共查询到20条相似文献,搜索用时 250 毫秒
1.
2.
3.
提出了一种降低300MW汽轮机组主蒸汽管道T形异径三通结构应力的设计方法。该方法利用三通在工作载荷下的变形数据修正原有结构,首先建立了一个有限元分析模型,并用实验结果考核了模型的有效性。在这个模型的基础上,计算了不同修正量下的结构应力。发现在修正量比较小的范围内,结构的最高应力随修正量的增大显著降低。这一结论为进一步改进三通的结构设计提供了一个新的途径。 相似文献
4.
为了得到相变温度低且变色性能优越的光学材料,使其能够广泛应用于智能窗领域,对周期结构VO2纳米点阵的相变和光学特性展开了研究。用修正的Sellmeier色散模型结合二维点阵周期结构的等效折射率计算了VO2纳米点阵在不同占空比下的反射率和透射率。利用多孔氧化铝模板掩膜溅射法,先在玻璃上制备钒金属纳米点阵,再经热氧化工艺制备出VO2纳米点阵,测试其表面形貌、组分结构、红外反射和透射谱线。结果表明,占空比为0.83的纳米点阵其相变温度有效降低至43℃,在1700 nm处透射率改变量达到29%,表现出良好的变色特性,且透射率整体高于VO2薄膜。说明通过制备较佳占空比的纳米点阵可以有效降低材料的相变温度,提升材料的热致变色性能。 相似文献
5.
采用有限元法模拟两构件间的弹性冲击接触过程,并将计算结果与冲击实验进行对比。在有限元模型中引入指数型接触约束,以实验结果为依据对其进行修正。修正模型与实验值相对误差的绝对值小于10%,修正后得到的冲击脉冲峰值、脉宽和最大变形量与实验值吻合较好。利用修正有限元模型计算得到的冲击脉冲精度较高,可作为描述两构件间冲击接触的一种有效的数值计算手段。 相似文献
6.
考虑磨粒轨迹和研磨垫弹性的影响,分析磨粒间距的概率密度函数,计算磨粒轨迹重叠率;引入与研磨参数相关的修正因子,并确定其值,修正固结磨料研磨K9玻璃表面粗糙度公式,实验验证修正模型。结果表明:修正后,K9玻璃表面粗糙度模型计算值与实验值误差控制在4%以内。显著提高K9玻璃表面粗糙度的预测精度,有效指导其研磨方案设计,提高加工效率。 相似文献
7.
针对设施与装备选材时对金属材料大气腐蚀预测的需求,应用神经网络理论,在改进算法的基础上,建立了一种基于贝叶斯正则化算法的BP神经网络预测模型,探讨了小样本条件下的网络泛化问题,分析了算法对泛化精度的提高能力,并通过Matlab实现了仿真验证.通过对试验数据的测试,证实了改进算法和模型的有效性. 相似文献
8.
9.
针对传统带钢表面缺陷检测技术落后、效率不高及小目标识别能力不足等问题,提出一种改进的YOLOv5s-Tiny目标检测模型,在保持模型较小计算量的同时提升检测速度和识别精度。通过将主干网络GSP-Darknet53替换为轻量级GhostNet网络,减少模型参数的数量,提高推理速度。在主干网络加入CBAM注意力机制,通过通道注意力机制和空间注意力机制对特征信息进行融合增强,提高小目标检测精度,并将损失函数GIoU改进为EIoU,提高检测框定位能力。最后将改善后的训练模型格式转换后安装到手机安卓端验证优化的有效性。结果表明:在东北大学数据集中,改进后模型检测精度提高1.5%的同时,召回率提升了1.5%,参数量减少12.3%;安卓端检测速度约为120 ms,完成带钢缺陷的实时检测。 相似文献
10.
为降低热误差对加工精度的影响,以减少补偿成本、简化数据采集、提高补偿精度为目标,提出采用灰色GM(0,N)模型进行数控机床热误差建模预测;以优化数据配置、改善补偿系统动态品质、提高鲁棒性为目的,建立了GM(0,N)优化模型。采用智能温度传感器和位移传感器采集了MCH63精密卧式加工中心温度数据和主轴3个方向热位移量,并根据采集数据构建热误差模型。试验结果表明:GM(0,N)建模方法简单,数据量少,运算时间短,预测精度较高;优化模型可根据在线输入的新数据不断修正模型本身,其精度高、鲁棒性强、通用性好,适合于在线建模。 相似文献
11.
