Filtering of discrete time series by symmetric least-squares operators

Least-squares operators with real and symmetric coefficients are shown to be equivalent to low-pass digital filters. By viewing these operators as digital filters one gains considerable insight into their properties. This in turn leads to a better understanding of their usefulness and limitations in data smoothing. It is shown that complete removal of noise from a given input time series is possible with the use of least-squares operators if spectral overlapping between signal and noise does not exist. Power-spectral analysis which provides information about the frequency composition of the input data is essential for successful application of least-squares operators.     

Prediction of pile capacity from stress-wave measurements: A neural network approach

A neural network approach for the prediction of pile bearing capacity by the stress-wave matching technique is presented. The main advantage of this approach over the traditional manual or automated matching approach is that it avoids the time-consuming process of iterative adjustment. This makes it feasible to determine the static pile capacity in real time in the field. Another benefit of this approach is that as more case histories become available, the neural network can be improved by learning from these new examples. A three-layer back-propagation network is set up to illustrate the capability of the proposed approach for 70 dynamically tested concrete bored piles. A wave equation model developed at the National University of Singapore and coded in the NUSWAP computer program is used to formulate the problem. Up to 14 of the 70 piles (20 percent) are used in training the network. The NUSWAP program is used to generate simulation training examples based on the manually fitted training examples for further training of the network. Different network configurations are examined. The trained network produces results exhibiting good stress-wave matching qualities compared to those obtained by manual fitting. The pile bearing capacities predicted by the two approaches agree very closely. The load-settlement curve and axial load distribution in the pile computed using the network-predicted soil parameters are in good agreement with the field measurements obtained from a maintained load test.     

Collapse of a radiating anisotropic star

Further results are obtained concerning the model of a collapsing anisotropic body by Kolassis and Santos. It is assumed an anisotropic equation of state for the static configuration, and a relation between the radiation density and heat flux. The total luminosity received by an observer at infinity is independent of the anisotropy of the fluid and of the radiation produced in the body. Numerical calculations are performed for a body having a mass of 5M in order to obtain the effective adiabatic index.     

Multiscaling properties of concentration fluctuations in dispersing plumes revealed using an orthonormal wavelet decomposition

The dynamical characteristics of concentration fluctuations in a dispersing plume over the energetic and inertial-convective range of scales of turbulent motion are studied using a multiscale analysis technique that is based on an orthonormal wavelet representation. It is shown that the Haar wavelet concentration spectrum is similar to the Fourier concentration spectrum in that both spectra exhibit an extensive inertial-convective subrange spanning about two decades in frequency, with a scaling exponent of -5/3. Analysis of the statistical properties (e.g., fluctuation intensity, skewness, and kurtosis) of the concentration wavelet coefficients (i.e., the concentration discrete detailed signal) suggests that the small scales are always more intermittent than the large scales. The degree of intermittency increases monotonically with decreasing scale within the inertial-convective subrange, reaching a plateau at the very small scales associated with the beginning of the near-dissipation subrange. The probability density function (pdf) of the concentration discrete detailed signal displays stretched exponential tails with an intermittency exponent (tail slope) q that increases as ^a , where is the scale or dilation and a is a power-law exponent that is dependent on downwind distance, plume height, and stratification strength with typical values in the range from about 0.25 to 0.35. It is shown that the concentration variance cascade process requires a phase coherency of eddies between different scales at the small-scale end of the inertial-convective subrange.The variation of the concentration wavelet statistics with height above the ground is investigated. The increased mean shear near the ground smooths the fine-scale plume structure for scales within the inertial-convective subrange, producing a weaker spatiotemporal intermittency in the concentration field compared to that measured higher up in the plume. The pdf of the concentration detailed signal at a fixed scale possesses less elongated tails with decreasing height z. The intermittency exponent q is found to decrease roughly linearly with increasing z.Finally, the results of the wavelet decomposition are combined to provide a conceptual model of the turbulent transport, stirring, and mixing regimes in a dispersing plume. The implications of the results for contaminant texture in a plume are discussed.     

Global Seismic Hazard Assessment Based on Area Source Model and Seismicity Data

A global seismic hazard assessment was conducted using the probabilistic approach in conjunction with a modified means of evaluating the seismicity parameters. The earthquake occurrence rate function was formulated for area source cells from recent instrumental earthquake catalogs. For the statistical application of the G–R relation of each source cell, the upper- and lower-bound magnitudes were determined from, respectively, historical earthquake data using a Kernel smoothing operator and detection thresholds of recent catalogs. The seismic hazard at a particular site was obtained by integrating the hazard contribution from influencing cells, and the results were combined with the Poisson distribution to obtain the seismic hazard in terms of the intensity at 10% probability of exceedance for the next 50 years. The seismic hazard maps for three countries, constructed using the same method, agree well with the existing maps obtained by different methods. The method is applicable to both oceanic and continental regions, and for any specific duration of time. It can be used for those regions without detailed geological information or where the relation between existing faults and earthquake occurrence is not clear.     

A Modified Cyclic Cracking Model for RC Structural Walls Behaviour Under Dynamic Excitation

In this paper, a simple cyclic cracking model incorporating crack dilatancy effect is proposed to model the behaviour of reinforced concrete structures under earthquake-like dynamic loading. This model has been implemented into a FE programme [LUSAS (2004) Luscas User Manual (version 12.3), FEA Ltd., London, England] to simulate reversed and cyclic loading. A shaking table test performed in Switzerland at the Swiss Federal Institute of Technology at Zurich (ETHZ) has been chosen for comparison. The test performed on the shaking table simulated a wall of a 3-storey building. The natural frequency and the crack pattern have been calculated and show reasonable agreement with the experimental results     

Numerical flow simulation of flush type intake duct of waterjet

Waterjet propulsion system is widely used to thrust high speed marine vessels in excess of 30–35 knots by virtue of high propulsive efficiency, good maneuverability, and less vibration. Since, however, approximately 7–9% of the total power is lost in intake duct due to flow separation, nonuniformity, etc., detail understanding of flow phenomena occurring within intake duct is essential to reduce the power loss. The present work solved 3D incompressible RANS equations on multiblocked grid system of the flush type intake duct of waterjet. The numerical results of surface pressure distributions, velocity vectors, and streamlines were compared with experiments and good agreements were obtained for three jet velocity ratios. Strong suction flow through the inlet was shown and the vortex induced by the separation along the corner of the side wall was clearly shown. Flow separation on the lip was also observed. The location of stagnation point on the lip was well predicted, in accordance with PIV measurement.     

Ecology of the marine cladoceran Penilia avirostris Dana in Tolo Harbour, Hong Kong

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Comparison of two bias correction methods for precipitation simulated with a regional climate model

This study evaluates the performance of two bias correction techniques—power transformation and gamma distribution adjustment—for Eta regional climate model (RCM) precipitation simulations. For the gamma distribution adjustment, the number of dry days is not taken as a fixed parameter; rather, we propose a new methodology for handling dry days. We consider two cases: the first case is defined as having a greater number of simulated dry days than the observed number, and the second case is defined as the opposite. The present climate period was divided into calibration and validation sets. We evaluate the results of the two bias correction techniques using the Kolmogorov-Smirnov nonparametric test and the sum of the differences between the cumulative distribution curves. These tests show that both correction techniques were effective in reducing errors and consequently improving the reliability of the simulations. However, the gamma distribution correction method proved to be more efficient, particularly in reducing the error in the number of dry days.