Dynamic response and reliability analysis of structures with uncertain parameters

An original approach for dynamic response and reliability analysis of stochastic structures is proposed. The probability density evolution equation is established which implies that incremental rate of the probability density function is related to the structural response velocity. Therefore, the response analysis of stochastic structures becomes an initial‐value partial differential equation problem. For the dynamic reliability problem, the solution can be derived through solving the probability density evolution equation with an initial value condition and an absorbing boundary condition corresponding to specified failure criterion. The numerical algorithm for the proposed method is suggested by combining the precise time integration method and the finite difference method with TVD scheme. To verify and validate the proposed method, a SDOF system and an 8‐storey frame with random parameters are investigated in detail. In the SDOF system, the response obtained by the proposed method is compared with the counterparts by the exact solution. The responses and the reliabilities of a frame with random stiffness, subject to deterministic excitation or random excitation, are evaluated by the proposed method as well. The mean, the standard deviation and the reliabilities are compared, respectively, with the Monte Carlo simulation. The numerical examples verify that the proposed method is of high accuracy and efficiency. Moreover, it is found that the probability transition of structural responses is like water flowing in a river with many whirlpools, showing complexity of probability transition process of the stochastic dynamic responses. Copyright © 2004 John Wiley & Sons, Ltd.     

Comparison of the response of three human monocytic cell lines to challenge with polyethylene particles of known size and dose

The response of three human monocytic cell lines (Monomac-1, U937 and THP-1) to challenge with polyethylene particles of known size and dose was evaluated. Particles with a mean size of 0.21, 0.49, 4.3, 7.2, and 88 m were co-cultured with the cells for 24 hours prior to the assessment of cell viability and production of the pro-inflammatory cytokines, IL-1, IL-6 and TNF. Additionally, GM-CSF and prostaglandin E₂ were measured in culture supernatants from particle stimulated U937 cells. All particle fractions were evaluated at particle volume (m³) to cell number ratios of 100 : 1, 10 : 1, 1 : 1 and 0.1 : 1. None of the test fractions had any effect on cell viability. Only the response of the U937 cell line was demonstrated to be comparable to that of primary macrophages as determined in a previous study. Furthermore only particle volume to cell number ratios of 10 : 1 or greater consistently stimulated significantly enhanced levels of cytokine secretion with particles within the phagocytosable size range (0.1 to 10 m) being the most biologically active. No response was observed when U937 macrophages were stimulated with the largest (88 m) particles at any of the volume ratios tested in this study. These results suggest that the size and volume of polyethylene particles are critical factors in macrophage activation. In addition, the U937 cell line has been shown to be a suitable model for the in vitro study of macrophage-particle interactions. © 2001 Kluwer Academic Publishers     

Calculating reliability in diagnosis and monitoring of an engineering system with several monitored parameters

Expressions are derived for the numerical characteristics of monitoring and diagnostic reliability for an entire system in terms of the reliability characteristics of each of the monitored parameters. The formulas and algorithm can be used to improve the quality and reliability of diagnosis for complicated engineering systems. __________ Translated from Izmeritel’naya Tekhnika, No. 6, pp. 9–11, June, 2006.     

Dynamic response of structures with uncertain parameters: A comparative study of probabilistic and fuzzy sets models

This paper presents the results of a study on the response of structures with uncertain properties such as mass, stiffness and damping. The effect of the uncertain parameters on the response and the effect of the modelling of the uncertainties on the response are investigated. In particular, two types of uncertainties are distinguished: random and fuzzy uncertainties. Two kinds of models are studied: probabilistic and fuzzy set models. The two approaches to uncertainty modelling are compared with regard to their impacts on the analysis and on the uncertain structural response obtained. The study considers free vibration, forced vibration with deterministic excitation, and forced vibration with Gaussian white noise excitation. It is concluded that, in general, fuzzy models are much easier to implement and the associated analysis easier to perform than their probabilistic counterparts. When the available data on the structural parameters are crude and do not support a rigorous probabilistic model, the fuzzy set approach should be considered in view of its simplicity.     

Wind-excited response of structures with uncertain parameters

The wind-excited response of structures is classically evaluated by considering the model parameters as deterministic. Due to this assumption, the density function of the maximum response is so narrow and sharp as to make the expected maximum a suitable pseudo-deterministic representation of the maximum response. Based on Taylor series expansions retaining up to the first and second-order derivative terms, this paper provides closed form expressions of the first and second statistical moments of the maximum response taking the uncertainties of the parameters and the model error into account. It is shown that such uncertainties may spread and shift the density function of the maximum response to the point at which the classical value of the expected maximum is no longer representative of the structural behaviour.     

