含柔顺关节的空间RSSP常力机构建模与分析

为了解决机构在一定输入范围内需要输出常力的问题,提出在一般初始位形下,空间曲柄滑块机构(RSSP)空间柔顺常力机构的建模与参数优化方法.建立机构柔顺关节的变形量与机构无量纲几何参数的关系.运用虚功原理,建立机构输出端与外部环境接触力与柔顺关节的扭矩的力学模型.以接触力采样点相邻差值和的方法表征接触力波动特征的大小,建立起表征接触力波动的目标函数.优化得出一般初始位形下的空间柔顺常力机构的无量纲化结构参数.设计出实验装置,测得实际输出接触力.结果表明,实际接触力围绕着理论接触常力在5%以内波动.

近似柔顺常力机构的研制及其实验研究

研制了一种柔顺常力滑块机构,在不同输入范围、不同运动速度、不同初始角度下,对机构滑块末端所受的压力进行了实验研究,从实验的角度研究了柔顺常力滑块机构的动力学特性.

基于正负刚度匹配原理的大行程常力微动平台设计

为解决常力微动平台的正负刚度匹配问题,提出一种利用具有线性力学关系的正负刚度结构形成常力平台的设计思路。为了形成零刚度结构,分别设计了Z字型和梯形两种力—位移关系为线性的正刚度结构。将所设计的两种正刚度结构与具有线性负刚度力学特性的双稳态梁结构进行组合,设计了两种新型的常力微动平台。采用伪刚体方法建立了平台的力学模型,基于该模型采用正负刚度匹配原理确定平台的结构参数。制作样机并与具有非线性力学关系的正刚度结构平台进行比较分析,理论和实验结果表明所设计的平台的常力范围可达2.4 mm,比非线性结构组成的平台增大了1.3 mm,说明了常力平台设计的可行性。所提方法为常力微动平台设计提供了一种更为简易的设计思路。

典型柔顺常力模块结构参数评估与有限元优化

为解决柔顺常力机构常力范围不足的问题,基于有限元方法分析结构参数对常力输出特性的影响,提出适应正负刚度组合常力机构的优化方法.首先,以一种Z型梁与双稳态梁并联的常力机构作为研究对象,通过对两种梁的力-位移特性进行分析,获得与机构常力特性相关的结构参数.然后,利用Workbench仿真,对比理论分析结果,得出未优化机构实现常力的输入位移区间为[1.2,2.5] mm,常力为18 N;并利用Matlab仿真,评估两种梁的主要结构参数对常力特性的影响.最终,运用有限元优化法求取结构参数组合的最优解,得出优化后机构实现常力的输入位移区间为[2.0,4.5] mm,常力为68.5 N.优化结果证明了该方法的有效性及可行性.

一种具有常力输出特性打磨机构的设计

针对精密加工过程对恒力控制的需求,利用折叠梁和双稳态梁,提出了一种基于正负刚度组合的常力机构,首先根据伪刚体模型得出了常力机构的整体数学模型,其次通过有限元仿真了常力机构输入位移与输出力之间的关系,并与理论计算结果进行对比验证,结果显示所建立的模型能准确反映常力机构的力学特性。使用粒子群算法(PSO)对常力机构的主要参数进行优化,结果表明优化后的常力机构能在输出位移为[2~4]mm的范围内保持约120N的常力,提升了机构的常力范围和平整度,可以满足加工过程中对恒力的需求。

Gated Neural Network-Based Unsteady Aerodynamic Modeling for Large Angles of Attack

Modeling of unsteady aerodynamic loads at high angles of attack using a small amount of experimental or simulation data to construct predictive models for unknown states can greatly improve the efficiency of aircraft unsteady aerodynamic design and flight dynamics analysis.In this paper,aiming at the problems of poor generalization of traditional aerodynamic models and intelligent models,an intelligent aerodynamic modeling method based on gated neural units is proposed.The time memory characteristics of the gated neural unit is fully utilized,thus the nonlinear flow field characterization ability of the learning and training process is enhanced,and the generalization ability of the whole prediction model is improved.The prediction and verification of the model are carried out under the maneuvering flight condition of NACA0015 airfoil.The results show that the model has good adaptability.In the interpolation prediction,the maximum prediction error of the lift and drag coefficients and the moment coefficient does not exceed 10%,which can basically represent the variation characteristics of the entire flow field.In the construction of extrapolation models,the training model based on the strong nonlinear data has good accuracy for weak nonlinear prediction.Furthermore,the error is larger,even exceeding 20%,which indicates that the extrapolation and generalization capabilities need to be further optimized by integrating physical models.Compared with the conventional state space equation model,the proposed method can improve the extrapolation accuracy and efficiency by 78%and 60%,respectively,which demonstrates the applied potential of this method in aerodynamic modeling.

