Discontinuous Research Articles

Generalized scattering matrix method for Lamb wave scattering analysis at cascaded notches

A thorough understanding of the scattering mechanism of Lamb waves at discontinuities is of interest for quantitative evaluation of structural properties and mode control. This study extends the generalized scattering matrix method to investigate the interaction of straight crested Lamb waves with multiple cascaded rectangular notches. Based on the orthogonality and completeness of Lamb modes, the mode matching method is utilized to determine the scattering matrices of downward and upward step discontinuities. After that, the generalized scattering matrix method is employed to determine the scattering matrices of a single rectangular notch and the recurrence relations between the scattering matrices of n + 1 cascaded notches and those of n cascaded notches. Finally, the scattering matrices of multiple cascaded notches can be easily obtained taking advantage of the recurrence relations. As the number of cascaded notches increases, more and sharper peaks appear in the scattering coefficient curves. The finite element simulations conducted in the time domain validate the theoretical results for cascaded notches with identical or different depths, which demonstrate that this method can be applied to find the scattering coefficients at piece-wise periodic or nonperiodic waveguides. The generalized scattering matrix method may have potential applications in quantitative nondestructive evaluation and mode control.

A moving discontinuous Galerkin finite element method with interface condition enforcement for compressible flows

A variation of moving discontinuous Galerkin finite element method with interface condition enforcement (MDG-ICE) is developed for solving the compressible Euler equations. The MDG-ICE method, originating from the work of Corrigan et al. [1–4], is based on the space-time DG formulation, where both flow field and grid geometry are considered as independent variables and the conservation laws are enforced both on discrete elements and element interfaces. The element conservation laws are solved in the standard discontinuous solution space to determine conservative quantities, while the interface conservation is enforced using a variational formulation in a continuous space to determine discrete grid geometry. The resulting over-determined system of nonlinear equations arising from the MDG-ICE formulation can then be solved in a least-squares sense, leading to an unconstrained nonlinear least-squares problem that is regularized and solved by Levenberg-Marquardt method. A number of numerical experiments for both 1D unsteady and 2D steady state compressible flow problems are conducted to assess the accuracy and robustness of the MDG-ICE method. Numerical results obtained indicate that the MDG-ICE method is able to implicitly detect and track all types of discontinuities via interface conservation enforcement and satisfy the conservation law on both elements and interfaces via grid movement and grid management, demonstrating that an exponential rate of convergence for Sod and Lax-Harden shock tube problems can be achieved and highly accurate solutions without overheating to both double-rarefaction wave and Noh problems can be obtained.

Numerical characterization of groundwater flow and fracture-induced water inrush in tunnels

Recently, the rapid increase in tunnel construction in karst areas across China has attracted considerable attention. However, frequently occurring groundwater inrush hazards induced by fractures within rocks are one of the greatest challenges faced during tunnel excavations. In this paper, we present a numerical investigation on the effect of fractures on fluid flow, considering the different types of discontinuities. A conceptual model of fracture-induced water inrush, which emphasizes the evolution of fracture connectivity, was developed to investigate the fluid flow through fractured rocks and consequently study the water inrush mechanism. The numerical results indicate that the rock fracture serves as the preferential flow channel and the aquifuge acts as a barrier to the groundwater flow. Groundwater is transported mainly through fractures with higher permeability. A case study demonstrated the accuracy of the proposed conceptual model. Finally, the influences of the connected fractures on water inflow and the sensitivity of the different types of connected fractures to tunnel inflow were investigated using the orthogonal experiment method. The proposed approach and results may contribute to the investigation of groundwater movement in fracture system, thereby providing a basis for the water-inrush theory and prevention of damage in karst areas.

