Efficient Structural Analysis Research Articles

Simplified methods for efficient seismic design and analysis of water-surrounded composite axisymmetric structures

Available simplified formulations for the seismic analysis of axisymmetric structures address materially homogeneous solids with uniform cross-sections, while generally neglecting the effects of higher vibration modes and soil flexibility. In this paper, we develop original simplified procedures that remove these restrictions for practical seismic design and safety evaluation of axisymmetric structures vibrating in contact with water. The procedures proposed take account of higher vibration modes, water compressibility and flexibility of underlying foundation of the structure. For practical purposes, the formulations are first derived while neglecting the effects of surface gravity waves, and are then extended to account for these effects when required. Composite axisymmetric structures made of different materials as well as those with non-uniform hollow cross-sections due to geometric irregularity of interior wall are covered. Step-by-step flowcharts are provided so that the calculations can be easily implemented in a daily practical engineering environment. Application of the proposed techniques is illustrated through the examples of homogeneous and composite axisymmetric tower–water systems with rigid and flexible foundations. The obtained results are successfully validated against advanced coupled fluid–structure finite element solutions.

Multi-objective shape optimization of plate structure under stress criteria based on sub-structured mixed FEM and genetic algorithms

This paper presents a methodology for the multi-objective (MO) shape optimization of plate structure under stress criteria, based on a mixed Finite Element Model (FEM) enhanced with a sub-structuring method. The optimization is performed with a classical Genetic Algorithm (GA) method based on Pareto-optimal solutions and considers thickness distributions parameters and antagonist objectives among them stress criteria. We implement a displacement-stress Dynamic Mixed FEM (DM-FEM) for plate structure vibrations analysis. Such a model gives a privileged access to the stress within the plate structure compared to primal classical FEM, and features a linear dependence to the thickness parameters. A sub-structuring reduction method is also computed in order to reduce the size of the mixed FEM and split the given structure into smaller ones with their own thickness parameters. Those methods combined enable a fast and stress-wise efficient structure analysis, and improve the performance of the repetitive GA. A few cases of minimizing the mass and the maximum Von Mises stress within a plate structure under a dynamic load put forward the relevance of our method with promising results. It is able to satisfy multiple damage criteria with different thickness distributions, and use a smaller FEM.

Lagrange‐type modeling of continuous dielectric permittivity variation in double‐higher‐order volume integral equation method

AbstractA novel double‐higher‐order entire‐domain volume integral equation (VIE) technique for efficient analysis of electromagnetic structures with continuously inhomogeneous dielectric materials is presented. The technique takes advantage of large curved hexahedral discretization elements—enabled by double‐higher‐order modeling (higher‐order modeling of both the geometry and the current)—in applications involving highly inhomogeneous dielectric bodies. Lagrange‐type modeling of an arbitrary continuous variation of the equivalent complex permittivity of the dielectric throughout each VIE geometrical element is implemented, in place of piecewise homogeneous approximate models of the inhomogeneous structures. The technique combines the features of the previous double‐higher‐order piecewise homogeneous VIE method and continuously inhomogeneous finite element method (FEM). This appears to be the first implementation and demonstration of a VIE method with double‐higher‐order discretization elements and conformal modeling of inhomogeneous dielectric materials embedded within elements that are also higher (arbitrary) order (with arbitrary material‐representation orders within each curved and large VIE element). The new technique is validated and evaluated by comparisons with a continuously inhomogeneous double‐higher‐order FEM technique, a piecewise homogeneous version of the double‐higher‐order VIE technique, and a commercial piecewise homogeneous FEM code. The examples include two real‐world applications involving continuously inhomogeneous permittivity profiles: scattering from an egg‐shaped melting hailstone and near‐field analysis of a Luneburg lens, illuminated by a corrugated horn antenna. The results show that the new technique is more efficient and ensures considerable reductions in the number of unknowns and computational time when compared to the three alternative approaches.

