我用SYSNOISE5.6的IBEM算一个薄壁开口箱子的在给定速度边界条件下的声辐射功率,在某些频率下出现了负的功率(注意不是DB),不知道是什么原因。如果是闭口的盒子,同样也有这个问题,这可能是非唯一性和奇异性造成的。但开口的结构应该不存在奇异性问题啊。有老各位解答,这个问题困扰我很久了。
New Name 'IBEM' Model 1 File IBEM.sdb Return
Option BEM Indirect Variational Uncoupled ubbaffled Frequency Return
Import Mesh Format Free File PLATE_MESH.fre Return
Set Name "Envelope" Envelope Return
Boundary Jump Pressure Real 0 Imag 0 Return
Material Fluid
Name 'air'
Sound Real 3.4000e+002 Rho Real 1.2250e+000
Return
Save Return
Point 0.3 0.2 0 Return
Point 0.3 0.2 10 Return
Point 2 0 0 Return
Point 0.15 0.5 0.5 Return
Generate
Element all
From Displacements File PLATE_DIS.fre Format Free
Load 1
Return
Parameter Model 1
PADE
Save Potentials Step 1
Save Results Step 1
Store Results none
Return
Near 2
Far 5
Quadrature 2 2 1
Positive
Return
Solve
Frequency 20 To 500 LinStep 20
Return
Store
Case Active
Results
Frequency 20 To 500 LinStep 20
Points 1 To 4 Step 1
Return
Return
Curve
Power Output
Format 5
NoBackground
Marker 0
Return
Return
Return