关键词： 软体机械臂   模态方法   能量   集中质量   动力学  

摘要： 由于软体机械臂的质量是沿臂的长度连续分布,因此采用拉格朗日方法建立软体机械臂的动力学模型时,涉及计算复杂的积分运算,采用离散化的集中质量模型降低了计算的复杂性,但准确性不足.为了提高软体机械臂动力学建模与仿真的准确度和计算效率,本文采用模态方法对软体机械臂进行运动学描述,并从能量的角度分析软体机械臂动力学特性,研究发现,角速度产生的转动动能计算复杂,影响动力学方程的求解效率.在给定条件下,占总动能的百分比不超过3%,对动力学结果影响很小,可以忽略.在此基础上,提出一种基于质心集中质量描述的软体机械臂动力学模型,该模型将软体机械臂的连续分布质量模型等效为位于质心的集中质量模型,利用统计的方法计算出动能等效系数,通过动能等效系数实现两种模型的动能匹配.仿真结果表明,与通常将集中质量放置在任意位置(例如,软体机械臂的中点或末端)的集中质量模型相比,该模型兼顾了连续分布质量模型的准确性,以及集中质量模型的计算高效性,能够准确、高效地获得软体机械臂的动力学特性,并且数值计算稳定.

关键词： 燕山大学   控制实验室   重型机械   重点实验室   固定研究人员   流体动力传输   博士生导师   重点学科实验室  

摘要： 燕山大学重型机械流体动力传输与控制实验室的前身为东北重型机械学院液压实验室,始建于1977年。2005年,实验室成为河北省重型机械流体动力传输与控制重点实验室,2006年成为国防重点学科实验室,2007年成为机械工业流体动力传输技术重点实验室。实验室现有固定研究人员34名,其中教授13人(含博士生导师10名),副教授9人。

关键词： 控制器   机械液压启闭机   动力节能   数值仿真   动力学模型  

摘要： 传统机械液压启闭机动力节能方法无法实现闸门的远程控制,导致机械液压启闭机动作不及时,节能效果不明显。为此引入机械系统动力学自动分析软件,仿真分析基于PLC的机械液压启闭机动力节能数值。利用PLC控制器设计机械液压启闭机,远程控制闸门的开启与关闭。以改装的启闭机为基础,通过三维建模软件Pro/Engineer构建启闭机的三维模型。在机械系统动力学自动分析软件中导入三维模型,构建启闭机动力学模型,仿真分析启闭机动力节能数值。仿真结果证明:所研究方法能够有效分析液压启闭机控制的起升机构振动力与钢丝绳收受力的动力节能数值,提升动力节能效果。

关键词： 超临界二氧化碳   印刷电路板换热器   热应力   机械应力   应力集中  

摘要： 超临界二氧化碳动力循环中印刷电路板换热器所处的高温高压工况可能导致芯体材料失效和结构破坏,有必要进行应力分析以优化通道结构,保证系统长期安全稳定运行。该文利用有限元方法对印刷电路板换热器芯体热冷通道特定路径的热应力、机械应力和总应力进行分析,比较487.6~537.1℃范围内的热应力,分析半圆通道尖角圆弧半径对应力变化的影响。结果表明:芯体所受应力是工质压力和温度梯度共同作用的结果,冷通道的总应力大于热通道;芯体半圆截面通道尖角的存在导致应力集中,半圆弧中间位置因温度梯度较大产生较大热应力;增大芯体半圆截面尖角圆弧半径能有效减小应力集中处的机械应力和热应力,且机械应力减小幅度更大。最后,指出在通道结构设计时应注意改善尖角处的应力集中,并控制蚀刻深度,相同当量直径下采用圆截面的通道最大热应力、最大机械应力和最大总应力都有大幅的减小。

