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A New inverse algorithm for Tomographic Reconstruction of Damage Images Using Lamb Waves

CMC-COMPUTERS MATERIALS & CONTINUA 2011年第1期26卷 37-65页

作者： Morii, M. Hu, N. Fukunaga, H. Li, J. H. Liu, Y. L. Atobe, S. Alamusi Qiu, J. H. Chiba Univ Chiba Japan Chongqing Univ Chongqing 630044 Peoples R China Tohoku Univ Sendai Miyagi 980 Japan Nanjing Univ Aeronaut & Astronaut Nanjing Jiangsu Peoples R China

Lamb wave tomography (LWT) is a potential and efficient technique for non-destructive tomographic reconstruction of damage images in structural components or materials. A new two-stage inverse algorithm with a small amount of scanning data for quickly reconstructing damage images in aluminum and CFRP laminated plates was proposed in this paper. Due to its high sensitivity to damages, the amplitude decrease of transmitted Lamb waves after travelling through the inspected region was employed as a key signal parameter related to the attenuation of Lamb waves in propagation routes. A through-thickness circular hole and a through-thickness elliptical hole in two aluminum plates, and an impact induced invisible internal delamination in a CFRP laminated plate were used to validate the effectiveness and reliability of the proposed method. it was concluded that the present new algorithm was capable of reconstructing the images of the above mentioned various damages successfully with much less experimental data compared with those needed by some traditional techniques.

关键词： Lamb wave tomography inverse algorithm damage image attenuation

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A Multifrequency inverse algorithm for 3-D Microwave Imaging

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IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION 2023年第11期71卷 9136-9141页

作者： Fang, Yuan Bakian-Dogaheh, Kazem Moghaddam, Mahta Univ Southern Calif Ming Hsieh Dept Elect Engn Microwave Syst Sensors & Imaging Lab MiXIL Los Angeles CA 90089 USA

A new multifrequency inverse algorithm is presented based on the improved variational Born iterative method (VBIM) for 3-D quantitative microwave imaging (MWI). The proposed method is capable of reconstructing the 3-D dielectric relaxation model using measured data acquired at multiple transmit frequencies. A least-squares optimization using the conjugate gradient method with Tikhonov regularization is applied at each VBIM step to relax the memory requirements. For evaluating the algorithm performance, two experiments are conducted with our newly designed MWI system, and image reconstruction is performed under black-box conditions with no a priori information. The phantom models in these experiments are: 1) a single ping-pong ball filled with 75% isopropyl-25% water mixture submerged into a plastic cup filled with 90% isopropyl-10% water mixture and 2) a coplanar distributed object consisting of five ping-pong balls filled with water at the same vertical level. Reconstructed 3-D dielectric images demonstrate the accuracy of our proposed VBIM-based multifrequency inverse algorithm using measured data with no a priori information.

关键词： Conjugate gradient for least-squares (CGLSs) inverse algorithm microwave imaging (MWI) single-pole Debye model variational Born iterative method (VBIM)

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Prediction of Longitudinal Cracks Based on a Full-Scale Finite-Element Model Coupled inverse algorithm for a Continuously Cast Slab

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STEEL RESEARCH INTERNATIONAL 2017年第10期88卷 n/a-n/a页

作者： Du, Fengming Wang, Xudong Liu, Yu Wei, Jingjing Yao, Man Dalian Univ Technol Sch Mat Sci & Engn 2 Linggong Rd Dalian 116024 Liaoning Peoples R China Dalian Maritime Univ Coll Marine Engn 1 Linghai Rd Dalian 116026 Liaoning Peoples R China Northeast Dianli Univ Sch Mech Engn 169 Changchun Rd Jilin 132012 Liaoning Peoples R China

A full-scale finite-element model of a slab and its mold is developed to predict the appearance of longitudinal cracks during continuous casting, in which the measured data are combined with the model through an inverse algorithm. The simulation results show that the stress distributions in the slab are not symmetrical, reflecting the non-uniformity of the thermo-mechanical behavior. The longitudinal crack sensitivity index is highest at 60-100 mm below the meniscus, and the position of an actual longitudinal crack agrees well with the calculated result. This illustrates the validity of the proposed method for predicting longitudinal cracks, and hence demonstrates the necessity of building the full-scale model integrated with measured data.

