基于案例《轮子》谈小学STEM课程的课堂组织与实施

在素质教育与创新教育的热潮中,STEM教育这样一种以动手操作和科学探究为外显特征的教育形式赢得了诸多教育工作者的青睐.一线教师实施STEM课程,需重点关注课程的准备（选题、选材和课程设计）、课程的组织实施（展开教学活动）和课程的评价三大内容（如图1）.下面我们以小学六年级《轮子》一课为例,重点谈谈小学STEM课程的准备与组织实施.

行走于传统意蕴与现代艺术审美之间——“行走集:彭小佳雕塑作品展”

满地的白桦树皮,游弋在木雕作品中的参观者——“行走集：彭小佳雕塑作品展”于2013年3月15日在上海油画雕塑院美术馆开幕。展览集中展出了彭小佳从1984年至今创作的多个系列的80余件作品,其中包括了代表作品《轮子》、《书》系列、《骰子》、《七宗罪》,《祭祖牌》、《山水》,以及新作《园中缘》。近半数作品为木雕,

PIV MEASUREMENT FOR SWIRLER FLOW FIELD IN GAS TURBINE COMBUSTOR

The characteristics of swirler flow field, including cold flow field and combustion flow field, in gas tur- bine combustor with two-stage swirler are studied by using particle image velocimetry （PIV）. Velocity compo- nents, fluctuation velocity, Reynolds stress and recirculation zone length are obtained, respectively. Influences of geometric parameter of primary hole, arrangement of primary hole, inlet air temperature, first-stage swirler an- gle and fuel/air ratio on flow field are investigated, respectively. The experimental results reveal that the primary recirculation zone lengths of combustion flow field are shorter than those of cold flow field, and the primary reeir- culation zone lengths decrease with the increase of inlet air temperature and fuel/air ratio. The change of the geo- metric parameter of primary hole casts an important influence on the swirler flow field in two-stage swirler com- bustor.

Triangular Au-Ag framework nanostructures prepared by multi-stage replacement and their spectral properties

Triangular Au-Ag framework nanostructures （TFN） were synthesized via a multi-step galvanic replacement reaction （MGRR） of single-crystalline triangular silver nanoplates in a chlorauric acid （HAuCl4） solution at room temperature. The morphological, compositional, and crystal structural changes involved with reaction steps were analyzed by using transmission electron microscopy（TEM）, energy-dispersive X-ray spectrometry （EDX）, and X-ray diffraction. TEM combined with EDX and selected area electron diffraction confirmed the replacement of Ag with Au. The in-plane dipolar surface plasmon resonance （SPR） absorption band of the Ag nanoplates locating initially at around 700 nm gradually redshifted to 1 100 nm via a multi-stage replacement manner after 7 stages. The adding amount of HAuCl4 per stage influenced the average redshift value per stage, thus enabled a fine tuning of the in-plane dipolar band. A proposed formation mechanism of the original Ag nanoplates developing pores while growing Au nanoparticles covering this underlying structure at more reaction steps was confirmed by exploiting surface-enhanced Raman scattering （SERS）.

A distributed dynamic mesh model of a helical gear pair with tooth profile errors

A dynamic model of a helical gear rotor system is proposed.Firstly,a generally distributed dynamic model of a helical gear pair with tooth profile errors is developed.The gear mesh is represented by a pair of cylinders connected by a series of springs and the stiffness of each spring is equal to the effective mesh stiffness.Combining the gear dynamic model with the rotor-bearing system model,the gear-rotor-bearing dynamic model is developed.Then three cases are presented to analyze the dynamic responses of gear systems.The results reveal that the gear dynamic model is effective and advanced for general gear systems,narrow-faced gear,wide-faced gear and gear with tooth profile errors.Finally,the responses of an example helical gear system are also studied to demonstrate the influence of the lead crown reliefs and misalignments.The results show that both of the lead crown relief and misalignment soften the gear mesh stiffness and the responses of the gear system increase with the increasing lead crown reliefs and misalignments.

