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Development of a hybrid light alloy - carbon fibre aerospace structural panelRoets, Philip J. 03 1900 (has links)
Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The development of light and sti aerospace structural panels is very important in the
aerospace industry, e.g. a lighter satellite requires less fuel to launch it into space which
in turn saves money for the owner of the satellite. This thesis describes the design,
optimisation, manufacturing and testing of a ribbed light alloy core - carbon bre face
sheets, sandwich-type, satellite panel operating at launch loading conditions (115 m/s2
accelerations and requiring a minimum structural natural frequency of 90 Hz) to determine
the optimum sti ness per mass ratio of the panel.
The panel layout was based on a satellite panel designed by SunSpace and Information
Systems for the Sumbandila satellite. Only the black box mounting positions of the original
panel were used in the optimisation of the new panel. The core of the evaluation panel
was manufactured from aluminium (6082-T6). The carbon bre skins were manufactured
from unidirectional high modulus carbon bre (K63712) in a [0/90/0] wet layup with
the 0± direction in the longitudinal direction of the panel. A three-dimensional model of
the panel consisting of 3D wedge elements and containing all the boundary conditions
was modelled with the use of the nite element software MSC Patran. The model was
optimised with the use of optimisation software Genesis to locate the rib positions. Genesis
removes all the elements containing the least amount of stress; only 30% of the core
elements were kept while restricting the elements to form an extruded con guration (for
milling machining) throughout the thickness of the panel. The rib elements remaining
were replaced in MSC Patran by shell elements and the shell element thicknesses were optimised
with the use of Genesis to ensure the lightest and sti est possible structure. The
optimised rib thicknesses were imported into MSC Patran and the numerically optimised
model could then be analysed with MSC Nastran.
The numerical model was converted into a manufacturable structure and the core was
machined from a solid aluminium sheet. The ribs were machined in the shape of an Ibeam
to allow for minimum weight and a su cient bonding area for the two carbon bre
face sheets. Elevated circular surfaces, protruding through the carbon bre sheets, were
machined in the position of the black box mountings to allow for better heat transfer
away from the black boxes. The carbon bre face sheets were bonded to the metal core
(3M Scotch-Weld 9323 B/A). The nished panel was put through various tests to determine whether it is suitable
for use in the aviation industry. The tests included modal testing, random vibration
testing and temperature testing to determine if the structure is durable enough for use in
satellites.
The test results are promising and show that a substantive amount of money can be
saved by reducing the mass on the structure. By using optimisation software and ribbed
light alloy - carbon bre face sheets sandwich structures the performance of the structures
can be improved without adding mass to the structure. / AFRIKAANSE OPSOMMING: Die ontwikkeling van ligter en stywer lugvaartstruktuur panele is baie belangrik in die
lugvaart-industrie, bv. 'n ligter satelliet benodig minder brandstof om tot in 'n wentelbaan
lanseer te word. Dit bespaar sodoende lanseerkostes vir die eienaar van die satelliet. In die
verslag word die ontwerp, optimering, vervaardiging en toets van 'n gewebde, ligte allooi
kern - koolstofveselvel, saamgestelde materiaal, satelliet struktuurpaneel wat onderwerp
word aan lanseer belastingstoestande van ongeveer 115 m/s2 versnellings ondersoek. Die
tegnieke word gebruik om die optimale styfheid per eenheidsmassa-verhouding te bepaal.
Die paneel benodig 'n minimum strukturele eerste natuurlike frekwensie van 90 Hz.
Die basiese paneel uitleg is verkry vanaf 'n satellietpaneel wat deur SunSpace and Information
Systems ontwerp is vir die basisplaat van die Sumbandila satelliet. Die enigste
geometrie wat van die oorspronklike struktuur behou is om die nuwe struktuur te optimeer
is die vashegtingspunt-posisies van die swart-kassies. Die kern van die ge-optimeerde
struktuur is vervaardig uit gemasjieneerde aluminium (6082-T6). Die koolstofvesel-velle
is vervaardig uit enkelrigting hoë-modulus koolstofvesel-doek (K63712). Die oplegging is
gedoen met 'n nat-opleggingsproses waar die drie lae van elke vel 'n [0/90/0] oriëntasie
het met, die 0± lae in die langsrigting van die paneel. 'n Drie-dimensionele eindige element
model van die paneel is geskep met behulp van die MSC Patran sagteware pakket met die
model hoofsaaklik opgebou uit 3D wig-elemente. Al die lanseertuig vashegtingsrandwaardes
is in die eindige element model ingebou. Om die web posisies te bepaal is die Genesis
optimeringsagteware pakket gebruik. Verskeie ontwerpsvoorwaardes is gespesi seer waaraan
die optimeringsproses moes voldoen. Slegs 30% van die wig-elemente mag behoue bly
in die optimeringsproses en al die elemente deur die dikte van die paneel moet of behou
of verwyder word. Dit verseker dat die resultaat masjieneerbaar is met 'n freesmasjien.
