ADAPTIVE GRID SIMULATION OF HYPERBOLIC EQUATIONS

HAOJUN LI,MYUNGJOO KANG 한국산업응용수학회 2013 Journal of the Korean Society for Industrial and A Vol.17 No.4

We are interested in an adaptive grid method for hyperbolic equations. A multiresolution analysis, based on a biorthogonal family of interpolating scaling functions and lifted interpolating wavelets, is used to dynamically adapt grid points according to the physical field profile in each time step. Traditional finite-difference schemes with fixed stencils produce high oscillations around sharp discontinuities. In this paper, we hybridize high-resolution schemes, which are suitable for capturing singularities, and apply a finite-difference approach to the scaling functions at non-singular points. We use a total variation diminishing Runge?Kutta method for the time integration. The computational cost is proportional to the number of points present after compression. We provide several numerical examples to verify our approach.

Studies on Organosoluble Polyimides Based on a Series of New Asymmetric and Symmetric Dianhydrides: Structure/Solubility and Thermal Property Relationships

Haojun Fan,Ke Zeng,Qiao Guo,Shuai Gao,Dimeng Wu,Gang Yang 한국고분자학회 2012 Macromolecular Research Vol.20 No.1

A series of new asymmetric biphenyl dianhydrides, 2-phenoxy(o-methylphenoxy, m-methylphenoxy, and p-methylphenoxy)-4,4,5,5-biphenyltetracarboxylic dianhydrides, was readily synthesized using a five-step route. A new symmetric biphenyl dianhydride, 2,2-di(o-methylphenoxy)-4,4,5,5-biphenyltetracarboxylic dianhydride, was also synthesized using the similar procedure. The polyimides were prepared from such new dianhydrides and commercial diamines by high-temperature one-step polymerization. The asymmetric and symmetric substituent solubility and thermal property relationships of the resulting polyimides were investigated. Interestingly, the thermally reversible sol–gel transitions were observed for the polymer solutions of the polyimides derived from those asymmetric dianhydrides and 1,4-phenylenediamine (p-PDA). Unexpectedly, the polyimides derived from asymmetric dianhydrides did not show better organosolubility than those of the homologous polyimides derived from symmetric dianhydrides. The structures of the substituents (phenoxy, o-methylphenoxy, m-methylphenoxy and p-methylphenoxy)have a significant effect on both the solubility and the thermal properties of these polyimides. The polyimides derived from asymmetric dianhydrides show enhanced thermal properties relative to the symmetric dianhydridesderived polyimides. These results can be attributed to their different degrees of molecular packing revealed by wideangle X-ray diffraction measurements.

ADAPTIVE WAVELET COLLOCATIONMETHOD FOR SIMULATION OF OPTICAL RING RESONATOR

Haojun Li,Kirankumar R. Hiremath,Andreas Rieder 한국산업응용수학회 2012 한국산업응용수학회 학술대회 논문집 Vol.7 No.1

Flutter performance of central-slotted plate at large angles of attack

Haojun Tang,Yongle Li,Xinzhong Chen,K.M. Shum,Haili Liao 한국풍공학회 2017 Wind and Structures, An International Journal (WAS Vol.24 No.5

The flutter instability is one of the most important themes need to be carefully investigated in the design of long-span bridges. This study takes the central-slotted ideal thin flat plate as an object, and examines the characteristics of unsteady surface pressures of stationary and vibrating cross sections based on computational fluid dynamics (CFD) simulations. The flutter derivatives are extracted from the surface pressure distribution and the critical flutter wind speed of a long span suspension bridge is then calculated. The influences of angle of attack and the slot ratio on the flutter performance of central-slotted plate are investigated. The results show that the critical flutter wind speed reduces with increase in angle of attack. At lower angles of attack where the plate shows the characteristics of a streamlined cross-section, the existence of central slot can improve the critical flutter wind speed. On the other hand, at larger angles of attack, where the plate becomes a bluff body, the existence of central slot further reduces the flutter performance.

