Dynamics of an elastically moored floating body by the three-dimensional infinite element method     

S. L. Lau  Z. Ji  C. O. Ng 《Ocean Engineering》1990,17(5)

The three-dimensional problem of the dynamics of a moored floating object under the action of regular waves is solved numerically as a boundary value problem by use of the finite-infinite element method. The cross-sectional shape of the floating body and the mooring arrangements may all be arbitrary. The mathematical formulations of the problem and procedures of the numerical method are presented in this paper. A corresponding computer program WALOAD has been developed, which is capable of computing wave forces on fixed and floating structures. Numerical computations using this program could give very accurate results, even though rather coarse meshes were used. The program is easy to use and is readily applicable in many practical situations.  相似文献   

Second order wave diffraction forces and runup by finite—infinite element method     

B.Y. Li  S.L. Lau  C.O. Ng 《Applied Ocean Research》1991,13(6):270-286

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Gas hydrate disturbance fabrics of southern Hydrate Ridge sediments (ODP Leg 204): Relationship with texture and physical properties   总被引：1，自引：0，他引：1  

Elena Piñero  Eulàlia Gràcia  Francisca Martínez-Ruiz  Juan Cruz Larrasoaña  Alexis Vizcaino  Gemma Ercilla 《Geo-Marine Letters》2007,27(2-4):279-288

Soupy and mousse-like fabrics are disturbance sedimentary features that result from the dissociation of gas hydrate, a process that releases water. During the core retrieval process, soupy and mousse-like fabrics are produced in the gas hydrate-bearing sediments due to changes in pressure and temperature conditions. Therefore, the identification of soupy and mousse-like fabrics can be used as a proxy for the presence of gas hydrate in addition to other evidence, such as pore water freshening or anomalously cool temperature. We present here grain-size results, mineralogical composition and magnetic susceptibility data of soupy and mousse-like samples from the southern Hydrate Ridge (Cascadia accretionary complex) acquired during Leg 204 of the Ocean Drilling Program. In order to study the relationship between sedimentary texture and the presence of gas hydrates, we have compared these results with the main textural and compositional data available from the same area. Most of the disturbed analyzed samples from the summit and the western flank of southern Hydrate Ridge show a mean grain size coarser than the average mean grain size of the hemipelagic samples from the same area. The depositional features of the sediments are not recognised due to disturbance. However, their granulometric statistical parameters and distribution curves, and magnetic susceptibility logs indicate that they correspond to a turbidite facies. These results suggest that gas hydrates in the southern Hydrate Ridge could form preferentially in coarser grain-size layers that could act as conduits feeding gas from below the BSR. Two samples from the uppermost metres near the seafloor at the summit of the southern Hydrate Ridge show a finer mean grain-size value than the average of hemipelagic samples. They were located where the highest amount of gas hydrates was detected, suggesting that in this area the availability of methane gas was high enough to generate gas hydrates, even within low-permeability layers. The mineralogical composition of the soupy and mousse-like sediments does not show any specific characteristic with respect to the other samples from the southern Hydrate Ridge.  相似文献   

The Creation of a National Agricultural Land Use Dataset: Combining Pycnophylactic Interpolation with Dasymetric Mapping Techniques     

Alexis Comber  Chris Proctor  Steve Anthony 《Transactions in GIS》2008,12(6):775-791

Agricultural Census data is summarised over spatially coarse reporting units for reasons of farm confidentiality. This is problematic for research at a local level. This article describes an approach combining dasymetric and volume preserving techniques to create a national land use dataset at 1 km² resolution. The results for an English county are compared with contemporaneous aggregated habitat data. The results show that the accurate estimates of local agricultural land use (Arable and Grass) patterns can be estimated when individual 1 km squares are combined into blocks of > 9 squares, thereby providing local estimates of agricultural land use. This in turn allows more detailed modelling of land uses related to specific livestock and cropping activities. The dataset created by this work has been subject to extensive external validation through its incorporation into a number of other national models: nitrate leaching (e.g. MAGPIE, NEAP‐N), waste, and pathogen modelling related to agricultural activity.  相似文献   

Crustal structure across the Grand Banks–Newfoundland Basin Continental Margin – II. Results from a seismic reflection profile     

K. W. Helen Lau  Keith E. Louden  Sharon Deemer  Jeremy Hall  John R. Hopper  Brian E. Tucholke  W. Steven Holbrook  Hans Christian Larsen † 《Geophysical Journal International》2006,167(1):157-170

New multichannel seismic reflection data were collected over a 565 km transect covering the non-volcanic rifted margin of the central eastern Grand Banks and the Newfoundland Basin in the northwestern Atlantic. Three major crustal zones are interpreted from west to east over the seaward 350 km of the profile: (1) continental crust; (2) transitional basement and (3) oceanic crust. Continental crust thins over a wide zone (∼160 km) by forming a large rift basin (Carson Basin) and seaward fault block, together with a series of smaller fault blocks eastwards beneath the Salar and Newfoundland basins. Analysis of selected previous reflection profiles (Lithoprobe 85-4, 85-2 and Conrad NB-1) indicates that prominent landward-dipping reflections observed under the continental slope are a regional phenomenon. They define the landward edge of a deep serpentinized mantle layer, which underlies both extended continental crust and transitional basement. The 80-km-wide transitional basement is defined landwards by a basement high that may consist of serpentinized peridotite and seawards by a pair of basement highs of unknown crustal origin. Flat and unreflective transitional basement most likely is exhumed, serpentinized mantle, although our results do not exclude the possibility of anomalously thinned oceanic crust. A Moho reflection below interpreted oceanic crust is first observed landwards of magnetic anomaly M4, 230 km from the shelf break. Extrapolation of ages from chron M0 to the edge of interpreted oceanic crust suggests that the onset of seafloor spreading was ∼138 Ma (Valanginian) in the south (southern Newfoundland Basin) to ∼125 Ma (Barremian–Aptian boundary) in the north (Flemish Cap), comparable to those proposed for the conjugate margins.  相似文献   

