Multilayer shallow water flow using lattice Boltzmann method with high performance computing

A multilayer lattice Boltzmann (LB) model is introduced to solve three-dimensional wind-driven shallow water flow problems. The multilayer LB model avoids the expensive Navier–Stokes equations and obtains stratified horizontal flow velocities as vertical velocities are relatively small and the flow is still within the shallow water regime. A single relaxation time BGK method is used to solve each layer coupled by the vertical viscosity forcing term. To increase solution stability, an implicit step is suggested to obtain flow velocities. The main advantage of using the LBM is that after selecting appropriate equilibrium distribution functions, the LB algorithm is only slightly modified for each layer and retains all the simplicities of the LBM within the high performance computing (HPC) environment. The performance of the parallel LB model for the multilayer shallow water equations is investigated on CPU-based HPC environments using OpenMP. We found that the explicit loop control with cache optimization in LBM gives better performance on execution time, speedup and efficiency than the implicit loop control as the number of processors increases. Numerical examples are presented to verify the multilayer LB model against analytical solutions. We demonstrate the model’s capability of calculating lateral and vertical distributions of velocities for wind-driven circulation over non-uniform bathymetry.     

Simplified seismic analysis of asymmetric building systems

The paper reviews the uncoupled modal response history analysis (UMRHA) and modal pushover analysis (MPA) procedure in the analysis of asymmetric structures. From the pushover curves in ADRS format, showing the relationships of base shear versus roof translation and base torque versus roof rotation, a bifurcating characteristic of the pushover curves of an asymmetric structure is observed. A two‐degree‐of‐freedom (2DOF) modal stick is constructed using lump mass eccentrically placed at the end of beam which is connected with the column by a rotational spring. By converting the equation of motion of a whole structure into 2DOF modal equations, all of the elastic properties in the 2DOF modal sticks can be determined accurately. A mathematical proof is carried out to demonstrate that the 2DOF modal stick is consistent with the single‐degree‐of‐freedom (SDOF) modal stick at elastic state. The bifurcating characteristic of modal pushover curves and the interaction of modal translation and rotation can be considered rationally by this 2DOF modal stick. In order to verify the effectiveness of this proposed 2DOF modal stick, a two‐storey asymmetric building structure was analysed by the UMRHA procedure incorporating this novel 2DOF modal sticks (2DMPA) and conventional SDOF modal sticks (SDMPA), respectively. The analytical results are compared with those obtained by nonlinear response history analysis (RHA). It is illustrated that the accuracy of the rotational response histories obtained by 2DMPA is much better than those obtained by SDMPA. Consequently, the estimations of translational response histories on flexible side (FS) and stiff side (SS) of the building structure are also improved. Copyright © 2006 John Wiley & Sons, Ltd.     

Recovery of Gallium and Arsenic from Gallium Arsenide Waste in the Electronics Industry

Gallium arsenide (GaAs) has both high saturated electron velocity and high electron mobility, making it useful as a semiconductor material in a variety of applications, including light‐emitting diodes (LEDs), integrated circuits (ICs), and microwave appliances. A side effect of the use of gallium (Ga) is the production of a relatively large amount of hazardous waste. This study aimed at the recovery of Ga and arsenic (As) from GaAs waste using hydrometallurgical methods involving leaching and coagulation and a dry annealing process that involves annealing, vacuum separation, and sublimation by heating. Our research has shown that GaAs can be leached using nitric acid (HNO₃) to obtain 100% Ga and As with a leaching solution at pH 0.1, with subsequent adjustment of the leaching solution to pH 3 with sodium hydroxide (NaOH). Another method used a leaching solution at pH 2, then adjusting to pH 11 using NaOH. Ferric hydroxide (FeO(OH)) was added at 90°C after NaOH was added to the leaching solution. At pH 2 and 11, 55.5 and 21.9% of the As could be removed from the hazardous waste, respectively. The Ga could also be precipitated. When GaAs powder was heated to 1000°C over 3 h, 100% As removal was achieved, and 92.6% of the Ga was removed by formation of 99.9% gallium trioxide (Ga₂O₃). Arsenic was vaporized when the temperature was elevated to 1000°C, allowing arsenic trioxide (As₂O₃) to condense with 99.2% purity. The Ga₂O₃ powder produced was then dissolved and electrolyzed, allowing for 95.9% recovery of Ga with a purity of 99.9%.     

