258 research outputs found
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Sliceforms: Deployable structures from interlocking slices
A sliceform is a volumetric, honeycomb-like structure assembled from an array of cross-sectional planar slices that are interlocked via pairs of complementary slots placed along each intersection. If the slices are thin, these slotted intersections function as revolute joints, and the sliceform is foldable if the geometry of the embedded spatial linkage permits it, for example a lattice sliceform (LS) is bi-directionally flat-foldable. This thesis concerns a study of such sliceforms toward the design of novel deployable structures.
A sliceform torus, composed of two sets of inclined slices arranged at regular intervals about a central axis of symmetry, has been discovered to exhibit a surprising and intriguing folding action whereby its incomplete form can be collapsed to a flat-folded stack of coplanar slices. On deployment, the assembly expands smoothly about an arc until the slices have rotated to their design inclination, then, without reaching any apparent physical limit, abruptly ‘locks out’. With a full complement of slices, the outermost intersections can be interlocked to complete and rigidify the ring. The torus is an example of a rotational sliceform (RS), and analysis of these structures proceeds by noting that their structural geometry comprises an array of pyramidal cells that is commensurate to a spherical scissor grid. The conditions for flat-foldability are determined by examination of the intrinsic geometry of each cell; the incompatibility of the slices with apparent rigid-folding revealed by assessment of the extrinsic motion of the slices. Investigation of their compliant kinematics reveals the articulation to be a bistable transition admitted by small transverse deflections of the slices.
This structural form is generalised by development of a technique for generating sliceforms along a smooth spatial curve – curve sliceforms (CS). Their synthesis is more involved than for an RS, but a range of sliceform ‘tubes’ are generated and manufactured. Each example retains the flat-foldable, deployable characteristic of an RS, despite the apparent intrinsic rigidity of each constituent skew cell. Examination of the small-scale models indicates that deployable motion is achieved via imperfect action of the slots, and a simple model of the articulation of a single cell is constructed to investigate how this proceeds, verifying that motion is kinematically admissible via local deformations
Simulation-Oriented Methodology for Distortion Minimisation during Laser Beam Welding
Distortion is one of the drawbacks of any welding process, most of the time needed to be suppressed. One doubtful factor that could affect welding deformation is the shape of the liquid melt pool, which can be modified via variation of process parameters. The aim of this work was to numerically study the dynamics of the weld pool and its geometrical influence on welding distortion during laser beam welding. To achieve such a goal, a promising novel process simulation model, employed in investigating the keyhole and weld pool dynamics, has successfully been invented. The model incorporated all distinctive behaviours of the laser beam welding process. Moreover, identification of the correlation between the weld pool geometry and welding distortion as well as, eventually, weld pool shapes that favour distortion minimisation has also been simulatively demonstrated
Simulation-Oriented Methodology for Distortion Minimisation during Laser Beam Welding
Distortion is one of the drawbacks of any welding process, most of the time needed to be suppressed. One doubtful factor that could affect welding deformation is the shape of the liquid melt pool, which can be modified via variation of process parameters. The aim of this work was to numerically study the dynamics of the weld pool and its geometrical influence on welding distortion during laser beam welding. To achieve such a goal, a promising novel process simulation model, employed in investigating the keyhole and weld pool dynamics, has successfully been invented. The model incorporated all distinctive behaviours of the laser beam welding process. Moreover, identification of the correlation between the weld pool geometry and welding distortion as well as, eventually, weld pool shapes that favour distortion minimisation has also been simulatively demonstrated
Flexible Cycle Embedding in the Locally Twisted Cube with Nodes Positioned at Any Prescribed Distance
[[abstract]]A Hamiltonian graph G is panpositionably Hamiltonian if for any two distinct vertices x and y of G, it contains a Hamiltonian cycle C such that dC(x, y) = l for any integer l satisfying dG(x, y) ⩽ l ⩽ ⌈∣V(G)∣/2⌉, where dG(x, y) (respectively, dC(x, y)) denotes the distance between vertices x and y in G (respectively, on C), and ∣V(G)∣ is the total number of vertices in G. As the importance of Hamiltonian properties for data communication between units in parallel and distributed systems, the panpositionable Hamiltonicity involves more flexible cycle embedding for message transmission. This paper shows that for two arbitrary nodes x and y of the n-dimensional locally twisted cube LTQn, n ⩾ 4, and for any integer l ∈ {d} ∪ {d + 2, d + 3, d + 4, … , 2n−1}, where d=dLTQn(x,y), there exists a Hamiltonian cycle C of LTQn such that dC(x, y) = l
Structured grid generation for gas turbine combustion systems
Commercial pressures to reduce time-scales encourage innovation in the design and
analysis cycle of gas turbine combustion systems. The migration of Computational
Fluid Dynamics (CFD) from the purview of the specialist into a routine analysis tool is
crucial to achieve these reductions and forms the focus of this research. Two significant
challenges were identified: reducing the time-scale for creating and solving a CFD prediction
and reducing the level of expertise required to perform a prediction.