下卧基岩饱和地基在移动荷载作用下的动力响应

基于Biot多孔弹性介质波动理论,在平面应变条件下研究了下卧基岩饱和地基在移动线荷载作用下的动力响应。通过引入势函数并利用Helmholtz原理,再经过Fourier变换和逆变换,获得了移动线荷载作用下饱和地基的位移、应力、孔隙水压力解答。最后通过快速逆傅里叶变化（IFFT）得到数值计算结果,详细分析了土颗粒的压缩性、孔隙水的压缩性、饱和土的剪切模量、孔隙率、渗透性、移动荷载速度和饱和土层厚度等参数对动力响应的影响     

Dynamic response to demand variability for precast production rescheduling with multiple lines

Production scheduling plays a crucial role in the prefabricated construction productivity and on-time delivery of precast components (PCs). However, previous studies mainly focused on the static scheduling of single production line without considering the demand variability in practice. To achieve dynamic production planning, a Two-level Rescheduling Model for Precast Production with multiple production lines is developed to minimise the rescheduling costs based on genetic algorithm, from the two levels of (1) selection of production line and (2) rescheduling of jobs based on PCs’ priority. Further, two scenarios of different and shared mould types are investigated to represent real-world production environments. Finally, a real case study is conducted to test the validity of proposed rescheduling model. 58.1 and 48.5% cost savings are achieved by comparison to no response to changes and heuristic rescheduling methods, respectively. This research contributes to the precast production theory by expanding the insight into dynamic rescheduling with multiple production lines. The methodology will promote the on-time delivery of PCs and enhance the dynamic precast production management.     

Non-stationary random response analysis of structures with uncertain parameters

This paper proposes a non-stationary random response analysis method of structures with uncertain parameters. The structural physical parameters and the input parameters are considered as random variables or interval variables. By using the pseudo-excitation method and the direct differentiation method (DDM), the analytical expression of the time-varying power spectrum and the time-varying variance of the structure response can be obtained in the framework of first order perturbation approaches. In addition, the analytical expression of the first-order and second-order partial derivative (e.g., time-varying sensitivity coefficient) for the time-varying power spectrum and the time-varying variance of the structure response expressed via the uncertainty parameters can also be determined. Based on this and the perturbation technique, the probabilistic and non-probabilistic analysis methods to calculate the upper and lower bounds of the time-varying variance of the structure response are proposed. Finally the effectiveness of the proposed method is demonstrated by numerical examples compared with the Monte Carlo solutions and the vertex solutions.     

区间参数结构动力特征值分析的仿射算法

将不确定结构系统中的区间参数用仿射型来表示,对获得的广义区间特征值方程的求解方法进行了研究,提出了一种改进的仿射算法。此方法考虑到广义特征值方程中各区间元素的相关性,通过独立的区间参数在子区间上转为仿射型,将特征值方程的求解转化为相应的确定性问题,再利用常规的仿射算法,搜索方程解中的最大最小值来确定各阶特征值边界。先用数学算例对所提改进的仿射算法的有效性进行了验证,随后将其应用于工程算例的特征值区间分析中,并与其它算法进行了比较。结果表明该算法是合理可行的,有较高的准确性。     

三自由度动态角度实时测量系统

提出一种基于二维PSD和激光自准直测量原理的三自由度动态角度实时测量系统。介绍激光自准直测量的工作原理,采用一种新颖的标定方法建立测量模型,并进行系统动态和静态测试。结果表明,测量范围为±1°,响应频率为4kHz,静态测试RMS误差为0.35′,动态测试RMS误差为0.36′。系统已成功应用于某型号仪器半实物仿真实验中,并取得了满意的结果。     

Dynamic viscosity of aqueous solutions of hydrazine with high state parameters

We report the results of measurements of the dynamic viscosity of aqueous solutions of hydrazine with a molar concentration of water ranging from 10 to 90%, in the temperature interval 293–558.4 K and the pressure interval 0.101–58.86 MPa.Translated from Izmeritel'naya Tekhnika, No. 9, pp. 43–45, September, 1994.     

