• 무역학회지
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• 제44권2호
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• pp.127-141
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• 2019

In this study, the relationship between Baltic Dry Index(BDI) and maritime trade volume in the dry cargo market was verified using the vector autoregressive (VAR) model. Data was analyzed from 1992 to 2018 for iron ore, steam coal, coking coal, grain, and minor bulks of maritime trade volume and BDI. Granger causality analysis showed that the BDI affects the trade volume of coking coal and minor bulks but the trade volume of iron ore, steam coal and grain do not correlate with the BDI freight index. Impulse response analysis showed that the shock of BDI had the greatest impact on coking coal at the two years lag and the impact was negligible at the ten years lag. In addition, the shock of BDI on minor cargoes was strongest at the three years lag, and were negligible at the ten years lag. This study examined the relationship between maritime trade volume and BDI in the dry bulk shipping market in which uncertainty is high. As a result of this study, there is an economic aspect of sustainability that has helped the risk management of shipping companies. In addition, it is significant from an academic point of view that the long-term relationship between the two time series was analyzed through the causality test between variables. However, it is necessary to develop a forecasting model that will help decision makers in maritime markets using more sophisticated methods such as the Bayesian VAR model.

• 한국응급구조학회지
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• 제24권1호
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• pp.37-55
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• 2020

Purpose: The purpose of this study was to provide basic data for improving the response capacity of 119 EMS systems by analyzing the effects of particulate matter on cardio-cerebrovascular and respiratory symptoms in the pre-hospital stage. Methods: We examined 46,389 patients who transferred to the hospital with complaints of cardiopulmonary arrest and cardio-cerebrovascular and respiratory symptoms by 119 ambulances in Incheon from 2016 to 2018. Results: The probability of 119 emergency dispatch for patients with cardiopulmonary arrest increased 2.8-4.0% from the day of symptom onset until two days before hospital presentation as particulate matter 10㎛ or less in diameter(PM₁₀) increased by 10㎍/㎥ (OR=1.028; 95% CI=1.014-1.041, p=0.000, lag 0), (OR=1.040; 95% CI=1.024-1.056, p=0.000, lag 1), (OR=1.032; 95% CI=1.016-1.049, p=0.000, lag 2). Meanwhile, emergency dispatch increased 3.6-6.1% for PM_2.5 in creased by 10㎍/㎥ (OR=1.046; 95% CI=1.024-1.068, p=0.000, lag 0), (OR=1.061; 95% CI=1.035-1.088, p=.000, lag 1), and (OR=1.036; 95% CI=1.010-1.063, p=0.006, lag 2). Conclusion: Emergency medical technicians (EMTs) who respond to 119 calls should rapidly and accurately evaluate patients and provide professional emergency care by identifying the characteristics of the vulnerable groups relative to particulate matter size. To prevent the occurrence and exacerbation of symptoms caused by particulate matter, EMTs should be prepared and equipped with a response system for high particulate matter in the EMS system.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제20회 춘계학술대회 논문집
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• pp.253-257
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• 2003

Theoretical-numerical analysis of wave instability is conducted with parametric response function model. Fluctuating instantaneous mass evaporation rate functionally coupled with pressure perturbations with phase lag is assumed to examine the validity of the method. With sufficiently large amplitude and less phase lag to perturbation, combustion response is resonant to pressure waves, unstable waves are amplified, and the system is driven to instability. Magnitude of response is a crucial instability parameter in the determination of a stability margins and makes a critical change of balancing conditions between the amplifying and damping acoustic energies. In the phase regime the unstable waves are amplified, whereas, the acoustic waves are attenuated in the out-of-phase regime. In the intermediate regime, no distinct tendency of unstable waves was determined.

• Journal of Advanced Marine Engineering and Technology
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• 제34권7호
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• pp.951-962
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• 2010

An experimental study was performed to investigate the improvement of response performance of a turbocharged diesel engine under the operating conditions of low speed and fast acceleration. In this study, the experiment for improving the low speed and acceleration performance is performed by means of injecting air into the intake manifold of compressor exit during the period of low speed and application of a fast acceleration from low speed. The effects of air injection into the intake manifold on the response performance were investigated at various applicant parameters such as air injection pressure, accelerating rate, accelerating time, engine speed and load. The experimental results show that air injection into the intake manifold at compressor exit is closely related to the improvement of turbocharger lag under low speed and accelerating conditions of a turbocharged diesel engine. During the rapid acceleration period, the air injection into the intake manifold of turbocharged diesel engine indicates the improvement of the combustion characteristics and gas pressure in the cylinder. At low speed range of the engine, the effect of air injection shows the improvement of the pressure distribution of turbocharger and combustion pressure during the period of gas exchange pressure.

