• Proceeding of EDISON Challenge
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• 2017.03a
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• pp.259-269
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• 2017

Gust load is a very important load factor in designing various structures of an aircraft and judging its stability. This is because the blast effect on the aircraft in operation increases the risk of damage to the structure of the aircraft and causes a negative impact such as shortening the fatigue life by generating vibration. Particularly in the case of wing, a change in angle of attack is caused by gust load, and an additional lift acts on the wing, thereby being exposed to various excitational environments. Severe structural damage to the aircraft may occur if the natural frequencies of the aircraft wing are close to or coincident with the frequencies of the gust load applied to the wing. Recent trends of research include flight dynamics analysis considering discontinuous gusts or structural optimization of the blades under gust load. A number of studies have been conducted to interpret gust load response in consideration of irregularities in gusts. In this paper, we tried to imagine the situation of the aircraft subjected to the gust load as realistic as possible, and proposed an algorithm to track back the critical gust profile according to given aircraft characteristics from the viewpoint of preliminary engineering prediction.

• Journal of Convergence Society for SMB
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• v.4 no.2
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• pp.25-31
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• 2014

Sliding mode design and analysis for nonlinear system was carried out. A designer will determine the parameters to know about the performance and robustness of the system dynamics. To investigate the characteristics of sliding mode control, an inverted pendulum model is applied by the sliding mode control and the state concerned is output. Comparison is made by evaluating different initial conditions, sliding numerical components for sliding surface, and input gain, the dynamic of output will be investigated to conclude the generality. Control approaches have their limitations and sliding mode control is no exception. The chattering problem is its main negative effect to overcome. This effect is displayed and in this project chattering problem is suppressed by a modified discontinuous controller.

• Advances in aircraft and spacecraft science
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• v.9 no.5
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• pp.415-431
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• 2022

Secondary flows have a huge impact on losses generation in modern low pressure gas turbines (LPTs). At design point, the interaction of the blade profile with the end-wall boundary layer is responsible for up to 40% of total losses. Therefore, predicting accurately the end-wall flow field in a LPT is extremely important in the industrial design phase. Since the inlet boundary layer profile is one of the factors which most affects the evolution of secondary flows, the first main objective of the present work is to investigate the impact of two different inlet conditions on the end-wall flow field of the T106A, a well known LPT cascade. The first condition, labeled in the paper as C1, is represented by uniform conditions at the inlet plane and the second, C2, by a flow characterized by a defined inlet boundary layer profile. The code used for the simulations is based on the Discontinuous Galerkin (DG) formulation and solves the Reynolds-averaged Navier-Stokes (RANS) equations coupled with the Spalart Allmaras turbulence model. Secondly, this work aims at estimating the influence of viscosity and turbulence on the T106A end-wall flow field. In order to do so, RANS results are compared with those obtained from an inviscid simulation with a prescribed inlet total pressure profile, which mimics a boundary layer. A comparison between C1 and C2 results highlights an influence of secondary flows on the flow field up to a significant distance from the end-wall. In particular, the C2 end-wall flow field appears to be characterized by greater over turning and under turning angles and higher total pressure losses. Furthermore, the C2 simulated flow field shows good agreement with experimental and numerical data available in literature. The C2 and inviscid Euler computed flow fields, although globally comparable, present evident differences. The cascade passage simulated with inviscid flow is mainly dominated by a single large and homogeneous vortex structure, less stretched in the spanwise direction and closer to the end-wall than vortical structures computed by compressible flow simulation. It is reasonable, then, asserting that for the chosen test case a great part of the secondary flows details is strongly dependent on viscous phenomena and turbulence.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.2
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• pp.395-400
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• 2017

The paper discussed the air-to-fuel ratio control of automotive fuel-injection systems using the cerebellar model articulation controller(CMAC) neural network. Because of the internal combustion engines and fuel-injection's dynamics is extremely nonlinear, it leads to the discontinuous of the fuel-injection and the traditional method of control based on table look up has the question of control accuracy low. The advantages about CMAC neural network are distributed storage information, parallel processing information, self-organizing and self-educated function. The unique structure of CMAC neural network and the processing method lets it have extensive application. In addition, by analyzing the output characteristics of oxygen sensor, calculating the rate of fuel-injection to maintain the air-to-fuel ratio. The CMAC may easily compensate for time delay. Experimental results proved that the way is more good than traditional for petrol control and the CMAC fuel-injection controller can keep ideal mixing ratio (A/F) for engine at any working conditions. The performance of power and economy is evidently improved.