The commercial pressure for the rapid production of CFD predictions, coupled with the
desire to reduce the risk associated with adopting a new technology led, following a
review of available techniques, to the identification of structured grids as the current
optimum methodology.
It was decided that the task of geometry definition would be entirely performed within
commercial Computer Aided Design (CAD) systems. A critical success factor for this
research was the adoption of solid models for the geometry representation. Solids
ensure consistency, and accuracy, whilst eliminating the need for the designer to undertake
difficult, and time consuming, geometry repair operations. The versatility of parametric
CAD systems were investigated on the complex geometry of a combustion system and found to be useful in reducing the overhead in altering the geometry for a
CFD prediction. Accurate and robust transfer between CAD and CFD systems was
achieved by the use of direct translators.
Restricting the geometry definition to solid models allowed a novel two stage grid generator
to be developed. In stage one an initial algebraic grid is created. This reduces
user interaction to a minimum, by the employment of a series of logical rules based on
the solid model to fill in any missing grid boundary condition data. In stage two the
quality of the grid is improved by redistributing nodes using elliptical partial differential
equations. A unique approach of improving grid quality by simultaneously smoothing
both internal and surface grids was implemented. The smoothing operation was
responsible for quality, and therefore reduced the level of grid generation expertise
required.
The successful validation of this research was demonstrated using several test cases
including a CFD prediction of a complete combustion system
Structured meshes: composition and remeshing guided by the Curve-Skeleton
Virtual sculpting is currently a broadly used modeling metaphor with rising
popularity especially in the entertainment industry. While this approach
unleashes the artists' inspiration and creativity and leads to wonderfully
detailed and artistic 3D models, it has the side effect, purely technical,
of producing highly irregular meshes that are not optimal for subsequent
processing. Converting an unstructured mesh into a more regular and struc-
tured model in an automatic way is a challenging task and still open prob-
lem.
Since structured meshes are useful in different applications, it is of in-
terest to be able to guarantee such property also in scenarios of part based
modeling, which aim to build digital objects by composition, instead of
modeling them from a scratch.
This thesis will present methods for obtaining structured meshes in two
different ways. First is presented a coarse quad layout computation method
which starts from a triangle mesh and the curve-skeleton of the shape. The
second approach allows to build complex shapes by procedural composition
of PAM's. Since both quad layouts and PAMs exploit their global struc-
ture, similarities between the two will be discussed, especially how their
structure has correspondences to the curve-skeleton describing the topology
of the shape being represented. Since both the presented methods rely on
the information provided by the skeleton, the difficulties of using automat-
ically extracted curve-skeletons without processing are discussed, and an
interactive tool for user-assisted processing is presented
Structured meshes: composition and remeshing guided by the Curve-Skeleton
Virtual sculpting is currently a broadly used modeling metaphor with rising
popularity especially in the entertainment industry. While this approach
unleashes the artists' inspiration and creativity and leads to wonderfully
detailed and artistic 3D models, it has the side effect, purely technical,
of producing highly irregular meshes that are not optimal for subsequent
processing. Converting an unstructured mesh into a more regular and struc-
tured model in an automatic way is a challenging task and still open prob-
lem.
Since structured meshes are useful in different applications, it is of in-
terest to be able to guarantee such property also in scenarios of part based
modeling, which aim to build digital objects by composition, instead of
modeling them from a scratch.
This thesis will present methods for obtaining structured meshes in two
different ways. First is presented a coarse quad layout computation method
which starts from a triangle mesh and the curve-skeleton of the shape. The
second approach allows to build complex shapes by procedural composition
of PAM's. Since both quad layouts and PAMs exploit their global struc-
ture, similarities between the two will be discussed, especially how their
structure has correspondences to the curve-skeleton describing the topology
of the shape being represented. Since both the presented methods rely on
the information provided by the skeleton, the difficulties of using automat-
ically extracted curve-skeletons without processing are discussed, and an
interactive tool for user-assisted processing is presented
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