wind farm at sunset

Plant Noise v Environmental Noise
Heavy Rotating Machinery
Flow Induced Vibration
Vortex Shedding

Flow-Induced Vibration

Reference is made on our forensics page to a catastrophic event affecting the recuperator stage of a large thermal oxidizer in Kentucky. It reports resonant failure under flow induced vibration, arising from an oscillating force acting outside the tubes and causing natural resonance under the prevailing gas-side conditions. The force was generated by vorrtex-shedding into the von Karman vortex street at a coincident forcing frequency, demonstrated by calculation of the Strouhal Number for the array. It was a classic FMEA investigation into the failure of 30% of the 6,000 installed tubes over a 12-hour period.

Solid State Balancing

Dove Thermal Engineering has innovated a compact and low-cost reactive mass balancing system for heavy rotating machinery that eliminates machine vibration and reduces plant noise from centrifuging dryers - in which mass and load distribution varies with run time. In contrast to the intricacies of conventional electro-mechanical systems that partially limit out-of-balance forces, the only moving part in its detection stage is the core of an LVDT (Linear Variable Differential Transformer). This gauges micron-scale displacements between shaft and foundation ring and signals to a modular PLC.

A set of three equi-spaced radial water pockets let into the rear of the load drum distribute a fixed mass of water between them by means of solenoid-operated valves, continuously resolving dynamic balance and zeroing eccentric forces within the system. Engineers of a certain age will appreciate the entire set-up being built as a working Meccano model before translation onto full-size machines. It employed a dry ballasting arrangement which we later developed for use in other types of rotating equipment where mutually variable masses and their distribution give rise to noise and vibration issues.

Passive Attenuation

In schemes to reduce transmissions of environmental and plant noise, passive arrangements can be an effective means of machine vibration noise control - either at source, or at the building limits. Whilst no substitute for good machine design, maintenance and operation, compliant mountings offer low cost attenuation across the offending frequency range.

Boundary Emissions

Various classes of plant must be rigidly connected to massive embedded or floating foundations to counteract cyclically shifting forces. For example, to overcome problems of boundary plant noise emission from heavy, low speed rotating equipment at a Leicester dyeworks, we designed a set of architectural acoustic doors with compliantly-mounted internal leaves tuned to absorb plant noise at prevailing frequencies and harmonics. The company had been issued with a Prohibition Order limiting hours of operation to uneconomic levels, whilst frequent street access was required. The replacement doors had a leaf area of around 10 sq.m, and gave SRI values of 27, 40, 55 and 73 dB at 63, 125, 250 and 500 Hz respectively. The Order was lifted and 12-hour working could be resumed.

It was one of many projects within the UK dyeing industry dealing with machine vibration noise control, effluent handling, fabric processing, steam raising and other manufacturing services requirements. Beyond this, we have undertaken environmental noise surveys to BS4142 in support of planning applications, public inquiries and factory development programmes.

Dove Thermal Engineering Limited, Uttoxeter, ST14 8QX

Telephone: 01889 569933