Edge Effect Problem Research Articles

A wavelet based data coupling method for spatial damage detection in beam-type structures.

Spatial damage identification is of great significance in mechanical, aerospace, and civil engineering. In this study, a data coupling method based on continuous wavelet transform (CWT) is proposed to identify the spatial damage location of beam-type structures. The singularity of the wavelet coefficient can be used to identify the signal singularity, and data coupling method calculates the spatial location of the damage. Numerical simulations and experimental analyses of different type of beams with transfixion damage are carried out to evaluate the accuracy of the method. The results show that the wavelet based data coupling method (W-DCM) can identify the minimum 4.9% damage severity of fixed beam and continuous beam, and can also identify the damage of non-free end of cantilever beam. However, the 9.7% damage severity of the free end of the cantilever beam cannot be identified. It is also found that the W-DCM can effectively circumvent the problem of wavelet coefficients edge effect. This method and wavelet singularity are used to provide a solution to the problem of structural edge damage identification.

Correction algorithm of edge effects in inductively coupled plasma processing

Atmospheric plasma processing is a new type of non-contact processing method. And it mainly aimed at the processing of optical components or freeform mirrors without surface damage. The edge effect in plasma processing will cause the removal function to be unstable, and the convergence efficiency will be reduced. Therefore, it is necessary to improve the stability of the removal function and reduce the edge effect. Therefore, in this paper, it will focus on the edge effect problem in plasma processing, analyze the cause of the edge effect, and propose solutions for the edge effect. And, it is found that the edge effect is caused by the removal function. The area which is influenced by the edge effect will be reduced when the size of the removal function is reduced. Moreover, it is found the relationship between the removal function and radial position. Finally, the processing error will be reduced from 20 % to 10 % with the correction algorithm, which is aimed at the dwell time algorithm.

Some advances in high-performance finite element methods

PurposeThe purpose of this paper is to give a review on the newest developments of high-performance finite element methods (FEMs), and exhibit the recent contributions achieved by the authors’ group, especially showing some breakthroughs against inherent difficulties existing in the traditional FEM for a long time.Design/methodology/approachThree kinds of new FEMs are emphasized and introduced, including the hybrid stress-function element method, the hybrid displacement-function element method for Mindlin–Reissner plate and the improved unsymmetric FEM. The distinguished feature of these three methods is that they all apply the fundamental analytical solutions of elasticity expressed in different coordinates as their trial functions.FindingsThe new FEMs show advantages from both analytical and numerical approaches. All the models exhibit outstanding capacity for resisting various severe mesh distortions, and even perform well when other models cannot work. Some difficulties in the history of FEM are also broken through, such as the limitations defined by MacNeal’s theorem and the edge-effect problems of Mindlin–Reissner plate.Originality/valueThese contributions possess high value for solving the difficulties in engineering computations, and promote the progress of FEM.

Prospects for future satellite estimation of small-scale variability of ocean surface velocity and vorticity

Prospects for future satellite estimation of small-scale variability of ocean surface velocity and vorticity

Super-Resolution Reconstruction via Multi-frame Defocused Images Based on PSF Estimation and Compressive Sensing

Image super-resolution reconstruction is an effective method to improve image resolution, but most reconstruction methods rely on the clear low resolution images ignoring the blurred images which are also effective observations of the scene. Aiming at the problem, a super-resolution reconstruction (SRR) method via multi-frame defocused images is proposed. Firstly, according to the image degraded model, we establish the cost function of the point spread function (PSF) and utilize the particle swarm optimization algorithm to estimate it. Then, based on the multi-frame defocused images and PSFs, a joint reconstruction model is established to realize SRR by compressive sensing (CS) theory. In the CS framework, only the interpolated version of the low-resolution image is used for training purpose and the K-Singular Value Decomposition method is used for dictionary training. In addition, to solve the edge effect problem, an internal blur matrix is constructed according to the image blurring process, and a weight coefficient is introduced in the patch splicing process. Experiments show that the proposed algorithm can accurately estimate the defocused image PSF and achieve a good reconstruction effect.

Research on Automatic Adaptation Method for Reflector of Linear Fresnel Collector

For the solar linear Fresnel collector, the arc of the primary reflective mirror is usually fixed to a certain degree, because of which, the light spot will be oversized when the solar incident angle varies within a certain range, thus affecting the concentration effect and the collecting efficiency. Moreover, the “edge effect” of the reflective mirror also has a detrimental effect on the concentration accuracy. Based on the theoretical analysis, this paper proposes a method to automatically adjust the arc of the primary reflective mirror in accordance with tracking angle, and then the method of solving the problem of edge effect is also suggested.

