Compressive behavior of concrete under high strain rates after freeze-thaw cycles

Xudong Chen,Chen Chen,Zhiheng Liu,Jun Lu,Xiangqian Fan 사단법인 한국계산역학회 2018 Computers and Concrete, An International Journal Vol.21 No.2

The dynamic compressive behavior of concrete after freezing and thawing tests are investigated by using the split Hopkinson pressure bar (SHPB) technique. The stress-strain curves of concrete under dynamic loading are measured and analyzed. The setting numbers of freeze-thaw cycles are 0, 25, 50, and 75 cycles. Test results show that the dynamic strength decreases and peak strain increases with the increasing of freeze-thaw cycles. Based on theWeibull distribution model, statistical damage constitutive model for dynamic stress-strain response of concrete after freeze-thaw cycles was proposed. At last, the fragmentation test of concrete subjected to dynamic loading and freeze-thaw cycles is carried out using sieving statistics. The distributions of the fragment sizes are analyzed based on fractal theory. The fractal dimensions of concrete increase with the increasing of both freeze-thaw cycle and strain rate. The relations among the fractal dimension, strain rates and freeze-thawing cycles are developed.

Wind turbine airfoils optimization design by generalized regression neural network under small sample

Xudong Wang,Hao Ju,Jiahong Lu 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.1

Neural network models can quickly and accurately predict the aerodynamic performance of wind turbine airfoils based on existing data, but the construction of a large number of learning samples requires a high upfront time cost. To address this problem, a generalized regression neural network (GRNN) model of wind turbine airfoils based on a small sample set is established, and an optimal design method for airfoil aerodynamic performance under multiple constraints is proposed. This method is used to improve the prediction accuracy of the model in the optimization process and to solve the problem of insufficient learning caused by poor training data. Based on the established optimal design model, we applied the particle swarm optimization (PSO) algorithm to complete the optimal design of NACA44XX series airfoils and obtained the optimized airfoils with maximum relative thicknesses of 15 %, 18 %, 21 %, and 24 %, respectively. The aerodynamic characteristics of the new airfoils were analyzed in comparison with the baseline airfoils. The results show that the aerodynamic properties of the new airfoils are significantly improved, with the maximum lift coefficient and maximum lift-to-drag ratio increasing by up to 16.93 % and 10.41 %. Moreover, the optimization efficiency of the method is much higher than that of the traditional one. Thus, it was verified that the method is feasible and effective.

Dynamics of Soil Amino Sugars during Maize Growing Season under Different Management

Lu Huijie,He Hongbo,Zhang Xudong 한국토양비료학회 2014 한국토양비료학회 학술발표회 초록집 Vol.2014 No.6

Experimental Study on Low Cyclic Loading Tests of Steel Plate Shear Walls with Multilayer Slits

JinYu Lu,Shunji Yu,XuDong Qiao,Na Li 한국강구조학회 2018 International Journal of Steel Structures Vol.18 No.4

A new type of earthquake-resisting element that consists of a steel plate shear wall with slits is introduced. The infi ll steel plate is divided into a series of vertical fl exural links with vertical links. The steel plate shear walls absorb energy by means of in-plane bending deformation of the fl exural links and the energy dissipation capacity of the plastic hinges formed at both ends of the fl exural links when under lateral loads. In this paper, fi nite element analysis and experimental studies at low cyclic loadings were conducted on specimens with steel plate shear walls with multilayer slits. The eff ects caused by varied slit pattern in terms of slit design parameters on lateral stiff ness, ultimate bearing capacity and hysteretic behavior of the shear walls were analyzed. Results showed that the failure mode of steel plate shear walls with a single-layer slit was more likely to be out-of-plane buckling of the fl exural links. As a result, the lateral stiff ness and the ultimate bearing capacity were relatively lower when the precondition of the total height of the vertical slits remained the same. Diff erently, the failure mode of steel plate shear walls with multilayer slits was prone to global buckling of the infi ll steel plates; more obvious tensile fi elds provided evidence to the fact of higher lateral stiff ness and excellent ultimate bearing capacity. It was also concluded that multilayer specimens exhibited better energy dissipation capacity compared with single-layer plate shear walls.