Die oorblywende wig-elemente is in MSC Patran vervang met dop-elemente. Die dopelemente
se diktes is ge-optimeer met Genesis om die ligste en styfste struktuur moontlik
te kry. Die ge-optimeerde dop-element diktes is in die MSC Patran model ingetrek. Die
numeries ge-optimeerde model is daarna met behulp van MSC Nastran ge-analiseer. Nadat die numeriese model omgeskakel is in 'n vervaardigbare struktuur is die kern
gemasjieneer uit 'n soliede blok aluminium. Die webbe is ontwerp en vervaardig in 'n
I-balk vorm. Dit laat toe dat die webbe 'n minimum gewig en genoegsame area het
waarop die koolstofvesel velle geheg kan word. Verhewe vlakke is gemasjieneer op die
aluminium kern in die posisies van die swart-kassie vashegtingpunte. Hierdie verhewe
vlakke steek deur die koolstofvesel-vel aan die kant waar die swart-kassies vasgeheg word.
Dit verseker 'n metaal-op-metaal verbinding tussen die kern en die swart-kassies vir beter
hittegeleiding. 3M Scotch-Weld 9323 B/A epoksie is gebruik om die koolstofvesel-velle
aan die aluminium kern te heg.
Die voltooide struktuur is aan 'n reeks toetse onderwerp om te bepaal of dit geskik
is om in die ruimtevaart-industrie gebruik te kan word. Dit sluit modale toetse, lukrake
vibrasie toetse en temperatuursverandering toetse in. Die toetsresultate sal bepaal of die
struktuur duursaam genoeg is om in satelliete gebruik te word.
Die toetsresultate is belowend en dui daarop dat deur massa te bespaar op die struktuur,
'n aansienlike bedrag op satelliet lanseer-kostes bespaar kan word. Deur optimeringsagteware
tesame met gewebde ligte allooi kern - koolstofvesel vel, saamgestelde materiaal
strukture te gebruik kan die werksverrigting van die strukture verbeter sonder dat
massa bygevoeg word.
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DESIGN OF MULTI-MATERIAL STRUCTURES FOR CRASHWORTHINESS USING HYBRID CELLULAR AUTOMATONSajjad Raeisi (11205861) 30 July 2021 (has links)
<p>The design of vehicle components for crashworthiness is one
of the most challenging problems in the automotive industry. The safety of the occupants during a crash
event relies on the energy absorption capability of vehicle structures.
Therefore, the body components of a vehicle are required to be lightweight and
highly integrated structures. Moreover, reducing vehicle weight is another
crucial design requirement since fuel economy is directly related to the mass
of a vehicle. In order to address these requirements, various design concepts
for vehicle bodies have been proposed using high-strength steel and different
aluminum alloys. However, the price factor has always been an obstacle to
completely replace regular body steels with more advanced alloys. To this end,
the integration of numerical simulation and structural optimization techniques
has been widely practiced addressing these requirements. Advancements in
nonlinear structural design have shown the promising potential to generate
innovative, safe, and lightweight vehicle structures. In addition, the
implementation of structural optimization techniques has the capability to
shorten the design cycle time for new models. A reduced design cycle time can
provide the automakers with an opportunity to stay ahead of their competitors. During the last few decades, enormous
structural optimization methods were proposed. A vast majority of these methods
use mathematical programming for optimization, a method that relies on
availability sensitivity analysis of objective functions. Thus, due to the necessity of sensitivity
analyses, these methods remain limited to linear (or partially nonlinear)
material models under static loading conditions. In other words, these methods
are no able to capture all non-linearities involved in multi-body crash
simulation. As an alternative solution,
heuristic approaches, which do need sensitivity analyses, have been developed
to address structural optimization problems for crashworthiness. The Hybrid
Cellular Automaton (HCA), as a bio-inspired algorithm, is a well-practiced
heuristic method that has shown promising capabilities in the structural design
for vehicle components. The HCA has been
continuously developed during the last two decades and designated to solve
specific structural design applications.
Despite all advancements, some fundamental aspects of the algorithm are
still not adequately addressed in the literature. For instance, the HCA
numerically implemented as a closed-loop control system. The local controllers,
which dictate the design variable updates, need parameter tuning to efficiently
solve different sets of problems.
