倾斜面上直射辐射计算方法的探讨

在太阳能系统的设计中常涉及倾斜面上日总直射辐射的计算。计算倾斜面上日总直射辐射最常用的方法是Liu and Jordan所提出的数学方法,该方法是在假设地球表面没有大气层的情况下得出的,是一个典型的近似计算方法。研究通过直接数值积分和Collares-Pereira and Rabl辐射计算经验关系对Liu and Jordan计算方法的正确性进行分析。结果表明:Liu and Jordan所提出的计算倾斜面上日总直射辐射的方法存在明显的计算误差,误差的大小与倾斜面的倾角和方位角有关,且方位角越大,计算误差越大;对于垂直表面,计算误差随着方位角的增加迅速增加,当方位角偏离正南90度时,由Liu andJordan方法所计算出的年总直射辐射误差高达20%以上。

A simple compliance modeling method for flexure hinges

Various types of flexure hinges have been introduced and implemented in a variety of fields due to their superior performances.The Castigliano’s second theorem,the Euler–Bernoulli beam theory based direct integration method and the unit-load method have been employed to analytically describe the elastic behavior of flexure hinges.However,all these methods require prior-knowledge of the beam theory and need to execute laborious integration operations for each term of the compliance matrix,thus highly decreasing the modeling efficiency and blocking practical applications of the modeling methods.In this paper,a novel finite beam based matrix modeling(FBMM)method is proposed to numerically obtain compliance matrices of flexure hinges with various shapes.The main concept of the method is to treat flexure hinges as serial connections of finite micro-beams,and the shearing and torsion effects of the hinges are especially considered to enhance the modeling accuracy.By means of matrix calculations,complete compliance matrices of flexure hinges can be derived effectively in one calculation process.A large number of numerical calculations are conducted for various types of flexure hinges with different shapes,and the results are compared with the ones obtained by conventional modeling methods.It demonstrates that the proposed modeling method is not only efficient but also accurate,and it is a more universal and more robust tool for describing elastic behavior of flexure hinges.

Analysis of heat transfer performance for turbulent viscoelastic fluid-based nanofluid using field synergy principle

In this paper,the field synergy principle is firstly performed on the viscoelastic fluid-based nanofluid and other relevant fluid in channel at turbulent flow state to scrutinize their heat transfer performance based on our direct numerical simulation database.The cosine values of intersection angle between velocity vector and temperature gradient vector are calculated for different simulated cases with varying nanoparticle volume fraction,nanoparticle diameter,Reynolds number and Weissenberg number.It is found that the filed synergy effect is enhanced when the nanoparticle volume fraction is increased,nanoparticle diameter is decreased and Weissenberg number is decreased,i.e.the heat transfer is also enhanced.However,the filed synergy effect is weakened with the increase of Reynolds number which may be the possible reason for the power function relationship in empirical correlation of heat transfer between heat transfer performance and Reynolds number with the constant power exponent lower than 1.Finally,it is also observed that the field synergy principle can be used to analyze the heat transfer process of viscoelastic fluid-based nanofluid at the turbulent flow state even if some negative cosine values of intersection angle exist in the flow field.