Concept Of Wave Propagation Research Articles

Diagnosing Students' Conception of Wave Propagation Using the Five-Tier Isomorphic Instrument

This research aims to develop and apply a five-tier isomorphic instrument to determine the concept of wave propagation. The research design in this study is a mixed method research design in development and implementation instrument. Quantitative data was collected on 151 students in class XII MIPA SMA Negeri 1 Jambi City using an isomorphic instrument in the form of a five-tier diagnostic test. The test instrument was first tested for validity and reliability. The validity performed includes content and construct validity. Content validity is determined based on the % False Positive (FP) and False Negative (FN), which must be <10%. Construct validity is carried out by calculating factor analysis. Meanwhile, reliability is determined based on Cronbach's Alpha coefficient with r table = 0.413 (significance level 5%). The research results show that the instrument is very valid and reliable. The average understanding of students' concepts in wave propagation material is classified in the low category because the percentage obtained is <30%, namely 16% in all four tiers. Most students' conceptions are in the category of lack of knowledge regarding wave propagation, with a percentage of 23.5%.

A strategy based on Wave Swarm for the formation task inspired by the Traveling Salesman Problem

Multi-robots can perform complex tasks such as exploration, foraging, and formation. Efficient communication between robots can contribute to the accomplishment of collective tasks through efficient message exchange. This paper proposes a strategy based on the message’s propagation technique, Wave Swarm, for the formation task inspired by the Traveling Salesman Problem. The Wave Swarm communication approach uses the concept of wave propagation for message exchange between neighbors, establishing a Father and Son relationship between robots. However, different pairs of Father and Son robots can impact the simulation time, the average distance traveled by each robot, and the number of messages exchanged during the formation task. Thus, given a random distribution of robots into a swarm, we model the problem of assigning one position and route for each robot to achieve its place in the formation as a Traveling Salesman Problem. The routes resulting from the TSP solution establish a new parental relationship between the robots in the swarm. We performed preliminary experiments to define the technique used in the TSP resolution. We tested reinforcement learning and the genetic algorithm using the TSPLIB95 library. Thus, we develop a strategy for formation tasks based on Wave Swarm and TSP solved with reinforcement learning. We adopted the leader–follower approach in an unknown environment to validate the proposal. The results show the behavior of different sizes of robot groups for various desired shapes. Experiments with the robot simulator CoppeliaSim (V-REP) validate the proposed strategy and highlight its efficiency and robustness while running the formation task.

Distributed strategy for communication between multiple robots during formation navigation task

Swarm robotics involves the study of the behavior of a set of robots in carrying out collective tasks, such as alignment, navigation and formation. During cooperative tasks execution, the communication among robots can contribute to successfully performing tasks through an efficient messages exchange. This paper proposes a communication strategy for swarm robots, the so-called Double-Wave Swarm, aiming at alignment and navigation tasks. The Double-Wave Swarm is an improvement of a prior Wave Swarm communication approach that uses the concept of wave propagation for message exchange between neighbors. Double-Wave Swarm provides better communication network connectivity when compared to the former approach. Experiments with the robot simulator CoppeliaSim (V-REP) validate the proposed communication and highlight its efficiency and robustness while running alignment and navigation tasks. Also, the Double-Wave Swarm proved to be superior during swarm formation navigation into environments with obstacles in different scenarios if compared with Wave Swarm.

