作为片断的系统,作为系统的片断——曹敏硕和MASS STUDIES事务所的建筑语汇

<正>我们如何构建高密度建筑的理论?社区的概念能否与这种大都市建筑契合?亦即,当建筑周边土地价格和空间成本十分高昂,以至于在某种程度上可以说每一寸土地都在为资本主义服务的时候,应该如何实现建筑和社区的概念?这些问题当然不甚鲜见。在战后美国、欧洲和日本经济扩张的背景下,路易·康、十人小组、阿     

Reliability-based design optimization of axial compressor using uncertainty model for stall margin

Reliability-based design optimization (RBDO) of the NASA stage 37 axial compressor is performed using an uncertainty model for stall margin in order to guarantee stable operation of the compressor. The main characteristics of RBDO for the axial compressor are summarized as follows: First, the values of mass flow rate and pressure ratio in stall margin calculation are defined as statistical models with normal distribution for consideration of the uncertainty in stall margin. Second, Monte Carlo Simulation is used in the RBDO process to calculate failure probability of stall margin accurately. Third, an approximation model that is constructed by an artificial neural network is adopted to reduce the time cost of RBDO. The present method is applied to the NASA stage 37 compressor to improve the reliability of stall margin with both maximized efficiency and minimized weight. The RBDO result is compared with the deterministic optimization (DO) result which does not include an uncertainty model. In the DO case, stall margin is slightly higher than the reference value of the required constraint, but the probability of stall is 43%. This is unacceptable risk for an aircraft engine, which requires absolutely stable operation in flight. However, stall margin obtained in RBDO is 2.7% higher than the reference value, and the probability of success increases to 95% with the improved efficiency and weight. Therefore, RBDO of the axial compressor for aircraft engine can be a reliable design optimization method through consideration of unexpected disturbance of the flow conditions.     

Inter-laboratory correlation exercise on a light-duty diesel passenger vehicle to verify nano-particle emission characteristics by Korea particle measurement program

The Light Duty Inter-Laboratory Correlation Exercise (ILCE) final report, performed with the ‘PMP Golden Vehicle’ at nine laboratories in the EU, Korea and Japan to demonstrate repeatability and reproducibility of the particle number concentration emissions measurement techniques proposed by the Particle Measurement Program (PMP), was released in 2007. The ILCE was conducted by the Korea Particle Measurement Program (KPMP) with a domestic diesel passenger vehicle equipped with a diesel particulate filter (DPF) between three certification laboratories and the research center of an automotive manufacturer to meet future regulations (EURO 5 and EURO 6) of particle number concentration for light-duty vehicles in early 2008. This research focused on measuring the particulate matter emission (particle number and mass) levels of a representative light-duty diesel passenger vehicle during new European driving cycle (NEDC) mode to analyze the repeatability and reproducibility between laboratories in Korea. From the ILCE test results in Korea, the mean total particle number concentration levels ranged from 5.43E+10 #/km to 1.58E+11 #/km and 0.0003 g/km to 0.0036 g/km for particle mass. Repeatability between participating laboratories ranged from 32% to 66% for particle number, 11% to 70% for particle mass; the reproducibility level was 46% for particle number, and 66% for particle mass emission. This paper was recommended for publication in revised form by Associate Editor Kyoung Doug Min Simsoo Park received his B.S. and M.S. degrees from Seoul National University in 1997 and 1979, respectively, and a Ph.D. from the State University of New York at Stony Brook. He served as a Chief Research Engineer at Hyundai Motor Company, a Director for Publication of the KSME, a Technical Advisor of Hyundai-Kia Motor Company, and an Editing Director, Project Director, International Director, Accounting Director, and General Affair Director of KSAE. He is currently Vice President and of Editor-in-Chief of IJAT at KSAE and a professor in school of mechanical engineering at Korea University.     

High-throughput preparation of complex multi-scale patterns from block copolymer/homopolymer blend films

A simple, straightforward process for fabricating multi-scale micro- and nanostructured patterns from polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP)/poly(methyl methacrylate) (PMMA) homopolymer in a preferential solvent for PS and PMMA is demonstrated. When the PS-b-P2VP/PMMA blend films were spin-coated onto a silicon wafer, PS-b-P2VP micellar arrays consisting of a PS corona and a P2VP core were formed, while the PMMA macrodomains were isolated, due to the macrophase separation caused by the incompatibility between block copolymer micelles and PMMA homopolymer during the spin-coating process. With an increase of PMMA composition, the size of PMMA macrodomains increased. Moreover, the P2VP blocks have a strong interaction with a native oxide of the surface of the silicon wafer, so that the P2VP wetting layer was first formed during spin-coating, and PS nanoclusters were observed on the PMMA macrodomains beneath. Whereas when a silicon surface was modified with a PS brush layer, the PS nanoclusters underlying PMMA domains were not formed. The multi-scale patterns prepared from copolymer micelle/homopolymer blend films are used as templates for the fabrication of gold nanoparticle arrays by incorporating the gold precursor into the P2VP chains. The combination of nanostructures prepared from block copolymer micellar arrays and macrostructures induced by incompatibility between the copolymer and the homopolymer leads to the formation of complex, multi-scale surface patterns by a simple casting process.     