Effective design and characterization of flutter-based piezoelectric energy harvesters with discontinuous nonlinearities

A comprehensive study on the design and nonlinear characterization of a two-degree of freedom piezoaeroelastic energy harvesting system with freeplay and multi-segmented nonlinearities in the pitch degree of freedom is explored and discussed. The nonlinear governing equations of the considered piezoaeroelastic energy harvesting system are derived and the unsteady representation based on the Duhamel formulation is employed to represent the aerodynamic loads. Nonlinear piezoaeroelastic response analysis is carried out in the presence of freeplay and multi-segmented nonlinearities before and after the linear onset of flutter. Such nonlinearities can be introduced to piezoaeroelastic energy harvesters for performance enhancement through the possible existence of subcritical Hopf bifurcation and aperiodic responses due to the grazing and grazing/sliding bifurcations. It is shown that the existence of discontinuous effects result in the possibility of harvesting energy at lower speeds than the linear onset speed of instability due to the activation of the subcritical Hopf bifurcation. Additionally, the increase of the strength of the multi-segmented nonlinearities leads to the existence of aperiodic responses with the presence of several bifurcations limiting the system's dynamics at low pitch angles with limiting stall issues. It is proved that an effective design with harvesting energy at low wind speeds can be carried out for wing-based energy harvesters by carefully selecting the linear stiffness of the pitch degree of freedom, gap and type of the multi-segmented discontinuity, and electrical load resistance.

A tutorial on capturing mental representations through drawing and crowd-sourced scoring

When we draw, we are depicting a rich mental representation reflecting a memory, percept, schema, imagination, or feeling. In spite of the abundance of data created by drawings, drawings are rarely used as an output measure in the field of psychology, due to concerns about their large variance and their difficulty of quantification. However, recent work leveraging pen-tracking, computer vision, and online crowd-sourcing has revealed new ways to capture and objectively quantify drawings, to answer a wide range of questions across fields of psychology. Here, I present a tutorial on modern methods for drawing experiments, ranging from how to quantify pen-and-paper type studies, up to how to administer a fully closed-loop online experiment. I go through the concrete steps of designing a drawing experiment, recording drawings, and objectively quantifying them through online crowd-sourcing and computer vision methods. Included with this tutorial are code examples at different levels of complexity and tutorials designed to teach basic lessons about web architecture and be useful regardless of skill level. I also discuss key methodological points of consideration, and provide a series of potential jumping points for drawing studies across fields in psychology. I hope this tutorial will arm more researchers with the skills to capture these naturalistic snapshots of a mental image.

Continuous type of intra-abdominal splenogonadal fusion: A case report with review of literature

Background: SplenoGonadal Fusion (SGF) is a very rare anomaly in which accessary splenic tissue are fused to the left testis. It is either continuous or discontinuous type. Many cases end up having orchidectomy due to lack of awareness of the condition as it mimic a testicular tumor. Case report: A 22 months old boy with severe penoscrotal hypospadias, bilateral impalpable testes and major cardiac anomalies, had a laparoscopy for his testes, which revealed left testicular mass with accessary splenic tissues attached to the upper pole. It was in turn connected to the normal spleen with a cord of splenic beads. Successful two stage FS procedure was performed for his testis. Conclusion: Possibility of SGF should be considered when seeing a testicular mass with accessary spleens attached to the testis.

Magnetic Particle Inspection Optimization Solution within the Frame of NDT 4.0

The quality of product and process is one of the most important factors in achieving constructively and then functionally safe products in any industry. Over the years, the concept of Industry 4.0 has emerged in all the quality processes, such as nondestructive testing (NDT). The most widely used quality control methods in the industries of mechanical engineering, aerospace, and civil engineering are nondestructive methods, which are based on inspection by detecting indications, without affecting the surface quality of the examined parts. Over time, the focus has been on research with the fourth generation in nondestructive testing, i.e., NDT 4.0 or Smart NDT, as a main topic to ensure the efficiency and effectiveness of the methods for a safe detection of all types of discontinuities. This area of research aims at the efficiency of methods, the elimination of human errors, digitalization, and optimization from a constructive point of view. In this paper, we presented a magnetic particles inspection method and the possible future directions for the development of standard equipment used in the context of this method in accordance with the applicable physical principles and constraints of the method for cylindrical parts. A possible development direction was presented in order to streamline the mass production of parts made of ferromagnetic materials. We described the methods of analysis and the tools used for the development of a magnetic particle inspection method used for cylindrical parts in all types of industry and NDT 4.0; the aim is to provide new NDT 4.0 directions in optimizing the series production for cylindrical parts from industry, as given in the conclusion of this article.

