ガス爆発の影響度評価を行うために，ガス爆発時に大きな被害をもたらす

圧を予測することは必要不可欠である．本稿では，数値流体力学計算に比べ圧を簡易的に予測できるモデルについて解説する．特に，火炎の不安定性による火炎伝播の加速現象は圧に大きく影響を与えることを述べる．これは，火炎のスケールが大きくなると流体力学的不安定性による火炎伝播加速の影響が非常に大きくなるためである．さらに，火炎伝播の加速現象を考慮した圧予測手法を解説し，高い精度でガス爆発時の圧を予測できることを示す．

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の問題の解は数値解を含めて, 殆んどすべて近似解であるが, 応用上からも, その絶対的な評価が必要であるという観点にたって, その最も基本的である理想気体中の, 点源 (線源, 面源) からの球対称 (輪対称, 1次元) のの方程式の解の存在を議論とする.そのために, 運動方程式からBlast Wave変換によって得られる方程式系を基礎とする.この方程式系については, 多くの近似解が知られているが, その内で基本的なy (=C²/U², C : 音速, U : 波面の速度) のべき級数展開解を考える.とくに, この解の収束性がしばしば問題となる点にかんがみ, この展開解が収束し, 上式の解となっている事を示す.その証明は, 級数の収束を直接考える代りに, 収束するyについての級数の集まり (関数空間) を考え, そこでの縮小写像の原理 (不動点の存在定理) を用いる事によってなされる.

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  This study was aimed at evaluations of the blast characteristics by the arrival time of blast wave in the air. Some experimental explosions with small explosives less than a hundred gram were carried out in an explosion chamber. The signal from a handmade blast switch, which used aluminum foil as a blast-pressure acceptor, showed the same time to the edge position of time-pressure waveform observed by piezoelectric pressure sensor. It meant the arrival time of shock wave could be measured by the blast switch. According to the result of some experiments with several weights of Composition C-4, it was recognized that the arrival time apparently followed Sachs' scaling law because the plots of scaled arrival time against scaled distance came together on a line. The performance of Chlorate explosive, a mixture of potassium chlorate and sugar, was examined. The Composition C-4 equivalence of the chlorate explosive was led by two parameters that were peak overpressure and arrival time. The values 42.3% and 36.0% were given by the two parameters respectively.
  A measuring method of the arrival time for explosion accompanied with fragments was also examined. Composition C-4 put in a round-bottom flask was applied to the experiment. While the face-on blast switch was interfered by numerous glass particles scattered by the explosion, the side-on blast switch could avoid the glass particles clearly. The result suggested that the arrival time could be measured in spite of an explosion with scattering of fragments by the side-on blast switch.

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損傷は爆発に伴い発生するに暴露され生じる．一般の臨床医が経験する外傷機転に加えて，穿通物による機序，衝撃波を伴う圧損傷による機序が複合的に生体に影響を及ぼし，損傷が発生する．外傷初期診療ガイドラインに沿った対応を行うとともに，損傷時の状況の把握を含めて衝撃波を伴う圧損傷のリスク階層化と病態を考慮した治療を行う．通常の外傷とは異なる点があり，外科的あるいは脳血管内治療に際しては特徴を理解しておく必要がある．

　2020年東京オリンピック，パラリンピックを迎えるにあたり，わが国においても救急に携わる医療従事者，関係者も病態と診断・治療に関する一定の知識を持っていることが望ましい．本稿では，

損傷の機序，病態生理も含めた特徴，による傷病者への初期対応を含めた診断，治療について概説する．衝撃波工学の見地から衝撃波，の生体に及ぼす作用，による外傷性脳損傷の発生機序，現在のによる外傷性脳損傷研究の問題点についても概説する．

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It is important to investigate a pressure profile when a shock wave interacts with a reflector from a safety point of view. In this study, experiments are carried out using a shock tube of 50mm diameter and 8m in total length with a cylindrical reflector of 50mm in the observation section. The behavior of reflection process of diffracted shock wave is visualized with the aid of Schlieren techniques. As a result, (i) a pressure histories on the reflector coincides between numerical and experimental results. (ii) The sequential flow-field behind the shock wave is clearified. (iii) An empirical formula of maximum pressure is obtained with a parameter of a energy pen unit area.

