Relative rotation number for stochastic systems: dynamical and topological applications

We introduce a concept of relative rotation number to unify many different approaches of rotation number in non-linear dynamical systems. We present an ergodic result of existence a.s. for stochastic systems. In higher dimension, we show that the natural idea of projecting into a plane does work well a.s. for any plane (different from deterministic systems where projections may be degenerate). A number of further properties (invariance by homotopy and by conjugacy) and applications are presented.     

双向气动软体执行器的设计与分析

设计了由两种尺寸气囊交替连通而成的新型软体执行器,该结构可实现两个方向固定角度摆动.首先建立双向弯曲软体执行器的非线性力学模型,得到形式为三段的分段函数,每一段表示软体执行器在相应阶段的弯曲角度和驱动气压的函数关系.其次,应用仿真软件描绘出软体执行器的摆动角度和驱动气压的线性关系,并与经典软体执行器进行了对比,发现两者不同之处在于未充气侧大小气囊之间挤压的弹性势能.最后,制作了双向固定角度摆动的软体执行器模型,通过实验验证了数值结果的可靠性.结果表明,本文提出的双向弯曲气动网格软体执行器的非线性建模和设计是可行的.     

Preparation of defined bulk densities for using the capillary rise method in the case of fine powders

The wetting properties of powders are important in many technological processes. Contact angles can be characterized by an effective contact angle of the particle arrangement relative to the wetting liquid, but their quantification is problematic. An exact determination depends on an accurate preparation of the test samples. A defined pre-consolidation by vertical shocks is introduced in this paper.     

激光织构化不同材料表面对润湿性能的影响

采用激光微织构加工技术分别在SAF2507双相不锈钢和碳纤维增强聚醚醚酮(CF/PEEK)表面制备不同形状、面积占有率的微织构凹坑，通过润湿性试验分析时间、液滴体积、微织构形状与面积占有率、液滴种类对润湿性的影响。结果表明：液滴润湿材料表面过程中，固液接触角先随时间迅速减小，后保持在一个较为稳定的值；使用体积较大的液滴测量接触角时，液滴铺展的速度减缓，接触角的测量值变小；CF/PEEK表面的接触角随微织构面积占有率的增大而减小，SAF2507表面的接触角随微织构面积占有率的增大而增大；微织构面积占有率相同的表面，方柱形微织构表面的接触角小于圆柱形微织构表面，润湿效果更好；天然海水在光滑和织构表面的接触角均小于蒸馏水。     

Study of the hydraulic properties of the cylindrical crested weirs

Since the cylindrical and circular crested weirs are economical and easily made compared to some other weirs, they can be used to measure the flow velocity, the water discharge and flow surface control structures in the canals and reservoirs. In this paper, the hydraulic properties of the cylindrical and circular crested weirs, such as the discharge coefficient, the depth on the crest of the weir and the energy loss in 18 laboratory models categorized in 5 categories have been investigated. The results of the experiments indicated that in both the cylindrical and circular crested weirs by increasing the total partial head, the discharge coefficient increases and any changes in the upstream wall slope has no effect on the discharge coefficient. Also, the partial energy loss more occurs in the cylindrical weirs than the half shaped cylindrical weirs and by increasing the downstream inclination angle, the partial energy loss increases subsequently. The partial flow depth on the crest of both the cylindrical and half shaped cylindrical weirs is equal to 0.7 and by increasing of the upstream inclination angle, the partial flow depth on the crest in the values greater than 0.6, increases slightly and the downstream inclination angle changes of the partial flow depth has no effect on the crest.     

Finite element modelling of shear angle and cutting force variation induced by material anisotropy in ultra-precision diamond turning

This paper addresses a key theoretical problem in the mechanics of ultra-precision machining – shear angle prediction and cutting force variation induced by crystallographic anisotropy. The constitutive equation of crystal plasticity is implemented in the finite element modelling of the chip formation at micro-scale to take into account the effect of crystallographic orientations of the work piece to be cut. The theoretical prediction of shear angle and cutting force variation reveals two distinguished phases of pre-compression and steady-state cutting in ultra-precision diamond turning. The predicted patterns of cutting force variation are in good agreement with published experimental results.     

