Stability Analysis Of Structures Research Articles

Unusual Combination Parametric Resonance

The purpose of this study is to present the computational method applicable for stability analyses of structures. In this paper, a typical complex eigenproblem for a monodromy matrix is solved in order to perform the stability analysis of vehicle streams moving along the bridge. The inertia forces of vehicles and the springing of vehicles are taken into account. Unstable structure vibrations were detected. The instability is a combination parametric resonance one. The combination parametric resonance is not a typical one as it involves the interaction of not two or three but numerous modal forms simultaneously

Comparative Epitope Stability Analysis of Influenza A Virus Antigenic Proteins

Influenza A Viruses are the most virulent human pathogens among the three influenza types (Influenza A, B, C) and cause the most severe disease. The influenza A virus are subdivided into different serotypes based on the antibody response to these viruses and they resulted in many number of human pandemic deaths. The known flu pandemics are from 1918 Spanish flu, which is the serious pandemic in recent history and the most recent one was the 2009 flu pandemic. In each of the pandemics, different subtypes of H & N of Influenza A virus strain are involved. The process of antigenic shift in between species as well subtype combinations are leading to the novel strains which are highly virulent. As the subtypes are based on two important proteins viz. Hemagglutinin and Neuraminidase (H&N), our focus is to identify the amino acid changes/mutations in the epitopes of H1-H16 and N1-N9 strains which are evolved through time. The epitopic regions are predicted using Immune Epitope DataBase, and the predicted epitopic peptide is modeled using the CPH modeling server and each of the modeled epitope(s) are subjected to structural stability analysis using Hyperchem program. Epitope modeling and energy value comparison studies of Influenza A Virus epitopes showed that recent (2010) strains - H5 and N6 are possessing higher energies indicating their instability and thereby are more prone to mutations and may become highly pathogenic (virulent) in the near future than the earlier H1 and N1 strains.

Structural Stability Analysis of Pneumatic Membrane Architecture under Influence of Internal Fire

A coal storage shed taking advantage of pneumatic membrane structure was taken for example to research structural stability of pneumatic membrane architecture under influence of internal fire. Combustion characteristics of the membrane material was studied experimentally and the critical temperature generating holes on the heated material was got. Then, mathematical model of the structure was established to calculate the minimum difference between internal air pressure and the external required for stability, and to critical hole area in fire. Last, full-size fire field model of the shed was built to simulate membrane surface temperature distribution, and structural stability of the pneumatic membrane shed under influence of internal fire was judged with the critical hole temperature and the area. The results show that: critical hole temperature is somewhere between 365.5°C and 437.6°C. The minimum difference is 34.73 Pa, and the critical hole area is 19.579 m2. In the worst fire scene, the shed collapses likely for hole area on the membrane surface is bigger than the critical hole area. In engineering applications of pneumatic membrane architecture, there should be a safe distance from internal fire loads to the membrane above them.

Structural Analysis of Voltage Stability in Power Systems Integrating Wind Power

This paper presents a structural voltage stability analysis of a power system integrating induction generator wind turbines. The approach is based on restructuring the system load flow matrix (JLF) with respect to bus types instead of the usual active-reactive power equations arrangement. The row sub-matrices of the modified JLF are used to generate sub-matrices candidates representing associations of bus types. Singular value decomposition (SVD) of the generated sub-matrices is used as a rank deficiency indicator. The approach is tested on a nine-bus system. The proximity to voltage collapse is monitored by tracking the smallest SVD and points of limit induced bifurcations are tracked. The interactions between the system buses are structurally analyzed for wind power increase and loading tests. Two-bus bifurcations are shown to be a precursor to system voltage collapse. The analysis is helpful for problem diagnosis and remediation planning in power systems.

Electronic Properties of Boron and Nitrogen Doped Graphene

Graphene is the thinnest 2-D material which can be regarded as a single layer of graphite. The unique electrical, mechanical and optical properties of graphene can be used in many technological applications. 2-D nanomaterials with semiconducting properties are of great interest since they can be applied in electronics industry. Pure graphene is a zerogap semiconductor or semimetal, since the electron states just cross the Fermi energy. However, the electronic properties of graphene can be tuned by doping boron or nitrogen atoms. Understanding the electronic properties in terms of density of states and band structure of doped graphene is of great relevance today. In our work, we have analyzed the electronic properties of boron and nitrogen doped graphene using Density Functional Theory (DFT). The stability and charge analysis of doped structures have been studied. The Local Density Approximation (LDA) calculations have been used to find the total energies of the structures. In addition to the electronics industry, doped graphene also has great potential to adsorb gas molecules. Therefore, we have analyzed the H2 molecule adsorption in pure, B-doped and N-doped graphene.