Miniaturized Double-Layer EBG Structures for Broadband Mutual Coupling Reduction Between UWB Monopoles

Novel miniaturized two-layer electromagnetic band gap (EBG) structures are presented for reducing the electromagnetic coupling between closely spaced ultra wideband (UWB) planar monopoles on a common ground. The proposed EBG structures employ two closely coupled arrays, one comprising linear conducting patches and the other comprising apertures (slits) in the ground plane. The two arrays are printed on either side of a very thin dielectric layer (55 μm) with a rotation between the elements to produce maximum coupling for miniaturizing. A microstrip line excitation is initially used for the efficient analysis and design of the slit-patch EBG structures, which are subsequently employed between two UWB printed monopoles. The proposed EBG structure has a small footprint and produces a significant reduction of the mutual coupling across the wide operating band of the UWB antennas. Simulated results and measurements of fabricated prototypes are presented.

Generation of artificial accelerograms for efficient life-cycle cost analysis of structures

The main objective of the study is to propose a methodology for generating the minimum number of required seismic accelerograms for performing with reliability and computational efficiency life-cycle cost analysis (LCCA) studies. The implementation of LCCA framework in earthquake engineering requires the calculation of different cost components that are related to structural performance assessed for multiple earthquake hazard levels. The selection of the ground motions plays an important role in the efficiency and reliability of the LCCA procedure. In this study, three different suites of accelerograms are considered and their effect on LCCA is examined in two 3D reinforced concrete buildings. The first suite is composed by natural records originated from the region of interest and are scaled to the hazard levels considered. The second suite comprises of artificial accelerograms generated based on the elastic response spectra of the considered hazard levels. Previous studies have shown that artificial accelerograms underestimate the maximum drift and maximum floor acceleration responses. On the other hand, the number of natural records required for reliable calculation of life-cycle cost is high, thus the computational effort also increases. Consequently, in order to combine robustness and computational efficiency, the third suite is formed by generating representative artificial accelerograms for the hazard levels considered, where the random characteristics of peak ground acceleration are taken into account.

Dynamics of steel offshore platforms under ship impact

This paper deals with the prediction of the dynamic response of steel offshore platforms to high energy impacts from typical supply vessels. The contribution of the high modes of a cantilever beam type structure with a concentrated top mass subjected to transverse impact from rigid and deformable strikers is analysed. A procedure to develop simplified equivalent systems for efficient structural response analysis is presented and its reliability tested by comparing the results from the explicit non-linear FE simulations. Effects such as the overall rotation of the installation, plastic deformations in the contact area, different impact locations and different hinge mechanisms are taken into account. It is shown that the use of the proposed equivalent systems with a reduced number of DOF's can provide accurate results at significantly less computational efforts as compared to the FE simulations. The derivation of some parameters of the equivalent dynamic elastic–plastic SDOF/2SDOF systems, however, needs to consider the complexity of the analysed steel frames and perform preliminary non-linear static analyses. Therefore, further studies of different impact scenarios on platforms with different configurations are recommended to augment the results presented here.

Efficient Sensitivity Analysis of Structures with Local Modifications. II: Transfer Functions and Spectral Densities

The deterministic frequency response analysis and the stationary random vibration of large, linear structural models are often computationally intensive tasks. The computational expense is only exacerbated when stiffness and damping variabilities are present in the system’s description. This paper proposes an approach for the highly computationally efficient and accurate computation of the sensitivities, to changes in design parameters that are spatially localized within some small portion of the computational model, of the transfer functions (TFs), power spectral densities, and mean-square responses of a structural system. The proposed method is derived, first for system TFs and then their sensitivities; the corresponding spectral densities are then derived using the TF approach. Finally, the proposed method is applied to two examples, one simple model where exact solutions can be computed, and a second, more realistic, building example with a high-order model that causes significant difficulties for standard state-space (SS) approaches in MATLAB as a result of numerical inaccuracies in the computations for very high-order SS models. The proposed method is shown to be highly accurate, with relative errors on the order of 10−10, but is 4–6 orders of magnitude faster than conventional approaches.

