Wells turbine with end plates for wave energy conversion

In order to improve the performance of the Wells turbine for wave energy conversion, the effect of end plate on the turbine characteristics has been investigated experimentally by model testing. As a result, it is found that the characteristics of the Wells turbine with end plates are superior to those of the original Wells turbine, i.e., the turbine without end plate and the characteristics are dependent on the size and position of end plate. Furthermore, by using a computational fluid dynamics (CFD), reason of the performance improvement of the turbine has been clarified and the effectiveness of the end plate has been demonstrated.     

Regional groundwater flow in an area mapped as continuous permafrost, NE Alaska (USA)

Fundamental knowledge of groundwater systems in areas of permafrost is often lacking. The likelihood of finding good quality groundwater resources of acceptable quantities generally decreases as the areal coverage of permafrost increases. In areas of continuous permafrost, the probability of finding areas of groundwater recharge and discharge are minimal. Still, in northeastern Alaska (USA), the presence of numerous springs and associated downstream aufeis formations clearly indicates that there has to be a groundwater system with the required complementary areas of groundwater recharge and transmission. Recharge zones and transmission pathways in this area of extensive permafrost, however, are essentially unknown. This study shows that the recharge occurs on the south side of the Brooks Range in northeastern Alaska, where extensive limestone outcrops are found. The transmission zone is beneath the permafrost, with discharge occurring through the springs via taliks through the permafrost (where faults are present) and also likely at the northern edge of the permafrost along the Beaufort Sea coast.     

Temperature correlations in a compact hyperbolic universe

The effect of a non-trivial topology on the temperature correlations of the cosmic microwave background (CMB) in a small compact hyperbolic universe with volume comparable to the cube of the curvature radius is investigated. Because the bulk of large-angle CMB fluctuations are produced at the late epoch in low-Ω₀ models, the effect of a long-wavelength cut-off owing to the periodic structure does not lead to significant suppression of large-angle power as in compact flat models. The angular power spectra are consistent with COBE data for Ω₀0.1.     

Prediction of the largest peak nonlinear seismic response of asymmetric buildings under bi-directional excitation using pushover analyses

A simplified procedure is proposed to predict the largest peak seismic response of an asymmetric building to horizontal bi-directional ground motion, acting at an arbitrary angle of incidence. The main characteristics of the proposed procedure is as follows. (1) The properties of two independent equivalent single-degree-of-freedom models are determined according to the principal direction of the first modal response in each nonlinear stage, rather than according to the fixed axis based on the mode shape in the elastic stage; the principal direction of the first modal response in each nonlinear stage is determined based on pushover analysis results. (2) The bi-directional horizontal seismic input is simulated as identical spectra of the two horizontal components, and the contribution of each modal response is directly estimated based on the unidirectional response in the principal direction of each. (3) The drift demand at each frame is determined based on four pushover analyses considering the combination of bi-directional excitations. In the numerical example, nonlinear time-history analyses of six four-story torsionally stiff (TS) asymmetric buildings are carried out considering various directions of seismic inputs, and these results are compared with the predicted results. The results show that the proposed procedure satisfactorily predicts the largest peak response displacement at the flexible-side frame of a TS asymmetric building.     

Development of a flood water level estimation method using satellite images and a digital elevation model for the Mekong floodplain

We have developed a flood water level estimation method that only employs satellite images and a DEM. The method involves three steps: (1) discriminating flood areas and identifying clumps of each flood area, (2) extracting the edges of the identified flood area using a buffering technique, and (3) performing spatial interpolation to transform the extracted elevation to flood water levels. We compared the estimated flood water levels with the observed ones. The RMSE using the RADARSAT was 1.99 and 1.30 m at river and floodplain points, respectively, whereas the RMSE using the MODIS was 4.33 and 1.33 m at the river and floodplain points, respectively. Given that most errors are attributed to the DEM, the method exhibited good performance. Furthermore, the method reproduced the flow directions and flood water level changes during the flooding period. Thus, we demonstrated that the characteristics of flood inundation can be understood even when ground observation data cannot be obtained.     

