Shock, vibration, and G-force protection of liquid-cooled, compact airborne electronics system

• Main Author: Haji Hosseinloo, Ashkan
• Other Authors: Yap Fook Fah
• Format: Theses and Dissertations
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Mechanical engineering::Mechanics and dynamics
• Online Access: http://hdl.handle.net/10356/51776
• Institution: Nanyang Technological University

High-powered embedded computing equipment using the ATR form-factors are playing an ever-increasing role in critical military applications in air, land and sea environments. High power and wattage of the electronics and processors require high heat dissipation, and thus more sophisticated and efficient thermal cooling systems like loop heat pipes or jet impingement systems. However, these thermal solutions are more susceptible to the harsh military environments and thus, for proper performance of thermal and electronic equipment, they need to be protected against shock and vibration inherent in the military environments. In this study shock, vibration and high gravity effects on a jet impingement cooling system is investigated and then it is ruggedized against these harsh environmental conditions using vibration isolators. Two different designs for the impingement cooling system are considered in the study. The shock input is a sawtooth end-terminating pulse. The vibration excitation comprises of operating vibration and road transportation, and g-force of the g-loading conditions can reach up to 100 g. Based on experimental and numerical (FE software ANSYS) modal analysis of the cooling system, different mathematical models are developed in this study to model the cooling chamber and its chassis. Single degree of freedom (SDOF) and 3DOF models are the discrete mathematical models of the isolated system developed in this study. Furthermore, as a more complex model, continuous thin plate models of the impingement and nozzle plates of the cooling system are integrated to the SDOF model of the system and its mathematics are developed. Analytical response of the models to shock, vibration and g-force are presented and analyzed. It is found that there is an optimum damping ratio for the isolators that maximizes the attenuation factor (the ratio of rms acceleration of a desired point to rms acceleration of input) of the chassis for SDOF and 3DOF models. This optimum damping ratio varies from 0.2 to 0.3 for an isolation frequency range of [20,50] Hz. This optimum damping ratio minimizes the nozzle plate deflection of the 3DOF model of the first design of the cooling system. For the SDOF and 3DOF models, an optimum damping ratio of 0.25 minimizes the shock acceleration transmission to the system. The optimum dampings slightly change for the continuous model of the cooling system. The damping ratio that maximizes the attenuation factor at the impingement plate and the nozzle plate for the continuous model of the second design of the cooling system varies from 0.13 to 0.22 for isolation frequency range of [20,50] Hz. The continuous model gives us the advantage to measure the change in impingement height (the clearance between the nozzle plate and the impingement plate) due to the vibration. It is found that there is also an optimum damping ratio that minimizes the change in impingement height. This damping ratio varies from 0.33 to 0.45 for isolation frequency range of [20,50] Hz. A new isolation design is also proposed in this study that caters for the case when g-force and vibration excitation are applied to the payload concurrently for some time and separately for some other time. In this design, a nonlinear isolation subsystem consisting of a linear damper and a bilinear softening spring is integrated with a linear subsystem consisting of linear spring and linear damper. The linear subsystem caters for the case when the system is subjected to vibration excitation at zero g-force. When the system is subjected to g-force, the nonlinear subsystem is also involved and the stiff region of its bilinear spring opposes the g-loading while its operating soft region provides the required vibration isolation. An analytical optimization procedure is carried out for design parameters of the isolation system. It is shown that the new isolation system can be designed so that it can provide the required vibration isolation while opposing the g-force and confining the chassis in the stringently compact rattle space. Experimental tests are also conducted on the hard-mounted chassis to investigate the harsh environmental conditions on the jet impingement cooling mechanism, and on the isolated chassis to evaluate and qualify the isolation system capability in mitigating the shock and vibration. It is found that the shock, vibration and g-force have not much effect on the cooling system mechanism but can severely bring about mechanical failures like water leakage from connections or from the chamber, tubing breakage, spoiling the pumps’ water sealing, and etc. The selected isolation system can well protect the cooling system against the shock and vibration, and the experimental results of the isolation system performance are comparable with the analytical results.