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Influence of support viscoelastic properties on the structural wave propagation
Junhong Park 대한기계학회 2007 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.21 No.12
The dissipation of the structural vibration energy at viscoelastic supports is an efficient method of reducing modal resonances and consequent noise and fatigue related problems. The support stiffness has significant impact on the modal characteristics. The dissipation capabilities of the viscoelastic support depend on its stiffness. Methods to optimally tune this support stiffness are proposed in this study. The characteristic mechanical impedance for structural vibration is obtained from wave propagation analysis and non-reflecting boundary conditions. The wave propagation is analyzed near the supports installed at edges, middle of a structure, and for the tuned vibration absorber. The dependence of the optimal stiffness on the location and mass of the supports is identified. A simple analytical solution for optimal support stiffness for maximum dissipation of propagating vibration energy at supports is presented.
Park, Hyun Ju,Park, Young-Kwon,Dong, Jong-In,Kim, Joo-Sik,Jeon, Jong-Ki,Kim, Seung-Soo,Kim, Jinsoo,Song, Byungho,Park, Junhong,Lee, Kyung-Jin Elsevier 2009 Fuel processing technology Vol.90 No.2
<P><B>Abstract</B></P><P>The kinetic parameters for the pyrolysis of Oriental white oak were evaluated by thermogravimetric analysis (TGA). The white oak was pyrolyzed in a fluidized bed reactor with a two-staged char separation system under a variety of operating conditions. The influence of the pyrolysis conditions on the chemical and physical characteristics of the bio-oil was also examined. TGA showed that the Oriental white oak decomposed at temperatures ranging from 250 to 400?°C. The apparent activation energy ranged from 160 to 777?kJ mol<SUP>−1</SUP>. The optimal pyrolysis temperature for the production of bio-oil in the fluidized bed unit was between 400 and 450?°C. A much smaller and larger feed size adversely affected the production of bio-oil. A higher fluidizing gas flow and higher biomass feeding rate were more effective in the production of bio-oil but the above flow rates did not affect the bio-oil yields significantly. Recycling a part of the product gas as a fluidizing medium resulted the highest bio-oil yield of 60?wt.%. In addition, high-quality bio-oil with a low solid content was produced using a hot filter as well as a cyclone. With exception of the pyrolysis temperature, the other pyrolysis conditions did not significantly affect the chemical and physical characteristics of the resulting bio-oil.</P>
Sensing of fluid viscoelasticity from piezoelectric actuation of cantilever flexural vibration
Park, Jeongwon,Jeong, Seongbin,Kim, Seung Joon,Park, Junhong American Institute of Physics 2015 Review of scientific instruments Vol.86 No.1
<P>An experimental method is proposed to measure the rheological properties of fluids. The effects of fluids on the vibration actuated by piezoelectric patches were analyzed and used in measuring viscoelastic properties. Fluid-structure interactions induced changes in the beam vibration properties and frequency-dependent variations of the complex wavenumber of the beam structure were used in monitoring these changes. To account for the effects of fluid-structure interaction, fluids were modelled as a simple viscoelastic support at one end of the beam. The measured properties were the fluid's dynamic shear modulus and loss tangent. Using the proposed method, the rheological properties of various non-Newtonian fluids were measured. The frequency range for which reliable viscoelasticity results could be obtained was 10-400 Hz. Viscosity standard fluids were tested to verify the accuracy of the proposed method, and the results agreed well with the manufacturer's reported values. The simple proposed laboratory setup for measurements was flexible so that the frequency ranges of data acquisition were adjustable by changing the beam's mechanical properties.</P>