Validation study on numerical simulation of RC response to close-in blast with a fully coupled model

Yong Lu,Shunfeng Gong,Zhenguo Tu,Weiliang Jin 국제구조공학회 2009 Structural Engineering and Mechanics, An Int'l Jou Vol.32 No.2

The characteristic response of a structure to blast load may be divided into two distinctive phases, namely the direct blast response during which the shock wave effect and localized damage take place, and the post-blast phase whereby progressive collapse may occur. A reliable post-blast analysis depends on a sound understanding of the direct blast effect. Because of the complex loading environment and the stress wave effects, the analysis on the direct effect often necessitates a high fidelity numerical model with coupled fluid (air) and solid subdomains. In such a modelling framework, an appropriate representation of the blast load and the high nonlinearity of the material response is a key to a reliable outcome. This paper presents a series of calibration study on these two important modelling considerations in a coupled Eulerian-Lagrangian framework using a hydrocode. The calibration of the simulated blast load is carried out for both free air and internal explosions. The simulation of the extreme dynamic response of concrete components is achieved using an advanced concrete damage model in conjunction with an element erosion scheme. Validation simulations are conducted for two representative scenarios; one involves a concrete slab under internal blast, and the other with a RC column under air blast, with a particular focus on the simulation sensitivity to the mesh size and the erosion criterion.

Modelling of concrete structures subjected to shock and blast loading: An overview and some recent studies

Yong Lu 국제구조공학회 2009 Structural Engineering and Mechanics, An Int'l Jou Vol.32 No.2

The response of concrete structures subjected to shock and blast load involves a rapid transient phase, during which material breach may take place. Such an effect could play a crucial role in determining the residual state of the structure and the possible dispersion of the fragments. Modelling of the transient phase response poses various challenges due to the complexities arising from the dynamic behaviour of the materials and the numerical difficulties associated with the evolving material discontinuity and large deformations. Typical modelling approaches include the traditional finite element method in conjunction with an element removal scheme, various meshfree methods such as the SPH, and the mesoscale model. This paper is intended to provide an overview of several alternative approaches and discuss their respective applicability. Representative concrete material models for high pressure and high rate applications are also commented. Several recent application studies are introduced to illustrate the pros and cons of different modelling options.

Numerical simulation of concrete confined by transverse reinforcement

Yong Lu,Zhenhuan Song 사단법인 한국계산역학회 2011 Computers and Concrete, An International Journal Vol.8 No.1

The behaviour of concrete confined by transverse reinforcement is a classical topic. Numerous studies have been conducted to establish the stress-strain relationships for concrete under various confining reinforcement arrangements. Many empirical and semi-empirical formulas exist. Simplified analytical models have also been proposed to evaluate the increase in the strength and ductility of confined concrete. However, relatively few studies have been conducted to utilise advanced computational models for a realistic simulation of the behaviour of concrete confined by transverse reinforcement. As a matter of fact, high fidelity simulations using the latest numerical solvers in conjunction with advanced material constitutive models can be a powerful means to investigating the mechanisms underlying the confining effects of different reinforcement schemes. This paper presents a study on the use of high fidelity finite element models for the investigation of the behaviour of concrete confined by stirrups, as well as the interpretation of the numerical results. The development of the models is described in detail, and the essential modelling considerations are discussed. The models are then validated by simulating representative experimental studies on short columns with different confining reinforcement schemes. The development and distribution of the confining stress and the subsequent increase in the axial strength are examined. The models are shown to be capable of reproducing the behaviour of the confined concrete realistically, paving a way for systematic parametric studies and investigation into complicated confinement, load combination, and dynamic loading situations.

Mesoscale modelling of concrete for static and dynamic response analysis Part 2: numerical investigations

Yong Lu,Zhenguo Tu 국제구조공학회 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.37 No.2

As a brittle and heterogeneous material, concrete behaves differently under different stress conditions and its bulk strength is loading rate dependent. To a large extent, the varying behavioural properties of concrete can be explained by the mechanical failure processes at a mesoscopic level. The development of a computational mesoscale model in a general finite element environment, as presented in the preceding companion paper (Part 1), makes it possible to investigate into the underlying mechanisms governing the bulk-scale behaviour of concrete under a variety of loading conditions and to characterise the variation in quantitative terms. In this paper, we first present a series of parametric studies on the behaviour of concrete material under quasi-static compression and tension conditions. The loading-face friction effect, the possible influences of the non-homogeneity within the mortar and ITZ phases, and the effect of randomness of coarse aggregates are examined. The mesoscale model is then applied to analyze the dynamic behaviour of concrete under high rate loading conditions. The potential contribution of the mesoscopic heterogeneity towards the generally recognized rate enhancement of the material compressive strength is discussed.

Weighting factor design based on SVR–MOPSO for finite set MPC operated power electronic converters

Yonglu Liu,Zhengmao Yang,Xubin Liu,Hanbing Dan,Wenjing Xiong,Tao Ling,Mei Su 전력전자학회 2022 JOURNAL OF POWER ELECTRONICS Vol.22 No.7

Selecting weighting factors is a challenge for the finite set model predictive control (FS-MPC). Based on the support vector regression (SVR) algorithm and the multi-objective particle swarm optimization (MOPSO) algorithm, this paper proposes a new weighting factor design principle. SVR is used to establish the functional relationship between the input weighting factors and the output performance indexes (such as the average switching frequency (fsw) and the total harmonic distortion of the output voltage). Even in the case of small samples, this can provide accurate performance index estimates for any combination of weighting factors. The established SVR function is taken as the fitness function. Then, MOPSO is used to search for Pareto optimal weighting factor combinations. The proposed method can converge in a few steps and does not require tedious calculations. Moreover, it is applicable to optimization problem with two or more weighting factors for arbitrary topology models. It also provides a range of optimal weighting factor solution sets. Finally, the proposed methodology is verified on a practical weighting factor design problem in a FS-MPC regulated voltage source inverter. Experimental results confirm the correctness of the theoretical analysis.

