Effect of sidewall boundary conditions on unsteady high speed cavity flow and acoustics

The effect of sidewall boundary conditions on the computed unsteady flow and sound pressure level is investigated in a transonic open cavity. The hybrid approach used for modeling turbulence combines a Reynolds averaged mode in the boundary layer, and a large eddy simulation mode in the massively separated flow region within the cavity to resolve the wide dynamic range involved. Computational results are presented for the instantaneous vorticity and for the sound pressure level spectra. Comparison of the results obtained using inviscid and periodic sidewall boundary conditions show the sensitivity of the computed SPL spectra and autocorrelation to the conditions enforced at the sidewalls. The computed SPL spectra are also compared with available experimental results, with LES computational results, and with prior investigations based on the same hybrid turbulence model without the wall function used in the current investigation. The comparisons show that the current results obtained using inviscid sidewall boundary conditions are closest to the experimental sound pressure level spectra and that agreement is achieved at considerable saving in required computational resources.     

门式起重机在特殊危险工况下的安全性能分析和评价

为全面分析和评价门式起重机在特殊危险工况下的安全性能,用MSC Adams进行虚拟样机动力学分析,用ANSYS进行有限元应力分析.结合实际运行情况和典型事故原因分析,提出门式起重机涉及吊重突然卸载、吊重自由跌落后紧急制动、大车碰撞轨道端部止挡、歪拉斜吊、台风下防风抗滑装置失效和吊物碰撞支腿等6种特殊危险工况;分析和评价...     

Cognitive task performance under (combined) conditions of a metabolic and sensory stressor

Cognition, Technology & Work - Effects of stressors on cognitive task performance have primarily been studied in isolation, and little is known about the combined effects of two or more...     

Attenuation performance of four hearing protectors under dynamic movement and different user fitting conditions

An experiment was conducted to determine the effects of movement activities and alternative fitting procedures on protection levels afforded by four hearing protection devices (HPDs). Psychophysical attenuation measurements at nine one-third-octave bands from 125 to 8000 Hz were obtained prior to, during, and following a 2-hr wearing stint that included periods of either highly kinematic but controlled work activity or vigorous temporomandibular movement. The 40 subjects, who were nonusers of HPDs, initially fit the protectors according to either the instructions on the package (i.e., subject fit) or after receiving interactive training on proper fit (i.e., trained fit). Thereafter no further protector adjustments were allowed during the wearing period. The subject-fit condition resulted in significantly lower protection levels, from 4 to 14 dB, at 1000 Hz and below for a premolded polymer earplug, a user-molded foam earplug, and a double protector consisting of a muff over the foam plug. The muff alone was significantly more resilient to fitting effects on attenuation than were the plugs. Movement activity caused up to a 6-dB significant reduction in frequency-specific attenuation over time for the premolded plug, muff, and muff-plug combination. The compliant foam earplug was largely resistant to either type of movement effect but did benefit more than the other devices from use of the trained-fit procedure. Implications of the results for hearing protector testing protocol, device selection, and user training are discussed.     

The influence of colour on CRT reading performance and subjective comfort under operational conditions

Performance and reports of comfort when proof-reading text displayed on a CRT were investigated as a function of the text/background colour. Luminances were those typically produced by commercially available hardware and software, and task conditions were designed to simulate those experienced by typical users. Colours from the extremes of the spectrum (red, blue) were shown to produce poorer reading performance, higher ratings of discomfort and a higher incidence of reported symptoms of discomfort than those from mid-spectrum and white stimulus conditions.     

Diagnostic techniques for the dynamics of a thin liquid film under forced flow and evaporating conditions

Motivated by quantification of micro-hydrodynamics of a thin liquid film which is present in industrial processes, such as spray cooling, heating (e.g., boiling with the macrolayer and the microlayer), coating, cleaning, and lubrication, we use micro-conductive probes and confocal optical sensors to measure the thickness and dynamic characteristics of a liquid film on a silicon wafer surface with or without heating. The simultaneous measurement on the same liquid film shows that the two techniques are in a good agreement with respect to accuracy, but the optical sensors have a much higher acquisition rate up to 30 kHz which is more suitable for rapid process. The optical sensors are therefore used to measure the instantaneous film thickness in an isothermal flow over a silicon wafer, obtaining the film thickness profile and the interfacial wave. The dynamic thickness of an evaporating film on a horizontal silicon wafer surface is also recorded by the optical sensor for the first time. The results indicate that the critical thickness initiating film instability on the silicon wafer is around 84 μm at heat flux of ~56 kW/m². In general, the tests performed show that the confocal optical sensor is capable of measuring liquid film dynamics at various conditions, while the micro-conductive probe can be used to calibrate the optical sensor by simultaneous measurement of a film under quasi-steady state. The micro-experimental methods provide the solid platform for further investigation of the liquid film dynamics affected by physicochemical properties of the liquid and surfaces as well as thermal-hydraulic conditions.     