南京常力蜂业有限公司——全国蜂产品行业龙头企业

南京常力蜂业有限公司是集养蜂、蜂产品研发、生产、销售为一体并享有自主进出口经营权的专业化企业。公司环境、区域优势明显,交通十分便利,地处宁杭高速、宁高高速公路交会处,距南京禄口国际机场不足15公里。

特征系统实现算法的识别特性研究及算法的推广

特征系统实现算法是近年来出现的时域模态参数识别技术。本文首先研究了该算法对混有白噪音的加速度及位移自由响应信号的识别特性,并发现辊速度信号和位移信号分别对系统的高频模态和低频模态敏感;然后结合算法的高速识别特点及滑动时间窗技术,研究了算法对振动水平的跟踪能力,并在此基础上提出识别混叠频率的方法;最后将该算法推广至利用常力强迫响应数据进行模态参数的情况,导出了相应的算法,并进行了算例验证。

具有零刚度特性的微动平台优化设计

针对传统常力机构存在的运动副间隙、装配误差和摩擦磨损等问题,设计了一种基于柔顺机构的常力微动平台。平台利用直梁正刚度和双稳态梁屈曲行为产生负刚度来实现其零刚度特性。平台由对称的直梁、双稳态梁和刚性连接块组成,直梁和双稳态梁通过连接块并联连接。采用伪刚体法和椭圆积分法相结合的建模方法,建立反映常力平台力学性能的理论模型。通过与有限元分析结果进行比较,分析结果显示所建立的模型能准确反映常力平台的力学性能。基于所建立的力学模型,提出一种提高平台常力运动范围和承载能力的优化设计方法。制作样机对该平台力学性能进行实验测试,实验结果表明,平台能在输出位移范围为[0.6~1.7]mm内能够保持约48N常力,证明了常力平台设计思路的可行性、所建模型的准确性和优化方法的有效性。

阀控非对称油缸正反向速度比的分析

本论文分析了阀控非对称油缸在正反向阀开口量相等时 ,其正反向油缸速度比并不等于油缸面积比 η。在空载时等于 η;而在有常力负载时等于 ηps+po/ps-po。

科学理论的解释力评价

提出科学理论的解释力评价方法,是为了克服证据评价方法所遇到的一时难以解决的困难。这种解释力评价方法,是功能评价的基本形式之一。根据科学理论的说明能力、预言能力的强弱来对理论的合理性程度作出比较,就是解释力评价的根本特征。

Full gravity gradient tensors from vertical gravity by cosine transform

We present a method to calculate the full gravity gradient tensors from pre-existing vertical gravity data using the cosine transform technique and discuss the calculated tensor accuracy when the gravity anomalies are contaminated by noise. Gravity gradient tensors computation on 2D infinite horizontal cylinder and 3D ＂Y＂ type dyke models show that the results computed with the DCT technique are more accurate than the FFT technique regardless if the gravity anomalies are contaminated by noise or not. The DCT precision has increased 2 to 3 times from the standard deviation. In application, the gravity gradient tensors of the Hulin basin calculated by DCT and FFT show that the two results are consistent with each other. However, the DCT results are smoother than results computed with FFT. This shows that the proposed method is less affected by noise and can better reflect the fault distribution.

新型限力输出保护功能柔性夹钳的设计与参数评估

柔性夹钳因具有微/纳精密操作能力,常应用于微操作系统中,但因抓爪无法提供恒定输出力或恒力范围小,容易造成操作对象的损伤或脱落。根据放大模块与常力模块串联的结构形式,设计了一种具有常力特性的柔性夹钳。基于伪刚体法,建立放大模块中桥式机构与杠杆机构的刚度和放大率数学模型,通过对倾斜导向梁进行分析,得到常力模块的力−位移关系式,计算出恒定输出力为42.5 N,输出范围为370μm。最后,结合不同柔顺梁的结构参数,运用MATLAB仿真探究了各关键参数对常力特性的影响。研究结果可为常力柔性夹钳的构型设计和分析提供一定的理论支撑。

First-principle calculations of ductile CeAg intermetallic compound

The first-principle calculations were performed to investigate the structural,mechanical,electronic and thermal properties of the binary ductile intermetallic compound CeAg with B2（CsCl） structure.The calculated value of lattice constant a0 for CeAg with generalized gradient approximation is 3.713-,which is in better agreement with experimental data than local spin density approximation.The negative energy of formation implies that CeAg with B2 structure is thermodynamically stable phase.The greater separation between the d bands of Ce and Ag results in weaker bond hybridization of Ce d—Ag d,which prevents formation of directional covalent bonding.The three independent elastic constants（C11,C12 and C44） are derived and the bulk modulus,shear modulus,elastic modulus,anisotropy factor,and Poisson ratio are determined to be 57.6 GPa,15.8 GPa,43.4 GPa,3.15 and 0.374,respectively.The elastic constants meet all the mechanical stability criteria.The value of Pugh＇s criterion is 3.65.The ductility of CeAg is predicted if Pugh＇s criterion is greater than 1.75.Furthermore,the variations of volume,bulk modulus,heat capacity,and thermal expansion coefficient with temperature and/or pressure were calculated and discussed.

