Identification of uncertainties in the shape of geophysical objects with level sets and the adjoint method     

Dimitris Papadopoulos  Michael Herty  Volker Rath  Marek Behr 《Computational Geosciences》2011,15(4):737-753

A shape reconstruction method for geophysical objects by temperature measurements is presented which uses adjoint equations and a level set function approach. Temperature is measured on subdomains, e.g., representing boreholes. This information is used to reconstruct the shape of the geophysical layers. For this purpose, shape optimization techniques are applied. The method uses a representation of the layers by a so-called level set function. The evolution of this level set function is then used to determine the optimal shape. The “speed” of the evolution is computed using adjoint equations. Synthetic examples demonstrate the use of the inverse method and its behavior in different configurations.  相似文献   

Evaluation of soil salinization in a Mediterranean site (Agoulinitsa district—West Greece)     

Dimitris Alexakis  Dimitris Gotsis  Spyros Giakoumakis 《Arabian Journal of Geosciences》2015,8(3):1373-1383

Soil salinization is an environmental problem having significant impacts on the soil–water–plant system. This problem is more frequent in coastal areas due to seawater intrusion into the land. Assessing the soil salinization is a critical issue for the agricultural areas situated in the Mediterranean basin. This paper examines the deterioration of soil quality in the cultivated land of a Mediterranean site (Agoulinitsa district—West Greece). Soil samples were collected in both pre-irrigation and post-irrigation seasons. Electrical conductivity (EC), pH and the ions Br^?, Ca²⁺, Cl^?, F^?, K⁺, Li⁺, Mg²⁺, Na⁺, NH₄ ⁺, NO₂ ^?, NO₃ ^?, PO₄ ^3? and SO₄ ^2? were determined by the 1:2 (soil/water ratio on weight basis) method. The salts which were present in both seasons in the soils of the area studied are KCl, MgCl₂, NaCl, CaSO₄ and K₂SO₄. The wide spatiotemporal variation of EC in the cultivated land in both seasons demonstrates that soil salinity is controlled mainly by seawater intrusion and anthropogenic factors such as the application of salt-rich water which is directly pumped from the drainage ditches. Seawater intrusion provides the affected soil with elevated contents of Ca²⁺, Cl^?, K⁺, Mg²⁺, Na⁺ and SO₄ ^2?. Classification of the soils by using criteria given by the literature is discussed. Practices to prevent, or at least ameliorate, salinization in the cultivated land of Agoulinitsa district are proposed.  相似文献   

Safety level of damaged RoPax ships: Risk modelling and cost-effectiveness analysis     

Luis Guarin  Dimitris Konovessis  Dracos Vassalos 《Ocean Engineering》2009,36(12-13):941-951

This paper elaborates on results of a recent risk analysis study for RoPax vessels, carried out as part of the activities of the SAFEDOR Integrated Project, targeting possible improvements on safety levels following large scale flooding. The study is based on a comprehensive analysis of accident statistics for the period 1994–2004, through which a high-level risk model (in the form of event trees) is established. This is then used to determine the current safety level of RoPax vessels (in various risk metrics, such as individual risk, potential loss of life and on an F–N curve), reconfirming that even though safety levels are improving, risk is still “high in the ALARP region”. In search of ways to further improve the situation possible risk control options are examined, by performing a sensitivity analysis on the effects of the Attained Index of Subdivision A onto the safety levels and by evaluating their cost-effectiveness.  相似文献   

Burned area mapping and post-fire impact assessment in the Kassandra peninsula (Greece) using Landsat TM and Quickbird data     

Dimitris Palandjian  Ioannis Z. Gitas  Robert Wright 《国际地球制图》2013,28(3):193-205

The purpose of this study was to assess the environmental impacts of forest fires on part of the Mediterranean basin. The study area is on the Kassandra peninsula, prefecture of Halkidiki, Greece. A maximum likelihood supervised classification was applied to a post-fire Landsat TM image for mapping the exact burned area. Land-cover types that had been affected by fire were identified with the aid of a CORINE land-cover type layer. Results showed an overall classification accuracy of 95%, and 83% of the total burned area was ‘forest areas’. A normalized difference vegetation index threshold technique was applied to a post-fire Quickbird image which had been recorded six years after the fire event to assess the vegetation recovery and to identify the vegetation species that were dominant in burned areas. Four classes were identified: ‘bare soil’, ‘sparse shrubs’, ‘dense shrubs’ and ‘tree and shrub communities’. Results showed that ‘shrublands’ is the main vegetation type which has prevailed (65%) and that vegetation recovery is homogeneous in burned areas.  相似文献   

Environmental Economics and the Mining Industry: Monetary benefits of an abandoned quarry rehabilitation in Greece     

Dimitris?DamigosEmail author  Dimitris?Kaliampakos 《Environmental Geology》2003,44(3):356-362

