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Title: Design and analysis of inflatable space structures
Author: Puri, Manpreet Singh
ISNI:       0000 0004 6422 9250
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2016
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This thesis gives the conceptualization of inflation of inflatable membrane space structures. Although there has been little study using software simulation and the majority of documented research is based on theoretical numerical calculations. This research advanced the prior understanding of wrinkling within inflated membranes by using complex structures subjected to deformation loads. Within this thesis, a computational framework for the numerical analysis of the interaction between acting forces on the membrane and the membrane structure dynamics is presented. Moreover, in the case with thin membrane deformations, the synergy between the membrane wrinkling and structural forces has to be examined. This membrane structure-anatomical forces correlation results in a dynamic wrinkling problem, which can only be modelled easily and effectively by a simulation software that can integrate each assumption and attribute within the analysis. In the structural simulation within Abaqus FEA software, key consideration has to be given in modelling the geometric non-linearity behaviour of the membrane. By using the existing continuum expression for the virtual internal work in curvilinear coordinates. This is used to derive the modified fundamental formulation in which all subsequent analysis is established on and the initial equilibrium shape of the membrane. A critical feature of the new formulation is the prospect of adding pre-stressed forces to the membrane structure. The approach developed, established on an alteration of the material stiffness matrix to integrate the effects of wrinkling and deformation, can be utilized to calculate the behaviour of the membrane within a finite element simulation. In the wrinkling model, the state of the membrane element (taut, wrinkled or slack) is characterized by a mixed wrinkling criterion. Once it has been identified that the membrane element is wrinkled, an iterative scheme looks for the wrinkled orientation angle and the precise stress distribution, including only uni-axial tension in the wrinkle direction, is then derived. The wrinkling model has been verified and validated by contrasting the simulated conclusions with documented results for the instance of a time-independent isotropic membrane subjected to shear and axial loading. Utilizing the time integration method, a time-dependant pseudo-elastic stiffness matrix was represented and therefore, rather than calculating the convolution integral all through the Abaqus simulation, then we can calculate the behaviour of a membrane structure by superposition of a series of step by step increments in basic finite element software. The theoretical computations from the Abaqus/Explicit analysis were compared with documented results for the shear and axial loading. The results agreed very well, assuming friction and any relativistic dynamic effects were excluded. The discrepancy between the shear loading solution is 7% while the discrepancy between the axial loading is only 5% between the Abaqus modeland the documented model. This discrepancy could be the resultant of the source of energy dissipation from the visco-elastic behaviour during the loading and unloading of forces. It can be stated that for the Kapton HN membrane, this result falls within acceptable range but to increase accuracy, the load and unloading will be carried out on a set steady amplitude to inhibit in shock effects within the model. A three-dimensional finite element model which integrates wrinkling and frictionless contact has been developed to simulate the adaptive smart cell and cylindrical membrane structure. The loading of both structures is given by a non-uniform differential inflation pressure with a continual gradient adjacent to height. The resultant solutions are computed using Abaqus/Explicit software, with an integrated user-defined material subroutine to account for elastic wrinkling deformation that administers a combined stress-strain criterion. Frictionless contact within the membrane structure is prescribed for both complex structures (Adaptive Smart Structures Model and Inflatable Beam Model) in order to prohibit the penetration of the membrane structure through itself. Both the complex inflatable membrane wrinkling models accomplish the purpose of exceptional subgrid scale performance in relation to accuracy, competency, computing hardware & software expense, complexity and the model convergence rate. The numerical algorithm is created in general context and is flexible for a large variety of material models. For a closed membrane structure, the skew symmetric constraint parameters vanish, while the existing symmetric domain variables mirror preservation of the system. This procedure does not demand the discretization of the fluid (gas) domain or the link between coupling of fluid (gas) and membrane. As a result of this basic fact, the computation is drastically simplified. The adaptive structures model introduces a novel approach in harnessing solar power for reuse on the ground as a stable source of power. The simulations were based on the space part of the stiff structure created of hexagonal membrane cells. Simulations are carried out in Abaqus Finite Element Analysis software for simplicity & a comparison for validation purposes is tested against an experimental inflatable cell within a vacuum chamber. It was showcased that the final configuration could be achieved regardless of the packaging shape of the inflatable cell array. The inflatable beam model is comprised of two sections, the bending & buckling of the inflated beam and the post-inflation of the bent and buckled beam. Abaqus software was used to simulate the inflatable beam during each configuration utilizing the integration of a modified VUMAT subroutine. A comparison is showcased representing the importance of the integration of the VUMAT subroutine within our Abaqus model.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral