THE APPLICATION OF BRANCH MODE METHOD TO THE CRITICAL SPEED ANALYSIS OF COMPOUND ROTATING SYSTEMS

This paper is devoted to the application of branch mode method in the critical speed ana-lysis of compound rotating systems, in which the distributed inertia including gyroscopic effectand distributed elastic support are taken into account. Finally, the method introduced in this paper is used to calculate the critical speeds of anew-type spindle on the spinning frame. The first three critical Speeds are calculated and com-pared with the values obtained from the experimental approach and other theoretical methods.The results show that they are in good agreement with each other.

Nonlinear dynamic modeling of planar moving Timoshenko beam considering non-rigid non-elastic axial effects

Due to the importance of vibration effects on the functional accuracy of mechanical systems,this research aims to develop a precise model of a nonlinearly vibrating single-link mobile flexible manipulator.The manipulator consists of an elastic arm,a rotary motor,and a rigid carrier,and undergoes general in-plane rigid body motion along with elastic transverse deformation.To accurately model the elastic behavior,Timoshenko’s beam theory is used to describe the flexible arm,which accounts for rotary inertia and shear deformation effects.By applying Newton’s second law,the nonlinear governing equations of motion for the manipulator are derived as a coupled system of ordinary differential equations(ODEs)and partial differential equations(PDEs).Then,the assumed mode method(AMM)is used to solve this nonlinear system of governing equations with appropriate shape functions.The assumed modes can be obtained after solving the characteristic equation of a Timoshenko beam with clamped boundary conditions at one end and an attached mass/inertia at the other.In addition,the effect of the transverse vibration of the inextensible arm on its axial behavior is investigated.Despite the axial rigidity,the effect makes the rigid body dynamics invalid for the axial behavior of the arm.Finally,numerical simulations are conducted to evaluate the performance of the developed model,and the results are compared with those obtained by the finite element approach.The comparison confirms the validity of the proposed dynamic model for the system.According to the mentioned features,this model can be reliable for investigating the system’s vibrational behavior and implementing vibration control algorithms.

基于主客观环流分型的强降水数值预报MODE检验方法及其在2019年暖季东北地区的应用

本文构建了基于主客观环流分型的强降水数值预报空间检验(MODE)方法框架,并利用该框架对欧洲中期天气预报中心全球模式(ECMWF)和中国气象局区域中尺度数值天气预报模式(CMA_MESO)的2019年暖季东北地区强降水预报进行检验。结果表明,2019年暖季东北地区54个强降水日的环流型可分为:西风槽型(15个)、副热带高压影响型(13个)、急流型(5个)、西部(12个)和东部冷涡型(9个)。其中,西风槽型和急流型以区域性强降水为主,模式对其强降水发生与否的预报能力强,TS评分较高;西部、东部冷涡型强降水的局地性强,模式对其强降水发生与否的预报能力差,TS评分低;副热带高压影响型也以区域性强降水为主,模式对其强降水发生与否的预报能力也比较强,但是对其强降水质心位置、强度、面积等属性预报偏差较大,TS评分也相对较低。另外,从两种模式预报性能对比看,CMA_MESO强降水强度和面积预报较实况普遍偏强,虽然其预报的TS评分一般高于ECMWF,但其对强降水预报的空报率也都比ECMWF大,对强降水的属性预报偏差一致性一般也低于ECMWF,其预报的可订正性整体上不及ECMWF。

Range of applicability of real mode superposition approximation method for seismic response calculation of non-classically damped industrial buildings

An industrial building is a non-classically damped system due to the different damping properties of the primary structure and equipment.The objective of this paper is to quantify the range of applicability of the real model superposition approximation method to the seismic response calculation of industrial buildings.The analysis using lumped mass-and-shear spring models indicates that for the equipment-to-structure frequency ratiosγf>1.1 orγf<0.9,the non-classical damping effect is limited,and the real mode superposition approximation method provides accurate estimates.For 0.9<γf<1.1,the system may have a pair of closely spaced frequency modes,and the non-zero off-diagonal damping terms have a non-negligible effect on the damping ratios and mode shape vectors of these modes.For 0.9<γf<1.1 and the equipment-to-structure mass ratiosγm<0.07,the real mode superposition approximation method results in large errors,while the approximation method can provide an accurate estimation for 0.9<γf<1.1 andγm>0.07.Furthermore,extensive parametric analyses are conducted,where both steel structures and reinforced concrete structures with equipment with various damping ratios are considered.Finally,the finite element analysis of a five-story industrial building is adopted to validate the proposed range of applicability.

