基于反应谱法的核级承压容器应力分析与评定

核级承压容器力学分析是核设备分析法设计的重要组成部分.核级承压起动空气瓶,作为核电站应急柴油机厂房中的重要设备,它的工作状况直接影响到应急柴油机厂房中柴油机的正常运行.本文对核级承压起动空气瓶进行自重、设计压力、安全阀设定压力下的静态分析、结构屈曲分析、模态分析及地震载荷下的反应谱动态分析,并对结构在各使用限制条件下的...     

The wave and vibratory power transmission in a finite L-shaped Mindlin plate with two simply supported opposite edges

In this paper,wave and vibratory power transmission in a finite L-shaped Mindlin plate with two simply supported opposite edges are investigated using the wave approach.The dynamic responses,active and reactive power flow in the finite plate are calculated by the Mindlin plate theory (MPT) and classic plate theory (CPT).To satisfy the boundary conditions and continuous conditions at the coupled junction of the finite L-shaped plate,the near-field and far-field waves are entirely contained in the wave approach.The in-plane longitudinal and shear waves are also considered.The results indicate that the vibratory power flow based on the MPT is different from that based on the CPT not only at high frequencies but also at low and medium frequencies.The influence of the plate thickness on the vibrational power flow is investigated.From the results it is seen that the shear and rotary inertia correction of the MPT can influence the active and reactive power at the junction of the L-shaped plate not only at high frequencies but also at low and medium frequencies.Furthermore,the effects of structural damping on the active and reactive power flow at the junction are also analyzed.     

Influence of the aspect ratio on boiling flows in rectangular mini-channels

This article presents experiments conducted with two single rectangular mini-channels of same hydraulic diameter (1.4 mm) and different aspect ratios for conditions of horizontal boiling flow. The Forane® 365 HX used was subcooled (ΔT_sub = 15 °C) for all the boiling curves presented in the paper. Local heat transfer coefficients were measured for heat flux ranging from 25 to 62 kW m⁻² and mass flux from 200 kg m⁻² s⁻¹ to 400 kg m⁻² s⁻¹. The boiling flows were observed with two different cameras (depending on the flow velocity) through a visualization window. The flow patterns in the two channels were compared for similar conditions. The results show that the boiling heat transfer coefficient and the pressure drop values are different for the two single mini-channels. For low heat flux condition, the channel with lowest aspect ratio (H/W = 0.143) has a higher heat transfer coefficient. On the other hand, for high heat flux condition, the opposite situation occurs, namely the heat transfer coefficient becomes higher for the channel with highest aspect ratio (H/W = 0.43). This is probably due to the earlier onset of dryout in the channel with lowest aspect ratio. For the two cases of heating, the pressure drop for the two-phase flow remains lower for the channel with lowest aspect ratio. These results show that the aspect ratio plays a substantial role for boiling flows in rectangular channels. As for single-phase flows, the heat transfer characteristics are significantly influenced (even though the hydraulic diameter remains the same) by this parameter.     

EFFECT OF DAMAGE EVOLUTION ON POISSON’S RATIO OF CONCRETE UNDER SULFATE ATTACK

Experimental results about concrete under sulfate attack are summarized,which include the variation of mass density of samples and velocity of ultrasonic wave propagating in samples.The evolution damage is analyzed in terms of the experimental results,and close attention is paid to the effect of damage evolution on Poisson’s ratio.This study shows that Poisson’s ratio is significantly affected by the concentration of solution and water-cement ratio.Poisson’s ratio of concrete changes very little when the water-cement ratio is selected as 0.6 or 0.8,so that such change may be neglected.If water-cement is 0.4,however,the Poisson’s ratio of the sample significantly changes.When the concrete sample of 0.4 water-cement ratio is immersed in sodium sulfate solution of 8% concentration for 285 days,Poisson’s ratio increase 10.14% compared with its initial value.There exist a sensitive region and a non-sensitive region for the change rate of Poisson’s ratio with respect to corrosion time.The change rate of Poisson’s ratio monotonously decreases with corrosion time in the sensitive region;in the non-sensitive region,the change rate of Poisson’s ratio is almost equal to zero.     