Structural damage detection through longitudinal wave propagation using spectral finite element method

This paper investigates the damage identification of the concrete pile element through axial wave propagation technique using computational and experimental studies. Now-a-days, concrete pile foundations are often common in all engineering structures and their safety is significant for preventing the failure. Damage detection and estimation in a sub-structure is challenging as the visual picture of the sub-structure and its condition is not well known and the state of the structure or foundation can be inferred only through its static and dynamic response. The concept of wave propagation involves dynamic impedance and whenever a wave encounters a changing impedance (due to loss of stiffness), a reflecting wave is generated with the total strain energy forked as reflected as well as refracted portions. Among many frequency domain methods, the Spectral Finite Element method (SFEM) has been found suitable for analysis of wave propagation in real engineering structures as the formulation is based on dynamic equilibrium under harmonic steady state excitation. The feasibility of the axial wave propagation technique is studied through numerical simulations using Elementary rod theory and higher order Love rod theory under SFEM and ABAQUS dynamic explicit analysis with experimental validation exercise. Towards simulating the damage scenario in a pile element, dis-continuity (impedance mismatch) is induced by varying its cross-sectional area along its length. Both experimental and computational investigations are performed under pulse-echo and pitch-catch configuration methods. Analytical and experimental results are in good agreement.

Wave Propagation in 1D EBGs: Periodic Multilayer Films Consisting of Two Different Materials [This Issue's Contribution

This paper presents the fundamental concept of wave propagation in periodic multilayer films consisting of two different materials, so-called one-dimensional electromagnetic bandgap (EBG) materials. To this end, Floquet's theorem is first presented. Next, the transmission-line analogy is used to simplify the concept of wave propagation in one dimension. The Bloch impedance concept is then presented, and its usefulness is illustrated in the applications of truncated periodic structures. Through a few case studies, it is shown that the ripples usually appearing in the pass band of the EBGs are due to the mismatch of the transmission-line ports. When the EBG structures are terminated to appropriate Bloch impedances, the ripples disappear. The material can be used in undergraduate or graduate Microwave or Advanced Engineering Electromagnetics courses. The students need to know about the ABCD matrix in advance. The material helps students in better understanding of microwave filters, and shows the importance of matching the terminal ports and number of unit cells. Students can use software packages such as MATLAB to obtain the Bloch impedances, and such as Ansoft HFSS to reproduce the scattering parameters presented in this paper. The materials in this paper are consistent with those in [3, 7, 8, 9] and, in some cases, are summarized from these references to improve the clarity.

Physical modeling and analysis of P-wave attenuation anisotropy in transversely isotropic media

Anisotropic attenuation can provide sensitive attributes for fracture detection and lithology discrimination. This paper analyzes measurements of the P-wave attenuation coefficient in a transversely isotropic sample made of phenolic material. Using the spectral-ratio method, we estimate the group (effective) attenuation coefficient of P-waves transmitted through the sample for a wide range of propagation angles (from [Formula: see text] to [Formula: see text]) with the symmetry axis. Correction for the difference between the group and phase angles and for the angular velocity variation help us to obtain the normalized phase attenuation coefficient [Formula: see text] governed by the Thomsen-style attenuation-anisotropy parameters [Formula: see text] and [Formula: see text]. Whereas the symmetry axis of the angle-dependent coefficient [Formula: see text] practically coincides with that of the velocity function, the magnitude of the attenuation anisotropy far exceeds that of the velocity anisotropy. The quality factor [Formula: see text] increases more than tenfold from the symmetry axis (slow direction) to the isotropy plane (fast direction). Inversion of the coefficient [Formula: see text] using the Christoffel equation yields large negative values of the parameters [Formula: see text] and [Formula: see text]. The robustness of our results critically depends on several factors, such as the availability of an accurate anisotropic velocity model and adequacy of the homogeneous concept of wave propagation, as well as the choice of the frequency band. The methodology discussed here can be extended to field measurements of anisotropic attenuation needed for AVO (amplitude-variation-with-offset) analysis, amplitude-preserving migration, and seismic fracture detection.