Slip, Stress Drop and Ground Motion of Earthquakes: A View from the Perspective of Fractional Brownian Motion

—The characteristics of slip and stress drop distributions accompanying earthquakes are explored from the perspective of fractional Brownian motion (fBm). Slip and stress drop distributions are assumed to be processes of fBm.The Hurst exponent (H), which reveals the roughness of a random process of fBm, is first estimated from ten inferred slip maps for six crustal earthquakes occurring in California. The relationships between the Hurst exponents with respect to static slip (H _u ),stress (H _τ ), static stress drop (H _δσ ) and slip velocity (H _ú ) are then established following Andrews (1980). They are found to be H _δσ = H _τ = H _u -1 = H _ú -0.5. Empirically, H _u is recognized as being about 1 which, according to the theory of fBm, implies that the static slip distribution of an earthquake is just on the margin between being and not being self-similar, depending on the individual case. Cases where H _u is less than 1 (i.e., self-similar) suggest that H _δσ < 0(i.e., the distribution of static stress drop diverges), which is, in light of fBm, invalid. One possible explanation for this paradox is that H _u is less than 1 in crustal earthquake phenomena only over a certain specific bandwidth of wavenumbers, or it could be that the relation H _δσ = H _u -1 is not valid, which implies that static stress drop in the wavenumber domain is not the product of stiffness and slip as described in Andrews (1980). It could be that some different physics apply over this particular bandwidth. In such cases, multi-fractals may be a better way to explore the characteristics of the Hurst exponents of slip. In general, static stress drop and stress distributions are more likely to be self-similar than static slip distribution. H _u ≌ 1 and H _δσ ≌ 0 are good first approxima tions for the slip and stress drop distributions. The spectrum of ground motion displacement falls off as ω ^{-(Hδσ + 2)} with H _δσ ≌ 0, consistent with an ω^-2 model of the earthquake source.     

Reflection of typhoon morakot �� the challenge of compound disaster simulation

Climate change has altered locally single-type disasters to large-scale compound disasters because of increasing intensity and frequency of extreme rainfall events. The compound disasters can combine small-scale floods, debris flows, shallow landslides, deep-seated landslides, and landslide lakes into a large-scale single disaster event. Although simulation models and evaluation tools are available for single-type disasters, no single model is well developed for compound disasters due to the difficulty of handling the interrelationship between two successive single-type disasters. This study proposes a structure for linking available single-type simulation models to evaluate compound disasters and provides a useful tool of decision making for warning and planning of disaster reduction.     

Tomographic imaging of the ionosphere using the GPS/MET and NNSS data

The earlier experiments of ionospheric tomography were conducted by receiving satellite signals from ground-based stations and then reconstructing electron density distribution from measures of the total electron content (TEC). In June 1994, National Central University built up the low-latitude ionospheric tomography network (LITN) including six ground stations spanning a range of 16.7° (from 14.6°N to 31.3°N) in latitude within 1° of 121°E longitude to receive the naval navigation satellite system (NNSS) signals (150 and 400 MHz). In the study of tomographic imaging of the ionosphere, TEC data from a network of ground-based stations can provide detailed information on the horizontal structure, but are of restricted utility in sensing vertical structure. However, an occultation observation mission termed the global positioning system/meteorology (GPS/MET) program used a low Earth orbiting (LEO) satellite (the MicroLab-1) to receive multi-channel GPS carrier phase signals (1.5 and 1.2 GHz) and demonstrate active limb sounding of the Earth's atmosphere and ionosphere. In this paper, we have implemented the multiplicative algebraic reconstruction technique (MART) to reconstruct and compare two-dimensional ionospheric structures from measured TECs through the receptions of the GPS signals, the NNSS signals, and/or both of the systems. We have also concluded the profiles retrieved from tomographic reconstruction showing much reasonable electron density results than the original vertical profiles retrieved by the Abel transformation and being in more agreement in peak electron density to nearby ionosonde measurements.     

