Active Control of Gear Mesh Induced Vibration

Gearboxes are typically sources of vibration, either because they are in the transmission path from the engine to the structure so they transmit vibration coming from the engine or they transmit their own vibration at the gear mesh frequency and its corresponding side-bands. The latter can be heard as a whining noise coming from the gears. The level of whining noise can be exacerbated if the gear mesh frequency matches one of the natural frequencies of any of the components or subsystems in the transmission path. In vehicular applications, rear axle gear whine noise is caused mainly by the gear mesh vibration in the powertrain. This vibration is in turn transmitted thru the rear axle gear housing, the corresponding sub-frame, as well as other support structures to the vehicle cabin as an unpleasant tonal noise dubbed gear whine.

Active vibration control, using proof mass actuation of the rear sub-frame was used to mitigate gear mesh vibration in an all-wheel drive test vehicle exhibiting whine noise at around 450 Hz. Proof mass actuators (PMAs) generate force by pushing against a suspended mass and thus do not need an anchor point.

The effectiveness of active control in absorbing the shaker induced vibration of rear sub-frame of a test car was successfully demonstrated by examining the extent of reduction in the vibration of the rear sub-frame as well as the sound pressure inside the vehicle. Two electromagnetic proof mass actuators, mounted on the rear sub-frame of the vehicle, were used as the active elements. An accelerometer placed next to each actuator was used as the feedback sensor. Moreover, rolling dynamometer tests showed the effectiveness of active control in substantial reduction in vibration of the rear sub-frame and pressure inside the cabin caused by the rear differential gear mesh. More

Posted in Uncategorized

Paper on Floor Vibration Control in the The Structural Engineer

Wide column spans along with the use of high strength material make modern floor systems flexible and oscillatory. Walking (as well as other human activities) can induce high levels of vibration in such floors. When the traditional floor vibration control solutions, such as adding architectural features, mass, and/or stiffness to the floor are either not practical or ineffective, reactive damping provided by tuned mass dampers (TMDs) are used for quieting vibrating floors. High level of effectiveness, negligible weight penalty and ease of installation make TMDs a cost-effective and non-intrusive vibration control solution for both new and existing floors. In addition contrary to the damping that can be provided by non-structural elements such as partitions, raised floors and paneling which is not readily quantifiable and may not be an option for a space in which a light fitout is required, tuned mass dampers provide predictable damping and can easily be retrofitted. The installation of TMDs on existing floors is the least disruptive (to the occupants) of any floor vibration control solution <\p>

The Structural Engineer Vol94 article on floor vibration control

The paper titled “Vibration abatement of rectangular, trapezoidal and irregular-shaped joist-framed floors, using tuned mass dampers” on mitigating floor vibration has recently been published in “The Structural Engineer”, the flagship publication of The Institution of Structural Engineers. The subject of the paper is about one of the DEICON’s projects on mitigating floor vibration using tuned mass dampers. The citation for the paper is:
Kashani, R., 2015 “Vibration Abatement of Rectangular, Trapezoidal, and Irregular-Shaped J oist Framed Floors, Using Tuned Mass Dampers” The Institution of the Structural Engineers The Structural Engineer Journal, Volume 94, Issue 1, (2016).

Posted in Uncategorized

Numerical Analysis and Tuned Damping of a Floor System

In order to design and specify vibration abatement solutions (via tuned damping) for a multi-bay floor system, a reasonably accurate knowledge of the dynamic attributes of that floor system is required. These can be evaluated numerically (using finite element analysis) and verified experimentally by vibration measurement. Finite element modal analysis allows for the prediction of the natural frequencies, their corresponding mode shapes and modal masses. Vibration measurement enables the finite element model to be fine-tuned and the inherent level of damping in the structure measured. The correlated model can then be used to design tuned mass dampers for the floor system.

floor vibration 1 DEICON recently completed the modeling and analysis of a 16-bay dance floor, with some irregularities in its geometry. As in most floor systems, the vibratory motion of a mode was not just confined to a single bay. For example, the first mode shown in Figure has the shape of a spatial sinusoidal wave vibrating the two adjacent bays an out of phase manner, i.e. as one bay is moving up the other is moving down. The outcomes of the analyses are being used in designing 10 tuned mass dampers (TMDs) for the floor system.

Posted in Uncategorized

Vibration Control of an Office Floor System Using Tuned Mass Dampers

installed tuned mass damperFollowing the occupants’ (office workers’) complaints about the floor vibration at a certain area in an office building, vibration measurements were conducted by an acoustics consulting firm, the results of which indicated that the floor system was lightly damped and that the vibration associated with occupant activities (mainly walking) was exacerbated by resonant amplification of the first mode of the floor system. Based on the consultants opinion, improvements in the perception of floor vibration could be achieved by installing tuned mass dampers.

DEICON designed and fabricated tuned mass dampers (TMDs) to abate the vibration of the composite steel beam and girder framed floor system. The TMDs were tuned to the first natural frequency of the structure (floor system). The tuned mass dampers added substantial damping to the floor system, lowering its vibration level to an imperceptible level. More

Posted in Uncategorized

Publication on Tuned Damping of a Balcony System

Cantilevered structures, such as balconies, when subject to human activity such as walking and jumping, can be susceptible to levels of vibration that may be deemed annoying by some users. If the structure is an irregular shape, the affected areas can often be fairly localized, with the rest of the space performing appropriately. Traditional approaches to controlling vibration include stiffening the structure and adding mass. However, in many cases, architectural, structural or cost constraints mean that these are not acceptable solutions, particularly where wholesale design changes would be required to achieve the desired effect in the localized area being considered. Adding damping to the structure, using tuned mass dampers, is a very effective way of controlling vibration. By increasing the amount of energy that is dissipated when the structure oscillates, excessive build-up is avoided. <\p>

ASCE Journal Vol28 article on balcony vibration control

The paper titled “Tuned Damping of Balcony Vibration” on abating the vibration of a balcony system in a performing arts center has recently been published in “Journal of Performance of Constructed Facilities”, a publication of The American Society of Civil Engineers. The subject of the paper is about a collaborative project between ARUP of New York and DEICON on mitigating the vibration in a stack of three balconies using tuned mass dampers. The citation for the paper is:
Kashani, R., Pearce, A., and Markham, B., 2014 “Tuned Damping of Balcony Vibration,” ASCE Journal of Performance of Constructed Facilities, Volume 28, Issue 3 (2014). More

Posted in Uncategorized