Keywords: a metal stamped blank, form producing, reservoir, nomogram

 1. The analysis showed that the search of new design solutions for reservoirs that should be characterized by simplicity in manufacturing to ensure high operational reliability and have minimum weight is needed. Intensive search for new constructions of buildings and structures [1] on the basis of improving the technology of their producing under the guidance of the author is carried out in BITTU. Features of formation of the wall of a cylindrical reservoir of the double layer rolled steel stamped blanks: without end sections (Fig.1, a); with one end section of the pyramidal type (Fig.1, b); with two terminal sections of the pyramidal type (1, c) are proposed. Key 1 – shaped shell; 2 – line of cut of the shell; 3 – soft material; 4 – collapsible diaphragms; 5 – pyramidal roof; 6 – pyramidal bottom

Fig.1. Forming of mini-shells

The construction of reservoir of rolled stamped blanks is as follows. The roll of steel stamped blanks, attached along the longitudinal edges with weld or special adhesive composition is unrolled on the construction site [2]. While doing it the strips are shifted one with respect to another to 50 thickness of sheet elements for the formation of consoles. Transverse edges are covered with soft waterproof material after being unrolled. The compressed air between the strips is carried out through the fitting welded on one side of the workpiece. The formation of the end sections is done in special soft shells (Fig.1, a). After pressure relieving the formed element is cut into the parts (mini-shells), which are installed vertically and connected to each other with consoles resulting in reservoir forming (Fig.2, a).

The production of reservoirs made of prefabricated elements (mini-shells) with two pyramidal end sections is as follows. The roll of stamped blanks attached with weld or a special glue on the edges with the formation of longitudinal and transverse consoles is unrolled on the construction site. Compressed air is supplied through the fitting. Forming both of the end of the sections and of the central part of the element occurs simultaneously within the entire workpiece. Both end sections of prefebricated elements with variable cross-section gain pyramidal shape (Fig.1, b). Then the elements are set vertically on the rack (Fig.2, b). Prefabricated elements are connected between each other with longitudinal consoles for reservoir forming. One of the end sections is used as the roof and another one is used for funnel.

Fig. 2. Reservoirs made of prefabricated elements (mini-shells):

a – installation on the foundation; b – installing on racks; c – installing on the platform

The studies to determine the rational cross-sectional shape of the mini-shell have been carried out. The search for optimal structural shape and topology of the metallic cylindrical mini-shells was carried out by minimization of the target function based on the optimization criteria. The optimization problem of mini-shell forming is as follows:

 to minimize the objective function

q

under the conditions

,

key  – parameters of mini-shell.

Specific gravity is taken as the main criterion of optimality. The system in which the objective function takes the smallest value: q = q min is found. The results of the research of two types of mini-shells: with a cylindrical shell, a flat bottom and conical roof; with a cylindrical shell, a pyramidal roof and a flat bottom are shown at Fig. 3.

Regularity of increasing specific consumption of steel q depending on the reducing diameter and the relationship between the main geometrical parameters (height and diameter of mini shell (H─D) is observed on the nomogram, based on the results of the numerical experiment. Minimizational zone is well traced, topological relationships between the investigated types of mini shells created from double rolled stamped blanks is seen.

Search of the expression describing the optimum layout of the pyramidal shell element was carried out with the thickness of the roof and wall equal to 1.5 mm and the thickness of the bottom and bottom shell (up to the height of the wall 1,5D) – 3 mm. The analysis of the diagram (Fig.3) shows that the cubic approximation allows to obtain superlinear convergence point of the true minimum. The accuracy of the cubic approximation is quite high, so the found mathematical model can be taken when finding points of optimal solutions.

Fig.3. The search for optimal solutions

Thus, the proposed metal reservoirs made of the double layer stamped blanks produced by using a high tech method of rolling, reduce construction time and the cost of construction, and improve the transportability of structures. The presented diagram is recommended to be used when designing the mini-shells of the optimal size and minimum weight.