Showing papers by "Congrès International d'Architecture Moderne published in 2008"

Improving the CERES-Maize Model Ability to Simulate Water Deficit Impact on Maize Production and Yield Components

Abstract: Crop models are potential tools for designing water-efficient strategies and should be tested for accurate prediction of water deficit effects on production. The objective of this research was to test and improve the CERES-Maize model (CERES-4.0) for ability to predict accurately maize biomass and grain yield components under water-limiting conditions in an environment where the model had previously given good predictions under irrigated conditions. Under a water-limited environment in northwest Spain, CERES-4.0 failed to simulate sufficiently high growth and yield; thus we evaluated aspects of model believed responsible for the poor performance. The model was tested with two evapotranspiration options [Priestley-Taylor (PT) and Penman-Monteith reference method (PFA056, FAO no. 56 manual)] and with two values for the coefficient (KEP) that partitions evapotranspiration (ET) between crop transpiration and soil evaporation (default: KEP = 0.685; alternate: KEP = 0.500). The PT option with KEP = 0.685 underpredicted grain yield and biomass due to too early and too severe simulated water extraction. Predictions of biomass and grain yield with both PT and PFAO56 were improved when a KEP of 0.500 was used instead of the default 0.685. The PFAO56, the less water demanding of the tested crop reference (ETo) equations, gave the best predictions. In addition, a systematic underprediction of grain number and grain size with the default model in response to water deficit was observed, regardless of ET option or KEP value. Model predictions of the latter two variables was improved by replacing the default CERES-4.0 function that computes seed number per plant with the function of Edmeades and Daynard (1979).

The use of Taguchi method to determine factors affecting the performance of destination sequence distance vector routing protocol in mobile ad hoc networks

Abstract: In this study, Taguchi method was used to identify the several factors that may affect the performance of Destination Sequence Distance Vector (DSDV) routing protocol. The performance of DSDV routing protocol in mobile ad hoc networks were greatly influence by factors such as node speed, node pause time and traffic load. Problem statement: By using orthogonal experimental design and analysis techniques, the protocol performance can be analyzed with more objective conclusion through only a small number of simulation experiments. Approach: The performance was measured with respect to packet delivery ratio. Analysis of variance (ANOVA) was carried out to identify the significant factors affecting the response and the best possible factor level combination was determined through analysis of the signal-to-noise ratio. Results: It was found that the traffic load has a stronger influence on the packet delivery ratio, followed by the pause time. Conclusions/Recommendations: The optimal setting of the best performance is determined. The optimal setting has resulted in increased packet delivered. These findings demonstrate that Taguchi method may be valuable tool for the investigation of main effect or interactions of multiple factors in the performance of mobile ad hoc network routing protocols.

Application of Casing Circumferential Grooves to Counteract the Influence of Tip Clearance

Abstract: Widening of surge margin of a transonic compressor stage is the main objective of the paper. This stage is a typical middle stage of a modern high pressure compressor (HPC) with decreased number of stages. Hot tip clearance of the stage being integrated into a six-stage HPC providing total pressure ratio π* HPC ≥ 12 and mass flow-rate < 16 kg/sec is estimated at 2.5 – 3% of blade height and is classified as a large tip clearance. In this paper experimental and 3D viscous numerical performances of the stage are obtained for two values of rotor tip clearance — equal to 0.76% (small size) and 2.66% (large size) of blade height. In doing so, tip clearance enlargement from 0.76% to 2.66% has been made by increase of casing (shroud) radius. This increase is manufactured as a circumferential trench (recess) with axial width 30% larger than rotor axial chord. Below this tip clearance is called “recessed” tip clearance. A distinguishing feature of leakage flow in case of large tip clearance is a formation of reversed flow near rotor casing. This backflow being intensified by throttling causes increase of incidence at the rotor leading edge and development of rotor stall. Casing treatments are intended to inhibit and delay the process. Among them circumferential grooves is the simplest casing treatment. Investigated in this paper casing circumferential grooves cover 82% of rotor axial chord. Numerical visualization of the near-casing streamlines demonstrates that tip leakage flow drains into the casing grooves giving rise to extended domains of positive axial velocity. Calculated mass flow-rate through groove’s cross-section demonstrates maximum over the rotor blade tip (flow into the groove) and minimum at mid-pitch (flow out of the groove). Amplitude of this variation depends on the groove location and stage throttling.© 2008 ASME

Numerical Method for Turbomachinery Tonal Noise Generation and Radiation Simulation Using CAA Approach

Abstract: The numerical method for 3D calculation of the turbomachinery tonal noise generation, propagation and radiation in the near and far fields taking account of the rotor-stator interaction is developed in CIAM. The method is based on the direct numerical solution of three-dimensional Euler equations for disturbances in time or in frequency domain using numerical methods of computational acoustics (CAA). For far-field radiation calculation the Ffowcs Williams method is used. The method is build into CIAM domestic aeroacoustic solver 3DAS (3 Dimensional Acoustics Solver). In this paper we present some examples of our method applications for calculation of rotor-stator interaction and propagation: • Ducted fan tonal noise simulation; • Ducted counter-rotated fan noise simulation; • Low pressure turbine tonal noise simulation.Copyright © 2008 by ASME

United Modeling of Working Process in Aircraft Gas Turbine Engines

Abstract: This paper is about the modern mathematical models of working process in the whole flow passage of aviation gas turbine engines. These models are referred as high-level models, based on real 3D geometry of engine flow passage. They allow to simulate steady and unsteady processes in 1D, 2D and 3D formulations, calculate engine performances, determine propagation of radial and circular parameter no uniformities in engine flow passage and predict influence of main parameters on engine efficiency. Typical examples of working process simulation in whole engine and their components are presented below.Copyright © 2008 by ASME

An experimental study of the influence of outflow conditions on the acoustomechanic efficiency of a turbulent jet

Abstract: The acoustomechanic efficiency of a turbulent jet is determined as the ratio of acoustic radiation power to the kinetic energy flux of the jet. According to the Lighthill acoustic analogy, the acoustomechanic efficiency of axially symmetric jets is proportional to the fifth power of the Mach number. In this paper, on the basis of an experimental study and an analysis of published data, the influence of various factors that can affect the structure of a jet and, consequently, its acoustomechanic efficiency is investigated. In particular, the influence of water injection on the reduction of the jet noise is analyzed. The results of analyzing experimental data show that a systematic deviation from the relation between acoustic and mechanical jet energies obtained from the Lighthill acoustic analogy arises in the case of the outflow of low-velocity jets of low density and with the development of longitudinal vorticity in the flow.