New hybrid-Trefftz Mindlin–Reissner plate elements for efficiently modeling the edge zones near free/SS1 edges

PurposeThe purpose of this paper is to propose a new finite element method (FEM) solving strategy for efficient analysis of the challenging edge effect problem in plate structures. Its main ideas are to develop special-purpose plate element models to effectively simulate the behaviors in the plate’s edge zones near free/SS1 edges.Design/methodology/approachThese new elements are developed based on the hybrid-Trefftz element method. During their construction procedures, the analytical solutions of the edge effect problem, which are in exponential forms, are used to enhance the interior displacement fields. Besides, the Lagrangian multipliers are introduced into the modified hybrid-Trefftz functional for considering the stress resultant constraints at free/SS1 edges. Thus, these elements theoretically possess the abilities to correctly capture the very steep gradients of the resultant distributions in the boundary layers.FindingsThese new specialized hybrid-Trefftz plate elements can very efficiently solve the edge effect problem with high accuracy, even when distorted meshes are used. Moreover, because these elements’ construction procedures contain only boundary integrals, the computation expense for accurately integrating the exponential trial functions can be considerably saved.Originality/valueThis work presents an alternative novel idea for using the FEM to more effectively handle the local stress problems by incorporating the use of the analytical trial functions.

Electrodynamical Model of Composite Cylindrical Structure with Laminated Dielectric

The article is devoted to the problem of the natural electromagnetic modes, the regions of their existence and the relationship with all possible types of resonances in the waveguide junction of a cylindrical and radial waveguides with a layered (laminated) filling of the radial waveguide with dielectric material. An electrodynamic model is created on the basis of a rigorous method of modal matching technique, with the separation of the common waveguide coupling region and the representation of the field in it in the form of a superposition of the fields of the partial waveguide eigenmodes. The structure under investigation can be used to measure the electrical parameters of dielectric samples of a cylindrical cross-section. It is shown that the measurements will have a local character, since the spectral characteristics of the junctions are determined mainly by the size of the central coupling region of the waveguides and by the electrical parameters of the dielectric that is in the junction. The problem of edge effects for samples of finite length (partial filling of a radial waveguide with dielectric) is investigated. Taking into account the edge effect enables reducing the error in measuring the permittivity for samples of arbitrary sizes in the investigated structure.

ADVANCES IN SHAPE-FREE FINITE ELEMENT METHODS: A REVIEW

As the most important tool for simulation and computation, the finite element method has been widely applied in engineering and scientific problems. However, this powerful method still suffers from some inherent deficiencies, such as the sensitivity problem to mesh distortion and so on, which have not been completely solved yet. This paper systematacially introduces some research developments on new finite element methods, i.e., the shape-free finite element methods, including the hybrid stress-function elements for plane and 2D fracture problems, the hybrid displacement-function elements for Reissner-Mindlin plate bending problem, and new unsymmetric finite element for plane and 3D elasticity. Based on the existing hybrid stress and unsymmetric finite element methods, some advanced techniques, including the analytical trial function method, new natural coordinate method, generalized conforming technique, etc., were adopted in the aforementioned new approaches. The resulting new finite element models possess high precision and good robustness. In particular, they can keep their level of performance even in extremely distorted meshes. Furthermore, some historical challenges in the finite element method, such as the limitation defined by the MacNeal's theorem, the edge effect problem of the Resissner-Mindlin plate, were also successfully solved. At the end of this paper, some features of the new methods and further development are discussed.

Bending analysis of a general cross-ply laminate using 3D elasticity solution and layerwise theory

In this study, the analytical solution of inter- laminar stresses near the free edges of a general (symmetric and unsymmetric layups) cross-ply composite laminate subjected to pure bending loading is presented based on Reddy's layerwise theory (LWT) for the first time. First, the reduced form of displacement field is obtained for a general cross-ply composite laminate subjected to a bend- ing moment by elasticity theory. Then, first-order shear deformation theory of plates and LWT is utilized to determine the global and local deformation parameters appearing in the displacement fields, respectively. One of the main advantages of the developed solution based on the LWT is exact prediction of interlaminar stresses at the boundary layer regions. To show the accuracy of this solution, three-dimensional elasticity bending problem of a laminated composite is solved for special set of boundary conditions as well. Finally, LWT results are presented for edge-effect problems of several symmetric and unsym- metric cross-ply laminates under the bending moment. The obtained results indicate high stress gradients of interlam- inar stresses near the edges of laminates.

Design of Capacitance Probe Sensor in Deep Hole Diameter Measurement

Based on the working principle of the capacitive sensor, according to the requirements of deep hole diameter measuring, a capacitance probe sensor was designed, and then the design and type-selection of probe structure, cable inner structure to the capacitance probe sensor were done. At the same time, in order to overcome the measurement error caused by eccentricity, the capacitance sensor probe and inner hole of the corresponding fastener both are designed to a taper, taper positioning is relatively accurate positioning way. The design is to avoid the measurement position offset, and ensures the coaxality on the mechanical structure. The equipotential ring technology effectively overcomes the problem of edge effect of capacitance sensor, and makes the probe’s effective measurement electrode under the condition of limited long, can effectively guarantee the measure precision. By moving the capacitance probe in the hole to the different position, we will realize the deep hole diameter measurement in different cross section.

A direct heating model to overcome the edge effect in microplates

Array-based tests in a microplate format are complicated by the regional variation in results of the outer against the inner wells of the plate. Analysis of the evaporation mechanics of sessile drops showed that evaporation rate increase with temperature was due to changes in the heat of vaporization, density and diffusion coefficient. In simulations of direct bottom heating of standard microplates, considerable heat transfer via conduction from the side walls was found to be responsible for lower temperatures in the liquid in wells close to the edge. Applying a two temperature heating mode, 304K at the side compared to 310K at the bottom, allowed for a more uniform temperature distribution. Transparency microplates were found to inherently possess immunity to the edge effect problem due to the presence of air between the liquid and solid wall.

Analysis of Free Edge Stresses in Composite Laminates Using Higher Order Theories

This paper presents the determination of the interlaminar stresses close to the free edges of general cross-ply composite laminates based on higher order equivalent single-layer theory (HESL). The laminates with finite dimensions were subjected to a bending moment, an axial force, and/or a torque for investigation. Full three-dimensional stresses in the interior and the boundary-layer regions were determined. The computed results were compared with those obtained from Reddy’s layerwise theory. It was found that HESL theory predicts precisely the interlaminar stresses near the free edges of laminates. Besides, high efficiency in terms of computational time is obtainable when HESL theory is used as compared with layerwise theory. Finally, various numerical results were presented for the cross-ply laminates. Also design guidelines were proposed to minimize the edge-effect problems in composite laminates.

A comparative assessment of edge-effect with syntax integration generated in axial and unit-segment approaches to modelling vehicular movement networks

Unit-segment analysis – a recent development in space syntax – has shown better results in modelling vehicular movement networks than the traditional axial analysis merely by using configurational measures, integration results, of roadway segments of urban grids. Despite this advancement, some of the findings of the unit-segment model have remained controversial especially in the academic community. The concern of edge-effect is one of them. That is, at the practical level, how is it possible for a unit segment analysis to predict vehicular movement of a specified urban roadway grid with high accuracy when the analysis model does not consider trips that enter into the grid from outside? This paper throws a deeper insight into this question by evaluating the intensities of edge-effect generated by both the syntax models. By using the case of Tech Terrace, a residential neighbourhood of the city of Lubbock in West Texas, and then the city itself, the study produces extensive theoretical as well as empirical evidence showing that vehicular traffic predictions made by both the models are not free from edge-effect, but the generated effect in the unit-segment model is somewhat reduced than that of the axial counterpart. The findings also suggest that the problem of edge-effect is deep founded in the perception of network topology of an urban grid, and without understanding its role in assigning trips, brought from outside the grid into the grid itself, we indeed cannot understand the space syntax approach to modelling vehicular movement networks in a comprehensive way.

The finite element analysis of the surface transformation hardening process using the power control strategy in order to reduce edge effect problems

A power control strategy was adopted in the finite element analysis of the surface transformation hardening of S355 steel in order to adjust temperature at the surface of the workpiece in the vicinity of edges. This strategy which is based on controlling the input power of the heat source as a function of the maximum temperature at the surface, allows for gaining a more uniform microstructure as a result of a uniform thermal history at the surface. The results indicate that the applied strategy is highly effective. Besides, the results obtained from the simulations suggest a combination of a large beam size and a high traveling speed in the absence of the proposed approach.

