Mechanical characterization of jute-basalt hybrid composites with graphene as nanofiller

Natural fibre composites, due to their biodegradable and eco friendly nature, are being explored for potential application in wide areas. But their strengths need to be enhanced. Hybridization of the natural fibres with incorporation of nanofillers helps to tailor the properties of nanofillers, and individual fibers and enhance the properties of resultant composite. The present work aims to explore the mechanical propertis of jute-basalt hybrid composites by incorporating graphene nanofillers of varying concentrations. Basalt, jute and jute-basalt hybrid composites with varying concentrations of graphene (0 wt%, 0.2 wt%, 0.4 wt%, 0.6 wt%, 1 wt%) are prepared. Effect of hybridization of different fibers and influence of graphene on mechanical properties are analyzed. The effect of nature of top and bottom laminates on mechanical properties is also observed. Maximum improvement in tensile strength, flexural strength and hardness is found to be 13 %, 29 % and 55 %, respectively, with hybrid composite containing 1 wt.% graphene compared to hybrid composite without graphene. Impact strength is found to be highest for hybrid composite containing 0.4 wt.% graphene with 17 % increase compared to hybrid composite without graphene.

     

膨胀石墨填料密封机理研究

介绍了膨胀石墨填料材料的特点、密封机理和性能，并与其他种类填料作了比较分析。     

基于PSO的波纹管结构完整性设计

作为工程上应用广泛的波纹管,其结构完整性设计即是在满足疲劳寿命、强度、稳定性、刚度、生产工艺及补偿量的条件下,设计合理的波纹管结构参数.以单位重量下波纹管的补偿量最大为目标,建立波纹管结构完整性优化设计模型,采用优化领域的最新研究方法一粒子群算法(PSO)实现其结构参数优化设计.并给出了具体应用算例,其结果显示使用方法设计出的波纹管性能比在用的波纹管性能更佳,表明提出的波纹管结构完整性优化设计模型正确,使用PSO法求解波纹管结构优化设计高效、可行.     

The mechanism of ripple generation on sandblasted ductile solids

Studies of the erosion rate-incidence angle function and the characteristic parameters of wavelength, amplitude, facet angle and velocity of well-developed ripple patterns on sandblasted copper are reported. A microscope investigation of the morphology of individual impact craters and their integration to form initially a random collection of depressions and ridges and gradually a phase-locked repetitive ripple pattern is also presented. Both areas of study suggest that earlier theories of the erosion of ductile solids are open to doubt, and a new model of surface morphology generation based upon the production of embrittled ridges and wave crests which are induced by plastic flow and ablated by impact is proposed.     

Pre-compression volume on flow ripple reduction of a piston pump

Axial piston pump with pre-compression volume（PCV） has lower flow ripple in large scale of operating condition than the traditional one. However, there is lack of precise simulation model of the axial piston pump with PCV, so the parameters of PCV are difticult to be determined. A finite element simulation model for piston pump with PCV is built by considering the piston movement, the fluid characteristic（including fluid compressibility and viscosity） and the leakage flow rate. Then a test of the pump flow ripple called the secondary source method is implemented to validate the simulation model. Thirdly, by comparing results among the simulation results, test results and results from other publications at the same operating condition, the simulation model is validated and used in optimizing the axial piston pump with PCV. According to the pump flow ripples obtained by the simulation model with different PCV parameters, the flow ripple is the smallest when the PCV angle is 13~, the PCV volume is 1.3 ~ I0-4 m3 at such operating condition that the pump suction pressure is 2 MPa, the pump delivery pressure 15 MPa, the pump speed 1 000 r/min, the swash plate angle 13~. At the same time, the flow ripple can be reduced when the pump suction pressure is 2 MPa, the pump delivery pressure is 5 MPa,15 MPa, 22 MPa, pump speed is 400 r/min, 1 000 r/rain, 1 500 r/rain, the swash plate angle is ll~, 13~, 15~ and 17~, respectively. The finite element simulation model proposed provides a method for optimizing the PCV structure and guiding for designing a quieter axial piston pump.     

Feedforward suppression of force ripple based on a simplex-optimized dither signal

This paper presents the design and realization of a feedforward dither signal to reduce the force ripple in an iron-core permanent magnet linear motor (PMLM). A composite control structure is used, consisting of three components: a simple feedforward component, a PID feedback component, and a ripple compensator (RC). The first two components are designed based on a dominant linear model of the motor. The dither signal is generated based on a signal model which is identified using a multidimensional simplex downhill method. In this way, a simple approach is available to eliminate or suppress the inherent force ripple, thus facilitating smooth precise motion while uncompromising on the maximum force achievable. Real-time experimental results verify the effectiveness of the proposed scheme for high precision motion trajectory tracking.     

A kinematic wave description of ripple development on sand-blasted ductile solids

The evolution of a sand-blasted solid surface through a random periodic structure to a coherent moving transverse wave or ripple structure is discussed in general terms by using the theory of kinematic waves. In such wave processes the local velocity is a function of local parameters such as elevation and slope, and it is shown how a stable ripple structure may ensue in which the component velocities of the wave are minimized with respect to neighbouring values.     

Synthesis,characterization and tribological properties of Cu/reduced graphene oxide composites

In this paper, nano-copper/reduced graphene oxide (Cu/rGO) composites were synthesized by the facile one step in-situ reduction method. The as-prepared Cu/rGO composites were characterized by means of transmission electron microscopy (TEM), X-ray photoelectron spectroscope (XPS), X-ray diffraction (XRD) and Raman. Mechanism of reduction and growth of Cu/rGO composites were also discussed. The friction and wear properties of oleic acid (OA) modified composites as additives in poly-alpha-olefin (PAO) were investigated using four-ball wear tester.     

基于鲁棒迭代学习控制的永磁同步电机转矩脉动抑制

为了提高永磁同步电机转速伺服系统的性能,抑制转矩脉动对控制系统的影响,提出了滑模控制与迭代学习控制相结合的鲁棒迭代学习控制方法(RILC)。设计了迭代学习控制器抑制周期性转矩脉动,提出了滑模控制器提高系统的抗扰动性能,保证系统强鲁棒性及响应快速性。实验结果显示,电机以900r/min的速度运行时,采用鲁棒迭代学习控制可将速度脉动6次谐波幅值由0.89降低到0.56;加入0.5N·m的负载扰动后,转速波动最大值为22r/min,比PI-迭代学习控制法得到的值减小了1.8%。电机以60r/min运行时,采用鲁棒迭代学习控制可将速度脉动6次谐波幅值由4.87降低到0.45;加入0.5N·m的负载扰动的,转速波动最大值为24r/min,比PI-迭代学习控制法得到的值减小了23%。得到的结果表明,鲁棒迭代学习控制方法可有效抑制转矩脉动,同时可提高永磁同步电机转速伺服系统的鲁棒性和动态响应性能。     

无位置传感器BLDCM换相转矩脉动抑制的研究

针对无刷直流电机换相时产生转矩脉动给系统带来的不利影响,提出了一种无位置传感器无刷直流电机换相时抑制转矩脉动的三相PWM调制技术.利用反电势过零点法确定无刷直流电机转子位置信息从而获知电机转速.在换相开始后通过检测与功率管并联支路电流续流情况确定三相PWM调制时间.通过简单的比较电路实现了反电势过零点与换相期间的电流续流情况检测,与已有方法相比,节省了系统资源,提高了系统可靠性,且无需电机准确参数.实验结果表明:在无位置传感器情况下,无刷直流电机在换相期间转矩脉动得到了明显抑制.     

基于自抗扰控制的无刷直流电机换相转矩脉动抑制的研究

针对无刷直流电机在运动中会产生转矩脉动且转矩脉动会影响无刷直流电机运行的稳定性和可靠性的问题,结合现代控制理论,研究了无刷直流电机的数学模型,设计了一种基于自抗扰控制器的无刷直流电机换相转矩脉动抑制的方法。通过降低无刷直流电机的转矩脉动并且结合DSP高速运算处理器实现了其算法的控制,更好地提高了其稳态性能。采用自抗扰控制技术对无刷直流电机的换相转矩脉动进行了抑制。通过消除转速响应的超调,扩张状态观测器检测系统的相电流脉动以及用非线性状态反馈控制率对检测到的电流脉动误差值进行补偿抵消,以达到了抑制相电流脉动的效果,从而抑制了转矩的脉动。通过实验验证,自抗扰控制器比PI控制能够较好的抑制直流电机的换相转矩脉动,从而能够提高电机在运动中的稳定性。     

定子分段式永磁直线同步电机速度波动抑制方法研究

为了解决定子分段式永磁直线同步电机(PMLSM)存在的因磁阻效应、负载阻力、摩擦力、参数摄动以及动子进出定子时耦合面积变化所造成的控制性能下降的难题,根据动子和定子的耦合状态,提出一种在完全耦合阶段和动子退出定子阶段的分段式控制方法。首先,在动子与定子完全耦合阶段采用改进滑模控制器减小推力波动导致的速度波动,再通过加入扰动观测器降低滑模切换项所带来的抖振现象;在动子退出定子阶段,建立相关电磁参数与动子位置的函数关系,实时补偿由耦合面积变化引起的动子失速,使动子速度在退出时接近给定值。仿真及实验结果表明动定子完全耦合过程中的速度稳态误差为0.005 m/s,收敛时间为0.3 s,动子退出定子阶段的速度波动不超过0.04 m/s,满足定子分段式PMLSM用于长行程自动运输系统对平稳性及快速性的需求。     

