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Optimum pre-stress design for frequency requirement of tensegrity structures
KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.ORCID-id: 0000-0002-5819-4544
KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.ORCID-id: 0000-0001-6802-8331
2011 (engelsk)Inngår i: Proceeding of 10th World Congress on Computational Mechanics, 2011Konferansepaper, Publicerat paper (Annet (populærvitenskap, debatt, mm))
Abstract [en]

Structures composed of tension and compression elements in equilibrium are denoted tensegrity structures. Stability of tensegrity structures is achieved through introducing initial member forces (pre-stress). The pre-stress design can be seen consisting of three different stages: (i) finding the bases of possible pre-stress states, (ii) finding admissible distributions considering unilateral properties of the elements and stability of the structure, (iii) finding the optimum pre-stress pattern for certain magnitude from compatible pre-stress states. So far, no research has been carried out to connect the three steps, i.e. finding a suitable pre-stress pattern which also considers mechanical properties of the highly pre-stressed structure e.g. its natural frequencies. This paper aims at finding an optimum pre-stress pattern and level of pre-stress for the maximum frequency. The pre-stress problem is on a linear static level where no slackening is allowed. An optimization is performed to find the optimum pre-stress pattern fromthe self-stress modes obtained by a singular value decomposition (SVD) of the equilibrium matrix. The objective function is the first natural frequency of the structure. Finite element analysis is employed for the linear analysis of the structure and a genetic algorithm for optimization i.e., a non-gradient method. The example considered is a double layer tensegrity grid consisting of 29 independent self-stress states. The method is applicable to complex asymmetric three-dimensional structures. The new aspect of this work is a link between the SVD analysis, finite element analysis and genetic algorithm.

sted, utgiver, år, opplag, sider
2011.
HSV kategori
Identifikatorer
URN: urn:nbn:se:kth:diva-101779OAI: oai:DiVA.org:kth-101779DiVA, id: diva2:549284
Konferanse
10th World Congress on Computational Mechanics
Merknad

QC 20120904

Tilgjengelig fra: 2012-09-04 Laget: 2012-09-04 Sist oppdatert: 2012-09-04bibliografisk kontrollert
Inngår i avhandling
1. Stiffness and vibration properties of slender tensegrity structures
Åpne denne publikasjonen i ny fane eller vindu >>Stiffness and vibration properties of slender tensegrity structures
2012 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

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.

sted, utgiver, år, opplag, sider
Stockholm: KTH Royal Institute of Technology, 2012. s. vii, 25
Emneord
Tensegrity booms, Tensegrity grids, Tensegrity power lines, Finite element analysis, Genetic algorithm, Flexibility analysis, Form-finding, Pre-stress design, Optimization
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-101769 (URN)978-91-7501-461-6 (ISBN)
Disputas
2012-09-20, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (engelsk)
Opponent
Veileder
Merknad

QC 20120904

Tilgjengelig fra: 2012-09-04 Laget: 2012-09-03 Sist oppdatert: 2012-09-04bibliografisk kontrollert

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