Non-contact point excitation of ultra lightweight structures: membranes

摘要

Given the lightweight and sensitive nature of gossamer structures, applying non-intrusive excitation and measurement techniques is beneficial during either the design stage or in operational conditions. The use of non-contact measurement techniques, such as laser vibrometry, has been extensively used in testing of lightweight structures and proven beneficial. The successful implementation of non-contact excitation techniques, however, is more difficult. Commonly used and seen in past literature, has been the implementation of boundary excitation and acoustics in order to generate a non-contact type of excitation source. Both these techniques distribute the excitation generated on the surface of the specimen as opposed to a point source. A SISO or SIMO type of approach cannot be used for system identification as the nature of these excitations are not single input. The implementation of a MIMO approach should not be used either, as the excitation cannot be measured directly nor are the inputs uncorrelated. The work here investigates the use of a pressurized solenoid valve with compressed air to generate a point excitation on an ultra-lightweight circular membrane. The experimental results are compared with a previously validated theoretical model of a membrane in air. An impedance-based model of a circular membrane is used which takes into account the energy loss due to radiation to the far field. This work also attempts to quantify in a general sense the errors induced when neglecting these differences using distributed type excitations versus single point.