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Transient performance comparison of grid-forming converters with different FRT control strategies

《能源前沿（英文）》 2023年 第17卷 第2期   页码 239-250 doi: 10.1007/s11708-022-0856-2

摘要： Grid-forming converters (GFMs) are faced with the threat of transient inrush current and synchronization instability issues when subjected to grid faults. Instead of disconnecting from the grid unintentionally, GFMs are required to have fault ride through (FRT) capability to maintain safe and stable operation in grid-connected mode during grid fault periods. In recent studies, different FRT control strategies with distinguishing features and that are feasible for different operation conditions have been proposed for GFMs. To determine their application scope, an intuitive comparison of the transient performance of different FRT control strategies is presented in this paper. First, three typical FRT control strategies (virtual impedance, current limiters, and mode-switching control) are introduced and transient mathematical models are established. A detailed comparison analysis on transient inrush current and transient synchronization stability is then presented. The results will be useful for guiding the selection and design of FRT control strategies. Finally, simulation results based on PSCAD/EMTDC are considered to verify the correctness of the theoretical analysis.

关键词： grid-forming converters (GFMs)     fault ride through (FRT)     transient stability     transient inrush current     transient modeling    

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Topology optimization of transient problem with maximum dynamic response constraint using SOAR scheme

《机械工程前沿（英文）》 2021年 第16卷 第3期   页码 593-606 doi: 10.1007/s11465-021-0636-4

摘要： This paper proposes a novel method for the continuum topology optimization of transient vibration problem with maximum dynamic response constraint. An aggregated index in the form of an integral function is presented to cope with the maximum response constraint in the time domain. The density filter solid isotropic material with penalization method combined with threshold projection is developed. The sensitivities of the proposed index with respect to design variables are conducted. To reduce computational cost, the second-order Arnoldi reduction (SOAR) scheme is employed in transient analysis. Influences of aggregate parameter, duration of loading period, interval time, and number of basis vectors in the SOAR scheme on the final designs are discussed through typical examples while unambiguous configuration can be achieved. Through comparison with the corresponding static response from the final designs, the optimized results clearly demonstrate that the transient effects cannot be ignored in structural topology optimization.

关键词： topology optimization     solid isotropic material with penalization     transient response     aggregation function     second-order Arnoldi reduction    

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Development of new transient liquid phase system Au-Sn-Au for microsystem technology

Kirsten BOBZIN, Nazlim BAGCIVAN, Lidong ZHAO, Stefania FERRARA, Jan PERNE

《机械工程前沿（英文）》 2010年 第5卷 第4期   页码 370-375 doi: 10.1007/s11465-010-0107-9

摘要： In the last decade, microsystems evolved to decisive technology in many technical applications. With increasing requirements on the performance of microsystems, more and more dissimilar materials are used in the same assembly. Correspondingly, suitable joining methods are required to fulfil the requirements on good properties of joints. In this study, a new transient liquid phase (TLP) system Au-Sn-Au was developed for potential medical applications in hybrid microsystems. The high and low melting phases Au and Sn were deposited onto diverse substrates by magnetron-sputter-ion plating. The coated substrates were soldered in a microsoldering station under different conditions. The influence of soldering conditions on the microstructure and properties of the joints was investigated. Results show that the developed solder led to high-quality joints that can be used in microsystems for medical applications.

关键词： transient liquid phase     microtechnology     soldering     diffusion     physical vapor deposition (PVD)    

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Sensitivity analysis and numerical experiments on transient test of compact heat exchanger surfaces

REN Hesheng, LAI Lingjun, CUI Yongzheng

《能源前沿（英文）》 2008年 第2卷 第4期   页码 374-380 doi: 10.1007/s11708-008-0079-1

摘要： A single-blow transient testing technique considering the effect of longitudinal heat conduction is suggested for determining the average convection heat transfer coefficient of compact heat exchanger surface. By matching the measured outlet fluid temperature variation with similar theoretical curves, the dimensionless longitudinal conduction parameter , the time constant of the inlet fluid temperature , and the number of heat transfer units can be determined simultaneously using the Levenberg-Marquardt nonlinear parameter estimation method. Both sensitivity analysis and numerical experiments with simulated measurements containing random errors show that the method in the present investigation provides satisfactory accuracy of the estimated parameter , which characterizes the heat transfer performance of compact heat exchanger surfaces.