关键词： 农业劳动力老龄化   农业机械应用   农地转入   调节效应  

摘要： 农地流转是促进农地要素优化配置与农业适度规模经营的主要途径。文章基于中国劳动力动态调查数据,实证分析了农业劳动力老龄化与农业机械应用对农地转入的影响。结果表明:农业劳动力老龄化抑制家庭农地转入,且农业劳动力老龄化程度越深,对农地转入的抑制作用越明显;农业机械应用对农地转入存在显著正向影响,且能够有效缓解农业劳动力老龄化对农地转入的负向影响;仅东部和中部地区,农业劳动力老龄化对农地转入存在显著负向影响,农业机械应用均显著正向影响农地转入。因此,应继续提升农业机械应用水平,加快农业生产效率的提高;完善农村农地经营补偿机制,创造老龄农户生产经营条件;加大新型农业经营主体培育力度,提高种田农户职业素质;针对地区差异,发展实用性强的农业机械,缓解农业劳动力老龄化对农业生产的不利影响,从而提高农民农地转入参与积极性,实现农业规模经营。

关键词： Polypropylene   Crystallization   Mechanical characteristics  

摘要： The non-isothermal crystallization of the isotactic Polypropylene (iPP) was studied using differential scanning calorimetry and polarizing optical microscopy. Jeziorny's model and Ozawa's theoretical approaches were applied to study the non-isothermal kinetics of the iPP. Jeziorny's approach proved to be the most relevant model to the present material. Simultaneously, the activation energy was calculated with Kissinger's method and Vyazovkin's iso-conversional approach. Indeed, the latter provides an activation energy varying between 100 and 176 kJ/mol. Furthermore, the WAXD scans indicated the presence of a single crystalline form in the used material. To study the effect of the microstructure on the mechanical properties of the iPP, multiscale tensile tests were carried out for different film microstructures. At macroscopic scale, the increase in the diameter of spherulites, inevitably accompanied by a rise in the crystallinity rate, induces the growth of rigidity, brittleness, and elastic limit. Moreover, the results of the in-situ micro-tensile tests present the evolution of spherulites during loading.

关键词： In silico model   Dissolution   Hydrodynamics   Coning   Sedimentation   Physiologically based biopharmaceutics model   Viscosity   Agitation rate   Immediate release  

摘要： Drug product dissolution is a key input to Physiologically Based Biopharmaceutics Models (PBBM) to be able to predict in vivo dissolution. The integration of product dissolution in PBBMs for immediate release drug products should be mechanistic, i.e. allow to capture the main determinants of the in vitro dissolution experiment, and extract product batch specific parameter(s). This work focussed on the Product Particle Size Distribution (P-PSD), which was previously shown to integrate the effect of dose, volume, solubility (pH), size and concentration of micelles in the calculation of a batch specific input to PBBMs, and proposed new hydrodynamic (HD) models, which integrate the effect of USP2 apparatus paddle rotation speed and medium viscosity on dissolution. In addition, new models are also proposed to estimate the quantitative impact of formulation and drug sedimentation or "coning" on dissolution. Model "HDC-1" predicts coning in the presence of formulation insoluble excipients and "HDC-2" predicts the sedimentation of the drug substance only. These models were parameterized and validated on 166 dissolution experiments and 18 different drugs. The validation showed that the HD model average fold errors (AFE) for dissolution rate prediction of immediate release formulations, is comprised between 0.85 and 1.15, and the absolute average fold errors (AAFE) are comprised between 1.08 and 1.28, which shows satisfactory predictive power. For experiments where coning was suspected, the HDC-1 model improved the precision of the prediction (defined as ratio of "AAFE-1"values) by 2.46 fold compared to HD model. The calculation of a P-PSD integrating the impact of USP2 paddle rotation, medium viscosity and coning, will improve the PBBM predictions, since these parameters could have an influence on in vitro dissolution, and could open the way to better prediction of the effect of prandial state on human exposure, by developing new in silico tools which could integrate variati

关键词： LDH   Layered Double Hydroxide   NiCoAl-LDH   Eosin Yellow   Malachite Green   Dye Adsorption   Purification of Water  

