Implicit high-order time-marching schemes for the linearized euler equations

High-order-accurate implicit time-marching methods are presented for discontinuous Galerkin and spectral volume high-order-accurate spatial discretizations of the linearized Euler equations that govern propagation of aeroacoustic disturbances. It is found that despite the additional computational time that is required for the solution of the large, sparse linear system for the degrees of freedom of high-order spectral volume or discontinuous Galerkin discretizations, implicit methods offer an attractive alternative for practical aeroacoustic computations with these high-order methods. Several explicit and implicit methods for time advancement are tested. The advantages of implicit higher-order-accurate (in time) methods that involve multiple implicit steps are demonstrated. The efficiency and accuracy of time-marching methods is evaluated for test problems with exact solutions. It is shown that complex domain aeroacoustic predictions can be obtained at a reduced computational cost with the use of high-order-accurate implicit methods. Copyright © 2007 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved

Wastewater Reuse Planning in Agriculture: The Case of Aitoloakarnania, Western Greece

In the present paper, the possibility of the treated municipal wastewater (TMWW) reuse in agriculture, produced by the Wastewater Treatment Plants of Aitoloakarnania prefecture, one of the greatest agricultural regions of Greece, has been investigated. The boundaries of agricultural soils and the irrigated crops were defined, and the water requirements of crops were calculated. Also the chemical characteristics of the TMWW were determined for the safe reuse in crop production, and for the protection of soils from potential pollution. The research conducted in this area is expected to constitute the basis for an integrated TMWW reuse planning in soils and crops, in the context of sustainable agriculture, and environmental protection. It must be mentioned that the Messolongion-Aitolikon lagoon is in the area under investigation, one of the largest wetland ecosystem of Mediterranean region, which makes the area ecologically sensitive. The ultimate scope of this study is to describe the planning of the TMWW reuse on the basis of soil characteristics, climatic factors, and irrigation water requirements of the crops, grown in this ecologically sensitive area. The volume of the effluents produced by the wastewater treatment plants of Messolonghion, Agrinion, Nafpaktos, Aitoliko and Thermo could cover 19.3%, 25.14%, >100%, 17.18 and 87.84% of the irrigation water requirements, respectively