Aspect ratio effects on three-dimensional incompressible flow in a two-sided non-facing lid-driven parallelepiped cavity

A numerical study of the three-dimensional fluid flow has been carried out to determine the effects of the transverse aspect ratio, Ay, on the flow structure in two-sided non-facing lid-driven cavities. The flow is complex, unstable and can undergo bifurcation. The numerical method is based on the finite volume method and multigrid acceleration. Computations have been investigated for several Reynolds numbers and various aspect ratio values. At a fixed Reynolds number, Re=500, the three-dimensional flow characteristics are analyzed considering four transverse aspect ratios, Ay=1,0.75,0.5 and 0.25. It is observed that the transition to the unsteady regime follows the classical scheme of a Hopf bifurcation. An analysis of the flow evolution shows that, at Ay=0.75, the flow bifurcates to a periodic regime at (Re=600) with a frequency f=0.093 less than the predicted value in the cubical cavity. A correlation is established when Ay=0.5 and gives the critical Reynolds number value. At Ay=0.25, the periodic regime occurs at high Re value beyond 3500, after which the flow becomes chaotic. It is shown that, when increasing Ay over the unit, the flow in the cavity exhibits a complex behavior. The kinetic energy transmission from the driven walls to the cavity center is reduced at low Ay values.     

Cohen–Macaulayness of monomial ideals and symbolic powers of Stanley–Reisner ideals

We present criteria for the Cohen–Macaulayness of a monomial ideal in terms of its primary decomposition. These criteria allow us to use tools of graph theory and of linear programming to study the Cohen–Macaulayness of monomial ideals which are intersections of prime ideal powers. We can characterize the Cohen–Macaulayness of the second symbolic power or of all symbolic powers of a Stanley–Reisner ideal in terms of the simplicial complex. These characterizations show that the simplicial complex must be very compact if some symbolic power is Cohen–Macaulay. In particular, all symbolic powers are Cohen–Macaulay if and only if the simplicial complex is a matroid complex. We also prove that the Cohen–Macaulayness can pass from a symbolic power to another symbolic powers in different ways.     

The golden ratio and super central configurations of the n-body problem

In this paper, we consider the problem of central configurations of the n-body problem with the general homogeneous potential 1/rα. A configuration q=(q₁,q₂,…,qn) is called a super central configuration if there exists a positive mass vector m=(m₁,…,mn) such that q is a central configuration for m with mi attached to qi and q is also a central configuration for m^′, where m^′≠m and m^′ is a permutation of m. The main discovery in this paper is that super central configurations of the n-body problem have surprising connections with the golden ratio φ. Let r be the ratio of the collinear three-body problem with the ordered positions q₁, q₂, q₃ on a line. q is a super central configuration if and only if 1/r₁(α)<r<r₁(α) and r≠1, where r₁(α)>1 is a continuous function such that , the golden ratio. The existence and classification of super central configurations are established in the collinear three-body problem with general homogeneous potential 1/rα. Super central configurations play an important role in counting the number of central configurations for a given mass vector which may decrease the number of central configurations under geometric equivalence.     

鞅分析在具有红利支付的n次幂型欧式期权定价中的应用

本文探讨了鞅分析在具有红利支付的n次幂型欧式期权定价中的应用,即用鞅分析的技巧与方法研究了在标的资产服从分数布朗运动的条件下具有红利支付的n次幂型欧式期权定价问题,并获得了其公式。丰富了已有期权定价结果,使期权定价公式更有利于实际的应用。     

改进的GM（1,1）幂模型及其参数优化

为了提高灰色GM（1,1）幂模型的拟合精度,对灰色GM（1,1）幂模型的背景值进行了改进,建立了一类改进GM（1,1）幂模型.利用粒子群优化算法给出了改进GM（1,1）幂模型的参数优化.实例分析结果表明基于粒子群算法的改进的GM（1,1）幂模型具有更高的预测和拟合精度.