Study on the mechanism of the vortex-induced vibration of a bluff double-side box section

Yu Li,Chen Li,Feng Wang,Jia-Wu Li 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.41 No.2

At present, researchers mainly focused on the vortex-induced vibration (VIV) of the double-side I-shaped girder, while there are only a few literatures focused on the VIV of the bluff double-side box girder, especially the study on the synchronous pressure- and vibration- measured test for the bluff double-side box girder has not been reported. Therefore, in this study, the vibration-measured test, the Numerical Wind Tunnel Simulation, and the synchronous pressure- and vibration- measured test were conducted to study the VIV mechanism of the bluff double-side box girder. Firstly, a section model of the bluff double-side box girder was designed, and the vibration-measured test was conducted to study the influence of mass ratio, damping ratio, and aerodynamic countermeasures on the VIV of the bluff double-side box girder. Secondly, the Numerical Wind Tunnel Simulation was conducted to simulate the vorticity evolution of the bluff double-side box girder, which was used to help analyze the results of the synchronous pressure- and vibration- measured test. Finally, the synchronous pressure- and vibration- measured test was conducted to investigate the wind pressure distribution and aerodynamic forces on the surface of the double-side box girder, which was then used to study the VIV mechanism of the bluff double-side box girder by combining the simulated vorticity evolutions. So, when the VIV of the double-side box girder occurs, it is found that: there is a significant difference in the mean and fluctuating wind pressure between the upper and lower surfaces; moreover, at the leading and trailing edges, the aerodynamic forces contribute greatly to the VIV, the correlation between the aerodynamic forces and the vortex-induced aerodynamic forces is positive, and with the increase of this coefficient, it will lead to the more significant VIV.

Study on the Effects of Pedestrians on the Aerostatic Response of a Long-Span Pedestrian Suspension Bridge

Yu Li,Zhe Chen,Shi-Jie Dong,Jia-Wu Li 대한토목학회 2021 KSCE Journal of Civil Engineering Vol.25 No.10

According to a long-span pedestrian suspension bridge, the sectional models of the human-footbridge system were proposed, and then the force measurement tests were performed to study the effects of the pedestrian density (ρ), pedestrian permutation, and wind attack angle (α) on the drag force coefficient (CH), lift force coefficient (CV), and pitching moment coefficient (CM), respectively. So, it is found that: (1) with the increase of ρ, both CH and CV with α < -2o increase, while both CV with α ≥ -2o and CM with ρ ≠ 0.0 P/m2 decrease. (2) when ρ> 0.2 P/m2, there is a significant effect of the pedestrian permutations on CH and CM, while the effect of the pedestrian permutations on CV is small. Then, the static wind forces were calculated and applied to the pedestrian suspension bridge, and the effects of ρ and pedestrian permutations on the aerostatic response were studied. So, it is found that: 1) with the increase of ρ, the aerostatic response increases; 2) the effects of the pedestrian permutations with ρ ≤ 0.5 P/m2 on the aerostatic response can be ignored, while there are disadvantageous effects of the pedestrian permutations with ρ > 0.5 P/m2 and larger wind-blocking area on the aerostatic response.

Experimental Investigations on the Flutter Derivatives of the Pedestrian-Bridge Section Models

Yu Li,Chen Li 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.11

Based on a suspension footbridge, the pedestrian-bridge section models were first proposed and designed. Then, the free vibration tests were carried out to study the influence of pedestrians on the flutter derivatives (H1*, A2*, A3*, H4*, and A1* × H3*) which significantly affect the flutter of suspension footbridges. It can be found that: 1) with an increase in the pedestrian density, the H1*, H4* and A1* × H3* increase, which will lead to the decrease in the positive vertical aerodynamic damping, the positive vertical aerodynamic stiffness and the positivevertical and torsional aerodynamic damping, respectively. Meanwhile, with an increase in the pedestrian density, the A2* and A3* decrease, which will lead to a decrease in the negative torsional aerodynamic damping and the negative torsional aerodynamic stiffness, respectively. 2) The arrangement of walking side by side is advantageous to the positive vertical aerodynamic damping and disadvantageous to the negative torsional aerodynamic stiffness. The arrangements of random walking with low-medium pedestrian densities and walking in line with high-medium pedestrian densities are disadvantageous to the vertical aerodynamic stiffness and the positive vertical and torsional aerodynamic damping. Besides, all the pedestrian arrangements have a significant influence on the torsional aerodynamic damping.

Research on Core Competence of Cultural Industry in Korea

Yu Li,Hao Li 한국유통과학회 2017 Asian Journal of Business Environment (AJBE) Vol.7 No.2

Purpose - This paper will go deep into the analysis of Korean Cultural industry development, and the result of the analysis shows that the cultural value of cultural product, competitive product lines and mature Market Mechanism are core competences of Korean Cultural industry. Research design, data, and methodology – This is a case study in the era of knowledge based economy, Cultural industry has become a new increasing point of economic development. Cultural industry, commonly regarded as an industry with high-ended value, is occupying more important role in economic development and social welfare promotion process. Results - Moreover the increasingly important role of cultural industry will hopefully help to promote industrial upgrading process and finally become a driving force for economic growth and technological innovation. During the process of cultural development, improving core competence of Cultural industry is a key consideration to help the development of Cultural industry in a positive way. Conclusions - From the study above, we find that in order to ensure sustainable development of Cultural industry, emphasis should be put on finding and improving core competence. Core competence of Korean Cultural industry is important and inspiring to the development of Chinese Cultural industry and regional integration in the East Asian area.

