径向双球头柱塞泵广义心形型线的特性分析

观察心形线,对其幅值和波动进行相应的扩展,可得到广义心形型线,该封闭曲线简单连续且高次可导。将其应用到径向双球头柱塞泵中,得到一种新的径向双球头内作用曲线柱塞泵,并提出一种新的计算方法进行MATLAB仿真运算,求得对应的球头导轨曲线。并对此应用广义心形型线的径向双球头柱塞泵的输出特性进行分析,推导其流量公式、流量脉动公式,并探究柱塞个数、作用次数、长短轴比例系数对其流量脉动率的影响,为以后设计和开发新型的广义心形型线的径向双球头柱塞泵提供了理论依据。

形式生成笔记--L形图解

以L形图解为载体,运用逻辑推导与类型归纳方法,探讨建筑内在形式生成机制。首先根据L形的图形特征,将其划分为“线型-L形”与“形心型-L形”;然后在二维平面上,对整体与局部进行L形平面的空间解析;再从空间单元、线形空间和几何空间三种类型出发,推演出L形图解在三维空间中的组合与衍生变换,构建动态空间操作方法。研究成果能够深化对基于几何图解的空间营造认知,对探索建筑设计隐含的形式内在逻辑与外在呈现具有一定的启示借鉴作用。

Non-linear 2-DOF model and centre manifold theory to study limit cycle oscillations caused by drum-brake judder

This paper presents the research on the laws of systematic-parameter dependent variation in the vibration amplitude of drum-brake limit cycle oscillations (LCO). We established a two-degree non-linear dynamic model to describe the low-frequency vibration of the drum brake, applied the centre manifold theory to simplify the system, and obtained the LCO amplitude by calculating the normal form of the simplified system at the Hopf bifurcation point. It is indicated that when the friction coefficient is smaller than the friction coefficient at the bifurcation point, the amplitude decreases; whereas with a friction coefficient larger than the friction coefficient of bifurcation point, LCO occurs. The results suggest that it is applicable to suppress the LCO amplitude by changing systematic parameters, and thus improve the safety and ride comfort when applying brake. These findings can be applied to guiding the design of drum brakes.

Analysis of a Class of Symmetric Equilibrium Configurations for a Territorial Model

Motivated by an animal territoriality model,we consider a centroidal Voronoi tessellation algorithm from a dynamical systems perspective.In doing so,we discuss the stability of an aligned equilibrium configuration for a rectangular domain that exhibits interesting symmetry properties.We also demonstrate the procedure for performing a center manifold reduction on the system to extract a set of coordinates which capture the long term dynamics when the system is close to a bifurcation.Bifurcations of the system restricted to the center manifold are then classified and compared to numerical results.Although we analyze a specific set-up,these methods can in principle be applied to any bifurcation point of any equilibrium for any domain.

Study on the Flow of Rural Labor Force and the Contribution of Terrain Factor in Shaanxi,China

The flow of rural labor to urban is a significant phenomenon in China during the last 20 years.In spite of many researches focus on the driving force of economy,terrain is an important index in the rural development.There is a question that whether the flow of rural labor has some relationships with terrain.The study used the relief degree of land surface (RDLS) as terrain index,and the cost distance model and the center of gravity model to analyze the relationship between terrain and labor flows.The results indicated:(1) In the last 20 years,the rural labor force was not simply flowing to the low terrain region in Shaanxi province.And the RDLS was constantly strengthening the influence on the movement.(2) The RDLS was low in Guanzhong region,and the translation of rural labors relatively was not significant.Since North Shaanxi act as the energy industry base,the number of rural labors there increased faster than in South Shaanxi.(3) The movements of economical centers took an important role in the change of rural labor centers,and terrain factors also showed a high correlation with them.It is found that the lower of the terrain index,the higher of the land intensive degree,the more intensive of nonagriculturalization process.