Uplift force, seepage, and exit gradient under diversion dams

Correct estimation of uplift force, seepage discharge and exit gradient is very important in stability analysis of hydraulic structures. In this research, by carrying out a set of experiments on a laboratory model, the application of various methods for estimating uplift pressure and seepage discharge under hydraulic structures, and the exit gradient have been investigated. The results show that for the soil type used in the experiments, the method of Khosla et al. gives a better estimation of seepage effects than creep theories. Moreover, compared with Lane's method, it is found that Bligh's theory has better agreement with the observed data of uplift pressure, seepage discharge and piping. By using the finite-element method, the magnitude of pressure head upon a dam foundation in different conditions is calculated, and a relationship between the anisotropic conductivity ratio and the ratio of coefficients in Lane's creep theory is introduced. It is found that while the accuracy of Lane's theory is reduced by increasing the anisotropic conductivity ratio, the new relation estimates the amount of uplift force very well. Based on the finite-element method, a set of graphs is presented to estimate the exit gradient in different conditions with the presence of a cutoff wall at the downstream end or without any cutoff wall.

Effects of Anthropogenic Disturbance Measures on Plant Diversity of Understory Vegetation in Moso Bamboo Forests

Anthropogenic disturbance measures have complex effects on understory plants. In order to establish a theoretical basis for moso bamboo forest sustainable management, three types of moso bamboo forests with many years not weeding, hilltops weeding and herbicides weeding were choosed. And species names, numbers and coverages of all arbors, shrubs, herbs and vines were recorded in every quadrat. Species composition and α-diversity were analyzed to compare understory vegetation under the three types of moso bamboo forests with consistent stand structure and site conditions. There are four major findings in this study: (1) 74 species belonged to 47 families and 58 generas which are recorded in the three types of moso bamboo forests. Many years not weeding, hilltops weeding and herbicides weeding are respectively 33 families 39 genera 40 species, 33 families 37 genera 41 species and 37 families 43 genera 49 species. (2) Dominant species of arbors and shrubs within hilltops weeding and herbicides weeding moso bamboo forests are less than the ones of many years not weeding moso bamboo forest, whereas dominant species of herbs increased. Meanwhile, co-dominant specie of arbors is Cunninghamia lanceolata, shrubs is Rubus reflexus, and herbs are Melastoma dodecandrum and Dicranopteris dichotoma. (3) Richness of herbicides weeding and hilltops weeding moso bamboo forests is significantly lower than (p<0.05) the one of many years not weeding moso bamboo forest, and Containing absolute abundance diversity index (I) of hilltops weeding moso bamboo forest is also significantly lower than (p<0.01) many years not weeding moso bamboo forest. The differences of Simpson dominance index (C), Simpson diversity index (D),Shannon-Wiener diversity index (H) and Pielou evenness index (J) among the three types of moso bamboo forests are not significant. Considering understory plant diversity and system structure stability analysis, anthropogenic hilltops weeding measure is suggested to be used for understory vegetation interference.

Effects of Shear Rate on Cyclic Loading Shear Behaviour of Rock Joints Under Constant Normal Stiffness Conditions