THE CHARACTERISTIC RECEPTANCE METHOD FOR DAMAGE DETECTION IN LARGE MONO-COUPLED PERIODIC STRUCTURES

An approach based on the concept of wave propagation to detect the structural damage in large mono-coupled periodic structures is presented in this paper. The free vibration analysis of a finite mono-coupled periodic structure with a single disorder has been conducted by the characteristic receptance method, and the sensitivity of the natural frequencies to the disorder in flexibility has been discussed. Based on the sensitivity analysis, the locations and magnitude of damage in large mono-coupled periodic systems have been estimated using measured changes in the natural frequencies. The paper also introduces a substructure-based method for improving the computational efficiency and the accuracy of damage detection in large mono-coupled periodic structures. Numerical results from two periodic mass-spring-structures show that the proposed method can provide good predictions of both the locations and magnitude of damage at one or more sites. Furthermore, the proposed method, in which a priori information about the nature such as stiffness of the undamaged structure is not needed, and only measurements of the change in a few of the structure's natural frequencies between the undamaged and damaged states are required, is particularly attractive in practice. However, some issues such as the role of noise in actual measurements, application to multi-coupled periodic structures with complex boundary conditions remain to be resolved before this approach becomes a truly variable method of structural damage assessment.

Vibration analysis of multi-supported curved panel using the periodic structure approach

This papers deals with the radial vibration of a row of cylindrical panels of finite length using the concept of wave propagation in periodic structures. For this study, the structure is considered as an assemblage of a number of identical cylindrically curved panels each of which will be referred to as a periodic element. For a given geometry dispersion curves of the propagation constant versus (non-dimensional) natural frequency have been drawn corresponding to the circumferential wave propagation. New conclusions that have emerged from this study are as follows. It is shown that by a proper choice of the periodic element the bounding frequencies and the corresponding modes in all the propagation bands can be determined. These have been shown to correspond to a single curved panel with all its edges simply supported. It is noted that there are no attenuation gaps in the entire frequency spectrum beyond the lowest bounding frequency. This is a unique feature of circumferential wave propagation around circular cylindrical shells and panels, as opposed to the wave propagation of periodically supported beams and rectangular panels without curvature. The natural frequency corresponding to every circumferential mode of the complete shell has been identified on the propagation constant curve. It has been observed that the natural frequencies of a cylindrically curved panel of a given curvature and length but of different circumferential arc length (corresponding to different angles subtended at the centre of any circular cross-section) may also be identified on the same propagation constant curve. Finally, it is shown that the same propagation constant curve may also be used to determine all the natural frequencies of a finite row of curved panels with the extreme edges simply supported. Wherever possible the numerical results have been compared with those obtained independently from finite element analysis and/or results available in the literature. Flutter analysis of multi-span curved panels using a wave approach is the ultimate objective of this work.

Intelligent finite element mesh generation

A knowledge-based and automatic finite element mesh generator (INTELMESH) for two-dimensional linear elasticity problems is presented. Unlike other approaches, the proposed technique incorporates the information about the object geometry as well as the boundary and loading conditions to generate an a priori finite element mesh which is more refined around the critical regions of the problem domain. INTELMESH uses a blackboard architecture expert system and the new concept of substracting to locate the critical regions in the domain and to assign priority and mesh size to them. This involves the decomposition of the original structure into substructures (or primitives) for which an initial and approximate analysis can be performed by using analytical solutions and heuristics. It then uses the concept of wave propagation to generate graded nodes in the whole domain with proper density distribution. INTELMESH is fully automatic and allows the user to define the problem domain with minimum amount of input such as object geometry and boundary and loading conditions. Once nodes have been generated for the entire domain, they are automatically connected to form well-shaped triangular elements ensuring the Delaunay property. Several examples are presented and discussed. When incorporated into and compared with the traditional approach to the adaptive finite element analysis, it is expected that the proposed approach, which starts the process with near optimal initial meshes, will be more accurate and efficient.

