Edge Constraints Research Articles

Natural vibration analysis of stiffened panels with arbitrary edge constraints using the assumed mode method

Natural vibration analysis of stiffened panels represents an important issue in different kinds of engineering applications. In this article, a procedure for the vibration analysis of stiffened panels with arbitrary edge constraints is presented. It is based on the assumed mode method, where natural frequencies and modes are determined by solving an eigenvalue problem of a multi-degree-of-freedom system matrix equation derived by using Lagrange’s equations of motion. The Mindlin thick plate theory is applied for a plate, while the effect of stiffeners having the properties of Timoshenko beams is accounted for by adding their strain and kinetic energies to the corresponding plate energies. The accuracy of the proposed procedure is justified by several numerical examples which include the natural vibration analysis of stiffened panels with different framing sizes, their lengths and orientations, plate thicknesses and different combinations of boundary conditions. A comparison of results with those obtained by the finite element method is provided, and good agreement is achieved.

Filtering Airborne Lidar Data by Modified White Top-Hat Transform with Directional Edge Constraints

Filtering Airborne Lidar Data by Modified White Top-Hat Transform with Directional Edge Constraints

Free Vibration Analysis of Moderately Thick Antisymmetric Angle-Ply Laminated Rectangular Plates with Elastic Edge Constraints

A simple formulation for studying the free vibration of shear-deformable antisymmetric angle-ply laminated rectangular plates having translational as well as rotational edge constraints is presented. The aim is to fill the void in the available literature. The spatial discretization of the resulting mathematical model in five field variables is carried out using the two-dimensional Differential Quadrature Method. Validation of the formulation is done with the help of convergence studies with respect to the number of nodes. The results are compared with those from past investigations available only for simpler problems. Effects of material, geometrical, and support parameters are studied.

Postbuckling of functionally graded cylindrical shells with tangential edge restraints and temperature-dependent properties

This paper presents an analytical approach to investigate the buckling and postbuckling behavior of functionally graded cylindrical shells subjected to thermal and axial compressive loads. Material properties are assumed to be temperature dependent and graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of constituents. The governing equations are established within the framework of classical thin shallow shell theory taking both geometrical nonlinearity in von Karman–Donnell sense and initial imperfection into consideration. Thermal stability analysis also incorporates the effects of tangential edge constraints. A Galerkin procedure is applied to derive expressions of load-deflection relations from which the thermal buckling loads and postbuckling curves of the shells are obtained by an iteration. Effects played by material and geometrical properties, tangential stiffness, imperfection and buckling modes are discussed.

Stereo matching by using the global edge constraint

Stereo matching, the key problem in the field of computer vision has long been researched for decades. However, constructing an accurate dense disparity map is still very challenging for both local and global algorithms, especially when dealing with the occlusions and disparity discontinuities. In this paper, by exploring the characteristics of the color edges, a novel constraint named the global edge constraint (GEC) is proposed to discriminate the locations of potential occlusions and disparity discontinuities. The initial disparity map is estimated by using a local algorithm, in which the GEC could guarantee that the optimal support windows would not cross the occlusions. Then a global optimization framework is adopted to improve the accuracy of the disparity map. The data term of the energy function is constructed by using the reliable correspondences selected from the initial disparity map; and the smooth term incorporates the GEC as a soft constraint to handle the disparity discontinuities. Optimal solution can be approximated via existing energy minimization approaches such as Graph cuts used in this paper. Experimental results using the Middlebury Stereo test bed demonstrate the superior performance of the proposed approach.

Influence of plasma diagnostics and constraints on the quality of equilibrium reconstructions on Joint European Torus