Parallelization of MIN3P-THCm: A high performance computational framework for subsurface flow and reactive transport simulation

This paper presents the development of ParMIN3P-THCm, a parallel version of the reactive transport code MIN3P-THCm, which can run efficiently on machines ranging from desktop PCs to supercomputers. Parallelization of ParMIN3P-THCm was achieved through the domain decomposition method based on the PETSc library. The code has been developed from the ground up for parallel scalability and has been tested for up to 768 processors with problem sizes up to 100 million unknowns, showing strong scalability in modeling large-scale reactive transport problems. The total speedup tends to be ideal and near linear up to 768 processors when the degrees of freedom per processor is larger than 8000–15,000, depending on the relative complexity of the reactive transport and flow problems. The improved code efficiency allows refining of the model discretization in both space and time and will facilitate 3D simulations that were impractical to carry out with the sequential version of MIN3P-THCm.     

Analysis of flow instabilities in convex and concave floating zones heated by an equatorial ring under microgravity conditions

This analysis deals with advances in models concerning the floating zone technique as well as with novel results on the relative importance of various parameters in the crystal-growth process. The attention is focused in particular on microgravity fluid-dynamic aspects and on the effect of the volume of the liquid melt since the cylindrical configuration is expected to be only a very special case under microgravity conditions. The instability of Marangoni flow is investigated by direct three-dimensional and time-dependent simulation of the problem and parallel computations. Body-fitted curvilinear co-ordinates are adopted to handle the non-cylindrical shape. A novel realistic distribution is considered to model the surface heat flux generated by a ring heater positioned around the equatorial plane at a fixed distance from the axis of the liquid (full) zone.The fluid-dynamic environment that occurs inside the melt is very sensitive to the geometrical aspect ratio A_F (length/diameter) of the floating zone and to the volume factor S (ratio of the volume of the liquid zone and the volume of the corresponding cylindrical configuration: convex S>1, concave S<1). The role played by the geometrical constraints and degrees of freedom of the Marangoni toroidal rolls in determining the azimuthal structure and the stability of the flow field is discussed.     

Evolutionary dynamics and the coding structure of sequences: Multiple coding as a consequence of crossover and high mutation rates

In this paper we explore the influence of the dynamics of evolution on coding structures of sequences. We show that, in systems with crossover, high mutation rates cause the most conserved subsequences to be preferentially used as recognition sites for newly evolving sequences. In other words: “multiple coding” evolves in these systems. Multiple coding often does not increase the fitness of the population; nevertheless it is selected. By contrast, in systems without crossover, a low mutation rate causes multiple coding to be avoided, so that only single coding evolves. Again this “choice” is not reflected in the fitness of the population, but is dictated by the evolutionary dynamics. We conclude that the genetic operator crossover turns evolutionary processes in pattern detectors rather than optimizers.     

Using leg muscles as shock absorbers: theoretical predictions and experimental results of drop landing performance

The use of muscles as power dissipators is investigated in this study, both from the modellistic and the experimental points of view. Theoretical predictions of the drop landing manoeuvre for a range of initial conditions have been obtained by accounting for the mechanical characteristics of knee extensor muscles, the limb geometry and assuming maximum neural activation. Resulting dynamics have been represented in the phase plane (vertical displacement versus speed) to better classify the damping performance. Predictions of safe landing in sedentary subjects were associated to dropping from a maximum (feet) height of 1.6-2.0 m (about 11 m on the moon). Athletes can extend up to 2.6-3.0 m, while for obese males (m = 100 kg, standard stature) the limit should reduce to 0.9-1.3 m. These results have been calculated by including in the model the estimated stiffness of the ‘global elastic elements’ acting below the squat position. Experimental landings from a height of 0.4, 0.7, 1.1 m (sedentary males (SM) and male (AM) and female (AF) athletes from the alpine ski national team) showed dynamics similar to the model predictions. While the peak power (for a drop height of about 0.7 m) was similar in SM and AF (AM shows a + 40% increase, about 33 W/kg), AF stopped the downward movement after a time interval (0.219±0.030 s) from touch-down 20% significantly shorter than SM. Landing strategy and the effect of anatomical constraints are discussed in the paper.     