关键词： coefficient     dimensionless longitudinal     longitudinal     temperature     conduction    

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State identification of home appliance with transient features in residential buildings

《能源前沿（英文）》 2022年 第16卷 第1期   页码 130-143 doi: 10.1007/s11708-022-0822-z

摘要： Nonintrusive load monitoring (NILM) is crucial for extracting patterns of electricity consumption of household appliance that can guide users’ behavior in using electricity while their privacy is respected. This study proposes an online method based on the transient behavior of individual appliances as well as system steady-state characteristics to estimate the operating states of the appliances. It determines the number of states for each appliance using the density-based spatial clustering of applications with noise (DBSCAN) method and models the transition relationship among different states. The states of the working appliances are identified from aggregated power signals using the Kalman filtering method in the factorial hidden Markov model (FHMM). Thereafter, the identified states are confirmed by the verification of system states, which are the combination of the working states of individual appliances. The verification step involves comparing the total measured power consumption with the total estimated power consumption. The use of transient features can achieve fast state inference and it is suitable for online load disaggregation. The proposed method was tested on a high-resolution data set such as Labeled hIgh-Frequency daTaset for Electricity Disaggregation (LIFTED) and it outperformed other related methods in the literature.

关键词： nonintrusive load monitoring (NILM)     load disaggregation     online load disaggregation     Kalman filtering     factorial hidden Markov model (FHMM)     Labeled hIgh-Frequency daTaset for Electricity Disaggregation (LIFTED)    

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Collapse fragility assessment of steel roof framings with force limiting devices under transient wind

Linjia BAI, Yunfeng ZHANG

《结构与土木工程前沿（英文）》 2012年 第6卷 第3期   页码 199-209 doi: 10.1007/s11709-012-0168-4

摘要： Steel structural frame is a popular structural form to cover large-span roof space and under high winds. Either part of the roof enclosure or the entire roof structure can be lifted off a building, particularly for low sloped roofs subject to wind-induced suction force. Collapse of roof could cause severe economic loss and poses safety risk to residents in the building. The buckling of members in a steel roof frame structure, which may lead to progressive collapse, may be dynamic in nature. This paper presents a fragility analysis of the collapse of steel roof frame structures under combined static and transient wind loading. Uncertainties associated with wind load change rate and member imperfections are taken into account in this study. A numerical example based on a Steel Joist Institute (SJI) K series joist was used to demonstrate the use of force limiting devices for collapse risk mitigation. For the presented fragility assessment of steel roof collapse, a Monte Carlo method combined with response surface approach was adopted, which greatly reduces the computation time and makes the Monte Carlo simulation feasible for probabilistic collapse analysis of steel roof frame structures.

关键词： collapse     dynamic response     fragility analysis     Monte Carlo simulation     wind load    

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Photodynamic therapy combined with intravitreal injection of triamcinolone acetonide for choroidal neovascularization

YU Xiaobing, DAI Hong, LU Yingyi, LONG Li

《医学前沿（英文）》 2007年 第1卷 第4期   页码 405-409 doi: 10.1007/s11684-007-0079-2

摘要： The aim of this research was to evaluate the efficacy and safety of photodynamic therapy (PDT) combined with intravitreal injection of triamcinolone acetonide (TA) in the treatment of choroidal neovascularization (CNV) secondary to age-related macular degeneration (AMD) and pathological myopia. PDT combined with intravitreal injection of TA was performed on 16 eyes of 16 patients with CNV diagnosed by visual acuity, fluorescein fundus angiography (FFA) and optical coherent tomography (OCT), including 14 eyes secondary to age-related macular degeneration and two eyes secondary to pathological myopia. TA was injected intravitreally 72 h post PDT on 12 eyes and from three months to one year (mean nine months) post PDT on four eyes respectively. All the patients were followed up for 3 to 18 months (mean 18.6 months). Best-corrected visual acuity, intraocular pressure, retinal thickness and FFA were observed. The visual acuity was improved in seven eyes (43.8%) of all the 16 eyes and stable in nine eyes (56.2%), respectively. FFA revealed complete or partial closure of CNV in all patients. OCT showed that the macular edema disappeared or was alleviated. Transient intraocular pressure elevation occurred in one patient (6.25%) of all the 16 eyes and intraocular pressure returned to the normal after a transient treatment with anti-glaucoma medication. The mean number of PDTs during the first year was 1.1. PDT combined with intravitreal injection of TA for CNV is safe and effective. It can reduce the risk of visual loss and the treatment frequency.

