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71.
72.
73.
压-剪复合应力波作用下材料动态断裂韧性研究 总被引:2,自引:0,他引:2
提出亚微秒单脉冲应力波载荷作用下Ⅱ型裂纹的平板冲击实验技术 .加载率为dK dt~ 10 8MPa·m1 2 ·s-1.实验中由锰铜应力片和弹性波理论分别测定和计算了压应力 ;通过微观分析确定了动态裂纹的平均扩展长度 ;引进等效应力强度因子 ,用动态断裂理论确定了 6 0 #钢的动态断裂韧性KⅠd和KⅡd ;建立了亚微秒冲击载荷作用下确定材料动态断裂韧性的方法 相似文献
74.
碳纤维布与钢板复合加固梁剥离破坏研究 总被引:1,自引:0,他引:1
通过12根碳纤维布与钢板复合加固钢筋混凝土梁的抗弯性能研究,结果表明复合加固方式能有效地改善被加固构件的受力性能,但常由于复合加固层的剥离可能导致加固效果的降低。复合加固层与被加固构件之间的剥离是由于薄弱截面在剪应力及正应力的集中作用下而产生的,文中对复合加固层与混凝土之间的粘结剪应力及剥离正应力的计算公式分别进行推导,并进一步对碳纤维布与钢板复合加固的剥离机理进行分析,为工程应用提供依据。 相似文献
75.
First-Passage Time of Duffing Oscillator under Combined Harmonic and White-Noise Excitations 总被引:1,自引:0,他引:1
The first-passage time of Duffing oscillator under combined harmonic andwhite-noise excitations is studied. The equation of motion of the system is firstreduced to a set of averaged Itô stochastic differential equations by using thestochastic averaging method. Then, a backward Kolmogorov equation governing theconditional reliability function and a set of generalized Pontryagin equationsgoverning the conditional moments of first-passage time are established. Finally, theconditional reliability function, and the conditional probability density and momentsof first-passage time are obtained by solving the backward Kolmogorov equation andgeneralized Pontryagin equations with suitable initial and boundary conditions.Numerical results for two resonant cases with several sets of parameter values areobtained and the analytical results are verified by using those from digital simulation. 相似文献
76.
A rectangular loop (thermosyphon) was used to measure the average heat transfer coefficients for water at atmospheric pressure under natural circulation conditions. A twenty-one tube bundle with tubes 1.65 m long and 9.55 mm in diameter, and a pitch-to-diameter ratio of 1.33, was used as a test heat exchanger in one of the vertical legs of the loop. A natural circulation flow in the loop developed due to buoyancy differences of the fluid in its two vertical legs. Flow visualization experiments were performed to determine the flow regimes associated with natural circulation flow longitudinal to a tube bundle. Empirical correlations for the average Nusselt number have been developed and are reported. Grid spacers arranged on tube bundles were shown to enhance heat transfer, especially for laminar flow, without any noticeable increase in pressure drop. 相似文献
77.
A novel kind of supported combined liquid membrane(SCLM) has been studied for the Gd(Ⅲ) transfer.SCLM contained polyvinylidene fluoride membrane(PVDF) as the liquid membrane support and renewal solution including HNO3 solution as the stripping solution and 2-ethyl hexyl phosphonic acid-mono-2-ethyl hexyl ester(HEH(EH)P) as the carrier dissolved in kerosene. The mixed solution of carrier and kerosene was membrane solution.The optimum transport conditions of Gd(Ⅲ) were that concentration of HNO3 solution was 4.00 mol/L,concentration of carrier was 0.16 mol/L,and volume ratio of membrane solution to stripping solution was 30:30 of the renewal phase,and pH value was 4.80 of the feed phase.Under the optimum condition studied, when initial concentration of Gd(Ⅲ) was 1.00×10-4 mol/L,the transfer rate of Gd(Ⅲ) was 96.8%during 130 min. 相似文献
78.
A nonlinear model of a low pressure cylinder-generator rotor system is presented to study sub-synchronous resonance and combined
resonance. Analytical results are obtained by an averaging method. Transition sets and bifurcation diagrams are obtained based
on the singularity theory for the two-state variable system. The bifurcation characteristics are analyzed to provide a basis
for the optimal design and fault diagnosis of the rotor system. Finally, the theoretical results are verified with the numerical
results. 相似文献
79.
How to solve the inference problem of candidate database web surveys is an urgent problem to be solved in the development of web survey. In order to solve this problem, the inference method of non-probability sampling based on superpopulation pseudo design and the combined sample is proposed. A superpopulation model is firstly built up to construct pseudo weights for a survey sample of the web candidate database. The estimator of the population mean is then computed according to the combined sample composed of the survey sample of the web candidate database and a probability sample. The variance estimator of the population mean estimator is lastly derived according to the variance estimation theory of the superpopulation model. The Bootstrap and Jackknife methods are also used to compute the variance estimator. And all these variance estimation methods are compared. The research results show that the population mean estimator based on superpopulation pseudo design and the combined sample is better, and has higher efficiency than the estimator only using the probability sample and the weighted estimator only using the survey sample of the web candidate database. The variance estimator computed by using the VM1, VM2 and VM3 method are relatively better. 相似文献
80.
Recent manipulations on vertebrates showed that the fear of preda-
tors, caused by prey after they perceived predation risk, could reduce the prey''s
reproduction greatly. And it''s known that predator-prey systems with fear ef-
fect exhibit very rich dynamics. On the other hand, incorporating the time
delay into predator-prey models could also induce instability and oscillations
via Hopf bifurcation. In this paper, we are interested in studying the com-
bined effects of the fear effect and time delay on the dynamics of the classic
Lotka-Volterra predator-prey model. It''s shown that the time delay can cause
the stable equilibrium to become unstable, while the fear effect has a stabi-
lizing effect on the equilibrium. In particular, the model loses stability when
the delay varies and then regains its stability when the fear effect is stronger.
At last, by using the normal form theory and center manifold argument, we
derive explicit formulas which determine the stability and direction of periodic
solutions bifurcating from Hopf bifurcation. Numerical simulations are carried
to explain the mathematical conclusions. 相似文献