Investigating the causes of 'silo honking' during discharge

• Main Author: Chavez-Sagarnaga, Jesus
• Published: University of Edinburgh 2005
• Subjects: 620.3
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.642773

An industrial honking silo was extensively instrumented to examine its wall vibration and acoustic response. Spectral analyses acceleration and acoustic pressure measurements show that honking comprises of a fundamental acoustic frequency and a harmonic series of peaks at integer multiples of the fundamental frequency. The results indicate that the sound is generated by the silo walls acting as large speakers and is not due to resonance inside the silo, as in a flute or organ pipe. The above measurements indicate that during honking the silo vibrates in some of its specific natural modes. Finite element (FE) models are used to examine the free vibration characteristics of the instrumented silo and other silos that are known to honk. Both 3D and axisymmetric models are considered. Considerable attention is focused on the latter as excitations that cause honking are expected to by axisymmetric. In addition closed form solutions on vibration characteristics of thin cylindrical shells are discussed. The latter are used to develop an understanding of free vibration characteristics and to validate the FE models. The FE models of the simple cylindrical shell are transformed to a real silo structure by additions such as roof, hopper and thickness variations and the influence of these implementations is examined. It is found that introduction of hopper and the roof introduces additional modes and thickness variation makes a small change to the natural frequencies. Additionally, the influence of the bulk solid stored in the silo is also considered. The analyses indicate that during honking the stored solid is uncoupled from the shell.