Finite volume multigrid prediction of laminar natural convection: Bench-mark solutions

A finite volume multigrid procedure for the prediction of laminar natural convection flows is presented, enabling efficient and accurate calculations on very fine grids. The method is fully conservative and uses second-order central differencing for convection and diffusion fluxes. The calculations start on a coarse (typically 10 × 10 control volumes) grid and proceed to finer grids until the desired accuracy or maximum affordable storage is reached. The computing times increase thereby linearly with the number of control volumes. Solutions are presented for the flow in a closed cavity with side walls at different temperatures and insulated top and bottom walls. Rayleigh numbers of 10⁴, 10⁵ and 10⁶ are considered. Grids as fine as 640 × 640 control volumes are used and the results are believed to be accurate to within 0–01%. Second-order monotonic convergence to grid-independent values is observed for all predicted quantities.     

Interactive decision software and computer graphics for architectural and space planning

We describe the development and successful implementation of a decision support system now being used by several leading firms in the architecture and space planning industries. The system, which we call SPDS (spatial programming design system) has the following characteristics: (i) user-friendly convenience features permitting architects and space planners to operate the system without being experienced programmers; (ii) interactive capabilities allowing the user to control and to manipulate relevant parameters, orchestrating conditions to which his or her intuition provides valuable input; (iii) informative and understandable graphics, providing visual displays of interconnections that the computer itself treats in a more abstract methematical form; (iv) convenient ways to change configurations, and to carry out ‘what if’ analyses calling on the system’s decision support capabilities; (v) a collection of new methods, invisible to the user, capable of generating good solutions to the mathematical programming problems that underlie each major design component. These new methods succeed in generating high quality solutions to a collection of complex discrete, highly nonlinear problems. While these problems could only be solved in hours, or not at all, with previously existing software, the new methods obtain answers in seconds to minutes on a minicomputer. Major users, including Dalton, Dalton, Newport, and Marshal Erdwin, report numerous advantages of the system over traditional architectural design methods.     

感应同步器鉴幅测角系统静态误差分析及关键电路设计

本文系统论述了采用感应同步器进行角位置测量的连续绕组激磁，分段绕组输出的鉴幅方案，对这个方案的工作原理进行介绍，并对此方案产生的静态误差进行分析，给出减小误差的方法，最后得出相关结论。     

数字滤波器在惯性测量装置中的应用

分析了数字电压表和数字示波器对惯性测量装置（IMU）模拟输出的测量数据，为了减少惯性测量装置模拟输出中的干扰信号对模数转换结果的影响，设计了数字巴特沃斯滤波器和中值平均滤波器。通过计算机仿真和实测说明：这两种数字滤波方法均可以在几乎不增加硬件的条件下提高IMU数字输出精度。     

异质传感器数据的最优线性融合

研究了异质传感器对参数矢量进行的测量，测量数据基于线性均方估计的最优融合算法。提出和证明了异质传感器数据的最优线性融合定理，并得出“精度再差的传感器参与数据融合后都有利于提高系统的测量精度”这一结论。     

The reference shrinkage curve of clay soil

The objective of this work is to develop and validate a model that predicts the reference soil shrinkage curve, that is one without crack volume contribution, as a necessary preliminary step in future estimation of soil crack volume from soil shrinkage data. Current soil shrinkage models are based on the approximation of soil shrinkage data by some a priori taken mathematical expressions and justified by the fitting of their parameters to the data. However, the crack volume entering the data is not single valued and depends on shrinkage conditions. Unlike that the reference shrinkage curve is single valued. For soils with sufficiently high clay content when there are no large pores (lacunar pores) inside the intra-aggregate clay, the reference shrinkage curve is derived from the assumption of the rigid superficial (interface) layer of aggregates with changed pore-size range and distribution compared with the intra-aggregate matrix. This consideration is based on accounting for contributions of the interface aggregate layer and intra-aggregate matrix to the soil volume and water content during shrinkage. The reference shrinkage curve is predicted by eight fundamental physical immediately measured parameters of (i) the intra-aggregate matrix (including clay content); (ii) the aggregate structure; and (iii) the mean silt-sand grain size or mean interface layer thickness. The model was validated using the data for eight soils. In addition to the major potential application for estimating a soil crack volume, the model explains differences between the observed shrinkage curves of soil and pure clay, and it can have other numerous applications.     

多级轴流压气机叶栅内三维紊流流场的数值模拟

对多级轴流压气机叶栅内三维紊流流场进行数值模拟,采用高精度高分辨率的三阶ENN格式以保证对激波的捕捉和对紊流特征的正确模拟,利用LU-SGS隐式解法提高了计算速度,从而构成了一种既准确又高效的多级跨声速轴流压气机紊流流动数值求解系统。重点研究了动静网格的交接方法及相应的动静交接面处理模型。计算了某带进口导叶的三级轴流压气机,计算结果与实验数据吻合较好。     

高精度转台控制系统研究

—本文针对精密转台控制系统在大偏差下的不稳定问题，对其控制系统进行了分析和设计，同时对其高分辨率的指令系统进行了设计，为提高转台的精度及其动态性能提供了新的途径。     

Modeling fluid and heat transport in the reactive, porous bed of downdraft (biomass) gasifier

A fluid flow and heat transfer model has been developed for the reactive, porous bed of the biomass gasifier to simulate pressure drop, temperature profile in the bed and flow rates. The conservation equations, momentum equation and energy equation are used to describe fluid and heat transport in porous gasifier bed. The model accounted for drag at wall, and the effect of radial as well as axial variation in bed porosity to predict pressure drop in bed. Heat transfer has been modeled using effective thermal conductivity approach. Model predictions are validated against the experiments, while effective thermal conductivity values are tested qualitatively using models available in literature. Parametric analysis has been carried out to investigate the effect of various parameters on bed temperature profile and pressure drop through the gasifier. The temperature profile is found to be very sensitive to gas flow rate, and heat generation in oxidation zone, while high bed temperature, gas flow rate and the reduction in feedstock particle size are found to cause a marked increase in pressure drop through the gasifier. The temperatures of the down stream zones are more sensitive to any change in heat generation in the bed as compared to upstream zone. Author recommends that the size of preheating zone may be extended up to pyrolysis zone in order to enhance preheating of input air, while thermal insulation should not be less than 15 cm.     

Modeling the dynamic behavior of shape memory alloys

The paper studies the single degree of freedom vibration of a rigid mass suspended by a thin-walled shape memory alloy tube under torsional loading. The behavior is analyzed for the cases of quasiplasticity (low temperatures) and pseudoelasticity (high temperatures) on the basis of an improved version of the Müller–Achenbach model. To illustrate the strong hysteresis-induced damping capacity and the non-linear vibration characteristics, both, free and forced vibrations are considered in the first part of the paper. This is done on the basis of an isothermal version of the model, while the second part of the paper focuses on the effect of non-constant temperature caused by the rate-dependent release and absorption of latent heats.