*parameter
neig=60
**set neig=189 to obtain the results in the manuals 
**------------------------------------------------
*Node
1, 15, 25, 0
2, 15, 20, 0
3, 15, 15, 0
4, 15, 10, 0
5, 15, 5, 0
6, 15, 0, 0
7, 15, -5, 0
8, 15, -10, 0
9, 15, -15, 0
10, 15, -20, 0
11, 15, -25, 0
12, 20, 25, 0
13, 20, 20, 0
14, 20, 15, 0
15, 20, 10, 0
16, 20, 5, 0
17, 20, 0, 0
18, 20, -5, 0
19, 20, -10, 0
20, 20, -15, 0
21, 20, -20, 0
22, 20, -25, 0
23, 25, 25, 0
24, 25, 20, 0
25, 25, 15, 0
26, 25, 10, 0
27, 25, 5, 0
28, 25, 0, 0
29, 25, -5, 0
30, 25, -10, 0
31, 25, -15, 0
32, 25, -20, 0
33, 25, -25, 0
34, 30, 25, 0
35, 30, 20, 0
36, 30, 15, 0
37, 30, 10, 0
38, 30, 5, 0
39, 30, 0, 0
40, 30, -5, 0
41, 30, -10, 0
42, 30, -15, 0
43, 30, -20, 0
44, 30, -25, 0
45, 35, 25, 0
46, 35, 20, 0
47, 35, 15, 0
48, 35, 10, 0
49, 35, 5, 0
50, 35, 0, 0
51, 35, -5, 0
52, 35, -10, 0
53, 35, -15, 0
54, 35, -20, 0
55, 35, -25, 0
56, 40, 25, 0
57, 40, 20, 0
58, 40, 15, 0
59, 40, 10, 0
60, 40, 5, 0
61, 40, 0, 0
62, 40, -5, 0
63, 40, -10, 0
64, 40, -15, 0
65, 40, -20, 0
66, 40, -25, 0
67, 45, 25, 0
68, 45, 20, 0
69, 45, 15, 0
70, 45, 10, 0
71, 45, 5, 0
72, 45, 0, 0
73, 45, -5, 0
74, 45, -10, 0
75, 45, -15, 0
76, 45, -20, 0
77, 45, -25, 0
*Element, type=AC2D4
1, 1, 2, 13, 12
2, 2, 3, 14, 13
3, 3, 4, 15, 14
4, 4, 5, 16, 15
5, 5, 6, 17, 16
6, 6, 7, 18, 17
7, 7, 8, 19, 18
8, 8, 9, 20, 19
9, 9, 10, 21, 20
10, 10, 11, 22, 21
11, 12, 13, 24, 23
12, 13, 14, 25, 24
13, 14, 15, 26, 25
14, 15, 16, 27, 26
15, 16, 17, 28, 27
16, 17, 18, 29, 28
17, 18, 19, 30, 29
18, 19, 20, 31, 30
19, 20, 21, 32, 31
20, 21, 22, 33, 32
21, 23, 24, 35, 34
22, 24, 25, 36, 35
23, 25, 26, 37, 36
24, 26, 27, 38, 37
25, 27, 28, 39, 38
26, 28, 29, 40, 39
27, 29, 30, 41, 40
28, 30, 31, 42, 41
29, 31, 32, 43, 42
30, 32, 33, 44, 43
31, 34, 35, 46, 45
32, 35, 36, 47, 46
33, 36, 37, 48, 47
34, 37, 38, 49, 48
35, 38, 39, 50, 49
36, 39, 40, 51, 50
37, 40, 41, 52, 51
38, 41, 42, 53, 52
39, 42, 43, 54, 53
40, 43, 44, 55, 54
41, 45, 46, 57, 56
42, 46, 47, 58, 57
43, 47, 48, 59, 58
44, 48, 49, 60, 59
45, 49, 50, 61, 60
46, 50, 51, 62, 61
47, 51, 52, 63, 62
48, 52, 53, 64, 63
49, 53, 54, 65, 64
50, 54, 55, 66, 65
51, 56, 57, 68, 67
52, 57, 58, 69, 68
53, 58, 59, 70, 69
54, 59, 60, 71, 70
55, 60, 61, 72, 71
56, 61, 62, 73, 72
57, 62, 63, 74, 73
58, 63, 64, 75, 74
59, 64, 65, 76, 75
60, 65, 66, 77, 76
*Elset, elset=AIR-1__I1
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16
17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32
33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48
49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60
*solidsection, elset=AIR-1__I1, material=AIR
1., 
** ----------------------------------------------------------------
*Node
78, 45, 25, 0
79, 45, 30, 0
80, 15, 30, 0
81, 15, 25, 0
82, 45, -25, 0
83, 50, -25, 0
84, 50, 30, 0
85, 10, -25, 0
86, 15, -25, 0
87, 10, 30, 0
88, 10, -30, 0
89, 50, -30, 0
90, 39, 30, 0
91, 33, 30, 0
92, 27, 30, 0
93, 21, 30, 0
94, 21, 25, 0
95, 27, 25, 0
96, 33, 25, 0
97, 39, 25, 0
98, 45, 18.64305, 0
99, 45, 12.18657, 0
100, 45, 5.914043, 0
101, 45, -0.2971706, 0
102, 45, -6.487946, 0
103, 45, -12.67191, 0
104, 45, -18.8536, 0
105, 50, -18.87713, 0
106, 50, -12.73857, 0
107, 50, -6.594023, 0
108, 50, -0.4452127, 0
109, 50, 5.711833, 0
110, 50, 11.89206, 0
111, 50, 18.14134, 0
112, 50, 24.38045, 0
113, 15, -18.7963, 0
114, 15, -12.60802, 0
115, 15, -6.424897, 0
116, 15, -0.2434842, 0
117, 15, 5.937357, 0
118, 15, 12.11801, 0
119, 15, 18.2986, 0
120, 10, 24.25926, 0
121, 10, 18.07484, 0
122, 10, 11.91613, 0
123, 10, 5.765978, 0
124, 10, -0.3813907, 0
125, 10, -6.528022, 0
126, 10, -12.67498, 0
127, 10, -18.82376, 0
128, 15.47619, -30, 0
129, 21.25573, -30, 0
130, 27.04292, -30, 0
131, 32.8397, -30, 0
132, 38.66085, -30, 0
133, 44.55362, -30, 0
134, 38.85714, -25, 0
135, 32.90476, -25, 0
136, 27.01587, -25, 0
137, 21.14815, -25, 0
*Element, type=CPS4
