as shown in Figure 9, three piezoelectric PZT-5H patches are served as actuators, which are labeled as 1, 2, 3.

The detailed components of control system are shown in Figure 10. Collocated accelerometers are bonded to the central of the piezoelectric patches, which are used for structural sensing. Control algorithms are programed using LabVIEW™ and subsequently compiled and downloaded into a CompactRIO target for real-time implementation. A Virtex-5 LX110 FPGA chip guarantees the control loops can be implemented with high throughput and in parallel physically [21].

The digital control loop's updating rate is set to 20 kHz. To transform the continuous transfer function into discretized form, bilinear transformation method is adopted. The equation of the bilinear transformation is shown as follows:

Effective Low Frequency Noise Insulation Adopting Active Damping Approaches DOI: http://dx.doi.org/10.5772/intechopen.85427

$$z = \frac{\mathbf{1} + \mathbf{T}\mathbf{s}/2}{\mathbf{1} - \mathbf{T}\mathbf{s}/2} \tag{9}$$

where T is the sampling time.

The components of the control system is shown in Figure 10. Band-limited noise (20–500 Hz) is sent to the loudspeaker, which can excite multiple vibration modes of the CFRP panel. Besides, the 1-1 mode is a global vibration mode, which needs more control effort. In view of the above circumstances, a hybrid control law is proposed to solve the problem.

In the hybrid scheme, the NAF control puts control authority to the plate's 1-1 mode and FVF control puts control authority to multiple modes of the plate.

#### Figure 10.

the outside is the latter. To evaluate the control law's performance, in front of the CFRP plate, a microphone sensor (G.R.A.S 40 ph) is used to monitor the sound pressure level (SPL) value. The distance between the microphone sensor and CFRP

adopted. Correspondingly, as shown in Figure 9, three piezoelectric PZT-5H

The digital control loop's updating rate is set to 20 kHz. To transform the continuous transfer function into discretized form, bilinear transformation method

is adopted. The equation of the bilinear transformation is shown as follows:

patches are served as actuators, which are labeled as 1, 2, 3.

implemented with high throughput and in parallel physically [21].

For the control system implementation, three independent control channels are

The detailed components of control system are shown in Figure 10. Collocated accelerometers are bonded to the central of the piezoelectric patches, which are used for structural sensing. Control algorithms are programed using LabVIEW™ and subsequently compiled and downloaded into a CompactRIO target for real-time implementation. A Virtex-5 LX110 FPGA chip guarantees the control loops can be

plate is 1 m.

90

Figure 9.

Photograph of the test structure.

Figure 8.

Schematic diagram for the active sound insulation test.

Noise and Vibration Control - From Theory to Practice

Components of the control system.

Figure 11. Schematic diagram of the hybrid control system.

Therefore, it is anticipated that this hybrid control law can exert sufficient active damping to the CFRP panel, which is suitable for the noise insulation application.

At 83 Hz, as anticipated, this first vibration mode contribute to the SPL spectrum significantly. After the active damping treatment, at this frequency, the SPL reduction value is up to 15.3 dB. For the entire interesting frequency band, the SPL reduction value comes up to 7.3 dB. These measured experimental results prove that the proposed active damping control method can improve the structure's sound

Effective Low Frequency Noise Insulation Adopting Active Damping Approaches

In this chapter, the active damping approaches are adopted to improve structure's sound insulation performance in the low frequency range. The collocated sensor/actuator configuration is adopted to simplify the control law design. The NAF control law is proposed to suppress the plate's 1-1 mode, which radiates sound effectively and needs more control authority. The FVF control is proposed to suppress multiple vibration modes in wide range. In the experimental study, a CFRP panel is utilized as the control target and the NAF and FVF control laws are

combined together to generate active damping to the CFRP structure. Experimental test results show the hybrid control law can realize wideband active damping and

This work was funded by the National Natural Science Foundation of China (grant numbers 61701250, 51605202), the Natural Science Foundation of Jiangsu

1 School of Automation, Nanjing University of Posts and Telecommunications,

2 School of Naval Architecture and Ocean Engineering, Jiangsu University of

\*Address all correspondence to: yuanming@njupt.edu.cn and yangf@just.edu.cn

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

improve the plate's sound insulation performance significantly.

Province (grant number BK20160895, BK20160550).

The authors declare no conflict of interest.

\*

\* and Fan Yang<sup>2</sup>

Science and Technology, Zhenjiang, China

provided the original work is properly cited.

insulation performance in an effective way.

DOI: http://dx.doi.org/10.5772/intechopen.85427

6. Conclusions

Acknowledgements

Conflict of interest

Author details

Ming Yuan<sup>1</sup>

Nanjing, China

93

The schematic diagram of the hybrid control system is shown Figure 11.

When the active insulation system starts to work, the acceleration signal spectrums before control and after control are shown in Figure 12.

From the measured data, the proposed hybrid control scheme can realize wideband vibration reduction. For instance, at 83 Hz, the vibration reduction value is 13 dB; at 143 Hz, the vibration reduction value is 6.6 dB; at 194 Hz, the vibration reduction value is 5.3 dB; at 216 Hz, the vibration reduction value is 5.2 dB; at 273 Hz, the vibration reduction value is 4.3 dB; at 305 Hz, the vibration reduction value is 5.9 dB.

The SPL spectrums before control and after control are shown in Figure 13.

Figure 12. Measured acceleration signal (solid line: before control, dashed line: after control).

Figure 13. Measured sound pressure level (solid line: without control, dashed line: with control).

Effective Low Frequency Noise Insulation Adopting Active Damping Approaches DOI: http://dx.doi.org/10.5772/intechopen.85427

At 83 Hz, as anticipated, this first vibration mode contribute to the SPL spectrum significantly. After the active damping treatment, at this frequency, the SPL reduction value is up to 15.3 dB. For the entire interesting frequency band, the SPL reduction value comes up to 7.3 dB. These measured experimental results prove that the proposed active damping control method can improve the structure's sound insulation performance in an effective way.
