电磁力及其对MIG焊接熔池流场的影响

MIG焊接熔池具有不规则的表面边界,温度较高且分布极不均匀,在电磁力、浮力、表面张力等的作用下发生剧烈运动.基于熔池表面变形较大时电弧电流密度的双峰分布模型,建立了电磁力的计算模型.采用数值模拟技术研究了熔池中的流体力学行为,揭示了焊接工艺参数对熔池流场的影响规律.实验表明,计算与实测结果符合良好.     

Study of the Magnitude-Redshift Relation for Type Ia Supernovae in a Model Resulting from a Ricci-Symmetry

Models with a dynamic cosmological term (t) are becoming popular as they solve the cosmological constant problem in a natural way. Instead of considering any ad-hoc assumption for the variation of , we consider a particular symmetry, the contracted Ricci-collineation along the fluid flow, in Einstein's theory. We show that apart from having interesting properties, this symmetry does demand to be a function of the scale factor of the Robertson-Walker metric. In order to test the consistency of the resulting model with observations, we study the magnitude-redshift relation for the type Ia supernovae data from Perlmutter et al. The data fit the model very well and require a positive non-zero and a negative deceleration parameter. The best-fitting flat model is obtained as ₀ 0.5 with q ₀ –0.2.     

苯乙烯基吡啶类液晶化合物的分子结构及相变过程的光谱研究

通过本乙烯基吡啶和不同脂肪羧酸间的氢键作用构成液晶的方法具有合成路线灵活、简便、易于变化的特点,本文通过变温红外光谱对做为质子受体的苯乙烯基吡啶粉液晶化合物的分子结构和相变过程中分子排列的变化进行了研究,结果表明在液晶分子中象羰基这样的偶极矩较大的极性基团,对分子所处的相态分子间的相互排列比较敏感。在红外光谱中羰基伸缩振动的变化可以看作是液晶分子相态转变的标志。     

磁流变体流变学特性研究

对所研制的矿物油介质和硅油介质磁流变体样品的零场粘度、磁流变性能、示功及速度特性进行了系统的测试和分析,并对其影响因素进行了详细的讨论。研制的磁流变体零场粘度小于0．5Pas(γ=81s^-1)且具有良好的粘温特性;磁流变体的剪切应力接近和超过70kPa(B＝6000Gs);在智能减振器的应用试验中获得理想的示功特性曲线。     

Observations on the role of MgCl2 in the Weissler reaction

Aqueous solutions of Nal containing CCl₄ and MgCl₂ at various concentrations were irradiated under air with 1 MHz ultrasound and the yield of I₃⁻ was determined. The yield was not affected by MgCl₂ at concentrations up to 0.1 M. This contrasts with the finding of Lepoint and co-workers, who reported a sharp minimum in the yield at a MgCl₂ concentration of 2.5 × 10⁻³M, the yield decreased to 60% at 1 M MgCl₂, the reason being the lower solubility of CCl₄ at high MgCl₂ concentrations. In the absence of CCl₄, another dependence on the MgCl₂ concentration was observed: the yield was not affected up to 1 M, and at higher MgCl₂ concentrations the yield rapidly decreased owing to the increased viscosity of the solution. On the basis of these observations, there is no strong reason to postulate an electrical mechanism for the initiation of chemical reactions in the cavitation bubbles.     

Phase space density representations in fluid dynamics

Phase space density representations of inviscid fluid dynamics were recently discussed by Abarbanel and Rouhi. Here it is shown that such representations may be simply derived and interpreted by means of the Liouville equation corresponding to the dynamical system of ordinary differential equations that describes fluid particle trajectories. The Hamiltonian and Poisson bracket for the phase space density then emerge as immediate consequences of the corresponding structure of the dynamics. For barotropic fluids, this approach leads by direct construction to the formulation presented by Abarbanel and Rouhi. Extensions of this formulation to inhomogeneous incompressible fluids and to fluids in which the state equation involves an additional transported scalar variable are constructed by augmenting the single-particle dynamics and phase space to include the relevant additional variable.     

Wronskian Form Solutions for a Variable Coefficient Kadomtsev–Petviashvili Equation

Starting from a simple transformation, and with the aid of symbolic computation, we establish the relation- ship between the solution of a generalized variable coefficient Kadomtsev-Petviashvili （vKP） equation and the solution of a system of linear partial differential equations. According to this relation, we obtain Wronskian form solutions of the vKP equation, and further present N-soliton-like solutions for some degenerated forms of the vKP equation. Moreover, we also discuss the influences of arbitrary constants on the soliton and N-soliton solutions of the KPII equation.     

多尺度变步长最小均方自适应算法在光纤陀螺数据处理中的应用

为有效抑制光纤陀螺(FOG)随机噪声,提出将一种多尺度变步长最小均方(MVSLMS)自适应算法应用于FOG数据处理中。根据FOG输出数据的特点,构建了MVSLMS自适应滤波器,提出了FOG信号滤波算法的实现步骤。对FOG实测静态数据、振动数据和速率测试数据进行了滤波实验,结果表明所提算法对FOG随机噪声的抑制效果明显,相比LMS滤波,MVSLMS自适应滤波后的静态数据零偏稳定性数值减小了72.0%,振动数据在振前、振中、振后零偏稳定性数值分别减小91.5%,77.4%和96.5%,速率测试数据标准差减小了54.4%。摇摆测试滤波实验结果表明所用算法对FOG真值信号具有较好的跟踪能力。     

超声速转子叶片非定常引射器流场特性数值模拟

采用计算流体力学方法,结合适当的边界条件,对超声速转子叶片非定常引射器进行了模拟。从结果可以看出:此类引射器内流态复杂,主气流出口斜激波干扰现象明显,叶片设计参数对引射器性能影响很大。叶片尾部的膨胀波有效诱导了被引射气流,在短距离内增强了气流混合,湍流效应对引射器性能的影响较小;叶片可维持自旋转,提升叶片转速可增强引射效率。最后,对引射器内的流动机理进行了探讨。     

Sloshing waves in a heated viscoelastic fluid layer in an excited rectangular tank

In this paper, we have investigated the motion of a heated viscoelastic fluid layer in a rectangular tank that is subjected to a horizontal periodic oscillation. The mathematical model of the current problem is communicated with the linearized Navier–Stokes equation of the viscoelastic fluid and heat equation together with the boundary conditions that are solved by means of Laplace transform. Time domain solutions are consequently computed by using Durbin's numerical inverse Laplace transform scheme. Various numerical results are provided and thereby illustrated graphically to show the effects of the physical parameters on the free-surface elevation time histories and heat distribution. The numerical applications revealed that increasing the Reynolds number as well as the relaxation time parameter leads to a wider range of variation of the free-surface elevation, especially for the short time history.