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Effect of Thermal Radiation on the Thermal Properties of Parietodynamic Walls

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SSRN 2023年

作者： Dong, Xianzhang Lin, Baochen Xiao, Huigang Liu, Min School of Civil Engineering Harbin Institute of Technology Harbin150090 China Key Lab of Structures Dynamic Behavior and Control Ministry of Education Harbin Institute of Technology Harbin150090 China Heilongjiang Heijianyi Construction Engineering Co. Ltd 150040 China

The parietodynamic wall, a type of dynamic insulation, has been identified as an effective technology to reduce energy loss in buildings by recovering heat and cold energy through forced convection. However, current research on the thermal performance of parietodynamic walls has neglected the influence of thermal radiation, a crucial factor in energy transfer within the air layer of the wall. To address this gap, a numerical model that couples thermal radiation, heat transfer in solids and fluids, and turbulence is established to evaluate the effect of thermal radiation. Our results indicate that emissivity, the thermal resistance of the insulation layer, and air layer thickness significantly affect the proportion of thermal radiation in heat transfer. Specifically, when the emissivity is 1, the contribution ratio of thermal radiation to the heat transfer coefficient (HTC) of the parietodynamic wall is by up to 80.7%. Moreover, low thermal resistance of the insulation layer can increase the HTC by 268%-630% through thermal radiation gain. These findings improve our understanding of the effect of thermal radiation in parietodynamic walls, which would aid in the development of more energy-efficient buildings. © 2023, The Authors. All rights reserved.

关键词： Heat radiation

Experimental Study on Flexural Performance of Ultra-High-Performance Concrete with Recycled Aggregate Co-Modified by Nano-Silica and Steel Fiber

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SSRN 2023年

作者： Luo, Liang Shi, Jun Wang, Jianan Qu, Yiwen Dai, Bin School of Civil Engineering Central South University Changsha410075 China Key Lab of Structures Dynamic Behavior and Control of the Ministry of Education Harbin Institute of Technology Harbin150090 China School of Civil Engineering Harbin Institute of Technology Harbin150090 China

Expanding the application of defective recycled aggregates (RA) to ultra-high performance concrete (UHPC), it is necessary to modify them with nano-silica (NS) in conjunction with steel fibers (SF), and it is worthwhile to investigate the bending behavior under the typical characteristics of this new *** study investigates the flexural performance of recycled aggregate ultra-high-performance concrete (RA-UHPC) using a four-point bending test and analyzes the influence of RA substitution rates (0%, 50%, and 100%), SF content (0%, 1%, and 2%), and NS content (0%, 1%, 3%, and 5%) on its flexural toughness and microstructure. Additionally, digital image correlation (DIC) technology was employed to capture crack evolution during the test, and SEM microstructural analysis was used to elucidate the flexural mechanism of this fiber-nano composite concrete. The results show that the load-deflection curves of specimens without SF exhibit initial linear-elastic growth, followed by a sharp decrease in load after the peak without a distinct descending stage. In contrast, specimens with SF display three typical stages, with a smoother and flatter descending stage. The cross-distributed SF enhances post-peak ductility, transforming the failure behavior from quasi-brittle to ductile. Increasing SF content significantly enhances the flexural strength and toughness of the specimens, while an increase in RA substitution rate and NS content results in a slight reduction in flexural strength (fp). The changes in residual strength observed through both methods are consistent, with almost no residual strength in the brittle failure specimens. Moreover, DIC technology, relying on precise image capture, can predict crack positions before the peak load is reached. Finally, the microstructural analysis in SEM is combined to illustrate the flexural mechanism of this fiber-nanocomposite concrete. © 2023, The Authors. All rights reserved.

关键词： Image correlation

Mechanical Properties and Microstructure of Ultra-High-Performance Concrete Containing Recycled Aggregates Co-Modified with Steel Fibres and Nanosilica after Exposure to Elevated Temperatures

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SSRN 2023年

作者： Sun, Hang Luo, Liang Yuan, Huan Li, Xi Key Lab of Structures Dynamic Behavior and Control The Ministry of Education Harbin Institute of Technology Harbin150090 China School of Transportation and Science Engineering Harbin Institute of Technology Harbin150090 China School of Civil Engineering Harbin Institute of Technology Harbin150090 China

This study explores the mechanical properties and microstructure of ultra-high-performance concrete with recycled aggregates (UHPC-RA) enhanced by nanosilica (NS) and steel fibers (SF) at elevated temperatures. Thirty-six mixtures, varying in RA replacement rates, SF, and NS content, were prepared and tested for compressive strength, splitting tensile strength, and elastic modulus. Microstructural analyses included SEM morphology, XRD composition, pore size distribution, thermal conductivity, and elemental distribution studies. Results show temperature-induced changes, including SF oxidation and spalling, causing brittle failures due to weakened cementitious matrix and ITZ bonding. Moisture evaporation and hydration product decomposition lead to mass loss. Compressive strength initially increases and then decreases with rising temperatures, while overall splitting tensile strength decreases. Deterioration in UHPC-RA's microstructure is main reason for macroscopic mechanical property degradation. Linear relationships between compressive and splitting tensile strength were established. SEM and XRD confirmed that NS particles contribute to the conversion of CH to C-S-H gels. © 2023, The Authors. All rights reserved.