Chip Control Analysis in Low-Frequency Vibration-Assisted Drilling of Ti–6Al–4V Titanium Alloys

Haojun Yang,Yan Chen,Jiuhua Xu,Mathieu Ladonne,Julian Lonfier,Wenfeng Ding 한국정밀공학회 2020 International Journal of Precision Engineering and Vol.21 No.4

In this study, control research of chip morphology and removal is conducted theoretically and experimentally on the basis ofthe low-frequency vibration-assisted drilling process of titanium alloy. The chip morphology prediction model is establishedon the basis of the modifi ed kinematic model, in which the shear angle variation, critical cutting thickness, and stiff ness ofa vibration generator system are considered. In terms of chip removal monitoring, a new monitoring method based on highspeed camera is proposed in this paper. And the reliability of the new method is verifi ed by comparing the signals obtainedby the power sensor and the force sensor. An empirical prediction model for chip removal is also established on the basis ofthe modifi ed kinematical model, the chip morphology prediction model, and the force balance analysis of fragmental chips. Validation experiments show that the mean error of chip radian, which can refl ect the diff erence between the predicted chipmorphology and the experimental one, is 6%. The mean error of the predicted chip removal index compared with the experimentalone is 10.4%. The results obtained show that chip removal can be controlled eff ectively by low rotation speed, smallchip radian, light chip weight, high minimum quantity lubrication cooling pressure, and high oscillation frequency. On thebasis of the prediction model of chip removal, the eff ects of drilling parameters on chip removal behavior are analyzed, andthe optimal drilling parameter combination with highest processing effi ciency is given.

Flutter performance of box girders with different wind fairings at large angles of attack

Haojun Tang,Hang Zhang,Wei Mo,Yong-Le Li 한국풍공학회 2021 Wind and Structures, An International Journal (WAS Vol.32 No.5

The streamlined box is a common type of girders for long-span suspension bridges. Spanning deep canyons, long-span bridges are frequently attacked by strong winds with large angles of attack. In this situation, the flow field around the streamlined box changes significantly, leading to reduction of the flutter performance. The wind fairings have different effects on the flutter performance. Therefore, this study examines the flutter performance of box girders with different wind fairings at large angles of attack. Computational fluid dynamics (CFD) simulations were carried out to extract the flutter derivatives, and the critical flutter state of a long-span bridge was determined. Further comparisons of the wind fairings were investigated by a rapid method which is related to the input energy by the aerodynamic force. The results show that a reasonable type of wind fairings could improve the flutter performance of long-span bridges at large angles of attack. For the torsional flutter instability, the wind fairings weaken the adverse effect of the vortex attaching to the girder, and a sharper one could achieve a better result. According to the input energies on the girder with different wind fairings, the symmetrical wind fairings are more beneficial to the flutter performance.

Flutter performance of central-slotted plate at large angles of attack

Tang, Haojun,Li, Yongle,Chen, Xinzhong,Shum, K.M.,Liao, Haili Techno-Press 2017 Wind and Structures, An International Journal (WAS Vol.24 No.5

The flutter instability is one of the most important themes need to be carefully investigated in the design of long-span bridges. This study takes the central-slotted ideal thin flat plate as an object, and examines the characteristics of unsteady surface pressures of stationary and vibrating cross sections based on computational fluid dynamics (CFD) simulations. The flutter derivatives are extracted from the surface pressure distribution and the critical flutter wind speed of a long span suspension bridge is then calculated. The influences of angle of attack and the slot ratio on the flutter performance of central-slotted plate are investigated. The results show that the critical flutter wind speed reduces with increase in angle of attack. At lower angles of attack where the plate shows the characteristics of a streamlined cross-section, the existence of central slot can improve the critical flutter wind speed. On the other hand, at larger angles of attack, where the plate becomes a bluff body, the existence of central slot further reduces the flutter performance.