直流力矩电机力矩波动的自适应补偿控制

为解决伺服系统在低速状态下其电机力矩波动影响速度稳定性的问题,提出了一种基于自适应补偿的控制策略。从电机结构出发,分析了电机力矩波动产生的机理,建立了力矩波动的数学模型,提出了基于鲁棒自适应的控制策略。系统控制器由两部分组成:超前-滞后校正用于保证系统的名义稳定性和鲁棒性;自适应补偿控制则采用最小二乘法在线辨识力矩波动,并给予自适应补偿。实验结果显示:与仅使用超前-滞后方法相比,当采用自适应补偿时,速度波动的峰-峰值由4.21%下降到1.77%,均方根值由0.97%下降为0.39%,得到的结果说明提出的方法能够有效降低电机力矩波动对速度稳定度的不利影响。     

宏指令编程在波纹法兰加工中的应用

针对智能仪表关键元件——波纹法兰数控加工程序的编写．介绍宏指令的变量、结构及功能，重点论述宏指令参数化编程在系列波纹法兰加工中的应用，给出较为通用的加工程序，简化系列波纹法兰加工中程序编制及调试的辅助工作，有效提高零件加工效率，对于许多系列零件加工程序的编写具有借鉴和指导意义。     

Torque ripple reduction of brushless DC motor based on adaptive input-output feedback linearization

Torque ripple reduction of Brushless DC Motors (BLDCs) is an interesting subject in variable speed AC drives. In this paper at first, a mathematical expression for torque ripple harmonics is obtained. Then for a non-ideal BLDC motor with known harmonic contents of back-EMF, calculation of desired reference current amplitudes, which are required to eliminate some selected harmonics of torque ripple, are reviewed. In order to inject the reference harmonic currents to the motor windings, an Adaptive Input-Output Feedback Linearization (AIOFBL) control is proposed, which generates the reference voltages for three phases voltage source inverter in stationary reference frame. Experimental results are presented to show the capability and validity of the proposed control method and are compared with the vector control in Multi-Reference Frame (MRF) and Pseudo-Vector Control (P-VC) method results.     

重载交流电动轮扭矩脉动的影响及改善

针对重载电动轮对输入转矩脉动敏感的缺点,提出减小电动轮总成中感应牵引电动机输出转矩脉动的方法.描述感应电动机的矢量控制数学模型,并应用Matlab/Simulink软件建立传动系统仿真模型.分析矢量控制中滞环脉冲发生器环宽对电动机转矩脉动的影响,以及磁链给定值对电动机输出转矩脉动的影响.仿真结果表明:通过以上方法可以较好地改善电动机转矩脉动问题,改善电动轮的使用性能.     

有源纹波补偿电流平方降压型LED驱动电路

LED理想的驱动方式是恒流驱动,在输出端常采用电解电容进行滤波,但电解电容的寿命与LED寿命不匹配;峰值电流控制是实现恒流驱动的常用控制方式,但该方式仅控制了流过LED的峰值电流,而未精确地控制其平均电流,这对LED的发光效率、可靠性等都有较大的影响。为解决以上问题,将省略了滤波电容的有源纹波补偿电路结构与电流平方控制技术应用于LED驱动电路中,基于电流平方控制对平均电流的控制,以及有源纹波补偿电路对纹波电流的补偿,开展了该驱动电路工作原理的研究及分析,并基于PSIM6．0进行了仿真验证,最后进行了实物仿真。仿真及研究结果表明：通过电流平方控制可以精确地控制平均电流,并且有源补偿环节可以全补偿由于省略滤波电容所带来的电流纹波,使流过LED的电流为近似直流。     

基于石墨烯太赫兹调制器的研究

利用石墨烯的电导率可以通过电压调节的特性,研究了一种基于单层石墨烯的太赫兹调制器。为了提高太赫兹-石墨烯相互作用强度,调制器采用一种石墨烯-金属复合结构。全波电磁数值仿真结果表明,在反射工作模式下,该器件在3.5 THz的调制深度大于90%。采用平面半导体工艺,实现了调制器原型器件,并对其反射谱进行了测试,实验数据与仿真结果相符,这为以后实现高质量的太赫兹调制器奠定了基础。     

Microspectroscopy on single domains of phase-separated monolayers

A versatile and inexpensive, but fully equipped apparatus is presented, which enables detailed optical studies on amphiphilic molecules at the liquid-gas interface. Structural and spectroscopic information, particularly in small areas of single domains of phase-separated monolayers, can be achieved by combination of this miniaturized Langmuir trough and spectralphotometer microscope. The potential of this apparatus is demonstrated with some measurements on a diyne-substituted polymerizable lipid analogue at the air-water interface.