46,936 research outputs found
Experimental and numerical investigation of Helmholtz resonators and perforated liners as attenuation devices in industrial gas turbine combustors
This paper reports upon developments in the simulation of the passive control of combustion dynamics in industrial gas turbines using acoustic attenuation devices such as Helmholtz resonators and perforated liners. Combustion instability in gas turbine combustors may, if uncontrolled, lead to large-amplitude pressure fluctuations, with consequent serious mechanical problems in the gas turbine combustor system. Perforated combustor walls and Helmholtz resonators are two commonly used passive instability control devices. However, experimental design of the noise attenuation device is time-consuming and calls for expensive trial and error practice. Despite significant advances over recent decades, the ability of Computational Fluid Dynamics to predict the attenuation of pressure fluctuations by these instability control devices is still not well validated. In this paper, the attenuation of pressure fluctuations by a group of multi-perforated panel absorbers and Helmholtz resonators are investigated both by experiment and computational simulation. It is demonstrated that CFD can predict the noise attenuation from Helmholtz resonators with good accuracy. A porous material model is modified to represent a multi-perforated panel and this perforated wall representation approach is demonstrated to be able to accurately predict the pressure fluctuation attenuation effect of perforated panels. This work demonstrates the applicability of CFD in gas turbine combustion instability control device design
Automation of The Guiding Center Expansion
We report on the use of the recently-developed Mathematica package
\emph{VEST} (Vector Einstein Summation Tools) to automatically derive the
guiding center transformation. Our Mathematica code employs a recursive
procedure to derive the transformation order-by-order. This procedure has
several novel features. (1) It is designed to allow the user to easily explore
the guiding center transformation's numerous non-unique forms or
representations. (2) The procedure proceeds entirely in cartesian position and
velocity coordinates, thereby producing manifestly gyrogauge invariant results;
the commonly-used perpendicular unit vector fields are never even
introduced. (3) It is easy to apply in the derivation of higher-order
contributions to the guiding center transformation without fear of human error.
Our code therefore stands as a useful tool for exploring subtle issues related
to the physics of toroidal momentum conservation in tokamaks.Comment: 34 page
A Generic Conceptual Model for Risk Analysis in a Multi-agent Based Collaborative Design Environment
Organised by: Cranfield UniversityThis paper presents a generic conceptual model of risk evaluation in order to manage the risk through
related constraints and variables under a multi-agent collaborative design environment. Initially, a hierarchy
constraint network is developed to mapping constraints and variables. Then, an effective approximation
technique named Risk Assessment Matrix is adopted to evaluate risk level and rank priority after probability
quantification and consequence validation. Additionally, an Intelligent Data based Reasoning Methodology
is expanded to deal with risk mitigation by combining inductive learning methods and reasoning
consistency algorithms with feasible solution strategies. Finally, two empirical studies were conducted to
validate the effectiveness and feasibility of the conceptual model.Mori Seiki ā The Machine Tool Compan
The significance of information visualisation based on the symbolic semantics of Peking Opera Painted Faces (POPF)
Peking Opera as a branch of Chinese traditional cultures and arts has a very distinct colourful facial make-up for all actors in the stage performance. Such make-up is stylised in typical cultural elements which all combined together to form the painted faces to describe and symbolise the background and characteristic of specific roles. The Peking Opera Painted Faces (POPF) was taken as an example to study the information visualisation and transmission, to see how information and meanings can be effectively expressed through the colourful visual elements. In order to identify the state-of-the-art in the related Culture Inspired Design as one of the design principles, the literature resources including illustrations of POPF were investigated, and also the semantic features and elements of other similar forms of modern design which has close connection with multiple aspects of social life. The study has proved that the visual elements of POPF played the most effective role in the information transmittion. Future application of this culture resource may include product design, interaction design, system design and service design around the world
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Shadow Banking and Systemic Risk in Europe and China
We compare the European and Chinese shadow banking systems. While the European shadow banking system is better developed than the Chinese shadow banking system, herd behavior and other factors in European markets create systemic risk, which contributed in part to the financial crisis. Dispersion of risk across the "under-developed" shadow banking system in China has led to some cases of localized, concentrated risk, but not to systemic risk. We discuss proposed European shadow banking regulation and its implications for systemic risk, and discuss what lessons China might glean from such policies. We also discuss what lessons
China's diverse and systemically uncoordinated shadow banking sector might provide for Europe
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