damping structure
Friday, January 11, 2019 4:27:14 PM
Stuart

Thus causing the damping to be large. Unfortunately, our editorial approach may not be able to accommodate all contributions. I have seen a book which defines equivalent viscous damping ratios for structural damping that can be added to the material damping and then used in the Rayleigh damping model. Global definition does not arise. Most of this energy transformation occurs at the micro level that arises from the thermal effect of repeated elastic straining of the material and from the internal friction when a solid is deformed.

Material Loss Factor, η Aluminum 0. It's not mathematically possibility for it to be constant over all frequencies because that would violate the , but it can be and often is constant over many orders of magnitude if it rolls off at both ends. Shock absorbers in automobiles and carpet pads are examples of damping devices. In an actual structure consisting of many elements how can you distinguish between the contributions from material and structural damping as the structure vibrates? Then α and β can be determined by measuring D at two frequencies and solving 2 equations with two unknowns. The key difference between critical damping and overdamping is that, in critical damping, the system returns to equilibrium in the minimum amount of time. This will put us back to square one where a specific damping ratio 'eta' coming from material damping and another one from the structural damping.

Internal Losses in the Material All real materials will dissipate some energy when strained. Additional damping causes the system to be overdamped, which may be desirable, as in some door closers. Then run multiple analyses to see if it works anyhow, You might want to ignore it, but I suspect it will be difficult to duck. Such components obviously have a large influence on the total damping in a structure, at least with respect to some vibration modes. If the joined surfaces are sliding relative to each other during the vibration, the energy is dissipated through friction. This corresponds with the level of damping that the response becomes non-oscillatory. Usually, however, there are gradients in the stress field with associated gradients in the temperature distribution.

There is the theory which you describe here, the computational aspects which you will cover I guess in your next blog post, and there is also the experimental determination of the damping constants. In my opinion, damping models, at best, are approximate. Fig-19 Displacement Amplitude y plotted against Time t for a System undergoing Free Vibration. That is why effect of both components are lumped together and classified as structural damping. In a world without damping, the tone would linger forever.

Some experimental results demonstrate that damping ratio for reinforced concrete structures are normally less than 5% in normal conditions. Already a two dof system has unexpected solutions of dynamic damping where one mass don't move. Comparison of dynamic response for viscous damping solid lines and loss factor damping dashed lines. By increasing the effective damping of the structure, we can alter the response of the structure without significantly changing the natural frequency of the structure. Fundamentally, this is a reversible process, so the temperature will return to the original value if the stress is released.

Viscous damping is caused by such energy losses as occur in liquid lubrication between moving parts or in a fluid forced through a small opening by a piston, as in automobile shock absorbers. The loss factor concept can be generalized by defining the loss factor in terms of energy. In this blog post, we will discuss how damping can be represented, and the physical phenomena that cause damping in vibrating structures. In magnetic damping, energy of motion is converted to heat by way of electric eddy currents induced in either a coil or an aluminum plate attached to the oscillating object that passes between the poles of a magnet. Another measure in use is the logarithmic decrement, δ. What I actually meant was that there is a specific damping ratio 'eta' coming from 1 material damping and 2 structural damping. Firstly, the contact characteristic between a single ball and groove is analyzed, and the relative contact stiffness of single ball is determined under different preload levels.

A reliablesimulation model is helpfulto calibrate the apparatus as well as the backcalculation programs. I can send you my model. But, we all know this from riding the swing when we were small. In this sense, the friction is similar to internal losses in the material. It is of the utmost importance to reduce the vibration levels in buildings if hit by an earthquake. The damping ratio provides a mathematical means of expressing the level of damping in a system relative to critical damping.

The signal to which the receiver is tuned supplies energy synchronously to maintain. For a problem in which the system is represented by discrete masses the mass matrix is diagonal so that the damping matrix is also diagonal and the solution is considerably simplified 8 Finally, in your problem it is best to obtain an approximate solution using Raleigh proportional damping before an attempt is made with non Raleigh damping. This case is called overdamped. As for a typical value, 5% is correct for concrete structures, being lower for steel structures. It is possible to back out the effects of the window and get the actual damping value.