• Computers and Concrete
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• v.26 no.1
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• pp.11-20
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• 2020

Concrete are the most widely used manmade materials for infrastructure construction across the world. These constructions gradually aged and damaged due to long-term use. However, there does not exist an efficient concrete recycling method with low energy consumption. In this study, concrete was regarded as a heterogeneous material composed of coarse aggregate and cement mortar. And the failure mode of concrete under ultrasonic dynamic loading was investigated by finite element (FE) analysis. Simultaneously, a 3D random aggregate concrete model was programmed by APDL and imported into ABAQUS software, and the damage plastic constitutive model was applied to each phase to study the damage law of concrete under dynamic loading. Meanwhile, the dynamic damage process of concrete was numerically simulated, which observed ultrasonic propagating and the concrete crushing behavior. Finally, the FE simulation considering the influence of different aggregate volume and aggregate size was carried out to illustrate the damage level of concrete.

• Smart Structures and Systems
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• v.5 no.4
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• pp.415-426
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• 2009

This study focuses on the concept of multi-scale wireless sensor networks for damage detection in civil infrastructure systems by first over viewing the general network philosophy and attributes in the areas of data acquisition, data reduction, assessment and decision making. The data acquisition aspect includes a scalable wireless sensor network acquiring acceleration and strain data, triggered using a Restricted Input Network Activation scheme (RINAS) that extends network lifetime and reduces the size of the requisite undamaged reference pool. Major emphasis is given in this study to data reduction and assessment aspects that enable a decentralized approach operating within the hardware and power constraints of wireless sensor networks to avoid issues associated with packet loss, synchronization and latency. After over viewing various models for data reduction, the concept of a data-driven Bivariate Regressive Adaptive INdex (BRAIN) for damage detection is presented. Subsequent examples using experimental and simulated data verify two major hypotheses related to the BRAIN concept: (i) data-driven damage metrics are more robust and reliable than their counterparts and (ii) the use of heterogeneous sensing enhances overall detection capability of such data-driven damage metrics.

• Journal of Korean Society on Water Environment
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• v.35 no.2
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• pp.115-122
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• 2019

The objective of this study was to investigate the sonophysical and sonochemical effects induced by acoustic cavitation in heterogeneous systemin a 28 kHz double-bath reactor using calorimetry, the aluminiumfoil erosion test, and the luminol test. With no glass beads, calorimetric power in the inner vessel increased as much as the outer sonoreactor lost and total calorimetric power was maintained for various liquid height conditions (0.5 ~ 7 cm) in the vessel. Higher calorimetric energy was obtained at higher liquid height conditions. Similar results were obtained when glass beads were placed with various beads heights (0.5 ~ 2.0 cm) and relatively high calorimetric energy was obtained in spite of large attenuation in the glass beads layer. An aluminium foil placed between the bottom of the inner vessel and the glass beads layer was damaged, indicating significant sonophysical effects. Much less damage was detected when the foil was placed above the beads layer due to large attenuation of ultrasound. Sonochemical effects, visualized by sonochemiluminescence (SCL), also decreased significantly when the beads were placed in the vessel. It was established that the optimization of the liquid height above the solid-material layer could enhance the sonophysical and sonochemical effects in the double-bath sonoreactors.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.4
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• pp.225-235
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• 2020

Ultrasonic investigation of damage detection has been widely used for non-destructive testing of various concrete structures. This study focuses on damage detection analysis with the aid of wave propagation in two-phase composite concrete with aggregate (inclusion) and mortar (matrix). To fabricate a realistic simulation model containing a variety of irregular aggregate shapes, the mesh generation technique using an image processing technique was proposed. Initially, the domains and boundaries of the aggregates were extracted from the digital image of a typical concrete cut-section. This enables two different domains: aggregates and mortar in heterogeneous concrete sections, and applied the grids onto these domains to discretize the model. Subsequently, finite element meshes are generated in terms of spatial and temporal requirements of the model size. For improved analysis results, all meshes are designed to be quadrilateral type, and an additional process is conducted to improve the mesh quality. With this simulation model, wave propagation analyses were conducted with a central frequency of 75 kHz of the Mexican hat incident wave. Several void damages, such as needle-shaped cracks and void-shaped holes, were artificially introduced in the model. Finally, various formats of internal damage were detected by implementing energy mapping based signal processing.

• Food Science and Biotechnology
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• v.17 no.6
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• pp.1131-1138
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• 2008

Diabetic complications are a leading cause of blindness, renal failure, and nerve damage. Additionally, diabetes-accelerated atherosclerosis leads to increased risk of myocardial infarction, stroke, and limb amputation. At the present time, 4 main molecular mechanisms have been implicated in hyperglyceamia-mediated vascular damage. In particular, advanced glycation endproducts (AGE), which are formed by complex, heterogeneous, sugar-derived protein modifications, have been implicated as a major pathogenic process for diabetic complications. Recently, AGE inhibitors such as aminoguanidin, ALT-946, and pyridoxamine have been reported. Such an integrating paradigm provides a new conceptual framework for future research on diabetes complications and on discovering drugs to prevent the progression of AGE-induced maladies.

• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.7_spc
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• pp.509-516
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• 2016

Secure operation of hospitals during and right after earthquake is essential. Past lessons from earthquake damages have shown that most of the injured and the death occurred within 30 minutes after earthquake and the portion of nonstructural damage has become significant. However, hospital buildings in Korea have not prepared fully to address such rising issues. This paper is to study what type of damage patterns are related to hospital buildings and how to develop a preparedness plan to keep hospitals operational at all earthquakes if possible. This paper first reviews on past earthquake damages reported as critical to hospital buildings while classifying them into four groups: (1) structural element; (2) architectural-nostructural element; (3) medical equipments and contents; and (4) utility facility. Upon such classification, some detailed concerns can be specified under each group explicitly. Then a hierarchy for hospital building is also developed for the classified groups, which enables us to identify required things for the enhancement of seismic performance of hospital building that consists of heterogeneous elements. To upgrade the level of seismic performance for existing hospital buildings, the concept of performance-based approach can be adopted to address the heterogeneous problems in a systematic and stepwise manner. Finally a conceptual framework for the seismic risk assessment for hospital building is proposed toward the seismic enhancement of hospital buildings using performance-based approach.

• Journal of the Korea Concrete Institute
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• v.18 no.1 s.91
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• pp.37-46
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• 2006

The principal objective of this study is to assess the hierarchical effects of defects on the elastic stiffness properties at different levels of observation. In particular, quantitative damage measures which characterize the fundamental mode of degradation in the form of elastic damage provide quite insightful meanings at the level of constitutive relations and at the level of structures. For illustration, a total of three model problems of increasing complexity, a 1-D bar structure, a 2-D stress concentration problem, and a heterogeneous composite material made of a matrix with particle inclusions. Considering a damage scenario for the particle inclusions the material system degrades from a composite with very stiff inclusions to a porous material with an intact matrix skeleton. In other damage scenario for the matrix, the material system degrades from a composite made of a very stiff skeleton to a disconnected assembly of particles because of progressive matrix erosion. The trace-back and forth of tight bounds in terms of the reduction of the lowest eigenvalues are extensively discussed at different levels of observation.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.11
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• pp.988-996
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• 2012

This paper presents a distributed task assignment algorithm for the suppression of enemy air defense (SEAD) mission of heterogeneous UAVs, based on the consensus-based bundle algorithm (CBBA). SEAD mission can be modeled as a task assignment problem of multiple UAVs performing multiple air defense targets, and UAVs performing SEAD mission consist of the weasel for destruction of enemy's air defense system and the striker for the battle damage assessment (BDA) or other tasks. In this paper, a distributed task assignment algorithm considering path-planning in presence of terrain obstacle is developed for heterogeneous UAVs, and then it is applied to SEAD mission. Through numerical simulations the performance and the applicability of the proposed method are tested.

• Structural Engineering and Mechanics
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• v.44 no.5
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• pp.663-680
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• 2012

Previous major earthquakes revealed that most damage of the buried segmented pipelines occurs at the joints of the pipelines. It has been proven that the differential motions between the pipe segments are one of the primary reasons that results in the damage (Zerva et al. 1986, O'Roueke and Liu 1999). This paper studies the combined influences of ground motion spatial variations and local soil conditions on the seismic responses of buried segmented pipelines. The heterogeneous soil deposits surrounding the pipelines are assumed resting on an elastic half-space (base rock). The spatially varying base rock motions are modelled by the filtered Tajimi-Kanai power spectral density function and an empirical coherency loss function. Local site amplification effect is derived based on the one-dimensional wave propagation theory by assuming the base rock motions consist of out-of-plane SH wave or combined in-plane P and SV waves propagating into the site with an assumed incident angle. The differential axial and lateral displacements between the pipeline segments are stochastically formulated in the frequency domain. The influences of ground motion spatial variations, local soil conditions, wave incident angle and stiffness of the joint are investigated in detail. Numerical results show that ground motion spatial variations and local soil conditions can significantly influence the differential displacements between the pipeline segments.

• Coupled systems mechanics
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• v.11 no.1
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• pp.15-32
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• 2022

The comprehensive understanding of the fiber reinforced polymer behavior requires the use of advanced non-destructive testing methods due to its heterogeneous microstructure and anisotropic mechanical proprieties. In addition, the material response under load is strongly associated with manufacturing defects (e.g., voids, inclusions, fiber misalignment, debonds, improper cure and delamination). Such imperfections and microstructures induce various damage mechanisms arising at different scales before macrocracks are formed. The origin of damage phenomena can only be fully understood with the access to underlying microstructural features. This makes X-ray Computed Tomography an appropriate imaging tool to capture changes in the bulk of fibrous materials. Moreover, Digital Volume Correlation (DVC) can be used to measure kinematic fields induced by various loading histories. The correlation technique relies on image contrast induced by microstructures. Fibrous composites can be reinforced by different fiber architectures that may lead to poor natural contrast. Hence, a priori analyses need to be performed to assess the corresponding DVC measurement uncertainties. This study aimed to evaluate measurement resolutions of global and regularized DVC for glass fiber reinforced polymers with different fiber architectures. The measurement uncertainties were evaluated with respect to element size and regularization lengths. Even though FE-based DVC could not reach the recommended displacement uncertainty with low spatial resolution, regularized DVC enabled for the use of fine meshes when applying appropriate regularization.