Understanding Adaptive Passive Vibration Absorbers and AVC Systems
Adaptive Passive Vibration Absorber (APVA) & Methods: An Adaptive Passive Vibration Absorber is a device that reduces unwanted vibrations in machines or structures. Unlike normal (fixed) passive absorbers, an APVA can adjust its own properties β such as mass, stiffness, or damping β to work effectively even when the vibration frequency changes. It does not require active control or high power, so it is still considered passive, but it can adapt automatically or semi-automatically to new vibration conditions.
π¦ Need for APVA: In real systems, vibration frequencies change with time, load, or speed (for example, in engines, turbines, or rotating machines). A fixed passive absorber is only effective at one frequency. Therefore, an adaptive absorber is used to track and adjust to the new excitation frequency.
Method | Description | Parameter Adjusted |
1. Variable Mass Method | The absorber changes its mass using movable weights or fluids. | Mass (m) |
2. Variable Stiffness Method | Uses mechanical, magnetic, or fluid-based systems to adjust stiffness. | Stiffness (k) |
3. Variable Damping Method | The damping coefficient is changed using smart materials like MR (Magnetorheological) or ER (Electrorheological) fluids. | Damping (c) |
4. Shape or Geometry Change | Adjusting the length, tension, or geometry of the absorber spring or beam. | Natural frequency (Οn) |
5. Temperature-Dependent Control | Uses materials whose stiffness changes with temperature, helping automatic tuning. | Stiffness (k) indirectly |
π₯ Advantages | π§ Applications |
|
|
π© Actuators and Sensors for Active Vibration Control (AVC): Active Vibration Control (AVC) systems use sensors and actuators to detect and counteract vibrations in real time. The basic idea is to measure the vibration, process the signal through a controller, and then use an actuator to produce a counteracting force that cancels or reduces the vibration.
π¦ 1. Sensors in AVC: Sensors are used to measure motion, such as displacement, velocity, or acceleration of the vibrating structure. The sensor converts this motion into an electrical signal that is sent to the controller.
Common types of sensors: Accelerometers β measure acceleration of vibrating structures. Force sensors / transducers β measure dynamic loads or forces. Displacement sensors (LVDTs) β measure small movements.
π¨ 2. Actuators in AVC: Actuators generate a controlled force or motion to reduce vibration based on the command from the controller. They act as the βmusclesβ of the system and directly influence the vibrating structure.
Common types of actuators: Hydraulic pistons β for large force applications (bridges, buildings). Piezoelectric actuators β produce small but very fast movements; suitable for precise control. Electromagnetic shakers β used in lab testing and experimental setups. Electric motors / servos β for mechanical motion control.
π₯ Examples of AVC Applications: Active tendons in bridges (like cable-stayed bridges) β control cable vibrations using sensors and actuators. Active trusses β some bars in a truss are replaced by piezoelectric linear actuators with force sensors to actively control vibration. Piezoelectric beam actuators β thin piezo layers bonded to structures; voltage applied across them induces strain and cancels vibration.
π§ Working Principle of AVC System: The sensor detects the vibration signal. The signal is sent to a controller, which calculates the required control force. The actuator applies this control force to the system in opposite phase to the vibration. The combined effect results in vibration cancellation or reduction.