摘要： The use of highly efficient, environment-friendly and economically inexpensive materials for the adsorption removal of contaminants from water has always been considered as emerging task. In this study, we synthesized hybrid tri-metallic nickel cobalt layered double hydroxide (NiCoAl-LDH) porous material for the adsorption removal of Eosin yellow (EY) and Malachite green (MG) from water. The characterization results disclosed that tri-metallic LDH has been synthesized with extraordinary purity, identical morphology and high surface area (134.21 m(2)center dot g(-1)). The NiCoAl-LDH performs the best for adsorption of EY (q(e)=37.30mg center dot g(-1) at pH=2) and MG (q(e)=39.61 mg center dot g(-1) at pH=10). The Langmuir and Freundlich isotherm models were applied to explain the adsorption process of dyes on the surface of LDH. The Langmuir model (R-2=0.991 and 0.999 for Eosin Y and Malachite G, respectively) was very appropriate to explain the process of adsorption on NiCoAl-LDH as homogeneous (monolayer). The maximum adsorption capacity of EY and MG calculated with Langmuir model was 78.74 and 110.13 mg center dot g(-1) at 30 degrees C, respectively. Also with 240 minutes contact time 94.8% EY and 89.9% MG was adsorbed by as synthesized NiCoAl-LDH nanosheets. The NiCoAl-LDH nanosheets showed excellent performance of reusability of up to five regeneration cycles. The results showed that the adsorption capacity of NiCoAl-LDH nanosheets after five regeneration cycles, to adsorb EY, decreased only from 40.80 to 36.93 mg center dot g(-1) and that of MG from 79.21 to 75.42 mg center dot g(-1), which is acceptable. The overall results Suggest that the fabricated NiCoAl-LDH is favorable for the purification of dye contaminated water.

关键词： curing agent   curing kinetics   differential scanning calorimetry   epoxy resin   mechanical properties  

摘要： The current research work presents a novel nonionic curing agent (AEDA) synthesized by utilizing ethylene glycol diglycidyl ether (EGDE), 3,4-dimethoxyaniline (DI), and triethylenetetramine (TETA). Infrared spectroscopy and nuclear magnetic resonance spectroscopy were used to characterize the structure of AEDA curing agent. Non-isothermal scanning calorimetry was used to determine the activation energy and curing conditions of epoxy resin in the curing process. An impact testing machine, a tensile testing machine and a scanning electron microscope (SEM) were used to analyze the impact strength, tensile strength, bending strength, and micromorphology of the AEDA/E-51 system with different mass ratios. The results show that AEDA is an effective high-temperature curing agent. For the AEDA/E-51 system with the optimal mass ratio of 10:100, the best curing temperature is 92.15 degrees C, and the post-curing temperature is 135.65 degrees C. Furthermore, the apparent activation energy (E-a) of 1670 J/mol, the pre-exponential factor (A) of 3.7 x 10(-4), and the reaction series (n) value of 0.76 are obtained for the AEDA/E-51 system. The impact strength of AEDA/E-51 epoxy resin polymer is 7.82 kJ/m(2), tensile strength is 14.2 MPa, and bending strength is 18.92 MPa. The micromorphological results of the AEDA/E-51 system are consistent with the results of DSC test and mechanical properties test. Hence, this study provides theoretical support for the practical applications of AEDA as curing agent.

关键词： Time delay   Autonomous mechanical governor system   Two-parameter dynamics   Bifurcations   Multistability phenomena   Chaotic transition  

摘要： A deep understanding of the dynamical behavior in the parameter-state space plays a vital role in both the optimal design and motion control of mechanical systems. By combining the GPU parallel computing technique with two determinate indicators, namely the Lyapunov exponents and Poincare section, this paper presents a detailed study on the two-parameter dynamics of a mechanical governor system with different time delays. By identifying different responses in the two-parameter plane, the effect of time delay on the complexity of the evolutionary process is fully revealed. The path-following calculation scheme and time domain collocation method are used to explore the detailed bifurcation mechanisms. An interesting phenomenon that the number of intersection points of some periodic responses on the specified Poincare section differs from the actual period characteristics is found in classifying the dynamic behavior. For example, the commonly exhibited period-one orbit may have two or more intersection points on the Poincare section rather than one point. The variations of the basins of attraction are also discussed in the plane of initial history conditions to demonstrate the multistability phenomena and chaotic transitions.