轴承自供能监测的径向电磁式能量俘获建模与实验研究

无线网络和低功耗微电子技术的进步推动着设备健康监测技术的网联化和智能化发展.轴承作为旋转设备的关键部件,对国防、轨道交通、风电等重大装备的健康状态起到了非常重要的作用,实现轴承状态监测的微型化和自供能是装备智能化的重要技术基础.论文针对于轴承无线传感器网络的供能问题,提出了一种用于轴承自供能监测的径向电磁式旋转能量俘获建模方法,并通过引入环形Halbach永磁阵列增强了线圈中的磁场强度,提高了能量俘获系统的输出性能.基于磁荷理论和空间坐标变换给出了环形Halbach永磁阵列的径向磁场计算方法,进而利用电磁感应原理建立了电磁式旋转能量俘获系统的输出电压模型,仿真分析了不同参数对系统输出电压的影响.有限元仿真和不同转速下的实验结果验证了所建立模型预测输出电压的准确性,同时功率测试实验表明设计的俘能系统在1000 rpm转速下可实现81.2 mW的输出功率.     

Transient analysis of Cosserat rod with inextensibility and unshearability constraints using the least-squares finite element model

In this study, time-dependent fully discretized least-squares finite element model is developed for the transient response of Cosserat rod having inextensibility and unshearability constraints to simulate a surgical thread in space. Starting from the kinematics of the rod for large deformation, the linear and angular momentum equations along with constraint conditions for the sake of completeness are derived. Then, the α-family of time derivarive approximation is used to reduce the governing equations of motion to obtain a semi-discretized system of equations, which are then fully discretized using the least-squares approach to obtain the non-linear finite element equations. Newton׳s method is utilized to solve the non-linear finite element equations. Dynamic response due to impulse force and time-dependent follower force at the free end of the rod is presented as numerical examples.     

Formulation and numerical implementation of a constitutive law for concrete with strain-based damage and plasticity

A triaxial constitutive law for concrete within the framework of isotropic damage combined with plasticity is proposed in this paper. It covers typical characteristics of concrete like non-linear uniaxial compression and tension, bi- and triaxial failure criteria and dilatancy with a unified strain-based approach. Thus, this model is quite simple and especially suitable for strain-driven methods like common finite elements. It is complemented with a regularization method based on the crack band approach. A further issue is discussed with procedures for the model parameter determination for a wide range of concrete grades. The application of the model is demonstrated with typical benchmark tests for plain concrete.     

壁面加热湍流相干结构的子波分析实验研究

通过在平板湍流边界层沿流向固壁表面平行放置若干条通电加热的金属细丝,在平板表面形成沿展向周期性分布的温度场,利用该温度场引起的空气热对流,在湍流边界层近壁区域产生一组沿湍流边界层展向周期分布的大尺度流向涡结构,改变了平板湍流边界层中不同尺度结构及其能量分布。采用对壁湍流多尺度结构的子波分析表明,在湍流边界层近壁区域产生规则的流向涡结构将壁湍流各种尺度湍涡结构不规则的脉动有序地组织起来,抑制了壁湍流各种尺度湍涡结构脉动,特别抑制了能量最大尺度湍涡结构的脉动,减小由于湍流脉动引起的在湍流边界层法向和展向的动量和能量损耗,从而减小了湍流的阻力。     

悬停状态下无铰式旋翼动力学参数试验研究

旋翼结构参数及动力学参数对旋翼动力学特性有着重要影响。随着旋翼结构型式的不断更新,在旋翼设计中需要考虑的动力学参数也相应增加,从而使旋翼的动力学问题更加复杂化。本文通过在２米旋翼试验台上进行的试验,用测量桨叶频响函数和稳态响应的方法研究了悬停状态预锥角、预掠角和总距角等旋翼结构参数对桨叶固有特性及气动弹性稳定性的影响规律,并同计算结果进行了比较,得到了一些对旋翼设计有实用意义的结论     

Dynamics of Multi-Body Rotors: Numerical and Experimental FEM Analysis of the Scientific Earth Experiment Galileo Galilei Ground

Some small scientific satellites can be regarded as free, multi-body, supercritical and statorless rotors. Classical rotordynamics does not cover the dynamic behaviour and the stability analysis of such rotating systems, being focused on fixed rotors. Attitude dynamics usually deals with single rigid spacecrafts, sometimes equipped with flexible appendices like solar arrays or antennas. The case of the Galileo Galilei Ground (GGG) test facility is herewith analyzed through a numerical and experimental investigation on the dynamic behaviour of a fixed multi-body fast-spinning rotor in order to validate the design approach proposed for Galileo Galilei (GG) spacecraft.     

爆破震动信号的小波分析与HHT变换

以实测的爆破震动信号为例,分别应用小波分析和HHT(Hilbert-Huang Transform)变换从不同方面进行对比分析,讨论了爆破震动信号的特征提取和时频分布。结果表明：小波分析和HHT变换都是处理非平稳信号的两种好方法,都能很好地提取信号的主要特征信息和进行滤波、消噪。然而,小波分析存在选择小波基的困难,而HHT变换不需要预先选择基函数,其EMD（empirical mode decomposition）得到的IMF(intrinsic mode function)能反映原始信号的固有特性,通常具有实际物理意义;小波谱的能量在频率范围内分布较宽,而Hilbert能量谱能清晰地表明能量随时频的具体分布,大部分能量都集中在有限的能量谱线上;小波分析中时间、频率分辨率受Heisenberg测不准原理的限制,而HHT变换中时间分辨率不变且精度很高,其频率分辨率则可随信号内在的特性进行自适应调节。分析表明：HHT变换在分析非平稳信号时较小波分析更具适应性,在岩石中波的传播、衰减规律、结构动态响应特征和爆破震动破坏等研究中有着广阔的应用前景。     

Experimental validation of the tip asymptotics for a fluid-driven crack

This paper provides experimental confirmation of the opening asymptotes that have been predicted to develop at the tip of fluid-driven cracks propagating in impermeable brittle elastic media. During propagation of such cracks, energy is dissipated not only by breaking of material bonds ahead of the tip but also by flow of viscous fluid. Theoretical analysis based on linear elastic fracture mechanics and lubrication theory predicts a complex multiscale asymptotic behavior of the opening in the tip region, which simplifies either as or as power law of the distance from the tip depending on whether the dominant mechanism of energy dissipation is bond breaking or viscous flow. The laboratory experiments entail the propagation of penny-shaped cracks by injection of glycerin or glucose based solutions in polymethyl methacrylate (PMMA) and glass specimens subjected to confining stresses. The full-field opening is measured from analysis of the loss of intensity as light passes through the dye-laden fluid that fills the crack. The experimental near-tip opening gives excellent agreement with theory and therefore confirms the predicted multi-scale tip asymptotics.     

螺桨转子颤振涡动的一种算法

介绍螺桨转子系统颤振涡动的一种算法。本算法考察桨叶的振动变形，桨轴－支承系统的振动特性，以及螺转子的不平衡力。利用本算法对一模型螺桨转子和一实际螺桨转子进行了分析计算，对螺桨转子轴头动刚度、浆叶弹性变形、桨盘不平衡度等因素对螺桨转子系统颤振涡动的影响进行了分析，表明螺桨转子轴头动刚度下降时，螺浆发生颤振涡动的极限飞行速度下降。模型螺桨转子的计算结果与风洞试验结果相当吻合，证明本算法是正确的。     

Dynamic fracture of concrete compact tension specimen: Experimental and numerical study

Compared to quasi-static loading concrete loaded by higher loading rates acts in a different way. There is an influence of strain-rate and inertia on resistance, failure mode and crack pattern. With increase of loading rate failure mode changes from mode-I to mixed mode. Moreover, theoretical and numerical investigations indicate that after the crack reaches critical velocity there is progressive increase of resistance and crack branching. These phenomena have recently been demonstrated and discussed by O?bolt et al. (2011) on numerical study of compact tension specimen (CTS) loaded by different loading rates. The aim of the present paper is to experimentally verify the results obtained numerically. Therefore, the tests and additional numerical studies on CTS are carried out. The experiments fully confirm the results of numerical prediction discussed in O?bolt et al. (2011). The same as in the numerical study it is shown that for strain rates lower than approximately 50/s the structural response is controlled by the rate dependent constitutive law, however, for higher strain rates crack branching and progressive increase of resistance is observed. This is attributed to structural inertia and not the rate dependent strength of concrete. Maximum crack velocity of approximately 800 m/s is measured before initiation of crack branching. The comparison between numerical and experimental results shows that relatively simple modeling approach based on continuum mechanics, rate dependent microplane model and standard finite elements is capable to realistically predict complex phenomena related to dynamic fracture of concrete.     