关键词： intraocular pressure     fluorescein fundus     transient treatment     Transient intraocular     number    

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Predictor-corrector algorithm for solving quasi-separated-flow and transient distributed-parameter model

Ping ZHANG, Guoliang DING

《能源前沿（英文）》 2010年 第4卷 第4期   页码 535-541 doi: 10.1007/s11708-010-0113-y

摘要： The successive sub?stitution (SS) method is a suitable approach to solving the transient distributed-parameter model for heat exchangers. However, this method must be enhanced because its convergence heavily depends on the iterative initial pressure. When the iterative initial pressure is improperly assigned, the calculated flow rates become negative values, causing the state parameters to exhibit negative values as well. Therefore, a predictor-corrector algorithm (PCA) is proposed to improve the convergence of the SS method. A predictor is developed to determine an appropriate iterative initial pressure. Total fluid mass is adopted as the convergence criterion of pressure iteration instead of outlet flow rate as is done in the SS method. Convergence analysis and case study of the PCA and SS method are conducted, which show that the PCA has better convergence than the SS method under the same working conditions.

关键词： algorithm     convergence     heat exchanger     modeling     transient    

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A fast compound direct iterative algorithm for solving transient line contact elastohydrodynamic lubrication

null

《机械工程前沿（英文）》 2014年 第9卷 第2期   页码 156-167 doi: 10.1007/s11465-014-0297-7

摘要：

A fast compound direct iterative algorithm for solving transient line contact elastohydrodynamic lubrication (EHL) problems is presented. First, by introducing a special matrix splitting iteration method into the traditional compound direct iterative method, the full matrices for the linear systems of equations are transformed into sparse banded ones with any half-bandwidth; then, an extended Thomas method which can solve banded linear systems with any half-bandwidth is derived to accelerate the computing speed. Through the above two steps, the computational complexity of each iteration is reduced approximately from O(N3/3) to O(β2N), where N is the total number of nodes, and β is the half-bandwidth. Two kinds of numerical results of transient EHL line contact problems under sinusoidal excitation or pure normal approach process are obtained. The results demonstrate that the new algorithm increases computing speed several times more than the traditional compound direct iterative method with the same numerical precision. Also the results show that the new algorithm can get the best computing speed and robustness when the ratio, half-bandwidth to total number of nodes, is about 7.5%–10.0% in moderate load cases.

关键词： elastohydrodynamic lubrication     transient     line contact     matrix splitting iteration method     the Thomas method    

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Charge-carrier photogeneration and extraction dynamics of polymer solar cells probed by a transient photocurrent

Boa Jin, Hyunmin Park, Yang Liu, Leijing Liu, Jongdeok An, Wenjing Tian, Chan Im

《化学科学与工程前沿（英文）》 2021年 第15卷 第1期   页码 164-179 doi: 10.1007/s11705-020-1976-z

摘要： To understand the complex behaviors of photogenerated charge carriers within polymer-based bulk-heterojunction-type solar cells, the charge-carrier photogeneration and extraction dynamics are simultaneously estimated using a transient photocurrent technique under various external-bias voltages, and a wide range of excitation intensities are analyzed. For this purpose, conventional devices with 80 nm thick active layers consisting of a blend of representative P3HT and PTB7 electron-donating polymers and proper electron-accepting fullerene derivatives were used. After the correction for the saturation behavior at a high excitation-intensity range nearby the regime of the space charge-limited current, the incident-photon-density-dependent maximum photocurrent densities at the initial peaks are discussed as the proportional measures of the charge-carrier-photogeneration facility. By comparing the total number of the extracted charge carriers to the total number of the incident photons and the number of the initially photogenerated charge carriers, the external quantum efficiencies as well as the extraction quantum efficiencies of the charge-carrier collection during a laser-pulse-induced transient photocurrent process were obtained. Subsequently, the charge-carrier concentration-dependent mobility values were obtained, and they are discussed in consideration of the additional influences of the charge-carrier losses from the device during the charge-carrier extraction that also affects the photocurrent-trace shape.