• Journal of Ocean Engineering and Technology
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• v.32 no.6
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• pp.419-426
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• 2018

Recently, in an effort to reduce the energy efficiency design index (EEDI), studies on energy saving devices (ESDs) have been conducted. In this study, we designed a post-device suitable for a KRISO container ship (KCS) using computational fluid dynamics (CFD). In order to increase the efficiency of the post-device, a twisted rudder was used, which has a proven performance (showing a 1.34% reduction in DHP compared to the bare hull at 24 knots) in previous research at Pusan National University. In addition, an increase in efficiency was expected by the use of a rudder bulb, including the discontinuous section of the twisted rudder and a divergent propeller cap to prevent the contraction of the wake. The optimization criterion was the case where the delivery power was the least compared with the bare hull. We analyzed the cause of the efficiency increase through an analysis of the self-propulsion factor. The case study for optimization was divided into 4 types (1. clearance of the bulb and cap, 2. shape of the bulb, 3. size of the bulb and cap, and 4. asymmetric bulb). Finally, with a clearance of 50 mm from the ship, a spherical bulb with the cap having an angle of $5^{\circ}$, and an asymmetric rudder bulb with a bulb diameter of 1.2HH/1.4H (horizontal/vertical) showed a 2.05% reduction in DHP compared to the bare hull at 24 knots. We will fabricate a post-device that will be optimized in the future and verify the performance of the post-device through model tests.

• Steel and Composite Structures
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• v.49 no.5
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• pp.487-502
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• 2023

In the realm of nanotechnology, the nonlocal strain gradient theory takes center stage as it scrutinizes the behavior of spinning cantilever nanobeams and nanotubes, pivotal components supporting various mechanical movements in sport structures. The dynamics of these structures have sparked debates within the scientific community, with some contending that nonlocal cantilever models fail to predict dynamic softening, while others propose that they can indeed exhibit stiffness softening characteristics. To address these disparities, this paper investigates the dynamic response of a nonlocal cantilever cylindrical beam under the influence of external discontinuous dynamic loads. The study employs four distinct models: the Euler-Bernoulli beam model, Timoshenko beam model, higher-order beam model, and a novel higher-order tube model. These models account for the effects of functionally graded materials (FGMs) in the radial tube direction, giving rise to nanotubes with varying properties. The Hamilton principle is employed to formulate the governing differential equations and precise boundary conditions. These equations are subsequently solved using the generalized differential quadrature element technique (GDQEM). This research not only advances our understanding of the dynamic behavior of nanotubes but also reveals the intriguing phenomena of both hardening and softening in the nonlocal parameter within cantilever nanostructures. Moreover, the findings hold promise for practical applications, including drug delivery, where the controlled vibrations of nanotubes can enhance the precision and efficiency of medication transport within the human body. By exploring the multifaceted characteristics of nanotubes, this study not only contributes to the design and manufacturing of rotating nanostructures but also offers insights into their potential role in revolutionizing drug delivery systems.

• Korea journal of population studies
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• v.25 no.2
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• pp.107-138
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• 2002

In general, women's labor force participation follows a M-curve pattern because women's state of economic activity usually changes by their life course stage. This research attentions that the effect of sequence of life course as well as the effects of‘marriage bar’, or‘maternity leave’is very important in understanding women's chaning economic activity status. First, this research hypothesizes that women's four patterns of job career such as‘continuous pattern’,‘discontinuous pattern’,‘non-economic activity pattern’,‘marriage leave pattern’result a significant difference in social and demographic variables. Second, this research analyzes the effect of ordering and timing of life events on women's work transition. This research investigates labor market dynamics to conceptualize labor market behaviors using longitudinal data and sequence analysis and event history analysis. We find that four patterns of job career vary by age, educational attainment, having a certificate or not, their parents’human capital and health status. And we find that the ordering and timing of‘participation in labor market’and‘marriage’determine the pattern of women's work transition.

• Journal of the Korean association of regional geographers
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• v.13 no.6
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• pp.623-638
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• 2007

This paper debates on two different theoretical positions in explaining corporate adaptation. Until the 1980s, a restructuring perspective had dominated in explaining corporate success and adaptation. However, this perspective pays little attention to how firms adapt to environmental change and why some firms adapt successfully, while some others fail to adapt. Thus a restructuring perspective does not give insights into a context-specific explanation of corporate learning and adaptation. More recently, especially since the 1990s, academic focus on corporate adaptation and evolution has shifted towards exploring the nature of learning that leads to the dynamic competitiveness. A learning perspective emphasizes the influence of knowledge, learning and competence on corporate evolution. However, it reveals that this view is also less appropriate for explaining corporate adaptation in radical shifts in environment. In this context, the evolutionary theories of the firm need to seek to maintain a balance between two theoretical positions in order to understand more effectively the dynamic evolution and adaptation of the firm. This paper shows that the dynamics of corporate adaptation and evolution are an outcome of the mixture of perpetual processes of restructuring and learning, both continuous and discontinuous.