Graduate Student , Massachusetts Institute of Technology
Slocum gliders are low-power underwater vehicles that can carry payloads designed for ocean data collection, deep sea exploration, and/or military surveillance. The duration of deployment is incredibly dependent on the energy stored in the battery packs. Gliders currently use alkaline or lithium primary battery packs to power the onboard payloads and sensors, and any onboard propulsion systems. As with any primary battery, the vehicle’s battery packs must be replaced when the batteries are drained. To replace the batteries, the vehicle must be disassembled and reassembled with the new primary batteries, and may need to be re-ballasted, a process which must be done in a tank on land. In order to streamline the recharging process, and to make the vehicle a much more valuable asset at sea, rechargeable battery packs, including support structures, were designed and built to replace the existing primary alkaline battery packs. The primary alkaline packs supplied approximately 2.29 kW-hr of energy, while the new design provided 2.4 kW-hr. The support structure features aluminum and carbon fiber alignment and end plates, held together with titanium tie rods and carbon fiber support tubes. Through simulations and material modeling, the battery packs’ support structures can survive high G-force launch/recovery, where the vehicle could experience up to 5g forces.
Abstract: Blended-wing-body underwater glider (BWBUG), which has excellent hydrodynamic performance, is a new kind of underwater glider in recent years. In the shape optimization of BWBUG, the lift to drag ratio is often used as the optimization target. However this results in lose of internal space. In this paper, the energy reserve is defined as the direct proportional function of the internal space of BWBUG. A motion model, which relates gliding range to steady gliding motion parameters as well as energy consumption, is established by analyzing the steady-state gliding motion. The maximum gliding range is used as the optimization target instead of the lift to drag ratio to optimizing the shape of BWBUG. The result of optimization shows that the maximum gliding range of initial design is increased by 32.1% though an efficient global optimization (EGO) process.
Pub.: 24 Feb '17, Pinned: 28 Jun '17
Abstract: Underwater gliders are buoyancy propelled vehicle which make use of buoyancy for vertical movement and wings to propel the glider in forward direction. Autonomous underwater gliders are a patented technology and are manufactured and marketed by corporations. In this study, we validate the experimental lift and drag characteristics of a glider from the literature using Computational fluid dynamics (CFD) approach .This approach is then used for the assessment of the steady state characteristics of a laboratory glider designed at Indian Institute of Technology (IIT) Madras. Flow behavior and lift and drag force distribution at different angles of attack are studied for Reynolds numbers varying from 105 to 106 for NACA0012 wing configurations. The state variables of the glider are the velocity, gliding angle and angle of attack which are simulated by making use of the hydrodynamic drag and lift coefficients obtained from CFD. The effect of the variable buoyancy is examined in terms of the gliding angle, velocity and angle of attack. Laboratory model of glider is developed from the final design asserted by CFD. This model is used for determination of static and dynamic properties of an underwater glider which were validated against an equivalent CAD model and simulation results obtained from equations of motion of glider in vertical plane respectively. In the literature, only empirical approach has been adopted to estimate the hydrodynamic coefficients of the AUG that are required for its trajectory simulation. In this work, a CFD approach has been proposed to estimate the hydrodynamic coefficients and validated with experimental data. A two-mass variable buoyancy engine has been designed and implemented. The equations of motion for this two-mass engine have been obtained by modifying the single mass version of the equations described in the literature. The objectives of the present study are to understand the glider dynamics adopting a CFD approach, fabricate the glider and its variable buoyancy engine and test its trajectory in water and compare it with numerically obtained trajectory in the vertical plane.
Pub.: 09 Apr '17, Pinned: 28 Jun '17
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