SEISMIC EVALUATION OF HIGH RISE BUILDING WITH VERTICAL IRREGULARITIES BY PUSHOVER ANALYSIS

During earthquake motion. The seismic behavior depends upon the strength, mass, and stiffness are distributed in both horizontal and vertical planes. the buildings structural damage was severe the frame is caused due to the discontinuity in the stiffness mass and strength between the alongside stories. The same type of discontinuity is vertical geometric irregularity which is due to the irregular building configuration in vertical plane so there is to know the seismic response of building modals in different structural irregularities. Non-linear static (pushover analysis) which is used for Investigation. The purpose of study doing nonlinear static (pushover analysis) by conventional design methodology G+12 High rise buildings this work shows seismic performance and behavior of building frame with and without vertical irregularity in terms of base shear, story shear, story displacement the performance point of all models are considered also found that irregularity in assessment of the structure decreases the performance level of building there is also reduces in deformation or displacement of the structure. all the models analyzed by using ETABS and design as per IS 456:200 and 1893:2016

Solar Wind Discontinuity Transformation at the Bow Shock

Abstract Solar wind plasma at the Earth’s orbit carries transient magnetic field structures including discontinuities. Their interaction with the Earth’s bow shock can significantly alter discontinuity configuration and stability. We investigate such an interaction for the most widespread type of solar wind discontinuities—rotational discontinuities (RDs). We use a set of in situ multispacecraft observations and perform kinetic hybrid simulations. We focus on the RD current density amplification that may lead to magnetic reconnection. We show that the amplification can be as high as two orders of magnitude and is mainly governed by three processes: the transverse magnetic field compression, global thinning of RD, and interaction of RD with low-frequency electromagnetic waves in the magnetosheath, downstream of the bow shock. The first factor is found to substantially exceed simple hydrodynamic predictions in most observed cases, the second effect has a rather moderate impact, while the third causes strong oscillations of the current density. We show that the presence of accelerated particles in the bow shock precursor highly boosts the current density amplification, making the postshock magnetic reconnection more probable. The pool of accelerated particles strongly affects the interaction of RDs with the Earth’s bow shock, as it is demonstrated by observational data analysis and hybrid code simulations. Thus, shocks should be distinguished not by the inclination angle, but rather by the presence of foreshocks populated with shock reflected particles. Plasma processes in the RD–shock interaction affect magnetic structures and turbulence in the Earth’s magnetosphere and may have implications for the processes in astrophysics.

Investigation of Unstable Failure Potential of a Shear Slip Using DEM at an Underground Mine

Geological structures and discontinuities subjected to the perturbations posed by mining operations in underground mining can be re-activated and cause fault-slip rockbursts. This study investigates geomechanical stability in terms of shear slip behavior along discontinuities using 3DEC with focusing on sudden changes of shear stress and shear displacement. A direct shear test is performed using a continuously yielding joint model to examine the evolution of shear stress and shear displacement on this joint. Further, this continuously yielding joint model is applied in major discontinuities of an underground mine to examine whether an unstable shear slip behavior exists, which is represented by a significant shear stress decrease and a shear displacement increase. By referring to geological mapping of this mine, four cases are developed and each case is set up with one type of major discontinuities with identically simulated mining operations. Results imply that the amplitude of shear stress decrease and shear displacement increase along discontinuities substantially increases with the depth due to higher virgin stresses and mining-induced stresses at greater depths. The discontinuity parallel to the interface between footwall and orebody is the least safe case and subjects to the largest potential of triggering seismic events. Keywords: Shear slip behavior, Unstable failure, Mining-induced seismicity, Continuously yielding joint model, DEM.

Jump Point Search with Temporal Obstacles

In 4-connected grid-based path planning one often needs to account for temporal and moving obstacles: ones that appear, disappear and which can prevent the agent from reaching its target. Such problems are common in a variety of settings (games, robotics etc.) and they can be surprisingly challenging to solve. First, because the temporal aspect increases the size of the search space; second because the search space contains many symmetric paths, indistinguishable from one another except by the order in which grid moves appear. To tackle such problems we consider a new optimal algorithm – in the style of Jump Point Search – which can identify and break these symmetries and thus improves performance; from several factor to more than one order of magnitude vs. SIPP, arguably the gold standard baseline in the area.