Use of a submodel method to check the bolt strength of marine equipment

A submodel method was proposed that works from computational models of marine gear cases to verify that the proposed bolts will give it sufficient structural integrity. Calculations for marine equipment using this system accorded well with conventional results. As an example, an anti-shock computation was processed for a gear case, and the submodel was then employed to check the strength of individual components. The results showed that the gear case connecting structure can satisfy relative anti-shock requirements, and the dynamic response characteristics seen in the bolt structures had a close relationship with the method used for attaching the bolt. This provides a new means for checking the strength of connecting structures on large-scale equipment and thus has significant reference value.

Computation of rolling resistance caused by rubber hysteresis of truck radial tire

Applying the results of stress and strain calculated by 3D finite element model of truck radial tire 11.00R20, a MATLAB program used to compute rolling resistance of the tire caused by hysteresis rolling resistance (HRR) is worked out. The HRR distribution on different part of tire section, and the effects of speed, load, internal pressure and the width of the rim on HRR are analyzed. The analysis results showed that energy loss produced by tread rubber contributes the most part to HRR of the whole tire, and that to decrease the HRR, the hysteresis factor of the tread rubber should be reduced, and the distribution of the stress and strain on the section be optimized.

Optimal rotor wear design in hypotrochoidal gear pump using genetic algorithm

The wear rate between the rotors of a hypotrochoidal gear pump is characterized.Using the knowledge of shape design on the rotors,the contact stresses without hydrodynamic effect between the rotor teeth were evaluated through the calculation of the Hertzian contact stress.Based on the above results and the sliding velocity between the rotors,a genetic algorithm (GA) was used as an optimization technique forminimizing the wear rate proportional factor (WRPF).The result shows that the wear rate or the WRPF can be reduced considerably,e.g.approximately 12.8%,throughout the optimization using GA.

Effect of flank angle and friction coefficient on contact stress of turbine rotor

In order to simulate the stress of turbine rotor in aeroengine, based on the ANSYS, the simplification model of the turbine rotor was built up. By applying the simplification model, the contact stress of turbine rotor was computed. The maximum contact stress appears at the chamfer below the flank, which agrees with experiment result. At the same time, the contact stress changing with the flank angle and friction coefficient was calculated, The results show that the contact stress in the flank increases slowly with the increase of flank angle; with the friction coefficient increasing, the contact stress in flank length decreases; the contact stress will not change when the friction coefficient is over 0.25.

OPTIMIZATION METHOD ON IMPELLER MERIDIONAL CONTOUR AND 3D BLADE

An optimization method for 3D blade and meridional contour of centrifugal or mixed-flow impeller based on the 3D viscous computational fluid dynamics （CFD） analysis is proposed. The blade is indirectly parameterized using the angular momentum and calculated by inverse design method. The design variables are separated into two categories： the meridional contour design vari- ables and the blade design variables. Firstly, only the blade is optimized using genetic algorithm with the meridional contour remained constant. The artificial neural network （ANN） techniques with the training sample data schemed according to design of experiment theory are adopted to construct the response relation between the blade design variables and the impeller performance. Then, based on the ANN approximated relation between the meridional contour design variables and impeller per- formance, the meridional contour is optimized. Fewer design variables and less calculation effort is required in this method that may be widely used in the optimization of three-dimension impellers. An optimized impeller in a mixed-flow pump, where the head and the efficiency are enhanced by 12.9% and 4.5% respectively, confirms the validity of this newly proposed method.