During the last decades legislative actions on environmental issues have dramatically increased all over the world. The impacts of environmental legislation on the mining sector are quite significant. Although an extensive list of legislation exists, this paper focuses on an issue that currently has a significant influence on the mining industry: natural resource damage assessment and, in particular, the valuation of non-market goods. Therefore, the basic elements of the most important valuation methods are outlined and a demonstrative example is presented, in the context of appraising a reclamation scheme of an abandoned quarry site. The analysis is fairly general, and it does not intend to comprise either a complete introduction to environmental economics or a comprehensive presentation of valuation techniques. Still, it provides an idea of how these methods can be applied to mining issues. Further, the findings may prove useful to practitioners and mining managers, providing information about the monetary benefits of mined land reclamation that could contribute to sound decision- and policy-making.  相似文献   

B-Spline impulse response functions (BIRF) for transient SSI analysis of rigid foundations     

Edward H. Stehmeyer III  Dimitris C. Rizos   《Soil Dynamics and Earthquake Engineering》2006,26(5):421-434

This work presents a simplified, yet accurate model of rigid foundation-soil systems for the dynamic analysis of structures including SSI effects. The simplified model is based on closed form solutions that reproduce the characteristic B-spline impulse response functions (BIRF) of 3D continuous soil-foundation systems, as obtained from rigorous boundary element method (BEM) analysis. The proposed simplified model is used within the framework of B-spline impulse response techniques and can be coupled directly to other solution techniques, such as the finite element method (FEM). Validation and application studies demonstrate the accuracy and versatility of the simplified model for the direct time domain solution of dynamic SSI problems involving rigid square surface foundations of any size. The proposed model, although simplified, demonstrates similar high accuracy to that of more rigorous solutions based on domain discretizations.  相似文献   

Combining microsimulation and spatial interaction models for retail location analysis     

Tomoki Nakaya  A. Stewart Fotheringham  Kazumasa Hanaoka  Graham Clarke  Dimitris Ballas  Keiji Yano 《Journal of Geographical Systems》2007,9(4):345-369

Although the disaggregation of consumers is crucial in understanding the fragmented markets that are dominant in many developed countries, it is not always straightforward to carry out such disaggregation within conventional retail modelling frameworks due to the limitations of data. In particular, consumer grouping based on sampled data is not assured to link with the other statistics that are vital in estimating sampling biases and missing variables in the sampling survey. To overcome this difficulty, we propose a useful combination of spatial interaction modelling and microsimulation approaches for the reliable estimation of retail interactions based on a sample survey of consumer behaviour being linked with other areal statistics. We demonstrate this approach by building an operational retail interaction model to estimate expenditure flows from households to retail stores in a local city in Japan, Kusatsu City.   相似文献   

3-D dynamic foundation-soil-foundation interaction on layered soil   总被引：1，自引：0，他引：1  

Dimitris L. Karabalis  Mohsen Mohammadi 《Soil Dynamics and Earthquake Engineering》1998,17(3):139-152

In this work the interaction between adjacent rigid, surface foundations resting on a viscoelastic layered soil medium is studied. A 3-D frequency domain BEM formulation in conjunction with infinite space fundamental solutions and the so called `successive stiffness method', initially developed for elastostatics and adapted here for the solution of elastodynamic problems, are used for the simulation of a layered soil medium. As a result, a discretization of the soil-foundation interface and the surrounding free surface as well as the soil layers' interfaces is necessary. However, it is shown in this work that reasonably accurate results can be obtained by using a substantially reduced discretization scheme involving only a small portion of the free surface surrounding the foundation and the corresponding interfaces of the soil layers. The presented numerical results demonstrate the importance of the dynamic foundation-soil-foundation interaction phenomenon which becomes even more pronounced where the supporting soil medium is made up of relatively shallow layers close to its free surface.  相似文献   

Wave field mapping with particle image velocimetry     

Dimitris Stagonas  Gerald Müller   《Ocean Engineering》2007,34(11-12):1781-1785

A number of different methods for the 3D measurement of the water surface in wave fields have been proposed in the literature, based mostly on refraction, photogrammetry and/or reflected light intensity. Although these methods can map the distorted water surface, they appear to be difficult in practical applications in hydraulic engineering laboratories. A novel wave mapping technique using particle image velocimetry to measure surface flow velocities, and linear wave theory to determine wave heights from the measured velocities, has been developed and validated for regular waves. The method allows for the mapping even of complex wave fields with simple means and appears robust enough for application in the laboratory.  相似文献   

Scour effects in piled structures—A sensitivity analysis     

Dimitris Diamantidis  Knut Arnesen 《Ocean Engineering》1986,13(5)

A sensitivity analysis is presented in this paper to judge the importance of several parameters influencing scour effects on piles of offshore foundations. The decrease of the pile reliability due to scour is also studied by applying the first-order reliability method. Suggestions for lateral pile resistance in design are included.  相似文献