Experimental Study and Numerical Simulation on Steel Plate Shear Walls with Non-uniform Spacing Slits

JinYu Lu,XuDong Qiao,Jie Liao,Yi Tang 한국강구조학회 2016 International Journal of Steel Structures Vol.16 No.4

Numerous experimental and finite element studies have shown that steel plate shear walls with slits have several beneficial characteristics, such as good ductility and excellent energy dissipation capacity, which make them a feasible lateral load resisting and energy dissipation system for high-rise buildings in high seismic regions. The width of the flexural links between slits has a significant effect on the mechanical behavior and hysteretic performance of steel plate shear walls with slits. This paper presented two kinds of steel plate shear walls with non-uniform spacing slits (SPWNS) and investigated their performance under low-cycle loading based on tests and finite element software. The study mainly focused on the ultimate bearing capacity, the lateral stiffness, the energy dissipation capacity and the ductility of SPWNS. The results from numerical analysis and test study were compared with each other. The ultimate bearing capacity and the lateral stiffness of traditional steel plate shear walls with uniform spacing slits (SPWUS) were similar to that of SPWNS. In contrast, the ductility and the energy dissipation capacity of SPWUS were much higher.

The characteristics investigation under the unsteady cavitation condition in a centrifugal pump

Jiaxing Lu,Shouqi Yuan,Parameswaran Siva,Jian-Ping Yuan,Xudong Ren,Banglun Zhou 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.3

Numerical simulation and experimental method are combined to investigate the pump inlet and outlet pressure fluctuations, the vibration characteristics and the internal flow instabilities under the unsteady cavitation condition in a centrifugal pump. It is found that the unsteady cavitation starts to generate as the NPSHa is lower than 5.93 m. Apparent asymmetric and uneven cavity volume distribution on each blade and in the impeller can be observed as the NPSHa decreases from 4.39 m to 1.44 m, which includes the cavitation develops from cavitation surge, rotating cavitation to asymmetric cavitation. The flow vortexes in each blade channel are produced in the cavity trailing edges by the shedding and collapse of cavitation, which interfere with each other and aggravate the flow instabilities. The dominant frequencies of the pump inlet and outlet pressure fluctuations are the shaft frequency and blade passing frequency under the unsteady cavitation conditions, respectively. Broadband pulses are obtained from both the pump inlet and outlet pressure pulsations, which results from the random shedding and collapse of unsteady cavitation bubbles. Obvious corresponding relationship between the root mean squares of the vibration measured in different positions and the suction performance curve is found under both the non-cavitation and unsteady cavitation conditions.

Analysis of notch depth and loading rate effects on crack growth in concrete by FE and DIC

Xiangyi Zhu,Xudong Chen,Jun Lu,Xiangqian Fan 사단법인 한국계산역학회 2019 Computers and Concrete, An International Journal Vol.24 No.6

In this paper, the fracture characteristics of concrete specimens with different notch depths under three-point flexural loads are studied by finite element and fracture mechanics methods. Firstly, the concrete beams (the size is 700×100×150 mm) with different notch depths (a=30 mm, 45 mm, 60 mm and 75 mm respectively) are tested to study the influence of notch depths on the mechanical properties of concrete. Subsequently, the concrete beams with notch depth of 60 mm are loaded at different loading rates to study the influence of loading rates on the fracture characteristics, and digital image correlation (DIC) is used to monitor the strain nephogram at different loading rates. The test results show that the flexural characteristics of the beams are influenced by notch depths, and the bearing capacity and ductility of the concrete decrease with the increase of notch depths. Moreover, the peak load of concrete beam gradually increases with the increase of loading rate. Then, the fracture energy of the beams is accurately calculated by tail-modeling method and the bilinear softening constitutive model of fracture behavior is determined by using the modified fracture energy. Finally, the bilinear softening constitutive function is embedded into the finite element (FE) model for numerical simulation. Through the comparison of the test results and finite element analysis, the bilinear softening model determined by the tail-modeling method can be used to predict the fracture behavior of concrete beams under different notch depths and loading rates.