Efficient Sensitivity Analysis of Structures with Local Modifications. I: Time Domain Responses

The time evolution of the parameter sensitivity of a nonlinear dynamical system is essential to its successful design, control, and identification. For an important class of systems, the governing equations of motion can be expressed as a linear system of ordinary differential equations augmented with a low-rank parameter-dependent (generally nonlinear) vector function. This paper builds on previous efforts by the authors to devise an approach for computing not only the responses of such systems but also the sensitivities of their responses to changes in design parameters in a computationally efficient manner. The proposed solution procedure first segregates the degrees of freedom appearing in the augmented functions from those that involve only linear deterministic operations. Second, the responses and sensitivities of the augmented terms are determined by solving the Volterra integral equations of reduced dimension. Finally, the responses and sensitivities of all remaining desired outputs are computed through a convolution approach using the fast Fourier transform to further increase the computational efficiency. The proposed method is applied to two examples, one simple linear model where exact solutions can be computed, and a second, more realistic, example of a wind-excited 20-story building augmented with nonlinear tuned mass dampers on its roof. The proposed method is shown to possess accuracy levels similar to those obtained through the time integration of the corresponding analytical sensitivity equations; however, it is several orders of magnitude faster than conventional sensitivity analysis approaches.

A Linear Strain, Curvature-Driven Triangular Element for the Analysis of Membrane Structures

The analysis of membrane structures is made complex by the essentially anti-clastic geometry and flexibility introducing significant geometric non-linearities. With the increasing application of these structures in high-profile projects, the introduction of new materials in the form of ETFE foil, for example, and the impending requirements of a membrane structures-specific Eurocode, the need for high quality analysis capabilities is paramount. Existing formulations lag behind shell element counterparts and are based on a range of principles, from discrete to continua, and uniaxial to plane stress constitutive laws. In this paper, we present a linear strain triangular element for the efficient and accurate analysis of membrane structures. The triangular geometry of the element meets typical patterning needs, whilst the novel inclusion of curvature means that each element closely matches the characteristics of the local surface of the membrane efficiently. This is achieved without the introduction of rotational degrees-of-freedom, therefore negating bending stiffnesses that may compromise the quality of the simulation. The element is also shown to work well in predicting the onset and development of wrinkling.

Mathematical Foundations for Efficient Structural Controllability and Observability Analysis of Complex Systems

The relationship between structural controllability and observability of complex systems is studied. Algebraic and graph theoretic tools are combined to prove the extent of some controller/observer duality results. Two types of control design problems are addressed and some fundamental theoretical results are provided. In addition new algorithms are presented to compute optimal solutions for monitoring large scale real networks.

Efficient integral equation-based analysis of finite periodic structures in the optical frequency range

The optical response of dense finite arrays of nanoparticles can be efficiently analyzed with the help of macro basis functions obtained by employing the array scanning method. This is demonstrated by analyzing optical collimation in arrays of silver nanorods. The accuracy of the solution obtained with the proposed method has been validated by comparison with solutions obtained employing the Krylov subspace iterative method. The relative error in the electric field distribution on an observation plane above the finite array is of the order of -25 dB, while the number of unknowns is reduced by a factor of 32.

A superelement formulation for efficient structural analysis in progressive collapse

An integrated superelement concept is proposed to improve the computational efficiency when analyzing structural responses during progressive collapses of large-scale structures, such as multi-storey reinforced concrete buildings. While the proposed methodology is straightforward and can be implemented into an existing finite element program with little effort, it is able to significantly reduce the computational cost without the loss of any critical information of the structural responses. Compared with the models without superelement, significant saving in computational cost and satisfactory prediction accuracy can be obtained with the proposed approach.

Efficient structural analysis of wall–frame structures

SUMMARYIn this study, an efficient analytical model for the dynamic analysis of tall buildings with a shear wall–frame structural system has been proposed. A shear wall–frame structural system usually consists of a core wall showing flexural behavior and a frame presenting shear behavior. Therefore, the deformed shape of the shear wall–frame structural system is shown by the combination of flexural mode and shear mode. To consider this characteristic in developing an efficient analytical model, the effect of shear wall and frame on the dynamic behavior of a tall building with a dual system has been separately investigated. In order to consider the effect of the shear wall in the frame model without shear wall, a rigid body was used instead of the shear wall. Each equivalent model for the separated shear wall part and frame part has been independently developed, and two equivalent models were then combined to create an efficient analytical model for tall buildings with a shear wall–frame structural system. In order to verify the efficiency and accuracy of the proposed method, time history analyses of tall buildings with a shear wall–frame system were performed. With analytical results, it has been confirmed that the proposed method can provide accurate results with significantly reduced computational time and memory. Copyright © 2013 John Wiley & Sons, Ltd.

