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Shock wave configurations and reflection hysteresis outside a planar Laval nozzle

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Chinese Journal of Aeronautics 2015年第5期28卷 1362-1371页

作者： Wang Dan yu yong School of Aerospace Engineering Beijing Institute of Technology

When the pressure ratio increases from the perfectly expanded condition to the third limited condition in which a normal shock is located on the exit plane, shock wave configurations outside the nozzle can be further assorted as no shock wave on the perfectly expanded condition, weak oblique shock reflection in the regular reflection （RR） pressure ratio condition, shock reflection hysteresis in the dual-solution domain of pressure ratio condition, Mach disk configurations in the Mach reflection （MR） pressure ratio condition, the strong oblique shock wave configurations in the corresponding condition, and a normal shock forms on the exit plane in the third limited con- dition. Every critical pressure ratio, especially under regular reflection and Mach reflection pressure ratio conditions, is deduced in the paper according to shock wave reflection theory. A hysteresis phenomenon is also theoretically possible in the dual-solution domain. For a planar Laval nozzle with the cross-section area ratio being 5, different critical pressure ratios are counted in these con- ditions, and numerical simulations are made to demonstrate these various shock wave configurations outside the nozzle. Theoretical analysis and numerical simulations are made to get a more detailed understanding about the shock wave structures outside a Laval nozzle and the RR←→MR transition in the dual-solution domain.

关键词： Critical pressure ratios Hysteresis Mach reflection Regular reflection Shock wave configurations

L^(p)-Estimate for Linear Forward-Backward Stochastic Differential Equations

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Acta Mathematica Sinica,English Series 2023年第5期39卷 827-845页

作者： Bing XIE Zhi yong yu School of Mathematics Shandong UniversityJinan 250100P.R.China

This paper is concerned with coupled linear forward-backward stochastic differential equations(FBSDEs,for short).When the homogeneous coefficients are deterministic(the non-homogeneous coefficients can be random),we obtain an L^(P)-result(p>2),including the existence and uniqueness of the p-th power integrable solution,a p-th power estimate,and a related continuous dependence property of the solution on the coefficients,for coupled linear FBSDEs in the monotonicity framework over large time *** order to get rid of the stubborn constraint commonly existing in the literature,i.e.,the Lipschitz constant of σ with respect to z is very small,we introduce a linear transformation to overcome the difficulty on small intervals,and then"splice"the L^(P)-results obtained on many small intervals to yield the desired one on a large interval.

关键词： Forward-backward stochastic differential equation L^(P)-estimate monotonicity condition large interval

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3-D distribution of tensile stress in rock specimens for the Brazilian test

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Journal of University of Science and Technology Beijing 2005年第6期12卷 495-499页

作者： yong yu Chunyan Meng Department of Applied Mechanics and Engineering Southwest Jiaotong University Chengdu 610031 China Department of Computing Science University of Alberta Edmonton T6G 2C5 Canada

It is claimed that the formula used for calculating the tensile strength of a disk-shaped rock specimen in the Brazilian test is not accurate, because the formula is based on the 2-dimensional elastic theory and only suitable for very long or very short cylinders. The Matlab software was used to obtain the 2-dimensional distribution of stress in the rock specimen for Brazilian test. Then the 2-dimensional stress distribution in Brazilian disk was analyzed by the Marc FEM software. It can be found that the results obtained by the two software packages can verify each other. Finally, the 3-dimensional elastic stress in the specimen was calculated. The results demonstrate that the distribution of stress on the cross section of the specimen is similar to that in 2-dimension. However, the value of the stress on the cross section varies along the thickness of the specimen and the stress is bigger when getting closer to the end of the specimen. For the specimen with a height-to-diameter ratio of 1 and a Poisson＇s ratio of 0.25, the tensile strength calculated with the classical 2-D formula is 23.3% smaller than the real strength. Therefore, the classical 2-D formula is too conservative.