Free and Forced Vibrations of Periodic Multispan Beams

In this study, the following two topics are considered for uniform multispan beams of both finite and infinite lengths with rigid transversal and elastic rotational constraints at each support: (a) free vibration and the associated frequencies and mode shapes; (b) forced vibration under a convected harmonic loading. The concept of wave propagation in periodic structures of Brillouin is utilized to investigate the wave motion at periodic supports of a multispan beam. A dispersion equation and its asymptotic form is obtained to determine the natural frequencies. For the special case of zero rotational spring stiffness, an explicit asymptotic expression for the natural frequency is also given. New expressions for the mode shapes are obtained in the complex form for multispan beams of both finite and infinite lengths. The orthogonality conditions of the mode shapes for two cases are formulated. The exact responses of both finite and infinite span beams under a convected harmonic loading are obtained. Thus, the position and the value of each peak in the harmonic response function can be determined precisely, as well as the occurrence of the so-called coincidence phenomenon, when the response is greatly enhanced.

Free and Forced Vibrations of Periodic Multispan Beams

In this study, the following two topics are considered for uniform multispan beams of both finite and infinite lengths with rigid transversal and elastic rotational constraints at each support: (a) free vibration and the associated frequencies and mode shapes; (b) forced vibration under a convected harmonic loading. The concept of wave propagation in periodic structures of Brillouin is utilized to investigate the wave motion at periodic supports of a multispan beam. A dispersion equation and its asymptotic form is obtained to determine the natural frequencies. For the special case of zero rotational spring stiffness, an explicit asymptotic expression for the natural frequency is also given. New expressions for the mode shapes are obtained in the complex form for multispan beams of both finite and infinite lengths. The orthogonality conditions of the mode shapes for two cases are formulated. The exact responses of both finite and infinite span beams under a convected harmonic loading are obtained. Thus, the position and the value of each peak in the harmonic response function can be determined precisely, as well as the occurrence of the so-called coincidence phenomenon, when the response is greatly enhanced.

A knowledge‐based A‐priori approach to mesh generation in thermal problems

AbstractA new approach to the finite element mesh generation for two‐dimensional steady state thermal problems of conduction and convection is presented. Unlike other approaches, the proposed technique incorporates the information about the object geometry as well as the boundary and loading conditions to generate an a‐priori finite element mesh which is more refined around the critical regions of the problem domain. A blackboard architecture expert system is developed to intelligently identify critical regions and to choose the proper mesh size for them by performing an approximate heat flux calculation. From the results of the blackboard system, nodes are generated in the problem domain using the new concept of wave propagation. The wave propagation technique is fully automatic and does not require any user‐provided information except the data which define the object geometry and boundary conditions. After nodes are generated, well‐shaped triangular elements are formed ensuring the Delaunay property. During the triangulation process and to reduce the computation time for checking the overlapping problem, a new and efficient algorithm is proposed which defines a certain range only in which a potential triangular element might overlap the previously generated elements and boundary segments. Several examples are presented and discussed. When incorporated into and compared with the traditional approach to the adaptive finite element analysis, it is expected that the proposed approach, which starts the process with near‐optimal initial meshes, will result in lower levels of error and faster convergence of the solution to the desired accuracy in less time and at less cost.

The existence of an electron shock structure in the electrical breakdown of nitrogen

Experimental evidence is presented to show the existence of a regularly repeating structure in the luminous core that appears during the final stage in the electrical breakdown of N2 at atmospheric pressure. A simple analysis identifies this pattern as an electron shock structure in the inviscid core of an underexpanded jet originating at the cathode spot. The results support the concept of wave propagation through the collision-dominated electrons.

System concepts in Kron's polyhedron model and the scattering problem

Abstract Kron's polyhedron model based on a sequence of transformations related to the orthogonal electrical network problem was proposed for a wide range of system problems. The scattering formulation for a flow process introduces a similar sequence of ‘ obstacles ’ and can form an analytical basis for many of the concepts discussed by Kron. It can be associated with the system problems incorporating an optimality condition and the updating of a priori information, and can also be identified in the sweep method of solution of the two-point boundary-value problems for optimal control and estimation, which would appear to be related to the concept of wave propagation in Kron's model. The sequential networks in the polyhedron model and the scattering problem thus provide a basic analytical structure which has important applications in general systems theory.