Detecting transverse material boundaries in multilayer anthropogenic structures

The Kirchhoff approximation has been used to analytically determine the field that is generated by the reflection of an acoustic wave from an interface with a sharp acoustic impedance gradient. Visual formulas have been derived to describe the incoming signal when the boundary is exposed to a pulsed point source. On the basis of numerical modeling and an experimental study of multilayer systems, the suggested approach is applicable for detecting flaws in planar and cylindrical structures under pulse excitation. An algorithm is given for improving the accuracy of locating the rupture boundary. It is based on revealing correlations in wave field parameters at various points in the system.     

Computational relationships for the development of software for calculating magnetostatic fields from flaws in arbitrarily shaped ferromagnetic products

Based on the integral equation for the stray magnetic field strength inside a magnetized article, computational relationships have been derived in the form of a matrix equation that is convenient when developing software for modeling the distribution of magnetization in arbitrarily shaped articles with different flaws and for calculating and imaging external magnetic fields of the magnetized article. On this basis, a program has been developed that is most suitable for the case where the article boundaries and flaws can be sufficiently accurately defined on a three-dimensional grid with identical rectangular cells.     

基于"生死单元"技术的焊缝缺陷模拟

应用有限元方法，计算分析带几何缺陷焊接接头力学性能。通过杀死焊接接头有限元模型中相应位置的单元，模拟存在的几何缺陷。计算分析带有气孔或咬边缺陷的焊接接头应力分布特性和应力集中程度，验证了应用生死单元模拟几何缺陷的有效性。通过对建模方法的比较，表明生死单元技术能够灵活模拟缺陷。     

Nondestructive testing for flaws in the insulation of winding wires

Peculiarities of discharge that is initiated by a flawed section of wire insulation that passes through a primary gas-discharge flaw transducer have been studied. Analysis of the structure of signals has been carried out, and possible mechanism and type of discharge in the sensor have been considered. Informative zones have also been singled out in the signal structure. A technique is described for testing enamel-insulated wires for flaws. The technique makes it possible to determine the number and extent of flawed sections in an enameled wire that is fed through the system at any variable speed. Ways and means are considered for reducing the errors in evaluating the number and extent of flaws. Flow chart of a faultiness-measurement device is suggested, and the principle of its operation is described.     

聚乙烯管道电熔焊接接头的超声检测

聚乙烯管连接中大量使用电熔接头,其质量的好坏直接影响管道系统的安全。分析了超声聚焦检测技术对聚乙烯管电熔接头各类缺陷的检出能力。在此基础上,运用相控阵超声技术及B扫描实时成像超声方法检测大量含缺陷接头,对比超声成像图与接头实剖图,发现该方法有较高的检测灵敏度和检出精度,可以应用于工程实践。     

PROPER ORTHOGONAL DECOMPOSITION FOR MODEL UPDATING OF NON-LINEAR MECHANICAL SYSTEMS

Proper orthogonal decomposition (POD), also known as Karhunen–Loeve (K–L) decomposition, is emerging as a useful experimental tool in dynamics and vibrations. The POD is a means of extracting spatial information from a set of time-series data available on a domain. The use of (K–L) transform is of great help in non-linear settings where traditional linear techniques such as modal-testing and power-spectrum analyses cannot be applied. These decomposition can be used as an orthogonal basis for efficient representation of the ensemble. The POM have been interpreted mainly as empirical system modes and the application of POD to measured displacements of a discrete structure with a known mass matrix leads to an estimation of the normal modes. We investigate the use of the proper orthogonal modes of displacements for the identification of parameters of non-linear dynamical structures with an optimisation procedure based on the difference between the experimental and simulated POM. A numerical example of a beam with a local non-linear component will illustrate the method.     

圆锥型压电换能器的动态设计与实验研究

对一种圆锥型夹心式压电换能器进行了动态设计与实验分析。利用有限元分析方法对换能器进行了动态设计,给出了该类压电换能器有限元建模方法,分析了换能器主要结构尺寸对振动模态、固有频率的影响。依据有限元分析结果,提出了一种基于数值分析的换能器优化设计方法,简化了设计过程。在数值分析的基础上,设计、研制了圆锥型夹心式压电换能器,并对压电换能器进行了性能测试。并将实验测试数据和有限元分析结果进行了对比,测试结果验证了数值分析与设计方法的合理性。     

Acoustic Emission Method for Testing Oil and Gas Tanks

Results of practical hydraulic tests of railway tanks owned by Altaivagon Corporation by the method of acoustic emission (AE) are given. A new technique for localization of AE signals and an appropriate software package have been developed to detect with a high certainty both internal and penetrating flaws in tanks under a load of 0.5 atm. A technique for estimating the hazard presented by the flaws in railway tanks based on detection of AE signals is discussed.     