关键词： charge-carrier photogeneration     transient photocurrent     polymer solar cells     charge-carrier extraction     space charge-limited current    

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An isogeometric numerical study of partially and fully implicit schemes for transient adjoint shape sensitivity

Zhen-Pei WANG, Zhifeng XIE, Leong Hien POH

《机械工程前沿（英文）》 2020年 第15卷 第2期   页码 279-293 doi: 10.1007/s11465-019-0575-5

摘要： In structural design optimization involving transient responses, time integration scheme plays a crucial role in sensitivity analysis because it affects the accuracy and stability of transient analysis. In this work, the influence of time integration scheme is studied numerically for the adjoint shape sensitivity analysis of two benchmark transient heat conduction problems within the framework of isogeometric analysis. It is found that (i) the explicit approach ( = 0) and semi-implicit approach with <0.5 impose a strict stability condition of the transient analysis; (ii) the implicit approach ( =1) and semi-implicit approach with > 0.5 are generally preferred for their unconditional stability; and (iii) Crank–Nicolson type approach ( =0.5) may induce a large error for large time-step sizes due to the oscillatory solutions. The numerical results also show that the time-step size does not have to be chosen to satisfy the critical conditions for all of the eigen-frequencies. It is recommended to use for unconditional stability, such that the oscillation condition is much less critical than the Crank–Nicolson scheme, and the accuracy is higher than a fully implicit approach.

关键词： isogeometric shape optimization     design-dependent boundary condition     transient heat conduction     implicit time integration     adjoint method    

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Overexpression of netrin-1 improves neurological outcomes in mice following transient middle cerebral

null

《医学前沿（英文）》 2011年 第5卷 第1期   页码 86-93 doi: 10.1007/s11684-011-0118-x

摘要：

Netrin-1 (NT-1) is one of the axon-guiding molecules that are critical for neuronal development. Because of its structural homology to the endothelial mitogens, NT-1 may have similar effects on vascular network formation. NT-1 was shown to be able to stimulate the proliferation and migration of human cerebral endothelial cells in vitro and also promote focal neovascularization in adult brain in vivo. In the present study, we reported the delivery of NT-1 using an adeno-associated virus (AAV) vector (AAV-NT-1) into mouse brain followed by transient middle cerebral artery occlusion (tMCAO). We found that AAV vectors did not elicit a detectable inflammatory response, cell loss or neuronal damage after brain transduction. The level of NT-1 was increased in the AAV-NT-1-transduced tMCAO mice compared with the control mice. Furthermore, the neurobehavioral outcomes were significantly improved in AAV-NT-1-transduced mice compared with the control animals (P<0.05) 7 days after tMCAO. Our data suggests that NT-1 plays a neuronal function recovery role in ischemic brain and that NT-1 gene transfer might present a valuable approach to treat brain ischemic disorders.

关键词： adeno-associated virus     angiogenesis     gene transfer     ischemia     middle cerebral artery occlusion     netrin-1    

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埋地热含蜡原油管道的非稳态传热问题

崔秀国,张劲军

《中国工程科学》 2003年 第5卷 第7期   页码 77-83

摘要：

我国生产的原油大多为含蜡原油，加热输送是含蜡原油的主要输送方式。埋地热含蜡原油管道的运行中涉及若干复杂的非稳态传热问题。从管内原油传热（内部传热）和管道与外部环境的传热（外部传热）两方面，分析和总结了含蜡原油管道非稳态传热问题的研究现状，介绍了管道在土壤中传热的影响因素，比较了其各种解析和数值解法，阐述了管道停输状态下管内含蜡原油相变传热的规律及研究方法，讨论了非稳定流动状态下管内油流的水力—热力耦合问题及求解方法，指出了埋地热含蜡原油管道的非稳态传热方面需进一步研究的问题。

