Actual time integration methods for elastic wave propagation analysis

For the simulation of the interaction of elastic waves in CFRP plates with inhomogeneities and defects the spectral finite element method (SEM) is under investigation. The SEM uses high-order shape functions which are composed of Lagrange polynomials with nodes at the Gauss-Lobatto quadrature (GLq) points. In this way we obtain a diagonal mass matrix which makes an explicit time scheme more efficient. In this paper we analyse how actual time integration methods perform in combination with the SEM. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Simulation of Lamb wave interaction with defects in laminated plates by SEM

For the simulation of the interaction of elastic waves in CFRP Plates with inhomogeneities and defects the spectral finite element method (SEM) is under investigation. The SEM uses high-order shape functions which are composed of Lagrange polynomials with nodes at the Gauss-Lobatto quadrature (GLq) points. In this way we obtain a diagonal mass matrix which makes an explicit time scheme more efficient. In a numerical example based on the first order shear deformation theory (FSDT) a computation by FEAP of an interaction with an inhomogeneity is presented. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

SEM Modeling with Singular Moment Matrices Part I: ML-Estimation of Time Series

A structural equation model (SEM) with deterministic intercepts is introduced. The Gaussian likelihood function does not contain determinants of sample moment matrices and is thus well-defined for only one statistical unit. The SEM is applied to the dynamic state space model and compared with the Kalman filter (KF) approach. The likelihood of both methods are shown to be equivalent, but for long time series numerical problems occur in the SEM approach, which are traced to the inversion of the latent state covariance matrix. Both approaches are compared on several aspects. The SEM approach is now open for idiographic (N = 1) analysis and estimation of panel data with correlated units.     

A stochastic method to account for the ambient turbulence in Lagrangian Vortex computations

This paper describes a detailed implementation of the Synthetic Eddy Method (SEM) initially presented in Jarrin et al. (2006) applied to the Lagrangian Vortex simulation. While the treatment of turbulent diffusion is already extensively covered in scientific literature, this is one of the first attempts to represent ambient turbulence in a fully Lagrangian framework. This implementation is well suited to the integration of PSE (Particle Strength Exchange) or DVM (Diffusion Velocity Method), often used to account for molecular and turbulent diffusion in Lagrangian simulations. The adaptation and implementation of the SEM into a Lagrangian method using the PSE diffusion model is presented, and the turbulent velocity fields produced by this method are then analysed. In this adaptation, SEM turbulent structures are simply advected, without stretching or diffusion of their own, over the flow domain. This implementation proves its ability to produce turbulent velocity fields in accordance with any desired turbulent flow parameters. As the SEM is a purely mathematical and stochastic model, turbulent spectra and turbulent length scales are also investigated. With the addition of variation in the turbulent structures sizes, a satisfying representation of turbulent spectra is recovered, and a linear relation is obtained between the turbulent structures sizes and the Taylor macroscale. Lastly, the model is applied to the computation of a tidal turbine wake for different ambient turbulence levels, demonstrating the ability of this new implementation to emulate experimentally observed tendencies.     

Fracture and Damage Analysis of Crimped Glass Fibre Truss Type Elements

The paper deals with the damage behaviour of special glass fibre reinforced plastic truss type elements, called Polystal profiles, which are widely used as load bearing cables. To connect these profiles with other structural elements steelmade hulls are crimped onto the profiles. The challenge is to detect the optimal crimping ratio (CR) to realize maximum longitudinal loads in restraint systems. By using scanning electron microscopy (SEM) several damage states like fibre pullout and matrix cracking could be observed. To describe the failure behaviour within the rod during crimping a 3D strain based fracture criterion was developed and implemented within the commercial finte element package Abaqus. The verification of this criterion is done by simulating the crimping process followed by tensile tests. The numerical results are compared with the experiments and with the results obtained by SEM. An outlook on further work to improve the failure prediction is given. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A coupled finite and boundary spectral element method for linear water-wave propagation problems

A coupled boundary spectral element method (BSEM) and spectral element method (SEM) formulation for the propagation of small-amplitude water waves over variable bathymetries is presented in this work. The wave model is based on the mild-slope equation (MSE), which provides a good approximation of the propagation of water waves over irregular bottom surfaces with slopes up to 1:3. In unbounded domains or infinite regions, space can be divided into two different areas: a central region of interest, where an irregular bathymetry is included, and an exterior infinite region with straight and parallel bathymetric lines. The SEM allows us to model the central region, where any variation of the bathymetry can be considered, while the exterior infinite region is modelled by the BSEM which, combined with the fundamental solution presented by Cerrato et al. [A. Cerrato, J. A. González, L. Rodríguez-Tembleque, Boundary element formulation of the mild-slope equation for harmonic water waves propagating over unidirectional variable bathymetries, Eng. Anal. Boundary Elem. 62 (2016) 22–34.] can include bathymetries with straight and parallel contour lines. This coupled model combines important advantages of both methods; it benefits from the flexibility of the SEM for the interior region and, at the same time, includes the fulfilment of the Sommerfeld’s radiation condition for the exterior problem, that is provided by the BSEM. The solution approximation inside the elements is constructed by high order Legendre polynomials associated with Legendre–Gauss–Lobatto quadrature points, providing a spectral convergence for both methods. The proposed formulation has been validated in three different benchmark cases with different shapes of the bottom surface. The solutions exhibit the typical p-convergence of spectral methods.     

