Analytical Qualification of Heliborne TDEM Equipments Subjected to Static, Shock and Vibration Loadings

Abstract

In geophysical survey system, a Time Domain Electro-Magnetic (TDEM) technique is used to detect the presence of uranium in the earth crust. For heliborne survey, certain equipments, such as power converter and data acquisition system are installed on a helicopter. The power converter is responsible for the generation of high current pulses to feed the transmitter for setting up the required electromagnetic field. The power converter consists of a free running inverter, which sits over a DC-DC converter. Data acquisition system acquires data from various sensors for further processing and interpretation. Data acquisition system consists of a highly vibration sensitive onboard computer (IDAN boxes) rigidly mounted over a plate inside the data acquisition system enclosure. Since the power converter and data acquisition system are installed on the floor inside the surveying helicopter, it is mandatory to qualify these equipments for vibration & shock as per MIL standard before onboard installation. To evaluate the structural integrity of power converter and data acquisition system under various loading conditions of vibration and shock, a preliminary estimation of stresses and deflections was made by hand calculations and then, finite element analysis has been performed to optimize the design. Modal analysis has been performed to estimate the natural frequencies of power converter. Since the natural frequencies of the power converter were within the disturbing frequency range (i.e., 10 to 84 Hz), thickness of converter base plate and inverter base plate has been increased to avoid resonance. Since the data acquisition system consists of a highly vibration sensitive onboard computer, it has been proposed to mount it on isolators to minimize the vibration. To evaluate the structural integrity of data acquisition system under various loading conditions, finite element analysis has been performed. This paper presents the methodology adopted for design and analysis of the equipments for the specified input of vibration and shock.