Transient response of three layered composites with two interface cracks due to a line load

Summary The dynamic response of three layered composites, with two interface cracks, subjected to an antiplane line load is analyzed. The Green's function for the uncreacked medium is used along with the representation theorem to derive the scattered field. Satisfaction of the traction free condition at the crack surfaces gives rise to a system of singular integral equations for determining crack opening displacements (COD), which are then solved by expanding the unknown COD in a complete set of Chebyshev polynomials. Numerical results for two sample problems are presented, for both isotropic and anisotropic materials. Results show how significantly material anisotropy and interaction between two cracks can affect the COD in a three layered plate.With 9 Figures     

Passage of light through a general three dimensional model—equations linking characteristic parameters with system parameters

The determination of the secondary principal stress difference and their orientations for a discrete slice of thickness dz along a particular light path in a three dimensional photoelastic model is discussed in this paper. These quantities are determined in terms of the characteristic parameters¹ and their variations at discrete points distance z and z + dz along the light path. The variations of the characteristic parameters are obtained by deriving the equations linking the characteristic parameters for the light path and the system parameters of the discrete element. The validity of the equations so derived has also been checked by applying these equations to the solution of the problem of a uniformly twisted prismatic bar.     

In vitro cellular response to titanium electrochemically coated with hydroxyapatite compared to titanium with three different levels of surface roughness

The in vitro response of primary human osteoblast-like (HOB) cells to a novel hydroxyapatite (HA) coated titanium substrate, produced by a low temperature electrochemical method, was compared to three different titanium surfaces: as-machined, Al₂O₃-blasted, plasma-sprayed with titanium particles. HOB cells were cultured on different surfaces for 3, 7 and 14 days at 37 °C. The cell morphology was assessed using scanning electron microscopy (SEM). Cell growth and proliferation were assessed by the measurement of total cellular DNA and tritiated thymidine incorporation. Measurement of alkaline phosphatase (ALP) production was used as an indicator of the phenotype of the cultured HOB cells. After three days incubation, the electrochemically coated HA surface produced the highest level of cell proliferation, and the Al₂O₃-blasted surface the lowest. Interestingly, as the incubation time was increased to 7 days all surfaces produced a large drop in tritiated thymidine incorporation apart from the Al₂O₃-blasted surface, which showed a small increase. Cells cultured on all four surfaces showed an increased expression of ALP with increased incubation time, although there was not a statistically significant difference between surfaces at each time point. Typical osteoblast morphology was observed for cells cultured on all samples. The HA coated sample showed evidence of a deposited phase after three days of incubation, which was not observed on any other surface. Cells incubated on the HA coated substrate appeared to exhibit the highest number of cell processes attaching to the surface, which was indicative of optimal cell attachment. The crystalline HA coating, produced by a low temperature route, appeared to result in a more bioactive surface on the c.p. Ti substrate than was observed for the other three different Ti surfaces.     

Invariant polarimetric contrast parameters of light with Gaussian fluctuations in three dimensions

We propose a rigorous definition of the minimal set of parameters that characterize the difference between two partially polarized states of light whose electric fields vary in three dimensions with Gaussian fluctuations. Although two such states are a priori defined by eighteen parameters, we demonstrate that the performance of processing tasks such as detection, localization, or segmentation of spatial or temporal polarization variations is uniquely determined by three scalar functions of these parameters. These functions define a "polarimetric contrast" that simplifies the analysis and the specification of processing techniques on polarimetric signals and images. This result can also be used to analyze the definition of the degree of polarization of a three-dimensional state of light with Gaussian fluctuations in comparison, with respect to its polarimetric contrast parameters, with a totally depolarized light. We show that these contrast parameters are a simple function of the degrees of polarization previously proposed by Barakat [Opt. Acta 30, 1171 (1983)] and Set?l? et al. [Phys. Rev. Lett. 88, 123902 (2002)]. Finally, we analyze the dimension of the set of contrast parameters in different particular situations.     

复合材料加筋壁板鸟撞动响应分析

考虑复合材料蜂窝夹芯结构的冲击损伤,采用接触碰撞耦合方法研究了复合材料加筋壁板的抗鸟撞性能。鸟撞方式包括垂直冲击和斜冲击两种,复合材料的冲击损伤模型采用Chang-Chang模型,分析了三种鸟撞速度下鸟撞性能参数如复合材料壁板的失效单元数、鸟体剩余动能和筋条的变形,以及复合材料壁板和筋条在某一鸟撞速度下应力随筋条数的变化规律。计算结果表明：垂直冲击和斜冲击下复合材料加筋壁板的抗鸟撞性能不同,并非筋条越多越有利于改善抗鸟撞性能,筋条有时还可能起反作用。