Global Search of a Three-dimensional Low Solidity Circular Cascade Diffuser for Centrifugal Blowers by Meta-model Assisted Optimization

A three-dimensional blade of a low solidity circular cascade diffuser in centrifugal blowers is designed by means of a multi-point optimization technique. The optimization aims at improving static pressure coefficient at a design point and at a small flow rate condition. Moreover, a clear definition of secondary flow expressed by positive radial velocity at hub side is taken into consideration in constraints. The number of design parameters for three-dimensional blade reaches to 10 in this study, such as a radial gap, a radial chord length and mean camber angle distribution of the LSD blade with five control points, control point between hub and shroud with two design freedom. Optimization results show clear Pareto front and selected optimum design shows good improvement of pressure rise in diffuser at small flow rate conditions. It is found that three-dimensional blade has advantage to stabilize the secondary flow effect with improving pressure recovery of the low solidity circular cascade diffuser.

Numerical Investigation of Centerline Curvature Effects on a Compact S-shaped Intake

Taking into account stealth, structure and maintenance, ultra-compact S-shaped intake has been widely used in modem vehicles. In this paper a series of steady numerical simulation were carried out to investigate the complex flow mechanism in s-shaped intake, particular attention was given to examining the effect of centerline curvature on the performance and flowfield of an ultra-compact S-shaped intake. In order to validate the multi-block model, the computational results for Royal Aircraft Establishment intake 2129-M2129 which had modest centerline cur- vature distribution were corrected with available experimental test data. The numerical simulation results agreed fairly well with the experimental data, and the computational method was then used to investigate the effects of different centerline curvature distributions on performance and flow field in compact S-shaped intake. Detailed analyses of the flow visualization had exposed the different flow topologies between the cases with different cen- terline curvature. It was found that different centerline curvature distributions changed the initial location and the size of separation bubble, as well as the strength of two counter-rotating vortices at the entrance of engine.

Bifurcation behaviors analysis of a plankton model with multiple delays

A mathematical model describing the dynamics of toxin producing phytoplankton- zooplankton interaction with instantaneous nutrient recycling is proposed. We have explored the dynamics of plankton ecosystem with multiple delays; one due to gestation period in the growth of phytoplankton population and second due to the delay in toxin liberated by TPP. It is established that a sequence of Hopf bifurcations occurs at the interior equilibrium as the delay increases through its critical value. The direction of the Hopf bifurcation and the stability of the bifurcating periodic solutions are determined using the theory of normal form and center manifold. Meanwhile, effect of toxin on the stability of delayed plankton system is also established numerically. Finally, numerical simulations are carried out to support and supplement the analytical findings.

MODELING THE IMPACT OF VOLUNTARY TESTING AND TREATMENT ON TUBERCULOSIS TRANSMISSION DYNAMICS

A deterministic model for evaluating the impact of voluntary testing and treatment on the transmission dynamics of tuberculosis is formulated and analyzed. The epidemio- logical threshold, known as the reproduction number is derived and qualitatively used to investigate the existence and stability of the associated equilibrium of the model system. The disease-free equilibrium is shown to be locally-asymptotically stable when the reproductive number is less than unity, and unstable if this threshold parameter exceeds unity. It is shown, using the Centre Manifold theory, that the model undergoes the phenomenon of backward bifurcation where the stable disease-free equilibrium co- exists with a stable endemic equilibrium when the associated reproduction number is less than unity. The analysis of the reproduction number suggests that voluntary tuber- culosis testing and treatment may lead to effective control of tuberculosis. Furthermore, numerical simulations support the fact that an increase voluntary tuberculosis testing and treatment have a positive impact in controlling the spread of tuberculosis in the community.

STABILITY ANALYSIS OF A PREDATOR-PREY MODEL

In this paper, a time-delayed predator-prey system is considered. The existence of Hopf bifurcations at the positive equilibrium is established by analyzing the distribution of the characteristic values. An explicit algorithm for determining the direction of the Hopf bifurcation and the stability of the bifurcating periodic solutions are derived by using the normal form and the center manifold theory. Numerical simulations to support the analytical conclusions are carried out.