One of the main approaches to thermonuclear fusion relies on confining high temperature plasmas with properly shaped magnetic fields. The determination of the magnetic topology is, therefore, essential for controlling the experiments and for achieving the required performance. In Tokamaks, the reconstruction of the fields is typically formulated as a free boundary equilibrium problem, described by the Grad-Shafranov equation in toroidal geometry and axisymmetric configurations. Unfortunately, this results in mathematically very ill posed problems and, therefore, the quality of the equilibrium reconstructions depends sensitively on the measurements used as inputs and on the imposed constraints. In this paper, it is shown how the different diagnostics (Magnetics Measurements, Polarimetry and Motional Stark Effect), together with the edge current density and plasma pressure constraints, can have a significant impact on the quality of the equilibrium on JET. Results show that both the Polarimetry and Motional Stark Effect internal diagnostics are crucial in order to obtain reasonable safety factor profiles. The impact of the edge current density constraint is significant when the plasma is in the H-mode of confinement. In this plasma scenario the strike point positions and the plasma last closed flux surface can change even by centimetres, depending on the edge constraints, with a significant impact on the remapping of the equilibrium-dependent diagnostics and of pedestal physics studies. On the other hand and quite counter intuitively, the pressure constraint can severely affect the quality of the magnetic reconstructions in the core. These trends have been verified with several JET discharges and consistent results have been found. An interpretation of these results, as interplay between degrees of freedom and available measurements, is provided. The systematic analysis described in the paper emphasizes the importance of having sufficient diagnostic inputs and of properly validating the results of the codes with independent measurements.

Approximate natural vibration analysis of rectangular plates with openings using assumed mode method

Natural vibration analysis of plates with openings of different shape represents an important issue in naval architecture and ocean engineering applications. In this paper, a procedure for vibration analysis of plates with openings and arbitrary edge constraints is presented. It is based on the assumed mode method, where natural frequencies and modes are determined by solving an eigenvalue problem of a multi-degree-of-freedom system matrix equation derived by using Lagrange's equations of motion. The presented solution represents an extension of a procedure for natural vibration analysis of rectangular plates without openings, which has been recently presented in the literature. The effect of an opening is taken into account in an intuitive way, i.e. by subtracting its energy from the total plate energy without opening. Illustrative numerical examples include dynamic analysis of rectangular plates with rectangular, elliptic, circular as well as oval openings with various plate thicknesses and different combinations of boundary conditions. The results are compared with those obtained by the finite element method (FEM) as well as those available in the relevant literature, and very good agreement is achieved.

Approximate natural vibration analysis of rectangular plates with openings using assumed mode method

Natural vibration analysis of plates with openings of different shape represents an important issue in naval architecture and ocean engineering applications. In this paper, a procedure for vibration analysis of plates with openings and arbitrary edge constraints is presented. It is based on the assumed mode method, where natural frequencies and modes are determined by solving an eigenvalue problem of a multi-degree-of-freedom system matrix equation derived by using Lagrange's equations of motion. The presented solution represents an extension of a procedure for natural vibration analysis of rectangular plates without openings, which has been recently presented in the literature. The effect of an opening is taken into account in an intuitive way, i.e. by subtracting its energy from the total plate energy without opening. Illustrative numerical examples include dynamic analysis of rectangular plates with rectangular, elliptic, circular as well as oval openings with various plate thicknesses and different combinations of boundary conditions. The results are compared with those obtained by the finite element method (FEM) as well as those available in the relevant literature, and very good agreement is achieved.

Dynamic Relaxation Nonlinear Viscoelastic Bending Analysis of Higher-Order Annular Sector Plates

Using higher-order shear deformation theory (HSDT), nonlinear analysis of polymeric plate under uniform transverse pressure is studied considering material nonlinearity for viscoelastic material. The multiaxial stress state of the Schapery single integral equation describes the material behavior by recursive-iterative formulation. The finite difference Dynamic Relaxation (DR) method is utilized to study the annular sector plate, including geometric nonlinearity with in-plane fixed and free clamped and hinged edge constraints. The plate is considered as a laminate of isotropic layers, in which the viscoelastic properties of each layer have their own parameters during the loading. The plate deflection is predicted for different thicknesses and also various pressures at the beginning and end of loading and compared with elastic finite element results. The normal and through-thickness shear stresses are also determined in different time steps.

Edge Detection of the Impulse Noise Pollution Image Based on the Rough Set

The rough set is an effective tool to deal with incomplete, uncertain and fuzzy problem. In order to extract the edges information of the image by impulse noise pollution, further service for the follow-up image analysis and understanding, on the basis of the impulse noise pollution image preprocessing, an adaptive edge detection algorithm is put forward to process the impulse pollution image using rough set theory in this paper. Considering the target edge features can form a series of edge point constraints as the algorithm foundation,this method starts from the characteristics difference of the image edge and target area. Firstly, series edge constraint points are defined, and then the related questions of these conditions are solved by using rough set theory, so the edge detection algorithm is established. The experimental results show that this algorithm can effectively extract edge from the noise image information, to overcome the sensitivity of traditional algorithm for noise.

