Rate-dependent hydroelastic response of self-adaptive composite propellers in fully wetted and cavitating flows

The objectives of this work are to investigate the fully wetted and cavitating performance of a self-adaptive composite propeller and its dependence on the propeller rotational frequency (RPM or revolution per minute) in addition to the advance coefficient and ambient pressure. Self-adaptive composite propellers are designed to take advantage of the intrinsic deformation coupling behavior of anisotropic composites to improve propeller performance via automatic, passive blade pitch adjustment in spatially or temporally varying flow. The design methodology, numerical and experimental studies of selfadaptive composite propellers in fully wetted flow can be found in [1-7]. In past studies, the primary focus was the fully wetted performance of the composite propellers operating at the design RPM. However, since the deformations of adaptive composite propellers depend on the hydrodynamic load, which in turn depends on the propeller RPM, the response of adaptive composite propellers depend on both the advance coefficient and RPM. Moreover, at high RPMs, composite propellers may be subject to resonant vibration failure due to the inherent flexibility needed to achieve the desired self-adaptive behavior, and due to the decrease in natural frequency caused by added mass effects. Hence, it is important to evaluate the ratedependent behavior of self-adaptive composite propellers. It is also important to evaluate the cavitating performance of self-adaptive composite propellers since cavitation can lead to thrust breakdown, decrease in efficiency, as well as erosion and localized impact damage to the composite blades. In this work, a previously validated coupled boundary element method finite element method (BEMFEM) is used to analyze the rate-dependent response of self-adaptive composite propellers in fully wetted and cavitating flows. Implications of the rate-dependent behavior on the design and interpretation of experimental studies, particularly cavitation tunnel studies, are discussed.http://deepblue.lib.umich.edu/bitstream/2027.42/84256/1/CAV2009-final60.pd

Transient hydroelastic analysis of surface-piercing propellers

A coupled boundary element method finite element method (BEMFEM) is presented for the transient hydroelastic analysis of surfacepiercing propellers (SPPs). The method is used to help the design and analysis of three different size SPPs that deliver a constant advance speed of 25.72 m/s (50 knots). Numerical validation studies are shown. The mean and unsteady responses of the three SPPs are presented. Finally, limitations of the BEM-FEM method are discussed. 100L upper and lower tanks. The working fluids were water and liquid nitrogen. Experiments with emphasis on periodical shedding of cloud cavitation were performed for three channels, 20, 30 and 60 mm in width, and two hydrofoils, 20 and 60mm in chord length LC. Inlet velocity uin and cavitation number ? were varied between 3.8 andhttp://deepblue.lib.umich.edu/bitstream/2027.42/84255/1/CAV2009-final59.pd

Cavity induced vibration of flexible hydrofoils

The objective of this work is to investigate the influence of cavity-induced vibrations on the dynamic response and stability of a NACA66 hydrofoil at 8° angle of attack at Re=750 000 via combined experimental measurements and numerical simulations. The rectangular, cantilevered hydrofoil is assumed to be rigid in the chordwise direction, while the spanwise bending and twisting deformations are represented using a two-degrees-of-freedom structural model. The multiphase flow is modeled with an incompressible, unsteady Reynolds Averaged Navier–Stokes solver with the k–ω Shear Stress Transport (SST) turbulence closure model, while the phase evolutions are modeled with a mass-transport equation based cavitation model. The numerical predictions are compared with experimental measurements across a range of cavitation numbers for a rigid and a flexible hydrofoil with the same undeformed geometries. The results showed that foil flexibility can lead to: (1) focusing – locking – of the frequency content of the vibrations to the nearest sub-harmonics of the foil׳s wetted natural frequencies, and (2) broadening of the frequency content of the vibrations in the unstable cavitation regime, where amplifications are observed in the sub-harmonics of the foil natural frequencies. Cavitation was also observed to cause frequency modulation, as the fluid density, and hence fluid induced (inertial, damping, and disturbing) forces fluctuated with unsteady cavitation.The authors gratefully acknowledge Ms. Kelly Cooper (program manager) and the Office of Naval Research (ONR), for their financial support through Grant nos. N00014-11-1-0833 and N0014-12-C-0585, as well as ONR Global and Dr. Woei-Min Lin (program manager) through grant no. N62909-12-1-7076