Study on Decision Method of Neutral Point Grounding Mode for Medium-Voltage Distribution Network

The neutral grounding mode of medium-voltage distribution network decides the reliability, overvoltage, relay protection and electrical safety. Therefore, a comprehensive consideration of the reliability, safety and economy is particularly important for the decision of neutral grounding mode. This paper proposes a new decision method of neutral point grounding mode for mediumvoltage distribution network. The objective function is constructed for the decision according the life cycle cost. The reliability of the neutral point grounding mode is taken into account through treating the outage cost as an operating cost. The safety condition of the neutral point grounding mode is preserved as the constraint condition of decision models, so the decision method can generate the most economical and reliable scheme of neutral point grounding mode within a safe limit. The example is used to verify the feasibility and effectiveness of the decision method.

Comparison of Three Methods in Extracting Coherent Modes from a Doppler Backscatter System

We compare three different methods to extract coherent modes from Doppler backscattering （DBS）, which are center of gravity （COG） of the complex amplitude spectrum, spectrum of DBS phase derivative （phase derivative method）, and phase spectrum, respectively. These three methods are all feasible to extract coherent modes, for example, geodesic acoustic mode oscillation. However, there are stilI differences between dealing with high frequency modes （several hundred kHz） and low frequency modes, （several kHz） hiding in DBS signal. There is a significant amount of power at low frequencies in the phase spectrum, which can be removed by using the phase derivative method and COG. High frequency modes are clearer by using the COO and the phase derivative method than the phase spectrum. The spectrum of DBS amplitude does not show the coherent modes detected by using COG, phase derivative method and phase spectrum. When two Doppler shifted peaks exist, coherent modes and their harmonics appear in the spectrum of DBS amplitude, which are introduced by the DBS phase.

A NEW MOMENT METHOD FOR THE FAST AND ACCURATE ANALYSIS OF NORMAL MODE HELICAL ANTENNAS

In this letter, a new moment method using helical segments is presented to model Normal Mode Helical Antenna (NMHA). Using this method, the NMHA can be modeled by a few segments. The current distributions and radiation patterns of some NMHAs are calculated.A comparison is made between results obtained using this helical segment algorithm and a linear segment algorithm, and the results of the two algorithms agree fairly well. When calculating the impedance matrix [Z], all the elements of the matrix can be obtained by only calculating a few elements with the application of the symmetric and periodic characteristics of the NMHA.Therefore, the CPU time and the memory storage are significantly reduced, with the accuracy and speed enhanced.

MESHLESS METHOD FOR 2D MIXED-MODE CRACK PROPAGATION BASED ON VORONOI CELL

A meshless method integrated with linear elastic fracture mechanics(LEFM)is presented for 2D mixed-mode crack propagation analysis.The domain is divided automatically into sub-domains based on Voronoi cells,which are used for quadrature for the potential energy. The continuous crack propagation is simulated with an incremental crack-extension method which assumes a piecewise linear discretization of the unknown crack path.For each increment of the crack extension,the meshless method is applied to carry out a stress analysis of the cracked structure.The J-integral,which can be decomposed into mode Ⅰ and mode Ⅱ for mixed-mode crack,is used for the evaluation of the stress intensity factors(SIFs).The crack-propagation direction,predicted on an incremental basis, is computed by a criterion defined in terms of the SIFs. The flowchart of the proposed procedure is presented and two numerical problems are analyzed with this method.The meshless results agree well with the experimental ones,which validates the accuracy and efficiency of the method.

Mode Ⅲ fracture analysis by Trefftz boundary element method

This paper presents a hybrid Trefftz （HT） boundary element method （BEM） by using two indirect techniques for mode III fracture problems. Two Trefftz complete functions of Laplace equation for normal elements and a special purpose Trefftz function for crack elements are proposed in deriving the Galerkin and the collocation techniques of HT BEM. Then two auxiliary functions are introduced to improve the accuracy of the displacement field near the crack tips, and stress intensity factor （SIF） is evaluated by local crack elements as well. Furthermore, numerical examples are given, including comparisons of the present results with the analytical solution and the other numerical methods, to demonstrate the efficiency for different boundary conditions and to illustrate the convergence influenced by several parameters. It shows that HT BEM by usingthe Galerkin and the collocation techniques is effective for mode III fracture problems.

师范院校高等数学教学存在的问题与对策

高等数学是诸多师范专业必修的公共基础课,对于培养学生的专业学科素养和思维能力发挥着不可替代的作用。师范院校高等数学教学存在教学大纲一刀切,教学方法因循守旧,评价方式单一的问题,应对教学大纲进行优化调整,细化到每个学院的每个专业;改进教学方法,以线上线下的混合式教学模式代替单一的线下教学模式,同时将翻转课堂引进高数课堂;建立以专业为导向的多元、科学、有效的课程评价方式,以更大程度上促进高等数学课程目标的实现。

Calculation of the Coupling Coefficient of Twin-Core Fiber Based on the Supermode Theory with Finite Element Method

Currently, coupled mode theory (CMT) is widely used for calculating the coupling coefficient of twin-core fibers (TCFs) that are used in a broad range of important applications. This approach is highly accurate for scenarios with weak coupling between the cores but shows significant errors in the strong coupling scenarios, necessitating the use of a more accurate method for coupling coefficient calculations. Therefore, in this work, we calculate the coupling coefficients of TCFs using the supermode theory with finite element method (FEM) that has higher accuracy than CMT, particularly for the strong coupling TCF. To investigate the origin of the differences between the results obtained by these two methods, the modal field distributions of the supermodes of TCF are simulated and analyzed in detail.

