摘要:The transverse free vibration of nanobeams subjected to an initial axial tension based on nonlocal stress theory is presented. It considers the effects of nonlocal stress field on the natural frequencies and vibration modes. The effects of a small scale parameter at molecular level unavailable in classical macro-beams are investigated for three different types of boundary conditions:simple supports,clamped supports and elastically-constrained supports. Analytical solutions for transverse deforma-tion and vibration modes are derived. Through numerical examples,effects of the dimensionless nanoscale parameter and pre-tension on natural frequencies are presented and discussed.
摘要:The endurance time (ET) method is a time history based dynamic analysis in which structures are subjected to gradually intensifying excitations and their performances are judged based on their responses at various excitation levels. Using this method, the computational effort required for estimating probable seismic demand parameters can be reduced by an order of magnitude. Calculation of the maximum displacement or target displacement is a basic requirement for estimating performance based on structural design. The purpose of this paper is to compare the results of the nonlinear ET method with the nonlinear static pushover (NSP) method of FEMA 356 by evaluating performances and target displacements of steel frames. This study will lead to a deeper insight into the capabilities and limitations of the ET method. The results are further compared with those of the standard nonlinear response history analysis. We conclude that results from the ET analysis are in proper agreement with those from standard procedures.
摘要:An infinite slope stability numerical model driven by the comprehensive physically-based integrated hydrology model(InHM) is presented.In this approach,the failure plane is assumed to be parallel to the hydraulic gradient instead of the slope surface.The method helps with irregularities in complex terrain since depressions and flat areas are allowed in the model.The present model has been tested for two synthetic single slopes and a small catchment in the Mettman Ridge study area in Oregon,United States,to estimate the shallow landslide susceptibility.The results show that the present approach can reduce the simulation error of hydrological factors caused by the rolling topography and depressions,and is capable of estimating spatial-temporal variations for landslide susceptibilities at simple slopes as well as at catchment scale,providing a valuable tool for the prediction of shallow landslides.
摘要:The three-axis active attitude control method with a momentum wheel and magnetic coils for a pico-satellite is considered. The designed satellite is a 2.5 kg class satellite stabilized to nadir pointing. The momentum wheel performs a pitch-axis momentum bias, nominally spinning at a particular rate. Three magnetic coils are mounted perpendicularly along the body axis for precise attitude control through the switch control mechanism. Momentum wheel start up control, damping control and attitude acquisition control are considered. Simulation results show that the proposed combined control laws for the pico-satellite is reliable and has an appropriate accuracy under different separation conditions. The proposed strategy to start up the wheel after separation from the launch vehicle shows that its pitch momentum wheel can start up successfully to its nominal speed from rest, and the attitude convergence can be completed within several orbits, depending on separation conditions.
摘要:In this study,ground vibrations due to dynamic loadings from trains moving in subway tunnels were investigated using a 2.5D finite element model of an underground tunnel and surrounding soil interactions.In our model,wave propagation in the infinitely extended ground is dealt with using a simple,yet efficient gradually damped artificial boundary.Based on the assumption of invariant geometry and material distribution in the tunnel's direction,the Fourier transform of the spatial dimension in this direction is applied to represent the waves in terms of the wave-number.Finite element discretization is employed in the cross-section perpendicular to the tunnel direction and the governing equations are solved for every discrete wave-number.The 3D ground responses are calculated from the wave-number expansion by employing the inverse Fourier transform.The accuracy of the proposed analysis method is verified by a semi-analytical solution of a rectangular load moving inside a soil stratum.A case study of subway train induced ground vibration is presented and the dependency of wave attenuation at the ground surface on the vibration frequency of the moving load is discussed.
摘要:The domestic rainwater harvesting system (DRHS) is an important freshwater source for Zhoushan,China to meet water demands. A computer model has been generated to analyze the performance of the DRHS with different ratios of D/(AR) (water demand/average annual collected runoff) and S/(AR) (storage capacity/average annual collected runoff). The performance of the DRHS was analyzed by means of the model simulation,which is described by its water shortage rate (WSR) and water loss rate (WLR). Using the data,a set of dimensionless design calculation chart is introduced. When the water demand and requirement of the design are known,the established chart can be used to easily determine the storage capacity and catchment (roof and other surface) area required to achieve a desired performance level.
