... k5 k6 k7 k8 k9 k 10 k11 7 7 4 3 6 8 10 5 10 5 4.0x105 5.0x105 7.0x105 2.0x105 8.0x105 3.0x105 6.0x105 3.0x105 5.0x105 13 12 ... Operational Modal Analysis Conference (IMAC XXVII), Orlando, Florida, U.S.A. Vibration Analysis and Control – New Trends and Developments 190 The error function, erf(x) ,and the unit step ... and 2 are now zero, i.e., 120==XX . External forces are applied at co-ordinates 5 and 6 and the reactions happen at co-ordinates 1 and 2. Vibration Analysis and Control – New Trends and...