Thermochronology and the three-dimensional cooling pattern of a granitic pluton: an example from the Toki granite,Central Japan

The three-dimensional spatial variations in the cooling pattern of the Toki granitic body, a zoned pluton in Central Japan, have been evaluated quantitatively by thermochronology using cooling age determination based on the different closure temperatures for target mineral species. The Toki granite has hornblende K–Ar ages of about 74.3 ± 3.7 Ma (N = 2; closure temperature of 510 ± 25°C), biotite K–Ar ages of 78.5 ± 3.9 to 59.7 ± 1.5 Ma (N = 33; 300 ± 50°C), and zircon fission-track ages of 75.6 ± 3.3 to 52.8 ± 2.6 Ma (N = 44; 240 ± 50°C). The spatial variation in the biotite K–Ar age is similar to that in the zircon fission-track age in samples collected from 11 boreholes and seven outcrop sites in the Toki granite, indicating that cooling was effectively from the roof and also from the northwest margin. This cooling pattern shows a strong correlation with the Alumina Saturation Index (ASI) distribution of the body. Larger ASI values correspond to earlier and more rapid cooling after emplacement and smaller value to slower cooling. Toki granite was effectively cooled from the peraluminous regions where assimilation of country sedimentary rock was most extensive.     

Spreading of river water in Suruga Bay

We have investigated the spreading of river water in Suruga Bay by performing numerical experiments and conducting field surveys with drifting buoys. There are clear seasonal variations in the large river discharges into the bay: increased discharge in the rainy summer season and decreased discharge in the dry winter season. The numerical model reproduces the main feature that has been observed in the actual sea: the river water extends gradually from the northwestern to the southeastern regions in the bay, especially in summer. The river water spreading is greatly influenced by the bottom topography of the bay: the Fuji River water spreads over a deep continental slope as a surface-advected plume and extends well offshore, since a large bulge (anticyclonic eddy at the river mouth) extends well offshore and effectively transports the river water offshore. On the other hand, the Oi River water tends to flow parallel to isobaths (along a coastline) on a shallow continental shelf as a bottomadvected plume. Moreover, the influences of seasonal variations in the stratification and a bay-scale, wind-driven circulation are also investigated. Trajectories of the drifting buoys, which were released around the Fuji River mouth, certainly suggest that the bulge exists there.     

Discriminating residual and colluvial soils using topographic analysis in a small,forested catchment in Japan

Soil moisture plays an important role in hydrology. Understanding factors (such as topography, vegetation, and meteorological conditions) that influence spatio‐temporal variability in soil moisture, and how this influence is manifested, is important for understanding hydrological processes. A number of distributed (quasi‐)physical hydrological models have been developed to investigate this subject. Previous studies have shown that the spatial differences in the distribution of soil types (residual and colluvial soils) dominantly reflect spatio‐temporal fluctuations in soil moisture and runoff. We present a methodology for assessing the spatial distribution of residual and colluvial soils, which differ with respect to their physical characteristics, in a 0·88 km² forested catchment with complex topography and a complex land‐use history. Our method is based on penetration resistance profile data; in this data set, each data point represents soil physical characteristics within an area of about 25 m². If the spatial distribution of soils under similar meteorological, geological, historical land use, and other conditions could be characterized on the basis of similarity in topographic features, then the spatial distribution of soil could be predicted based on relationships between various topographic indices (e.g. topographic index and local slope). We tested whether our model correctly assessed the reference data. The model's results were 90·5% correct for residual soils and 87·3% correct for colluvial soils. Further studies will quantify the relationships between topographic features of land covered by residual and colluvial soils and changes in spatio‐temporal variations in the catchment (e.g. vegetation and land use) as a function of geology or meteorology. Copyright © 2007 John Wiley & Sons, Ltd.