Although the concept of tensegrity structures was invented in the beginning of the twentieth century, the applications of these structures are limited, partially due to their low stiffness. The stiffness of tensegrities comes from topology, configuration, pre-stress and initial axial element stiffnesses.  The first part of the present work is concerned with finding the magnitude of pre-stress. Its role in stiffness of tensegrity structures is to postpone the slackening of cables. A high pre-stress could result in instability of the structure due to buckling and yielding of compressive and tension elements, respectively. Tensegrity structures are subjected to various external loads such as self-weight, wind or snow loads which in turn could act in different directions and be of different magnitudes. Flexibility analysis is used to find the critical load combinations. The magnitude of pre-stress, in order to sustain large external loads, is obtained through flexibility figures, and flexibility ellipsoids are employed to ensure enough stiffness of the structure when disturbances are applied to a loaded structure.  It has been seen that the most flexible direction is very much sensitive to the pre-stress magnitude and neither analytical methods nor flexibility ellipsoids are able to find the most flexible directions. The flexibility figures from a non-linear analysis are here utilized to find the weak directions.  In the second part of the present work, a strategy is developed to compare tensegrity booms of triangular prism and Snelson types with a truss boom. It is found that tensegrity structures are less stiff than a truss boom when a transversal load is applied. An optimization approach is employed to find the placement of the actuators and their minimum length variations. The results show that the bending stiffness can be significantly improved, but still an active tensegrity boom is less stiff than a truss boom. Genetic algorithm shows high accuracy of searching non-structural space. / QC 20110524

The stiffness and frequency properties of tensegrity structures are functions of the pre-stress, topology, configuration, and axial stiffness of the elements. The tensegrity structures considered are tensegrity booms, tensegrity grids, and tensegrity power lines. A study has been carried out on the pre-stress design. It includes (i) finding the most flexible directions for different pre-stress levels, (ii) finding the pre-stress pattern which maximizes the first natural frequency. To find the optimum cross-section areas of the elements for triangular prism and Snelson tensegrity booms, an optimization approach is utilized. A constant mass criterion is considered and the genetic algorithm (GA) is used as the optimization method. The stiffness of the triangular prism and Snelson tensegrity booms are modified by introducing actuators. An optimization approach by means of a GA is employed to find the placement of the actuators and their minimum length variations. The results show that the bending stiffness improves significantly, but still an active tensegrity boom is less stiff than a passive truss boom. The GA shows high accuracy in searching the non-structural space. The tensegrity concept is employed to design a novel transmission power line .A tensegrity prism module is selected as the building block. A complete parametric study is performed to investigate the influence of several parameters such as number of modules and their dimensions on the stiffness and frequency of the structure. A general approach is suggested to design the structure considering wind and ice loads. The designed structure has more than 50 times reduction of the electromagnetic field and acceptable deflections under several loading combinations. A study on the first natural frequencies of Snelson, prisms, Micheletti, Marcus and X-frame based tensegrity booms has been carried out. The result shows that the differences in the first natural frequencies of the truss and tensegrity booms are significant and not due to the number of mechanisms or pre-stress levels. The tensegritybooms of the type Snelson with 2 bars and prism with 3 bars have higher frequencies among tensegrity booms. / <p>QC 20120904</p>

With the growing interest in converting a wide variety of biomass-based feedstocks to biofuels, there is a need to develop effective procedures for the design and optimization of multi-feedstock biorefineries. The unifying goal of this work is the development of systematic methodologies and procedures for designing flexible multifeedstock biorefineries. This work addresses four problems that constitute building blocks towards achieving the unifying goal of the dissertation. The first problem addresses the design and techno-economic analysis of an integrated system for the production of biodiesel from algal oil. With the sequestration of carbon dioxide from power plant flue gases, algae growth and processing has the potential to reduce greenhouse gas emissions. Algae are a non-food oil feedstock source and various pathways and technologies for obtaining algal oil were investigated. Detailed economic and sensitivity analysis reveal specific scenarios that lead to profitability of algal oil as an alternative feedstock. In the second problem, a new safety metric is introduced and utilized in process design and selection. A case study was solved to assess the potential of producing biodiesel from sewage sludge. The entire process was evaluated based on multiple criteria including cost, technology and safety. The third problem is concerned with incorporating flexibility in the design phase of the development of multi-feedstock biofuel production processes. A mathematical formulation is developed for determining the optimal flexible design for a biorefinery that is to accommodate the use of multiple feedstocks. Various objective functions may be utilized for the flexible plant depending on the purpose of the flexibility analysis and a case study is presented to demonstrate one such objective function. Finally, the development of a systematic procedure for incorporating flexibility and heat integration in the design phase of a flexible feedstock production process is introduced for the fourth problem. A mathematical formulation is developed for use in determining the heat exchange network design. By incorporating the feedstock scenarios under investigation, a mixed integer linear program is generated and a flexible heat exchange network scheme can be developed. The solution provides for a network that can accommodate the heating and cooling demands of the various scenarios while meeting minimum utility targets.