Experimental Investigation of Dynamics and Bifurcations of an Impacting Spherical Pendulum

Since Newton first considered the motion of a spherical pendulum over 200 years ago, many researchers have studied its dynamic response under a variety of conditions. The characteristic of the problem that has invited so much investigation was that a spherical pendulum paradigms much more complex phenomena. Understanding the response of a paradigm gives an almost multiplicative effect in the understanding of other phenomena that can be modeled as a variant of the paradigm. The spherical pendulum has been used to damp irregular motion in helicopters and on space stations as well as for many other applications. In this study an inverted impacting spherical pendulum with large deflection was investigated. The model was designed to approximate an ideal pendulum, with the pendulum bob contributing the vast majority of the mass moment of inertia of the system. Two types of bearing mechanisms and tracking devices were designed for the system, one of which had low damping coefficient and the other with a relatively high damping coefficient. An experimental investigation was performed to determine the dynamics of an inverted, impacting spherical pendulum with large deflection and vertical parametric forcing. The pendulum system was studied with nine different bobs and two different base configurations. During the experiments, the frequency of the excitation remained between 24.6 and 24.9 Hz. It was found that sustained conical motions did not naturally occur. The spherical pendulum system was analyzed to determine under what conditions the onset of Type I response (a repetitive motion in which the pendulum bob does not traverse through the apex. The bob strikes the same general area of the restraint without striking the opposite side of the restraint.), sustainable Type II response (this is the repetitive motion in which the pendulum bob traverses through the apex. The bob strikes opposite sides of the restraint.), and mixed mode response (motion in which the pendulum bob randomly strikes either the same area of the restrain or the opposite side of the restraint) occurred.     

Porous Burner for Application in Stationary Gas Turbines: An Experimental Investigation of the Flame Stability, Emissions and Temperature Boundary Condition

A possible solution to ensure the stability of lean premixed flames over an extended operational range is to provide enhanced heat recirculation by employing porous inert material. A potential application of the porous burner concept is the generation of the pilot flames based on lean premixed combustion which is a prerequisite for ultra low NO_x emission. For the optimization of the porous burner an experimental study investigating flame stability and emissions was conducted. In particular axial concentration profiles of the stable species and temperature within the porous burner reaction zone are presented. Furthermore the surface temperature of the burner having a 10 PPI SiSiC material was measured for various operating conditions using two colour pyrometry.     

Effects of tire inflation pressure and tractor velocity on dynamic wheel load and rear axle vibrations

The objective of this study was to evaluate the effects of agricultural tire characteristics on variations of wheel load and vibrations transmitted from the ground to the tractor rear axle. The experiments were conducted on an asphalt road and a sandy loam field using a two-wheel-drive self-propelled farm tractor at different combinations of tractor forward speeds of approximately 0.6, 1.6 and 2.6 m/s, and tire inflation pressures of 330 and 80 kPa. During experiments, the vertical wheel load of the left and right rear wheels, and the roll, bounce and pitch accelerations of the rear axle center were measured using strain-gage-based transducers and a triaxial accelerometer. The wavelet and Fourier analyses were applied to measured data in order to investigate the effects of self-excitations due to non-uniformity and lugs of tires on the wheel-load fluctuation and rear axle vibrations. Values for the root-mean-square (RMS) wheel loads and accelerations were not strictly proportional and inversely proportional to the forward speed and tire pressure respectively. The time histories and frequency compositions of synthesized data have shown that tire non-uniformity and tire lugs significantly excited the wheel load and accelerations at their natural frequencies and harmonics. These effects were strongly affected by the forward speed, tire pressure and ground deformation.     

鸭式旋翼/机翼飞机悬停及小速度前飞气动干扰实验研究

鸭式旋翼/机翼飞机是一种新概念可垂直起降高速飞行器,为了解该飞机在悬停及小速度前飞时的全机气动干扰特性,在南京航空航天大学开口风洞中进行了飞机全机气动力实验,实验采用多台测力天平分别测量主机翼和机身的气动力.结果表明,悬停时受主机翼高速旋转产生的下洗尾流影响,机身产生了较大的法向力和低头力矩;前飞时下洗尾流对机身的法向力和俯仰力矩有比较严重的干扰,对滚转力矩和偏航力矩干扰较小,对侧向力有一定影响.实验结果为飞机的飞行动力学特性研究以及控制律设计提供了参考.＃     

芳纶纤维约束混凝土的力学性能研究

通过对比普通混凝土试件和用芳纶纤维约束混凝土试件的抗压、抗劈裂和抗折(弯拉)试验，研究了芳纶纤维约束混凝土的基本力学性能，定量地得到了芳纶纤维对混凝土试件承载力的加强效果。     