Characterization of mechanical discontinuities based on data-driven classification of compressional-wave travel times

Wave propagation and diffusive transport phenomena are influenced by the mechanical discontinuities in material. This study shows that certain bulk properties of the network of low-velocity mechanical discontinuities (e.g. air-filled cracks) in a material can be characterized by processing compressional-wave travel times using traditional data-driven classification techniques. To that end, we perform three tasks in chronological order: (1) use the discrete fracture network (DFN) method to create two-dimensional (2D) numerical models of crack-bearing material embedded with various types of low-velocity mechanical discontinuities, (2) use the fast marching method (FMM) to simulate the propagation of the wave/diffusion front from a single source through the 2D crack-bearing material to multiple receivers placed on the boundary of the material, and (3) train 9 data-driven classifiers to characterize the crack-bearing materials (i.e. bulk properties of the network of mechanical discontinuities in the crack-bearing material) by learning from the simulations of travel times detected by multiple receivers placed around the crack-bearing material. The classifiers identified the orientation, spatial distribution, and dispersion of the low-velocity mechanical discontinuities. Voting classifier performs the best among the 9 classifiers. For the characterization of bulk dispersion and distribution of discontinuities, the sensors located on the adjacent boundaries are more important; whereas for the characterization of bulk orientation of discontinuities, the sensors located on the opposite side are more important.

Performance analysis of a Scalar Coupled and Decoupled PWM Technique for a Three Level symmetrical Dual Inverter Fed OEWIM Drive

Dual inverter fed IM drive is commonly employed in EV applications. In this application, SVPWM based PWM generator was utilised. However, they produce a high common-mode voltage(CMV). Because of this, bearing of motor will be affected and in turn, results in EMI problems. Hence, to overcome this problem, this work introduced a novel PWM generation techniques named scalar coupled and decoupled PWM topology to control a three-level symmetrical DI fed OEWIM. Hence, to find out the effectiveness of the proposed topologies, its operation is examined under both continuous and discontinuous modes of operation using MATLAB simulation. From the acquired results, it is concluded that this coupled PWM topology topology exhibits reduced CMV and harmonics when compared to decoupled topology

Assessment of Structural Dynamic Response and Vehicle-Track Interaction of Precast Slab Track Systems

Recently, precast slab tracks have been used widely in railway applications, especially in conventional urban railway lines. These types of tracks are rapidly constructed and limit interruptions to train operation. However, the problems of dynamic stability when the trains run on the discontinuous type of tracks must be seriously considered. This paper focuses on analyzing the train-track interaction in two types of tracks under the dynamic load by using the numerical analysis program (APATSI) to evaluate the structural response as well as the running safety to precisely understand the load transfer efficiency of precast slab track systems.

The classical solution of the mixed problem for the one-dimensional wave equation with the nonsmooth second initial condition

In this article, we study the classical solution of the mixed problem in a quarter of a plane for a one-dimensional wave equation. On the bottom of the boundary, the Cauchy conditions are specified, and the second of them has a discontinuity of the first kind at a point. The smooth boundary condition is set at the side boundary. The solution is built using the method of characteristics in an explicit analytical form. The uniqueness is proved, and the conditions under which a piecewise-smooth solution exists are established. The problem with conjugate conditions is considered

Automatic Generation of Piano Score Following Videos

This article studies the problem of generating a piano score following video from an audio recording in a fully automated manner. This problem contains two components: identifying the piece and aligning the audio with raw sheet music images. Unlike previous work, we focus primarily on working with raw, unprocessed sheet music from IMSLP, which may contain filler pages, other unrelated pieces or movements, or repeats and jumps whose locations are unknown a priori. To solve this problem, we combine state-of-the-art methods with a novel alignment algorithm called Hierarchical DTW to handle discontinuities, which are the bottleneck on system performance. Hierarchical DTW handles repeats and jumps by considering all line breaks as possible jump locations, and it applies DTW at both a feature level and a segment level. We evaluate our algorithm with 200 PDFs from IMSLP and real audio recordings from Youtube. Our experiments show that Hierarchical DTW consistently outperforms a previously proposed Jump DTW algorithm in handling various types of discontinuities. We present extensive experimental results and analysis of the proposed algorithm.