水稻种植模式与秸秆还田方式对土壤养分的影响

为探明水稻不同种植模式与还田方式下土壤养分含量的变化。以辽星21号为试验材料,在大田条件下,比较移栽与直播种植2种模式下秸秆还田、炭化还田和不还田3种方式土壤中有机碳、速效氮、速效磷、速效钾、全氮、全磷、全钾含量的差异。研究结果表明,直播种植模式较移栽方式土壤速效磷含量、速效钾含量和全磷含量增加0.9%、5.4%和7.1%,生物炭还田较不还田处理分别显著增加土壤有机碳含量、速效钾含量、全氮含量和全磷含量9.6%、20.1%、5.3%和8.1%。因此,直播种植结合生物炭还田可作为提高农田肥力、改善土壤养分的一项促进北方寒地稻田资源再利用有效措施。

基于在线开放的高职技能型课程混合式教学模式探究

“碳达峰碳中和”政策为能源电力行业的转型升级提供了根本遵循。电工技术课程作为能源电力行业的一门专业技能型课程,传统的教学模式已经不能满足该行业对新能源的需求。为了提升能源电力行业技能型课程的教学质量及综合育人质量,本研究以高职在线精品课程“电工技术”教学改革实践为例,探索实施岗位、课程、竞赛、证书与思政教育、劳动教育的有机融通,以及线上线下混合式深度融合的教学方式,构建了“岗课赛证思劳”六位一体混合式教学模式。该模式能够有效提升学习者的学习效果和实践能力,对培养新时代高素质技术技能人才具有一定的借鉴意义。

植入雨课堂智慧模式的教学法在产科线上实习带教中的应用

目的研究线上实习带教时采用植入雨课堂智慧模式的教学法对产科实习教学效果的影响。方法回顾分析2022年5月—2023年2月在中山大学附属第三医院产科实习的五年制、八年制及内外全科医学士(bachelor of medicine and bachelor of surgery,MBBS)实习学生147名实习成绩,分为研究组65名,对照组82名。对照组开展正常的线下实习,研究组采用植入“雨课堂”智慧模式的新型教学方法开展线上实习。比较2组实习生的实习效果并对研究组实习生进行线上教学满意度调查。结果研究组实习生总成绩、平时成绩与对照组相比[五年制:(82.13±2.95)分vs.(83.03±3.44)分;八年制:(82.18±2.47)分vs.(83.52±3.13)分;MBBS:(81.82±2.41)分vs.(80.03±2.80)分],差异无统计学意义(P>0.05);研究组中五年制、八年制实习生理论考核成绩与对照组相比[五年制:(73.11±7.94)分vs.(73.82±8.50)分;八年制:(70.28±4.66)分vs.(69.03±6.56)分],差异无统计学意义(P>0.05),而研究组MBBS实习生理论考核成绩高于对照组[(74.89±5.40)分vs.(65.25±7.81)分],差异有统计学意义(P<0.05);研究组中实习生技能考核成绩均低于对照组[五年制:(78.89±4.76)分vs.(81.27±4.77)分;八年制:(80.78±3.42)分vs.(84.29±6.12)分;MBBS:(76.78±3.93)分vs.(80.38±1.77)分],差异有统计学意义(P<0.05)。研究组实习生对植入雨课堂智慧模式的教学法在产科线上实习带教中的满意度高,非常满意者占66.15%,无不满意者。结论植入雨课堂智慧模式的教学法在产科线上实习带教中的应用基本达到了产科实习的要求,虽然在临床技能培养上存在一定的局限性,但仍是一种可开展的线上实习教学法。