Free vibration analysis of laminated composite plates with elastically restrained edges using FEM

Abstract The application of FEM is shown for free vibration analysis of moderately thick laminated composite plates with edges elastically restrained against translation and rotation. The governing equations employed are based on the first order shear deformation theory including the effects of rotary inertia. Several combinations of translational and rotational elastic edge constraints are considered. Convergence study with respect to the number of nodes has been carried out and the results are compared with those from past investigations available only for simpler problems. Angle-ply and cross-ply laminates with different thickness-to-length ratios are examined. Comparisons are made with results for thin as well as moderately thick laminated plates.

Denoising diffusion-weighted magnitude MR images using rank and edge constraints.

To improve signal-to-noise ratio for diffusion-weighted magnetic resonance images. A new method is proposed for denoising diffusion-weighted magnitude images. The proposed method formulates the denoising problem as an maximum a posteriori} estimation problem based on Rician/noncentral χ likelihood models, incorporating an edge prior and a low-rank model. The resulting optimization problem is solved efficiently using a half-quadratic method with an alternating minimization scheme. The performance of the proposed method has been validated using simulated and experimental data. Diffusion-weighted images and noisy data were simulated based on the diffusion tensor imaging model and Rician/noncentral χ distributions. The simulation study (with known gold standard) shows substantial improvements in single-to-noise ratio and diffusion tensor estimation after denoising. In vivo diffusion imaging data at different b-values were acquired. Based on the experimental data, qualitative improvement in image quality and quantitative improvement in diffusion tensor estimation were demonstrated. Additionally, the proposed method is shown to outperform one of the state-of-the-art nonlocal means-based denoising algorithms, both qualitatively and quantitatively. The single-to-noise ratio of diffusion-weighted images can be effectively improved with rank and edge constraints, resulting in an improvement in diffusion parameter estimation accuracy.

Vibration Based Prediction of Noise in Passenger Car Gearbox Structures

In this paper, a method for predicting the contributions to noise radiated by a vehicle gearbox structure using measured vibration responses is presented. The gearbox structure is idealised as a set of flat plates. The radiation efficiency is calculated from the physical properties and edge constraints of each plate and the measured vibration response of the gearbox structure surfaces. These data were used in a simple acoustical power theory to determine 1/3-octave band sound pressure level under free field conditions for the whole and individual noise sources. The predicted individual noise sources are then used to pinpoint the exact problem area in the gearbox structure with a view to noise reduction.

Postbuckling behavior of functionally graded cylindrical panels with tangential edge constraints and resting on elastic foundations

This paper presents an analytical approach to investigate the effects of tangential edge constraints on the buckling and postbuckling behavior of functionally graded flat and cylindrical panels subjected to thermal, mechanical and thermomechanical loads and resting on elastic foundations. Material properties are assumed to be temperature independent, and graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of constituents. Governing equations are derived basing on the classical shell theory incorporating von Karman–Donnell type nonlinearity, initial geometrical imperfection and Pasternak type elastic foundations. Approximate solutions are assumed and Galerkin procedure are applied to obtain explicit expressions of buckling loads and load–deflection relations. The effects of in-plane edge restraint, elastic foundation, temperature and imperfection on the nonlinear response of the panels are graphically analyzed.

Analytical Technique for Predicting Passenger Car Gearbox Structure Noise Using Vibration Response Analysis

The gear pair assembly remains one of the major noise and vibration sources in power transmission systems typically used in automotive, aerospace and industrial applications. The gearbox structure vibration and noise signatures are often dominated by several high-level tonal peaks that occur at the fundamental gear mesh frequency and its harmonics and other sources. In this paper, development of the concept of a method for predicting the contributions to exterior noise radiated by an original vehicle gearbox structure using measured vibration response. An idealization of the gearbox surface as a set of flat plates was used to calculate the radiation efficiency from physical properties and edge (end) constraints of each plate, and the vibration response of the gearbox structure surface was measured using accelerometers. These data were used in a simple acoustical power theory to determine 1/3-octave band sound pressure level under free field conditions for the whole and individual noise sources. Moreover, the prediction of the individual noise sources in order to pinpoint the exact problem area in the gearbox structure so that treatment or redesign can be carried out in correct way. Research Article British Journal of Applied Science & Technology, 3(4): 860-883, 2013 861