• 산업기술연구
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• 제21권B호
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• pp.273-280
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• 2001

In this study, a driver model based on the lead-lag controller for stable maneuver of a highly nonlinear, multi-dimensional, numerically stiff multibody vehicle model according to the various handling test requirements such as steady-state cornering, double lange change, etc. is presented The lead-lag controller is developed with lead and lag compensation. which use the transfer function with cross-over frequency by frequency response method. The proposed driver model is applied to a vehicle model in steady-state and slalom maneuver to verify its effectiveness and validity. The results show that the proposed path control strategy is excellent both in pursuing the desired course and stability of the vehicle.

• Structural Engineering and Mechanics
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• 제75권2호
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• pp.133-144
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• 2020

This investigation is to study the effect of gravitational field and diffusion on a microstretch thermoelastic medium heating by a non-Gaussian laser beam. The problem was studied in the context of the dual-phase-lag model. The normal mode analysis is used to solve the problem to obtain the exact expressions for the non-dimensional displacement components, the micro-rotation, the stresses, and the temperature distribution. The effect of time parameter, heat flux parameter and gravity response of three theories of thermoelasticity i.e. dual-phase-lag model (DPL), Lord and Shulman theory (L-S) and coupled theory (CT) on these quantities have been depicted graphically for a particular model.

• 한국추진공학회지
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• 제16권1호
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• pp.1-8
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• 2012

희석된 수소-공기 확산화염의 응향 응답 특성을 저압과 고압 영역에서의 화염 구조 해석을 토대로 수치적으로 조사하였다. 음향 주파수가 증가함에 따라 어느 압력 영역에서든 열방출율의 비선형 축적현상에 의해 유한 화학반응의 효과가 증진된다. 이는 결국 높은 음향 증폭으로 이어지게 된다. 동일한 계산 결과를 압력 감응 시간지연 모델에 의해 재해석하였다. 시간 지연 모델의 적절한 적용을 통해, 각 압력 영역에서 시간지연과 간섭지수 인자가 정량화되었다. 음향 증폭의 정도를 나타내는 간섭지수는 어느 압력 영역에서든 1000 Hz 근처에서 최고값을 나타내었고, 고압영역에서 화염이 더 불안정한 응답을 보였다. 음향 주파수에 따른 간섭지수의 변화 경향은 기존의 증폭지수 변화 경향과 잘 일치하였다.

• Steel and Composite Structures
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• 제45권4호
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• pp.535-546
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• 2022

The memory response of nonlocal systematical formulation size-dependent coupling of viscoelastic deformation and thermal fields for piezoelectric materials with dual-phase lag heat conduction law is constructed. The method of the matrix exponential, which constitutes the basis of the state-space approach of modern control theory, is applied to the non-dimensional equations. The resulting formulation together with the Laplace transform technique is applied to solve a problem of a semi-infinite piezoelectric rod subjected to a continuous heat flux with constant time rates. The inversion of the Laplace transforms is carried out using a numerical approach. Some comparisons of the impacts of nonlocal parameters and time-delay constants for various forms of kernel functions on thermal spreads and thermo-viscoelastic response are illustrated graphically.

• Structural Engineering and Mechanics
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• 제69권5호
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• pp.567-577
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• 2019

Guyed steel lattice towers (or guyed masts) are widely used for supporting antennas for telecommunications and broadcasting. This paper presents a numerical study on the static and dynamic response of guyed towers. Three-dimensional nonlinear finite-element models are used to simulate the response. Through performing static pushover analyses and free-vibration (modal) analyses, the effect of different bracing configurations is investigated. In addition, seismic analyses are performed on towers of different heights to study the influence of earthquake excitation time-lag (or the earthquake travel distance between tower anchors) and antenna weight on the seismic response of guyed towers. The results show that the inclusion of time lag in the seismic analysis of guyed towers can influence shear and moment distribution along the height of the mast. Moreover, it is found that the lateral response is insensitive to bracing configurations. The results also show that, depending on the mast height, an increased antenna weight can reduce the tower maximum base shear while other response quantities, such as cables tension force are found to be insensitive to variation in the antenna weight.

• Journal of Electrical Engineering and Technology
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• 제12권1호
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• pp.378-384
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• 2017

In this paper, an efficient short-time Fourier analysis method for the quasi-periodic signals is proposed via an optimal fixed-lag finite impulse response (FIR) smoother approach using a receding horizon scheme. In order to deal with time-varying Fourier coefficients (FCs) of quasi-periodic signals, a state space model including FCs as state variables is augmented with the variants of FCs. Through an optimal fixed-lag FIR smoother, FCs and their increments are estimated simultaneously and combined to produce final estimates. A lag size of the optimal fixed-lag FIR smoother is chosen to minimize the estimation error. Since the proposed estimation scheme carries out the correction process with the estimated variants of FCs, it is highly probable that the smaller estimation error is achieved compared with existing approaches not making use of such a process. It is shown through numerical simulation that the proposed scheme has better tracking ability for estimating time-varying FCs compared with existing ones.