Development of an empirical model for rainfall-induced hillside vulnerability assessment: a case study on Chen-Yu-Lan watershed,Nantou, Taiwan

In Taiwan, the hillside is about 70 % of total area. These areas also have steep topography and geological vulnerability. When an event of torrential rain comes during a typhoon, the landslide disasters usually occur at these areas due to the long duration and high intensity of rainfall. Therefore, a design which considers the potential landslide has become an important issue in Taiwan. In this study, a temporal characteristic of landslide fragility curve (LFC) was developed, based on the geomorphological and vegetation factors using landslides at the Chen-Yu-Lan watershed in Taiwan, during Typhoon Sinlaku (September 2008) and Typhoon Morakot (August 2009). This study addressed an effective landslide hazard assessment process, linking together the post-landslide damage and post-rainfall data for LFC model. The Kriging method was used to interpolate the rainfall indices (R ₀, R, I) for numerical analysis. Remote sensing data from SPOT images were applied to analyze the landslide ratio and vegetation conditions. The 40-m digital elevation model was used for slope variation analysis in the watershed, and the maximum likelihood estimate was conducted to determine the mean and standard deviation parameters of the proposed empirical LFC model. This empirical model can express the probability of exceeding a damage state for a certain classification (or conditions) of landslides by considering a specific hazard index for a given event. Finally, the vulnerability functions can be used to assess the loss from landslides, and, in the future, to manage the risk of debris flow in the watershed.     

Effect of growing watershed imperviousness on hydrograph parameters and peak discharge

An increasing impervious area is quickly extending over the Wu‐Tu watershed due to the endless demands of the people. Generally, impervious paving is a major result of urbanization and more recently has had the potential to produce more enormous flood disasters than those of the past. In this study, 40 available rainfall–runoff events were chosen to calibrate the applicable parameters of the models and to determine the relationships between the impervious surfaces and the calibrated parameters. Model inputs came from the outcomes of the block kriging method and the non‐linear programming method. In the optimal process, the shuffled complex evolution method and three criteria were applied to compare the observed and simulated hydrographs. The tendencies of the variations of the parameters with their corresponding imperviousness were established through regression analysis. Ten cases were used to examine the established equations of the parameters and impervious covers. Finally, the design flood routines of various return periods were furnished through use of approaches containing a design storm, block kriging, the SCS model, and a rainfall‐runoff model with established functional relationships. These simulated flood hydrographs were used to compare and understand the past, present, and future hydrological conditions of the watershed studied. In the research results, the time to peak of flood hydrographs for various storms was diminished approximately from 11 h to 6 h in different decrements, whereas peak flow increased respectively from 127 m³ s^?1 to 629 m³ s^?1 for different storm intensities. In addition, this study provides a design diagram for the peak flow ratio to help engineers and designers to construct hydraulic structures efficiently and prevent possible damage to human life and property. Copyright © 2007 John Wiley & Sons, Ltd.     

High-frequency near-bottom acoustic reflection signatures of hydrocarbon seeps on the Northern Gulf of Mexico continental slope

Acoustic reflection signatures of four hydro-carbon seeps were classified using near-bottom 25-kHz echosounder profiles. Echo patterns were compared with ground-truth data obtained by submersible observations and shallow coring. Six echo types were distinguished: strong reflections from (1)?exposed or (2)?buried hard substrates, such as authigenic carbonate or gas hydrate; acoustic scattering in (3)?unlayered or (4)?layered sediments owing to gas, shells, or disseminated carbonates; (5)?attenuation caused by gas; and (6)?undisturbed sediments. Echo type distributions suggest that high spatial variability indicates a younger, vigorous seep, whereas extensive hard substrate implies an older, encrusted seep.     

Adaptive Surface Interference Suppression for Matched-Mode Source Localization

Localizing a quiet submerged target in the presence of loud interfering surface ships is an important problem for matched-field processing (MFP) in shallow water. Typically, a data-driven interference suppression scheme is employed which requires neither prior information of the interferer's location nor filter design optimization and iterative estimation. However, the target and the interferers are usually in motion resulting in spreading or mixing of signal energies in their subspaces, thus making it difficult to determine the interference subspace dimension. In this paper, we exploit the difference in modal amplitudes for surface and submerged sources by eigenanalysis of the modal cross-spectral density matrix (CSDM). Simulation and experimental data results show that the interference subspace can be estimated adaptively and the beam output for the target is enhanced.      