关键词： Steel fibers

Experimental investigation on the impingement of synthetic jet vortex rings on a spherical wall

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Physical Review Fluids 2022年第4期7卷 044703-044703页

作者： Changlong Chen Donglai Gao Wen-Li Chen Key Laboratory of Smart Prevention and Mitigation of Civil Engineering Disasters The Ministry of Industry and Information Technology Harbin Institute of Technology Harbin 150090 China Key Laboratory of Structures Dynamic Behavior and Control The Ministry of Education Harbin Institute of Technology Harbin 150090 China

An experimental study was conducted to investigate the influence of sphere diameter and Reynolds number on synthetic jet vortex rings impinging on a spherical wall. Laser-induced fluorescence and two-dimensional particle image velocimetry techniques were applied to visualize flow and measure flow velocity, respectively. In this experiment, the stroke length was kept constant (L=3.6), and different diameters (d/D=1, 6, and 16) and Reynolds numbers (Resj=227 and 682) were analyzed. In addition to flow visualization images and phase-averaged λci fields, the vortex ring trajectories and circulation are presented to reveal the evolution features of the vortex rings. The results demonstrated that the Reynolds number mainly determined the strength and induced ability of the primary vortex ring (PVR) and the sphere-diameter effect was reflected by the expansion distance of the PVR and its separation from the wall boundary layer. It was found that only a secondary vortex ring (SVR) was induced in the case of a small diameter or a low Reynolds number. As the diameter and Reynolds number increased, the PVR expanded continuously along the wall and induced a SVR and tertiary vortex ring. In particular, driven by the curve, the strength of the induced vortex ring decreased with the increase in the sphere diameter.

关键词： Vortex flows Wakes & jets

Convective meta-thermal concentration for ultrahigh efficient Stirling engine with waste heat and cold utilization

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arXiv

arXiv 2023年

作者： Zhou, Xinchen Xu, Xiang Ouyang, Xiaoping Huang, Jiping Fudan University Shanghai200433 China Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters the Ministry of Industry and Information Technology Key Lab of Structures Dynamic Behavior and Control the Ministry of Education Harbin Institute of Technology Harbin150090 China School of Materials Science and Engineering Xiangtan University Xiangtan411105 China

The Stirling engine, which possesses external combustion characteristics, a simple structure, and high theoretical thermal efficiency, has excellent potential for utilizing finite waste heat and cold resources. However, practical applications of this technology suffered from thermal inefficiency due to the discontinuity and instability of waste resources. Despite advances in energy storage technology, temperature variations in the heat-exchanging fluids at the hot and cold ends of the Stirling engine remained significant obstacles. In this work, convective meta-thermal concentration (CMTC) was introduced between the heating (cooling) fluids and the hot (cold) end of the Stirling engine, employing alternating isotropic materials with high and low thermal conductivities. It was demonstrated that CMTC effectively enhanced the temperature difference between the hot and cold ends, leading to a remarkable improvement in Stirling engine efficiency. Particularly, when the Stirling engine efficiency tended to zero due to the limited availability of waste heat and cold resources, CMTC overcame this limitation, surpassing existing optimization technology. Further analysis under various operating conditions showed that CMTC achieved a significant thermal efficiency improvement of up to 1460%. This work expanded the application of thermal metamaterials to heat engine systems, offering an exciting avenue for sustainable energy utilization. Copyright © 2023, The Authors. All rights reserved.

关键词： Waste heat

Experimental and Numerical Studies of Compressive Strength of 3d Printed Concrete Considering Interlayer Bonding Performance

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SSRN 2023年

作者： Tang, Boyang Yan, Jiachuan Han, Xiaoyu Lin, Yini Fan, Feng Key Lab of Structures Dynamic Behavior and Control of the Ministry of Education Harbin Institute of Technology Harbin150090 China Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters the Ministry of Industry and Information Technology Harbin Institute of Technology Harbin150090 China School of Civil Engineering Harbin Institute of Technology Harbin150090 China

This paper studied the compressive properties of 3D printed concrete and analyzed their influencing factors, including layer thickness and printing time interval. The investigation also explored the impact of inter-layer and inter-bar bonding properties on concrete's compressive strength by examining key factors. The findings revealed that compressive strength decreases as layer thickness decreases and printing time interval increases. Moreover, interlayer tensile and shear strength decrease with longer printing time intervals, while the anisotropic mechanical properties of 3D printed concrete become more pronounced as the number of printed layers increases. The study employed cohesive elements to numerically simulate the compressive strength of concrete specimens with varying number of layers and interlayer intervals. Parametric analysis was conducted to investigate bonding layer failure under different loading directions, and damage modes were analyzed. Finally, an empirical equation for predicting the compressive strength of 3D printed concrete was proposed and validated using experimental data. © 2023, The Authors. All rights reserved.

