• Structural Engineering and Mechanics
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• 제16권2호
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• pp.195-217
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• 2003

This paper, which is an extension of a previous work by Viola et al. (2002), deals with the dynamic stability of beams under a triangularly distributed sub-tangential forces when the effect of an elastically restrained end is taken into account. The sub-tangential forces can be realised by a combination of axial and tangential follower forces, that are conservative and non-conservative forces, respectively. The studied beams become unstable in the form of either flutter or divergence, depending on the degree of non-conservativeness of the distributed sub-tangential forces and the stiffness of the elastically restrained end. A non-conservative parameter ${\alpha}$ is introduced to provide all possible combinations of these forces. Problems of this kind are usually, at least in the first approximation, reduced to the analysis of beams according to the Bernoulli-Euler theory if shear deformability and rotational inertia are negligible. The equation governing the system may be derived from the extended form of Hamilton's principle. The stability maps will be obtained from the eigenvalue analysis in order to define the divergence and flutter domain. The passage from divergence to flutter is associated with a noticeable lowering of the critical load. A number of particular cases can be immediately recovered.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1996년도 제23회 학술대회
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• pp.41-46
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• 1996

For a vertical type crankshaft-journal bearing system used in scroll compressor, nonlinear transient response analysis is applied includung nonlinear fluid film reaction forces of journal beatings. By a connected behavior analysis of crankshaft and orbiting scroll, the radial clearance of scroll wraps is calculated. Considering tangential leakage for this clearance, a coupled analysis model for leakage and dynamic behavior of the orbiting scroll is made, and analyzed by iterative calculation. By regarding clearances of main, sub bearing of crankshaft and orbiting scroll shaft bearing clearance as design parameters, the radial clearance of scroll wraps is analyzed.

• 대한기계학회논문집
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• 제5권2호
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• pp.88-93
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• 1981

The three force components of shear spinning are calculated by a newly proposed deformation model. The spinning process is understooed as shearing deformation arter uniaxial yuelding by ending, and shear stress .tau.$\sub$rz/ becomes .kappa. the yueld limit in pure shear, in the deformation zone. The tangential forces are calculated and then the feed forces and normal foeces are obtained by assuming a nuiform distribution of roller pressure on the contact surface. An optimum contact area is obtaned by minimizing the bending energy required to obtain the assumed deformation mechanism. The calculated forces are compared with experimental data form published literature and present experiments. Good agreement cetween calculated and experimental values for working forces is obtained over a wide range of process variables.

• 한국소음진동공학회논문집
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• 제26권6_spc호
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• pp.635-643
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• 2016

안정성 지도(stability map)을 이용하여 부분 종동력(sub-tangentailly follower force)를 받는 외팔 기둥의 동적안정성 이론을 요약한다. Rayleigh 감쇠를 가정하여 내적 및 외적 감쇠효과를 2개의 감쇠비를 통하여 반영하고, 감쇠비 변화에 따른 플러터하중의 변화와 관련된 매개변수 연구를 수행한다. 또한, 종동력을 받는 외팔기둥에 대한 진동수 방정식의 엄밀해를 유도하고, 특정 감쇠비 범위에 대한 안정성 지도를 유한요소 해석결과와 함께 비교/분석한다.

• Structural Engineering and Mechanics
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• 제84권1호
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• pp.17-33
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• 2022

An experimental study is carried out to investigate the performance of the cutting tool regarding the insert wear, surface roughness, cutting forces, cutting power and material removal rate of three coated carbides GC2015 (TiCN-Al₂O₃-TiN), GC4215 (Al₂O₃-Ti(C,N)) and GC1015 (TiN) during the dry turning of AISI4140 steel. For this purpose, a Taguchi design (L₉) was adopted for the planning of the experiments, the effects of cutting parameters on the surface roughness (R_a), tangential cutting force (F_z), the cutting power (P_c) and the material removal rate (MRR) were studied using analysis of variance (ANOVA), the response surface methodology (RSM) was used for mathematical modeling, with which linear mathematical models were developed for forecasting of R_a, F_z, P_c and MRR as a function of cutting parameters (V_c, f, and a_p). Then, Multi-Objective Ant Lion Optimizer (MOALO) has been implemented for multi-objective optimization which allows manufacturers to enhance the production performances of the machined parts. Furthermore, in order to characterize and quantify the flank wear of the tested tools, some machining experiments were performed for 5 minutes of turning under a depth of 0.5 mm, a feed rate of 0.08 mm/rev, and a cutting speed of 350 m/min. The wear results led to a ratio (V_B-GC4215/V_B-GC2015) of 2.03 and (V_B-GC1015/V_B-GC2015) of 4.43, thus demonstrating the efficiency of the cutting insert GC2015. Moreover, SEM analysis shows the main wear mechanisms represented by abrasion, adhesion and chipping.

• Structural Engineering and Mechanics
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• 제36권4호
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• pp.421-445
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• 2010

In this paper the formulation of an efficient frame element applicable for nonlinear analysis of 3D reinforced concrete (RC) frames is outlined. Interaction between axial force and bending moment is considered by using the fibre element approach. Further, section warping, effect of normal and tangential forces on the torsional stiffness of section and second order geometrical nonlinearities are included in the model. The developed computer code is employed for nonlinear static analysis of RC sub-assemblages and a simple approach for extending the formulation to dynamic cases is presented. Dynamic progressive collapse assessment of RC space frames based on the alternate path method is undertaken and dynamic load factor (DLF) is estimated. Further, it is concluded that the torsional behaviour of reinforced concrete elements satisfying minimum standard requirements is not significant for the framed structures studied.

• 한국항공우주학회지
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• 제50권1호
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• pp.1-12
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• 2022

소형무인기의 틸팅방식 추진장치로 소형덕티드팬을 적용하였을 때 나타나는 공력특성을 분석하기 위해 직경 104mm 전기추진 덕티드팬의 공력특성을 풍동시험을 통해 살펴보았다. 소형무인기 운영조건에서 나타나는 현상을 살펴보기 위해 OPPAV 축소시제기의 제자리비행, 전진비행 및 천이비행 조건을 시험조건으로 채택하였으며, 6분력 발란스를 사용하여 덕티드팬의 추력 및 측력, 토크를 측정하였다. 비행체 주날개 및 꼬리날개에 영향을 미칠 수 있는 팬 후류를 파악하기 위해 5공 프로브를 사용하여 덕트 후방 250mm 단면의 3차원 속도벡터를 측정하였다. 제자리비행 및 전진비행 조건에서 덕티드팬의 추력 및 토크 특성을 파악하였으며, OPPAV 축소시제기에 적용하기 위한 조건을 도출하였다. 천이비행 조건에서 틸트각 40° 이하에서는 각도가 변하여도 추력이 유지되는 특성을 보이고 있으며 그 이후 각에서는 점차 증가하는 경향이 나타났다. 측력은 틸트각 75°까지 지속적으로 증가하는 경향이 나타났다. 제자리비행 및 전진비행 조건에서 60m/s 수준의 축방향 속도성분과 12m/s 수준의 원주방향 속도성분이 측정되었다. 틸트각이 증가함에 따라 축방향 속도 최대값 위치가 회전중심선을 벗어나는 경향이 나타나고 있으며, 단면 와류 중심도 유사한 위치로 이동하는 경향이 나타나고 있다.