The Impact of Workplace Spirituality on Job Performance : Focused on Moderating Effect of Job Satisfaction

Zhou HaoJun,Chung, Soo-Jin 한국상업교육학회 2021 상업교육연구 Vol.35 No.4

본 연구는 일터 영성이 직무 성과에 미치는 영향을 직무 만족의 조절 효과를 중심 으로 검증하는 데 목적을 두고 있다. 설문조사를 통해 중국 내 기업 종사자로부터 유 효 표본 457부를 수집하였으며, 이론적 연구를 바탕으로 일터 영성, 과업 성과, 맥락 성과, 직무 만족에 대한 가설모형을 설정하여 4가지 주요 연구가설을 제시하였다. 가 설검증을 위해 SPSS 23.0 프로그램을 사용하였으며, 요인분석, 상관분석, 회귀분석을 통해 정량분석을 시행한 결과 일터 영성은 과업 성과와 맥락 성과에 유의한 상관관계 를 보였으며, 직무 만족은 일터 영성, 과업 성과, 맥락 성과 간에 조절 효과를 보였다. 이와 같은 연구결과에 대한 실증적 결과는 다음과 같다. 조직은 직무에서 영성을 강 조해야 하며, 관리자는 직무 만족을 높이기 위해 다양한 방법을 장려하여 직무 성과 에 미치는 영향을 강화해야 한다. 본 연구는 일터 영성이 직무 성적에 미치는 영향 메커니즘을 어느 정도 밝혀냈으며, 상업 교육의 활용 방향이라는 측면에서 상업 교육 에 중요한 역할을 할 것이다.향후 상업 교육 분야와 관련된 설문과 연구 대상에 대해 중요한 의사 결정에 참고가 된다. The aim of this study is to verify the influence of workplace spirituality on job performance and the moderating effect of job satisfaction. Through the questionnaire survey, a total of 457 valid samples were received from employees of Chinese enterprises. On the basis of theoretical research, 4 key research hypotheses are proposed and the hypothesis models of workplace spirituality, task and contextual performance ,job satisfaction are established. SPSS 23.0 software was used to conduct hypothesis testing by using factor analysis, correlation analysis, regression analysis and other methods for quantitative analysis. The results show that workplace spirituality has a significant correlation with task and contextual performance. Job satisfaction has a moderating effect between workplace spirituality with task performance. The empirical results suggest that organizations should emphasize workplace spirituality at work, and managers should encourage more methods to improve employees' perception of job satisfaction, so as to strengthen the impact of workplace spirituality on job performance. To a certain extent, this study reveals the influence mechanism of workplace spirituality on job performance, which will play an important role in business education from the perspective of the active application direction of business education. It provides an important reference for decision-making of the questionnaire and research objects in the field of business education in the future.

Modelling and Optimization of a Magnetic Spring Based Electromagnetic Vibration Energy Harvester

Liao Haojun,Ye Tingcong,Pang Yu,Feeney Ciaran,Liu Lei,Zhang Zhengmin,Saha Chitta,Wang Ningning 대한전기학회 2022 Journal of Electrical Engineering & Technology Vol.17 No.1

This paper presents the development of an AA battery size electromagnetic vibration energy harvester with an aim to maximize the output power density. A tube shape and stacked opposing permanent magnets with magnetic spring were used to suit the shape constraint as well as to achieve high fl ux linkages. An initial prototype of electromagnetic vibration harvester with AA battery size was built and tested on a controllable shaker to obtain its output voltage and power level at diff erent frequencies for fi xed accelerations. A single magnet was fi xed at the bottom of the harvester to provide levitation force in this development in order to lower the resonant frequency. A special time-domain based analytical model was also developed using both Finite Element Analysis and Simulink simulation. The time-domain analytical model is easier to implement than other frequency domain based analytical models which generally applied in literatures for modelling of the electromagnetic vibration energy harvesters. The analytical model was verifi ed by the measured results obtained from the initial prototype. The validated analytical model was successfully applied to optimize the harvester. Two more generator prototypes were further built and tested after the optimization study. The optimized harvester using three stacked opposing permanent magnets could achieve a normalized power density of 12,655 μWcm −3 g −2 at 9.9 Hz frequency with 0.22 g acceleration, which is signifi cantly higher than other reported electromagnetic vibration energy harvesters

SD-IOT 프레임워크 구축을 위한 OpenFlow Agent의 구현

조호준(Haojun Zhao),이시샤(Xisha Li),천세준(Chun Se Joon),이양(Yang Li),최진식(Jin Seek Choi) 한국통신학회 2017 한국통신학회 학술대회논문집 Vol.2017 No.6