Discontinuous solutions of the unsteady boundary-layer equations for a rotating disk of finite radius

Abstract

Investigation of continuous and discontinuous contact cases in the contact mechanics of graded materials using analytical method and FEM

The aim of this paper was to examine the continuous and discontinuous contact problems between the functionally graded (FG) layer pressed with a uniformly distributed load and homogeneous half plane using an analytical method and FEM. The FG layer is made of non-homogeneous material with an isotropic stress–strain law with exponentially varying properties. It is assumed that the contact at the FG layer-half plane interface is frictionless, and only the normal tractions can be transmitted along the contacted regions. The body force of the FG layer is considered in the study. The FG layer was positioned on the homogeneous half plane without any bonds. Thus, if the external load was smaller than a certain critical value, the contact between the FG layer and half plane would be continuous. However, when the external load exceeded the critical value, there was a separation between the FG layer and half plane on the finite region, as discontinuous contact. Therefore, there have been some steps taken in this study. Firstly, an analytical solution for continuous and discontinuous contact cases of the problem has been realized using the theory of elasticity and Fourier integral transform techniques. Then, the problem modeled and twodimensional analysis was carried out by using ANSYS package program based on FEM. Numerical results for initial separation distance and contact stress distributions between the FG layer and homogeneous half plane for continuous contact case; the start and end points of separation and contact stress distributions between the FG layer and homogeneous half plane for discontinuous contact case were provided for various dimensionless quantities including material inhomogeneity, distributed load width, the shear module ratio and load factor for both methods. The results obtained using FEM were compared with the results found using analytical formulation. It was found that the results obtained from analytical formulation were in perfect agreement with the FEM study.

Jump point identification in hydro-meteorological time series by crossing methodology

The climate change impact appears as a decreasing or increasing monotonic trend in hydro-meteorology time series records due to greenhouse gas (GHG) emissions causing to global warming and climate change impacts. On the other hand, there may be abrupt changes in the form of jumps in these series due to natural and engineering activities. Although trend identification methods are rather common in the literature, jump determination conventional methodologies are rather rare and their applications present some restrictive asumptions like the serial independence and normal (Gaussian) probability distribution function (PDF). The methodology presented in this paper is away from each of such assumptions and it depicts the minimum number of upcrossing along horizontal truncation levels within the time series variation domain. The applications of the methodology are given for annual Danube River discharge records, Romania; New Jersey rainfall and temperature records, USA; monthly rainfall records and Van Lake level fluctuations, Turkey.

Regarding Goal Bounding and Jump Point Search

Jump Point Search (JPS) is a well known symmetry-breaking algorithm that can substantially improve performance for grid-based optimal pathfinding. When the input grid is static further speedups can be obtained by combining JPS with goal bounding techniques such as Geometric Containers (instantiated as Bounding Boxes) and Compressed Path Databases. Two such methods, JPS+BB and Two-Oracle Path PlannING (Topping), are currently among the fastest known approaches for computing shortest paths on grids. The principal drawback for these algorithms is the overhead costs: each one requires an all-pairs precomputation step, the running time and subsequent storage costs of which can be prohibitive. In this work we consider an alternative approach where we precompute and store goal bounding data only for grid cells which are also jump points. Since the number of jump points is usually much smaller than the total number of grid cells, we can save up to orders of magnitude in preprocessing time and space.
 Considerable precomputation savings do not necessarily mean performance degradation. For a second contribution we show how canonical orderings, partial expansion strategies and enhanced intermediate pruning can be leveraged to improve online query performance despite a reduction in preprocessed data. The combination of faster preprocessing and stronger online reasoning leads to three new and highly performant algorithms: JPS+BB+ and Two-Oracle Pathfinding Search (TOPS) based on search, and Topping+ based on path extraction. We give a theoretical analysis showing that each method is complete and optimal. We also report convincing gains in a comprehensive empirical evaluation that includes almost all current and cutting-edge algorithms for grid-based pathfinding.