When water conduits operate with velocities exceeding 20-25 m/sec, high-vacuum regions are created, which result in the development of cavitation, followed by heavy erosion of the concrete, and in many cases by damages to the hydraulic equipment and the steel facings of concrete surfaces.This article presents some results of work carried out at the S. u Zhuk Scientific-Research Department of the All-Union Design and Scientific-Research Institute for Hydraulic Structures (NIS Gidroproekta), which permit preparing recommendations for the prevention of hazardous cavitation erosion of elements of hydraulic structures.Cavitation on Surface Irregularities of Water Conduits. In order to prevent cavitation erosion, the allowable dimensions of irregularities on the surfaces of water conduits should be specified for each structure.The degree of cavitation under a flow is determined by the cavitation index [1?. ]')o~ --/OjWoo c% in which L,e --2g P~,is thecharacteristicpressureinkg/mZ, v~oisthevelocityinm/sec, Pv is the saturated vapor pressure of the fluid in kg/m 2, and y is the unit weight of water, in kg/m 3.

Multipurpose high-head hydrostations have become widespread in hydrotechnical construction. Many have earth dams, which require the construction of long tunnel spillways for temporary discharges during construction and then for operating discharges.To reduce the cost of constructing such spillways and shortening the time of constructing the complete hydrostation, it is expedient to increase the discharges in the tunnels and heads on the gates. In the completed Charvak hydrostation and the Nurek hydrostation (under construction) the design discharges of the i0 • ii m tunnels exceeded 2000 m3/sec, the heads on the gates were ii0 m, and the velocity beyond the gate chambers was 40 m/sec. The Rogun hydrostation is being constructed with a head on the gates up to 200 m, which leads to an increase in velocity to 60 m/set. All this requires the solution of a number of problems, including reduction of a certain part of the kinetic energy of the flow inside the tunnel directly past the gate chambers in order to lessen the dynamic effect on elements of the structures and cavitation erosion of the conduit surfaces.Methods for reducing the kinetic energy in the form of baffle devices and ejection of the jet that have gained popularity in high overflow dams are not applicable for tunnel spillways owing to the limited height and closed state of the conduit.

The history of hydrotechnical construction in our country is rich in unique designs. Many of them have permanent significance. Others are a memorial to an epoch when the severest shortage of metal and cement in the country brought to life maximally simplified designs, which played, however, an enormous role in the realization of structures that provided the power and transport needs of the country. This article will acquaint the reader with some such designs;on the development and realization of which the author had direct bearing.As early as the first days of formation of Soviet power the construction of the Volkhov hydroelectric station began on the Zvanka River 113 km from Petrograd on the initiative of V. I. Lenin in 1918 for the purpose of supplying the city with electricity. The outfitting Of hydrotechnical construction with equipment at that time was extremely low, and practice was forced to introduce substantial corrections into the engineering decisions made. Thus, the spillway dam of the Volkhov hydrostation was contemplated as self-regulating the discharge, without metal spillway gates. The level of the reservoir in this case substantially fluctuated from maximally high during passage of the flood to the elevation of the crest of the ungated dam. Since this reduced the constancy of energy output, the operating management of the hydrostation (electrician Prof. A. A. Bolotin) arranged above the dam crest a braced wooden shield installed immediately after passage of the flood and maintaining a higher elevation of the reservoir level in the period when the inflow was completely passed by the turbines of the hydrostation. This measure noticeably increased the power production of the hydrostation.The design called for a high-voltage cable transmission line from the hydrostation to Petrograd with a length of 110 km without noise-suppressing insulation, which in practice led to the creation of considerable noise in the operation of the telephone line adjacent to the transmission line. Noise-suppressing insulation of the high-voltage cable was created by works of the prominent scientist Prof. A. F. Ioffe, which was used over the entire length of the line between the Volkhov hydrostation and Leningrad. The experience of hydropower construction in the USSR after constructing the Volkhov hydrostation was continued on the Svir' River. The hydrostations constructed here expanded the electric power supply of Leningrad both for industrial and for municipal purposes, having made it possible to use electricity for heating residential buildings and having reduced in so doing large-scale works on lumbering and transporting firewood.In 1929 the construction of the White Sea--Baltic Waterway was undertaken for the purpose of an unimpeded outlet to ports of the White and Barents Seas and development of the use of the richest natural resources of the Karelo-Murmansk territory.The acute shortage of material resources required that the builders maximally use local materials and minimally use metal and cement.This problem was su...

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