2,278 research outputs found
Rapid Prediction of Installed Jet Noise from RANS
A new method of computing jet noise, called mSrc, was developed on the general principles of acoustic analogies. In the method, the problem of translating turbulent flow energy into acoustic energy at a far-field observer is broken into two parts, a calculation of acoustic source strengths and then their propagation. The acoustic sources are related to turbulent quantities in the jet plume in a robust manner. The propagation, which is more properly computed using a Green's function accounting for nonuniform speed of sound and solid surfaces, is instead modeled using commonly observed features of jet acoustic far field directivity, and by diffraction barrier theory for surfaces. The mSrc method does not require gradients of the predicted flow field, allowing it to make use of robust unstructured RANS CFD methods, including embedded boundary codes. Such codes do not require specification of surface meshes, and auto-refine their grid to resolve flow gradients, putting resolution where it is required without a priori user input. The ability of mSrc to use such radically unstructured flow input results in an efficient method of estimating noise from jet flows from complex nozzles installed on aircraft. Many validation cases are presented to demonstrate the accuracy and range of applicability of the mSrc method for representative jet noise applications
Knowledge-based automatic tolerance analysis system
Tolerance measure is an important part of engineering, however, to date the system of
applying this important technology has been left to the assessment of the engineer using
appropriate guidelines. This work offers a major departure from the trial and error or random
number generation techniques that have been used previously by using a knowledge-based
system to ensure the intelligent optimisation within the manufacturing system. A system to
optimise manufacturing tolerance allocation to a part known as Knowledge-based Automatic
Tolerance Analysis (KATA) has been developed. KATA is a knowledge-based system shell
built within AutoCAD. It has the ability for geometry creation in CAD and the capability to
optimise the tolerance heuristically as an expert system. Besides the worst-case tolerancing
equation to optimise the tolerance allocation, KATA's algorithm is supported by actual
production information such as machine capability, types of cutting tools, materials, process
capabilities etc. KATA's prototype is currently able to analyse a cylindrical shape workpiece
and a simple prismatic part. Analyses of tolerance include dimensional tolerance and
geometrical tolerance. KATA is also able to do angular cuts such as tapers and chamfers. The
investigation has also led to the significant development of the single tolerance reference
technique. This method departs from the common practice of multiple tolerance referencing
technique to optimise tolerance allocation. Utilisation of this new technique has eradicated
the error of tolerance stackup. The retests have been undertaken, two of which are cylindrical
parts meant to test dimensional tolerance and an angular cut. The third is a simple prismatic
part to experiment with the geometrical tolerance analysis.
The ability to optimise tolerance allocation is based on real production data and not imaginary
or random number generation and has improved the accuracy of the expected result after
manufacturing. Any failure caused by machining parameters is cautioned at an early stage
before an actual production run has commenced. Thus, the manufacturer is assured that the
product manufactured will be within the required tolerance limits. Being the central database
for all production capability information enables KATA to opt for several approaches and
techniques of processing. Hence, giving the user flexibility of selecting the process plan best
suited for any required situation
XVoxel-Based Parametric Design Optimization of Feature Models
Parametric optimization is an important product design technique, especially
in the context of the modern parametric feature-based CAD paradigm. Realizing
its full potential, however, requires a closed loop between CAD and CAE (i.e.,
CAD/CAE integration) with automatic design modifications and simulation
updates. Conventionally the approach of model conversion is often employed to
form the loop, but this way of working is hard to automate and requires manual
inputs. As a result, the overall optimization process is too laborious to be
acceptable. To address this issue, a new method for parametric optimization is
introduced in this paper, based on a unified model representation scheme called
eXtended Voxels (XVoxels). This scheme hybridizes feature models and voxel
models into a new concept of semantic voxels, where the voxel part is
responsible for FEM solving, and the semantic part is responsible for
high-level information to capture both design and simulation intents. As such,
it can establish a direct mapping between design models and analysis models,
which in turn enables automatic updates on simulation results for design
modifications, and vice versa -- effectively a closed loop between CAD and CAE.
In addition, robust and efficient geometric algorithms for manipulating XVoxel
models and efficient numerical methods (based on the recent finite cell method)
for simulating XVoxel models are provided. The presented method has been
validated by a series of case studies of increasing complexity to demonstrate
its effectiveness. In particular, a computational efficiency improvement of up
to 55.8 times the existing FCM method has been seen.Comment: 22 page
COTS GIS Integration and its Soap-Based Web Services
In the modern geographic information systems, COTS software has been playing a major role. However, deploying heterogeneous GIS software has the tendency to form fragmented data sets and to cause inconsistency. To accomplish data consolidation, we must achieve interoperability between different GIS tools. In my thesis project, I developed Vector and Raster Data Adapters to implement the spatial data consolidation. I deployed ArcIMS to publish the spatial data and metadata onto Internet. Furthermore, the SOAP-Based GIS Web services are implemented to achieve the enterprise information system integration. The contribution of ours in this project is we have streamlined the COTS GIS server, the J2EE coordinator server, the web service provider components, and the COTS web publishing tools into a hybrid web service architecture, in which the enterprise information system integration, the web publishing, and the business-to business online services are uniformed
COTS GIS Integration and its Soap-Based Web Services
In the modern geographic information systems, COTS software has been playing a major role. However, deploying heterogeneous GIS software has the tendency to form fragmented data sets and to cause inconsistency. To accomplish data consolidation, we must achieve interoperability between different GIS tools. In my thesis project, I developed Vector and Raster Data Adapters to implement the spatial data consolidation. I deployed ArcIMS to publish the spatial data and metadata onto Internet. Furthermore, the SOAP-Based GIS Web services are implemented to achieve the enterprise information system integration. The contribution of ours in this project is we have streamlined the COTS GIS server, the J2EE coordinator server, the web service provider components, and the COTS web publishing tools into a hybrid web service architecture, in which the enterprise information system integration, the web publishing, and the business-to business online services are uniformed
Pattern-theoretic foundations of automatic target recognition in clutter
Issued as final reportAir Force Office of Scientific Research (U.S.
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