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Aiming at the characteristics of closed fixtures such as large size, heavy weight and difficulty in high-altitude operation, this study proposed a design method to improve the clamping apparatus for replacement of insulator strings in the ultra-high-voltage (UHV) transmission line. After modelling through the finite element method, the mechanical p...
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Citations
... The benchmark consists in a simplified wing-box model, made of composite laminates, subject to bending and twist moment at the tip section, with a clamped root section (x = 0). The geometry of the structure is presented in composing the structure, is made of a carbon-epoxy T300/5208 pre-preg (Catapano, 2013;Zhang et al., 2019), whose properties are listed in Table 7.1, in terms of both technical constants and PPs. Optimisation regions are the upper (z = H) and lower (z = 0) skins of the wing-box. ...
L’objectif de cette Thèse est de développer une méthodologie de conception multi-échelle innovante utilisant un algorithme déterministe pour la conception de structures composites multicouches.L'innovation par rapport aux travaux existants est représentée par la formalisation de deux aspects qui influent grandement sur la fiabilité et la qualité de la solution finale.Le premier aspect porte sur la prise en compte de l'intégration dans la formulation du problème de conception des réponses structurelles critiques intervenants aux différentes échelles du problème. En effet, puisque certaines réponses se manifestent à différentes échelles d'observation, la transition d’échelle se révèle nécessaire afin de bien saisir ces phénomènes. Dans ce travail, une attention particulière sera portée sur l'évaluation de la charge critique de flambage de panneaux raidis constituant l'élément fondamental de la structure des aéronefs. Cependant, la transition d’échelle doit être prise en compte dans la dérivation du gradient des réponses physiques, nécessaire au bon fonctionnement de l'algorithme déterministe pour la recherche de l'optimum.Le deuxième aspect porte sur la contrainte technologique dite de textit{blending}, un problème intrinsèquement lié à la variation du nombre de plis (et des orientations associées) entre stratifiés adjacents de différentes épaisseurs. En effet, les plis des stratifiés plus minces doivent être contenus dans l'empilement des stratifiés les plus épais, sans intersection entre plis. De plus, le blending permet une modulation de l’épaisseur de la structure. De par son importance, il est nécessaire de prendre en compte la contrainte de blending dès les premières phases de conception. De plus, une stratégie générale dont l’objectif est d’identifier le séquence d’empilement des couches du composite en satisfant la contrainte de blending a été développée : permettant ainsi de proposer une solution faisable. Deux approches possibles sont présentées : la première est une approche numérique et la seconde une approche combinatoire, basée sur la recherche des solutions dans une classe particulière de stratifiés (les séquences quasi-triviales).Une fois formalisée, cette approche a été appliquée au problème de la conception d’une architecture aéronautique complexe et innovante : le caisson alaire du PrandtlPlane développé au sein du projet PARSIFAL. Les résultats obtenus sont prometteurs.A coté de ces aspects, les travaux de Thèse abordent aussi deux sujets purement théoriques : la non-convexité du domaine de faisabilité des laminés, ainsi que une justification variationnelle de la modélisation des panneaux raidis. Des résultats inattendus et originals ont été déterminés pour chacun de ces deux thèmes.
... The benchmark consists in a simplified wing-box model, made of composite laminates, subject to bending and twist moment at the tip section, with a clamped root section (x = 0). The geometry of the structure is presented in composing the structure, is made of a carbon-epoxy T300/5208 pre-preg (Catapano, 2013;Zhang et al., 2019), whose properties are listed in Table 7.1, in terms of both technical constants and PPs. Optimisation regions are the upper (z = H) and lower (z = 0) skins of the wing-box. ...
The goal of this Thesis is to provide an improved design framework for the optimal
design of multilayer composite structures by using deterministic algorithms. The
improvement is based on the formalisation of two aspects which deeply affect the reliability
and the likelihood of the final solution.
The first one involves multi-scale considerations of the structural responses. In fact, some
structural criticalities manifest themselves at different scales: the transition of scale is
required to better catch these phenomena. In this work, attention is paid on buckling
instability of stiffened panels. However, the scale transition must be considered in the
derivation of the response gradient, to be provided to the deterministic algorithm of the
solution search.
The second one involves the so-called blending requirement. It is a problem about the
correct junction of adjacent laminates of different thickness, requiring that all the plies of
the thinner laminate must be contained in the stack of the thickest one, without ply intersections.
Moreover, blending makes thickness variations possible. Due to its importance,
blending is a manufacturing requirement which must be assessed since the preliminary design
phases. Moreover, the development of a general strategy for the retrieval of blended
stacking sequence for the structure is faced in this work, to provide a solution which can
be manufactured. Two possible approaches are presented: a pure numerical one and a
combinatorial one, wherein the solution search is carried out in the class of quasi-trivial
stacking sequences. After a comparison, the former is preferred for the applications.
