Damping of Vibrations

Z. Osinski, Z. Osinski

• Publisher: CRC Press
• Year: 2018
• ISBN:
  9781351456678
• Edition: 1
• Topic: Technik & Maschinenbau
• Subtopic: Bauingenieurwesen

This monograph seeks to strengthen the contributions of Polish scientists and engineers to the study of problems of mechanical vibrations and noise. It presents research covering such topics as: structural damping; internal damping in composite materials; and noise attenuation in working machines.

CHAPTER 1

Vibration damping – basic concepts

1.1 INTRODUCTION

Vibration damping is one of the manifestations of the dissipation of mechanical energy related to motion in mechanical systems. Damping processes have been studied for a long time. The development of research on problems related to vibration entails studying its damping. Admittedly, those studies lag behind other aspects of the investigation of vibrating motion. It so happens that damping forces are small compared to other interactions present in a mechanical system, yet their mathematical description remains much more complicated. Therefore, as a first approximation those forces are neglected. As a next step viscous linear damping is introduced which makes the analysis of the vibration process easier. Actually, any process responsible for the occurrence of damping is very intricate and the knowledge of it is insufficient. At the same time the role of damping is significant, though not always fully appreciated. Machine elements undergoing vibration can suffer from some harmful phenomena which will be given in the following list:

1. Disturbances in the proper working of a machine. Excessive vibration can lead to the faulty performance of a machine or device. Heavy machinery can serve here as an example of such a situation. We observe severe vibration in crane-like machines, such as building and assembly cranes used for fitting up elements of buildings, ships, etc. Vibration of a crane jib or a line can cause undesirable motion of an element while being mounted, thus making it difficult and letting it take too long to fit it. Similar problems can appear in mine hoists where the vibration of a cage hinders bringing it to a fast standstill on the proper level. In machine tools vibration is responsible for a poor surface roughness. Vibration of plane panels and steering elements can affect the ability to control an airplane. Vibration of cable railway cars can result in failures, seizure of elements or any other symptoms of improper performance. Valve vibration can cause leaking. Vibration contributes to the disconnection of screws or tightening joints.

2. Shortening of the fatigue life of a machine. Vibrating motion is the main cause for the appearance of variable stresses in machine elements. This can lead to damage of fatigue character. Especially sensitive to such a kind of failure are the elements in which the stress tends to concentrate. The following machine elements, for example, are often exposed to fatigue cracking: shafts, bearings, rotor blades, welds. Damage of thin-walled elements, especially car bodies and fuselages of airplanes, also poses an example of the harmful influence of vibration. Naturally, all the elements used for working in vibrating motion, such as suspension springs, exhibit accelerated wear symptoms.

Vibration can indirectly lead to wear of other important machine elements. For instance, the transverse motion of rotating shafts implies a non-uniform pressure distribution between the teeth in gears. The same effect causes the fast wear of slide and rolling bearings. Vibration causes wear of fle...