关键词： Compressive strength

Detecting Multiple Change Points in Distributional Sequences Derived from Structural Health Monitoring Data: An Application to Bridge Damage Detection

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arXiv

arXiv 2023年

作者： Lei, Xinyi Chen, Zhicheng Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters of the Ministry of Industry and Information Technology Harbin Institute of Technology Harbin150090 China Key Lab of Structures Dynamic Behavior and Control of the Ministry of Education Harbin Institute of Technology Harbin150090 China School of Civil Engineering Harbin Institute of Technology Harbin150090 China

Detecting damage in critical structures using monitored data is a fundamental task of structural health monitoring, which is extremely important for maintaining structures' safety and life-cycle management. Based on statistical pattern recognition paradigm, damage detection can be conducted by assessing changes in the distribution of properly extracted damage-sensitive features (DSFs). This can be naturally formulated as a distributional change-point detection problem. A good change-point detector for damage detection should be scalable to large DSF datasets, applicable to different types of changes, and capable of controlling for false-positive indications. This study proposes a new distributional change-point detection method for damage detection to address these challenges. We embed the elements of a DSF distributional sequence into the Wasserstein space and construct a moving sum (MOSUM) multiple changepoint detector based on Fréchet statistics and establish theoretical properties. Extensive simulation studies demonstrate the superiority of our proposed approach against other competitors to address the aforementioned practical requirements. We apply our method to the cable-tension measurements monitored from a long-span cable-stayed bridge for cable damage detection. We conduct a comprehensive change-point analysis for the extracted DSF data, and reveal interesting patterns from the detected changes, which provides valuable insights into cable system damage. Copyright © 2023, The Authors. All rights reserved.

关键词： Damage detection

A robust deep learning-based damage identification approach for SHM considering missing data

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arXiv

arXiv 2023年

作者： Deng, Fan Tao, Xiaoming Wei, Pengxiang Wei, Shiyin Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters of the Ministry of Industry and Information Technology Harbin Institute of Technology Harbin150090 China Key Lab of Structures Dynamic Behavior and Control of the Ministry of Education Harbin Institute of Technology Harbin150090 China School of Civil Engineering Harbin Institute of Technology Harbin150090 China

Data-driven method for Structural Health Monitoring (SHM), that mine the hidden structural performance from the correlations among monitored time series data, has received widely concerns recently. However, missing data significantly impacts the conduction of this method. Missing data is a frequently encountered issue in time series data in SHM and many other real-world applications, that harms to the standardized data mining and downstream tasks, such as condition assessment. Imputation approaches based on spatiotemporal relations among monitoring data are developed to handle this issue, however, no additional information is added during imputation. This paper thus develops a robust method for damage identification that considers the missing data occasions, based on long-short term memory (LSTM) model and dropout mechanism in the autoencoder (AE) framework. Inputs channels are randomly dropped to simulate the missing data in training, and reconstruction errors are used as the loss function and the damage indicator. Quasi-static response (cable tension) of a cable-stayed bridge released in 1st IPC-SHM is employed to verify this proposed method, and results show that the missing data imputation and damage identification can be implemented together in a unified way. © 2023, CC BY.

关键词： Structural health monitoring

The Micro–Mechanical Mechanism of Multiple Cracking behavior Induced by Interface Strengthening for Ultra–High–Performance Concrete

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SSRN 2023年

作者： Du, Junjie Xiao, Huigang Zhang, Fengling Liu, Min Key Lab of Structures Dynamic Behavior and Control The Ministry of Education Harbin Institute of Technology Harbin150090 China School of Civil Engineering Harbin Institute of Technology Harbin150090 China School of Civil Engineering Shandong University 17923 Jingshi Road Jinan250061 China

The multiple cracking behavior of ultra–high–performance concrete （UHPC） is strongly dependent on the bridging of cracks by fibers and the spatial strength distribution of matrix. A good match between fiber bridging properties and matrix tensile strength can significantly improve the utilization of fibers and matrix. In this study, a micromechanics based theoretical model is proposed, which can match the matrix tensile strength with the fiber–matrix interface bonding strength. The spatial strength distribution of the matrix and the stress transfer between the fiber and the matrix is considered in the model. Bridge stresses, additional stresses, stress transfer distances, and pulley forces at the crack face for various crack openings are derived. Dense multiple cracks were observed in the UHPC tensile samples at a common condition ( ) designing based on the calculation results. The applicability of the model is validated by comparing the simulation results and the experimental results in previous investigations at the same paraments ( ). With the proposed model, the mechanism of fiber–matrix interface enhancement contributing to the multiple cracking behavior can be understood. The results of this study could provide fundamental insights for the design of UHPC for various ductility and strength requirements. © 2023, The Authors. All rights reserved.

关键词： Fibers