Once formalised and included in an optimisation framework, the multi-scale approach for
the deterministic optimisation, the blending requisite and the numerical approach for the
stack recovery are employed for a complete optimal design of an innovative as well as
complex aircraft structure: the wing-box of the PrandtlPlane developed within the PARSIFAL
project. The obtained results are encouraging.
Besides those aspects of the work, the Thesis also presents insights on two touched topics:
the non-convexity of the laminate feasibility domain and the rational modelling choice of
stiffened plates. For both topics new unexpected theoretical findings have been found.
... It relegalized the minimum number of clamps, maximum contrariety of clamping force components with respect to the twists tending to break contact between the workpiece and the locators, and maintenance of workpiece's static stability under different wrenches. Zhang et al. [16] proposed a design method to improve the clamping apparatus for replacement of insulator strings in the ultrahigh-voltage (UHV) transmission line. e mechanical properties of the clamping apparatus are analyzed to determine the structure with the fixtures of carbon fiber composites by the finite element method. ...
The fixture design of the bacteria bottle plays a vital role in designing a bottled fungus picking robot to save labor cost in the picking process of bottled fungus. This paper proposed a kind of clamping element design method based on regression models. Several sets of clamping elements were designed according to the appearance data of bacteria bottle. A single-factor test was conducted by using these clamping elements, and three levels of every factor were selected to obtain the desired values of clamping elements. Then, a Box–Behnken test was performed by selected levels. The established regression models described a numeric relationship between the variation of vital measurement points and all variation sources under a precise clamping element layout. To solve the problems in obtaining the direct parameters, a response surface method was presented based on the regression models. Finally, a test was used to demonstrate the effect of the optimized clamping elements when clamping a bacteria bottle. Through the related analysis and optimization, it was demonstrated that the holding effect of the clamping elements was the best under these conditions: the inner arc area was 4948 ; the downward displacement was 1.48 mm; and the rubber thickness was 3.69 mm. It showed that the proposed method was feasible, and the assembly quality after optimizing had been greatly improved. It can provide a reference for designing the bottle fixture of a picking machine.
... The constitutive ply, used for all laminates composing the structure, is made of a carbon-epoxy T300/5208 pre-preg (Zhang et al. 2019;Catapano 2013), whose properties are listed in Table 1, in terms of both technical constants and PPs. ...
This work deals with the multi-scale optimisation of composite structures by adopting a general global-local (GL) modelling strategy to assess the structure responses at different scales. The GL modelling approach is integrated into the multi-scale two-level optimisation strategy (MS2LOS) for composite structures. The resulting design strategy is, thus, called GL-MS2LOS and aims at proposing a very general formulation of the design problem, without introducing simplifying hypotheses on the laminate stack and by considering, as design variables, the full set of geometric and mechanical parameters defining the behaviour of the composite structure at each pertinent scale. By employing a GL modelling approach, most of the limitations of well-established design strategies, based on analytical or semi-empirical models, are overcome. The GL-MS2LOS makes use of the polar formalism to describe the anisotropy of the composite at the macroscopic scale (where it is modelled as an equivalent homogeneous anisotropic plate). In this work, deterministic algorithms are exploited during the solution search phase. The challenge, when dealing with such a design problem, is to develop a suitable formulation and dedicated operators, to link global and local models physical responses and their gradients. Closed-form expressions of structural responses gradients are rigorously derived by taking into account for the coupling effects when passing from global to local models. The effectiveness of the GL-MS2LOS is proven on a meaningful benchmark: the least-weight design of a cantilever wing subject to different design requirements. Constraints include maximum allowable displacements, maximum allowable strains, blending, manufacturability requirements and buckling factor.
... Material properties of the unidirectional T300/5208 carbon/epoxy ply[38]. ...
In this work, a multi-scale optimisation strategy for the preliminary design of composite structures involving design requirements at different scales, is presented. Such a strategy, denoted as GL-MS2LOS, has been formulated by integrating a dedicated global-local (GL) modelling approach into the multi-scale two-level optimisation strategy (MS2LOS).
The GL-MS2LOS aims at proposing a very general formulation of the design problem, without introducing simplifying hypotheses and by considering, as design variables, the full set of geometric and mechanical parameters defining the behaviour of the composite structure at each pertinent scale. By employing a GL modelling approach, most of the limitations of well-established design strategies based on analytical or semi-empirical models are overcome.
The effectiveness of the presented GL-MS2LOS is proven on a meaningful study case: the least-weight design of a composite fuselage barrel of a wide-body aircraft undergoing various loading conditions and subject to requirements of different nature. Fully parametric global and local FE models are interfaced with an in-house metaheuristic algorithm to perform the optimisation. Refined local FE models are created only for critical regions of the structure, automatically detected during the global analysis, and linked to the global one thanks to the implementation of a sub-modelling approach. The whole process is completely automated and, once set, it does not need any further user intervention. The general nature of the GL-MS2LOS allows finding an optimised configuration characterised by a weight saving of 40% when compared to an optimised aluminium solution obtained through a similar GL optimisation strategy.