关键词： 石蜡基原油     管道输送     非稳态传热    

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Transient imaging with a time-of-flight cameraand its applications

Jing-yu LIN, Ri-hui WU, Hong-man WANG, Ye-bin LIU

《信息与电子工程前沿（英文）》 2017年 第18卷 第9期   页码 1268-1276 doi: .org/10.1631/FITEE.1700556

摘要： Transient imaging is a technique in photography that recordsthe process of light propagation before it reaches a stationary statesuch that events at the light speed level can be observed. In thisreview we introduce three main models for transient imaging with atime-of-flight (ToF) camera: correlation model, frequency-domain model,and compressive sensing model. Transient imaging applications usuallyinvolve resolving the problem of light transport and separating thelight rays arriving along different paths. We discuss two of the applications:imaging objects inside scattering media and recovering both the shapeand texture of an object around a corner.

关键词： Transient imaging     Time-of-flight(ToF) camera     Scattering media     Around corners    

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使用成对机器人分散化搜索多个未知瞬时射电源 Article

Chang-Young Kim, 宋德臻, Jingang Yi, 吴新宇

《工程（英文）》 2015年 第1卷 第1期   页码 58-65 doi: 10.15302/J-ENG-2015010

摘要：

我们开发了一种分散化算法，来协调一组移动机器人搜索未知瞬时射电源。除了移动能力和通信及传感范围有限，机器人团队还必须应对信号源匿名性、短暂的传输时间和可变的发射功率带来的挑战。我们提出了一种两步式方法：首先，基于检查站的同步功能，对机器人用于追踪信号源位置的可信度函数进行了分散化；其次，提出了一种用于协调机器人的分散化规划策略，以确保存在检查站。我们分析了该算法的内存使用情况、通信数据量和搜索时间。实现了该算法，并将其与其他两种探索式算法进行了比较。实验结果显示，在三种算法中，分散化算法用最少的内存换来了最快的搜索时间。

关键词： 无线定位     联网机器人     瞬时目标    

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标题 作者 时间 类型 操作

Transient performance comparison of grid-forming converters with different FRT control strategies

期刊论文

Topology optimization of transient problem with maximum dynamic response constraint using SOAR scheme

期刊论文

Development of new transient liquid phase system Au-Sn-Au for microsystem technology

Kirsten BOBZIN, Nazlim BAGCIVAN, Lidong ZHAO, Stefania FERRARA, Jan PERNE

期刊论文

Sensitivity analysis and numerical experiments on transient test of compact heat exchanger surfaces

REN Hesheng, LAI Lingjun, CUI Yongzheng

期刊论文

State identification of home appliance with transient features in residential buildings

期刊论文

Collapse fragility assessment of steel roof framings with force limiting devices under transient wind

Linjia BAI, Yunfeng ZHANG

期刊论文

Photodynamic therapy combined with intravitreal injection of triamcinolone acetonide for choroidal neovascularization

YU Xiaobing, DAI Hong, LU Yingyi, LONG Li

期刊论文

Predictor-corrector algorithm for solving quasi-separated-flow and transient distributed-parameter model

Ping ZHANG, Guoliang DING

期刊论文

A fast compound direct iterative algorithm for solving transient line contact elastohydrodynamic lubrication

null

期刊论文

Charge-carrier photogeneration and extraction dynamics of polymer solar cells probed by a transient photocurrent

Boa Jin, Hyunmin Park, Yang Liu, Leijing Liu, Jongdeok An, Wenjing Tian, Chan Im

期刊论文

An isogeometric numerical study of partially and fully implicit schemes for transient adjoint shape sensitivity

Zhen-Pei WANG, Zhifeng XIE, Leong Hien POH

期刊论文

Overexpression of netrin-1 improves neurological outcomes in mice following transient middle cerebral

null

期刊论文

埋地热含蜡原油管道的非稳态传热问题

崔秀国,张劲军

期刊论文

Transient imaging with a time-of-flight cameraand its applications

Jing-yu LIN, Ri-hui WU, Hong-man WANG, Ye-bin LIU

期刊论文

使用成对机器人分散化搜索多个未知瞬时射电源

Chang-Young Kim, 宋德臻, Jingang Yi, 吴新宇

期刊论文