Numerical investigation of meniscus deformation and flow in an isothermal liquid bridge subject to high-frequency vibrations under zero gravity conditions

This paper deals with meniscus deformation and flow in an isothermal liquid bridge maintained between two circular rods, when one rod is subject to axial monochromatic vibrations. It concerns a fundamental aspect of the problem of crystal growth from melt by the floating-zone technique which is often considered in weightlessness conditions. In the absence of vibrations the bridge is cylindrical; but due to vibration the mean shape of the meniscus is no more cylindrical and the meniscus oscillates around this mean shape. Two models are developed. First, we take into account the pulsating deformations of the meniscus (free surface), but we assume that the mean shape of meniscus remains cylindrical (i.e., we neglect the influence of vibration on this mean shape). For this simple case, a solution of the problem for the pulsating meniscus deformations and the pulsating velocity field is found in explicit form. For the mean flow, the problem is solved numerically by a finite-difference method. The calculations demonstrate the contribution of two basic mechanisms of mean flow generation due to vibrations, related to the generation of mean vorticity in the viscous boundary layer near the rigid boundaries and surface-wave propagation at a free surface. The intensity of the mean flow induced by surface waves is found to be sharply increasing when the vibration frequency approaches the resonance values that are determined from the explicit form of the solution of pulsation problem. In the second model, we take into account both pulsating and mean deformations of the meniscus. The governing equations for the potential of pulsating velocity and mean velocity, and for the pressure, are solved by using a finite-difference method and a boundary-fitted curvilinear coordinate system fitting the free surface.     

Evaluation of spectral vegetation indices as an indicator of crop coefficient and evapotranspiration under full and deficit irrigation conditions

Two separate field experiments were conducted with sugar beet and green bean, at Ankara, Turkey during the 2005 growing season. Different amounts of irrigation water were applied, and various levels of water stress and vegetation occurred. Spectral reflectance, infrared canopy temperature, and some parameters related to crop evapotranspiration (ET _c) were observed. Daily ET _c values were calculated based on energy balance and soil water balance residual. The fraction of reference ET (ETrF), which is essentially the same with the crop coefficient (K _c), was determined, and relationships between spectral vegetation indices (SVIs) were analysed. Under water stress conditions, the ET _c and ETrF values estimated by means of energy balance were relatively high. In order to improve the correlation between ETrF and SVIs and for correction of ET _c for water‐stressed irrigation treatments, a modification ratio was calculated based on SVIs. Although all three SVIs have a significant relationship with ETrF, the correctness of the modification with a Simple Ratio (SR) was higher. As a consequence, ETrF or crop coefficient (K _c) could be estimated by SR, and this information could be used for irrigation water management of large‐scale agricultural lands.     

Effects of bending curvature and text/background color-combinations of e-paper on subjects’ visual performance and subjective preferences under various ambient illuminance conditions

The study used the simulated e-paper to investigate how the bending radius of curvature (−10 cm, plane, and 10 cm) and 12 text/background color-combinations of e-paper affect subjects’ visual performance and subjective preference under various ambient illuminance conditions (200 and 500 lx). Analysis results indicated that the bending curvature and ambient illuminance did not significantly affect subjects’ visual performance. However, subjects visual performance differed significantly for different text/background color combinations of the simulated e-paper. When the background color of the simulated e-paper was set to yellow-like condition and the luminance of the text was low (2.2 and 4.6 cd/m²), subjects’ visual performance was best. Regarding the subjective preferences of subjects, the results of this research also demonstrated that the bending curvature, text/background color combinations and ambient illuminance all significantly affected the subjective preferences of subjects. Subjects exhibited the best preference under the following settings: bending curvature of the simulated e-paper set to plane; background color of the simulated e-paper set to yellow-like condition and low text luminance (2.2 or 4.6 cd/m²); high ambient illuminance (500 lx).