# Vibration Control of an Aero Pipeline System with Active Constraint Layer Damping Treatment
## 1 Introduction  
Pipeline systems are widely used in engineering fields and play an important role in energy transmission in civil and military industries. The system is mainly composed of structural parts such as the pipeline body, joint, sealing element, clamp, valve and so on. Due to the installation requirements of different industrial equipment, the arrangement of the pipeline system has strict limitations. Therefore, higher requirements are placed on the stability and reliability of the piping system to avoid failure. Pipeline vibrations are a major problem that needs to be faced to improve the pipeline's stability and reliability. The excitations of vibration mainly come from: the actuator in the hydraulic system, pulsation excitation of the fluid output by the pump, and pulsation shock caused by movement of components such as valves. When the excitation frequency is close to the modal frequency of the pipeline, resonation of pipeline occurs, causing damage and failure. For a long time, pipeline system failures caused by vibrations have been very common and the economic losses caused have also been enormous. The main pipeline failures are: burst, collision, wear, joint loose, clamp failure, ferrule crack and so on. For example, oil leakage, joints and seal failures often occur in the hydraulic pipeline systems of engineering machinery; bursts and valve damage often occur in marine hydraulic systems; collisions, clamp failure and ferrule crack often occur in aviation hydraulic piping systems. These failures not only cause equipment damage and major safety accidents, but also cause great safety hazards for equipment users. Therefore, it is necessary to effectively control the vibrations of a pipeline system. Much research on the vibration mechanism of pipelines has been carried out by scholars. It is generally believed that the main causes of pipeline vibration are complex coupled vibration of hydraulic fluid and the coupled effect of components and substance in hydraulic systems. The vibration control of a pipeline is used to control the path of vibration transmission and dissipate the vibration energy of the system [1; 2; 3; 4; 5; 6]. This field has been utilized by some researchers. Vibration control can be divided into passive control and active control on the basis of the mechanism. Passive vibration control mainly includes measures of changing the ratio of the external excitation frequency and the modal frequency of the pipeline, increasing the structural damping, shifting the resonance frequency of a pipeline and dissipating the vibration energy. The traditional passive control method was to deploy a number of inertial attachments [7]. Some researchers [8; 9; 10] developed the emerging bounding tuned mass damper (PTMD) technology and explored its application with various materials. Experimental results demonstrate that the single-sided PTMD was a cost-effective method for efficiently and passively mitigating the vibration of suspended piping systems compared with the traditional tuned mass damper (TMD). Passive vibration control has the advantages of a clear damping mechanism, simple structure, no energy input and being easy to implement. However, its control frequency range is narrow, and it can only effectively control high-order vibration frequency [11]. The effect on low-frequency vibration is satisfactory. The control parameters cannot change with the excitation environment effectively, so the passive control effect is limited. Active vibration control of the pipeline generally needs to collect the vibration signal of the pipeline system through the sensors, then transmits the signal to the upper computer and obtains the control signal through a certain control algorithm [12; 13]. In the end, the control signal is applied on the actuation component to control the vibration of the pipeline system. The existing active control methods of pipelines mainly include: (1) controlling the pressure pulsation amplitude inside the pipeline system through active control components.