Extracting fixed base modal models from vibration tests on flexible tables.
a acceleration dof degree of freedom H Frequency response function f Applied force FE Finite Element FRF Frequency Response Function Φc The mode shape matrix of the bare table at dof to be constrained Subscripts c degree of freedom at locations to be constrained f dof at free locations t dof at tip of the slip table s dof at the classic shaker input location on the slip table i any other dof not including t or s
A Way of Getting Scaled Mode Shapes in Output Only Modal Testing
In this paper some further work is done following the idea introduced by Parloo et all [2] where they proposed that the scaling factor should be estimated by repeated testing introducing mass changes in different points on the structure. In this paper the approximate formula for determination of the scaling factor based on the frequency shift when introducing mass changes on the structure is derived directly from the governing equation of motion. Further the error sources are studied and a new formula introducing less approximation errors on the scaling factor is proposed. Using this new formula scaling factors can be estimated from relative large frequency shifts without introducing any approximation errors. Further it is explained how testing should be performed in order to significantly reduce approximation errors due to mode shape changes and random errors due to uncertainty on the mode shape values. It turns out that if the mass changes are well distributed over the structure, then both random errors and the approximation errors will be minimized.
Frequency selective surface design for blinds applications
In this paper, the reconfigurable blind structure with frequency selective surfaces(FSS) for the building applications are presented. Frequency transmission characteristics for different angles of the proposed blind-FSSs are investigated and verified through simulation and measurement. The simulation results show that we can implement the reconfigurable blind-FSS for multiband wireless applications. To verify the proposed paper, two kinds of blind-FSSs, crossed dipole FSS and circular ring FSS are fabricated and measurements are performed for different angles. The proposed structure in this paper which is very simple, can be easily applied to any planar surface for wireless security applications at low cost.