非线性吸振器的靶能量传递及参数设计

首先通过研究两个非线性耦合振子,阐明了非线性吸振器具有对初始能量的选择性.即吸振系统在一定带宽的初始能量(主结构中初始能量的大小)下具有很强的吸振能力,而随初始能量偏离一定值,吸振器耗散能量的能力有所减弱.随后提出,在不增加吸振器质量的前提下,采用两自由度的非线性吸振器不仅可以使得能量在吸振器中的耗散加快,靶能量传递效果更好,而且在保证吸振效率的同时,吸振器对于初始能量的有效带宽显著增加.给出了两自由度非线性吸振器的质量、阻尼、刚度等参数的设计方法,最后采用数值仿真验证了上述结论.     

非线性耦合振子间的靶能量传递研究:保守系统中的完全能量传递

研究了两自由度非线性耦合振子间的靶能量传递现象。第一部分基于非线性耦合振子内在保守系统的慢变动力学方程,推导出了该结构的保守系统中两振子间完全能量传递所需要的条件。经数值仿真验证,本部分所推导的方程可准确计算两振子间完全能量传递所需的初始能量,并适用于强非线性系统。     

非线性能量阱技术研究综述

结构振动问题普遍存在于各个工程领域,有效地抑制结构振动对提高零件的加工质量、延长机械的使用寿命以及增加结构的安全性与舒适度至关重要。非线性能量阱(NES)以其轻质,鲁棒性强,减振频带宽等优点,在非线性消能减振方面具有良好的应用前景;介绍了非线性能量阱的基本概念、发展与研究现状,综述了非线性能量阱在土木工程、航空航天领域、机械领域、生命线工程以及能量采集中的应用进展。在此基础上,对非线性能量阱的设计与应用进行了评述,指出其在工程应用中的优势与不足,并针对实际工程可能遇到的问题提出了建议,对非线性能量阱技术的后续研究进行了展望。     

可调永磁双稳态非线性能量阱及应用研究

为了实现对主系统的宽频振动抑制,研发了一种可调的双稳态非线性能量阱(BNES)。介绍了BNES的结构和工作原理;其次分析了BNES的刚度构成以及其非线性动力学特性,并建立了悬臂梁-BNES系统动力学微分方程;采用数值方法探究了不同磁铁间距时的BNES对悬臂梁瞬态时域振动抑制效果和稳态频域的宽频抑振能力;对两组不同的悬臂梁系统进行了实验,验证了不同磁铁间距时的双稳态非线性能量阱的宽频振动抑制能力。研究结果表明,该BNES对悬臂梁的瞬态时域响应和稳态频域响应都有很好的振动抑制能力。     

非线性能量阱刚度优化计算与振动台试验

Nonlinear energy sink (NES) was proposed and its main feature to mitigate vibrations in a broad frequency band range was explored here.Firstly,the expressions for the relation between frequency and energy under 1∶1 resonance were derived using the analytical method.According to the expressions,the frequency-energy plot was drawn.This plot intuitively revealed that when a NES is attached to a linear oscillator,its vibration frequency relative to the linear oscillator has a direct relation to the energy level of the system.Then,the formulas for the relationships among the stiffness of NES and energy,frequencies and modal shapes of linear oscillators were derived with the analytical method in the model space of a multi-DOF vibration system.The optimal solution to NES stiffness was calculated with these formulas under a certain energy level of the vibration system.Based on the optimal stiffness calculation method,the NES vibration control test was designed and the corresponding shaking table tests were conducted.To test the wide frequency vibration control features of NES,a set of springs with different stiffness were employed and dynamic properties of the controlled frame were changed through adding the mass of the frame.The test results demonstrated that NES has a good broad frequency band vibration control effect,it can work well even though its stiffness deviates from the optimal value or there are some changes in dynamic features of the controlled target.     

