Generalization of the Lamé problem for three-stage decelerated corrosion process of an elastic hollow sphere

The paper presents an analytical solution to Lamé's problem for a hollow sphere with unknown evolving boundaries. The double-sided uniform corrosion of a linearly elastic thick-walled spherical shell under internal and external pressure is considered. It is assumed that the corrosion rates are piecewise linear functions of the maximum principal stress on the related surface, and exponentially decaying with time. The corrosion process is supposed to be divided into three successive stages: constant rate double-sided corrosive wear, a stage of corrosion accelerated on only one of the surfaces of the shell, and a double-sided mechanochemical corrosion. Closed-formed expressions for all the consecutive stages are obtained with their junction points (corresponding to stress corrosion thresholds) being taken into account.     

Propagation of guided waves in pressure vessel

Pressure vessels usually operate under extremes of high/low temperatures and high pressures. Defect, such as crack and corrosion, can result in leakage or rupture failures, even catastrophic incidents. Guided wave-based structural health monitoring (SHM) technology is one of the most prominent options in non-destructive evaluation and testing (NDE/NDT) techniques. Propagation of guided waves in a typical pressure vessel is systematically investigated in this study for the application of guided wave-based SHM. Shape of the pressure vessel is a cylinder with two end caps. Because of geometric similarity, theory of guided wave propagation in the cylinderical structure is analyzed to study dispersive features of guided waves in the pressure vessel. Dispersion curves of three different types of guided wave modes, viz. the longitudinal, torsional and flexural modes, are calculated using theoretical method. Based on the analyses and experimental wave signals, central frequency and wave parameters of incident wave are optimized. Effect of contained liquid on propagation of guided waves, especially the L(0, 2) mode, in the pressure vessel is further investigated to minimize energy leakage of the wave to the contained liquid. The analytical method, finite element analysis (FEA) and experiments are applied to study propagation characteristics of guided waves in the pressure vessel, so as to demonstrate the feasibility of guided wave-based non-destructive evaluation and testing (NDE/NDT) for such kind of complex structures.     

Experimental investigation of hydrodynamic loads and pressure distribution during a pyramid water entry

In the maritime environment slamming is a phenomenon known as short duration impact of water on a floating or sailing structure. Slamming loads are local and could induce very high local stresses. This paper reports a series of impact test results and investigate the slamming loads and pressures acting on a square based pyramid. In this study the slamming tests have been conducted at constant velocity impact with a hydraulic high speed shock machine. This specific experimental equipment avoids the deceleration of the structure observed usually during water entry with drop tests. Three velocities of the rigid pyramid have been used (10, 13 and 15 m s⁻¹). Time-histories of local pressures, accelerations and slamming loads were successfully measured. The relationship between the pressure magnitude and the impact velocity is obtained and the spatial distribution of pressures on pyramid sides is characterized. The impact velocity was found to have a negligible influence in predicting the maximum pressure coefficient.     

An experimental study into the effect of injector pressure loss on self-sustained combustion instabilities in a swirled spray burner

Combustion instabilities depend on a variety of parameters and operating conditions. It is known, especially in the field of liquid rocket propulsion, that the pressure loss of an injector has an effect on its dynamics and on the coupling between the combustion chamber and the fuel manifold. However, its influence is not well documented in the technical literature dealing with gas turbine combustion dynamics. Effects of changes in this key design parameter are investigated in the present article by testing different swirlers at constant thermal power on a broad range of injection velocities in a well controlled laboratory scale single injector swirled combustor using liquid fuel. The objective is to study the impact of injection pressure losses on the occurrence and level of combustion instabilities by making use of a set of injectors having nearly the same outlet velocity profiles, the same swirl number and that establish flames that are essentially identical in shape. It is found that combustion oscillations appear on a wider range of operating conditions for injectors with the highest pressure loss, but that the pressure fluctuations caused by thermoacoustic oscillations are greatest when the injector head loss is low. Four types of instabilities coupled by two modes may be distinguished: the first group features a lower frequency, arises when the injector pressure loss is low and corresponds to a weakly coupled chamber-plenum mode. The second group appears in the form of a constant amplitude limit cycle, or as bursts at a slightly higher frequency and is coupled by a chamber mode. Spontaneous switching between these two types of instabilities is also observed in a narrow domain.     

Differences between PREMIER combustion in a natural gas spark-ignition engine and knocking with pressure oscillations

PREMIER (PREmixed Mixture Ignition in the End-gas Region) combustion occurs with auto-ignition in the end-gas region when the main combustion flame propagation is nearly finished. Auto-ignition is triggered by the increases in pressure and temperature induced by the main combustion flame. Similarly to engine knocking, heat is released in two stages when engines undergo this type of combustion. This pattern of heat release does not occur during normal combustion. However, engine knocking induces pressure oscillations that cause fatal damage to engines, whereas PREMIER combustion does not. The purpose of this study was to elucidate PREMIER combustion in natural gas spark-ignition engines, and differentiate the causes of knocking and PREMIER combustion. We applied combustion visualization and in-cylinder pressure analysis using a compression–expansion machine (CEM) to investigate the auto-ignition characteristics in the end-gas region of a natural gas spark-ignition engine. We occasionally observed knocking accompanied by pressure oscillations under the spark timings and initial gas conditions used to generate PREMIER combustion. No pressure oscillations were observed during normal and PREMIER combustion. Auto-ignition in the end-gas region was found to induce a secondary increase in pressure before the combustion flame reached the cylinder wall, during both knocking and PREMIER combustion. The auto-ignited flame area spread faster during knocking than during PREMIER combustion. This caused a sudden pressure difference and imbalance between the flame propagation region and the end-gas region, followed by a pressure oscillation.     