关键词： Brazilian test tensile strength FEM rock Marc Matlab

Effects ofmodulenumberand firing conditiononchargethermal safetyingunchamber

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Defence Technology（防务技术） 2022年第1期18卷 27-37页

作者： Huan-yu Qian yong-gang yu Jing Liu School of Energy and Power Engineering Nanjing University of Science and Technology Narjing 21094 China Acudemny of Opto-Electroric China Electronis Technology Group Corporation(AOE CETC)Tianjin300308China

Thermal safety of modular charge which is fed into and retained in the chamber after gun fires consecutively is first investigated with cook-off method,A two-dimensional cook-off model of modular charge in gun chamber is established and the cook-off process of modular charge in gun chamber is numerically *** the effects of module number and firing condition on charge thermal safety are evaluated by researching the cook-off response characteristics of *** results show that under conditions of different module numbers the cook-off responses all occur on the module closest to the boundary of missile,and the single-base propellants located at the inner surface of cartridge ignite *** the number of loaded module changes from 1 to 6,the cook-off response temperatures vary little,only in a small range of 478.1 K-482.4 *** cook-off response times decrease logarithmically in the range of 211.25-166.7 s with the increasing length of residual air gap in gun *** simulation results are well matched with the experimental ***,different firing conditions have greatinfluence on the cook-off response time,minor influence on the initial response position and little in-fluence on the response *** the three conditions of consecutive 32 launches with 5 rounds/min,43 launches with 1 round/min,and 41 launches with different firing frequencies,the cook off response temperatures are 479.2 K,481.1 K and 479.9 K respectively and the response times are 709.25,211.2 s and 214.4 s *** response position is near the middle area of the inner cartridge surface in the former condition and near the right area in the latter two conditions.

关键词： Thermal safety Modular charge Cook-off Firing condition

Reduced spin-down rate of PSR J0738–4042 explained as due to an asteroid disruption event

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Research in Astronomy and Astrophysics 2016年第5期16卷 41-46页

作者： yong-Bo yu yong-Feng Huang Department of Astronomy Nanjing UniversityNanjing 210046China Key Laboratory of Modern Astronomy and Astrophysics(Nanjing University) Ministry of EducationNanjing 2 1 0046China

Long term observations by Brook et al. reveal that the derivative of rotational frequency of PSR J0738-4042 changed abruptly in 2005. Originally, the spin-down rate was relatively stable, with the rotational frequency derivative being - 1.14 x 10-14 s-2. After September 2005, the derivative began to rise. About 1000 days later, it arrived at another relatively stable value of about -0.98 x 10-24 s-2, indicating that the pulsar is spinning-down relatively slowly. To explain the observed change in spin-down rate, we resort to an asteroid disrupted by PSR J0738-4042. In our model, the orbital angular momentum of the asteroid is assumed to be parallel to that of the rotating pulsar, so that the pronounced reduction in the spin-down rate can be naturally explained as due to the transfer of angular momentum from the disrupted material to the central pulsar. The derived magnetospheric radius is about 7.0 x 109 cm, which is smaller than the tidal disruption radius （8.7 x 10^10cm）. Our model is self-consistent. It is shown that the variability in the spin-down rate of PSR J0738-4042 can be quantitatively accounted for by accretion from the asteroid disrupted by the central pulsar.

关键词： stars: neutron -- planet-star interactions -- pulsars: individual (PSR J0738-4042)

A two-step energy injection explanation for the rebrightenings of the multi-band afterglow of GRB 081029

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Research in Astronomy and Astrophysics 2013年第6期13卷 662-670页

作者： yong-Bo yu yong-Feng Huang Department of Astronomy Nanjing University Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University) Ministry of Education

The afterglow of GRB 081029 showed unusual behavior, with a signifi- cant rebrightening being observed at the optical wavelength at about 3000 s after the burst. One possible explanation is that the rebrightening resulted from an energy in- jection. Here we present a detailed numerical study of the energy injection process and interpret the X-ray and optical afterglow light curves of GRB 081029. In our model, we have assumed two periods of energy injection, each with a constant injec- tion power. One injection starts at 2.8 × 10^3 s and lasts for about 2500 s, with a power of 7.0 × 10^47 erg s-1. This energy injection mainly accounts for the rapid rebrighten- ing at about 3000 s. The other injection starts at 8.0 × 10^3 s and lasts for about 5000 s. The injection power is 3.5 × 10^47 erg s-1. This energy injection can help to explain the slight rebrightening at about 10 000 s. It is shown that the observed optical after- glow, especially the marked rebrightening at about 3000 s, can be reproduced well. In the X-ray band, the predicted amplitude of the rebrightening is much shallower, which is also consistent with the observed X-ray afterglow light curve. It is argued that the two periods of energy injection can be produced by clumpy materials falling onto the central compact object of the burster, which leads to an enhancement of accretion and gives rise to a strong temporary outflow.

