Nonlinear forced vibration of damped plates by an asymptotic numerical method

International audienceThis work deals with damped nonlinear forced vibrations of thin elastic rectangular plates subjected to harmonic excitation by an asymptotic numerical method. Using the harmonic balance method and Hamilton’s principle, the governing equation is converted into a static formulation. A mixed formulation is used to transform the problem from cubic nonlinearity to quadratic one sequence. Displacement, stress and frequency are represented by power series with respect to a path parameter. Equating the like powers of this parameter, the nonlinear governing equation is transformed into a sequence of linear problems with the same stiffness matrix. Through a single matrix inversion, a considerable number of terms of the perturbation series can easily be computed with a limited computation time. The starting point, corresponding to a regular solution, is obtained by the Newton–Raphson method. In order to increase the step length, Padé approximants are used. Numerical tests are presented and compared with numerical and analytical results in the literature, for different boundary conditions, excitations and damping coefficients

CHARACTERIZING SLOT FILM COOLING THROUGH DETAILED EXPERIMENTS

ABSTRACT With the ever increasing operating temperatures of gas turbine engines, the surface cooling of hot section components remains a primary consideration in propulsion system design. At the same time, numerical tools are being used more extensively for hot-section flow-path design. Recognizing the need for detailed data to help develop and validate these numerical tools, the present study focuses on characterizing near-wall mixing and heat transfer in a canonical 2D slot film cooling configuration. The lack of comprehensive and detailed experimental film cooling data under realistic temperature and blowing ratio conditions has led the authors to develop and implement a unique experimental facility that will allow measuring velocity and temperature profiles as well as surface temperatures and heat transfer at the wall under adiabatic and isothermal conditions. This hot wind tunnel facility provides optical access for Laser Doppler Velocimetry (LDV) near the wall and wall surface temperature distribution with infrared (IR) thermography. In addition to these nonintrusive diagnostics, the gas-phase temperature is measured with a minimally intrusive micro-thermocouple probe with fast response time and high frequency sampling. The performance of selected film cooling effectiveness scaling laws is analyzed. The thermal and momentum mixing of the film described in terms of temperature and velocity profiles and associated statistics. These detailed measurements are hoped to provide guidance and validation for CFD model developers

Functional Analysis of the Kinome of the Wheat Scab Fungus Fusarium graminearum

As in other eukaryotes, protein kinases play major regulatory roles in filamentous fungi. Although the genomes of many plant pathogenic fungi have been sequenced, systematic characterization of their kinomes has not been reported. The wheat scab fungus Fusarium graminearum has 116 protein kinases (PK) genes. Although twenty of them appeared to be essential, we generated deletion mutants for the other 96 PK genes, including 12 orthologs of essential genes in yeast. All of the PK mutants were assayed for changes in 17 phenotypes, including growth, conidiation, pathogenesis, stress responses, and sexual reproduction. Overall, deletion of 64 PK genes resulted in at least one of the phenotypes examined, including three mutants blocked in conidiation and five mutants with increased tolerance to hyperosmotic stress. In total, 42 PK mutants were significantly reduced in virulence or non-pathogenic, including mutants deleted of key components of the cAMP signaling and three MAPK pathways. A number of these PK genes, including Fg03146 and Fg04770 that are unique to filamentous fungi, are dispensable for hyphal growth and likely encode novel fungal virulence factors. Ascospores play a critical role in the initiation of wheat scab. Twenty-six PK mutants were blocked in perithecia formation or aborted in ascosporogenesis. Additional 19 mutants were defective in ascospore release or morphology. Interestingly, F. graminearum contains two aurora kinase genes with distinct functions, which has not been reported in fungi. In addition, we used the interlog approach to predict the PK-PK and PK-protein interaction networks of F. graminearum. Several predicted interactions were verified with yeast two-hybrid or co-immunoprecipitation assays. To our knowledge, this is the first functional characterization of the kinome in plant pathogenic fungi. Protein kinase genes important for various aspects of growth, developmental, and infection processes in F. graminearum were identified in this study

Modeling and simulation of the effects of axial diffusion on fuel-air mixing lengths in micro-power systems

