A Block Iteration with Parallelization Method for the Greedy Selection in Radial Basis Functions Based Mesh Deformation

Greedy algorithm is one of the important point selection methods in the radial basis function based mesh deformation. However, in large-scale mesh, the conventional greedy selection will generate expensive time consumption and result in performance penalties. To accelerate the computational procedure of the point selection, a block iteration with parallelization method is proposed in this paper. By the block iteration method, the computational complexities of three steps in the greedy selection are all reduced from O ( n 3 ) to O ( n 2 ) . In addition, the parallelization of two steps in the greedy selection separates boundary points into sub-cores, efficiently accelerating the procedure. Specifically, three typical models of three-dimensional undulating fish, ONERA M6 wing and three-dimensional Super-cavitating Hydrofoil are taken as the test cases to validate the proposed method and the results show that it improves 17.41 times performance compared to the conventional method.

Radiated Sound From a Cross-Flow Turbine With Pitching Hydrofoils

An underwater drone turbine generator unit is currently under development. The turbine consists of three cross-flow pitching foils. While understanding single turbine lift, thrust, and torque performance in a reverberant tank with a six-component load cell, an opportunity arose to quantify its radiated sound performance since such information may have an environmental impact on marine mammals and fish. Unsteady lift and drag on a non-cavitating hydrofoil, quantified by the time-dependent load cell response, results in dipole sound. This radiated sound power within the reverberant tank also results in a uniform distribution acoustic pressure that can be measured with hydrophones. Given the tank properties such as volume and frequency dependent reverberation time constants, the radiated sound can be quantified. The low frequency sound power is therefore quantified using the load cell and the high frequency sound power by averaging hydrophone levels. The sound power for the two frequency ranges with excellent overlap are shown for a single turbine with a span of 900 mm and diameter of 450 mm operating at 107 rpm.

Risk-Adaptive Set-Based Design and Applications to Shaping a Hydrofoil

The paper presents a framework for set-based design under uncertainty and demonstrates its viability through designing a super-cavitating hydrofoil of an ultrahigh speed vessel. The framework achieves designs that safely meet the requirements as quantified precisely by superquantile measures of risk (s-risk) and reduces the complexity of design under uncertainty. S-risk ensures comprehensive and decision-theoretically sound assessment of risk and permits a decoupling of parametric uncertainty and surrogate (model) uncertainty. The framework is compatible with any surrogate building technique, but we illustrate it by developing for the first time risk-adaptive surrogates that are especially tailored to s-risk. The numerical results demonstrate the framework in a complex design case requiring multifidelity simulation.

Effects of Diffuser Length on Cloud Cavitation in an Axisymmetrical Convergent-Divergent Nozzle

Unsteady behavior of periodic cloud cavitation is typically observed in the field of fluid machinery under a high speed liquid flow such as a cavitating hydrofoil as well as cavitating water jet. The instability of cloud cavitation remains to be completely solved though it has been confirmed that there are two instabilities which is an intrinsic instability of cavitation and a system instability. Sato, et al. have found through previous investigations that the pressure wave at the collapse of shedding clouds can make a trigger to cause a reentrant motion. In the present study, the authors focus on a cavitating water jet to investigate the cavitation aspects in an axisymmetrical convergent-divergent nozzle and examine an unsteady behavior of cloud cavitation through high speed video observation and image analysis based on the frame difference method. Especially, the authors study the effect of nozzle divergent part (diffuser) as well as the upstream pressure effect on cloud cavitation in the nozzle. As a result the authors have found that there are two kinds in the shedding pattern and the reentrant motion pattern for cloud cavitation depending on the nozzle diffuser length.