The presence of joints and discontinuities within a rock mass can significantly affect its mechanical behaviour and therefore the stability of structures constructed at close proximity. Several studies have been carried out by previous researchers to understand the mechanical behaviour of joints under both constant normal load (CNL) conditions, in which the normal load remains unchanged during shearing, and constant normal stiffness (CNS) conditions to imitate the stiffness of the surrounding rock mass (Patton 1966; Ladanyi and Archambault 1969; Barton 1973, 1976; Seidel and Haberfield 1995; Indraratna and Haque 2000; Buzzi et al. 2008). The importance of CNS conditions to simulate the actual shear behaviour of rock joints in the field has been described by Johnston and Lam (1989), Skinas et al. (1990) and Indraratna et al. (1998). The above-mentioned studies focussed only on the monotonic loading shear behaviour of rock joints. The effects of cyclic loading on the shear behaviour of rock joints in earthquakes and blasting were investigated in detail by Plesha (1987), Hutson and Dowding (1990), Lee et al. (2001), Stupkiewicz and Mroz (2001), Grasselli and Egger (2003), Jafari et al. (2003) and Belem et al. (2009). As the shear rate might vary depending on the source of the load and rock media, Crawford and Curran (1981) carried out a series of experiments on artificial rock joints with various shear rates and normal stresses under CNL conditions. Based on the measured data, they concluded that the shear rate may influence the shear strength of hard and soft rock joints differently. In another study, Jafari et al. (2004) verified the results of Crawford and Curran (1981) for shear rates between 0.05 and 0.4 mm/min under monotonic loading. None of these researchers investigated the effects of shear rate on the cyclic loading shear behaviour of rock joints under CNS conditions, which is a critical issue in stability analysis of underground structures subjected to seismic events. Accordingly, three sets of cyclic loading shear tests with various shear rates and initial normal stresses were conducted on artificial triangular joints under CNS conditions. In this study, the experimental data are critically analysed.

A COMPARATIVE STUDY OF SEISMIC STABILITY OF COUPLED ARCH DAM-FOUNDATION-RESERVOIR SYSTEMS USING INFINITE ELEMENTS AND VISCOUS BOUNDARY MODELS

In the present paper, a direct time domain procedure is used for dynamic structural stability analysis of the dam-reservoir-foundation coupled system in 3D space considering the impact of the ground motion duration. The foundation medium is assumed to be massed and infinite elements are used for modeling the semi-infinite medium of the foundation. The nonlinear behavior of mass concrete is modeled using the coaxial rotating smeared crack approach with the ability of cracking at Gaussian points. The reservoir is assumed to be compressible and is modeled using fluid finite elements. In order to investigate the effects of the ground motion duration on dynamic stability of the coupled system, a set of artificially-generated ground motions with different duration but the same intensities are used to analyze the system. It is found that the responses of the system with the massed foundation including either infinite elements or viscous boundary on the far-end face of the foundation are the same. Using the massless foundation leads to conservative stresses within dam body. Implementation of the infinite elements leads to decreasing crack profile of the concrete dam compared to the massless model; however higher duration ground motions lead to more damage in both models.

Stability analysis of a nonlinear vehicle model in plane motion using the concept of Lyapunov exponents

For the first time, this paper investigates the application of the concept of Lyapunov exponents to the stability analysis of the nonlinear vehicle model in plane motion with two degrees of freedom. The nonlinearity of the model comes from the third-order polynomial expression between the lateral forces on the tyres and the tyre slip angles. Comprehensive studies on both system and structural stability analyses of the vehicle model are presented. The system stability analysis includes the stability, lateral stability region, and effects of driving conditions on the lateral stability region of the vehicle model in the state space. In the structural stability analysis, the ranges of driving conditions in which the stability of the vehicle model is guaranteed are given. Moreover, through examples, the largest Lyapunov exponent is suggested as an indicator of the convergence rate in which the disturbed vehicle model returns to its stable fixed point.

SNAP-THROUGH AND BIFURCATION OF NANO-ARCHES ON ELASTIC FOUNDATION BY THE STRAIN GRADIENT AND NONLOCAL THEORIES

This paper presents the snap-through and bifurcation elastic stability analysis of nano-arch type structures with the Winkler foundation under transverse loadings by the strain gradient and stress gradient (nonlocal) theories. The equations of equilibrium are derived by using the variational method and virtual displacement theorem of minimum total potential energy. In the elastic stability analysis, von Karman's nonlinear strain component is included, with the deformation represented by a series solution. It is concluded that in general, the strain gradient theory pushes the system away from instability as compared to the classical theory. However, the nonlocal theory does the reverse and causes the system to experience instability earlier than that of the classical theory. Moreover, theories with different small-size considerations change the mechanism of instability in different ways. For example, in similar conditions, the strain gradient theory causes the system to reach a snap-through point, while the nonlocal theory causes the system to stop at a bifurcation critical point.