An analytical model for fuel-oxidizer mixing that incorporates both axial and radial diffusion is developed to predict the mixing length - the distance required for fuel and oxidizer to mix via diffusive transport - in axisymmetric micro-power system configurations. The results are compared with mixing length estimates obtained for the case of mixing by radial diffusion only i.e. the traditional Burke-Schumann theory. The mixing length predictions are also compared with the results of inviscid CFD simulations of low Reynolds number fueloxidizer mixing in axisymmetric micro-power system configurations. The results indicate that axial diffusion becomes important for Re < 20 and imposes a limit on the extent to which it is possible (from a fuel-air mixing point of view) to miniaturize a power system

High-resolution solid-state 13C NMR spectroscopy of the paramagnetic metal-organic frameworks, STAM-1 and HKUST-1

Solid-state C-13 magic-angle spinning (MAS) NMR spectroscopy is used to investigate the structure of the Cu(II)-based metal-organic frameworks (MOFs), HKUST-1 and STAM-1, and the structural changes occurring within these MOFs upon activation (dehydration). NMR spectroscopy is an attractive technique for the investigation of these materials, owing to its high sensitivity to local structure, without any requirement for longer-range order. However, interactions between nuclei and unpaired electrons in paramagnetic systems (e.g., Cu(II)-based MOFs) pose a considerable challenge, not only for spectral acquisition, but also in the assignment and interpretation of the spectral resonances. Here, we exploit the rapid T-1 relaxation of these materials to obtain C-13 NMR spectra using a spin-echo pulse sequence at natural abundance levels, and employ frequency-stepped acquisition to ensure uniform excitation of resonances over a wide frequency range. We then utilise selective C-13 isotopic labelling of the organic linker molecules to enable an unambiguous assignment of NMR spectra of both MOFs for the first time. We show that the monomethylated linker can be recovered from STAM-1 intact, demonstrating not only the interesting use of this MOF as a protecting group, but also the ability (for both STAM-1 and HKUST-1) to recover isotopically-enriched linkers, thereby reducing significantly the overall cost of the approach.PostprintPeer reviewe

Asymptotic numerical method for steady flow of power-law fluids

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In situ species and temperature measurements in a millimeter-scale combustor

An FTIR-based spectroscopic technique is described that exploits silicon's transmissivity in the IR to make nonintrusive measurements of species concentration and temperature profiles in microcombustors. Species concentration is determined from the integrated absorbance (Beer's law), whereas gas temperature is determined by fitting a narrow-band spectral model (EM2C) to CO2 absorption spectra. The technique is demonstrated in a millimeter-scale combustor burning a lean ( = 0.86) CH4-air mixture. The results show that accuracies of 0.25 e-3 mol/L and 100C with spatial resolution 1 mm are possible. Heat fluxes to the wall are also estimated and thermal losses are found to be very high (90%)

Nonlinear forced vibration of damped plates coupling asymptotic numerical method and reduction models

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Near-Wall Measurements of Gas Temperature in Conventional-Scale and Micro-Scale Rockets

The Space Vehicle Technology Institute at University of Maryland is investigating film cooling performance for liquid propellant rockets as part of the NASA exploration initiative under the Constellation Project. Film cooling is widely used to protect critical sections of rockets and other propulsion devices from extreme heat loads in the internal flowpath. Many studies have been conducted to formulate scaling laws characterizing the effectiveness of film cooling in a variety of configurations and conditions for the development of engineering correlations. There is an emerging demand for detailed measurements near film-cooled surfaces to support CFD model development of these complex wall bounded flows. In this study a unique hot wind tunnel facility was used to perform detailed measurements in a canonical 2D thermally stratified wall jet configuration. Wall temperature, adiabatic effectiveness, and turbulent gas phase measurements were performed over a range of carefully controlled inlet conditions. Farfield laboratory effectiveness measurements compare well with previously developed scaling laws; however, the effect of temperature ratio, T(proportional)/Tc, is significantly underpredicted. The micro-thermocouple probe used in this study provided mean temperatures and detailed turbulent statistics charactering the near wall mixing behavior. The mean gas temperature measurements in the farfield demonstrate self-similar behavior while RMS temperatures in the same region indicate fully developed turbulence in the wall layer. The turbulent time scales, PDF's and RMS profiles provided in this study are especially useful for development and validation of CFD models of film-cooled surfaces