海洋平台对随机非线性波浪力的动力响应

本文系统地阐述了固定式海洋结构在考虑波浪与结构相互作用情况下的随机动力分析原理·问题的关键在于对波浪力中的非线性阻力项进行线性化,并使耦合的广义阻尼矩阵对角化,为此运用了统计等效线性化方法和迭代方法等,最后使问题归结为若干个独立的线性化的随机微分方程,而方便地予以解决。根据本文原理编成了SELIM和SELIM-1程序。经试用,获得满意的计算结果。七个自由度的算例只经过二、三次迭代即可使迭代误差小于百分之五。     

Experimental Setup and Standardization of a Continuous Flow Stable Isotope Mass Spectrometer for Measuring Stable Isotopes of Carbon,Nitrogen and Sulfur in Environmental Samples

We present here the experimental setup and standardization of a newly acquired stable isotope ratio mass-spectrometer (Isoprime 100, Isoprime^® UK) coupled with elemental analyzer (Pyrocube, Elementar^®-Germany) in a continuous flow mode, for the measurements of C, N and S isotopes in a variety of natural as well as synthetic organics and sulfur containing solid samples. We have calibrated our instrument using a suite of certified international standards supplied by International Atomic Energy Agency Vienna and cross-checked against several in-house laboratory standards used by other institutions of international repute. A synthetic organic compound Sulfanilamide was continuously used along with international standards to develop an in-house internal laboratory standard for the accurate and precise isotopic measurements. Important components contributing to the overall uncertainty of the isotopic measurements such as blank contributions, amount effect and response of mass-spectrometric current against thermal conductivity detector were performed using several aliquots of ε-Amino-n-caproic acid and sulfanilamide (in-house) standards. Both short and long term variabilities in the measure isotopic data were assessed using our in-house laboratory standard Sulfanilamide. Overall estimated uncertainties of C, N and S isotopic measurements are better than 0.2, 0.2 and 0.3 ‰, respectively; which are well within the recommended limits of aforementioned isotopic data.     

Bamboo-Inspired Structurally Efficient Materials with a Large Continuous Gradient

Because of its light weight and high strength, bamboo is used in many applications around the world. Natural bamboo is built from fiber-reinforced material and exhibits a porous graded architecture that provides its remarkable mechanical performance. This porosity gradient is generated through the unique distribution of densified vascular bundles. Scientists and engineers have been trying to mimic this architecture for a very long time with much of the work focusing on the effect of fiber reinforcement. However, there still lacks quantitative studies on the role of pore gradient design on mechanical properties, in part because the fabrication of bamboo-inspired graded materials is challenging. Here, the steep and continuous porosity gradient through an ingenious cellular design in Moso bamboo is revealed. The effect of gradient design on the mechanical performance is systematically studied by using 3D-printed models. The results show that not only the magnitude of gradient but also its continuity have a significant effect. By introducing a continuous and large gradient, the maximum flexural load and energy absorption capability can be increased by 40% and 110% when comparing to the structure without gradient. These bamboo-inspired cellular architectures can offer efficient solutions for the design of damage tolerant engineering structures.     

Characterization of a Polycrystalline Material with Laser-Excited Nonlinear Surface Acoustic Wave Pulses

High-amplitude nonlinear surface acoustic waves (SAWs) generated by laser pulses were observed in polycrystalline material (stainless steel), and the nonlinear acoustic parameters were evaluated. The velocities of bulk waves and the elastic moduli of the second order were determined by detecting the surface perturbations produced by longitudinal and shear bulk waves (precursors). Consequently, a consistent set of elastic and acoustic constants was obtained by performing all necessary measurements with the same sample using laser excitation and detection techniques.     

Nonlinear NMR in 3He-B with arbitrary orientation

The high -field nonlinear NMR absorption signal of the B phase of ³He with an arbitrary orientation of the rotation axis n with respect to the field is calculated to third order in the amplitude of the perpendicular magnetization. An instability like those in ferromagnetic resonances is predicted, which changes its asymmetry with respect to the sense of sweeping at an orientation angle of 35 .On leave of absence from the Technical University of Munich. Postdoctoral Research Fellow of the DFG (German Science Foundation).     

水下爆炸冲击波作用下自由环肋圆柱壳动态响应的数值仿真研究

运用大型商业有限元程序MSC.DYTRAN数值模拟了水下爆炸冲击波作用下自由环肋圆柱壳的非线性动 态响应。采用一般耦合算法(generalcoupling)模拟流体与结构的耦合效应,计算中考虑了材料的应变率强化效应,几何 非线性以及结构的初始缺陷的影响,计算结果与实验吻合较好。比较了肋骨和肋间壳板在迎爆面,侧爆面和背爆面处的 中面有效应力和应变,分析了壳体在三个不同部位的破坏机理。最后比较了计算中考虑应变率效应与否对壳体最终变 形的影响。     

Theory of Injection Locking for Large Magnetization Motion in Spin-Transfer Nano-Oscillators

We study magnetization dynamics in spin-transfer devices subject to DC and microwave injected currents. When the frequency of the injected current is sufficiently close to the self-oscillation frequency of the device, phase-locking occurs. This phenomenon is theoretically studied by using Landau-Lifshitz equation with Slonczewski spin-torque term. By exploiting separation of time scales and using averaging technique, we derive equations which are applicable to the study of phase-locking for arbitrary large magnetization motion. The stability diagram in the (detuning, ac current)-plane is determined and it is shown that phase locking is hysteretic at sufficiently large ac currents.     

