Motivated by the work of nelson and olsson and by dunn, we decided to further investigate the effect of string on damping of a simple pendulum. Pdf friction is a dissipative process, in which mechanical energy is transformed into heat. We anticipate and quantify the anisotropy in the damping behavior with respect to curvature. Cyclic plastic strain energy and fatigue of metals. The conversion of the mechanical vibrational energy of solids into heat energy by causing one dry member to slide on another explanation of friction damping. This damping is crucial to the operation of foil bearings, but is really not that well understood. In this type of damping a light vane or vanes having considerable area is attached to the moving system to develop a frictional force opposing the motion by reason of the air they displace. Because the sign of the damping force is always opposite to that of the velocity, the differential equation of. The friction generated by the relative motion of the two surfaces that press. Seismic dampers friction dampers quaketek earthquake. Influence of damping systems on building structures subject to seismic effects journal of engineering structures 26, november 2004, 19391956. The available friction force is sufficient to prevent motion between the contact points.
Friction dampers typically are more suitable for longer cables and those with more demanding damping requirements. Friction dampers from suspa are suitable for damping impacts and vibrations. The decay of oscillatory motion with viscous plus coulomb friction damping, displacement dark blue, velocity 0, red dot dashed, and acceleration 2 0 green double dot dashed. The damping ratio is a system parameter, denoted by. The relaxation damping solution gives a good measure of the energy dissipation, but cannot say how much of it goes in these three mechanisms friction, plasticity or waves without a more sophisticated treatment. The exact coincidence of the frictional damping in a true threedimensional contact and its onedimensional representation in the framework of the method of dimensionality reduction follows from general theorems concerning tangential contacts. In simplest terms, hysteretic damping is the energy lost in materials due to friction between molecules, and is related to displacements during vibration. The action is the same as in the air friction damping. Damping of a simple pendulum due to drag on its string.
There is a wide range of physical phenomena that cause friction, this includes elastic and plastic deformations. What is the difference between friction and damping in a. The influence of friction induced damping and nonlinear effects on brake squeal analysis andrzej bajer and vladimir belsky abaqus, inc. The motion of the moving system is always opposed by the friction of the damping oil on the vanes. This question is actually one of the lab exercises i teach. Apr 15, 2017 practical demonstration of air friction damping in moving iron instruments.
The damping torque is produced by the following methods. When the parts slide over each other, they create friction which uses some of the energy from the earthquake that goes into the building. One of the modeling difficulties with foil bearings is the friction damping in the compliant support structure. There are many types of dampers for buildings, and damping through friction tends to be one of the most efficient methods of dissipating seismic energy. Friction damping article about friction damping by the free. The tail drive shaft is modeled as a beam by using eulerbernoulli beam theory. This paper surveys the literature on the use of dry friction in passive damping and vibration isolation. The vanes are dipped into a pot of damping oil and are completely submerged by the oil.
However, if there is some from of friction, then the amplitude will decrease as a function of time g t a0 a0 x if the damping is sliding friction, fsf constant, then the work done by the. Oct 22, 2017 mechanical damping is, generally defined, as the measure or way a system has to dissipate vibration energy, in the forms of sound and heat by generated friction. Frequency domain identification of dynamic friction model parameters. The cable damping is assessed from free decay curves logarithmic decrement method 37, 38. D f dy, 1 then the specific damping coefficient is. This form is damping is similar to air friction damping. Here light vanes are attached to the spindle of the moving system. All friction dampers developed by suspa are designed for the respective product application so that an optimal movement sequence or optimal vibration behavior is achieved. The friction damper is based on rotational friction concept. This paper deals with the numerical model of a bracing friction damper system and its deployment using the optimal slip load distribution for the seismic retrofitting of a damaged building. The free vibration of dynamic systems with viscous damping is characterized by an exponential decay of the oscillation, whereas systems with coulomb damping possess a linear decay of oscillation. At nonlinear damping the hysteresis loop is peaked when damping is a result of friction figure 1b one possibility to quantify the level of damping is to determine the area captured within the hysteresis loop. Influence of damping systems on building structures subject to seismic effects ii publications international refereed journal papers. The friction produced at these contact interfaces, by sliding or slipping at the interface, is a source of energy dissipation, resulting in damping.
