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X-Pattern from HST obtained recentlyIt is well-known that branches of trees were heated and burnt at the region of the Tunguska blast (Yu.A.L’vov, N.V.Vasilijev 1976). A.E.Zlobin carried out special experimental investigation for determination of thermal properties of tree's rind and blast heat impulse. Rinds of pine and larch were investigated during heating by electrical heater. Obtained thermal properties were used for calculations of temperature distribution in cross section of branches. Heat impulse was determined during analysis with 2-D finite element method. Area of burn was closely inspected too. Clear picture of heat influence was obtained in accordance to value of heat impulse and clustering procedure (look at left Figure). Three considerable blasts here are visible (central "A", eastern "B" and western "C"). Fourth blast "D" is visible on some distance to north-west. Also three "horseshoe-like" burn structures "E" are visible on some distance to south. This picture is interpreted as blasts of four fragments and heat radiation influence by ballistic shock wave's surface (heat caustic influence). |
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It is necessary to mention the picture of Tunguska space body at flight, which was drawn by eyewitness T.N.Naumenko from the town Kezhma (look at left Figure). There is good correspondence between this picture and thin structure of burn area. Scale and size of comet's fragments is added by A.E.Zlobin. The picture of T.N.Naumenko demonstrate that Tunguska comet nucleus moved across the sky with low velocity. Certainly, only in case of low velocity of Tunguska comet at flight T.N.Naumenko was able to notice and draw form of the body with so many detailes. |
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Attentive analysis was carried out by A.E.Zlobin on the base of tree fall catalogue processing (W.H.Fast et al. 1976). There is thin structure like "horseshoe" in southern area of tree fall (look at left Figure). This structure was interpreted by A.E.Zlobin as influence of ballistic shock wave cone (gas dynamic caustic influence). The axis azimuth of "horseshoe" is in good correspondence to I.S.Astapovich's latest trajectory, which is directed from south-south-east to north-north-west (I.S.Astapovich 1965). There is good visible, that northern wing of “butterfly” forest fall was produced mainly by four final horizontal-directed blasts, but southern wing was produced mainly by ballistic and ablation shock wave. The influence of ballistic shock wave was increased due to concave form of trajectory. |
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Quasi 3-D modeling dealt with estimation of unsteady temperature distribution in the Tunguska space body before entering into atmosphere, estimation of mechanical properties of the body in accordance to its temperature, solution of equations of motion (three coordinates), calculations of pressure, heat and mass transfer at the region of stagnation point (for all body and then for all its fragments), strength and stress analysis for all body and then for all its fragments, deformation of all fragments, expansion of hot gas volumes in case of its known geometry, shock wave formation and heat radiation influence on forest and branches of trees, formation and raising of hot cloud, variation of local magnetic field. |
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It was shown in this study that Tunguska-size comets are able to penetrate considerable deep into dense atmosphere due to decrease of drag effect. A.E.Zlobin explained this decrease by forward-directed jet from cavern, which was located at the region of stagnation point of ice comet's body (or of each ice fragment). This cavern is formed due to most intensive heat and mass transfer processes at the region of stagnation point. Length of Tunguska's trajectory as function of altitude is shown at left Figure. |
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Expansion of hot gas volumes was calculated with the help of particle-in-cell method (PIC). A.E.Zlobin made special computer program based on PIC algorithm for calculations of gas expansion in horizontal plane. PIC-method is convenient for solution of this task because borders of hot gas volumes in the case of Tunguska blast are considerably curved. Also these calculations are more determined due to well-known geometrical form of each initial gas volume. Pressure, velocity and temperature distributions were estimated during calculations. Calculation process consisted of cells grid generation, initial positioning of particles, initial and boundary conditions set, solution of gasdynamic equations with Eulerien and Lagrangian procedures with time steps. Typical grid of cells was (50 x 50). Quantity of air particles was 4 per cell and quantity of comet's substance particles - 300 per cell. The view of initial distribution of all particles is visible in Figure. Model form of gas volume was stated approximately in accordance to form of blasts "A" and "B". The sample of pressure estimation is shown in Figure too. |
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Some results and conclusion
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