Robust design optimization of nonlinear energy sink under random system parameters

Generally, in designing nonlinear energy sink (NES), only uncertainties in the ground motion parameters are considered and the unconditional expected mean of the performance metric is minimized. However, such an approach has two major limitations. First, ignoring the uncertainties in the system parameters can result in an inefficient design of the NES. Second, only minimizing the unconditional mean of the performance metric may result in large variance of the response because of the uncertainties in the system parameters. To address these issues, we focus on robust design optimization (RDO) of NES under uncertain system and hazard parameters. The RDO is solved as a bi-objective optimization problem where the mean and the standard deviation of the performance metric are simultaneously minimized. This bi-objective optimization problem has been converted into a single objective problem by using the weighted sum method. However, solving an RDO problem can be computationally expensive. We thus used a novel machine learning technique, referred to as the hybrid polynomial correlated function expansion (H-PCFE), for solving the RDO problem in an efficient manner. Moreover, we adopt an adaptive framework where H-PCFE models trained at previous iterations are reused and hence, the computational cost is less. We illustrate that H-PCFE is computationally efficient and accurate as compared to other similar methods available in the literature. A numerical study showcasing the importance of incorporating the uncertain system parameters into the optimization procedure is shown. Using the same example, we also illustrate the importance of solving an RDO problem for NES design. Overall, considering the uncertainties in the parameters have resulted in a more efficient design. Determining NES parameters by solving an RDO problem results in a less sensitive design.     

Turbulent energy transfer in a nonlinear isotropic fluid

In this paper we consider a hypothetical non-Newtonian fluid, in which the usual Newtonian constitutive relationship is perturbed by the presence of a small quadratic term. It is argued that this model is worth studying because (a) such non-linearities are believed to lead to anomalous turbulent effects, (b) it is a necessary preliminary to a full treatment of a more realistic model, which takes account of fluid anisotropy. The equations of motion are derived in the Fourier wavenumber-time domain and specialised to the case of isotropic turbulence. Recent developments in the theory of turbulence are used to obtain a closed equation for the energy spectrum and this is solved for the dissipation-range energy spectrum. It is concluded that the inertial transfer of turbulent energy is reduced in such a way that the spectrum contains more energy, but falls off more rapidly, than in the Newtonian case.     

高层结构附加轨道非线性能量阱减振性能研究

轨道非线性能量阱(Track Nonlinear Sink,轨道NES)是一类被动减振控制装置,通过附加质量块沿轨道运动提供非线性回复力,以达到降低主体结构响应的目的。对轨道NES的回复力和控制系统的运动方程进行了理论分析和公式推导。对附加于32自由度主体结构的轨道NES进行了参数优化,优化后的轨道NES减振性能良好,并对装置刚度的变化具有较高的鲁棒性,但对装置阻尼变化较敏感。基于此问题,提出了单边碰振轨道非线性能量阱(Single-sided Vibro-impact Track Nonlinear Energy Sink,SSVI轨道NES),并考察了SSVI轨道NES装置刚度和阻尼同时发生变化时的减振性能。结果表明SSVI轨道NES能够有效降低结构响应,并同时具有良好的NES刚度和阻尼鲁棒性。     

Mass transfer in the mechanical mixing of heterogeneous systems

The influence of mixing on the kinetics and intensity of mass transfer is examined for dissolution and extraction in fluid-solid systems.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 42, No. 5, pp. 773–779, May, 1982.     

Variational solution of equation of nonlinear mass and energy transfer

The use of a variational principle of Hamilton type is considered for problems of nonlinear mass transfer in a semibounded plate with constant and variable diffusional properties.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 33, No. 4, pp. 671–677, October, 1977.     

多源激励下冷连轧F5轧机振动问题研究

研究了热轧过程机架间运动板带动力学特征及其影响因素。基于热轧过程板带张力形成机理,考虑机架间板带张力建立了动态张力模型;同时,考虑热轧机活套辊对运动板带的支撑作用,基于Hamilton理论建立了运动板带等效运动梁模型,并基于四阶Galerkin截断法对偏微分方程进行离散化,得到系统四阶常微分方程组。仿真分析机架间板带张力、速度和活套辊支承刚度对运动板带动力学特性的影响,以及运动板带在辊系振动引发的速度摄动下振动特征和影响规律。结果表明：张力、板带速度和活套支撑辊刚度均影响板带动力学模态特征,且活套辊支撑作用可降低板带振动幅值;在热轧工艺范围内,调整板带张力和速度对运动板带的稳定性影响不大;辊系振动造成板带运动速度呈摄动特征,且摄动频率和幅值与板带振动强度关系密切。该研究对热轧过程机架间运动板带稳定性分析和活套控制设计提供参考。