释“方马埋轮”与“拐子马”

《孙子·九地篇》“方马埋轮”四字本不误,意思是“缚住战马、埋起车轮”。但“方马埋轮”并非中国古代车战阵法之一,这里只是一个假设,用以突出置士卒于必死之地以激发战斗力的重要性。拐子马记载中的“韦索”是个关键词语,不是用来把三匹战马联在一起,而是把骑兵和自己的战马联在一起,这样在冲锋陷阵时不易坠落。且三人为一组,可以互相照应,从而大大地提高了骑兵的战斗力。“方马埋轮”与“拐子马”的共同之处在于,以往的解释都有作战时把战马绑在一起的说法,都是出于不合实际的牵强附会。

Numerical Study of a Novel Procedure for Installing the Tower and Rotor Nacelle Assembly of Offshore Wind Turbines Based on the Inverted Pendulum Principle

Current installation costs of offshore wind turbines(OWTs) are high and profit margins in the offshore wind energy sector are low, it is thus necessary to develop installation methods that are more efficient and practical. This paper presents a numerical study(based on a global response analysis of marine operations) of a novel procedure for installing the tower and Rotor Nacelle Assemblies(RNAs) on bottom-fixed foundations of OWTs. The installation procedure is based on the inverted pendulum principle. A cargo barge is used to transport the OWT assembly in a horizontal position to the site, and a medium-size Heavy Lift Vessel(HLV) is then employed to lift and up-end the OWT assembly using a special upending frame. The main advantage of this novel procedure is that the need for a huge HLV(in terms of lifting height and capacity) is eliminated. This novel method requires that the cargo barge is in the leeward side of the HLV(which can be positioned with the best heading) during the entire installation. This is to benefit from shielding effects of the HLV on the motions of the cargo barge, so the foundations need to be installed with a specific heading based on wave direction statistics of the site and a typical installation season. Following a systematic approach based on numerical simulations of actual operations, potential critical installation activities, corresponding critical events, and limiting(response) parameters are identified. In addition, operational limits for some of the limiting parameters are established in terms of allowable limits of sea states. Following a preliminary assessment of these operational limits, the duration of the entire operation, the equipment used, and weather-and water depth-sensitivity, this novel procedure is demonstrated to be viable.

Effects of stator bending on pressure field and loss of transonic turbine stage

To study effects of the upstream flow field changing on the downstream flow field of transonic turbine, different three-dimensional bowed blades, which are the stator blades of transonic turbine stage, were designed in this paper. And then numerical calculations were carried out. The effects on downstream flow field were studied and analyzed in detail. Results show that, at the middle of stator blades, although the increasing Maeh number causes the increase of shock-wave strength and friction, the middle flow field of downstream rotors is improved obviously. It is an important change in transonic condition. This causes the loss of the rotor＇ s middle part decreased greatly. Correspondingly, efficiency of the whole transonic stage can be increased.

Deformation behavior of explosive detonation in electroformed nickel liner of shaped charge with nano-sized grains

Nickel liner of shaped charge with nano-sized grains was prepared by electroforming technique and the ultra-highstrain-rate deformation was performed by explosive detonation.The as-electroformed and post-deformed microstructures of electroformed nickel liner of shaped charge were observed by optical metallography(OM),scanning electron microscopy(SEM) and transmission electron microscopy(TEM) and the orientation distribution of the grains was analyzed by electron backscattering pattern(EBSP) technique.Both melting phenomenon in the jet fragment and recovery and recrystallization in the slug after ultra-high-strain-rate deformation were observed.The research evidence shows that dynamic recovery and recrystallization play an important role in ultra-high-strain-rate deformation for electroformed nickel liner of shaped charge with nano-sized grain.

Numerical simulation of tire/soil interaction using a verified 3D finite element model

The compaction and stress generation on terrain were always investigated based on empirical approaches or testing methods for tire/soil interaction.However,the analysis should be performed for various tires and at different soil strengths.With the increasing capacity of numerical computers and simulation software,finite element modeling of tire/terrain interaction seems a good approach for predicting the effect of change on the parameters.In this work,an elaborated 3D model fully complianning with the geometry of radial tire 115/60R13 was established,using commercial code Solidwork Simulation.The hyper-elastic and incompressible rubber as tire main material was analyzed by Moony-Rivlin model.The Drucker-Prager yield criterion was used to model the soil compaction.Results show that the model realistically predicts the laboratory tests outputs of the modeled tire on the soft soil.