Low Complexity Image/Video Super Resolution Using Edge and Nonlocal Self-Similarity Constraint

In this letter, we present a fast image/video super resolution framework using edge and nonlocal constraint. The proposed method has three steps. First, we improve the initial estimation using content-adaptive bilateral filtering to strengthen edge. Second, the high resolution image is estimated by using classical back projection method. Third, we use joint content-adaptive nonlocal means filtering to get the final result, and self-similarity structures are obtained by the low resolution image. Furthermore, content-adaptive filtering and fast self-similarity search strategy can effectively reduce computation complexity. The experimental results show the proposed method has good performance with low complexity and can be used for real-time environment.

Pitting Corrosion Investigation of Cantilever Beams Using F. E. Method

Carbon steel cantilever beams are widely used in many applications in aerospace, civil and mechanical engineering. Pitting corrosion is a phenomenon which places severe limitations on the design of such applications. As such, understanding this phenomenon and the methods to deal with it, are of a great importance. This paper presents numerical investigation by using F. E. (Finite Element) simulation on the load carrying capacity of corroded cantilever beams with pitting corrosion damage. The pitting corrosion hole shape has been modeled using ASTM G46 Standard Guide. Several different cases of pitting corrosion, represented by hemispherical holes, were modeled and examined by using ANSYS computer program. Clamped edge constraint was used on one end, while the other end was free. In these F. E. models, element of Solid95 was used and comparison to Bernoulli-Euler theory was made. The effect of the radius of the pitting corrosion holes on the stresses in the beam was examined in comparison to yield stress. It has been found that the M. S. (Margin of Safety) has been reduced gradually with increasing radii. Agreement with Bernoulli-Euler theory has been achieved only for small radii. Moreover, three methods of pitting corrosion repairs were examined, together with Bernoulli-Euler theory comparison: 1) Regular surface repair; 2) Extension surface repair; and 3) “Handy Removal”. It was found that extension surface repair has the highest M. S. value.

Dynamic Characters of Stiffened Composite Conoidal Shell Roofs with Cutouts: Design Aids and Selection Guidelines

Dynamic characteristics of stiffened composite conoidal shells with cutout are analyzed in terms of the natural frequency and mode shapes. A finite element code is developed for the purpose by combining an eight-noded curved shell element with a three-noded curved beam element. The code is validated by solving benchmark problems available in the literature and comparing the results. The size of the cutouts and their positions with respect to the shell centre are varied for different edge constraints of cross-ply and angle-ply laminated composite conoids. The effects of these parametric variations on the fundamental frequencies and mode shapes are considered in details. The results furnished here may be readily used by practicing engineers dealing with stiffened composite conoids with cutouts central or eccentric.

Free vibration analysis of rectangular plate with arbitrary edge constraints using characteristic orthogonal polynomials in assumed mode method

An approximate method based on an assumed mode method has been presented for the free vibration analysis of a rectangular plate with arbitrary edge constraints. In the presented method, natural frequencies and their mode shapes of the plate are calculated by solving an eigenvalue problem of a multi-degree-of-freedom system matrix equation derived by using Lagrange's equations of motion. Characteristic orthogonal polynomials having the property of Timoshenko beam functions which satisfies edge constraints corresponding to those of the objective plate are used. In order to examine the accuracy of the proposed method, numerical examples of the rectangular plates with various thicknesses and edge constraints have been presented. The results have shown good agreement with those of other methods such as an analytic solution, an approximate solution, and a finite element analysis.

Network Coding for Line Networks with Broadcast Channels

An achievable rate region for line networks with edge and node capacity constraints and broadcast channels (BCs) is derived. The region is shown to be the capacity region if the BCs are orthogonal, deterministic, physically degraded, or packet erasure with one-bit feedback. If the BCs are physically degraded with additive Gaussian noise then independent Gaussian inputs achieve capacity.