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211.
多部件系统故障预防工作的组合优化   总被引:2,自引:0,他引:2  
研究了实践中常见的四种预防工作组合类型,即定时维修、功能检测、使用检查及检查与定时维修的组合策略,以单位时间维修费用最小为目标建立了多部件故障预防工作的组合优化模型.在此基础上,提出了两个故障预防工作的组合优化算法,并给出了计算示例以说明模型和算法的性能.  相似文献   
212.
A method of orthogonal polynomials is proposed to solve the contact problem for a rectangular die on an elastic foundation. For the case of an elastic half-space, an exact formula is derived for the translation of the die under symmetric loading  相似文献   
213.
We analyzed stress and heat transfer in attached planar waveguides. Die attaching adhesives were known to be the key to avoiding stress buildup in and dissipating heat from waveguides. When adhesives have a shear modulus of less than 1 MPa and a thermal conductivity of 2 w/mk, a 0.1-0.2-mm-thick layer of adhesive can eliminate stress-related effects and efficiently dissipate 30-50 mW/mm2 of heat, even if aluminum is used as a substrate. Supersoft thermal conductive adhesives were thus developed and used to attach 60-mm-long AWG dies to aluminum with excellent results.  相似文献   
214.
A new strategy employing an Ugi four-component reaction and a microwave-assisted intramolecular Heck cyclization in a sequential fashion to access an array of N-containing heterocycles is reported. The two-step sequence generated compounds of significant molecular complexity from trivial starting materials in an expedient fashion with excellent yields. The route was also amenable to solid-phase chemistry demonstrating potential for library generation.  相似文献   
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217.
本文叙述了采用聚碳酸脂材料模拟低碳钢和低碳合金钢一类金属的摩托车启动齿轮(下面陶称为端面齿轮)摆辗成形过程。运用光塑性法计算分析了氐形后的光塑性模型内部三维塑性应雯分布;对采用螺旋形轨迹和玫瑰线轨迹成形后的光塑性模型内部的三维塑性应变分布进行了分析比较。该方法已为摆辗最佳工艺参数的选择提供了有用的依据。  相似文献   
218.
In the thermally developing region, d yy /dx| y=h varies along the flow direction x, where yy denotes the component of stress normal to the y-plane; y = ±h at the die walls. A finite element method for two-dimensional Newtonian flow in a parallel slit was used to obtain an equation relating d yy /dx/ y=h and the wall shear stress 0 at the inlet; isothermal slit walls were used for the calculation and the inlet liquid temperature T0 was assumed to be equal to the wall temperature. For a temperature-viscosity relation /0 = [1+(T–T0]–1, a simple expression [(hd yy /dx/ y=h )/ w0] = 1–[1-F c(Na)] [M()+P(Pr) ·Q(Gz –1)] was found to hold over the practical range of parameters involved, where Na, Gz, and Pr denote the Nahme-Griffith number, Graetz number, and Prandtl number; is a dimensionless variable which depends on Na and Gz. An order-of-magnitude analysis for momentum and energy equations supports the validity of this expression. The function F c(Na) was obtained from an analytical solution for thermally developed flow; F c(Na) = 1 for isothermal flow. M(), P(Pr), and Q(Gz) were obtained by fitting numerical results with simple equations. The wall shear rate at the inlet can be calculated from the flow rate Q using the isothermal equation.Notation x,y Cartesian coordinates (Fig. 2) - , dimensionless spatial variables [Eq. (16)] - dimensionless variable, : = Gz(x)–1 - dimensionless variable [Eq. (28)] - t,t * time, dimensionless time [Eq. (16)] - , velocity vector, dimensionless velocity vector - x , velocity in x-direction, dimensionless velocity - y , velocity in y-direction, dimensionless velocity - V average velocity in x-direction - yy , * normal stress on y-planes, dimensionless normal stress - shear stress on y-planes acting in x-direction - w , w * value of shear stress stress at the wall, dimensionless wall shear stress - w0, w0 * wall shear stress at the inlet, dimensionless variable - , * rate-of-strain tensor, dimensionless tensor - wall shear rate, wall shear rate at the inlet - Q flow rate - T, T 0, temperature, temperature at the wall and at the inlet, dimensionless temperature - h, w half the die height, width of the die - l,L the distance between the inlet and the slot region, total die length - T 2, T 3, T 4 pressure transducers in the High Shear Rate Viscometer (HSRV) (Fig. 1) - P, P2, P3 pressure, liquid pressures applied to T 2 and T 3 - , 0, * viscosity, viscosity at T = T 0, dimensionless viscosity - viscosity-temperature coefficient [Eq. (8)] - k thermal conductivity - C p specific heat at constant pressure - Re Reynolds number - Na Nahme-Griffith number - Gz Graetz number - Pr Prandtl number  相似文献   
219.
The flow behaviour of four blend systems was determined at four shear rates and three processing temperatures using an extrusion rheometer. The blends were based on natural rubber/polybutadiene elastomers and were prepared using various mixing sequences with the carbon black being added in different ways.The degree of die swelling was found to depend on the blending technique, the processing temperature and the extrusion rate. A theoretical model was used to calculate the stored elastic energy, shear modulus and relaxation time. Melt fracture was observed when the carbon black was premixed in just one component of the blend.  相似文献   
220.
Plane and axisymmetric contact problems for a three-layer elastic half-space are considered. The plane problem is reduced to a singular integral equation of the first kind whose approximate solution is obtained by a modified Multhopp-Kalandiya method of collocation. The axisymmetric problem is reduced to an integral Fredholm equation of the second kind whose approximate solution is obtained by a specially developed method of collocation over the nodes of the Legendre polynomial. An axisymmetric contact problem for an transversely isotropic layer completely adherent to an elastic isotropic half-space is also considered. Examples of calculating the characteristic integral quantities are given. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 3, pp. 165–175, May–June, 2006.  相似文献   
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