关键词： continuous casting finite-element stress model inverse algorithm longitudinal crack simulation

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Investigation on non-uniform friction behaviors of slab during continuous casting based on an inverse algorithm

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JOURNAL OF MATERIALS PROCESSING TECHNOLOGY 2021年 288卷 116871-116871页

作者： Du, Fengming Zhang, Kaiguang Li, Chengdi Chen, Wenbin Zhang, Pengchao Wang, Xudong Dalian Maritime Univ Marine Engn Coll CN-116024 Dalian Peoples R China Xinyu Univ Xinyu Key Lab Mat Technol & Applicat Intelligent CN-338004 Xinyu Jiangxi Peoples R China Dalian Maritime Univ Coll Transportat Engn CN-116024 Dalian Peoples R China Dalian Univ Technol Mat Sci & Engn Coll CN-116024 Dalian Peoples R China

The non-uniform friction and lubrication are key factors that affect the slab quality during continuous casting. In order to present the complicated friction behavior of slab in the mold, a friction calculation model was built based on a full-scale heat transfer model. An inverse algorithm was applied to calculate the real heat flux by measuring temperatures from thermocouples buried in various locations of the mold. ANSYS software was used to solve the finite-element equations. The results showed that the friction state of the slab surface progressed from a liquid friction zone to a mixed friction zone, and then to a solid friction zone from the meniscus. In the casting direction, the liquid frictional stress gradually increased, which was between 0 and 1 kPa;the mixed frictional stress rapidly increased from 1 to 15 kPa;the solid frictional stress increased linearly, reaching 28.4 kPa at the exit. The slag solidification temperature, slag crystallization temperature and superheat could affect the states of liquid, solid or mixed friction.

关键词： Friction Continuous casting inverse algorithm Full-scale model Non-uniform

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An inverse algorithm for reconstructing the acoustic parameters of layered medium

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Chinese Journal of Acoustics 1994年第4期13卷 311-314页

作者： LIN Junxuao(Ocean University of Qingdao. Qingdao 266003)

The inverse problem in geophysics is to infer the vertical structure from the observed data. The crucial assumption in deriving inversion algorithms obtained for different elementary layer structures. Much of the previous work on this problem for the case of plane wave at normal incidence has consisted of deriving a Schrodinger equation from the basic acoustic and stress-strain equations, and then reconstructing the potential appearing in this equation by using the Gelfand-Levitan procedure. We shall be concerned with structures in which the unknown coefficient has jump discontinuities. Here the unknown potential in the corresponding Gelfand-Levitan framework is highly singular, so much so that the theory breaks down. In this paper it is presented an inversion algorithm based on the Riccati equation,which avoids to solve the problem of singularity. The model experiment was conducted in a sewage pool of a factory. The final result of inversion agrecd well with the direct experimental observation.

关键词： inverse algorithm Layered medium

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Comparative investigation of the inverse framework for resonant ultrasound spectroscopy

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COMPUTATIONAL & APPLIED MATHEMATICS 2025年第1期44卷 1-17页

作者： Shi, Chengyu Li, Hong Zhang, Jianhai Zhao, Hongwei Jilin Univ Sch Mech & Aerosp Engn Changchun 130025 Peoples R China Jilin Univ Key Lab CNC Equipment Reliabil Minist Educ Changchun 130025 Peoples R China Jilin Univ Chongqing Res Inst Chongqing 401120 Peoples R China

Resonant ultrasound spectroscopy (RUS), a nondestructive testing technology based on free resonance frequencies, can be employed to derive all anisotropic elastic constants in one test. In the inverse framework, the iterative algorithm is applied to constantly update elastic parameters in the calculation model to minimize the relative error between calculated and observed resonance frequencies. The process has a significant impact on the elastic identification efficiency. In this paper, existing inverse algorithms are evaluated by fitting error, iteration time and uncertainty in results to provide a basis for algorithm investigation. For rapid testing demands, the algorithm, in which fuzzy logic is introduced to adaptively modify the parameter in particle swarm optimization (PSO), is devised to solve the inverse issue. It has been proven to have the lowest final fitting error and superior repeatability independent of initial guesses. The calculation time is reduced by 15% and 52.9% for TC4 and human cortical bone compared with PSO, respectively. Furthermore, it still attains the best convergence performance for human cortical bone with one-third of measured resonance frequencies missing due to high material loss. The proposed inverse approach aims to accomplish rapid determination of low-symmetry elastic constants with imperfect measurement information.

关键词： inverse algorithm Resonant ultrasound spectroscopy Adaptive particle swarm optimization Fuzzy logic

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Comparative Study of Three-Dimensional Stress and Crack Imaging in Concrete by Application of inverse algorithms to Coda Wave Measurements

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SENSORS 2020年第17期20卷 4899.-4899.页

作者： Jiang, Hanwan Zhan, Hanyu Ma, Ziwei Jiang, Ruinian Univ Wisconsin Platteville Dept Civil Engn Platteville WI 53818 USA New Mexico State Univ Klipsch Sch Elect & Comp Engn Las Cruces NM 88003 USA Univ Tennessee Chattanooga Dept Math Chattanooga TN 37403 USA New Mexico State Univ Dept Engn Technol & Surveying Engn Las Cruces NM 88003 USA

The intrinsic heterogeneity property of concrete causes strong multiple scatterings during wave propagation, forming coda wave that follows very complex trajectories. As a superposition of multiply scattered waves, coda wave shows great sensitivity to subtle changes, but meanwhile lose spatial resolution. To make use of its sensitivity and turn the limitation into advantage, this paper presents an experimental study of three-dimensionally imaging local changes in concrete by application of inverse algorithms to coda wave measurements. Load tests are performed on a large reinforced concrete beam that contains multiple pre-existing millimeter-scale cracks in order to match real life situation. The joint effects of cracks and stresses on coda waves have been monitored using a network of fixed transducers placed at the surface. The global waveform decorrelations and velocity variations are firstly quantified through coda wave interferometry technique. Subsequently, two inverse algorithms are independently applied to map the densities of changes at each localized position. Using this methodology, the stress changes and subtle cracks in the concrete beam are detected and imaged for both temporal and spatial domains.