关键词： gamma-rays: bursts -- ISM: jets and outflows -- individual:GRB 081029

Efficient policy evaluation by matrix sketching

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Frontiers of Computer Science 2022年第5期16卷 97-105页

作者： Cheng CHEN Weinan ZHANG yong yu Department of Computer Science Shanghai Jiao Tong UniversityShanghai 200240China

In the reinforcement learning,policy evaluation aims to predict long-term values of a state under a certain *** high-dimensional representations become more and more common in the reinforcement learning,how to reduce the computational cost becomes a significant problem to the policy *** recent works focus on adopting matrix sketching methods to accelerate least-square temporal difference(TD)algorithms and quasi-Newton temporal difference *** these sketching methods,the truncated incremental SVD shows better performance because it is stable and ***,the convergence properties of the incremental SVD is still *** this paper,we first show that the conventional incremental SVD algorithms could have enormous approximation errors in the worst *** we propose a variant of incremental SVD with better theoretical guarantees by shrinking the singular values ***,we employ our improved incremental SVD to accelerate least-square TD and quasi-Newton TD *** experimental results verify the correctness and effectiveness of our methods.

关键词： temporal difference learning policy evaluation matrix sketching

Determination and occurrence of endocrine disrupting compounds, pharmaceuticals and personal care products in fish （Morone saxatilis）

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Frontiers of Environmental Science & Engineering 2015年第3期9卷 475-481页

作者： yong yu Laosheng WU Department of Environmental Sciences University of Califomia Riverside CA 92521 USA

Endocrine disrupting compounds （EDCs）, pharmaceuticals and personal care products （PPCPs） have attracted much attention due to widespread contamination in aquatic environment. In this study, we determined 13 EDCs and PPCPs in fish blood, bile and muscle by using gas chromatography-mass spectrometry （GC-MS）. The limits of quantitation （LOQ） were in the ranges of 0.23-2.54, 0.22-2.36ng·mL^-1, and 0.24-2.57 ng· g^-1 dry weight （dw） for fish blood, bile and muscle, respectively. Recoveries of target compounds spiked into sample matrices and passed through the entire analytical procedure ranged from 65% to 95%, from 60% to 92% and from 62% to 91% for blood, bile and muscle, respectively. The methods were applied to the analysis of fish from a lake in California. Target compounds were relatively low in bile, and only bisphenol A （BPA） and diclofenac were measurable near the LOQ. Seven of 13 compounds were detected in blood, with total concentrations up to 39 ng· g^-1. Only BPA was frequently found in muscle, with mean concentration of 7.26 ng· g^-1 dw. The estimated daily intake of BPA through fish consumption for U.S. resident was significantly lower than the tolerable daily intake recommended by the European Food Safety Authority. This study showed that the exposure to the bisphenol A from fish diet is unlikely to pose a health risk.

关键词： endocrine disrupting compounds (EDCs) pharmaceuticals and personal care products (PPCPs) fish bisphenol A (BPA) risk assessment

Microstructure and high-temperature tensile property of TiAl alloy produced by selective electron beam melting

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Rare Metals 2021年第12期40卷 3635-3644页

作者： Hang-yu yue Hui Peng yong-Jun Su Xiao-Peng Wang yu-yong Chen School of Materials Science and Engineering Jiangsu University of Science and TechnologyZhenjiang 212003China Key Laboratory of High-Temperature Structural Materials and Coatings Technology Ministry of Industry and Information TechnologyBeihang UniversityBeijing 100191China School of Materials Science and Engineering Beihang UniversityBeijing 100191China Department of Mechanics College of EngineeringLishui UniversityLishui 323000China State Key Laboratory of Advanced Welding and Joining Harbin Institute of TechnologyHarbin 150001China

The microstructure and high-temperature tensile property of a Ti-47Al-2Cr-2 Nb alloy fabricated via selective electron beam melting(SEBM) with hatch spacings of 85,100,and 115 μm were systematically *** the hatch spacing increased from 85 to 115 μm,the microstructure comprising the horizontal cross section changed from coarse lamellar(y/B2) colonies to an inhomogeneous structure and the grain morphology transformed from elongated grains to inhomogeneous and equiaxed grains along the building direction of the vertical cross *** boundary population of the SEBMproduced TiAl alloy samples was dominated by high-angle grain boundaries(≥ 15°),and the volume fraction of these boundaries decreased with hatch spacing ***,the as-built TiAl alloy sample produced under a spacing of 100 μm exhibited the highest room-and elevated-temperature tensile strengths,with the ultimate tensile strength at room temperature(642 MPa) increasing to 674 MPa at 700 ℃.Furthermore,the mechanism of anomalous strengthening at 700 ℃ was discussed in detail.

关键词： Selective electron beam melting TiAl alloy Hatch spacing Microstructure Tensile property