Effects of 3D contraction on pebble flow uniformity and stagnation in pebble beds

Wu, Mengqi,Gui, Nan,Yang, Xingtuan,Tu, Jiyuan,Jiang, Shengyao Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.5

Pebble flow characteristics can be significantly affected by the configuration of pebble bed, especially for HTGR pebble beds. How to achieve a desired uniform flow pattern without stagnation is the top priority for reactor design. Pebbles flows inside some specially designed pebble bed with arc-shaped contraction configurations at the bottom, including both concave-inward and convex-outward shapes are explored based on discrete element method. Flow characteristics including pebble retention, residence-time frequency density, flow uniformity as well as axial velocity are investigated. The results show that the traditionally designed pebble bed with cone-shape bottom is not the most preferred structure with respect to flow pattern for reactor design. By improving the contraction configuration, the flow performance can be significantly enhanced. The flow in the convex-shape configuration featured by uniformity, consistency and less stagnation, is much more desirable for pebble bed design. In contrast, when the shape is from convex-forward to concave-inward, the flow shows more nonuniformity and stagnation in the corner although the average cross-section axial velocity is the largest due to the dominant middle pebbles.

Prediction of the remaining time and time interval of pebbles in pebble bed HTGRs aided by CNN via DEM datasets

Wu Mengqi,Liu Xu,Gui Nan,Yang Xingtuan,Tu Jiyuan,Jiang Shengyao,Qian Zhao 한국원자력학회 2023 Nuclear Engineering and Technology Vol.55 No.1

Prediction of the time-related traits of pebble flow inside pebble-bed HTGRs is of great significance for reactor operation and design. In this work, an image-driven approach with the aid of a convolutional neural network (CNN) is proposed to predict the remaining time of initially loaded pebbles and the time interval of paired flow images of the pebble bed. Two types of strategies are put forward: one is adding FC layers to the classic classification CNN models and using regression training, and the other is CNNbased deep expectation (DEX) by regarding the time prediction as a deep classification task followed by softmax expected value refinements. The current dataset is obtained from the discrete element method (DEM) simulations. Results show that the CNN-aided models generally make satisfactory predictions on the remaining time with the determination coefficient larger than 0.99. Among these models, the VGG19þDEX performs the best and its CumScore (proportion of test set with prediction error within 0.5s) can reach 0.939. Besides, the remaining time of additional test sets and new cases can also be well predicted, indicating good generalization ability of the model. In the task of predicting the time interval of image pairs, the VGG19þDEX model has also generated satisfactory results. Particularly, the trained model, with promising generalization ability, has demonstrated great potential in accurately and instantaneously predicting the traits of interest, without the need for additional computational intensive DEM simulations. Nevertheless, the issues of data diversity and model optimization need to be improved to achieve the full potential of the CNN-aided prediction tool

Scattering Correction for Image Reconstruction in Flash Radiography

LIANGZHI CAO,Mengqi Wang,Hongchun Wu,Zhouyu Liu,Yuxiong Cheng,Hongbo Zhang 한국원자력학회 2013 Nuclear Engineering and Technology Vol.45 No.4

Scattered photons cause blurring and distortions in flash radiography, reducing the accuracy of image reconstruction significantly. The effect of the scattered photons is taken into account and an iterative deduction of the scattered photons is proposed to amend the scattering effect for image restoration. In order to deduct the scattering contribution, the flux of scattered photons is estimated as the sum of two components. The single scattered component is calculated accurately together with the uncollided flux along the characteristic ray, while the multiple scattered component is evaluated using correction coefficients pre-obtained from Monte Carlo simulations.The arbitrary geometry pretreatment and ray tracing are carried out based on the customization of AutoCAD. With the above model, an Iterative Procedure for image restORation code, IPOR, is developed. Numerical results demonstrate that the IPOR code is much more accurate than the direct reconstruction solution without scattering correction and it has a very high computational efficiency.

Comparative Study of Exposure Assessment of Dust in Building Materials Enterprises Using ART and Monte Carlo

Jiang Wei,Wu Zonghao,Zhang Mengqi,Zhang Haoguang 한국산업안전보건공단 산업안전보건연구원 2024 Safety and health at work Vol.15 No.1

Background Dust generated during the processing of building materials enterprises can pose a serious health risk. The study aimed to compare and analyze the results of ART and the Monte Carlo model for the dust exposure assessment in building materials enterprises, to derive the application scope of the two models. Methods First, ART and the Monte Carlo model were used to assess the exposure to dust in each of the 15 building materials enterprises. Then, a comparative analysis of the exposure assessment results was conducted. Finally, the model factors were analyzed using correlation analysis and the scope of application of the models was determined. Results The results show that ART is mainly influenced by four factors, namely, localized controls, segregation, dispersion, surface contamination, and fugitive emissions, and applies to scenarios where the workplace information of the building materials enterprises is specific and the average dust concentration is greater than or equal to 1.5 mg/m3. The Monte Carlo model is mainly influenced by the dust concentration in the workplace of building materials enterprises and is suitable for scenarios where the dust concentration in the workplace of the building materials enterprises is relatively uniform and the average dust concentration is less than or equal to 6mg/m3. Conclusion ART is most accurate when workplace information is specific and average dust concentration is > 1.5 mg/m3; whereas, The Monte Carlo model is the best when dust concentration is homogeneous and average dust concentration is < 6 mg/m3. Background Dust generated during the processing of building materials enterprises can pose a serious health risk. The study aimed to compare and analyze the results of ART and the Monte Carlo model for the dust exposure assessment in building materials enterprises, to derive the application scope of the two models. Methods First, ART and the Monte Carlo model were used to assess the exposure to dust in each of the 15 building materials enterprises. Then, a comparative analysis of the exposure assessment results was conducted. Finally, the model factors were analyzed using correlation analysis and the scope of application of the models was determined. Results The results show that ART is mainly influenced by four factors, namely, localized controls, segregation, dispersion, surface contamination, and fugitive emissions, and applies to scenarios where the workplace information of the building materials enterprises is specific and the average dust concentration is greater than or equal to 1.5 mg/m3. The Monte Carlo model is mainly influenced by the dust concentration in the workplace of building materials enterprises and is suitable for scenarios where the dust concentration in the workplace of the building materials enterprises is relatively uniform and the average dust concentration is less than or equal to 6mg/m3. Conclusion ART is most accurate when workplace information is specific and average dust concentration is > 1.5 mg/m3; whereas, The Monte Carlo model is the best when dust concentration is homogeneous and average dust concentration is < 6 mg/m3.

