Automatic dimensional reduction and meshing of stiffened thin-wall structures

The creation of idealised, dimensionally reduced meshes for preliminary design and optimisation remains a time-consuming, manual task. A dimensionally reduced model is ideal for assessing design changes through modification of element properties without the need to create a new geometry or mesh. In this paper, a novel approach for automating the creation of mixed dimensional meshes is presented. The input to the process is a solid model which has been decomposed into a non-manifold assembly of smaller volumes with different meshing significance. Associativity between the original solid model and the dimensionally reduced equivalent is maintained. The approach is validated by means of a free-free modal analysis on an output mesh of a gas turbine engine component of industrial complexity. Extensions and enhancements to this work are also discussed.     

A robust algorithm for white blood cell nuclei segmentation

Multimedia Tools and Applications - Segmentation of white blood cell nucleus is a crucial step in white blood cell counting and classification system based on peripheral blood smear images. It is...     

A virtual inspection framework for precision manufacturing of aerofoil components

The finite element method plays an extremely important role in forging process design as it provides a valid means to quantify forging errors and thereby govern die shape modification to improve the dimensional accuracy of the component. However, this dependency on process simulation could raise significant problems and present a major drawback if the finite element simulation results were inaccurate. This paper presents a novel approach to assess the dimensional accuracy and shape quality of aeroengine blades formed from finite element hot-forging simulation. The proposed virtual inspection system uses conventional algorithms adopted by modern coordinate measurement processes as well as the latest free-form surface evaluation techniques to provide a robust framework for virtual forging error assessment. Established techniques for the physical registration of real components have been adapted to localise virtual models in relation to a nominal design model. Blades are then automatically analysed using a series of intelligent routines to generate measurement data and compute dimensional errors. The results of a comparison study indicate that the virtual inspection results and actual coordinate measurement data are highly comparable and the procedures for registration and virtual inspection are computationally efficient, validating the approach as an effective and accurate means to quantify forging error in a virtual environment. Consequently, this provides adequate justification for the implementation of the virtual inspection system in the virtual process design, modelling and validation of forged aeroengine blades in industry.     

Automatic decomposition and efficient semi-structured meshing of complex solids

In this paper, a novel approach to automatically sub-divide a complex geometry and apply an efficient mesh is presented. Following the identification and removal of thin-sheet regions from an arbitrary solid using the thick/thin decomposition approach developed by Robinson et al. [1], the technique here employs shape metrics generated using local sizing measures to identify long-slender regions within the thick body. A series of algorithms automatically partition the thick region into a non-manifold assembly of long-slender and complex sub-regions. A structured anisotropic mesh is applied to the thin-sheet and long-slender bodies, and the remaining complex bodies are filled with unstructured isotropic tetrahedra. The resulting semi-structured mesh possesses significantly fewer degrees of freedom than the equivalent unstructured mesh, demonstrating the effectiveness of the approach. The accuracy of the efficient meshes generated for a complex geometry is verified via a study that compares the results of a modal analysis with the results of an equivalent analysis on a dense tetrahedral mesh.     

Ultrasonic characterization of the mechanical properties and polymerization reaction of acrylic-based bone cements

In this investigation the pulse-echo technique was validated as a method that could be used to monitor the complete polymerization of acrylic bone cement in a surgical theatre. Currently, orthopaedic surgeons have no objective method to quantify the state of cure of bone cement as it progresses through its polymerization cycle. Clear benefits of the pulse-echo technique are that it is easy to use, non-invasive, and non-destructive. Furthermore, the test results were found to be highly reproducible with minor deviations. Three proprietary cements were used to confirm the validity of the technique; CMW Endurance, Palacos R and Simplex P. The results showed that the acoustic properties of bone cement clearly demonstrated a relationship with the different stages of polymerization, and in particular with the transitions between the waiting, dough, and setting phases. Additionally, the cure time of the poly(methyl methacrylate) cements consistently correlated with the attainment of 75 per cent of the average maximum velocity of sound value. The measured cure times concurred with the ISO and ASTM standards. Moreover, measurements of the final sound velocity and broadband ultrasonic attenuation correlated strongly with the density and mechanical properties of the cured bone cement samples.