What is A Tuned Mass Damper?

Dynamic vibration absorbers, also known as tuned mass dampers, are mechanical appendages made up of inertia, stiffness, and damping elements that, when connected to a given structure or machine, referred to as the main system, are capable of absorbing vibratory energy at the connection point. Consequently, excessively high vibration levels may be avoided in the primary system. It's common to incorporate DVAs into initial system designs or implement them into an existing system as part of a corrective action plan. Read on to discover more about Tuned Mass Dumpers!

What Is A Tuned Mass Dumper?

A tuned mass damper (TMD), also known as a "Harmonic absorber or Vibration Absorbers," is a device installed in large structures, such as tall buildings and long bridges, to reduce vibrations caused by external forces. Tuned mass dampers are mainly constructed of large steel bodies mounted against the structure's oscillations in the opposite direction.

Vibrations coming from wind loads are important to dampen structures such as tall buildings and bridges because this ensures that they remain stable. Over the years, mass dampers in bridges and buildings have had a positive impact on keeping those structures safe and reducing the amount of damage they can withstand during harsh weather conditions.

Furthermore, vibrations can also be caused by man-made factors, such as cars crossing a bridge. In addition, TMDs reduce vibrations, resulting in less wear and tear on those structures, which in turn results in less frequent and less expensive maintenance and repairs.

Tuned Mass Dampers are classified into two types: horizontal and vertical. Horizontal TMDs are commonly seen in thin structures, communication towers, spires, and the like. As opposed to the Vertical TMD, they are widely used in horizontal constructions such as bridges, floors, and walkways. Their functions are similar, but there are some minor differences.

How does a Tuned Mass Damper work?

A damper's frequency is adjusted to a specified structural frequency to stabilize against the motion caused by harmonic vibration. A structure's first natural frequency contributes greatly to its dynamic response, which is why a TMD is often tuned to that frequency. When the frequency is stimulated, the damper vibrates out of phase with the structural motion, dissipating the energy. In addition, more intense vibrations are less likely to occur, making the structure more comfortable for occupants while reducing the possibility of material failure.

The efficiency of a TMD is determined by the accuracy of its tuning, its mass ratio, and the amount of internal dampening built into the TMD. If damping is too difficult or expensive, a TMD, like those found in crankshaft torsional dampers, can be used to provide damping to a resonance.

Other techniques of reducing vibration, such as increasing rigidity or an immobile mass, or modifying the form of the structure, are usually expensive and ineffective.

Overall, the system works by matching the TMD frequency to the inherent frequency of the structure itself. So, if the structure, for instance, has a frequency of 0.2 Hz, then the TMD must be tuned to the same frequency, or at least very close to it. This will make the TMD effective and conform to the structure; likewise, it will diminish acceleration more effectively. In order for a structure to function correctly, the Tuned Mass Dumpers’ frequency should match the structure itself; otherwise, the structure may not be serviceable when it's higher, or it might produce detrimental effects when it's lower.

Tuned Mass Damper Applications:

The following applications are commonly associated with tuned mass dampers:

buildings/skyscrapers: It is a common occurrence for tall and slender free-standing structures to be generated dangerously in one of their mode shapes by the wind.
Steel structures: A factory floor, for instance, can generate natural frequencies through machines like screens, centrifuges, fans, etc.
Bridges: There are various sources of vibration that may cause unwanted movements and damage to a bridge, including wind, waves, and earthquakes. The Tuned Mass Damper prevents these movements by oscillating bridges in the opposite direction. The result is a bridge that is safer for pedestrians and vehicles.
Ships: The main engines or even ship motion might cause them to leave in one of their natural frequencies.

Generally, tuning mass dampers are either already included in an original structure's design, or can be included later.

Tuned Mass Dumper Types:

There are two types of vibration absorbers: passive and active vibration absorbers.

Passive vibration absorbers:

There are various passive methods, including material damping, viscoelastic dampers, frictional dampers, and vibration absorbers. Passive devices are characterized by simple and inexpensive construction. They ensure that the control system is always stable since the control is conducted by energy dissipation and/or redistribution without required extra power input. However, because they generate set designs, such systems may be inefficient or even ineffective when the system or operational conditions change. Furthermore, these schemes typically operate well in the high-frequency region or within a restricted frequency range but often function poorly at low frequencies.

Through the use of a secondary input, a desired dynamic response pattern can be modified in the system, thereby controlling vibration. Active systems tend to be better than passive methods, but they have some disadvantages, including complicated and expensive construction, instability by system model errors, and being sensitive to uncertainties.

Active Vibration absorbers:

Active damping can be described as an increase in the damping of vibration modes. Due to its wide bandwidth, an active damping system typically limits actuator dynamics. Tuned vibration absorbers can only attenuate single-frequency vibrations. With a tuned absorber, the frequency of the structure matches the resonance frequency, and mechanical vibration is absorbed as well. Active vibration dampening systems, unlike passive systems, may be set to reduce resonances, allowing them to function at lower frequencies induced by structural resonances. Furthermore, they can provide dampening for vibrations and interference from equipment such as cabling noise or acoustic noise.

When selecting passive or active vibration damping systems, it is important to consider how sensitive the machine or process is to vibrations. For example, vibrations are more damaging to test and measurement equipment than industrial production machinery, as well as the kinds of vibrations that may occur.

Conclusion:

Over the past few years, tuned mass dampers (TMDs) have been widely used to mitigate structural vibration. The system is a simple yet effective mechanism that can provide significant benefits for both the occupant and the owner of a building. It's all about choosing a company that is certified and can provide you with the best dynamic solutions.