Unified elastoplastic finite difference and its application

Two elastoplastic constitutive models based on the unified strength theory (UST) are established and implemented in an explicit finite difference code, fast Lagrangian analysis of continua (FLAC/FLAC3D), which includes an associated/non-associated flow rule, strain-hardening/softening, and solutions of singularities. Those two constitutive models are appropriate for metallic and strength-different (SD) materials, respectively. Two verification examples are used to compare the computation results and test data using the two-dimensional finite difference code FLAC and the finite element code ANSYS, and the two constitutive models proposed in this paper are verified. Two application examples, the large deformation of a prismatic bar and the strain-softening behavior of soft rock under a complex stress state, are analyzed using the three-dimensional code FLAC3D. The two new elastoplastic constitutive models proposed in this paper can be used in bearing capacity evaluation or stability analysis of structures built of metallic or SD materials. The effect of the intermediate principal stress on metallic or SD material structures under complex stress states, including large deformation, three-dimensional and non-association problems, can be analyzed easily using the two constitutive models proposed in this paper.

Experimental Study on Mechanics Performance of Complex High Titanium Heavy Slag Concrete

In view of the present situation that the preparation of complex high titanium heavy slag concrete (hereinafter referred to as CHTHSC) by using all coarse aggregate, fine aggregate and ground admixture made of high titanium heavy slag, is in need of experiments and studies in detail, this paper, based on the verification and analysis of structural stability of complex high titanium heavy slag and through tests of preparing CHTHSC from C10 to C55, compares CHTHSC with ordinary concrete and high titanium heavy slag concrete (hereinafter referred to as HTHSC) from three aspects of mixture amount of coarse aggregate, fine aggregate and composite powder. Results show that the compression resistance, axial compression resistance and cleavage strength of CHTHSC are higher than those of the other two kinds of concrete. For CHTHSC, it is appropriate to have composite powder take the place of 15%-20% of cement content.

A new approach to stability analysis of frame structures using Trefftz-type elements

This paper presents some new developments in structural stability analysis. A novel Trefftz-type finite element and efficient algorithms are proposed for calculating numerically exact solutions for frame structures. New shape functions are constructed by using general solutions of the homogeneous governing equation and an exact Trefftz element is formulated. An iterative algorithm based on conventional eigenvalue extraction method is then proposed, with which very accurate solutions can be obtained efficiently by using coarse finite element meshes. Further, an efficient method based on the new element matrices and Rayleigh's quotient is developed for a posteriori error estimation and solution improvement. Numerical examples are presented to demonstrate the effectiveness of the proposed element and algorithms. Finally, concluding remarks are made including those on the further extension of the approach.

Impact of Linkage Group in Comb-Like Polymer on Dispersion Properties of Cement Pastes

The present study aimed to develop a full understanding of the effects of the linkage group type in comb-like polymers on dispersion and dispersion retention of concentrated cement pastes. Two comb-like copolymer dispersants with ester and ether linkage groups were produced. The effects of the linkage group type in the comb-like polymers on the adsorption, dispersion, dispersion retention of the concentrated cement suspensions were investigated systematically. The mechanism of dispersion retention was investigated using isothermal calorimetry measurements and structure stability analysis. The retention of dispersion had a close relationship with the hydration of cement and hydrolysis of side chains.

Structural Adaptation of Cold-Active RTX Lipase fromPseudomonassp. Strain AMS8 Revealed via Homology and Molecular Dynamics Simulation Approaches

The psychrophilic enzyme is an interesting subject to study due to its special ability to adapt to extreme temperatures, unlike typical enzymes. Utilizing computer-aided software, the predicted structure and function of the enzyme lipase AMS8 (LipAMS8) (isolated from the psychrophilic Pseudomonas sp., obtained from the Antarctic soil) are studied. The enzyme shows significant sequence similarities with lipases from Pseudomonas sp. MIS38 and Serratia marcescens. These similarities aid in the prediction of the 3D molecular structure of the enzyme. In this study, 12 ns MD simulation is performed at different temperatures for structural flexibility and stability analysis. The results show that the enzyme is most stable at 0°C and 5°C. In terms of stability and flexibility, the catalytic domain (N-terminus) maintained its stability more than the noncatalytic domain (C-terminus), but the non-catalytic domain showed higher flexibility than the catalytic domain. The analysis of the structure and function of LipAMS8 provides new insights into the structural adaptation of this protein at low temperatures. The information obtained could be a useful tool for low temperature industrial applications and molecular engineering purposes, in the near future.

