Master of Science in Civil Engineeringhttp://dl.lib.mrt.ac.lk/handle/123/7422019-07-18T17:08:38Z2019-07-18T17:08:38ZSimulation of fold-line stiffness in deployable membranesDharmadasa, BYhttp://dl.lib.mrt.ac.lk/handle/123/140572019-03-20T07:03:54ZSimulation of fold-line stiffness in deployable membranes
Dharmadasa, BY
New designs for space structures such as solar sails and star shades are based
on architectures that follow folding and packaging ofthin membranes. By leveraging
recent advances in origami science, it is possible to design structures in which folded
thin membranes deploy following a predetermined and robust path. Design and
product optimization of deployable space structures are limited by complex
environmental conditions experienced by them. However virtual simulations can be
the perfect solution provided proper idealization techniques are followed.
Presence of fold-lines alter the geometrical and mechanical properties ofthin
membranes which have not being accounted in previous virtual simulations. Two
major characteristics identified was the self-opening of the membrane to an
equilibrium angle (defined as neutral angle) and the rotational spring stiffness ofthe
membrane at the fold-line.
An experimental study was devised to investigate the variation of fold-line
stiffness while varying the neutral angles and membrane thickness for Kapton HN
polyimide. A linear empirical relationship between resistive moment and fold-angle is
proposed for each thickness.
Self-opening and subsequent unfolding of a single fold was modelled using
commercial finite element package, Abaqus/Explicit. Fold-line characteristics were
represented with rotational spring connector elements defined between two shell
portions. Compared to common idealization approaches (perfect hinge and perfect
weld), rotational spring connectors were able to accurately predict the deformation
profile and unfolding forces.
Finally, the developed fold idealization technique was applied in an
experimental case study of a deploying solar sail. It was shown that neglecting foldline stiffness underestimate the deploying force ofthe sail.
Master of Science in Civil EngineeringJasotharan, Shttp://dl.lib.mrt.ac.lk/handle/123/138782019-02-02T08:02:23ZMaster of Science in Civil Engineering
Jasotharan, S
Beams are common structural elements in most structures and generally they are analysed using classical beam theories to evaluate the stress and strain characteristics of the beam. But in the case of deep beams, higher order shear deformation beam theories predicts more accurate results than classical beam theories due its more realistic assumption regarding the shear characteristics of the beam.
In this study a hyperbolic shear deformation theory for thick isotropic beams is developed where the displacements are defined using a meaningful function which is more physical and directly comparable with other higher order theories. Governing variationally consistent equilibrium equations and boundary conditions are derived in terms of the stress resultants and displacements using the principle of virtual work. This theory satisfies shear stress free boundary condition at top and bottom of the beam and doesn’t need shear correction factor.
.A displacement based finite element model of this theory is formulated using the variational principle. Displacements are approximated using the homogeneous solutions of the governing differential equations that describe the deformations of the cross-section according to the high order theory, which includes cubic variation of the axial displacements over the cross-section of the beam. Also, this model gives the exact stiffness coefficients for the high order isotropic beam element. The model has six degrees of freedom at the two ends, one transverse displacement and two rotations, and the end forces are a shear force and two components of end moments.
Several numerical examples are discussed to validate the proposed shear deformation beam theory and finite element model of the beam theory. Results obtained for displacements using the present beam theory and the finite element model are compared with results obtained using other beam theories, 2D elastic theory and 2D and 3D finite element models. Solutions obtained using the proposed beam theory and finite element model are in close agreement with the solutions obtained using 2D elastic theory and 2D and 3D finite element models of ‘ABAQUS’.
Embodied analysis of a precast building systemDissanayake, DMKWhttp://dl.lib.mrt.ac.lk/handle/123/138452019-02-02T08:01:00ZEmbodied analysis of a precast building system
Dissanayake, DMKW
Buildings are evolving throughout the history of mankind. When a new building system is introduced, the usual evaluation method is the monetary value. The adaptability to the climate conditions, structural capabilities and constructability are some other criteria for the evaluation. The building industry is consuming a vast amount of natural resources and also been responsible for a significant energy usage. With the recent developments in the environmental concerns all over the world, there is an increased the attention for the building sector. Due to the above reason new buildings have to be more environmental friendly than more conventional building systems.
A novel walling system has been considered in this study, which consist of lightweight foam concrete panels manufactured with recycled expanded polystyrene (EPS) up to 50% of the total volume. Even though those panels have lot of advantages over the conventional construction methods, they need to be compared with the other conventional methods for the environmental aspects. Embodied energy analysis is such an established method to quantitatively analyse the environmental impact caused by a product. Therefore, detailed study was carried out to determine the embodied energy of those foam concrete panels. A comparative study carried out using a typical single storey and for a two-storey house and different building materials.
Final results done for the case studies, indicated that houses constructed with cement sand blocks has the least amount of embodied energy and embodied carbon. However, houses constructed with EPS based lightweight foam concrete precast panels, can be a good competitor in terms of embodied energy and embodied carbon analysis, since it yields results much closer to the cement sand blocks. Reduced sand usage of EPS panelled walls is also an added advantage. Hence, it has the potential to be promoted as a mainstream walling material.
Simulation of closed cross section dual matrix composite boomsUbamanyu, Khttp://dl.lib.mrt.ac.lk/handle/123/138442019-02-02T08:01:08ZSimulation of closed cross section dual matrix composite booms
Ubamanyu, K
The necessity of deployable mechanisms in the field of aerospace is inevitable due to volume limitations in the launch vehicles. Use of mechanical hinges with motors and springs for actuation make the structure heavy and complex. Alternatively, elastically deformable thin shell structures have become popular due to their light weight, ability to self-deploy using energy stored during folding and eliminating complex hinge mechanisms.
Self-deployable booms made of fibre composites are widely used in the space industry. Design of booms made with traditional epoxy matrix are limited by the low failure curvatures. The dual-matrix composite with soft elastomers in the folding region has been identified as a better alternative which allows for high curvature folds of as much as 180o. However, the behaviour of folding and deployment of dual-matrix composites has not been studied in detail.
This thesis presents a detailed study of finite element simulations of folding and deployment of a dual-matrix composite boom made of 3-ply plain-weave glass fibre laminates having a soft silicone matrix in the intended hinge region and rigid epoxy matrix elsewhere. Folding and deployment simulations were carried out under quasi static conditions using the commercial finite element package Abaqus/Explicit. The limitations and the necessary checks to obtain a robust solution are discussed in detail.
Moment-rotation relationship is used to characterize the deployment behaviour under quasi-static conditions, because it gives an indication whether the structure can self-latch and achieve the intended configuration during deployment. Initially a stable folded configuration was simulated from the unstressed configuration of the dual-matrix composite boom and then deployment was simulated by gradually decrease the relative rotation between two ends of the boom until it becomes zero.
Reduction in the bending stiffness of silicone matrix under high curvature significantly influencing the folded configuration of dual-matrix composite booms. A detailed study on the cross sections of the folded configurations reveals that a modified bending stiffness has to be used for simulations. 10% of original bending stiffness
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which corresponds to high curvature conditions was used for silicone region throughout the simulation.
The simulated response was compared against physical experiments carried out by Sakovsky et al. (2016) for validation. Simulation is capable of capturing both overall and localized deform configurations as well as the steady-state moment in the moment-rotation response. However it underestimates the peak moment because the modified bending stiffness leads to a weaker response. Further analysis was carried out using different bending stiffness modifications to understand the significance of the stiffness variation of silicone matrix. Also an attempt was made to understand the potential of dual matrix composite booms which is having a closed cross section by comparing with an equivalent tape spring hinge.