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Effect of beam slope on the static aerodynamic response of edge-girder bridge-deck
Lee, Hoyeop,Moon, Jiho,Chun, Nakhyun,Lee, Hak-eun Techno-Press 2017 Wind and Structures, An International Journal (WAS Vol.25 No.2
2-edge box girder bridges have been widely used in civil engineering practice. However, these bridges show weakness in aerodynamic stability. To overcome this weakness, additional attachments, such as fairing and flap, are usually used. These additional attachments can increase the cost and decrease the constructability. Some previous researchers suggested an aerodynamically stabilized 2-edge box girder section, giving a slope to the edge box instead of installing additional attachments. However, their studies are limited to only dynamic stability, even though static aerodynamic coefficients are as important as dynamic stability. In this study, focus was given to the evaluation of static aerodynamic response for a stabilized 2-edge box girder section. For this, the slopes of the edge box were varied from $0^{\circ}$ to $17^{\circ}$ and static coefficients were obtained through a series of wind tunnel tests. The results were then compared with those from computational fluid dynamics (CFD) analysis. From the results, it was found that the drag coefficients generally decreased with the increasing box slope angle, except for the specific box slope range. This range of box slope varied depending on the B/H ratio, and this should be avoided for the practical design of such a bridge, since it results in poor static aerodynamic response.
HTPB/AP계 고체 추진제의 연소속도 증진 방안 연구
이선영(Sunyoung Lee),류태하(Taeha Ryu),김낙현(Nakhyun Kim),홍명표(Myungpyo. Hong),이형진(Hyoungjin Lee) 한국추진공학회 2016 한국추진공학회 학술대회논문집 Vol.2016 No.12
본 논문은 HTPB/AP/Al계 추진제의 성능 개선을 위한 연소속도와 압력지수를 제어하기 위하여 AP입자 사이즈 비율 및 연소촉매로 사용된 Butacene의 함량에 따른 연소 특성을 조사하였다. 23%의 28 ㎛ Al과 3%의 Butacene을 포함하는 추진제 조성에서 연소속도와 압력지수는 9 ㎛ AP 입자의 함량이 증가함에 따라 증가하였다. 그리고 Butacene의 함량이 증가함에 따라 연소속도도 증가하였으며 Butacene을 함유하는 추진제는 비교적 낮은 압력지수 특성을 보였다. 그러나 Butacene의 함량에 의한 압력지수의 차이는 나타나지 않았다. In this paper, in order to control of burning rate and pressure exponent for the improvement in the performance of HTPB/AP/Al based propellant, the combustion properties on the size ratio of AP particles and a various contents of Butacene as burning catalyst are investigated. In the propellant formulation added both 28 ㎛ Al of 23% and Butacene of 3%, the burning rate and pressure exponent were increased according to more contents of 9 ㎛ AP particles. And the burning rate was increased according to more contents of Butacene, it was showed relatively low pressure exponent in the propellant containing Butacene. However the difference of pressure exponent by contents of Butacene didn’t show up.
Alternative numerical method for identification of flutter on free vibration
Chun, Nakhyun,Moon, Jiho,Lee, Hak-Eun Techno-Press 2017 Wind and Structures, An International Journal (WAS Vol.24 No.4
The minimization method is widely used to predict the dynamic characteristics of a system. Generally, data recorded by experiment (for example displacement) tends to contain noise, and the error in the properties of the system is proportional to the noise level (NL). In addition, the accuracy of the results depends on various factors such as the signal character, filtering method or cut off frequency. In particular, coupled terms in multimode systems show larger differences compared to the true value when measured in an environment with a high NL. The iterative least square (ILS) method was proposed to reduce these errors that occur under a high NL, and has been verified in previous research. However, the ILS method might be sensitive to the signal processing, including the determination of cutoff frequency. This paper focused on improving the accuracy of the ILS method, and proposed the modified ILS (MILS) method, which differs from the ILS method by the addition of a new calculation process based on correlation coefficients for each degree of freedom. Comparing the results of these systems with those of a numerical simulation revealed that both ILS and the proposed MILS method provided good prediction of the dynamic properties of the system under investigation (in this case, the damping ratio and damped frequency). Moreover, the proposed MILS method provided even better prediction results for the coupling terms of stiffness and damping coefficient matrix.