Reaction Kinetic Form for Lumped Process System Models

The class of isotherm lumped process systems with constant overall mass in each of its balance volumes is considered in this paper. It is shown that the convection and transfer mechanisms can be described by a mass action law chemical reaction network (MAL CRN) with only linear kinetics where the in- and outflow terms are represented using the zero complex. This gives rise to a convection and transfer reaction sub-graph that connects atomic complexes consisting of the components in the balance volumes of the system. The real chemical reactions in each of the balance volumes can be described by their own CRNs, where the chemical reaction sub-graphs may be disconnected from the convection and transfer reaction sub-graph when nonlinear reactions occur. In the case of chemical reactions with a finite number of steady state points, the underlying linear dynamical system enables us to construct a dynamically similar linear overall reaction graph for the whole process system. The resulting overall reaction graph can be used for structural stability analysis by applying its graph theoretical properties.

Structure stability analysis of Ni<SUB align="right">n(n = 2 - 22) using nature inspired algorithms: a performance study

Using nature inspired algorithms (NIAs) with plane-wave self-consistent field (PWSCF), density functional theory (DFT) and pseudo-potentials, the minimisation of potential energy and relative stability for Nin clusters (n = 2 – 22) were studied. The genetic algorithm (GA), differential evaluation (DE), particle swarm optimisation (PSO) and artificial bee colony (ABC) are used for global structural optimisations with space-fixed Cartesian coordinates. Clusters obtained from NIA search were further optimised by using first principals total energy calculations. We found that GA gives minimum energy for Nin (n = 6, 11, 16, 21), DE gives minimum energy for Nin (n = 2, 4, 7, 9, 15, 17), PSO gives minimum energy for Nin (n = 3, 10, 12, 14, 18, 20) and ABC gives minimum energy for Nin (n = 5, 8, 13, 19, 22).

Large displacement stability analysis of thin plate structures: Scope of MPI/OpenMP parallelization in harmonic coupled finite strip analysis

The paper presents large displacement stability analysis of orthotropic thin plate structures with different boundary conditions along the diaphragm-supported edges. A semi-analytical harmonic coupled finite strip method (HCFSM) is used to solve the large deflection and the post-buckling problems or may be applied to both problems simultaneously. The stability of equilibrium states is assessed by looking at the eigenvalues of tangent stiffness matrix of structure. In the HCFSM formulation the coupling of all series terms dramatically increases computation time when a large number of series terms are used. Therefore it is natural to use parallel programming standards, such as MPI and OpenMP to speed up computation. The examples provided justify the proposed improvements in the conventional FSM and are in accordance with the experimental data.

A generalized three-dimensional failure criterion for rock masses

The smooth convex generalized failure function, which represents 1/6 part of envelope in the deviatoric plane, is proposed. The proposed function relies on four shape parameters (Ls, a, b and c), in which two parameters (a and b) are dependent on the others. The parameter Ls is called extension ratio. The proposed failure function could be incorporated with any two-dimensional (2D) failure criteria to make it a three-dimensional (3D) version. In this paper, a mathematical formulation for incorporation of Hoek-Brown failure criterion with the proposed function is presented. The Hoek-Brown failure criterion is the most suited 2D failure criterion for geomaterials. Two types of analyses for best-fitting solution of published true tri-axial test data were made by considering (1) constant extension ratio and (2) variable extension ratio. The shape and strength parameters for different types of rocks have been determined by best-fitting the published true tri-axial test data for both the analyses. It is observed from the best-fitting solution by considering uniform extension ratio (Ls) that shape constants have a correlation with Hoek-Brown strength parameters. Thus, only two parameters (σc and m) are needed for representing the 3D failure criterion for intact rock. The statistical expression between shape and Hoek-Brown strength parameters is given. In the second analysis, when considering varying extension ratio, another parameter f is introduced. The modified extension ratio is related to f and extension ratio. The results at minimum mean misfit for all the nine rocks indicate that the range of f varies from 0.7 to 1.0. It is found that mean misfit by considering varying extension ratio is lower than that in the first analysis. But it requires three parameters. A statistical expression between f and Hoek-Brown strength parameters has been established. Though coefficient of correlation is not reasonable, we may eliminate it as an extra parameter. At the end of the paper, a methodology has also been given for its application to isotropic jointed rock mass, so that it can be implemented in a numerical code for stability analysis of jointed rock mass structures.