Cylinder Wall Velocities Research Articles

A quasi-isentropic model of a cylinder driven by aluminized explosives based on characteristic line analysis

A quasi-isentropic study on the process of driving a cylinder with aluminized explosives was carried out to examine the influence of the aluminum (Al) reaction rate on cylinder expansion and the physical parameters of the detonation products. Based on the proposed quasi-isentropic hypothesis and relevant isentropic theories, the characteristic lines of aluminized explosives driving a cylinder were analyzed, and a quasi-isentropic model was established. This model includes the variation of the cylinder wall velocity and the physical parameters of the detonation products with the Al reaction degree. Using previously reported experimental results, the quasi-isentropic model was verified to be applicative and accurate. This model was used to calculate the physical parameters for cylinder experiments with aluminized cyclotrimethylenetrinitramine explosives with 15.0 % and 30.0 % Al content. The results show that this quasi-isentropic model can be used not only to calculate the cylinder expansion rule or Al reaction degree, but also to calculate the physical parameters of the detonation products in the process of cylinder expansion. For explosives with 15.0 % and 30.0 % Al, 24.3 % and 18.5 % of the Al was found to have reacted at 33.9 μs and 34.0 μs, respectively. The difference in Al content results in different reaction intensity, occurrence time, and duration of two forms of reaction (diffusion and kinetic) between the Al powder and the detonation products; the post-detonation burning reaction between the Al powder and the detonation products prolongs the positive pressure action time, resulting in a continuous rise in temperature after detonation.

Surface roughness effect on cylinder vortex-induced vibration at moderate Re regimes

The marine riser is the key equipment connecting the floating platform with the seabed wellhead, and the vortex-induced vibration (VIV) is the main cause of its fatigue damage, which contains complex and substantial dynamics content. Marine risers are operated for a long time. As time goes by, marine organisms will attach on the marine riser surfaces, thus significantly affect their surface roughness of the riser. The increased surface roughness makes the dynamic characteristics of the riser VIV more abundant and complex, including jumping, multi-frequency vibration, broadband vibration, resonance and other dynamic contents. In this study, based on the bidirectional fluid-structure coupling method of computational fluid dynamics (CFD) and computational structure dynamics (CSD), the modified model of rough wall velocity gradient is introduced, and the calculation program of a rough cylinder wall velocity gradient is compiled and embedded into the numerical calculation program of a smooth cylinder VIV to construct the numerical calculation program of a rough cylinder VIV. The program is used to study effects of various key parameters, including surface roughness, and inflow velocities, on the vibration response characteristics, dynamic characteristics, wake vortex shedding patterns and vibration trajectories of a rough cylinder. The differences of VIV characteristics are systematically studied to reveal the nonlinear dynamic behavior of a rough cylinder VIV, such as jumping, multi-frequency vibration, resonance, etc. The influence mechanism of surface roughness on a cylinder VIV is explored to provide a scientific theoretical basis and a practical engineering method for vibration control of a rough marine riser.

Prediction of Cylinder Wall Velocity Profiles for ANFO Explosives Combining Thermochemical Calculation, Gurney Model, and Hydro‐Code

AbstractTheoretical prediction of performance indicators of explosives plays an important role in the development of new explosives and explosive formulations. Of particular interest is the possibility to estimate the velocity of metal liner driven by an explosive charge. We present a theoretical model for estimation of metal cylinder wall velocity profiles of non‐ideal ANFO explosives. The model is based on thermochemical calculations using EXPLO5 code, expressing the Gurney energy in terms of JWL equation of state, and using hydro‐code simulation. The Wood‐Kirkwood detonation theory, incorporated in EXPLO5, is applied for calculation of detonation parameters of non‐ideal ANFO explosives. It was found that this approach enables prediction of cylinder wall velocity for ANFO explosives, with the error at V/V0=7 expansion ratio not exceeding 100 m/s.

Estimation of Explosive Energy Output by EXPLO5 Thermochemical Code

Detonation velocity, detonation pressure, and detonation heat are usually used as a measure of explosive's performance. However, they do not answer the question how fast an explosive can accelerate the surrounding metal liner. A semi‐empirical solution to this problem was proposed byR. W. Gurneyin 1943. In this paper we used thermochemical calculations to calculate energy of detonation products along the expansion isentrope and to estimate the Gurney energy and cylinder wall velocity from it. It was found that for the same degree of the products expansion, experimentally determined Gurney energy is systematically less than calculated detonation energy due to the energy losses. At about threefold expansion of the products, the detonation energy matches very well with an experimental Gurney energy.

Evaluation of the Deuterium Isotope Effect in the Detonation of Aluminum Containing Explosives

AbstractDuring or shortly after a detonation in condensed explosives, the reaction rates and the physical mechanism controlling aluminum reaction is poorly understood. We utilize the kinetic isotope effect to probe Al reactions in detonation product gases in aluminized, protonated and deuterated high explosives using high‐fidelity detonation velocity and cylinder wall expansion velocity measurements. By observation of the profile of cylinder wall velocity versus time, we are able to determine the timing of aluminum contribution to energy release in product gases and observe the presence or absence of rate changes isotopic substitution. By comparison of the Al oxidation with lithium fluoride (LiF), data indicate that Al oxidation occurs on an extremely fast time scale, with post‐detonation kinetic isotope effects observed in carbon containing formulations.