穿孔区域中非线性波动方程解的存在性与齐次化

本文研究如下非线性波动方程的齐次化问题 uε'div(AεΔuε) g(uε') = fε in Ωε× (0,T),在Ωε× (0,T) 内,这里Ωε为一周期穿孔区域,g为一非降标量函数,我们首先证明该问题解的存在性与唯一性,然后论证该解收敛于其齐次化问题的解。     

空间行波管排气过程中残余气体的质谱分析

电真空器件内残余气体直接影响其阴极的发射能力与寿命。本文利用高灵敏度四极质谱仪监测了空间行波管在整个排气过程中的残余气体,对各阶段气体成分及含量进行了分析。结果表明:烘烤前,水为主要气体,占80%。前期擦拭用无水乙醇易污染真空系统;升温过程中氢迅速增多,当烘烤温度达到220℃时,H₂成为系统中主要气体;整个烘排过程H₂的分压小于10^-3Pa,其余气体分压均小于10^-4Pa;烘烤结束后,H₂分压为2.4×10^-8Pa,占74%。H₂O分压为6×10^-9Pa,占20%;离子泵与吸气剂泵组可有效抽除残余气体,且对H₂的抽速高于对其他气体抽速;另外,质谱仪自身会放出H₂、H₂O、CH₄、CO₂等气体,在真空系统压力达到10^-9Pa范围时,质谱仪自身放气已不可忽略。     

非谐晶体中弱阻尼非线性波吸引子

本文研究了非谐晶体中弱阻尼非线性波解的渐近性态：uxt 3/2ux^2uxx uxxxx-sinu εux=0我们首先对方程证明了在空间Hpεr^2中整体弱吸引子的存在性,然后利用能量方程方法证明了整体弱吸引子实际上是整体强吸引子。     

红外焦平面阵列非均匀性非线性校正新方法

针对红外焦平面阵列非均匀性线性校正方法存在较大误差,而考虑非线性响应的校正算法又过于复杂,难于在实际工程中获得运用等难题,本丈提出一种易于硬件实时处理、校正精度较高的红外焦平面阵列非均匀性非线性校正新方法.在介绍非线性校正新方法原理的基础上,推导出其数学模型,并给出实验结果.实验结果表明该校正方法的校正精度达到1.2%,校正过程中需要存储的参数仅为4个/1象素,易于硬件实现实时校正.     

Santa Cruz波的反应谱及阻尼影响分析

用线性加速度法分析了美国ＬｏｍａＰｒｉｅｔａ地震听ＳａｎｔａＣｒｕｚ地震波记录,得到了其三个方向上的加速度反应谱,并作了位移、速度和加速度反应谱在各种阻尼条件下的对比。通过分析,ＳａｎｔａＣｒｕｚ波反应谱中的结构最不利用周期为０．２５ｓ,而阻尼的增加可降低地震响应。     

Nonlinear Response of Photopolymers for Holography: Copolymerization Process

Abstract

A model is proposed which allows us to obtain the diffraction efficiency of photopolymeric materials with a nonlinear response to the refraction index, using the equations on the evolution of copolymerization reactions as a base. The photochemical material being analysed can be optimized by correctly selecting the material's parameters.     

Evaluation of Fatigue Specimens Using EMATs for Nonlinear Ultrasonic Wave Detection

It is suggested that the waveform of the received ultrasonic wave is slightly different from that of the incident ultrasonic wave when the displacement of an ultrasonic wave and the opening width of a crack are almost same. Thus, as regarding the incident ultrasonic wave, its harmonic frequency components change as it penetrates the crack. Since, the nonlinearity of a solid material is very small compared to that of a liquid medium with a high nonlinear efficiency when used as a coupling medium, we applied an electromagnetic acoustic transducer (EMAT), which does not require a coupling medium. In addition, we tried to develop the EMAT that could alternately drive S₀-Lamb wave and fundamental Shear Horizontal (SH₀)-plate wave to detect any nonlinearity in an ultrasonic wave. We actually tested the performance using the fatigue specimens we fabricated. As a result, we observed that the harmonic components changed when we used the specimen with a specific loading condition and a specific ultrasonic mode. This is indicated that the harmonic components detection using the trial EMAT could also provide useful information on the degree of damage to any structures or any materials.     

Efficient Numerical Scheme for Solving Large System of Nonlinear Equations

A fifth-order family of an iterative method for solving systems of nonlinear equations and highly nonlinear boundary value problems has been developed in this paper. Convergence analysis demonstrates that the local order of convergence of the numerical method is five. The computer algebra system CAS-Maple, Mathematica, or MATLAB was the primary tool for dealing with difficult problems since it allows for the handling and manipulation of complex mathematical equations and other mathematical objects. Several numerical examples are provided to demonstrate the properties of the proposed rapidly convergent algorithms. A dynamic evaluation of the presented methods is also presented utilizing basins of attraction to analyze their convergence behavior. Aside from visualizing iterative processes, this methodology provides useful information on iterations, such as the number of diverging-converging points and the average number of iterations as a function of initial points. Solving numerous highly nonlinear boundary value problems and large nonlinear systems of equations of higher dimensions demonstrate the performance, efficiency, precision, and applicability of a newly presented technique.     

三次型非线性包装系统跌落冲击响应分析

目的分析得到三次非线性包装系统跌落冲击的近似解析解,修正提高解的精度,以达到工程要求。方法采用解决普遍非线性振动问题的何氏参数展开法,并针对跌落冲击动态方程的求解进行算法修正,选取三次非线性包装系统跌落冲击模型为算例,求解得到一阶近似解;与包装工程中的能量法结合,对近似解进行修正。结果修正后的最大位移响应、最大加速度响应、系统响应周期与Runge-Kutta数值解非常接近,相对误差小于0.05%。结论为非线性包装系统跌落冲击响应分析提供了一种新的科学有效的近似分析方法。