Two Simplified Methods for Galloping of Iced Transmission Lines

Xiaohui Liu,Guangyun Min,Mengqi Cai,Bo Yan,Chuan Wu 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.1

For the galloping of iced transmission lines, the influences of two simplified methods of dynamic tension on the galloping characteristics of transmission lines are investigated. Based on the variational principle for Hamiltonian, the partial differential equation of galloping of iced transmission lines is derived, then it is transformed into ordinary differential equation by Galerkin method. Two different simplified methods are used to convert the partial differential equation into ordinary differential equation. One is to average the dynamic tension over the span length, then Galerkin method is used. The other is that Galerkin method is used to convert the partial differential equation into ordinary differential equation directly. Firstly, the influences of two simplified methods on coefficients of ordinary differential galloping equation are studied. Second, the influences of the bending stiffness on the first-order frequency have been researched. In addition, the average method of two degrees of freedom (DOFs) is proposed and the galloping characteristics of iced transmission lines are studied by using multiscale method and average method, then the results are compared with that obtained by using numerical method. The parameters analysis shows that the two simplified methods of dynamic tension have significant influences on the coefficients of the two DOFs ordinary differential equation. By comparing the coefficients of galloping equation obtained by the two simplified methods of dynamic tension, it can find that with the increasing of tension and span length, the influences of bending stiffness on in-plane and out-of-plane natural frequency becomes smaller and smaller. The results of multiscale method and average method both show that the two simplified methods of dynamic tension have certain influences on the frequency, phase and amplitude of galloping of iced transmission lines. The conclusions obtained by this paper would promote the perfection of theoretical modeling about iced transmission lines, and could also give some references to practical engineering.

SCATTERING CORRECTION FOR IMAGE RECONSTRUCTION IN FLASH RADIOGRAPHY

Cao, Liangzhi,Wang, Mengqi,Wu, Hongchun,Liu, Zhouyu,Cheng, Yuxiong,Zhang, Hongbo Korean Nuclear Society 2013 Nuclear Engineering and Technology Vol.45 No.4

Scattered photons cause blurring and distortions in flash radiography, reducing the accuracy of image reconstruction significantly. The effect of the scattered photons is taken into account and an iterative deduction of the scattered photons is proposed to amend the scattering effect for image restoration. In order to deduct the scattering contribution, the flux of scattered photons is estimated as the sum of two components. The single scattered component is calculated accurately together with the uncollided flux along the characteristic ray, while the multiple scattered component is evaluated using correction coefficients pre-obtained from Monte Carlo simulations.The arbitrary geometry pretreatment and ray tracing are carried out based on the customization of AutoCAD. With the above model, an Iterative Procedure for image restORation code, IPOR, is developed. Numerical results demonstrate that the IPOR code is much more accurate than the direct reconstruction solution without scattering correction and it has a very high computational efficiency.

The Chitin-Induced Chimeric LYK4-ER Gene Improves the Heat Tolerance of Arabidopsis at the Seedling Stage

Linxiao Chen,Wei Xia,Jinxing Song,Mengqi Wu,Zhizhen Xu,Xiangyang Hu,Wenqing Zhang 한국식물학회 2020 Journal of Plant Biology Vol.63 No.4

Due to global warming, high temperature has become the main abiotic stress affecting plant growth worldwide. LysM-containing receptor-like kinase 4 (LYK4) is the receptor for chitin, and ERECTA(ER) is a key factor in plant tolerance to high temperature. In this study, we constructed a chitin-induced chimeric LYK4-ER gene, in which the extracellular region and transmembrane domain of the LYK4 gene are fused with the intracellular region of the ER gene. Colony PCR, RT-PCR and western blot analyses of LYK4-ER transcription in plants, confirmed that the LYK4-ER gene was successfully constructed and transferred into Arabidopsis. The LYK4-ER gene localized to the cytomembrane and cytoplasm in vivo because of the binding properties of the transmembrane domain of the LYK4-ER gene to the cell membrane. The transgenic plants showed a higher germination rate and germination index as well as a shorter mean germination time than the wild-type plants, indicating that the LYK4-ER gene increases the heat tolerance of Arabidopsis. The lower H2O2 content and relative electrolytic leakage of the transgenic plants showed that the status of these plants under heat stress was improved. UPLC-MS/MS was used to analyze the phytohormones content, which suggested that the transgenic plants exhibited improved heat tolerance through jasmonic acid signal transduction pathways.