Conventional Triangulation Technique Research Articles

Acoustic source localization in anisotropic plates

The conventional triangulation technique cannot locate the acoustic source in an anisotropic plate because this technique requires the wave speed to be independent of the propagation direction which is not the case for an anisotropic plate. All methods proposed so far for source localization in anisotropic plates require either the knowledge of the direction dependent velocity profile or a dense array of sensors. In this paper for the first time a technique is proposed to locate the acoustic source in large anisotropic plates with the help of only six sensors without knowing the direction dependent velocity profile in the plate. Experimental results show that the proposed technique works for both isotropic and anisotropic structures. For isotropic plates the required number of sensors can be reduced from 6 to 4.

An improved algorithm for detecting point of impact in anisotropic inhomogeneous plates

Conventional triangulation techniques fail to correctly predict the acoustic source location in anisotropic plates due to the direction dependent nature of the elastic wave speeds. To overcome this problem, Kundu et al. [1] proposed an alternative method for acoustic source prediction based on optimizing an objective function. They defined an objective function that uses the time of flight information of the acoustic waves to the passive transducers attached to the plate and the wave propagation direction ( θ) from the source point to the receiving sensors. Some weaknesses of the original algorithm proposed in Ref. [1] were later overcome by developing a modified objective function [2]. A new objective function is introduced here to further simplify the optimization procedure and improve the computational efficiency. A new algorithm for source location is also introduced here to increase the source location accuracy. The performance of the objective function and source location algorithm were experimentally verified on a homogeneous anisotropic plate and a non-homogeneous anisotropic plate with a doubler patch. Results from these experiments indicate that the new objective function and source location algorithm have improved performance when compared with those discussed in Refs. [1,2].

Detection of the point of impact on a stiffened plate by the acoustic emissiontechnique

The applicability of guided waves to predict the point of impact in a stiffened plate isinvestigated. The conventional triangulation technique cannot predict the point of impactin a stiffened plate because the triangulation technique assumes that the wave speed isindependent of the direction of propagation, which is not true for stiffened plates. Analternative method based on the optimization scheme was proposed by Kundu et al (2007 J.Acoust. Soc. Am. 122 2057–66) to locate the point of impact in plates by analyzing the timeof arrival of the ultrasonic signals received by passive sensors attached to the plate. Aftersuccessful extension of this technique to predict the point of impact in anisotropicbut homogeneous composite plates (Kundu et al 2008 Ultrasonics 48 193–201) it isinvestigated in this paper whether this technique works well for predicting the pointof impact in an inhomogeneous plate where the stiffeners make the structureinhomogeneous. Experiments are carried out by dropping ping pong and metal balls onthe plate to simulate the impact phenomenon and recording acoustic signals bypassive transducers adhesively bonded to the plate at three different locations. Theimpact points are predicted and compared with the actual locations of impact.

The cranial instrument port in arthroscopy of the canine shoulder joint

We describe the creation of a cranial instrument portal for shoulder joint arthroscopy in the dog using a target device that has been successfully employed for the caudal access. We compared the method with a conventional triangulation technique. The shoulder joints of 60 dog cadavers were investigated by arthroscopy and the two methods were compared on the basis of pre-defined parameters of outcome. Time, the number of trials, success, damage to cartilage and the accessibility of intra-articular structures were assessed. The anatomical localisation of the working cannula in muscles was also documented. In general, the new method permitted more successful insertion of the working cannula. This was achieved in a shorter period of time and was associated with fewer insertion attempts as well as less damage to joint cartilage. Intra-articular structures could be readily approached through the working cannula with both methods. Predetermined, clinically relevant points were comparatively more accessible with the new technique. Independent of the method, in only a few cases, the working cannula perforated neither muscles nor tendons when accessing the joint. It may be concluded that the new method using a target device is simpler and safer and offers a standardised technique to establish a cranial instrument port.

