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Structural analysis of a scissor structure

Ario I., Yamashita T., Chikahiro Y., Nakazawa M., Fedor K., Graczykowski C., Pawłowski P.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2020

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Vol. 68, nr 6

1319--1332

EN

This paper presents equilibrium mechanics and a finite element model for analysing a scissor structure that contains pivots with zero bending stiffness representing structural instability. The pivot at the centre of each structural unit, which is a feature of scissor structures, can be used to transfer the displacement between the units. It cannot, however, transfer the rotation between these units, and the angular stiffness must be considered independently for each unit. To construct a general model of the scissor structure, a scissor unit was developed using the left and right boundary connections of adjacent units to simulate a periodically symmetric structure. The proposed method allows us to obtain an accurate distribution of the internal forces and deflections without the use of special elements to account for central pivots.

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Strategies for reduction of energy consumption during ascending and descending process of modern telescopic HAPS aerostats

Knap L., Graczykowski C., Holnicki-Szulc J., Wołejsza Z.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2020

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Vol. 68, nr 1

155--168

EN

In this article, the authors propose and investigate a new concept of HAPS aerostat design in a modular form, which allows for sequential increasing or decreasing of the total volume, up to the desired size. In its initial form, the aerostat has relatively small dimensions but its central cylindrical part is multi-segmented and can be easily extended. The application of controllable construction couplings enables precise control of the aerostat expansion process and significantly improves its vertical mobility. The paper describes details of telescopic aerostat construction, presents a mathematical model of its vertical motion and investigates numerically two volume control strategies aimed at maximization of operation efficiency and minimization of operation cost. The results obtained reveal the main problems that have to be addressed and the factors that play a key role in design of such telescopic aerostats and control of their vertical mobility.

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The lightest plane structures of a bounded stress level transmitting a point load to a circular support

Graczykowski C., Lewiński T.

Control and Cybernetics

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2005

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Vol. 34, no 1

227-253

EN

The paper refers to the problem of Michell (1904) of finding the lightest fully stressed structures, composed of possibly infinite number of members, trasmitting a given load to a support forming a circle. The point load can be located within or outside the circle. The known analysis by Hemp (1973) is enhanced here by disclosing the explicit formulae for the weights of the ribs and the interior (fibrous domain). The optimal weight can be found by two manners: by applying the primal integral formula involving the density of the reinforcement or by computing the work of the load on the adjoint displacement. One of the aims of the paper is to show that both these formulae are equivalent. This identity is essential since in the case of point loads the equivalence of the primal and dual formulations has not been proved till now. Tlie analytically found layouts are confirmed by analysis of trusses (of finite number of joints) approximating the exact Michell-like solutions.