Previous studies suggest that one can identify some default values for
the controllers. However, still, there is no well-organized strategy to tune
these parameters, and proper tuning still relies on the designer’s experience.</p>
<p> </p>
<p> Moreover, structures
with multiple materials have now become one of the perceived necessities for
the automotive industry to address vehicle design requirements such as weight,
safety, and cost. However, structural design methods for crashworthiness,
including the HCA, are mainly applied to binary structural design problems.
Furthermore, the conventional methods for the design of multi-material
structures do not fully utilize the capabilities of premium materials. In other
words, the development of a well-established method for the design of
multi-material structures and capable of considering the cost of the materials,
bonding between different materials (especially categorical materials), and manufacturing
considering is still an open problem. Lastly, the HCA algorithm relies only on
one hyper-parameter, the mass fraction, to synthesize structures. For a given problem, the HCA only provides
one design option directed by the mass constraint. In other words, the HCA
cannot tailor the dynamic response of the structure, namely, intrusion and
deceleration profiles.</p>
<p> </p>
<p>The main objective of this dissertation is to develop new
methodologies to design structures for crashworthiness applications. These
methods are built upon the HCA algorithm. The first contribution is about
introducing s self-tuning scheme for the controller of the algorithm. The
proposed strategy eliminates the need to manually tune the controller for
different problems and improve the computational performance and numerical
stability. The second contribution of this dissertation is to develop a
systematic approach to design multi-material crashworthy structures. To this
end, the HCA algorithm is integrated with an ordered multi-material SIMP (Solid
Isotropic Material with Penalization) interpolation. The proposed
multi-material HCA (MMHCA) framework is a computationally efficient method
since no additional design variables are introduced. The MMHCA can synthesize
multi-material structures subjected to volume fraction constraints. In
addition, an elemental bonding method is introduced to simulate the laser
welding applied to multi-material structures. The effect of the bonding
strength on the final topology designs is studied using numerical simulations.
In the last step, after obtaining the multi-material designs, the HCA is
implemented to remove the desired number of bonding elements and reduce the
weld length.</p>
<p> </p>
<p>The third contribution of this dissertation is to introduce
a new Cluster-based Structural Optimization method (CBSO) for the design of
multi-material structures. This contribution introduces a new Cluster Validity
Index with manufacturing considerations referred to as CVI<sub>m</sub>. The proposed index can characterize the quality of
the cluster in structural design considering volume fraction, size, interface
as a measure of manufacturability. This multi-material structural design
approach comprises three main steps: generating the conceptual design using adaptive
HCA algorithm, clustering of the design domain using Multi-objective Genetic
Algorithm (MOGA) optimization. In the third step, MOGA optimization is used to
choose categorical materials in order to optimize the crash indicators (e.g.,
peak intrusion, peak contact force, load uniformity) or the cost of the raw
materials. The effectiveness of the algorithm is investigated using numerical
examples.</p>
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Explorations structurelles de domaines de formes constructibles pour l’architecture non-standard / Structural explorations of fabrication-aware design spaces for non-standard architectureMesnil, Romain 03 February 2017 (has links)
Les dernières décennies ont vu l’émergence de formes architecturales non standard. Les concepteurs se retrouvent généralement démunis face à la complexité géométrique de ces objets, dont la fabrication rime souvent avec complication. De plus, les outils utilisés dissocient forme et fonctionnement structurel,ce qui complexifie le processus de décision pour ingénieurs et architectes. Ce mémoire prend un point de vue fondé sur la notion d’invariance par transformation géométrique et étudie plusieurs strategies de génération de formes naturellement constructibles pour remédier à ces manques. Trois contraintes constructives ont été identifiées et correspondent à trois contributions indépendantes de cette thèse.La répétition des noeuds d’assemblage est étudiée via les transformations par maillages parallèles. Ces dernières sont utilisées pour créer une généralisation des surfaces de révolution. On retrouve par là un paramétrage particulier des surfaces moulures de Monge avec une grande répétition d’éléments, et notamment de noeuds d’assemblage.Les réseaux de cyclides sont ensuite utilisés pour dessiner des formes parametrées par leurs lignes de courbures. Cela permet la couverture par panneaux plans ainsi que l’offset des éléments structurels sans excentricité. L’apport de cette thèse est l’implémentation de plusieurs améliorations, notamment l’introduction de plis à double courbure, un algorithme permettant de généraliser les réseaux de cyclides à des topologies quelconques, et la génération de surfaces généralisant les surfaces canal à partir de deux courbes rail et une courbe profil.Finalement, une méthode innovante inspirée de la géométrie descriptive permettant la génération de formes courbes couvertes par des quadrilatères plans est proposée. La méthode, baptisée méthode marionnette, réduit ce problème à un