联合PBL和iSIM情景模拟教学在产儿团体合作培训中的应用

目的将基于问题的学习(problem based learning,PBL)联合优化情景模拟教学模式(improving simulation instructional methods,iSIM)应用于产儿科团队合作培训,探讨该教学模式在产儿科对临床医学本科实习医师的团队合作能力、新生儿急救实践技能和学生对教学模式的满意度的影响。方法将2022年7月—2023年6月在中山市人民医院产科和新生儿科轮转的四年级实习医师共72人,按工号末位奇偶数随机分为试验组(n=36)和对照组(n=36)。两组均实行小组教学,每6人为一个小组。所有人员前期均接受产科危重症、新生儿复苏的理论培训。其中,对照组采用传统授课+操作示范的教学模式;试验组采用PBL+iSIM情景模拟教学模式,期间穿插标准家属进行医患沟通,试验组和对照组每1个小组6个实习医师,利用Excel现场随机抽签确定所演练的角色分工。教学结束后比较两组实习医师理论、操作考核成绩、医患沟通能力和学生的满意度,并用团队合作评价工具(CSAT)进行评价,应用统计学方法,分析并评估PBL+iSIM情景模拟教学模式在产儿科团体合作培训与传统的教学模式培训教学效果差异。结果两组实习医师除了理论成绩和个人准备工作项目得分差异无统计学意义(P>0.05)外,操作考核成绩、医患沟通能力、学生的满意度以及CSAT评价指标总分和其他项目的组间差异均具有统计学意义(均P<0.05),结果提示PBL联合iSIM情景模拟教学模式优于传统的教学模式。结论PBL联合iSIM情景模拟教学模式应用在临床本科实习生的产儿科合作项目中有较大的优势,有利于提高临床医学本科实习生对产科和新生儿急救技能的掌握水平,提高教学效果和教学质量。

食用菌栽培发展历程

回顾食用菌从野生、人工干预到人工栽培的发展历程,介绍食用菌栽培方式和栽培模式,总结中国为世界食用菌产业发展作出的贡献,展望食用菌栽培发展的方向。

带内埋质量超声速悬臂板的颤振特性

为提高具有内埋质量升力面的颤振速度,将其简化为带集中质量的矩形悬臂板。基于假设模态法和一阶活塞理论得到颤振模型,进而考察其颤振特性。首先,基于Kirchhoff薄板理论建立矩形悬臂板的结构动力学模型,并利用假设模态法得到带内埋质量时的模态属性。其次,引入一阶活塞理论近似求解在超声速条件下的模态气动力,代入结构动力学模型得到颤振方程的时域表达。最后,通过引入指数形式的模态位移将颤振方程变换至频域并通过p-k法求解颤振速度和颤振频率。通过改变内埋件的位置、质量和数目等参数,得到其对超声速悬臂板颤振特性的影响规律。研究结果表明,在悬臂板前缘靠近翼梢区域内埋小质量物体可有效提高升力面的颤振速度,而在翼根附近,颤振速度对内埋质量的变化不敏感。

产教融合视域下岗课赛证融通育人模式

产教融合是高职教育发展的重要举措和主要途径。产教融合要求高职院校的教学链、人才链与产业链在规模和结构上相互协调,人才培养模式与地方产业活动相互衔接,学校的人才培养方案、课程体系设置和各种资源配置与对应的岗位相互契合。高职院校可以通过教师、教材和教法“三教”改革推动“岗课赛证”融通。调研岗位职责以岗定课、重构课程体系以课育人、参与技能大赛以赛导课和获取资格证书以证验课,进一步深化产教融合、强化专业知识、优化信息能力、提升岗位技能和综合素养。

Research on the Equivalence Between Double Differential- mode Current Injection and Radiation Test Method

There are the application scope limits for single differential-mode current injection test method, so in order to carry out injection susceptibility test for two-pieces equipment interconnected with both ends of a cable simultaneously, a double differential-mode current in- jection test method (DDMCI) is proposed. The method adopted the equivalence source wave theorem and Baum-Liu-Tesche(BLT) equation as its theory foundation. The equivalent corresponding relation between injection voltage and radiation electric field intensity is derived, and the phase relation between the two injection voltage sources is confirmed. The results indicate that the amplitude and phase of the equivalent injection voltage source is closely related to the S parameter of directional coupling device, the transmission line length, and the source vector in BLT equation, but has nothing to do with the reflection coefficient between the two equipment pieces. Therefore, by choosing the right amplitude and phase of the double injection voltage sources, the DDMCI test is equivalent to the radiation test for two interconnected equipment of a system.

基于反步滑模方法的车辆纵向自适应控制

车辆纵向控制是自动驾驶研究的关键技术之一,建立了复杂的车辆纵向动力学模型,设计了合适的控制算法,并构造了控制器,提升了控制性能。首先,在考虑道路倾角、轮胎形变和车轮滑动等影响因素的基础上,建立了复杂的车辆纵向动力学模型;然后,综合运用自适应方法和反步滑模控制方法对所建模型设计控制器,并对控制系统的稳定性作了证明;最后,采用MATLAB/Simulink软件对控制系统进行仿真分析。研究结果表明:通过自适应反步滑模方法设计的控制器具有较好的稳定性,能够控制车辆以极小的误差以期望速度行驶。研究成果可为车辆自动驾驶及交通拥堵的缓解提供技术支撑。