A New Method for Assessment of Performing Mechanical Works of Energetic Compounds by the Cylinder Test

AbstractA new method is introduced for assessment of performing mechanical works of energetic compounds by cylinder wall velocities of CHNOFCl energetic compounds on the basis of the cylinder test. Four suitable decomposition paths are used to evaluate the number of moles of gaseous detonation products per gram of explosive, the average molecular weight of these gases, and the heat of detonation in calories per gram by considering different decomposition products HF, HCl, CO, N2, H2O, H2, and CO2. For CHNO and fluoro energetic compounds, the predicted cylinder wall velocities of these compounds give more reliable results than one of the best available empirical methods. The predicted root mean square (rms) deviations of cylinder wall velocities of the new model for some chloro explosives at actual radial expansions 0.6 and 1.9 mm are 0.010 and 0.062 km·s–1, which show high reliability of the new method.

Computational studies on thermodynamic properties, detonation properties and bond dissociation energies for polydifluoroaminopurine compounds

Abstract Density functional theory (DFT) was used to study the heat of formation (HOFs), electronic structure, energetic properties and thermal stability for a series of purine derivatives with difluoroamino groups. The isodesmic reaction method was employed to calculate the HOFs of the energies obtained from electronic structure calculations. Results indicated that the position of difluoroamino groups could influence the values of HOFs. The bond dissociation energies and bond orders of the weakest bonds were analyzed to investigate the thermal stability of the purine derivatives. Furthermore, the detonation velocities and pressure were evaluated by using the Kamlet–Jacobs equations based on the theoretical densities and detonation heat ( Q ). The cylinder wall velocities ( V ¯ ) were also calculated using the simplified calculational method. Compared with the conventional explosives, two purine derivatives may be regarded as the potential candidates for practical HEDCs.

The Role of Aluminum in the Detonation and Post‐Detonation Expansion of Selected Cast HMX‐Based Explosives

AbstractIn order to improve understanding of how aluminum contributes in non‐ideal explosive mixtures, cast‐cured formulations have been analyzed in a series of cylinder tests and plate‐pushing experiments. This study describes the contribution of 15 % aluminum (median size of 3.2 μm) vs. lithium fluoride (an inert substitute for aluminum; <5 μm) in cast‐cured HMX formulations in different temporal regimes. Small cylinder tests were performed to analyze the detonation and wall velocities (1–20 μs) for these formulations. Near‐field blast effects of 58 mm diameter spherical charges were measured at 152 mm and 254 mm using steel plate acceleration. Pressure measurements at 1.52 m gave information about free‐field pressure at several milliseconds. While the observed detonation velocities for all formulations were within uncertainty, significantly higher cylinder wall velocities, plate velocities, and pressures were observed for the aluminum formulations at ≥2 μs. Additionally, hydrocode calculations were performed to determine how non‐ideal behavior affected the plate test results. Collectively, this work gives a clearer picture of how aluminum contributes to detonation on timescales from 1 μs to about 2 ms, and how the post‐detonation energy release contributes to wall velocities and blast effects. The experiments indicate that significant aluminum reactions occur after the CJ plane, and continue to contribute to expansion at late times.

99/02677 Fuel and synthesis gas from waste

Density functional theory (DFT) was used to study the heat of formation (HOFs), electronic structure, energetic properties and thermal stability for a series of purine derivatives with difluoroamino groups. The isodesmic reaction method was employed to calculate the HOFs of the energies obtained from electronic structure calculations. Results indicated that the position of difluoroamino groups could influence the values of HOFs. The bond dissociation energies and bond orders of the weakest bonds were analyzed to investigate the thermal stability of the purine derivatives. Furthermore, the detonation velocities and pressure were evaluated by using the Kamlet–Jacobs equations based on the theoretical densities and detonation heat (Q). The cylinder wall velocities (V¯) were also calculated using the simplified calculational method. Compared with the conventional explosives, two purine derivatives may be regarded as the potential candidates for practical HEDCs.

Improved prediction of cylinder test energies

Energies delivered at 7 volumes expansion in the cylinder test are well correlated for 16 typical and atypical explosives. The criterion for a typical explosive is that it have approximately 0.40 mole fraction of water vapor in the detonation products. The correlation equation is (V 20) 2 = 0.200 ϕp 0 1.50[1.104 − 0.265 MF(H 2O) ], with ϕ = NM 1 2 Q 1 2 where V 20 is the cylinder wall velocity in mmμs at 20 mm expansion in the 1-in. cylinder test, ϱ 0 is the loading density, N is the number of moles of gaseous detonation products per gram of explosive (calculated by the H 2OCO 2 arbitrary), M is the average molecular weight of the gases, Q is the heat of detonation in cal/g, and MF(H 2O) is the mole fraction of water vapor in the detonation products. For reasons that are not now known, the insensitive explosives TATB and nitroguanidine underperform by about 15% relative to the above equation.

The chemistry of detonations. VIII. Energetics relationships on the detonation isentrope

The ratio of energy delivered at seven volumes expansion compared with two volumes expansion on the detonation isentrope is obtained from the square of the ratio of cylinder wall velocities at 20 mm expansion and 6 mm expansion in the Lawrence Livermore National Laboratory cylinder test. The velocities fit the relationship (V 20 V 6 2 =1.9197−0.327 ϱo−0.44 [MF( H 2 O)] 2 , where MF(H 2O) is the mole fraction of water in the detonation gas mixture, as calculated using an “H 2OCO 2 arbitrary.” The relationship applies to CHNO, CHNOF, CNO, and HNO explosives with a standard deviation which compares favorably with the experimental precision of the measurements. The correlation described here will serve as a benchmark against which we will later test whether nonideal explosives are still reacting in the time frame of the cylinder test.