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　本研究は，箱型構造物の前壁が構造物周囲の

圧特性に及ぼす影響を調べるため，実験および数値解析を行ったものである．まず，米国の防護施設基準の中で示されている構造物に作用する圧特性の評価方法について基礎的な考察を行った．次に，Composition C-4爆薬を用いた爆発実験を行い，箱型構造物前壁の寸法形状の変化が構造物の各面に作用する圧特性に及ぼす影響について調べた．また，実験に対する数値解析を行って実験結果の再現性を確認した上で，数値解析を用いて箱型構造物前壁の寸法形状の変化が構造物周囲の圧特性に及ぼす影響について考察した．

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　煙火工場等の火薬類を貯蔵する火薬庫の建設においては，万が一の爆発に際しても周辺への安全を確保する必要性から保安距離が定められている．保安距離は自由空間中における爆発事象を基準として定められているが，堅固な鉄筋コンクリート造の周囲を覆土した覆土式火薬庫の内部爆発事象は自由空間での爆発とは異なるはずである．本研究は，爆発実験室で模型火薬庫を用いた爆発実験を行い，構造物の破壊や圧の大きさに及ぼす覆土の効果について検討を行っている．模型火薬庫試験体は実規模の約1/20の縮尺とし，C4爆薬を試験体内部で爆発させた．実験では，覆土の厚さおよび爆薬量をパラメータとした．実験結果に基づいて覆土の有無や厚さが圧に及ぼす効果を考察し，換算距離と最大圧の関係を求め，現行の保安距離に係る規定との比較を行った．

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In the present study, the influences of flame propagation speed on the intensity of blast wave during unconfined gas explosions have been examined experimentally. The various scale tests of hydrogen/air deflagrations conducted. Results demonstrated the flame wrinkled and accelerated due to hydrodynamic instability with the flame scale and thereby the overpressure rapidly increased. In particular, the intensity of blast wave compared with the Peclet number defined as dimensional flame radius when the unburned mixture is combusted. The results of comparison show the dimensionless overpressure increased with the Peclet number, because of flame acceleration due to the hydrodynamic instability, as the explosion scale became larger.

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We have investigated hydrogen explosion risk and its mitigation, focusing on compact hydrogen refueling stations in urban areas. In this study, numerical analyses were performed of hydrogen blast propagation and the structural behavior of barrier walls. The explosive source was a prismatic 5.27 m3 volume that contained 30% hydrogen and 70% air. A reinforced concrete wall, 2 m tall by 10 m wide and 0.15 m thick, was set 2 or 4 m away from the front surface of the source. Each of the tests measured overpressures on the surfaces of the wall and on the ground, displacements of the wall and strains of the rebar inside the wall. The simulated overpressures were in good agreement with test results for all three test cases. DIANA, a finite element analysis code was used for the structural simulations of the barrier wall. The overpressures obtained by the blast simulations were used as external forces. The analyses simulated the displacements well.

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爆傷による身体への影響は一次から四次までの四相の衝撃による損傷を特徴とし,一次衝撃による損傷は,爆発の際に生じるが身体に直接的に作用することで生じる損傷である。一次衝撃による腹腔内損傷では,腸管が最も損傷を受けやすいと報告されている。また,爆傷ではによる一次衝撃の損傷機序のみならず飛来物による二次衝撃,により飛ばされて生じる三次衝撃,熱などによる四次衝撃をも考慮した診療と治療を行うことが重要である。今回,われわれは金属パイプ内で発生したによる一次衝撃の受傷機転から右胃大網動脈損傷を来したまれな爆傷症例を経験したので報告する。

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Nonlinear finite element dynamic analyses were conducted for the RC walls subjected to hydrogen explosive load in order to verify an applicability of the analysis method by comparison with experimental results obtained from past explosion tests. The analytical results show good correspondence with the test results. It is concluded that the nonlinear response of the walls subjected to the hydrogen explosive load can be estimated by the finite element model with sufficient accuracy. Furthermore numerical study was carried out with various wave forms of the explosive load. As results, it is found that the maximum displacement in the nonlinear response was not influenced on by the wave forms, but depends on the impulse of the explosive load. It is also found that negative pressure of the explosive load is needed to be considered to evaluate the maximum wall response accurately.