针对目前以假设检验等方法进行模型优选区分度和准确性不高的问题,提出了基于斜率相似和中值相近的灰色关联度模型优选方法,研究了该优选方法的算法。根据采集的数控磨床液压系统的可靠性数据,分别用5种概率密度函数对液压系统进行了建模,并利用所提模型优选方法对5种分布模型进行了拟合优度检验,结果显示液压系统最适合于伽马分布。与相关系数法、传统灰色关联度法、K-S检验等方法进行模型优选相比,基于改进灰色关联度的模型优选方法的区分度分别提高了86.42%、67.27%、2.59%,且准确性很高,优选效果良好。所述的模型优选方法可以用于可靠性模型的优选,也可以为其他曲线拟合的优选提供参考。 相似文献
12.
N. A. Barakat A. D. Spence M. A. Elbestawi 《International Journal of Machine Tools and Manufacture》2000,40(15):2267-2291
An adaptive compensation strategy for quasi-static error correction in intrinsic machines is proposed and tested. The proposed methodology consists of systematic modelling of the machine forward kinematics, including quasi-static errors, as well as direct modelling of the inverse kinematics using nonlinear regression analysis. The result is a model which is a hybrid of physical modelling and regression analysis modelling. In addition, the methodology includes a compensation strategy of the machine contouring errors using the state observer technique for on-line adaptive compensation. A CMM is chosen as a test bed for validation of the proposed methodology. Systematic modelling is carried out in two stages for the forward and inverse kinematics. Regression based models are verified using two different tests. The statistical analysis of variance technique (ANOVA) is used to select the best model in addition to model testing using an independent set equal to approximately 10% of the fitting data. The obtained models are then employed in two compensation strategies; one for the measurement error correction, and another one for the contouring error correction by motion command modification in the forward control path. For contouring tests, the CMM behavior at different thermal states is estimated using experimentally obtained Effective Coefficient of Thermal Expansion (ECTE). Simulations of the machine in contouring selected trajectories are carried out over a range of thermal states. Results obtained show an improvement in the CMM performance to a level close to the machine resolution. The CMM performance is tested using the standard ASME B.89.1.12M-1990 evaluation test, as well as a novel modified version of the test accounting for a thermally varying environment. Machine errors are significantly reduced using the proposed methodology. 相似文献
13.
在Gleeble-3500热机械模拟机上,获得了C71500白铜合金在1073-1273k和应变速率范围内等温压缩试验的真实应力应变数据(0.01分-10秒-1)。采用Johnson-Cook、Johnson-Cook、Zerilli-Armstrong、Arrhenius、Fields-Backofen-Zhang和Zhou-Guan模型对高温流动应力本构方程进行了回归分析。通过比较精度、相关系数(R)、均方根误差(RMSE)、平均绝对相对误差(AARE)、不确定度个数和计算这些参数所需的时间,评价了六种模型的适用性。根据参数和时间消耗的拟合结果,Zhou-Guan模型是预测C71500合金在不同应变率和温度下变形抗力的最佳模型。研究结果为C71500合金及其它类似的不易冷变形铜合金的性能选择和验证提供了理论依据。 相似文献
14.
Majid Mohammadi Mehdi Sedighi 《Protection of Metals and Physical Chemistry of Surfaces》2013,49(4):460-470
In this paper, the Langmuir isotherm, originally derived for the adsorption of three samples of asphaltenes and one sample of resin onto calcite, was modified to fit the adsorption isotherm. The modified Langmuir isotherm parameters obtained from the four linear equations using the different linear method. The aim of this modification is based on the fact that direct application of the Langmuir isotherm often leads to poor data fitting. In the present communication, it is shown that the level of data fitting to the Langmuir isotherm can be improved by a simple modification introducing a concentration dependent factor, X. Four Modified Langmuir linearized isotherm models and one non-linear isotherm model was discussed in this paper, and their coefficients were estimated. In the present study, to study non-linear isotherm model, genetic algorithm was used. A genetic algorithm procedure was utilized to optimize the modified Langmuir constants for a more accurate estimation of the set of model parameters. The obtained results demonstrate that the best fit is obtained using genetic algorithm. Furthermore, it is found that among the mentioned different samples of oil, filtered shale oil follows a multilayer adsorption isotherm. 相似文献
15.