Mechanical properties of pervious concrete with recycled aggregate

Xiangyi Zhu,Xudong Chen,Nan Shen,Huaxuan Tian,Xiangqian Fan,Jun Lu 사단법인 한국계산역학회 2018 Computers and Concrete, An International Journal Vol.21 No.6

In order to research the influence of different recycled aggregate contents on the mechanical properties of pervious concrete, the experimental study and numerical simulation analysis of the mechanical properties of pervious concrete with five kinds of recycled aggregates contents (0%, 25%, 50%, 75% and 100%) are carried out in this paper. The experimental test were first performed on concrete specimens of different sizes in order to determine the influence of recycled aggregate on the compressive strength and splitting tensile strength, direct tension strength and bending strength. Then, the development of the internal cracks of pervious concrete under different working conditions is studied more intuitively by PFC3D. The experimental results show that the concrete compressive strength, tensile strength and bending strength decrease with the increase of the recycled aggregate contents. This trend of reduction is not only related to the brittleness of recycled aggregate concrete, but also to the weak viscosity of recycled aggregate and cement paste. It is found that the fracture surface of pervious concrete with recycled aggregate is smoother than that of natural aggregate pervious concrete by PFC3D, which means that the bridging effect is weakened in the stress transfer between the left and right sides of the crack. Through the analysis of the development of the internal cracks, the recycled aggregate concrete generated more cracks than the natural aggregate concrete, which means that the recycled aggregate concrete is easier to form a coalescence fracture surface and eventually break.

Failure Mechanism of Single-layer Saddle-curve Reticulated Shells with Material Damage Accumulation Considered under Severe Earthquake

Zhiwei Yu,Xudong Zhi,Feng Fan,Chen Lu 한국강구조학회 2012 International Journal of Steel Structures Vol.12 No.1

This paper presents the study on failure mechanism of single-layer saddle-curve reticulated shells subjected to severe earthquake. Failure mode of single-layer saddle-curve reticulated shells is illustrated with the consideration of material damage accumulation. The effects of different parameters on failure characteristics of single-layer saddle-curve reticulated shells are discussed. The influence of substructure upon failure behaviors of single-layer saddle-curve reticulated shells is particularly investigated. It is observed that dynamic strength failure is the failure mode of single-layer saddle-curve reticulated shells. The substructure has great influence on failure characteristics of single-layer saddle-curve reticulated shells subjected to the severe earthquake.

TRPV1 regulates ApoE4-disrupted intracellular lipid homeostasis and decreases synaptic phagocytosis by microglia

Wang Chenfei,Lu Jia,Sha Xudong,Qiu Yu,Chen Hongzhuan,Yu Zhihua 생화학분자생물학회 2023 Experimental and molecular medicine Vol.55 No.-

Although the ε4 allele of the apolipoprotein E (ApoE4) gene has been established as a genetic risk factor for many neurodegenerative diseases, including Alzheimer’s disease, the mechanism of action remains poorly understood. Transient receptor potential vanilloid 1 (TRPV1) was reported to regulate autophagy to protect against foam cell formation in atherosclerosis. Here, we show that ApoE4 leads to lipid metabolism dysregulation in microglia, resulting in enhanced MHC-II-dependent antigen presentation and T-cell activation. Lipid accumulation and inflammatory reactions were accelerated in microglia isolated from TRPV1flox/flox; Cx3cr1cre-ApoE4 mice. We showed that metabolic boosting by treatment with the TRPV1 agonist capsaicin rescued lipid metabolic impairments in ApoE4 neurons and defects in autophagy caused by disruption of the AKT-mTOR pathway. TRPV1 activation with capsaicin reversed ApoE4-induced microglial immune dysfunction and neuronal autophagy impairment. Capsaicin rescued memory impairment, tau pathology, and neuronal autophagy in ApoE4 mice. Activation of TRPV1 decreased microglial phagocytosis of synapses in ApoE4 mice. TRPV1 gene deficiency exacerbated recognition memory impairment and tau pathology in ApoE4 mice. Our study suggests that TRPV1 regulation of lipid metabolism could be a therapeutic approach to alleviate the consequences of the ApoE4 allele.