General method of reducing switching voltage stress without extra voltage‑loop control for related switching‑capacitor high‑gain converters

Fan Wang,Yubin Wang,Menghan Chu,Chuhao Gao 전력전자학회 2024 JOURNAL OF POWER ELECTRONICS Vol.24 No.4

High-gain converters have been used on many occasions as interfaces for multiple energy conversions. Among these converters, a family of switching-capacitor high-gain converters is widely used due to its low cost, small volume, low loss, spontaneous capacitor voltages balance, and spontaneous inductor currents average. However, one or more of the switches in these converters suffer from the issue of withstanding higher voltage stresses than the other switches, which may limit the applications of these converters at high voltages. To solve this issue, a general method for reducing the switching voltage stresses for this high-gain converter family is proposed. This method can improve many kinds of high-gain converters, which can reduce the switching voltage stresses. Based on this method, a two-phase low-stress high-gain converter is proposed. The voltage stresses of all the switches in the proposed converter do not exceed half of the output voltage of the converter. Then, based on the proposed converter feature, a control method is proposed that can make the proposed converter have the automatic capacitor voltage balancing characteristic without an extra voltage-loop control. Finally, the proposed method is verified by prototype experiments.

Response of coal rock apparent resistivity to hydraulic fracturing process

Song, Dazhao,Wang, Enyuan,Qiu, Liming,Jia, Haishan,Chen, Peng,Wei, Menghan Techno-Press 2018 Geomechanics & engineering Vol.14 No.6

In order to explore the comprehensive evaluation means of the extent of hydraulic fracturing region in coal seams, we analyzed the feasibility of detecting the response of coal rock direct current (DC) apparent resistivity to hydraulic-fracturing using Archie's theory, and conducted experimental researches on the response of DC resistivity in the hydraulic fracturing process using small-scale coal rock samples. The results show that porosity and water saturation are the two factors affecting the apparent resistivity of coal rock while hydraulic fracturing. Water has a dominant effect on the apparent resistivity of coal rock samples. The apparent resistivity in the area where water flows through is reduced more than 50%, which can be considered as a core affect region of hydraulic fracturing. Stress indirectly impacts the apparent resistivity by changing porosity. Before hydraulic fracturing, the greater axial load applied, the more serious the rupture in the samples, resulting in the greater apparent resistivity. Apparent resistivity testing is a potential regional method to evaluate the influence range of hydraulic fracturing in coal seams.

Type Drive Analysis of Urban Water Security Factors

Li Gong,Hong Wang,Chunling Jin,Lili Lu,Menghan Ma 한국정보처리학회 2020 Journal of information processing systems Vol.16 No.4

In order to effectively evaluate the urban water security, the study investigates a novel system to assess factors that impact urban water security and builds an urban water poverty evaluation index system. Based on the contribution rates of Resource, Access, Capacity, Use, and Environment, the study adopts the Water Poverty Index (WPI) model to evaluate the water poverty levels of 14 cities in Gansu during 2011–2018 and uses the least variance method to evaluate water poverty space drive types. The case study results show that the water poverty space drive types of 14 cites fall into four categories. The first category is the dual factor dominant type driven by environment and resources, which includes Lanzhou, Qingyang, Jiuquan, and Jiayuguan. The secondcategory is the threefactor dominant type driven by Access, Use, and Capability, which includes Longnan, Linxia, and Gannan. The third category is the fourfactor dominant type driven by Resource, Access, Capability, and Environment, which includes Jinchang, Pingliang, Wuwei, Baiyin, and Zhangye. The fourth category is the fivefactor dominant type, which includes Tianshui and Dingxi. The driven types impacting theurban water security factors reflected by the WPI and its model are clear and accurate. The divisions of the urban water security level supply a reliable theoretical and numerical basis for an urban water security early warning mechanism.

The Agents Coordination and Templates Aggregation in Distributed Modeling

Cai Zhiming,Yang Zhe,Wang Menghan,Yin Jiangling 보안공학연구지원센터 2014 International Journal of Hybrid Information Techno Vol.7 No.2

Seismic Coefficients and Earthquake Damage Predictions for a Space Truss with a Supporting Structure

Zailin Yang,Ziwen Wang,Yang Yong,Menghan Sun 한국강구조학회 2022 International Journal of Steel Structures Vol.22 No.4

Previous studies have shown that when the lower support structure is considered, the dynamic characteristics of grid structures change signifi cantly, and the stress distributions are also noticeably diff erent. Therefore, this paper discusses whether other simple and feasible structural seismic damage prediction methods could be proposed after accounting for the infl uence of the lower supporting structure. Considering diff erent site types and diff erent intensities, a time-history analysis was conducted using the mode decomposition response spectrum method for frequent 8- and 9-degree earthquake intensity. Then, the acceleration response spectra for diff erent sites experiencing 8- and 9-degree intensity of frequently occurring earthquakes specifi ed in the Code for Seismic Design of Buildings (GB50011-2010) were used to calculate and discuss the distribution law for the seismic internal forces of space truss structures. Based on the calculation conclusion, the design method and damage prediction method for a plate-like space truss structure under earthquake actions are discussed. Then, a new value of the seismic action coeffi cient was proposed in this paper, and the ground motion peaks for various types of earthquake damage for diff erent site types were obtained using the functional relationship.