M. Mohammadi M. J. Ameri Shahrabi M. Sedighi 《Surface Engineering and Applied Electrochemistry》2012,48(3):234-243
In this paper, the Langmuir isotherm, originally derived for the adsorption of asphaltene extracted from shale oil and dissolved in toluene on Kaolin, Smectite, Fluorite and Hematite, was modified to fit the adsorption isotherm. The modified Langmuir isotherm parameters obtained from the four linear equations using the linear method differed. The aim of the proposed modification is based on the fact that direct application of the Langmuir isotherm often leads to poor data fitting. In the present communication, it is shown that the level of data fitting to the Langmuir isotherm can be improved by a simple modification through introducing a concentration dependent factor, X. The present paper discusses four modified Langmuir linearized isotherm models and one non-linear isotherm model: their coefficients are estimated and, for the study of non-linear isotherm model, genetic algorithm is used. A genetic algorithm procedure was utilized to optimize the modified Langmuir constants for a more accurate estimation of the set of model parameters. The obtained results demonstrated that the best fit was obtained using genetic algorithm. Furthermore, it was found out that from the surface minerals mentioned, Hematite mineral follows a multilayer adsorption isotherm. 相似文献
16.
17.
对模态参数识别的整体正交多项式分段拟合的处理方法 总被引:2,自引:0,他引:2
在整体正交多项式识别法的基础上,介绍了在分段拟合中消除段外模态影响的方法。通过对拟合频段外的低阶和高阶模态的分析和处理,提出了用邻近拟合段前后两个频段中的模态来修正频响数据,并建立了曲线拟合模型,将本文的方法识别结果与不考虑段外模态影响的方法以及局部识别法识别结果进行了比较,结果表明本文的方法具有较好的计算精度。 相似文献
18.
19.
为了降低弧齿锥齿轮在批量加工制造中存在的齿面偏差,提出一种基于自助法的弧齿锥齿轮齿面修正方法。以同一批次小样本弧齿锥齿轮作为研究对象,在自助法统计齿面偏差检测数据的基础上,得到大量的齿面偏差数据;利用NURBS曲面拟合方法构建齿面的均值差曲面,将它作为实际加工齿面,建立齿面偏差的数字化预控补偿模型,对它进行优化求解,得到批量齿面数控加工的机床修正参数,然后不断调整机床加工参数,实现齿面的预控修正补偿;最后对修正前、后齿面偏差作对比分析。结果表明:小轮齿面偏差比修正前降低了76.66%,验证了自助法齿面修正理论的有效性,对指导弧齿锥齿轮批量齿面修正提供了理论依据。 相似文献
20.
F.R. Marciano J.S. Marcuzzo L.F. Bonetti E.J. Corat V.J. Trava-Airoldi 《Surface & coatings technology》2009,204(1-2):64-68
Diamond-like carbon (DLC) films have been use in numerous industrial applications due to its mechanical properties such as low friction coefficient, high hardness, and high adherence on different substrate materials. It has been demonstrated that the DLC surface can be modified with oxygen plasma treatment. The purpose of this paper is to study two kinds of surface treatments (atmospheric and low pressures) using oxygen gas for different etching exposure times in DLC films. Plasma durability along the time was also evaluated. DLC films were deposited using plasma enhanced chemical vapor deposition technique. The properties of DLC treated for both techniques in different exposure times were investigated through Raman, AFM and contact angle measurements. D band position slightly shifts toward lower wave numbers after oxygen plasma etching treatment whilst the surface becomes rougher, although the roughness values are still lower. A conventional wetting contact angle method was used to study the surface properties of DLC films with different treatments. The wetting contact angle reduced significantly due to the increase of carbon–oxygen sites on the surface. 相似文献