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I want to compute the effect of road surface absorbing coefficients on the tire /road noise,but i donot know how to add this boundary condition to the BEM model in code SYSNOISE.Can someone help me?

if the driving force exerts at a point belong to the structural nodal lines,what value should the sound radiation efficiency at this modal frequency be? that is, is it possibly negative?thanks!

Thanks!At some frequencies, some parts of a structure absorbe energy and others emit energy,but we know the sound radiation efficiency is always positive. are there anybody who are familiar with sysnoise and tell me the method to solve this problem?thank you very much!

when i use BEM in sysnoise(rev5.6) to compute the sound radiation efficiency of a cylindrical shell with two end plates in water, i found the efficiencies at several frequencies are negative. can anybbody help me to explain it.thanks!

thank you for your reply, Greg Locock.From some information i got recently,i know the sigma for steel is about 0.03.So i use 0.03 for aluminium in my computation.Can you tell me where(books or websites) i can find the value for aluminium.Thanks!

when considering structural loss in vibration problems, young's modulus E is a complex,E=E1(1+i*sigma).I want to know the value of sigma for aluminium.who can help me? Thanks!