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    Effect of the variation of conical liner apex angle and explosive ignition point on shaped charge jet formation
    (Natl Inst Science Communication-Niscair, 2003) Aksoy, IG; Sen, S
    Shaped charge technology has an important role in the military and commercial areas, as bullets and warheads made by the shaped charge principle are especially used for penetration to target and demolition purposes. In early studies, the solution of shaped charge problems has been obtained by using analytical methods. However, over the past decade, numerical methods based on finite difference and finite element methods are used for simulating this complex process. In this study, the effects of varying parameters (conical liner apex angle and explosive ignition place) are investigated by a numerical modelling of the shaped charge performed using the Dyna2D hydrodynamic code. The 81 nm precision shaped charge warhead which is designed by Ballistic Research Laboratory (BRL) is taken as a reference charge. The simulations are carried out from 13degrees to 46degrees of the apex angle because both the jets do not occur completely for the apex angles equal or smaller than 13degrees and the velocity decreases for the apex angles larger than 46degrees. The velocity of the jet tip increases very slowly with the decrease of the apex angle from 38degrees to 13degrees. When the apex angle in this range decreases the jet tip becomes shorter while the jet slug gets longer and thicker. Additionally, it is realized that it needs longer time for the jet formation, and moreover, the jet does not occur completely. For those reasons, the parametric evaluations are realized by changing the conical liner apex angle (38degrees, 40degrees, 42degrees, 44degrees, 46degrees) and explosive ignition place (central point, plane and ring). As a result of the variation of the parameters, some important variations are determined in pressure, velocity gradient and jet formation of the shaped charge through simulation. The present results are found in good agreement with the reported results.
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    Enhancement of solar thermal energy storage performance using sodium thiosulfate pentahydrate of a conventional solar water-heating system
    (Elsevier Science Sa, 2005) Canbazoglu, S; Sahinaslan, A; Ekmekyapar, A; Aksoy, IG; Akarsu, F
    The time variations of the water temperatures at the midpoint of the heat storage tank and at the outlet of the collector in a conventional open-loop passive solar water-heating system combined with sodium thiosulfate pentahydrate-phase change material (PCM) were experimentally investigated during November and then enhancement of solar thermal energy storage performance of the system by comparing with those of conventional system including no PCM was observed. It was observed that the water temperature at the midpoint of the storage tank decreased regularly by day until the phase-change temperature of PCM after the intensity of solar radiation decreased and then it was a constant value of 45 degreesC in a time period of approximately 10 h during the night until the sun shines because no hot water is used. Heat storage performances of the same solar water-heating system combined with the other salt hydrates-PCMs such as zinc nitrate hexahydrate, disodium hydrogen phosphate dodecahydrate, calcium chloride hexahydrate and sodium sulfate decahydrate (Glauber's salt) were examined theoretically by using meteorological data and thermophysical properties of PCMs with some assumptions. It was obtained that the storage time of hot water, the produced hot water mass and total heat accumulated in the solar water-heating system having the heat storage tank combined with PCM were approximately 2.59-3.45 times of that in the conventional solar water-heating system. It was also found that the hydrated salts of the highest solar thermal energy storage performance in PCMs used in theoretical investigation were disodium hydrogen phosphate dodecahydrate and sodium sulfate decahydrate. (C) 2004 Elsevier B.V. All rights reserved.