A numerical study on electrohydrodynamic induction pumps using CFD modeling

The flow characteristics of EHD induction pumps have been investigated by a numerical method which adds an electric modeling to the conventional CFD. The governing equation for the electric modeling is derived and discretized using the electronic potential as the only dependent variable so that the boundary conditions are satisfied independent of convergence. The numerical results make a good prediction about the frequency-dependent characteristics, which are consistent with both the experiment and the theory. An improvement in understanding the cause of instabilities is achieved to show that the decrement of volumetric force in the local region induces backflow resulting in the instability. The vulnerability was discovered under the conditions of low frequency and large channel depth. The micropump has a maximum flow rate at an optimum channel depth due to the flow instability at larger depths and the flow resistance at smaller one have an undesirable influence upon the one-directionality of flows.     

Numerical calculation of energy release rates by virtual crack closure technique

A seamless analysis of material behavior incorporating complex geometry and crack- tip modeling is one of greatly interesting topics in engineering and computational fracture mechanics fields. However, there are still large gaps between the industrial applications and fundamental academic studies due to a time consuming detailed modeling. In order to resolve this problem, a numerical method to calculate an energy release rate by virtual crack closure technique was proposed in this paper. Both free mesh method and finite element method have been utilized and, thereafter, robust local and global elements for various geometries and boundary conditions were generated. A validity of the proposed method has been demonstrated through a series of fracture mechanics analyses without tedious crack-tip meshing.     

3D two scale X-FEM crack model with interfacial frictional contact: Application to fretting fatigue

A global approach coupling experiments and numerical modeling is proposed to enhance crack prediction. Fretting tests have been conducted under conditions leading to crack formation. Three dimensional crack shapes have been reconstructed from metallographic cross-sections and described with level set functions. They are then used as input data in 3D two-scale X-FEM model detailed in this paper. Frictional contact conditions holding between the crack faces are accounting for. The methodology developed to describe those contact conditions at the pertinent scale is detailed.A 3D fretting fatigue test is modeled to illustrate the coupling between experiments and numerical modeling.     

Lamb wave propagation modeling for structure health monitoring

This study aims to model the propagation of Lamb waves used in structure health monitoring. A number of different numerical computational techniques have been developed for wave propagation studies. The local interaction simulation approach, used for modeling sharp interfaces and discontinuities in complex media (LISA/SIM theory), has been effectively applied to numerical simulations of elastic wave interaction. This modeling is based on the local interaction simulation approach theory and is finally accomplished through the finite elements software Ansys11. In this paper, the Lamb waves propagating characteristics and the LISA/SIM theory are introduced. The finite difference equations describing wave propagation used in the LISA/SIM theory are obtained. Then, an anisotropic metallic plate model is modeled and a simulating Lamb waves signal is loaded on. Finally, the Lamb waves propagation modeling is implemented.     

Pattern-Noise in Ultrasonic Inspection of Articles Made of Complexly Structured Materials

Pattern-noise (PN) that occurs due to combined reflection of an ultrasonic probing signal from acoustic inhomogeneities in the material structure is an interference that conceals echo-signals from flaws. The most efficient method for extracting echo-signals from PN is multichannel spacetime signal processing (STSP). Different inspection purposes dictate different configurations of STSP schemes with the parameters that are determined by PN correlation characteristics. A theoretical model has been used to determine mutual PN correlation characteristics for the main types of transducers. The theoretical results have been confirmed experimentally.     

Physical and numerical modeling of the process of rolling off of a tapered shaft of aviation purpose

One of the most promising methods of manufacturing axisymmetric parts of gas turbine engines is local deformation on specialized rolling mills. To design this class of manufacturing operations and equipment, it is effective to use physical and numerical modeling. The article has provided the method and results of physical and numerical finite-element modeling of local deformation process of a detail of a cone-with-cylinder type made of EI962–Sh chromium steel. Analyses of the energy-power parameters of the technical process and the possibility of the destruction of a part during the deformation process have been carried out.     