Eddies in the southwestern East/Japan Sea

Closed loop mesoscale eddies were identified and tracked in the Ulleung Basin of the southwestern Japan/East Sea (JES) using the winding-angle (WA) methodology, for mapping the absolute geostrophic currents into surface streamlines of flow. The geostrophic velocity used here was the sum of the Archiving, Validation and Interpretation of Satellite Oceanographic data (AVISO), time variable velocity and the 1992–2007 mean geostrophic velocity. Local sampling bias was removed using the drifter observations. This WA methodology of deriving the Lagrangian path lines that drifters followed over a 7-day period was validated by individual drifter tracks and it demonstrated closed looping eddy motions. The WA method demonstrated that less than 6% of the closed streamlines appeared when drifters did not show a closed loop in their vicinity, compared to 30% of the excess detection rate by the Okubo–Weiss method of locating closed loop structures. Three groups of eddies were identified: (1) Coastal Cold and Warm Eddies, which appeared in the area between the coast of southern Korea and the East Korean Warm Current (EKWC), when a southward coastal current was present, (2) Frontal Cold and Warm Eddies, which were formed in the region of the seaward extension of the meandering EKWC, north of Ulleung Island and (3) Ulleung Warm Eddies (UWE) and Dok Cold Eddies (DCE), which appeared during meanders of the EKWC, in the Ulleung Basin. No seasonal concentration for eddy generation and eddy population was found. The average radius of eddies was about 38–60 km. These were born, moved in an erratic pattern and then died in the vicinity where the EKWC separated from the coast and formed a large meander. The time-mean large meander formed meridionally concentrated bands of positive and negative relative vorticity. The cyclonic (cold) eddies tend to reside within the band of positive time-mean relative vorticity, and the anticyclonic (warm) eddies reside within the bands of negative relative vorticity. Six UWE and four warm eddies, in the Yamato Basin (about 10% of warm eddies), were sustained longer than a year. Because the large meander of the EKWC appeared to be controlled by topography, and the JES is a nearly enclosed basin with rapid flow-out to the east through the narrow Tsugaru Strait, there was little eddy energy propagation to the west. The warm eddies in the southwestern part of the JES appeared to be interacting very locally with the mean flow.     

Variational principles and finite element simulations for thermo-elastic consolidation

In this paper, a general variational principle for the initial boundary value problem of quasi-static thermoelastic consolidation is developed by assuming infinitesimal deformation and an incompressible fluid flowing through a linearly elastic solid. By manipulating the coupling operators, an extended form of the variational pronciple is derved. The associated finite element formulation based on this principle is presented and numerical applications for plane strain thermo-elastic consolidation are revealed.     

Models of rapidly rotating neutron stars: remnants of accretion-induced collapse

Equilibrium models of differentially rotating nascent neutron stars are constructed, which represent the result of the accretion-induced collapse of rapidly rotating white dwarfs. The models are built in a two-step procedure: (1) a rapidly rotating pre-collapse white dwarf model is constructed; (2) a stationary axisymmetric neutron star having the same total mass and angular momentum distribution as the white dwarf is constructed. The resulting collapsed objects consist of a high-density central core of size roughly 20 km, surrounded by a massive accretion torus extending over 1000 km from the rotation axis. The ratio of the rotational kinetic energy to the gravitational potential energy of these neutron stars ranges from 0.13 to 0.26, suggesting that some of these objects may have a non-axisymmetric dynamical instability that could emit a significant amount of gravitational radiation.     

Properties of optical fibres at cryogenic temperatures

A perhaps surprising property of optical fibres is that they remain flexible at cryogenic temperatures. This implies that they may be used for multiple-object and integral field spectroscopy in the thermal infrared in cryogenic instrumentation. In this paper the results of performance tests of optical fibres (silica and zirconium fluoride) at cryogenic temperatures are presented. By mounting the fibres in glass tubes with the appropriate adhesive, it was found that only negligible focal ratio degradation occurs when the fibre is cooled to 77 K.     

Estimation of the Roll Hydrodynamic Moment Model of a Ship by Using the System Identification Method and the Free Running Model Test

When a fast container ship or a naval vessel turns, accompanying roll motions occur. This roll effect must be considered in the horizontal equations of the motion of the ship to predict the maneuverability of the ship properly. In this paper, a new method for determining a model structure of the hydrodynamic roll moment acting on a ship and for estimating the hydrodynamic coefficients is proposed. The method utilizes a system identification technique with the data from sea trial tests or from free running model (FRM) tests. To obtain motion data that is applied to the proposed algorithm, an FRM of a large container ship was developed. Using this model ship, standard maneuvering tests were carried out on a small body of water out of doors. A hydrodynamic roll moment model was constructed utilizing the data from turning circle tests and a 20-20 zig-zag test. This was then confirmed through a 10-10 zig-zag test. It was concluded that a model structure of the hydrodynamic roll moment model could be established without difficulty through a system identification method and FRM tests.     

A simplified pseudo-fluid model derived from biot theory through low grazing angle approximation

We propose an approximation technique with which the porous Biot model can be converted into a pseudo-fluid medium model, i.e., a medium represented by its sound speed and density. This technique begins from an analytic derivation of the reflection coefficient on a planar interface of fluid and porous ocean sediment. Invoking the low grazing angle approximation, useful for solving long range propagation problems, the pseudo-fluid medium is obtained. Alternate pseudo-fluid medium can be obtained through the weak frame approximation (Williams, J. Acoust. Soc. Am. 110, 2276-2281, 2001). In this paper, we discuss the accuracy and limitations of the low grazing angle approximation by numerically comparing the reflection coefficient to the full Biot model cases as functions of various Biot parameters, frequency, and water sound speed. The usefulness of the present low grazing angle approximated pseudo-fluid medium in ocean wave propagation modeling is demonstrated by comparing the transmission loss results with that of the full Biot model.