Aerodynamic optimisation of a low-pressure multistage turbine using the response-surface method

Yu Li,Liang Lin,Tong Zhao,Jun Li 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.8

Steam turbine plays an important role in the power-generation industry. The power output of the low-pressure (LP) cylinder accounts for about 50% of the total power output of a steam turbine. Therefore, improving the efficiency of the LP cylinder is important. The response-surface method is used in this work to optimise the seven-stage turbine in the LP cylinder of a 600 MW steam turbine. The LP cylinder’s efficiency is chosen as the objective function and the samples needed to establish the response surface are obtained by solving the three-dimensional Navier-Stokes equations with the ANSYS CFX. The stators’ stagger angles and stacking lines are selected as the design variables. The former is determined to redistribute the enthalpy drop among turbine stages more reasonably and the latter is used to improve each stage’s efficiency by forming bent and twisted stators. The efficiency and power of this LP cylinder are increased by 0.43% and 0.72%, respectively. Meanwhile, the mass flow rate is maintained nearly unchanged.

Investigations on the Influence of Pedestrians on the Buffeting of a Long-Span Suspension Footbridge

Yu Li,Jia-Xin Xiao,Chen Li,Jia-Wu Li 한국강구조학회 2023 International Journal of Steel Structures Vol.23 No.3

According to a suspension footbridge, the pedestrian-bridge section models with different pedestrian densities (μ) were proposed. The wind tunnel tests were performed to study the influence of pedestrians on aerostatic force coefficients and flutter derivatives, and it is found that: with the increase of μ, the drag force coefficient increases, and the lift force coefficient decreases, while the effect of μ on the pitching moment coefficient can be ignored; moreover, there is a significant influence of μ on the flutter derivatives. Then, the static wind forces, buffeting forces, and self-excited forces considering the influence of pedestrians were calculated by using the measured aerostatic force coefficients, the measured flutter derivatives, and the simulated fluctuating wind field. By applying these forces to the finite element model of the suspension footbridge, a buffeting analysis was conducted by using the ANSYS Parametric Design Language, and it is found that: with the increase of pedestrians on the long-span suspension footbridge, the buffeting increases, while the effect of wind attack angles (θ) on the buffeting decreases; Especially, when μ > 1.0 P/m2, the effect of θ on the buffeting can be ignored.

Framework for Calculating the Vertical Human-Induced Vibration of the Suspension Footbridge Under the Random Pedestrian Flow

Yu Li,Dong-Shuo Yin,Jia-Hao Wang,Jia-Wu Li 한국강구조학회 2022 International Journal of Steel Structures Vol.22 No.5

Currently, the problem of human-induced vibration of suspension footbridges is a research hotspot in bridge engineering. Moreover, on the suspension footbridge deck, the walking parameters of pedestrians, the simulation of random pedestrian fl ow, and the calculation method of human-induced vibration are the keys to solving the above problem. Therefore, in this paper, the following three studies have been carried out: (1) Firstly, the Jiufengshan suspension footbridge was taken as the observation site, and the statistical values of the step frequency ( f ), step length ( l ), and walking velocity ( v ) of pedestrians on the suspension footbridge deck were investigated and obtained. (2) Secondly, by combining the “social force model” with the obtained f , l , and v , a Matlab program was compiled to simulate the random pedestrian fl ow on the suspension footbridge deck. (3) Finally, by combining the above program with the vertical vibration equations of the human–footbridge coupling system, a Matlab program was compiled to calculate the vertical human-induced vibration of the suspension footbridge deck, which then was used to study the infl uence of the random pedestrian fl ow and human–footbridge coupling eff ect on the vertical human-induced vibration of the suspension footbridge deck. So, the above studies can provide a meaningful reference for the design of suspension footbridges.

[PA-0013] The transcription factor ERF55 regulates seed triacylglycerol synthesis

Yuli Choe(Yuli Choe),Inyoung Kim(Inyoung Kim),Hyun Uk Kim(Hyun Uk Kim) 한국육종학회 2022 한국육종학회 공동학술발표집 Vol.2022 No.-

The AP2/ERF transcription factor ERFSS regulates seed triacylglycerol biosynthesis

Yuli Choe,Inyoung Kim,Inyoung Kim 한국육종학회 2023 한국육종학회 공동학술발표집 Vol.2023 No.-

Transformer Oil Dielectric Characteristics in Microwave Assisted Reconditioning Processes

Yuli Rodiah,Tarcicius Haryono,Fransisco Danang Wijaya 대한전기학회 2020 Journal of Electrical Engineering & Technology Vol.15 No.3

Maintenance of transformer oil is needed to maintain the quality of power service. Thermal heating and fltering are the main ways to remove contaminants from the oil. In this research, a preliminary study was carried out using microwaves as thermal heaters in the reconditioning process of used transformer oil. The reconditioning process is carried out by fltering and thermal heating varies from temperatures of 40–100 °C using a microwave oven. Dielectric characteristics are shown by analyzing breakdown voltage, dielectric power loss, viscosity, and dc conductivity measurements. The amount of moisture content is also taken into account in measuring the level of thermal efciency of the heater. Under the infuence of microwaves, an increase in the characteristics of the dielectric strength in the form of an increase in breakdown voltage reaches 140.50%. Microwave heating is very good in reducing the water content in oil with a level of thermal efciency reaching 25.55–40.40%. Removal of contaminants is better done by microwaves characterized by a decrease in the value of the dielectric power loss and dc conductivity at each treatment.