Effects of open trench siding on vibration-screening effectiveness using the two-dimensional boundary element method

The two-dimensional boundary element method in frequency domain is used to investigate the screening effectiveness of the open trench–wall barrier system on reducing vibration generated by a footing. Sheet piles or diaphragm walls are on both sides of the open trench as a vibration barrier in this study. The results showed that screening effectiveness of the open trench without siding is greater than that of the open trench–wall barrier system, which is essential for stabilizing the excavation surface in practice. The trench depth of the barrier system appears to govern the screening efficiency of the barrier, and increase in depth results in better vibration-screening effectiveness. The influence of the open trench width, the embedded length of the trench wall and the distance between the vibration source and the barrier are proven to be insignificant. The screening effectiveness of an open trench barrier with walls increases with the frequency of the vibration.     

Seismic design and testing of the bottom vertical boundary elements in steel plate shear walls. Part 2: experimental studies

This paper describes an experiment to investigate the seismic design and responses of the bottom column, also called the bottom vertical boundary element (VBE), in steel plate shear walls (SPSWs). The main objectives of this experiment include validating the effectiveness of the design method developed in the companion paper, investigating the experimental performance of VBEs under large interstory drifts, and calibrating analytical models for earthquake engineering of SPSWs. Three full‐scale two‐story SPSWs were cyclically tested at the Taiwan National Center for Research on Earthquake Engineering in 2011. Test results and numerical simulations confirm that the proposed design procedures are effective in predicting the plastic zone forming elevation in the lower half of the bottom VBE and the occurrence of yielding at the VBE's top end. Test results show that the premature yielding occurring at the top end of a bottom VBE would result in a deformation concentration at the bottom of SPSWs. In addition, lateral torsional buckling could take place on the bottom VBE after significant plastic rotations have developed at the top end. Test results suggest that preventing the VBE's top end from yielding is the key issue in the seismic design of SPSWs, and the proposed method can be effectively adopted to achieve this objective. Furthermore, the inelastic responses of the SPSW specimens were satisfactorily simulated by using detailed finite shell elements or simplified frame response analysis models. Copyright © 2014 John Wiley & Sons, Ltd.     

Influence of gusset plate connections and braces on the seismic performance of X‐braced frames

Braced frames are one of the most economical and efficient seismic resisting systems yet few full‐scale tests exist. A recent research project, funded by the National Science Foundation (NSF), seeks to fill this gap by developing high‐resolution data of improved seismic resisting braced frame systems. As part of this study, three full‐scale, two‐story concentrically braced frames in the multi‐story X‐braced configuration were tested. The experiments examined all levels of system performance, up to and including fracture of multiple braces in the frame. Although the past research suggests very limited ductility of SCBFs with HSS rectangular tubes for braces recent one‐story tests with improved gusset plate designs suggest otherwise. The frame designs used AISC SCBF standards and two of these frames designs also employed new concepts developed for gusset plate connection design. Two specimens employed HSS rectangular tubes for bracing, and the third specimen had wide flange braces. Two specimens had rectangular gusset plates and the third had tapered gusset plates. The HSS tubes achieved multiple cycles at maximum story drift ratios greater than 2% before brace fracture with the improved connection design methods. Frames with wide flange braces achieved multiple cycles at maximum story drift greater than 2.5% before brace fracture. Inelastic deformation was distributed between the two stories with the multi‐story X‐brace configuration and top story loading. Copyright © 2010 John Wiley & Sons, Ltd.     

Analyzing Spatial and Temporal Changes of Aquaculture in Yunlin County,Taiwan*

This article analyzes spatial and temporal changes of aquaculture land use in Yunlin County, Taiwan, and discusses the driving forces for these changes. Digital land‐use maps and satellite imagery for 1982, 1988, 1994, and 2002 were used to extract aquaculture areas. A geographic information system was used to derive changes in aquaculture areas and to compute the spatial clustering statistics over time. A survey of eighty‐seven farmers was conducted to obtain their views and concerns about aquaculture. The results show a rapid expansion in aquaculture during the 1980s, driven mainly by exports to Japan, and a continuous decline since the mid‐1990s because of economic, environmental, and demographic factors.