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Motor Vibration and Acoustic Noise
Published in Wei Tong, Mechanical Design and Manufacturing of Electric Motors, 2022
Damping is a measure of an ability of a vibrating system to dissipate mechanical vibratory energy so that the amplitude and duration of vibration can be effectively reduced. In other words, damping creates a force that acts in the opposite direction to the object travel. It can be broadly classified into two categories: passive and active damping. Passive damping can be achieved by using mechanical properties of damping materials and/or by designing vibration-absorbing structures. In active damping, an actuator is used to generate force opposing the motion, regardless of the relative velocity across it [12.11]. Active damping employs sophisticated closed-loop control techniques to minimize the effect of vibration. The active controllers continuously regulate the damping characteristics and require measurements of response and feedback from the vibrating system.
Viscoelastic and Dynamic Behavior of Composites
Published in Sumit Sharma, Composite Materials, 2021
Damping is simply the dissipation of energy during dynamic deformation. As structures and machines are pushed to higher and higher levels of precision and performance, and as the control of noise and vibration becomes more of a societal concern, it is becoming essential to take damping into account in the design process. In conventional metallic structures, it is commonly accepted that much of the damping comes from friction in structural joints or from add-on surface damping treatments because the damping in the metal itself is typically very low. On the other hand, polymer composites have generated increased interest in the development of highly damped, lightweight, structural composites because of their good damping characteristics and the inherent design flexibility that allows trade-offs between such properties as damping and stiffness. The purpose of this section is to give a brief overview of the analysis of linear viscoelastic damping in composites.
Vibration and damping, sandwich structures
Published in József Farkas, Károly Jármai, Analysis and Optimum Design of Metal Structures, 2020
Structural damping means the capacity of a structure or structural component to dissipate a part of vibration energy. This removed energy may be converted directly into heat and transferred to connected structures and to the air. Damping has effect in controlling the amplitude of resonant vibrations, but also has other effects, such as reducing structural fatigue, and increasing structural life.
Seismic Earth Pressure Due to Rayleigh Waves in Viscoelastic Media
Published in Journal of Earthquake Engineering, 2022
When a seismic wave propagating through a medium, attenuation of wave amplitude may occur owing to different mechanisms, typically geometrical damping (radiation damping) and material damping (where the material is not linear elastic). Radiation damping occurs due to the spread of stress waves over an unbounded soil medium, resulting in a decrease in the density of energy or intensity of motion. Material damping is induced by non-elastic relative movement between soil particles, which converts part of the elastic energy to heat (or energy dissipation) accompanied by decreasing in the amplitude of the stress waves. This energy dissipation mechanism is known as hysteretic damping. As mentioned earlier, material damping is accounted for by introducing the correspondence principle, but radiation damping is neglected. Therefore, the damped version of Eq. (1) can be written as
Surge and heave hydrodynamic coefficients for a combination of a porous and a rigid cylinder in motion in finite ocean depth
Published in Waves in Random and Complex Media, 2021
Abhijit Sarkar, Swaroop Nandan Bora
Solving radiation problems for ocean waves yields the important hydrodynamic coefficients, namely, added mass and damping coefficients. These coefficients arise as the real and imaginary parts of the hydrodynamic reaction loads on the body due to the prescribed body motions. In physical sense, the added mass is the weight added to a system in a fluid due to the fact that an accelerating or decelerating body must move some volume of surrounding fluid with it as it moves. Damping is an influence within or upon an oscillatory system that has the effect of reducing, restricting or preventing its oscillations. The hydrodynamic forces in the x- and z-directions (i.e. for surge and heave motions) due to the motion of the cylinder in modes m = 1, 2 can be found out by integrating the corresponding pressure over the cylinder. For this configuration, only surge motion is considered. The following explains why heave motion is not considered for this problem:
Attenuation of micro-vibrations by varying the resonance extremity of a transitional composite structure
Published in Mechanics of Advanced Materials and Structures, 2021
Shanker Ganesh Krishnamoorthy, Inga Skiedraite
Equations (5) and (6) affirm the change in stiffness of active layers of the composite beam when their terminals are electrically shunted. However, for an initial interpretation of the design of a composite strut that bolsters the conceptual mechanical design noted in Figure 2, it is essential to evaluate the frequency response function of the composite strut. Therefore, an understanding of the characteristics of solid damping is vital. Structural damping occurs due to internal energy dissipation within the material of the vibrating body, which changes alongside the stiffness of the structure. Here, the frequency response function of the composite brace is dependent on the excitation voltage applied to the piezo layers, as the stiffness of the system changes.