Nonplanar Elements Research Articles

On the experimental characterisation of crack tip displacement fields on nonplanar elements: Numerical and experimental analysis

In this work, a numerical and experimental study about crack tip fields characterisation on curve-cracked elements has been performed. This study combines a novel differential geometry approach combined with 3D-DIC and FEA results to determine crack-tip parameters from the displacement field on a curved cracked element. The work aims to validate and compare some aspects that cannot be addressed using 3D-DIC. SIFs for different crack lengths are determined using DIC and FEA data and compared In addition, a comprehensive comparison between experimental and numerical fields is done using an Image Decomposition technique based on Tchebichef polynomials.

Non-Planar 3D Printed Elements on Textile Substrate Using a Fused Filament Fabrication 3D Printer

Abstract Adhesion between additively printed elements on textiles is one of the most important quality characteristics. Applied elements must form very good adhesion with the textile substrate in order to produce functional textiles. The request for non-planar printing directly on textiles is growing, especially in the fields of orthopaedic engineering and protective clothing. This new printing technique can open up new areas of application. For such a production of non-planar elements on textiles, new test methods have to be developed, as the current adhesion tests (180° peel test) are not applicable to non-planar prints on textiles. For non-planar additive printing on textiles, a cylindrical print bed for a fused filament fabrication printer was developed and modified accordingly in the first step. In the next step, a new measurement method was developed to investigate the adhesion between the textile and the non-planar three-dimensional-printed element. The study shows the challenges and the adhesion differences of non-planar printed objects on pre-stretched textiles on a cylindrical print bed. Several factors influencing adhesion were identified. The alignment of the printing nozzle to the textile substrate is the key factor influencing adhesion. The alignment also has a significant influence on the visual print quality.

A novel non-planar interlocking element for tubular structures

In this paper, a novel non-planar interlocking element is developed, which can be used to construct cylindrical structures. The proposed element has a symmetrical geometry with six curved side surfaces to be interlocked with adjacent elements. A tubular structure can be constructed by assembling a number of identical non-planar elements, and the movement of each element is naturally restricted in all directions. To investigate the performance of the proposed system, a 3D finite element model is established to simulate the dynamic response of a concrete tunnel assembled using the new non-planar elements. Compared to the monolithic concrete tunnel and the tunnel constructed of normal concrete segments, the interlocking tunnel has shown a lower peak contact force and a higher energy absorption capacity. Besides, the joint opening and the damage area could be significantly reduced by the interlocking feature. A parametric study is also conducted to investigate effects of the confining load and the initial impact velocity on the performance of the interlocking system.

Vibration modelling of complex waveguide structures

In this paper, a general wave propagation approach for the vibration analysis of three-dimensional waveguide structures is presented. The analysis is based on a ray tracing method that considers wave propagation and scattering in the formulation, including the effects of decaying near-field wave components. The waveguide dispersion characteristics of straight and curved beams, which govern the propagation and decay of waves as they travel through the different components, are taken into account for different wave types (flexural, torsional, and axial). Separate elements are coupled using reflection and transmission coefficients, and these are derived for a general connection between several non-planar elements. A matrix formulation is used that offers an automatic and concise method for tackling free and forced vibrations problems of complex ring-beam structural systems. The general methodology is demonstrated on simple applications, and the predictions made using the proposed approach are shown to be in excellent agreement with a conventional finite element analysis, with the advantage of reduced computational costs.

Analyzing mutual shading among buildings

A method for evaluating solar rights and shading requirements in an urban environment is presented. The method is embedded in a CAD tool developed and adapted for this purpose. With this tool one can analyze the mutual shading between buildings and other objects like trees. The purpose of this CAD tool is to allow the designer to plan efficiently the various functions of spaces among different structures, like buildings, as well as determining the location of the passive and active solar collectors. The method is a general one and allows a fast and efficient calculation of the ratio between insolated and total surface areas of any given examined object that is shaded by other irregular and nonplanar elements. The calculation of this ratio is carried out for all the months and hours for which either shading or insolation is required. The information obtained may serve as hourly input data for any dynamic simulation model which evaluates the thermal performance of the different external or internal shading systems. For a visual and a qualitative evaluation of the shadows among buildings, the suggested model permits a very realistic representation, in which the light source is defined according to the azimuth and the altitude of the Sun at the particular time of examination. The self shading and brightness of the different surfaces and the shadows cast by the various elements at the designated time are then generated and can be evaluated visually.

A Comparative Study of Angular Scattering Characteristics of a Class Of Nonplanar Frequency Selective Surfaces

ABSTRACT In this paper we use the Method of Moments to study the transmission properties of a number of frequency selective surfaces (FSS) with 3D elements, such as the tri-dipole, the dipole-loop, the tri-loop, and the bi-loop. The frequency responses of these 3D-FSSs and those of the planar frequency selective surfaces with 2D elements, such as the loop and the window, are presented graphically for normally as well as obliquely incident plane wave illuminations. In general, the 3D-FSSs degrade the wide-angle performance of the original planar loop structure. The non-planar elements do offer the flexibility of widening the bandwidth of the frequency response and introducing multi-band capabilities when the plane wave is incident from a wide angle. However, insofar as the wide-angle response is concerned, the planar loop is still the most robust of all the structures investigated in this study.

Shading: A design tool for analyzing mutual shading between buildings

A method and a model for analyzing visually and quantitatively mutual shading between buildings is presented. The method allows fast and efficient calculation of the ratio between insolated and total surface areas of any given examined object that is shaded by other irregular and nonplanar elements. The calculation of this ratio is carried out for all the months and hours for which either shading or insolation is required. The information obtained may serve as hourly input data for any dynamic simulation model which evaluates the thermal performance of the different external or internal shading systems. For a visual and a qualitative evaluation of the shadows among buildings, the suggested model permits a very realistic representation, in which the light source is defined according to the azimuth and the altitude of the sun at the particular time of examination. The self shading and brightness of the different surfaces and the shadows cast by the different elements at the designated time are then generated and can be evaluated visually. The method is demonstrated by a case study.

Accurate numerical integration of singular boundary element kernels over boundaries with curvature

AbstractUse of the Green function, for the solution of boundary‐value problems, frequently results in singular integral equations. Algorithms are presented for the accurate and efficient treatment of singular kernels frequently encountered in the boundary element method (BEM). They are based upon the use of appropriately weighted Gaussian quadrature formulae, together with numerical geometrical transformations of the region of integration. The use of high‐order subdomain expansion functions, for interpolation over nonplanar elements, allows boundary curvature to be accommodated. In particular, the handling of Green functions with logarithmic and r−1 behaviour are detailed. Volume integrals, with r−2 singularity, are outlined. Operations are performed on a simplex, thus resulting in generality and ease of automation. This scheme has been incorporated into boundary element method software and successfully applied to a variety of problems.