Theoretical foundations of ultrasonic nondestructive testing of multilayer articles manufactured from composites with rubbery coatings: II. Scattering of elastic waves at flaws involving poorly glued joints between plastic layers and between a plastic layer and a rubbery coating

The second part of this study is devoted to the solution of the following problems: (i) excitation of plate modes with a lumped force applied to the plate’s surface, (ii) scattering of a bending wave at a small crack parallel to the plate’s surface, and (iii) scattering at a flaw involving a poorly glued joint between a rubbery coating and a plastic layer. The final formulas and numerical dependences for calculating the parameters of a crack or a cleavage are presented. A mathematical model that describes the scattering of waves by flaws in a multilayer article made from a plastic composite material has been developed.     

Models of magnetic charges and fluxes in the problem of flaw detection with local magnetization

The results of experimental studies of the magnetic-field strength of surface flaws in magnetically soft and hard steels magnetized with a dipolar magnet are discussed. Peculiarities of the interrelationship between the formation of the magnetic fields of surface flaws and fluxes in a magnetic circuit have been determined. The obtained anomalous relationship of the magnetic-field strengths of flaws in magnetically soft and hard steels was considered in terms of a flux model. The distinctive feature of the model consists in the presence of an internal magnetization magnetic flux whose lines of force are closed within a magnetized body. A comparison of the charge and flux models is performed based on the results we obtained.     

磁光成像技术在航空构件涡流检测中的应用

近年来迅速发展的磁光成像（MOI）技术使涡流检测技术得到了新的进展,运用磁光／涡流成像的有限元模型可以对典型的飞机构件缺陷（如连接飞机表面两个铝层的紧固件下面的裂纹）进行模拟,模拟结果表明,其磁场垂直分量的变化对这种结构来说是相当灵敏的,采用MOI技术可以用来探测隐藏在紧固件帽下面的缺陷。     

A two-step algorithm for finite-element solution of electromagnetic-testing problems: Electric-capacitance testing

A procedure for numerical solution of 3D electromagnetic-testing problems is described. This procedure is intended for problems where approximation of the systems of differential equations through standard finite-element schemes requires significant computer resources. Such a situation is mainly typical of the problems where effects of 3D flaws are not significant relative to the value of the main (usually 2D) field but nevertheless have to be calculated with a sufficiently high accuracy. At the first stage of the finite-element simulation algorithm, a 2D problem is numerically solved for a “flaw-free” field. At the second stage, the field of the flaw’s effect is calculated, the sources of this field being localized in the vicinity of the flaw. Owing to such an approach, the computer resources needed to solve the problems of this type may be significantly reduced so that the problems become solvable by means of PCs. The proposed procedure has been implemented in the MagNum3D package [1, 2] and the procedure’s efficiency has been confirmed via solution of a model problem of electric-capacitance testing.     

Large deformation analysis of anisotropic rubber hose along cyclic path by homogenization and path interpolation methods

Automotive braking hose used to deliver the hydraulic braking force to the drake disc is in a lamination composition of rubber and fabric braided layers to prevent the oil leakage and the excessive radial deformation. Currently, the configuration and durability become a hot issue in the design of braking hose, because both substantially affect the oil leakage caused by the micro cracks and the interference with other adjacent parts. The design of braking hose including its configuration has been relied on the trial-and-error experiment because there is no reliable numerical analysis technique. A main obstacle in developing the numerical analysis technique is the geometry modeling of braided layer which is woven with fabric cords of small diameter. The microstructure of braided layer has been simplified as an isotropic layer because of its painstaking modeling job and the necessity of huge number of finite elements. However, such a simple model could not successfully reproduce the out-of-deformation of braking hose which is produced by the orthotropic braided layers. Meanwhile, the braking hose undergoes cyclic large deformation during the steering motion and bump/rebound motions of vehicle. In this context, the goal of this study is to introduce a modeling-effective but reliable large deformation analysis method for braking hose along the specified cyclic path making use of the homogenization and path interpolation methods. The numerical results are also presented to illustrate the proposed numerical analysis method.

     

Combustion dynamics in a model lean-premixed gas turbine with a swirl stabilized injector

Unsteady numerical study has been conducted on combustion dynamics of a lean-premixed gas turbine with a swirl injector. A three-dimensional computation method utilizing large-eddy-simulation (LES) technique with finite rate chemical reaction was applied with the message passing interface (MPI) parallel architecture. The unsteady turbulent flame dynamics are carefully simulated so that the flow motion can be characterized in detail, showing fairly comparable results with the experimental data. It was observed that some fuel lumps escape from the primary combustion zone, and move downstream and consequently produce hot spots and large vortical structures in the azimuthal direction. The correlation between pressure oscillation and unsteady heat release is examined by the spatial Rayleigh parameter. In addition, it is shown that the complicate heat-release-structure can be precisely regenerated by means of modal analysis using proper orthogonal decomposition (POD).