Independent power decoupling method using minimum switch devices for single-phase current source converters

Liu, Yonglu,Tang, Shunxin,Wang, Hui,Ning, Guangfu,Xiong, Wengjing The Korean Institute of Power Electronics 2021 JOURNAL OF POWER ELECTRONICS Vol.21 No.9

Independent power decoupling (IPD) topologies are used to mitigate the twice-line-frequency ripple power in single-phase systems. Then, bulky passive capacitors or inductors can be removed. This paper proposes an improved IPD topology for single-phase current source converters (SCSCs) to remove the bulky DC rail inductor. It only adds one active switch and one diode. When compared with existing IPD circuits, the required switch devices are minimum and control is flexible. In addition, due to the fact that two identical capacitors are used to buffer the ripple power, the buffer capacitor voltage stress and DC current ripple are significantly reduced. This paper introduces the operation mode and switching states of the proposed topology. Then, the modelling and control strategy are introduced. Moreover, the designs of the passive components are presented. Finally, the effectiveness of the proposed topology is verified by constructing a low-power experimental prototype.

Quasi-classical Trajectory Calculation of the Chemical Reactions Ba+C6H5Br, m-C6H4CH3Br

Wenwen Xia,Yonglu Liu,Haiyang Zhong,Li Yao 대한화학회 2012 Bulletin of the Korean Chemical Society Vol.33 No.2

In this paper, the reactive dynamics properties of the reactions Ba + C6H5Br and Ba + m-C6H4CH3Br were studied by means of the quasi-classical trajectory method based on the London-Eyring-Polanyi-Sato potential energy surfaces. The vibrational distributions, reaction cross sections, rotational alignments of the products BaBr all were obtained. The peak values of the vibrational distributions are located at ν = 0 for the reactions Ba + C6H5Br and Ba + m-C6H4CH3Br when the collision energies are 1.09 and 1.10 eV, respectively. The reaction cross sections increase with the increasing collision energy, which changes from 0.6 to 1.5 eV. The product rotational alignments deviate from −0.5 and firstly increase and then decrease while the collision energy is increasing, just like that of Heavy+Light-Light system.

Single-Phase Current-Source Bidirectional Converter for V2G Applications

Hua Han,Yonglu Liu,Yao Sun,Hui Wang,Mei Su 전력전자학회 2014 JOURNAL OF POWER ELECTRONICS Vol.14 No.3

In this paper, a single-phase current-source bidirectional converter topology for V2G applications is proposed. The proposed converter consists of a single-phase current-source rectifier (SCSR) and an auxiliary switching network (ASN). It offers bidirectional power flow between the battery and the grid in the buck or boost mode and expands the output voltage range, so that it can be compatible with different voltage levels. The topology structure and operating principles of the proposed converter are analyzed in detail. An indirect control algorithm is used to realize the charging and discharging of the battery. Finally, the semiconductor losses and system efficiency are analyzed. Simulation and experimental results demonstrate the validity and effectiveness of the proposed topology.

Patterning droplets with durotaxis

Style, Robert W.,Che, Yonglu,Park, Su Ji,Weon, Byung Mook,Je, Jung Ho,Hyland, Callen,German, Guy K.,Power, Michael P.,Wilen, Larry A.,Wettlaufer, John S.,Dufresne, Eric R. National Academy of Sciences 2013 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.110 No.31

<P>Numerous cell types have shown a remarkable ability to detect and move along gradients in stiffness of an underlying substrate—a process known as durotaxis. The mechanisms underlying durotaxis are still unresolved, but generally believed to involve active sensing and locomotion. Here, we show that simple liquid droplets also undergo durotaxis. By modulating substrate stiffness, we obtain fine control of droplet position on soft, flat substrates. Unlike other control mechanisms, droplet durotaxis works without imposing chemical, thermal, electrical, or topographical gradients. We show that droplet durotaxis can be used to create large-scale droplet patterns and is potentially useful for many applications, such as microfluidics, thermal control, and microfabrication.</P>

Quasi-classical Trajectory Calculation of the Chemical Reactions Ba+C₆H₅Br, m-C₆H₄CH₃Br

Xia, Wenwen,Liu, Yonglu,Zhong, Haiyang,Yao, Li Korean Chemical Society 2012 Bulletin of the Korean Chemical Society Vol.33 No.2

In this paper, the reactive dynamics properties of the reactions Ba + $C_6H_5Br$ and Ba + m-$C_6H_4CH_3Br$ were studied by means of the quasi-classical trajectory method based on the London-Eyring-Polanyi-Sato potential energy surfaces. The vibrational distributions, reaction cross sections, rotational alignments of the products BaBr all were obtained. The peak values of the vibrational distributions are located at $\nu$ = 0 for the reactions Ba + $C_6H_5Br$ and Ba + m-$C_6H_4CH_3Br$ when the collision energies are 1.09 and 1.10 eV, respectively. The reaction cross sections increase with the increasing collision energy, which changes from 0.6 to 1.5 eV. The product rotational alignments deviate from -0.5 and firstly increase and then decrease while the collision energy is increasing, just like that of Heavy+Light-Light system.