用MODIS遥感资料分析四川盆地气溶胶光学厚度时空分布特征   总被引：25，自引：1，他引：25       下载免费PDF全文

李成才  刘启汉等 《应用气象学报》2003,14(1):1-7

利用MODIS卫星遥感光学厚度产品，分析了四川盆地光学厚度分布和季节变化特征。由于受沙尘天气的影响，春季四川盆地具有最大的平均光学厚度。盆地内几个大值区中，西部成都一带的中心常年维持，季节变化小；南部中心位于宜宾到重庆沿长江流域一带；东部南充到重庆间的大值中心，季节变化大，在夏季消失。光学厚度分布和季节变化的数据结果为研究区域气候变化提供了依据。  相似文献   

Numerical simulation of a South China Sea typhoon Leo (1999)   总被引：6，自引：0，他引：6  

K.-H. Lau  Z.-F. Zhang  H.-Y. Lam  S.-J. Chen 《Meteorology and Atmospheric Physics》2003,83(3-4):147-161

Summary ?A South China Sea typhoon, Leo (1999), was simulated using the Penn State/NCAR mesoscale model MM5 with the Betts-Miller convective parameterization scheme (BMEX). The simulation had two nested domains with resolutions at 54 and 18 km, and the forecast duration was 36 hours. The model was quite successful in predicting the track, the rapid deepening, the central pressure, and the maximum wind speed of typhoon Leo as verified with reports from the Hong Kong Observatory (HKO). The structure of the eye, the eye wall, and the spiral convective cloud band simulated in the model are found to be comparable to corresponding features identified in satellite images for the storm, and also with those reported by other authors. A trajectory analysis was performed. Three kinds of trajectory were found: (1) spirally rising trajectories near the eye wall; (2) spirally rising/descending trajectories in the convective/cloud free belt; (3) straight and fast rising trajectories in a heavy convection zone along one of the cloud bands on the periphery of the tropical cyclone. Both the HKO and the U.S. Joint Typhoon Warning Center (JTWC) reported the rapid deepening of Leo started around 00 UTC 29 April. In the model, the eye was first formed in the lower troposphere, and it extended to the upper troposphere within a few hours. We speculate that the spin-up of cyclonic rotation in the low-level eye enhanced the positive vorticity along the low-level eye wall. The positive vorticity was then transported to the upper troposphere by convection, leading to an extension and growth of the eye into the upper troposphere. To examine the impact of convective parameterization scheme (CPS) on the simulation, the Grell scheme (GLEX) was also tested. The GLEX predicted a weaker typhoon with a wilder eye that extended not as high up in the upper troposphere as BMEX. The different structures of the eye between the BMEX and GLEX suggest that the mesoscale features of the eye are dependent on the convection. In other words, the vertical and horizontal distribution of convective heating is essential to the development and structure of the eye. Received December 18, 2001; accepted May 7, 2002 Published online: March 20, 2003  相似文献   

Abrasiveness of Common Rocks in Hong Kong     

Y. K. Ho  S. T. C. So  T. M. F. Lau  R. C. M. Kwok 《Rock Mechanics and Rock Engineering》2016,49(7):2953-2958

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Chemical Composition of Ancient Celadon Material （1127-1279 A.D.） from Zhejiang, China and Its Implication     

PENG Zicheng LEUNG Po Lau YU Peter CHENG Peikai LI Mai 《《地质学报》英文版》2006,80(5):759-762

The microprobe EDXRF equipment was used for analysis of the major and trace elements in glaze layer-transitive layer-body layer of the celadon from the Altar Yao （Kiln） and Laohudong Yao in the Southern Song Dynasty （1127-1279 A.D.）, Zhejiang, China. The K values of the discriminant factor for the celadon wares are larger than 8, which means the celadon of the Altar Yao and Laohudong Yao are different from that of the Longquan Yao. The former two belong to the Guan Yao system （the Chinese imperial kilns）, but the latter to the Min Yao system （the Chinese popular kilns）. The principle component analysis shows their relationship between the Altar and Laohudong wares with provenance postulation. The thickness of the transitive layer in the Altar and Laohudong wares is obviously different, which reveals the microstructure characteristics of the celadon even though both kinds of wares belong to the imperial kiln system.  相似文献   

A new method to determine the gravity field of small bodies from line-of-sight acceleration data     

Nian-Chuan Jian  Jian-Guo Yan  Jin-Song Ping  Jean-Pierre Barriot  J.Alexis P.Rodriguez 《天文和天体物理学研究(英文版)》2019,(3):155-164

We present a new method to derive line-of-sight acceleration observables from spacecraft radio tracking data. The observables can be used to estimate the mass and gravity of a natural satellite as a spacecraft flyby. The corresponding observation model adapts to one-way and two/three-way tracking modes. As a test case for method validation and application, we estimated the mass and degree two gravity field for the Martian moon Phobos using simulated tracking data when the spacecraft Mars Express flew by Phobos on 2013 December 29. We have a few real tracking data during flyby and they will be used to confirm raw data simulation. The main purpose of this paper is to demonstrate the method of line-of-sight acceleration reduction from raw tracking data and the feasibility to estimate mass and gravity of a natural satellite using this type of observable. This novel method is potentially applicable to planet and asteroid gravity field studies combined with Doppler tracking data.  相似文献