     

A nonlinear mechanism of the energy transfer by a perturbation front in the course of local high-energy loading

The features of perturbation propagation in a copper crystal grain under local high-energy loading conditions were studied. The process was studied by method of molecular dynamics using multiparticle model potentials calculated within the framework of the embedded atom approximation. It is shown that a nonlinear solitary pulse is formed in the crystal, which is capable (in contrast to the case of a linear perturbation) of transferring the energy at a high density over relatively large distances. The energy transfer range depends both on the area and on the rate of local loading.     

Choice of sink for air conditioning systems

This Paper presents general correlations to estimate the power demand of different conventional air conditioning (A/C) systems operating under varied climatological conditions. The results have been applied to estimate the peak power demand and annual energy consumption. As a case study, the analysis is applied to Kuwaiti buildings for quantitative assessments using a unit peak cooling load (1 kW_c). Contrary to general understanding and practice the results strongly favour the use of water-cooled systems for both the residential and the non-residential types of buildings.     

Molecular topology in ethylene copolymers studied by means of mechanical testing

The molecular topology of melt-crystallized ethylene-1-butene copolymers has been investigated by means of mechanical testing with the aid of suitable models. The number of regular folds between two consecutive interlamellar tie molecules has been estimated by means of a theoretical relationship of the tensile modulus as a function of temperature. In addition, the molecular weight between entanglements of the copolymers has been determined from an analysis of the post-yield strain-hardening, assuming an ideal network behaviour. It has been shown that the regular folded chain macroconformation turns gradually into a fringed micellar macroconformation as the co-unit concentration increases. The entanglement density increases in parallel. These results confirm the conclusion of a previous work stating that the rejection of the co-units within the amorphous phase disturbs the basic chain folding mechanism of crystallization and hampers the reeling-in motion of the chains from the melt on to the growth surfaces. Criticisms of the models have been developed taking into account some inconsistent aspects with regard to the experimental data.     

Spectrally resolved frequency domain analysis of multi-fluorophore systems undergoing energy transfer

Complex systems of fluorophores undergoing energy transfer can exhibit a variety of anomalous lifetime behavior when probed with frequency domain methods. When presented in traditional apparent lifetime format the data from such systems can exhibit "nodal" behavior in which the computed lifetime approaches +/-infinity. The location of the nodes is system and frequency dependent. In addition, simpler systems, not undergoing energy transfer, show ill behavior in the region of zero lifetime (tau(m)) and long lifetime (tau(pi)) due to noise in typical measurements. Here, we systematically investigate systems of multiple fluorophores with and without energy transfer to provide insight into frequency domain investigations of complex systems of fluorophores. The results of simulations are compared to data collected from a multi-fluorophore system designed to exhibit fluorescence resonance energy transfer (FRET) using imaging spectroscopic fluorescence lifetime imaging microscopy (ISFLIM). The results are applicable to both cuvette and imaging arrangements.     

Heat transfer enhancement in magnetic cooling by means of magnetohydrodynamic convection

In this work, we analyze the potential of magnetohydrodynamic (MHD) convection to increase heat transfer during magnetic cooling. To do this, we consider a section of an active magnetic regenerator, namely a flat gadolinium plate, immersed in an initially stagnant heat transfer fluid (NaOH) which is placed in a cuboid glass cell. To create the MHD flow, a small electric current is injected by means of two electrodes and interacts with the already present magnetic field. As a result, a Lorentz force is generated, which drives a swirling flow in the present model configuration. By means of particle image velocimetry and Mach–Zehnder interferometry, the flow field and its impact on the heat transfer at the gadolinium plate are analyzed. For the magnetization stage, we show that a heat transfer enhancement by about 40% can be achieved even with low currents of 3 mA.