A spectral element method using the modal basis and its application in solving second‐order nonlinear partial differential equations

We present a high‐order spectral element method (SEM) using modal (or hierarchical) basis for modeling of some nonlinear second‐order partial differential equations in two‐dimensional spatial space. The discretization is based on the conforming spectral element technique in space and the semi‐implicit or the explicit finite difference formula in time. Unlike the nodal SEM, which is based on the Lagrange polynomials associated with the Gauss–Lobatto–Legendre or Chebyshev quadrature nodes, the Lobatto polynomials are used in this paper as modal basis. Using modal bases due to their orthogonal properties enables us to exactly obtain the elemental matrices provided that the element‐wise mapping has the constant Jacobian. The difficulty of implementation of modal approximations for nonlinear problems is treated in this paper by expanding the nonlinear terms in the weak form of differential equations in terms of the Lobatto polynomials on each element using the fast Fourier transform (FFT). Utilization of the Fourier interpolation on equidistant points in the FFT algorithm and the enough polynomial order of approximation of the nonlinear terms can lead to minimize the aliasing error. Also, this approach leads to finding numerical solution of a nonlinear differential equation through solving a system of linear algebraic equations. Numerical results for some famous nonlinear equations illustrate efficiency, stability and convergence properties of the approximation scheme, which is exponential in space and up to third‐order in time. Copyright © 2014 John Wiley & Sons, Ltd.     

Inflow Treatment for the Simulation of Subsonic Jets with Turbulent Nozzle Boundary Layers

The state of the boundary layer at the nozzle exit of a circular nozzle-jet configuration has an important influence on the development of the shear layer and the emitted sound. Of special interest is the acoustic near-field obtained when the nozzle exit boundary layer is fully turbulent. The turbulent inflow generation and the inflow boundary treatment are important issues to be addressed. We use the Synthetic Eddy Method (SEM) to generate a turbulent inflow which reproduces mean flow and Reynolds stress profiles of specified reference data. The spatially and temporally varying synthetic fluctuations are imposed in the simulation by a forcing term added to the governing equations which is active in a small region downstream of the inflow boundary. This forcing in combination with characteristic boundary conditions allows for passing of upstream-propagating acoustic waves and avoids an uncontrolled drift of mean-flow quantities. We employ this inflow boundary treatment for a subsonic nozzle-jet flow simulation at a Reynolds number of ∼ 9500 and Mach number of 0.9. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Application of structural equation modeling to evaluate the intention of shippers to use Internet services in liner shipping

Operations research (OR) is the application of modeling techniques to formulate and analyze systems and problems for management decision-making. Structural equation modeling (SEM) is a modeling technique applied to social or behavioral systems to understand and explain relationships that may exist among elements of systems. Recently, the measurement of unobservable variables has gained increasing attention in operations management (OM) research, and the OR discipline has begun to recognize the value of applying SEM to analyze behavioral-related OR problems. To provide OR researchers with a better understanding of the application of this useful statistical modeling technique, this paper presents a tutorial on the application of SEM. Specifically, we investigate the key factors that affect the adoption of Internet services in the context of liner shipping services. Although [Fishbein, M.A., Ajzen, I., 1975. Belief, Attitude, Intention and Behavior: An Introduction to Theory and Research, Addison-Wesley, Reading, MA; Davis, F.D., 1989. Perceived usefulness, perceived ease of use, and user acceptance of information technology. MIS Quarterly 13 (3), 319–339; Ajzen, I., 1985. From intention to actions: A theory of planned behavior. In: Kuhl, J., Bechmann, J. (Eds.), Action Control: From Cognition to Behavior. Springer Verlag, New York, pp. 11–39; Ajzen, I., 1991. The theory of planned behavior. Organizational Behavior and Human Decision Processes 50, 179–211] have made important contributions to understanding users’ behavior of technology acceptance, shippers’ resistance to end-user systems is still a common problem in the liner shipping industry. To better predict, explain, and increase shippers’ acceptance of technology, we need to understand why shippers accept or reject Internet services provided by their liner shipping carriers. Another objective of this paper is to propose and empirically test a theoretical framework that relates the intention of shippers to use Internet services in liner shipping with its antecedents such as perceived usefulness, perceived ease of use, and the perceptions of security protection. Tests of the structural model confirm Davis’s (1989) notion that perceived ease of use explains the intention of shippers to use Internet services, and that perceived ease of use has a strong positive effect on perceived usefulness. The results also indicate that security protection influences perceived ease of use. The SEM analyses in this study offer OR researchers a methodological guide on how to assess the efficacy of both a measurement model that relates observed indicators to latent factors and a structural model that poses relationships between constructs.     