An efficient design tool based on FEM for evaluating effects of components properties and operating conditions on interaction of tire with rigid road

It is noted that any variation in operating conditions has a considerable effect on the tire/road interaction. Furthermore,choosing a range of proper values for carcass stiffness is very essential for both tire safety and effective driving action. In this work,an elaborated 3D model fully compliant with the geometrical size of radial tire 185/60 R15 is worked up, for evaluating the effects of components properties and working conditions on deformation and stress/strain fields created inside the tire. For the simulation, the tire structure is assumed to be composed of tread, carcass ply, and bead. The mechanical behavior of rubber as main component of tire is described by Mooney-Rivlin material model. The comparison of the obtained results and laboratory tests demonstrates the validity and high accuracy of analysis.

Proton Elastic Scattering from ^14Be and Halo Effects

The elastic scattering of p-^14Be system at Elab = 200 MeV is evaluated within the relativistic impulse approximation. We discuss the effects of the halo neutrons on the three observables of the elastic scattering system, such as differential cross section dσ/ dΩ, analyzing power Ay and spin rotation Q. The results of the three observables of the elastic scattering of p-^14Be system are compared with those of p-^12C and p-^16O systems at the same energy as E1ab = 200 MeV. We have found that in the small angular region the Ay and Q, as well as dσ/dΩ, are quite sensitive to the nucleon density distributions on the surface of the target nucleus and offer some unique behaviors of halo nuclei.

Dynamic modeling and direct power control of wind turbine driven DFIG under unbalanced network voltage conditions

This paper proposes an analysis and a direct power control (DPC) design of a wind turbine driven doubly-fed induction generator (DFIG) under unbalanced network voltage conditions. A DFIG model described in the positive and negative synchronous reference frames is presented. Variations of the stator output active and reactive powers are fully deduced in the presence of negative sequence supply voltage and rotor flux. An enhanced DPC scheme is proposed to eliminate stator active power oscillation during network unbalance. The proposed control scheme removes rotor current regulators and the decomposition processing of positive and negative sequence rotor currents. Simulation results using PSCAD/EMTDC are presented on a 2-MW DFIG wind power generation system to validate the feasibility of the proposed control scheme under balanced and unbalanced network conditions.

Energy Dissipation with Geometric Parameters in Unbaffled Surface Aerator

The dissipation rate of turbulent kinetic energy （ ε ） is the key process parameters for mixing in surface aerators. At constant dynamic variables （rotational speed）, ε is greatly affected by the geometric parameters, such as impeller diameter, cross-sectional area of the tank, liquid height, rotor blade length and immersion height. By doing numerical computation by visimix, present work analyzes the effect of non-dimensional （which is non-dimensionalized through rotor diameter） geometric parameters on ε. With an increase in liquid height, there is an increase in the case of energy dissipation. In the case of tank area and blade length, it is vice versa. Energy dissipation is not affected by the variation in immersion height of the impeller.

Detection of Blade Mistuning in a Low Pressure Turbine Rotor Resulting from Manufacturing Tolerances and Differences in Blade Mounting

For a serious prediction of vibration characteristics of any structure, a detailed knowledge of the modal characteristic is essential. This is especially important for bladed turbine rotors. Mistuning of the blading of a turbine rotor can appear due to manufacturing tolerances or because of the blading process itself due to unequal mounting of the blades into the disk. This paper investigates the mistuning of the individual blades of a low pressure turbine with respect to the effects mentioned above. Two different rotors with different aerodynamic design of the blades were investigated. The blades were mounted to the disk with a so-called hammer head root which is especially prone to mounting irregularities. For detailed investigations, the rotor was excited with a shaker system to detect the forced response behavior of the individual blades. The measurements were done with a laser vibrometer system. As the excitation of rotor structure was held constant during measurement, it was possible to detect the line of nodes and mode shapes as well. It could be shown that the assembly process has an influence on the mistuning. The data were analyzed and compared with numerical results. For this, different contact models and boundary conditions were used. The above described characterization of modal behavior of the rotor is the basis for the upcoming aeroelastic investigations and especially for the blade vibration measurements of the rotor, turning with design and off-design speeds.