压强对Zr_(67)Ni_(33)非晶合金结构和动力学性能的影响

采用分子动力学的方法模拟Zr_(67)Ni_(33)合金液体在不同压强下快速凝固过程,通过结构分析方法如对分布函数、配位数、Honeycutt-Andersen(HA)键型指数法,以及动力学参数如均方位移、自散射关联函数、非高斯参数研究压强对Zr_(67)Ni_(33)非晶合金局域原子结构和其过冷液体动力学性能的影响.研究结果表明:压强越大,Zr_(67)Ni_(33)非晶合金中Zr-Ni原子间的相互作用越强,体系结构有序性越强,过冷液体中动力学减慢和动力学不均匀现象越显著.     

Spectroscopic database of CO2 line parameters: 4300-7000 cm

A new spectroscopic database for carbon dioxide in the near infrared is presented to support remote sensing of the terrestrial planets (Mars, Venus and the Earth). The compilation contains over 28,500 transitions of 210 bands from 4300 to 7000 cm⁻¹ and involves nine isotopologues: ¹⁶O¹²C¹⁶O (626), ¹⁶O¹³C¹⁶O (636), ¹⁶O¹²C¹⁸O (628), ¹⁶O¹²C¹⁷O (627), ¹⁶O¹³C¹⁸O (638), ¹⁶O¹³C¹⁷O (637), ¹⁸O¹²C¹⁸O (828), ¹⁷O¹²C¹⁸O (728) and ¹⁸O¹³C¹⁸O (838). Calculated line positions, line intensities, Lorentz half-width and pressure-induced shift coefficients for self- and air-broadening are taken from our recent measurements and are presented for the Voigt molecular line shape. The database includes line intensities for 108 bands measured using the McMath-Pierce Fourier transform spectrometer located on Kitt Peak, Arizona. The available broadening parameters (half-widths and pressure-induced shifts) of ¹⁶O¹²C¹⁶O are applied to all isotopologues. Broadening coefficients are computed using empirical expressions that have been fitted to the experimental data. There are limited data for the temperature dependence of widths and so no improvement has been made for those parameters. The line intensities included in the catalog vary from 4×10⁻³⁰ to 1.29×10⁻²¹ cm⁻¹/(molecule cm⁻²) at 296 K. The total integrated intensity for this spectral interval is 5.9559×10⁻²⁰ cm⁻¹/(molecule cm⁻²) at 296 K.     

Pressure broadening by argon in the hyperfine resolved P(10) and P(70) (17,1) transitions of I2 XΣ(0g)→BΠ(0u) using sub-Doppler laser saturation spectroscopy

The dependence of pressure broadening upon hyperfine component in the P(10) and P(70) lines of the (17,1) band of the I₂ X¹Σ(0_g⁺)→B³Π(0_u⁺) has been studied using laser saturation spectroscopy. By limiting absorption to the zero velocity group, Doppler broadening is removed, lineshapes with widths (FWHM) <9 MHz are detectable, and collision-induced broadening is measured at pressures of 0.2-1.2 Torr. The rates for broadening by argon are 8.3±0.3 and 10.7±0.4 MHz/Torr for the P(70) and P(10) lines, respectively. No significant variation in broadening rates is observed for the 15 hyperfine components of these even rotational lines. The effects of velocity cross-relaxation introduce a broad baseline into the spectra, which is strongly dependent on rotational state, pressure, and laser modulation frequency. The observed broadening rates correlate well with prior measurements and the polarizability of the collision partner.     

解非定常不可压缩N-S方程的迭代压力Poisson方程法

１．引 言 数值求解不可压缩流体流动问题可以采用原始变量的方程作为控制方程,也可以用涡量一流函数方程作为控制方程．直接求解原始变量的不可压缩 Ｎａｖｉｅｒ—Ｓｔｏｋｅｓ方程存在一个主要困难：速度向量在每一时刻都必须满足零散度约束条件,即不可压缩性连续方程．用涡量一流函数方程求解时,连续方程自动满足,所以不存在约束条件的问题,但涡量的边界条件比较难处理,且不易应用于三维问题和带有自由表面或其它流体交界面的问题． 解决上述速度向量必须满足零散度约束条件的困难的方法有：人工压缩法［３,１７］;压力Ｐｏｉｓ…     

Particle mixing rates using the two-fluid model

In this work, a new methodology is introduced to calculate the solids mixing rate in dense gas-fluidized beds using the two-fluid model. The implementation of this methodology into an existing two-fluid model code was carefully verified. The solids phase continuity equation was satisfied using our method, and the sensitivity of the computational results to the time step, computational cell size, and discretization scheme was investigated to determine the optimal simulation settings. Using these simulation settings, the degree of solids mixing was observed to rapidly (exponentially) increase with increasing operating pressure and linearly decrease with increasing bed diameter. Our novel methodology can be applied to analyze mixing processes in large lab-scale beds as an alternative to existing time-consuming simulation techniques such as computational fluid dynamics combined with the discrete element model.