61, 78, 79, 90, 97
62, 97, 90, 91, 96
63, 96, 91, 92, 95
64, 95, 92, 93, 94
65, 94, 93, 80, 81
66, 79, 78, 112, 84
67, 78, 98, 111, 112
68, 98, 99, 110, 111
69, 99, 100, 109, 110
70, 100, 101, 108, 109
71, 101, 102, 107, 108
72, 102, 103, 106, 107
73, 103, 104, 105, 106
74, 104, 82, 83, 105
75, 85, 86, 113, 127
76, 127, 113, 114, 126
77, 126, 114, 115, 125
78, 125, 115, 116, 124
79, 124, 116, 117, 123
80, 123, 117, 118, 122
81, 122, 118, 119, 121
82, 121, 119, 81, 120
83, 120, 81, 80, 87
84, 85, 88, 128, 86
85, 86, 128, 129, 137
86, 137, 129, 130, 136
87, 136, 130, 131, 135
88, 135, 131, 132, 134
89, 134, 132, 133, 82
90, 82, 133, 89, 83
*Elset, elset=BOX-1__I1
61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76
77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90
*solidsection, elset=BOX-1__I1, material=SOLID
1., 
*surface, type=ELEMENT, name=AIR
AIR_S1, S1
AIR_S2, S2
AIR_S4, S4
AIR_S3, S3
*surface, type=ELEMENT, name=SOLID-S
SOLID-S_S4, S4
SOLID-S_S1, S1
SOLID-S_S2, S2
*tie, name=AIR-SOLID, adjust=YES
AIR, SOLID-S
**
** Assembly Nsets
**
*Nset, nset=AIR
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16
17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32
33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48
49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64
65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77
*Nset, nset=RIGHT
84
*Nset, nset=LEFT
87
*Nset, nset=LOAD
88, 89
*nset,nset=retained,unsorted
88,89,87,84
*Nset, nset=OUT_AIR
44, 45, 55, 56, 66, 67
*Nset, nset=OUT_BOX
79, 80, 84, 87, 90, 91, 92, 93
*Nset, nset=SIR_S
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 22, 23, 33, 34
44, 45, 55, 56, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77
*Nset, nset=SOLID_S
78, 81, 82, 86, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 113
114, 115, 116, 117, 118, 119, 134, 135, 136, 137
*Nset, nset=SET10
79, 80, 84, 87, 90, 91, 92, 93
**
** Assembly Elsets
**
*Elset, elset=AIR
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16
17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32
33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48
49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60
*Elset, elset=SIR_S
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 20, 21, 30, 31, 40
41, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60
*Elset, elset=SOLID_S
61, 62, 63, 64, 65, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77
78, 79, 80, 81, 82, 85, 86, 87, 88, 89
*Elset, elset=AIR_S1
1, 2, 3, 4, 5, 6, 7, 8, 9, 10
*Elset, elset=AIR_S2
10, 20, 30, 40, 50, 60
*Elset, elset=AIR_S3
51, 52, 53, 54, 55, 56, 57, 58, 59, 60
*Elset, elset=AIR_S4
1, 11, 21, 31, 41, 51
*Elset, elset=SET10
61, 62, 63, 64, 65, 66, 83
*Elset, elset=SOLID-S_S1
67, 68, 69, 70, 71, 72, 73, 74
*Elset, elset=SOLID-S_S2
75, 76, 77, 78, 79, 80, 81, 82
*Elset, elset=SOLID-S_S4
61, 62, 63, 64, 65, 85, 86, 87, 88, 89
*material, name=AIR
*acousticmedium
14.2E+3, 
*density
1.1E-3, 
*material, name=SOLID
*density
0.01, 
*elastic
100, 0.
*boundary
LEFT, 1, 2
RIGHT, 1, 2
**------------------------------------------------
*Step, name=Step-1, nlgeom
*static
0.2, 1., 1E-05, 1.
*DLOAD
SOLID-S_S4, P4,0.2
SOLID-S_S1, P1,0.2
SOLID-S_S2, P2,0.2
*adaptivemesh, frequency=1, meshsweeps=10, elset=AIR
*print, adaptivemesh=YES
*output, field
*elementoutput
S
*nodeoutput
U
*output, history, variable=PRESELECT
*endstep
**------------------------------------------------
*Step, name=Step-2, perturbation
*frequency,norm=mass
<neig>,,,-1
*boundary,op=new
retained,1,2
*output, field
*node output
u,
*endstep
**------------------------------------------------
*STEP,NLGEOM
*SUBSTRUCTURE GENERATE,type=z101,overwrite,library=box_ac2d4,
mass matrix=yes,recovery=yes
*BOUNDARY,op=new
*RETAINED NODAL DOFS,SORTED=NO
retained,
*RETAINED EIGENMODES, GENERATE
1,<neig>,1
*SUBSTRUCTURE MATRIX OUTPUT,mass=yes,sload=yes,file=box_ac2d4
*END STEP