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To understand the consequence of accidental gas explosions in an open space, the effects of flame propagation behavior on the blast wave were examined experimentally. The spherically propagating flames in the mixtures of methane and hydrogen with air were focused. The results show that the flames at equivalence ratios of 0.7, 1.0, and 1.3 were intensively wrinkled and accelerated with the increases of hydrogen addition in methane/air mixtures. The overpressure of the blast wave tends to increase acceleratingly by the flame wrinkling. The flame winkling is considered to be generated by diffusive-thermal instability according to the analysis of the Effective Lewis number. The overpressure can be predicted by the acoustic theory which indicates that the intensity of blast wave is affected, in particular, by burning velocity, volumetric expansion ratio and the flame acceleration. Especially, the intensity of the blast wave is strongly affected by the acceleration of the burning velocity.

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Experiments on the hydrogen gas explosion were performed to achieve the safe use of hydrogen energy, and the effect of explosion accidents on peripheral reinforced concrete (RC) structures was studied. Hydrogen gas with 37m³ in volume and 30% in volume concentration was detonated, and the response of the walls settled near the explosion center was measured in displacement, stress, cracks and damage situation. As the result, the damage mechanism of RC structures was studied. Fundamental data for the safety design of protective walls was obtained.

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The blast wave caused by the explosion shows the refractive index which is different from that of ambience because the wave is accompanied by discontinuous density shift of the medium. Schlieren method is often used as a technique to observe the behavior of Shockwave in a fluid. However, it is difficult to apply to outdoor experiments because the method needs arrangements of some optical equipment around the subject. In this study, it was tried that the visualization of the blast wave with small amount of explosives. The metho d was a simple and convenient procedure from the digital frame images which had been taken by digital high-speed camera in some past outdoor experiments without any optical equipment. This method was a kind of subtraction of images' digital data, or PIV analysis. The power of explosion could be estimated by the visualized propagation of blast wave.

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This paper visualizes explosions in a subsurface magazine model constructed underground to mitigate the effects of blast waves. Numerical simulations discuss the effect of water that is put inside the magazine model. The simulation data shows that the peak overpressures on the ground agree with those in the previous experiment. The increases of kinetic and internal energies of water are then estimated, and that the heat transfer at the interface of water and air is a dominant factor to mitigate the blast wave on the ground.

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In this study, the blast wave and flame propagation behavior during a gas explosion of homogeneous premixed combustible gas confined in a spherical soap bubble have been measured simultaneously. The results show that the measured values of the over pressure at various equivalence ratios were larger than those calculated by the acoustical theory. These discrepancies were found to be arisen by the change of the flame propagation velocity in the experiment. The increase of the over pressure in lean mixtures of combustible gas might be induced by diffusive-thermal instability in the flame front. On the other hand, the increase of the over pressure in rich mixtures of combustible gas might be induced by the acceleration of the flame propagation, which is considered to be generated by the sudden rupture of the soap bubble and mixing with the surrounding air.

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Hydrogen explosion tests were conducted to grasp nonlinear response and to get its fundamental data for reinforced concrete walls subjected to hydrogen explosive load. In the tests, an explosive source (37m^3 -volume) that contained 30% hydrogen and 70% air was detonated, and the responses of the walls close to the source were measured. Two preliminary and three main tests were conducted for a variety of wall types with different thickness, heights, and steel reinforcements. The walls were instrumented with pressure sensors, displacement sensors, strain gauges, accelerometers and thermocouple. Wide varieties of experimental data were obtained in damage ranging from elasticity to complete failure. It was also confirmed that the wall nonlinear response depends on the blast wave duration and initial natural period. With increasing the initial natural period, the higher vibration modes were appeared on the response of the walls. Furthermore effects of strain rate were quantitatively investigated on the basis of the test results.

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