Push-Out Tests on Interlocked Angles Connectors in Steel-Concrete-Steel Composite Structure

Junyi Chen,Yonghui Wang,Ximei Zhai,Xudong Zhi,Menghan Sun 한국강구조학회 2023 International Journal of Steel Structures Vol.23 No.2

This paper reported a new interlocked angle connector (IAC) for steel-concrete-steel sandwich structures. Shear performances of IACs embedded in normal concrete were studied via a push-out testing program, and the failure mode, shear resistance, and load–slip responses of IACs in normal concrete were obtained. The influences of height, width, thickness, orientation of steel angles, and interlocking bolts on shear behaviours of IACs were experimentally studied. The experimental results indicated that the ultimate shear resistances and slip capacities of IACs were improved via increasing the height, width and thickness of steel angles, while the orientation of steel angles exhibited limited influence on the ultimate shear resistances and failure modes of IACs. In addition, the analytical models were proposed for predicting ultimate shear resistances and load–slip behaviours of IACs. The experimental results were employed to validate the analytical models, and the proposed analytical models were found to provide more accurate predictions on ultimate shear resistances and load–slip behaviours of IACs as compared to the existing design codes.

Assessing Abdominal Aortic Aneurysm Progression by Using Perivascular Adipose Tissue Attenuation on Computed Tomography Angiography

Zhang Shuai,Gu Hui,Chang Na,Li Sha,Xu Tianqi,Liu Menghan,Wang Ximing 대한영상의학회 2023 Korean Journal of Radiology Vol.24 No.10

Objective: Recent studies have highlighted the active and potential role of perivascular adipose tissue (PVAT) in atherosclerosis and aneurysm progression, respectively. This study explored the link between PVAT attenuation and abdominal aortic aneurysm (AAA) progression using computed tomography angiography (CTA). Materials and Methods: This multicenter retrospective study analyzed patients with AAA who underwent CTA at baseline and follow-up between March 2015 and July 2022. The following parameters were obtained: maximum diameter and total volume of the AAA, presence or absence of intraluminal thrombus (ILT), maximum diameter and volume of the ILT, and PVAT attenuation of the aortic aneurysm at baseline CTA. PVAT attenuation was divided into high (> -73.4 Hounsfield units [HU]) and low (≤ -73.4 HU). Patients who had or did not have AAA progression during the follow-up, defined as an increase in the aneurysm volume > 10 mL from baseline, were identified. Kaplan–Meier and multivariable Cox regression analyses were used to investigate the association between PVAT attenuation and AAA progression. Results: Our study included 167 participants (148 males; median age: 70.0 years; interquartile range: 63.0–76.0 years), of which 145 (86.8%) were diagnosed with AAA accompanied by ILT. Over a median period of 11.3 months (range: 6.0–85.0 months), AAA progression was observed in 67 patients (40.1%). Multivariable Cox regression analysis indicated that high baseline PVAT attenuation (adjusted hazard ratio [aHR] = 2.23; 95% confidence interval [CI], 1.16–4.32; P = 0.017) was independently associated with AAA progression. This association was demonstrated within the patients of AAA with ILT subcohort, where a high baseline PVAT attenuation (aHR = 2.23; 95% CI, 1.08–4.60; P = 0.030) was consistently independently associated with AAA progression. Conclusion: Elevated PVAT attenuation is independently associated with AAA progression, including patients of AAA with ILT, suggesting the potential of PVAT attenuation as a predictive imaging marker for AAA expansion.

A Review of Advances in Triaxial Tests: Instruments, Test Techniques and Prospects

Jitao Bai,Yu Diao,Chenhang Jia,Chongyang Liu,Menghan Zhang,Chu Wang 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.8

Triaxial test is approved to be the most suitable method for studying the mechanical properties of rocks and soils in lab. Through conventional triaxial tests, parameters like the strength of rocks and soils can be obtained, thus providing guidance for the design and construction of geotechnical engineering. With the development of geotechnical engineering, more and more new problems that can hardly be solved by conventional triaxial tests have arisen, which can be classified into two categories: one is the mechanical properties of special soils (rocks), and the other is the mechanical properties of the soils (rocks) under special conditions like geologic hazards and multi-field coupling. The paper introduced several new types of triaxial instruments and test techniques developed in response to the problems, and prospects have been made for further study of triaxial tests, which may provide reference for the optimization of triaxial tests.