Comprehensive characterisation and analysis of PV module performance under real operating conditions

The specifications of photovoltaic modules show performance under standard testing conditions (STC), but only limited information relating to performance at non‐STC conditions. While performance is affected by irradiance, temperature, spectral composition of irradiance, angle‐of‐incidence of the irradiance and other parameters, specifications only partly give detail to consumers or retailers about the effect of irradiance and temperature. In this study, we characterise and analyse the performance of eight different, commercially available photovoltaic modules. We establish the effect of four different parameters on module performance: irradiance, temperature, spectral composition of irradiance (via the parameter average photon energy) and angle‐of‐incidence, by performing linear and nonlinear optimisation of physical or empirical models. Furthermore, we characterise the operating conditions and analyse the seasonal and annual development and contribution of the four parameters to energy losses or gains relative to STC operating conditions. We show a comprehensive way of presenting the deviation of performance from STC, combining the variation in operating conditions and the resulting variation in performance. Our results show that some effects on performance are attributable to the semiconductor material used in the modules (spectral composition and temperature), while especially angle‐of‐incidence effects seem more related to the type of glass used on as the front cover of the module. Variation in irradiance and module temperature generally affect performance the strongest, resulting in a performance effect ranging from  + 2.8% to  − 3.2% and  − 0.5% to  − 2.2%, respectively. The combined effect of all parameters results in an annual yield deviation ranging from  + 1.2% to  − 5.9%. © 2016 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons Ltd.     

The mathematical modelling of rotating capillary tubes for holey-fibre manufacture

Understanding and controlling the manufacturing process of producing (“drawing”) microstructured optical fibres (“holey fibres”) is of paramount importance in obtaining optimal control of the final fibre geometry and identifying industrially useful production regimes. The high cost of the manufacturing process and the challenge of ensuring reproducible final fibre geometries renders theoretical approaches invaluable. In this study the fluid dynamics of capillary drawing is examined using an extensional-flow asymptotic approach based on the small aspect ratio of the capillary. The key focus of the study is the additional effects that may be introduced by adding fibre rotation to the manufacturing process. Predictions are made concerning the effects of rotation, and a variety of asymptotic limits are examined in order to gain an understanding of the physics involved. Drawing regimes that are useful from a practical point of view are identified and the role of fibre rotation, both as a control measure (that may be used to influence the final geometry of a capillary) and as a means of reducing unwanted effects (such as fibre birefringence and polarisation model dispersion), is discussed.     

Hysteresis in Transport Critical-Current Measurements of Oxide Superconductors

We have investigated magnetic hysteresis in transport critical-current (I_c) measurements of Ag-matrix (Bi,Pb)₂Sr₂Ca₂Cu₃O_10–x (Bi-2223) and AgMg-matrix Bi₂Sr₂CaCu₂O_8+x (Bi-2212) tapes. The effect of magnetic hysteresis on the measured critical current of high temperature superconductors is a very important consideration for every measurement procedure that involves more than one sweep of magnetic field, changes in field angle, or changes in temperature at a given field. The existence of this hysteresis is well known; however, the implications for a measurement standard or interlaboratory comparisons are often ignored and the measurements are often made in the most expedient way. A key finding is that I_c at a given angle, determined by sweeping the angles in a given magnetic field, can be 17 % different from the I_c determined after the angle was fixed in zero field and the magnet then ramped to the given field. Which value is correct is addressed in the context that the proper sequence of measurement conditions reflects the application conditions. The hysteresis in angle-sweep and temperature-sweep data is related to the hysteresis observed when the field is swept up and down at constant angle and temperature. The necessity of heating a specimen to near its transition temperature to reset it to an initial state between measurements at different angles and temperatures is discussed.     

自升式钻井平台插桩深度计算及几个问题的探讨

在海上油气的勘探和开发中，自升式钻井平台发挥了很大的作用。自升式钻井平台就其基础类型不同分为桩基式和沉垫式2种。本文就桩基式钻井平台的桩靴在均一黏性土、砂土及粉土上的插桩深度计算方法及其强度参数的选取等问题进行探讨。