孔眼流入对水平井中流动影响的实验研究

设计并建立了水平井筒变质量流动模拟实验装置。对具有射孔完井的水平井筒变质量流动进行了实验研究,利用先进的数据采集系统获取了大量的实验数据。对水平井井筒单孔眼段流动阻力损失分析可知,流动阻力由三部分组成：管壁摩擦阻力、加速损失和混合损失。对实验数据进行处理得出了混合损失和主流流速与孔眼流速之间的关系。对于一定的主流流速,混合损失随孔眼流速的增大而增大,同时,对于一定的孔眼流速,混合损失随主流流速的增大而增大,此时孔眼的流入对水平井筒中的流动造成的影响比较显著。孔眼的流入增加了井筒中流动的复杂性。对实验数据进行的回归结果表明,在本实验条件和范围内,主流流速和孔眼流速是造成混合损失的主要因素。     

Non-linearities in rotation and thickness deformation in a new third-order thickness deformation theory for static and dynamic analysis of isotropic and laminated doubly curved shells

A geometrically non-linear theory is developed for shells of generic shape allowing for third-order thickness and shear deformation and rotary inertia by using eight parameters; geometric imperfections are also taken into account. The geometrically non-linear strain–displacement relationships are derived retaining full non-linear terms in all the 8 parameters, i.e. in-plane and transverse displacements, rotations of the normal and thickness deformation parameters; these relationships are presented in curvilinear coordinates, ready to be implemented in computer codes. Higher order terms in the transverse coordinate are retained in the derivation so that the theory is suitable also for thick laminated shells. Three-dimensional constitutive equations are used for linear elasticity. The theory is applied to circular cylindrical shells complete around the circumference and simply supported at both ends to study initially static finite deformation. Both radially distributed forces and displacement-dependent pressure are used as load and results for different shell theories are compared. Results show that a 6 parameter non-linear shell theory is quite accurate for isotropic shells. Finally, large-amplitude forced vibrations under harmonic excitation are investigated by using the new theory and results are compared to other available theories. The new theory with non-linearity in all the 8 parameters is the only one to predict correctly the thickness deformation; it works accurately for both static and dynamics loads.     

复合材料层合板的数值分析与实验

本文用云纹干涉法和逐层分析有限元法研究了Gr/PEEK[0/45－45/90]2S复合材抖层合板的变化特征,在层与层交接处,特别是0°与45°和一45°与90°层交接处,位移存在较明显的变化,说明这两种层接处有比较大的层间应力,是脱层的易发处.计算与实验结果都证实了这种变形特征．     

An Experimental Investigation of Deformation and Fracture of Nacre–Mother of Pearl

Nacre, also known as mother-of-pearl, is a hard biological composite found in the inside layer of many shells such as oyster or abalone. It is composed of microscopic ceramic tablets arranged in layers and tightly stacked to form a three-dimensional brick wall structure, where the mortar is a thin layer of biopolymers (20–30 nm). Although mostly made of a brittle ceramic, the structure of nacre is so well designed that its toughness is several order of magnitudes larger that the ceramic it is made of. How the microstructure of nacre controls its mechanical performance has been the focus of numerous studies over the past two decades, because such understanding may inspire novel composite designs though biomimetics. This paper presents in detail uniaxial tension experiment performed on miniature nacre specimens. Large inelastic deformations were observed in hydrated condition, which were explained by sliding of the tablets on one another and progressive locking generated by their microscopic waviness. Fracture experiments were also performed, and for the first time the full crack resistance curve was established for nacre. A rising resistance curve is an indication of the robustness and damage tolerance of that material. These measurements are then discussed and correlated with toughening extrinsic mechanisms operating at the microscale. Moreover, specific features of the microstructure and their relevance to associated toughening mechanisms were identified. These features and mechanisms, critical to the robustness of the shell, were finely tuned over millions of years of evolution. Hence, they are expected to serve as a basis to establish guidelines for the design of novel man-made composites.     

铝液在多孔介质中渗流过程的模拟试验研究

选择低压渗流法制备泡沫铝的工艺过程为模拟对象,根据相似原理,在有机玻璃模型中用液体作为流体,对铝液在多孔介质中的低压向上渗流过程进行了模拟试验研究。试验表明,在低压渗流制备泡沫铝的过程中,原型的渗流液面是以平面沿铅垂方向向上推进的,位移和时间的关系满足四次方根规律;渗流过程中某一时间t的雷诺数、阻力系数和沿程损失可用相应的公式计算;渗流过程中,外加渗流气压的最佳值为0.04kPa,高于该值的外加渗流气压对于渗流时间的影响不大。实验还将模拟实验得到的结果与原型进行了比较,模型的充填时间与原型的充填时间一致性良好,证实了本实验结果的正确性。