• 대한전자공학회논문지TC
• /
• 제44권4호
• /
• pp.65-71
• /
• 2007

Doherty 전력증폭기는 일반전력증폭기보다 효율은 뛰어나지만 많은 왜곡성분이 발생한다. 이러한 왜곡성분은 일반적인 진폭왜곡과 위상왜곡, 그리고 메모리 효과에 의한 왜곡성분으로 구분할 수 있다. 본 논문에서는 전기적인 비선형성을 정확히 모델링하고 열 메모리 효과가 Doherty 증폭기에 미치는 영향을 연구함으로써, 전치왜곡기에 적용할 수 있는 열 메모리 효과 보상기를 제안하였다. Doherty 증폭기의 열 메모리 특성을 모델링하기 위하여 순시적으로 소모되는 전력과 순시 접합온도의 정확한 관계식을 정립하여 제안하였다. 제안된 모델의 파라미터는 전치왜곡기를 사용한 Doherty 증폭기의 열 메모리효과를 효율적으로 억제한다. 이러한 열 메모리 보상기를 가진 전치왜곡기는 선형화된 전력증폭기의 출력스펙트럼에서 약 22 dB정도의 ACLR 개선효과를 보인다. 측정결과는 50W급 LDMOS Doherty 전력증폭기로 측정하였으며, 열 메모리 보상기를 가진 전치왜곡기는 ADS로 검증하였다.

• 한국유체기계학회 논문집
• /
• 제14권5호
• /
• pp.18-23
• /
• 2011

A CFD analysis method is developed and applied for investigating the gas flow and the byproduct particle trajectory in Roots type vacuum pump. The internal fluid flow and thermal fields between the rotors and the housing of vacuum pump are analyzed by using the dynamic mesh, the numerical methods for unsteady 2-D Navier-Stokes equation and the standard k-$\varepsilon$ turbulence model of the Fluent code. Coupled with the flow simulation results, the particle trajectory of the byproduct flowing into the pump with gas stream is analyzed by using discrete phase modeling technique. The CFD analysis results show the pressure, the velocity and the temperature distributions in pump change abruptly due to the rotation of rotors, and back flows are produced due to the strong reverse pressure gradients at rotor/rotor and rotor/housing clearances. The predicted byproduct particle trajectory results also show the particles impinge on the clearance surfaces between the housing and the rotor of pump and then may form the deposit layer causing the failure of pump.

• 한국물환경학회지
• /
• 제24권3호
• /
• pp.365-377
• /
• 2008

Large artificial dam reservoirs and associated downstream ecosystems are under increased pressure from long-term negative impacts of turbid flood runoff. Despite various emerging issues of reservoir turbidity flow, turbidity modeling studies have been rare due to lack of experimental data that can support scientific interpretation. Modeling suspended sediment (SS) dynamics, and therefore turbidity ($C_T$), requires provision of constitutive relationships ($SS-C_T$) and accounting for deposition of different SS size fractions/types distribution in order to display this complicated dynamic behavior. This study explored the performance of a coupled two-dimensional (2D) hydrodynamic and particle dynamics model that simulates the fate and transport of a turbid density flow in a negatively buoyant density flow regime. Multiple groups of suspended sediment (SS), classified by the particle size and their site-specific $SS-C_T$ relationships, were used for the conversion between field measurements ($C_T$) and model state variables (SS). The 2D model showed, in overall, good performance in reproducing the reservoir thermal structure, flood propagation dynamics and the magnitude and distribution of turbidity in the stratified reservoir. Some significant errors were noticed in the transitional zone due to the inherent lateral averaging assumption of the 2D hydrodynamic model, and in the lacustrine zone possibly due to long-term decay of particulate organic matters induced during flood runoffs.

• Journal of Information Processing Systems
• /
• 제15권4호
• /
• pp.717-723
• /
• 2019

Smart systems and services aim to facilitate growing urban populations and their prospects of virtual-real social behaviors, gig economies, factory automation, knowledge-based workforce, integrated societies, modern living, among many more. To satisfy these objectives, smart systems and services must comprises of a complex set of features such as security, ease of use and user friendliness, manageability, scalability, adaptivity, intelligent behavior, and personalization. Recently, artificial intelligence (AI) is realized as a data-driven technology to provide an efficient knowledge representation, semantic modeling, and can support a cognitive behavior aspect of the system. In this paper, an integration of AI with the smart systems and services is presented to mitigate the existing challenges. Several novel researches work in terms of frameworks, architectures, paradigms, and algorithms are discussed to provide possible solutions against the existing challenges in the AI-based smart systems and services. Such novel research works involve efficient shape image retrieval, speech signal processing, dynamic thermal rating, advanced persistent threat tactics, user authentication, and so on.