Multi-cell cooperation based on time reversal in heterogeneous wireless networks

Cooperation among heterogeneous base stations can improve spectrum efficiency through interference avoidance. This paper introduces a time reversal (TR) technique in multi-cell cooperation to mitigate interference and efficiently allocate spectrum resources. Exploiting its inherent power concentration feature, TR can effectively tackle the problem of edge effect. We present analysis and simulation results to demonstrate that proper use of TR significantly improves the spectrum efficiency of heterogeneous networks.

Edge Effect Elimination in Single-Mixture Blind Source Separation

Blind source separation (BSS) of single-channel mixed recording is a challenging task that has applications in the fields of speech, audio and bio-signal processing. Ensemble empirical mode decomposition (EEMD)-based methods are commonly used for blind separation of single input multiple outputs. However, all of these EEMD-based methods appear in the edge effect problem when cubic spline interpolation is used to fit the upper and lower envelopes of the given signals. It is therefore imperative to have good methods to explore a more suitable design choice, which can avoid the problems mentioned above as much as possible. In this paper we present a novel single-mixture blind source separation method based on edge effect elimination of EEMD, principal component analysis (PCA) and independent component analysis (ICA). EEMD represents any time-domain signal as the sum of a finite set of oscillatory components called intrinsic mode functions (IMFs). In extreme point symmetry extension (EPSE), optimum values of endpoints are obtained by minimizing the deviation evaluation function of signal and signal envelope. Edge effect is turned away from signal by abandoning both ends’ extension parts of IMFs. PCA is applied to reduce dimensions of IMFs. ICA finds the independent components by maximizing the statistical independence of the dimensionality reduction of IMFs. The separated performance of edge EPSE-EEMD-PCA-ICA algorithm is compared with EEMD-ICA and EEMD-PCA-ICA algorithms through simulations, and experimental results show that the former algorithm outperforms the two latter algorithms with higher correlation coefficient and lower relative root mean square error (RRMSE).

Characterisation of the LMS200 Laser Beam under the Influence of Blockage Surfaces. Influence on 3D Scanning of Tree Orchards

The geometric characterisation of tree orchards is a high-precision activity comprising the accurate measurement and knowledge of the geometry and structure of the trees. Different types of sensors can be used to perform this characterisation. In this work a terrestrial LIDAR sensor (SICK LMS200) whose emission source was a 905-nm pulsed laser diode was used. Given the known dimensions of the laser beam cross-section (with diameters ranging from 12 mm at the point of emission to 47.2 mm at a distance of 8 m), and the known dimensions of the elements that make up the crops under study (flowers, leaves, fruits, branches, trunks), it was anticipated that, for much of the time, the laser beam would only partially hit a foreground target/object, with the consequent problem of mixed pixels or edge effects. Understanding what happens in such situations was the principal objective of this work. With this in mind, a series of tests were set up to determine the geometry of the emitted beam and to determine the response of the sensor to different beam blockage scenarios. The main conclusions that were drawn from the results obtained were: (i) in a partial beam blockage scenario, the distance value given by the sensor depends more on the blocked radiant power than on the blocked surface area; (ii) there is an area that influences the measurements obtained that is dependent on the percentage of blockage and which ranges from 1.5 to 2.5 m with respect to the foreground target/object. If the laser beam impacts on a second target/object located within this range, this will affect the measurement given by the sensor. To interpret the information obtained from the point clouds provided by the LIDAR sensors, such as the volume occupied and the enclosing area, it is necessary to know the resolution and the process for obtaining this mesh of points and also to be aware of the problem associated with mixed pixels.

Numerical analysis of edge effects in laminated composites under uniaxial loading

Edge effects in a laminated composite with two isotropic components are analyzed. An exact approach (exact models and a quantitative criterion to assess the edge-effect zone) is used to solve the edge-effect problem. An analytic solution is found, and the nonperturbed stress state is determined. The edge-effect problem is solved approximately using a modified variational difference method and the concept of base scheme. Numerical results are presented and analyzed

Analysis of OSB Mat Structure Using CAD Technology

For further researching the structural characteristics of Orientated strand board (OSB) mat, a three-dimensional model was developed using computer-aided design (CAD) technology to simulate behaviors of individual strands in the mat-forming process. This model provided a more realistic description of the mat structure than the previous simulations in using varied strand geometry and different types of strand orientation, defining strand location, and solving the problem of edge effect. This model can be used to analyze the impact of strand orientation on the number of strand overlaps, and to identify the relationship of strand orientation and the horizontal voids distribution in the mat. Information provided by this model is the basis of further studying the effect of the mat formation on panel void characteristics, and the relationship of the voids volume to panel properties.