GlycReSoft: A Software Package for Automated Recognition of Glycans from LC/MS Data

Glycosylation modifies the physicochemical properties and protein binding functions of glycoconjugates. These modifications are biosynthesized in the endoplasmic reticulum and Golgi apparatus by a series of enzymatic transformations that are under complex control. As a result, mature glycans on a given site are heterogeneous mixtures of glycoforms. This gives rise to a spectrum of adhesive properties that strongly influences interactions with binding partners and resultant biological effects. In order to understand the roles glycosylation plays in normal and disease processes, efficient structural analysis tools are necessary. In the field of glycomics, liquid chromatography/mass spectrometry (LC/MS) is used to profile the glycans present in a given sample. This technology enables comparison of glycan compositions and abundances among different biological samples, i.e. normal versus disease, normal versus mutant, etc. Manual analysis of the glycan profiling LC/MS data is extremely time-consuming and efficient software tools are needed to eliminate this bottleneck. In this work, we have developed a tool to computationally model LC/MS data to enable efficient profiling of glycans. Using LC/MS data deconvoluted by Decon2LS/DeconTools, we built a list of unique neutral masses corresponding to candidate glycan compositions summarized over their various charge states, adducts and range of elution times. Our work aims to provide confident identification of true compounds in complex data sets that are not amenable to manual interpretation. This capability is an essential part of glycomics work flows. We demonstrate this tool, GlycReSoft, using an LC/MS dataset on tissue derived heparan sulfate oligosaccharides. The software, code and a test data set are publically archived under an open source license.

Superelements for a computationally efficient structural analysis of elliptical fuselage sections

The paper deals with the computationally efficient linear static analysis of cylindrical frame-stringer stiffened fuselage structures. In this regard a special dedicated finite element is proposed, which is a combination of curved beam elements and shell elements. This element is based on classical beam theory as well as on membrane shell theory. It is derived using approach functions that consider the differential couplings between the approach functions and hence allows for larger element sizes. Therefore an analysis can be carried out with only few degrees of freedom and hence the computational time for structural analyses is significantly reduced. An approximation technique is discussed to enable the analysis of elliptical cross-sections using circular elements. The element aids in a computationally efficient analysis of the entire fuselage, without compromising accuracy compared to other conventional finite element softwares. As an example for illustrating the application of the developed element a numerical analysis of an orthogonally stiffened fuselage structure made of a symmetric orthotropic laminate is presented.

5MW급 풍력발전기용 기어박스 하우징의 형상 최적설계

5MW급 풍력발전용 기어박스의 효율적인 구조해석과 근사모델을 생성하여 경량화를 위한 형상 최적설계를 수행하였다. 풍력발전용 기어박스의 구조는 기어 트레인, 축, 베어링, 하우징과 같이 복잡한 구성요소로 이루어져 있어 구조해석에 많은 요소 수를 요구하고 있다. 본 연구에서는 헬리컬 기어의 치강성 계수를 고려한 효과적인 기어박스의 구조해석 모델을 생성하였다. 치강성 계수를 사용한 유성 기어열은 상대적으로 적은 요소 수와 해석시간으로도 전체 기어박스 시스템의 구조해석과 형상 최적화를 가능케 한다. 치강성을 이용한 단순화된 해석모델과 근사모델을 적용하여 하우징 무게에 영향이 큰 부위의 두께를 설계변수로 설정하여 케이스 최적설계안을 도출하였으며, 최적설계를 위해 사용된 근사모델의 신뢰성과 최적 기어박스 하우징 형상의 수치해석을 통해 타당성을 검증하였다. The thickness optimization of the gearbox housing for 5MW wind turbine is carried out with the help of the efficient structure analysis model and the approximation model of objective function. Wind turbine gearbox is a complex structural system composed of a number of gear trains, shafts, bearing and gearbox housing, requiring a tremendous number of elements for the structural analysis and design. In this paper, an effective analysis and design model considering the tooth stiffness of helical gears is proposed. It enables to significantly reduce the total element number and the analysis time. Through the numerical optimization of housing thickness making use of the effective gearbox model and the approximate model of objective function, the total weight of the gearbox housing is minimized. It has been observed from the numerical experiment that the approximation model is reliable and the optimization result is acceptable and verified analysis.