• Structural Engineering and Mechanics
• /
• 제4권2호
• /
• pp.111-124
• /
• 1996

New active "intelligent" structural systems with integrated self-sensing, diagnosis, and control capabilities can lead to a new design dimension for the next generation high-performance structures and mechanical systems. However, temperature effects to the piezoelectric transducers are not fully understood. This paper is concerned with a mathematical modeling and analysis of a laminated piezothermoelastic cylindrical shell composite exposed to mechanical, electric, and thermal fields. Generic shell equations and solution procedures are derived. Contributions of spatial and time components in the mechanical, electric, and temperature excitations are discussed, and their analytical solutions derived. A laminated cylindrical shell composite with fully distributed piezoelectric layers is used in a case study; its multi-field step and impulse responses are investigated. Analyses suggest that the fully distributed actuators are insensitive to even modes due to load averaging and cancellation. Accordingly, these even modes are filtered from the total response and only the modes that are combinations of m = 1, 3, 5, ${\cdots}$ and n = 1, 3, 5, ${\cdots}$ participating in dynamic response of the shell.

• Journal of Advanced Research in Ocean Engineering
• /
• 제3권3호
• /
• pp.112-124
• /
• 2017

As an LNG carrier preserves and transports liquefied natural gas under minus $163^{\circ}C$, the cargo tank has to have sufficient hull strength against not only the wave loads but also against loads caused by loading and unloading and thermal expansion to keep the LNG safely. The main insulation types for a CCS are No.96 and Mark III from GTT for the membrane LNG carrier. Particularly, the invar membrane plate in No.96 is very thin and its connections could experience high local stresses owing to such dynamic loads. Therefore, it should be verified whether those connections have sufficient fatigue lives for the purpose of operation and maintenance. This research aims at performing fatigue analysis with 0.1 fatigue damage criteria for 40 years of design life to support new membrane CCS development using proper S-N curves and the associated finite element modeling technique for each connection and then propose a reasonable design methodology.

• 천문학회보
• /
• 제36권2호
• /
• pp.80.1-80.1
• /
• 2011

It is well known that chromospheric features are fine structured, short lived, and dynamic. Spectrograph-based observation have obvious advantage of getting physical properties of solar chromosphere than filter-based one. We developed and installed Fast Imaging Solar Spectrograph (FISS) attached on New Solar Telescope in Big Bear Solar Observatory. FISS have capabilities to take data with high time, spatial and spectral resolution at two wavelengths(Ha $6563{\AA}$ and CaII $8542{\AA}$) simultaneously. After FISS installation, we observed various chromospheric features : active regions, quiet regions, filaments/prominences and so on. As one of chromospheric studies, we analyzed solar prominences and got physical parameters by using simple radiative transfer modeling. The ranges of temperature and non-thermal velocities are found to be 7500-13000K and 5-11km/s, respectively.

• Advances in nano research
• /
• 제13권4호
• /
• pp.379-391
• /
• 2022

One factor that can heighten the risk of the rapture intracranial aneurysm (IA) is bifurcations, which can cause the IA to evaluate. This study presents the effect of geometric of intracranial vascular on the bifurcation analysis of the aneurysm occurrence. The aneurysm mechanism is mathematically modeled based on the nano pipe structures under the thermal stresses, and the impact of the aneurysm geometric on the stability and bifurcation points is analyzed. Because of the dimension of these structures, the classical theories could not predict their behavior perfectly, so the nonclassical and nonlocal theories are required for the mechanical modeling of the aneurysm. The presented results show that the bifurcation point of the aneurysm mechanism is dependent on the environment temperature, and the temperature change plays an essential role in the stability of these structures.

• 대한기계학회논문집
• /
• 제19권1호
• /
• pp.292-300
• /
• 1995

According to the number of cold-rolled coils, the amount of roll wear and thermal expansion, and roll gap profile were calculated, by using the actual data from the finishing mill. Also, based on those data, the calculations of the deflection, the flattening, and the contact pressure of vwork rolls and backup rolls were made respectively. Specially, in the calculation of contact pressure, the numerical results were obtained not only during the normal rolling, but also during the abnormal rolling, by modeling mathematically the dynamic impact force which occurs when the head section of the strip is threading through rolls. With those results the growth of the fatigue region and the fatigue damage of rolls were predicted. Also the optimum roll-grinding depth was determined to maximize the roll life.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2011년도 제42회 하계학술대회
• /
• pp.1804-1805
• /
• 2011

In recent year there has been an increasing interest in the dynamic simulation of complex systems. This study uses a large-scale forty-seventh order fossil fuel power plant. Twenty-three state variables are associated with the physical processes and twenty-four state variables associated with the control system. The plant model is expected to predict all dominant effects in a steady and transient state. In this study, the power plant model is reorganized into four subsystems, each with its controller, and the four connected to each other through a manager, which is a fifth part to the system. The four parts of the unit are the boiler system, steam turbine system, condenser system, and feedwater system.