8,514 research outputs found
Whirl and Stall Flutter Simulation Using CFD
This paper presents recent research on numerical methods for whirl and stall flutter using computational
fluid dynamics. The method involves coupling of the HMB3 CFD solver of the University of
Glasgow and a NASTRAN derived structural model. Based upon a literature survey, a significant amount
of research has been conducted on the numerical investigation of tiltrotors, with a focus on the XV-15
and V-22 aircraft. Within this paper, the coupling procedure is presented along with a steady CFD computation
to highlight the accuracy of the high-fidelity method. In addition to this, a simple method is used
to investigate the whirl flutter boundary of a standard propeller and the XV-15 blade
Qualitative System Identification from Imperfect Data
Experience in the physical sciences suggests that the only realistic means of
understanding complex systems is through the use of mathematical models.
Typically, this has come to mean the identification of quantitative models
expressed as differential equations. Quantitative modelling works best when the
structure of the model (i.e., the form of the equations) is known; and the
primary concern is one of estimating the values of the parameters in the model.
For complex biological systems, the model-structure is rarely known and the
modeler has to deal with both model-identification and parameter-estimation. In
this paper we are concerned with providing automated assistance to the first of
these problems. Specifically, we examine the identification by machine of the
structural relationships between experimentally observed variables. These
relationship will be expressed in the form of qualitative abstractions of a
quantitative model. Such qualitative models may not only provide clues to the
precise quantitative model, but also assist in understanding the essence of
that model. Our position in this paper is that background knowledge
incorporating system modelling principles can be used to constrain effectively
the set of good qualitative models. Utilising the model-identification
framework provided by Inductive Logic Programming (ILP) we present empirical
support for this position using a series of increasingly complex artificial
datasets. The results are obtained with qualitative and quantitative data
subject to varying amounts of noise and different degrees of sparsity. The
results also point to the presence of a set of qualitative states, which we
term kernel subsets, that may be necessary for a qualitative model-learner to
learn correct models. We demonstrate scalability of the method to biological
system modelling by identification of the glycolysis metabolic pathway from
data
A Preliminary Analysis of the Benefits of Introducing Apomixis into Rice
The objective of this research is to undertake an ex ante economic analysis of basic scientific research that aims to identify the gene(s) that control apomictic reproduction, with the ultimate aim of transferring the characteristic into commercially important crops. This paper reports very preliminary results, using the introduction of apomixis into rice as a case study. Apomixis is a natural, asexual method of plant reproduction resulting in offspring that are genetically identical to the mother plant. Apomixis promises to revolutionize plant breeding by providing a system for crop improvement that allows any desired variety, including hybrids, to breed true. This ability will make both breeding and seed production more efficient. It offers the opportunity for plant breeders to more readily develop varieties that are specifically adapted to local conditions, using, and thus conserving, greater genetic diversity. Apomixis will also allow resource-poor farmers to replant the seed they produce from locally bred varieties year after year, a strategy not possible with today's commercial hybrid varieties. Global changes in aggregate welfare, resource allocation, production and price levels are calculated using the global economy-wide computable general equilibrium model known as GTAP. Preliminary modeling results suggest that the overall welfare gains associated apomictic rice could be substantial.Agribusiness, Agricultural and Food Policy, Crop Production/Industries, Environmental Economics and Policy, Farm Management, Institutional and Behavioral Economics, Land Economics/Use, Production Economics, Research Methods/ Statistical Methods,
Sustainability issues for agriculture in Western Australia
Agriculture has been and will continue to be a major component of economic activity in several regions in Western Australia, and agricultural communities will remain an important part of the social fabric and landscape of the State. Promoting the sustainability of agriculture is likely to produce three main outcomes: vibrant rural communities; profitable agricultural systems; and conservation of the natural environment. This paper describes briefly the main challenges to the sustainability of agriculture and outlines some means of responding to the challenges: market-based approaches; agricultural and environmental research and development; accelerated adjustment; and global and national policy initiatives
- …