A study on the characteristics of spray and combustion in a HCCI engine according to various injection angles and timings

Premixed diesel engines have the potential to achieve a more homogeneous, leaner mixture near TDC compared to conventional diesel engines. Early studies have shown that the fuel injection timing and injection angle affect the mixture formation in a HCCI (Homogeneous Charge Compression Ignition) engine. Therefore in this study, we investigated the relationship between combustion and mixture formations accordance with injection conditions in a common rail direct injection type HCCI engine using an early injection strategy. From this results, we found that the fuel injection timing and injection angle affect the mixture formation and in turn affect combustion in the HCCI engine. In addition, this study revealed that the injection angle of 100° is effective to reduce smoke emission without any sacrificing power in the early injection case.     

Time-resolved particle emission and size distribution characteristics during dynamic engine operation conditions with ethanol-blended fuels

The effect of ethanol-blended gasoline fuels on the characteristics of time-resolved particle concentration and size distribution was investigated in a gasoline engine and in a flexible fuel vehicle. Particle concentration levels from the vehicle running on ethanol-blended gasoline were compared to those of diesel vehicles with and without diesel particulate filter (DPF). In the engine test, particle size distribution and number concentration using E0 and E10 fuels were analyzed with a differential mobility spectrometer (DMS500) at dynamic engine operation conditions. In the vehicle emission test, time-resolved particle concentrations with ethanol blending contents (E0, E10, and E85) during a new European driving cycle (NEDC) were analyzed with a golden particle measurement system (GPMS) as recommended by the particle measurement programme (PMP). As the excess air ratio is shifted to lean conditions and as the spark and intake valve opening timing are retarded, particle number levels were reduced with both E0 and E10. The particle concentration from ethanol-blended gasoline was slightly decreased regardless of engine operating conditions. From the driving test results, the total particle concentration from the spark ignition and the diesel vehicle with a DPF was decreased by two orders of magnitude compared to a non-DPF diesel vehicle. As the oxygenated component is increased, particle emissions decreased. The total particle concentration for E85 was reduced by 37% compared to E0.     

Continuum-based modeling of collective cell migration

Journal of Mechanical Science and Technology - In this paper, we present a computationally efficient cellular mathematical model that accounts for the boundary collective behavior of a cell group...     

Reliability based optimal design of a helicopter considering annual variation of atmospheric temperature

This study presents the Reliability Based Design Optimization (RBDO) of a helicopter, used in order to guarantee target performances for a large variation of annual atmospheric temperatures. To this end, analytic methods — statistical and empirical equations of aerodynamics, structure, propulsion and so on — are synthetically coupled within the multidisciplinary design analysis tool of the conceptual helicopter. Additionally, an atmospheric temperature model for annual air temperature variation is constructed in bimodal shape by considering 10 years worth of day-averaged air temperature data provided by the Korea Meteorological Administration. Based on this analysis tool and the annual atmospheric temperature model, the RBDO of a helicopter is performed to minimize maximum takeoff gross weight, with the helicopter rotor configuration parameters as a design variable. A Monte-Carlo simulation is used to accurately evaluate the reliabilities of endurance and range. This RBDO strategy is applied to a 22,000lb class medium utility helicopter, and the results are compared with those of a deterministic design optimization (DO) using constant air temperature and baseline helicopter. Through comparison of the results obtained from RBDO and those from the deterministic design optimization, it can be confirmed that the optimal design of RBDO results in greater improvements in performance over the baseline, for a wide range of operating air temperatures, than baseline helicopter and optimal shape of DO using constant air temperature. Therefore, in designing a helicopter to be operated in temperate climatic regions that show large variation in air temperature, such as Korea, China, the U.S.A, and so on, it is important to perform RBDO with reasonable annual air temperature models constructed from well-known and reliable data.     

Combustion and emission characteristics of a dual injection system applied to a DISI engine

Concerns about environmental pollution and energy shortages have increased worldwide. One approach to reduce CO2 emissions from gasoline engines is to achieve stratified charge combustion with various injection ratios using port fuel injection （PFI） and direct injection. The combustion and emission characteristics of a 4-valve direct injection spark ignition （DISI） engine equipped with a dual injection system were investigated while the injection ratio was varied. When the direct injection ratio increased, the lean limit A/F was extended. This suggests that the dual injection gasoline engine with both PFI and direct injection can meet severe vehicle emission and fuel economy requirements. The dual injection system had higher combustion pressure than that of either a conventional or direct injection systems. Therefore, the engine power of a dual injection DISI engine would be higher than that of a single injection DISI engine. However, NOx emissions increased compared with the emission levels in both PFI and DISI systems.