关键词： coda wave transducer network large concrete beam NDT sensitivity kernel inverse algorithm three-dimensional crack and stress imaging

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Analysis of Non-uniform Mechanical Behavior for a Continuous Casting Mold Based on Heat Flux from inverse Problem

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Journal of Iron and Steel Research International 2016年第2期23卷 83-91页

作者： Feng-ming DU Xu-dong WANG Yu LIU Tian-yi LI Man YAO School of Materials Science and Engineering Dalian University of Technology

The distortion of mold plates plays an important role in the formation of surface cracks on continuously cast steel products. To investigate the non-uniform distortion of a mold, a full-scale stress model of the mold was de veloped. An inverse algorithm was applied to calculate the heat flux using the temperatures measured by the thermo- couples buried inside the mold plates. Based on this, a full-scale, finite-element stress model, including four copper plates, a nickel layer and water slots in different depths, was built to determine the complex mechanical behavior of the continuous casting mold used to produce steel slabs. The heat flux calculated by the inverse algorithm was applied to the stress model to analyze the non-uniform mechanical behavior. The results showed that the stress and distortion distributions of the four copper plates were not symmetrical, which reflected the non-uniform distortion behaviors of copper plates, water slots, nickel layer and the corner region of the mold. The gap between the mold and the slab was increased because of the corner distortion, which was very important for the heat transfer of initial solidifying shell, and it may be a major reason for the slow cooling of the slab corner.

关键词： finite-element stress model inverse algorithm nickel layer water slots continuous casting mold

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Analysis of the non-uniform thermal behavior in slab continuous casting mold based on the inverse finite-element model

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JOURNAL OF MATERIALS PROCESSING TECHNOLOGY 2014年第11期214卷 2676-2683页

作者： Du, Fengming Wang, Xudong Yao, Man Zhang, Xiaobing Dalian Univ Technol Sch Mat Sci & Engn Dalian 116024 CN Peoples R China Jiangsu Shagang Grp Chief Engn Off Zhangjiagang 215625 CN Peoples R China

A full finite-element model of a mold, including four copper plates, nickel layer and water slots of different depths, was developed to reveal the complex thermal behavior of molds in slab continuous casting. An inverse algorithm was applied to calculate the heat flux and combined with the temperatures measured using thermocouples that were buried in different positions of the mold. The temperature distributions of the four copper plates are not symmetric, reflecting the non-uniform nature of heat transfer and the necessity of building a full model. The maximum hot surface temperature of the mold occurs in the region 70-100mm below the meniscus. At heights 100 mm below the meniscus, the average temperature of the deep water slot root is higher than that of the shallow water slot by approximately 10 degrees C. In the off-corner regions, the hot surface temperature differences between the narrow face and wide face near the corners are approximately 20-30 degrees C 100 mm below the meniscus. It will provide a helpful tool for further improving the casting parameters and operations. (C) 2014 Elsevier B.V. All rights reserved.

关键词： Full finite-element model inverse algorithm Nickel layer Water slots Continuous casting mold

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An inverse channel model for modeling contaminant transport

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ENERGY SOURCES 2002年第4期24卷 287-299页

作者： Jang, MC Choe, JG Seoul Natl Univ Geofluids Engn Lab Div Civil Urban & Geosyst Engn Seoul 151742 South Korea

Recent experimental and theoretical investigations of transport in a fracture indicate that fluid flows preferentially through flow channels in the fracture plane. Several one-dimensional (1D) channel models have been introduced to interpret flow and transport through two-dimensional (2D) fractured media. However, those models are not capable of reproducing a tracer breakthrough curve accurately, and the aperture distributions (i.e., aperture mean and standard deviation) predicted by those models cannot characterize flow channels in the fracture. In this paper, we present a new 1D channel model using an inverse algorithm. At a given breakthrough curve, we divide the time domain into a limited number of intervals based on the principle of superposition and then determine aperture distribution of each channel inversely. The new channel model reproduces the tracer breakthrough curve of a fracture almost exactly at a given pressure drop. In addition, the aperture distributions obtained by the new channel model have good agreement with those of 2D modeling of transport in the fracture. In parameter analyses, we found that flow channeling becomes dominant in fracture flow when the coefficient of variation is >0.3. Therefore the new channel model can effectively simulate flow and tracer transport in a fracture in that range.

关键词： channel model channeling fracture inverse algorithm solute transport

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