système linéaire, ce qui permet une manipulation de ces forms constructibles en temps réel. Une étude comparative montre que cette technique peut être utilisée pour paramétrer des problèmes d’optimisation de forme de coques sans perte de performance par rapport aux paramétrages utilisés de façon classique. L’intégration des contraintes de fabrication dans le processus d’optimisation structurelle ouvre de nouvelles possibilités d’applications, comme des résilles gauches et des coques plissées. La pertinence de ces nouvelles solutions est démontrée par de multiples études de cas / The last decades have seen the emergence of non-standard architectural shapes. Designers find often themselves helpless with the geometrical complexity of these objects. Furthermore, the available tools dissociate shape and structural behaviour, which adds another complication. This dissertation takes the point of view based on invariance under geometrical transformations, and studies several strategies for fabrication-aware shape modelling. Three technological constraints have been identified and correspond to three independent contributions of this thesis.The repetition of nodes is studied via transformations by parallelism. They are used to generalise surfaces of revolution. A special parametrisation of moulding surfaces is found with this method. The resulting structure has a high node congruence.Cyclidic nets are then used to model shapes parametrised by their lines of curvature. This guarantees meshing by planar panels and torsion-free beam layout. The contribution of this dissertation is the implementation of several improvements, like doubly-curved creases, a hole-filling strategy that allows the extension of cyclidic nets to complex topologies, and the generation of a generalisation of canal surfaces from two rail curves and one profile curves.Finally, an innovative method inspired by descriptive geometry is proposed to generate doubly-curved shapes covered with planar facets. The method, called marionette technique, reduces the problem to a linear problem, which can be solved in real-time. A comparative study shows that this technique can be used to parametrise shape optimisation of shell structures without loss of performance compared to usual modelling technique. The handling of fabrication constraints in shape optimisation opens new possibilities for its practical application, like gridshells or plated shell structures. The relevance of those solutions is demonstrated through multiple case-studies
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Application of Bennett mechanisms to long-span sheltersMelin, Nicholas O'Brien January 2004 (has links)
Rapidly assembled tent structures are temporary enclosures used to house people or goods. Their uses vary to include recreation, refugee housing, and military shelters. The structural concepts applied in these shelters are as variable as their uses. Some make use of a tensioned fabric and pole system to provide structural strength. Others have a load-bearing frame with attached fabric skin. Further variants make use of inflatable arches or consist of modular containers. Analysis of a number of different types of rapidly assembled tent structures reveals an area where innovation can occur. Conflicts in the last ten years suggest that rapidly assembled shelters for both military purposes and humanitarian relief have the greatest need for innovative solutions. Existing shelters used by the military lack the versatility and speed of deployment necessary in modern conflict. The lack of scalability in the designs makes it difficult to use an existing tent in different situations. They are slow to construct, heavy, and difficult to transport in large numbers. These problems suggest that there is a need for new shelters that better meet the needs of the military. The application of deployable structures technology meets military's needs for structures with the advantages of a small compacted volume, rapid assembly, and ease of deployment. This makes them ideal for application to shelter structures. The aim of this dissertation was to develop a new type of deployable, long-span shelter frame based upon tiled Bennett mechanisms. An overlapping combination of equilateral Bennett mechanisms yields a structure that opens into a half-cylinder shape, providing an enclosed space useful and applicable to the problem of deployable shelters. The specific application considered in the design portion of this process will be a long-span deployable shelter capable of housing military helicopters. This report details the development of the Bennett Shelter concept. Its deployed and compacted geometries are explored, and a procedure for determining structural properties and dimensions is presented. The full concept for the structure, from outer covering to foundation support is then detailed. Loads affecting the structure are determined, and the process of modelling and analysing the structure is then considered. Optimisation of the structure with respect to weight and serviceability requirements is conducted using a number of different materials, and full analysis of the optimal geometries is completed. As no method exists for evaluating the effect of imperfections on the deployment of overconstrained mechanisms, a procedure is derived. The effects of manufacturing imperfections on deployment of the Bennett mechanism are then explored using the method. A full examination of the variation of energy within the Bennett Shelter during deployment provides valuable insight into the performance of the structure. With the above analysis complete, it is shown that the Bennett Shelter is viable as a long-span deployable shelter.
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