Assessing Investigative Skill Development in Inquiry‐Based and Traditional College Science Laboratory Courses

A laboratory practical examination was used to compare the investigative skills developed in two different types of general‐chemistry laboratory courses. Science and engineering majors (SEM) in the control group used a traditional verification approach (SEM‐Ctrl), whereas those in the treatment group learned from an innovative, inquiry‐based approach (SEM‐Trt). A scoring rubric was developed from their examination sheets to assess six component investigative skills. Results indicated that SEM students in the SEM‐Trt group scored significantly higher than those in SEM‐Ctrl for all six skills. Furthermore, nursing and applied science majors (NonSEM) in the inquiry‐based group (NonSEM‐Trt) wrote significantly better discussions than did SEM students in SEM‐Ctrl group. Overall, competency at the mid‐range level of laboratory skills was attained by most SEM‐Trt students (72.5%) but by only 30.5% of SEM‐Ctrl and 28.6% of NonSEM‐Trt students. Apparently, during the semester students in the SEM‐Trt group were able to use the inquiry‐based method effectively to combine chemical tasks with writing tasks and postlaboratory discussions. One implication of this study for science instructors is that practical examinations can provide useful feedback regarding the quality of the laboratory experience. Another implication is that this study provides evidence for the use of the innovative inquiry‐based laboratory approach to support student learning of high‐level investigative skills. However, students' requisite background knowledge must match the level of these skills.     

计入气穴的水下爆炸作用下结构流固耦合三维数值模拟

水下爆炸在结构物面附近产生的气穴现象,严重影响水下爆炸作用下的流固耦合动响应,是舰船水下爆炸领域的难点,传统的边界元方法、有限元方法(FEM)难以解决水下爆炸气穴现象这类强非线性问题．针对此问题,计及流体中的气穴现象,考虑流体的可压缩型,忽略流体粘性,建立水下爆炸瞬态强非线性流固耦合三维数值模型,采用流体谱单元方法(SEM)和结构有限元方法求解该模型．计算结果表明:相对有限元法,谱单元法具有更高的计算精度,且谱单元解与解析解、试验值吻合良好．在此基础上,结合ABAQUS软件,分别探讨三维球壳、船体板架在水下爆炸作用下的瞬态流固耦合机理,给出气穴区域及其对水中结构物动响应的影响特征,旨在为舰船水下爆炸瞬态流固耦合问题的相关研究提供参考．     

A practical analytic model for predicting the performance of an encapsulated polymer composite

A novel model is presented for simulating the characteristics of a micro-encapsulated composite. The procedure initiated utilizing particle size analysis (PSA) to obtain the volume based average diameter and average spacing between the microcapsules in the composite. Results of this procedure were verified by scanning electron microscopy (SEM). Then, a simple model was presented to predict the healing percent of a triangular crack propagating in the composite. In order to obtain more detailed results, a probabilistic model was also suggested for the planar and triangular cracks, which gave the probability of crack incidence for different number of capsules to be intersected. Results of this method were then validated in comparison with the results independently obtained using a simulation by computer programming. The comparison showed close agreement between the analytical results and the simulations which present the current model and simulations as a promising method for investigating the characteristics of the encapsulated self-healing composites.     

Dispersion analysis of triangle-based spectral element methods for elastic wave propagation

We study the numerical dispersion/dissipation of Triangle-based Spectral Element Methods (TSEM) of order N????1 when coupled with the Leap-Frog (LF) finite difference scheme to simulate the elastic wave propagation over a structured triangulation of the 2D physical domain. The analysis relies on the discrete eigenvalue problem resulting from the approximation of the dispersion relation. First, we present semi-discrete dispersion graphs by varying the approximation polynomial degree and the number of discrete points per wavelength. The fully-discrete ones are then obtained by varying also the time step. Numerical results for the TSEM, resp. TSEM-LF, are compared with those of the classical Quadrangle-based Spectral Element Method (QSEM), resp. QSEM-LF.     