Pdf design of a bracingfriction damper system for seismic. Introduction service failures of gasturbine blades can be attributed in many cases to high cycle fatigue caused by large resonant stresses. The friction generated by the relative motion of the two surfaces that press against each other is a source of energy dissipation. The vane attached to the spindle is arranged to move in the damping oil. Martinez analysis of structural damping abstract one important parameter in the study of dynamic systems is material damping. In order to limit resonance vibrations of the tail drive shaft, dry friction dampers can be used.
Modeling and analysis of the dynamics of dryfrictiondamped. Damping estimation from free decay responses of cables with. Damping studies in materials science and materials engineering. This form of damping is observed to not increase with frequency, so instead of a viscous damping force. The exact coincidence of the frictional damping in a true threedimensional contact and its one. The damping ratio is a measure describing how rapidly the oscillations decay from one bounce to the next. While as structural damping caused by contact or impacts at joins, energy. Coulomb plus viscous friction serves as a simplified model. The advantage of these equations is that the relation between friction force ratio or friction force and equivalent damping ratio is derived analytically.
The coulomb friction model is as a rule used to describe energy dissipation caused by rubbing friction. Influence of damping systems on building structures subject. Since the hysteretic loop of the friction dampers is perfectly rectangular, similar to perfectly elastoplastic material, the friction dampers can be modeled as fictitious plasticity element having yield force equal to slip load. This patented device was developed by damptech in technical university of denmark.
Pdf a friction damping system imad mualla academia. Several analytical techniques are presented followed by applications from various areas. Physics 106 lecture 12 oscillations ii sj 7th ed chap 15. The influence of frictioninduced damping and nonlinear. If both yield stress and friction coefficient are finite, then there will be some dissipation in friction and some in plasticity. The identification procedure for the dynamic model parameters, i. Seismic dampers are used in damping the oscillations of a building during an earthquake. We also find that unlike static pure bending where friction increases bending stiffness. Mineral oil is used in place of air and as the viscosity of oil is greater, the damping force is also much greater. Hysteretic damping 3 for example, structural or hysteretic damping is a type of dissipation that is a function of friction within a material. Simple design procedure of a friction damper for reducing. For a springmass system, if the damping force is friction, then it is independent of velocity verified experimentally. This article examines the features of two vibration damping systems and factors to consider when choosing a damping system in the design of a cablestayed bridge. The force of dry friction is studied extensively in introductory physics but its effect on oscillations is hardly ever mentioned.
Therefore, in order to study the effect of dry friction damping on the response of tail drive shaft, a mathematical model is developed. Aug 20, 2014 for the investigation of damping caused by dry friction, a dynamic tangential contact is of interest. The damping caused by the friction between the internal planes that slip or slide as the material deforms is called hysteresis or solid or structural damping. Dry friction damping structures have been widely used in the structural design of the blade to decrease the vibration stress effectively, such as friction dampers, snubbers, lacing wire, and shrouds. For a given force and displacement in a damper, the energy dissipation of friction damper is the largest compared to other damping devices figure 6.
Once active, they protect the cable by providing damping across all. The motion of the system can be decaying oscillations if the damping is weak. However, as mentioned in the comments, the damping force may not always be friction. Modeling technique of material damping properties in ansys. Stp378 internal friction, damping, and cyclic plasticity. Coulombs law of sliding friction is modified by assuming that the coefficient of friction involves the energy of oscillation in a power law. Friction was studied extensively in classical mechanical engineering and. Macromechanisms of damping in composite structures. Sep 01, 20 vibration with hysteretic damping experiments on the damping that occurs in solid materials and structures that have been subjected to cyclic stressing have shown the damping force to be independent of frequency internal, or material, damping is referred to as hysteretic damping. Mechanical vibration systems with viscous and coulomb friction are of importance in the applications of dynamics and control problems. In order to make full use of the controllability of mr dampers, the damping force must be shaped by a superimposed negative stiffness force which is obtained from the clipped optimal control approach 2631, from amplitude proportional friction damping with negative stiffness or clipped viscous damping with negative stiffness 33, 34. Micromechanisms and phenomenology of damping in polymers. So there are different kinds of damping on simple harmonic oscillators, but the most common type is a force linearly proportional to velocity acting in the direction opposite to the direction of motion of the oscillator. The computer modeling of pall friction dampers is very easy.