# Vibration Control of an Aero Pipeline System with Active Constraint Layer Damping Treatment
## 4 Conclusions  
Through experimentally and theoretically analysis, the following conclusions can be drawn:  
1. The force analysis of the pipeline with ACLD patches under the harmonic voltage shows that the driving force is correlated with the piezoelectric constant of the active constraint layer, the control voltage, the shear modulus and thickness of the viscoelastic layer. The driving force transmitted by the viscoelastic layer increases as the shear modulus increases or the thickness decreases, but the modal loss factor of the system exhibits a peak when the shear modulus reaches \(10^{8}\) or the thickness reaches 0.75 mm for the VEM used in this research. Therefore, the optimal viscoelastic layer shear modulus and thickness can be selected to obtain the best performance of ACLD treatment.
2. Through the finite element analysis and experiment, the effectiveness of the ACLD patches for the vibration control of the pipeline is verified, and the damping effect reaches up to the highest being 58.14% when the amplitude of excitations is 0.1 g and decline with the growth of the excitation amplitude. The structure parameters and control parameters of the ACLD patches have a significant influence on the damping performance. The damping effect increases with the increase of the control voltage and coverage area.
3. Under the given excitation, it is effective to increase the coverage area of the ACLD patches and improve the amplitude of the control voltage to get a better vibration control effect. However, as the voltage increases, the acceleration response that can be reduced per unit voltage becomes smaller under the same excitation. Also, as the amplitude of the excitation increases, the control effect under the same voltage is gradually reduced. That is, under certain conditions, the effect of ACLD patches on vibration control is limited.  
The research on the vibration control of aero pipeline system using ACLD treatment needs further study, mainly in the following aspects:  
1. Due to limited time and energy, there is a lack of more in-depth research on research issues, and some theoretical and applied issues need further analysis. For example, the effects of pulsating pressure on vibration in actual conditions are not considered in the paper during the modeling and experimentation steps.
2. In the ACLD structure, the constitutive relationship of viscoelastic materials is greatly affected by the ambient temperature and vibration frequency. Therefore, the search for a reasonable description of the constitutive relationship of viscoelastic materials still needs to be studied.
3. The research on the control method of ACLD structure is still insufficient. The PID control currently used is too simple. Therefore, it is necessary to develop and study more suitable control methods, especially robust control, adaptive control and intelligent control, to overcome and solve the uncertainty and change affecting the model.  
Conceptualization, J.Z.; methodology, J.Z.; software, J.L.; validation, D.W., J.L. and P.G.; formal analysis, J.Z.; investigation, J.Z.; resources, Q.H.; data curation, Y.Y.; writing--original draft preparation, J.Z.; writing--review and editing, J.L. and P.G.; visualization, D.W.; supervision, Q.H.; project administration, P.G.; funding acquisition, P.G. This research was funded by National Natural Science Foundation of China, Grant No. 51805462.  
The authors declare no conflict of interest.