Biaxial tensile properties and elastic constants evaluation of envelope material for airship

This paper presents an experimental study to determine the tensile properties of the envelope fabric Uretek3216L under biaxial cyclic loading.First the biaxial cyclic tests were carefully carried out on the envelope material to obtain the stress-strain data and the corresponding nonlinearity and orthotropy of the material were analyzed. Then for some determination options with different stress ratios the least squares method minimizing the strain terms was used to calculate the elastic constants from the experimental data.Finally the influences of the determination options with different stress ratios and the reciprocal relationship on the elastic constants were discussed.Results show that the orthotropy of the envelope material can be attributed to the unbalanced crimp of their constitutive yarns in warp and weft directions and the elastic constants vary noticeably with the determination options as well as the normalized stress ratios.In real design practice it is more reasonable to use constants determined for specific stress states in particular stress ratios depending on the project＆#39;s needs.Also calculating the structures with two limitative sets of elastic constants instead of using only one set is recommendable in light of the great variety of the constant＆#39;s values.

Cascade Kalman filter for gravity anomaly distortion correction based on second order potential model

Using a gravity anomaly covariance function based on the second-order Ganssian Markov gravity anomaly potential model, the state equation of a gravity anomaly signal is obtained in marine gravimetry. Combined with the system state equation and the measurement equation, a new method of the cascade Kalman filter is proposed and applied to the correction of gravity anomaly distortion. In the signal processing procedure, an inverse Kalman filter is used to restore the gravity anomaly signal and high frequency noises first. Then an adaptive Kalman filter, which uses the gravity anomaly state equation as the system equation, is set to estimate the actual gravity anomaly data. Emulations and experiments indicate that both the cascade Kalman filter method and the single inverse Kalman filter method are effective in alleviating the distortion of the gravity anomaly signal, but the performance of the cascade Kalman filter method is better than that of the single inverse Kalman filter method.

Edge enhancement of gravity anomalies and gravity gradient tensors using an improved small sub-domain filtering method

In order to enhance geological body boundary visual effects in images and improve interpretation accuracy using gravity and magnetic field data, we propose an improved small sub-domain filtering method to enhance gravity anomalies and gravity gradient tensors. We discuss the effect of Gaussian white noise on the improved small sub-domain filtering method, as well as analyze the effect of window size on geological body edge recognition at different extension directions. Model experiments show that the improved small sub-domain filtering method is less affected by noise, filter window size, and geological body edge direction so it can more accurately depict geological body edges than the conventional small sub-domain filtering method. It also shows that deeply buried body edges can be well delineated through increasing the filter window size. In application, the enhanced gravity anomalies and calculated gravity gradient tensors of the Hulin basin show that the improved small sub-domain filtering can recognize more horizontal fault locations than the conventional method.

Forest structure,productivity and soil properties in a subtropical ever-green broad-leaved forest in Okinawa,Japan

Structure, species composition, and soil properties of a subtropical evergreen broad-leaved forest in Okinawa, Japan, were examined by establishment of plots at thirty sites. The forest was characterized by a relatively low canopy and a large number of small-diameter trees. Mean canopy height for this forest was 10 m and stands contained an average of 5400 stems-ha^-1 （ -〉 3.0 cm DBH）; 64% of those stems were smaller than 10 cm DBH. The total basal area was 54.4 m^2-ha^-1, of which Castanopsis sieboldii contributed 48%. The forest showed high species diversity of trees. 80 tree species （≥ 3.0 cm DBH） from 31 families was identified in the thirty sampling plots. C. sieboldii and Schima wallichii were the dominant and subdominant species in terms of importance value. The mean tree species diversity indices for the plots were, 3.36 for Diversity index （H＇）, 0.71 for Equitability index （J＇） and 4.72 for Species richness index （S＇）, all of which strongly declined with the increase of importance value of the dominant, C. sieboldii. Measures of soil nutrients indicated low fertility, extreme heterogeneity and possible A1 toxicity. Regression analysis showed that stem density and the dominant tree height were significantly correlated with soil pH. There was a significant positive relationship between species diversity index and soil exchangeable K^＋, Ca^2＋, and Ca^2＋/Al^3- ratio （all p values 〈0.001） and a negative relationship with N, C and P. The results suggest that soil property is a major factor influencing forest composition and structure within the subtropical forest in Okinawa.

Study on fault induced rock bursts

In order to study the rules of rock bursts caused by faults by means of mechanical analysis of a roof rock-mass balanced structure and numerical simulation about fault slip destabilization, the effect of coal mining operation on fault plane stresses and slip displacement were studied. The results indicate that the slip displacement sharply increases due to the decrease of normal stress and the increase of shear stress at the fault plane when the working face advances from the footwall to the fault itself, which may induce a fault rock burst. However, this slip displacement will be very small due to the increase of normal stress and the decrease of shear stress when the working face advances from the hanging wall to the fault itself, which results in a very small risk of a fault rock burst.