摘要:The optimization of the performance of a single-stage Linde-Hampson refrigerator (LHR) operating with six different binary refrigerants (R23/R134a,R23/R227ea,R23/R236ea,R170/R290,R170/R600a and R170/R600) with ozone depletion potentials (ODPs) of zero was conducted using a new approach at the temperature level of -60°C.Among these binary refrigerants,the 0.55 and the 0.6 mole fractions of R23 for R23/R236ea are the most prospective nonflammable ones for the medium and low suction pressure compressors,respectively.For these two kinds of compressors,the 0.6 and the 0.65 mole fractions of R170 for R170/R600,respectively,are the most prospective binary refrigerants with low global warming potentials (GWPs).The results of optimization of pressure levels indicate that the optimum low pressure value for coefficients of performance (COP) is achieved when the minimum temperature differences occur at both the hot and the cold ends of the recuperator at a specified composition and pressure ratio.Two useful new parameters,the entropy production per unit heat recuperated and the ratio of heat recuperating capacity to the power consumption of the compression,were introduced to analyze the exergy loss ratio in the recuperator.The new approach employed in this paper also suggests a promising application even to the optimization of the performance with multi-component refrigerants.
摘要:A new algorithm is proposed for restoring disocclusion regions in depth-image-based rendering (DIBR) warped images. Current solutions include layered depth image (LDI), pre-filtering methods, and post-processing methods. The LDI is complicated, and pre-filtering of depth images causes noticeable geometrical distortions in cases of large baseline warping. This paper presents a depth-aided inpainting method which inherits merits from Criminisi’s inpainting algorithm. The proposed method features incorporation of a depth cue into texture estimation. The algorithm efficiently handles depth ambiguity by penalizing larger Lagrange multipliers of filling points closer to the warping position compared with the surrounding existing points. We perform morphological operations on depth images to accelerate the algorithm convergence, and adopt a luma-first strategy to adapt to various color sampling formats. Experiments on test multi-view sequence showed that our method has superiority in depth differentiation and geometrical loyalty in the restoration of warped images. Also, peak signal-to-noise ratio (PSNR) statistics on non-hole regions and whole image comparisons both compare favorably to those obtained by state of the art techniques.
摘要:This paper describes the results of an investigation into the effect of the variation of curing temperatures between 0 and 60 °C on the hydration process,pore structure variation,and compressive strength development of activated coal gangue-cement blend(ACGC) . Hardened ACGC pastes cured for hydration periods from 1 to 360 d were examined using the non-evaporable water method,thermal analysis,mercury intrusion porosimetry,and mechanical testing. To evaluate the specific effect of activated coal gangue(ACG) as a supplementary cementing material(SCM) ,a fly ash-cement blend(FAC) was used as a control. Results show that raising the curing temperature accelerates pozzolanic reactions involving the SCMs,increasing the degree of hydration of the cement blends,and hence increasing the rate of improvement in strength. The effect of curing temperature on FAC is greater than that on ACGC. The pore structure of the hardened cement paste is improved by increasing the curing temperature up to 40 °C,but when the curing temperature reaches 60 °C,the changing nature of the pore structure leads to a decrease in strength. The correlation between compressive strength and the degree of hydration and porosity is linear in nature.
摘要:The presence of wrinkles in a membrane is the main factor that induces surface errors on space planar film reflect-arrays. Based on the commercial finite element (FE) package ABAQUS, a numerical procedure for membrane wrinkle analysis was set up, and used to analyze a square planar film reflect-array under pure shear force to evaluate its induced wrinkle characteristics. First, the effect of shear force on the wrinkle pattern of the array was studied and validated by experiment. Second, the effect of prestress was studied. When the prestress increases, the quantity of the wrinkles increases, and the amplitude of the wrinkles decreases. Third, the influence of the boundary conditions was investigated. A frame side edge structure has a relatively smooth surface, but also relatively high stress. Finally, the behavior of a joint seam was analyzed. The results indicate that a joint band has a significant influence on the wrinkle pattern of the membrane.
摘要:A new method for estimating the degree of [SiO4]4-polymerization of coal gangue is presented. The method uses the relative bridging oxygen number (RBO) based on nuclear magnetic resonance (NMR) techniques. X-ray diffraction (XRD) and 29Si NMR techniques have been used to study phase transitions and silicate polymerization of coal gangue calcined at different temperatures or co-calcined. It has been found that phase transition of clay minerals causes silicate polymerization to change with temperature. In this study, cementing activity and RBO were determined to be inversely related. Generally, activated coal gangue with lower RBO had better cementitious activity.