A parametric lifetime model for a multicomponents system with spatial interactions

In this paper, we consider a system made of n components displayed on a structure (eg, a steel plate). We define a parametric model for the hazard function, which includes covariates and spatial interaction between components. The state (nonfailed or failed) of each component is observed at some inspection times. From these data, we consider the problem of model parameter estimation. To achieve this, we suggest to use the SEM algorithm based on a pseudo‐likelihood function. A definition for the time‐to‐failure of the system is given, generalizing the classical cases. A study based on numerical simulations is provided to illustrate the proposed approach.     

基于结构方程模型的旅游网站使用者满意度量的比较研究

基于电子商务系统成功(ECSS)模型和旅游网站使用者满意(TWUS)模型,本文构建了评价旅游网站使用者满意的概念模型,并通过结构方程模型(SEM)分析方法,对度量模型与在线调查获得的837份有效数据的拟合程度进行了比较,发现TWUS模型对旅游网站使用者满意问题具有更强的解释能力。最后,本文对造成两个模型解释能力差异的原因进行了讨论。     

The design of symmetric, optimal supersonic and hypersonic flow profiles for arbitrary isoperimetric conditions

A simple and accurate approach to the design of symmetric profiles which are optimal in the supersonic and hypersonic flow with an attached shock is developed. Besides dimensional constraints, the bodies being optimized can satisfy arbitrary isoperimetric conditions. The approach which has been developed uses a modification of the “shock-expansion” method (SEM). The modified shock-expansion method (MSEM), unlike SEM, does not lead to a physically absurd result, that is, to a finite change in the flow parameters when the slope of the contour is solely changed at the leading point of the body. This makes MSEM suitable for solving two-dimensional variational problems in gas dynamics, by reducing any of them to a certain extension of the Lagrange problem for systems which are described by ordinary differential equations. The possibilities of the approach which has been developed are illustrated using examples of profiles which achieve a minimum wave drag coefficient, C_x. Profiles designed using the MSEM are compared with those obtained using the Newtonian model and linear theory and with wedges while the C_x values found for them using the above-mentioned approximate models and MSEM are compared with the results of the numerical integration of Euler's equations.     

Parabolic Littlewood-Paley g-function with rough kernel

In this note, we give the L^p （1 〈 p 〈∞） boundedness of the parabolic Littlewood Paley g-function with rough kernel.     

On Lagrangian submanifolds in complex hyperquadrics and isoparametric hypersurfaces in spheres

The n-dimensional complex hyperquadric is a compact complex algebraic hypersurface defined by the quadratic equation in the (n+1)-dimensional complex projective space, which is isometric to the real Grassmann manifold of oriented 2-planes and is a compact Hermitian symmetric space of rank 2. In this paper, we study geometry of compact Lagrangian submanifolds in complex hyperquadrics from the viewpoint of the theory of isoparametric hypersurfaces in spheres. From this viewpoint we provide a classification theorem of compact homogeneous Lagrangian submanifolds in complex hyperquadrics by using the moment map technique. Moreover we determine the Hamiltonian stability of compact minimal Lagrangian submanifolds embedded in complex hyperquadrics which are obtained as Gauss images of isoparametric hypersurfaces in spheres with g(=  1, 2, 3) distinct principal curvatures. Dedicated to Professor Hajime Urakawa on his sixtieth birthday. H. Ma was partially supported by NSFC grant No. 10501028, SRF for ROCS, SEM and NKBRPC No. 2006CB805905. Y. Ohnita was partially supported by JSPS Grant-in-Aid for Scientific Research (A) No. 17204006.     

SEM Modeling with Singular Moment Matrices Part II: ML-Estimation of Sampled Stochastic Differential Equations

Linear stochastic differential equations are expressed as an exact discrete model (EDM) and estimated with structural equation models (SEMs) and the Kalman filter (KF) algorithm. The oversampling approach is introduced in order to formulate the EDM on a time grid which is finer than the sampling intervals. This leads to a simple computation of the nonlinear parameter functionals of the EDM. For small discretization intervals, the functionals can be linearized, and standard software permitting only linear parameter restrictions can be used. However, in this case the SEM approach must handle large matrices leading to degraded performance and possible numerical problems. The methods are compared using coupled linear random oscillators with time-varying parameters and irregular sampling times.     

Diamond nucleation on surface of C60 thin layers

Diamond nucleation on the surface of C₆₀ thin layers and intermediate layer of Si substrates are studied by scanning electron microscopy (SEM). The cross-section SEM images of diamond films show that diamond grains really nucleate on the surface of C₆₀ thin layers. The SEM images of diamond nucleating sites show the nucleating aggregation of diamond on C₆₀ surfaces. The preferential oriented diamond films are observed. The plasma pretreatment of C₆₀ sublimating layers is a key factor for diamond nucleation.