Efficient single-step time-dependent analysis of PC structures

This paper describes an efficient single-step method to predict the time-dependent behaviour of prestressed concrete (PC) structures due to concrete creep, concrete shrinkage and cable relaxation. A versatile tendon sub-element is first developed to model prestressing cables of arbitrary profiles. To enable accurate estimation of losses of cable forces, a new relaxation model is formulated based on the equivalent creep coefficient, which is verified to work not only in the case of intrinsic relaxation but also under various boundary conditions. An efficient single-step finite-element method is then devised for time-dependent analysis of PC structures considering creep, shrinkage and relaxation based on the age-adjusted elasticity modulus, shrinkage-adjusted elasticity modulus and relaxation-adjusted elasticity modulus respectively. The effects of creep, shrinkage and relaxation on the long-term performance of PC structures are investigated. The numerical results obtained indicate not only the accuracy of the method but also the significance of considering the interaction among various time-varying factors.

Inferring Biological Structures from Super-Resolution Single Molecule Images Using Generative Models

Localization-based super resolution imaging is presently limited by sampling requirements for dynamic measurements of biological structures. Generating an image requires serial acquisition of individual molecular positions at sufficient density to define a biological structure, increasing the acquisition time. Efficient analysis of biological structures from sparse localization data could substantially improve the dynamic imaging capabilities of these methods. Using a feature extraction technique called the Hough Transform simple biological structures are identified from both simulated and real localization data. We demonstrate that these generative models can efficiently infer biological structures in the data from far fewer localizations than are required for complete spatial sampling. Analysis at partial data densities revealed efficient recovery of clathrin vesicle size distributions and microtubule orientation angles with as little as 10% of the localization data. This approach significantly increases the temporal resolution for dynamic imaging and provides quantitatively useful biological information.

Perturbation Finite Element Transfer Matrix Method for Random Eigenvalue Problems of Uncertain Structures

The rapid computation of random eigenvalue problems of uncertain structures is the key point in structural dynamics, and it is prerequisite to the efficient dynamic analysis and optimal design of structures. In this paper, by combining finite element-transfer matrix method (FE-TMM) with perturbation method, a new method named as perturbation FE-TMM is presented for random eigenvalue problems of uncertain structures. By using the proposed method, the rapid computation of random eigenvalue problems of uncertain structures with complicated shapes and boundaries can be achieved, and the repeated eignvalues and characteristic vectors can be solved conveniently. Compared with stochastic finite element method, this method has the low memory requirement, high computational efficiency and high computational stability. It has more advantages for dynamic design of uncertain structures. Formulations as well as some numerical examples are given to validate the method.

Preliminary design of composite fuselage structures using analytical rapid sizing methods

The increasing use of composite materials in aircraft structures aims in reducing the structural weight significantly. In order to exploit the advantages of composite materials especially within a large-scale optimization calculation, a model for a computationally efficient structural analysis needs to be developed. In this regard, algorithms need to be developed to rapidly compute stress distribution and critical loads for both strength and stability of the composite aircraft fuselage. Therefore, sizing methods for metallic and composite orthotropically stiffened fuselage structures have been reviewed. For critical load computation, fibre fracture and inter-fibre fracture need to be taken into consideration with respect to strength. Regarding stability, the critical buckling loads of skins and stringers as well as the critical crippling load need to be taken into account. The buckling of stringers often occurs after the skin buckling load is exceeded. Hence, the postbuckling behaviour needs to be analyzed and load redistributions in the postbuckling range have to be taken into consideration. These load redistributions can generally be calculated numerically using either the finite element method or the finite strip method (Mocker and Reimerdes in Compos Struct 73:237–243, 2006) as well as analytically. In order to minimize the computational time, the postbuckling behaviour of the skins regarded as composite plates is computed analytically within this work by means of a computation of effective stiffnesses for global analysis and local failure load computation. Even though the postbuckling behaviour of metallic and composite plates has been widely studied in literature, only few work has been spent on the analytical or semi-analytical derivation of methods for the common load case of combined compression and shear loading. As the preliminary design of an aircraft fuselage requires a rapid and sufficiently accurate description of the postbuckling behaviour, the postbuckling behaviour of an orthotropic composite plate under combined compression and shear loading is analytically analyzed within the present work. The derived rapid sizing method for postbuckling significantly reduces the computational time when compared to the computational time needed for a nonlinear finite element computation. In this regard, it even allows for the consideration of postbuckling behaviour within a large-scale optimization computation of complete fuselage structures.