Health Monitoring of a Thermal Protection System using Lamb Waves

The applicability of guided waves as a structural health monitoring (SHM) tool to predict the point of impact and detect delamination in a thermal protection system (TPS) is studied. A model TPS was designed by bonding ceramic porous tiles to a 2.2 mm thick 2124-T351 aluminum alloy plate. The delamination defect may be caused by the impact phenomenon or due to other reasons such as manufacturing defect, thermal, or mechanical fatigue, etc. Impact phenomenon is simulated by dropping a ping pong ball on the tiled structure. The delamination at the interface between the ceramic tile and the aluminum plate is simulated by removing the adhesive bond at the selected interface regions during the specimen fabrication process. The conventional triangulation technique cannot predict the point of impact in a tiled plate structure because the triangulation technique assumes that the wave speed is independent of the direction of propagation which is not the case for ceramic tile mounted plates. An alternative method based on the optimization scheme was proposed by Kundu et al. [1] to locate the point of impact in plates by analyzing the time of arrival of the ultrasonic signals received by passive sensors attached to the plate. This objective function based method is used to locate the impact point on the tiled plate. Experiments are carried out by dropping a ping pong ball on the tiled structure and recording acoustic signals by passive transducers adhesively bonded to the plate at three different locations. The impact point is predicted and compared with the actual location of impact. Delamination detection studies were conducted in the pitch-catch mode, by changing the angle of strike and the frequency of the transducer excitation to generate the appropriate guided wave mode. The delamination defect could be detected and the impact point could be identified underlining the importance of the use of guided waves as an SHM tool for TPS.

Locating point of impact in anisotropic fiber reinforced composite plates

The conventional triangulation technique cannot predict the point of impact in an anisotropic composite plate because the triangulation technique assumes that the wave speed is independent of the direction of propagation which is not the case for anisotropic plates. An alternative method based on the optimization scheme was proposed by Kundu et al. [T. Kundu, S. Das, K.V. Jata, Point of impact prediction in isotropic and anistropic plates from the acoustic emission data, J. Acoust. Soc. Am. 122, 2007, 2057–2066] to locate the point of impact in plates by analyzing the time of arrival of the ultrasonic signals received by the passive sensors attached to the plate. In this paper, that objective function is modified further to overcome the inherent difficulties associated with multiple singularities and to maximize the efficiency of the acoustic emission data for multiple receiving sensors. With this modified objective function the impact point on an anisotropic composite plate is predicted from the acoustic emission data. Experiments are carried out by dropping steel and ping pong balls on a graphite-epoxy composite plate and recording acoustic signals by passive transducers adhesively bonded to the plate at three different locations. The impact point is predicted by the proposed method and compared with the actual location of impact.

Point of impact prediction in isotropic and anisotropic plates from the acoustic emission data

It is shown in this paper that the conventional triangulation technique is not very reliable for locating the impact point even in isotropic plates when the sensors are placed close to the point of strike for two reasons: First, it is difficult to pinpoint the exact time of arrival of the signal and, second, the Lamb modes in a plate are dispersive. Dispersive signals attenuate differently at various frequencies and propagate with different speeds causing distortions in the received signals, and thus introduce error in the time of flight measurement. The triangulation technique assumes that wave speeds in all directions are the same, which is not true for anisotropic plates. Here an alternative approach based on an optimization scheme is proposed to locate the point of impact in isotropic and anisotropic plates. A formulation is presented for the general anisotropic case. Experiments are carried out with an aluminum plate by dropping balls on the plate and picking up acoustic signals at different locations. The impact points predicted by the conventional triangulation technique and the proposed modified method are compared for this isotropic plate. Then it is investigated how the prediction would change if the plate is assumed to have some anisotropy.

Robust uniform triangulation algorithm for computer aided design

This paper presents a new robust uniform triangulation algorithm that can be used in CAD/CAM systems to generate and visualize geometry of 3D models. Typically, in CAD/CAM systems 3D geometry consists of 3D surfaces presented by the parametric equations (e.g. surface of revolution, NURBS surfaces) which are defined on a two dimensional domain. Conventional triangulation algorithms (e.g. ear clipping, Voronoi-Delaunay triangulation) do not provide desired quality and high level of accuracy (challenging tasks) for 3D geometry. The approach developed in this paper combines lattice tessellation and conventional triangulation techniques and allows CAD/CAM systems to obtain the required surface quality and accuracy. The algorithm uses a Cartesian lattice to divide the parametric domain into adjacent rectangular cells. These cells are used to generate polygons that are further triangulated to obtain accurate surface representation. The algorithm allows users to control the triangle distribution intensity by adjusting the lattice density. Once triangulated, the 3D model can be used not only for rendering but also in various manufacturing and design applications. The approach presented in this paper can be used to triangulate any parametric surface given in S ( u , v ) form, e.g. NURBS surfaces, surfaces of revolution, and produces good quality triangulation which can be used in CAD/CAM and computer graphics applications.

A syntactic/Semantic technique for surface reconstruction from cross-sectional contours

Surface reconstruction from cross-sectional contours has become increasingly important in medicine. In this paper, a surface reconstruction technique has been developed to improve the conventional triangulation techniques by taking into account local shape characteristics of the surface being reconstructed. The technique involves a syntactic/semantic contour representation which allows a similarity relation, based on the weighted Levenshtein graph, to be established between adjacent contours. This similarity relation is then employed as a guide to form the surface by triangulating similar substructures.