Cloud cavitation behaviour on a hydrofoil due to fluid-structure interaction

International audienceDespite recent extensive research into fluid-structure interaction (FSI) of cavitating hydrofoils there remains insufficient experimental data to explain many of these observed phenomena. The cloud cavitation behaviour around a hydrofoil due to the effect of FSI is investigated utilizing rigid and compliant 3D hydrofoils held in a cantilevered configuration in a cavitation tunnel. The hydrofoils have identical undeformed geometry of tapered planform with constant NACA section. The rigid model is made of stainless steel and the compliant model of carbon and glass fibre reinforced epoxy resin with the structural fibres aligned along the span-wise direction to avoid material bend-twist coupling. Tests were conducted at an incidence of 6°, a mean chord based Reynolds number of $0.7 × 10^6$, and cavitation number of 0.8. Force measurements were simultaneously acquired with high-speed imaging to enable correlation of forces with tip bending deformations and cavity physics. Hydrofoil compliance was seen to dampen the higher frequency force fluctuations while showing strong correlation between normal force and tip deflection. The 3D nature of the flow field was seen to cause complex cavitation behaviour with two shedding modes observed on both models

Expression of stress-response ATF3 is mediated by Nrf2 in astrocytes

Activating Transcription Factor 3 (ATF3), a member of the ATF/CREB family, is induced rapidly by various stresses. Its induction mechanism and role in response to changes in cellular redox status, however, have not been elucidated. Here, we found that NF-E2-related factor 2 (Nrf2), a transcription factor known to bind to antioxidant response element (ARE) in promoters, transcriptionally upregulated ATF3 expression in astrocytes. Treatment with Nrf2 activators and oxidants provoked ATF3 induction in astrocytes, whereas its expression was reduced in Nrf2-depleted cells. We further demonstrated that the consensus ARE in the ATF3 promoter is critical for Nrf2-mediation by promoter analyses using an ATF3 promoter-driven luciferase construct and a chromatin immunoprecipitation assay. In addition, we found that Nrf2-dependent ATF3 induction contributed to the antioxidative and cytoprotective functions of Nrf2 in astrocytes. Taken together, our findings suggest that ATF3 is a new target for Nrf2 and has a cytoprotective function in astrocytes

SLX4 Assembles a Telomere Maintenance Toolkit by Bridging Multiple Endonucleases with Telomeres

SummarySLX4 interacts with several endonucleases to resolve structural barriers in DNA metabolism. SLX4 also interacts with telomeric protein TRF2 in human cells. The molecular mechanism of these interactions at telomeres remains unknown. Here, we report the crystal structure of the TRF2-binding motif of SLX4 (SLX4TBM) in complex with the TRFH domain of TRF2 (TRF2TRFH) and map the interactions of SLX4 with endonucleases SLX1, XPF, and MUS81. TRF2 recognizes a unique HxLxP motif on SLX4 via the peptide-binding site in its TRFH domain. Telomeric localization of SLX4 and associated nucleases depend on the SLX4-endonuclease and SLX4-TRF2 interactions and the protein levels of SLX4 and TRF2. SLX4 assembles an endonuclease toolkit that negatively regulates telomere length via SLX1-catalyzed nucleolytic resolution of telomere DNA structures. We propose that the SLX4-TRF2 complex serves as a double-layer scaffold bridging multiple endonucleases with telomeres for recombination-based telomere maintenance

Enhanced electrochemical reduction of hydrogen peroxide by Co3O4 nanowire electrode

Crystalline Co3O4 nanowire arrays with different morphologies grown on Ni foam were investigated by varying the reaction temperature, the concentration of precursors, and reaction time. The Co3O4 nanowires synthesized under typical reaction condition had a diameter range of approximately 500–900 nm with a length of 17 µm. Electrochemical reduction of hydrogen peroxide (H2O2) of the optimized Co3O4 nanowire electrode was studied by cyclic voltammetry. A high current density of 101.8 mA cm−2 was obtained at −0.4 V in a solution of 0.4 M H2O2 and 3.0 M NaOH at room temperature compared to 85.8 mA cm−2 at −0.35 V of the Co3O4 nanoparticle electrode. Results clearly indicated that the Ni foam supported Co3O4 nanowire electrode exhibited superior catalytic activity and mass transport kinetics for H2O2 electrochemical reduction