• 에너지공학
• /
• 제24권3호
• /
• pp.109-114
• /
• 2015

배열회수 보일러의 전열관군은 외부에 고온의 배기가스가 흐르면서 유동 유발 진동을 야기 시키며 배열회수 보일러의 전열관군에서 파손을 야기할 수 있어서 열교환기의 구조적 안정성을 위해 열교환기의 전열관군에서 유동 유발 진동 특성을 규명할 필요가 있다. 일반적인 열교환기 전열관군에서 유동 유발 진동에 관한 실험적 연구는 기존에 많이 진행되어 오고 있으며 유동 유발 진동에 대한 무차원 PSD(Power Spectral Density) 함수를 무차원 주파수인 Strouhal 수, fU/U의 함수로 도출된 실험적 결과들이 도출되어 있다. 본 연구는 열교환기 전열관군에서 유동 유발 진동에 관한 기존의 연구들의 결과를 전산유체해석을 통해 검증하고 배열회수 보일러의 전열관군의 유동 유발 진동 특성에 적용하기 위한 기반을 마련하는 것을 목적으로 한다. 이러한 것을 위해 단일 원관에서 비정상 상태 유동해석을 수행하여 주기적인 와동 발생 특성과 원관에서의 양력 변화 특성을 살펴보았다. 또한 원관에서 양력 변동 특성으로부터 유동 유발 진동에 따른 PSD 특성 결과를 도출하여 기존의 연구들과 비교를 통해 원관 주위의 PSD 특성을 정립하였다.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2009년 춘계학술대회논문집
• /
• pp.19-19
• /
• 2009

Dynamic Stall is a flow phenomenon which occurs on the retreating side of helicopter rotor blades during forward flight. It also occurs on blades of stall regulated wind turbines under yawing conditions as well as during gust loads. Time scales occurring during this process are comparable on both helicopter and wind turbine blades. Dynamic Stall limits the speed of the helicopter and its manoeuvrability and limits the amount of power production of wind turbines. Extensive numerical as well as experimental investigations have been carried out recently to get detailed insight into the very complex flow structures of the Dynamic Stall process. Numerical codes have to be based on the full equations, i.e. the Navier-Stokes equations to cover the scope of the problems involved: Time dependent flow, unsteady flow separation, vortex development and shedding, compressibility effects, turbulence, transition and 3D-effects, etc. have to be taken into account. In addition to the numerical treatment of the Dynamic Stall problem suitable wind tunnel experiments are inevitable. Comparisons of experimental data with calculated results show us the state of the art and validity of the CFD-codes and the necessity to further improve calculation procedures. In the present paper the phenomenon of Dynamic Stall will be discussed first. This discussion is followed by comparisons of some recently obtained experimental and numerical results for an oscillating helicopter airfoil under Dynamic Stall conditions. From the knowledge base of the Dynamic Stall Problems, the next step can be envisaged: to control Dynamic Stall. The present discussion will address two different Dynamic Stall control methodologies: the Nose-Droop concept and the application of Leading Edge Vortex Generators (LEVoG's) as examples of active and passive control devices. It will be shown that experimental results are available but CFD-data are only of limited comparison. A lot of future work has to be done in CFD-code development to fill this gap. Here mainly 3D-effects as well as improvements of both turbulence and transition modelling are of major concern.

• Smart Structures and Systems
• /
• 제25권1호
• /
• pp.81-96
• /
• 2020

Wind measurements were made on the Canton Tower at a height of 461 m above ground during the Typhoon Vincente, the wind-induced accelerations and displacements of the tower were recorded as well. Comparisons of measured wind parameters at upper level of atmospheric boundary layer with those adopted in wind tunnel testing were presented. The measured turbulence intensity can be smaller than the design value, indicating that the wind tunnel testing may underestimate the crosswind structural responses for certain lock-in velocity range of vortex shedding. Analyses of peak factors and power spectral density for acceleration response shows that the crosswind responses are a combination of gust-induced buffeting and vortex-induced vibrations in the certain range of wind directions. The identified modal frequencies and mode shapes from acceleration data are found to be in good agreement with existing experimental results and the prediction from the finite element model. The damping ratios increase with amplitude of vibration or equivalently wind velocity which may be attributed to aerodynamic damping. In addition, the natural frequencies determined from the measured displacement are very close to those determined from the acceleration data for the first two modes. Finally, the relation between displacement responses and wind speed/direction was investigated.

• Wind and Structures
• /
• 제34권1호
• /
• pp.81-90
• /
• 2022

To better understand the vortex-induced vibration (VIV) characteristics of a 5:1 rectangular cylinder, the distribution of aerodynamic force and the non-dimensional power spectral density (PSD) of fluctuating pressure on the side surface were studied in different VIV development stages, and their differences in the stationary state and vibration stages were analyzed. The spanwise and streamwise correlations of surface pressures were studied, and the flow field structure partitions on the side surface were defined based on the streamwise correlation analysis. The results show that the variation tendencies of mean and root mean square (RMS) pressure coefficients are similar in different VIV development stages. The RMS values during amplitude growth are larger than those at peak amplitude, and the smallest RMS values are observed in the stationary state. The spanwise correlation coefficients of aerodynamic lifts increase with increase of the peak amplitude. However, for the lock-in region, the maximum spanwise correlation coefficient for aerodynamic lifts occurs in the VIV rising stage rather than in the peak amplitude stage, probably due to the interaction of vortex shedding force (VSF) and self-excited force (SEF). The streamwise correlation results show that the demarcation point positions between the recirculation region and the main vortex region remain almost constant in different VIV development stages, and the reattachment points gradually move to the tailing edge with increasing amplitude. This study provides a reference to estimate the demarcation point and reattachment point positions through streamwise correlation and phase angle analysis from wind tunnel tests.

• Geomechanics and Engineering
• /
• 제35권5호
• /
• pp.487-497
• /
• 2023

Penetration rate (PR) and penetration depth (Pe) are crucial parameters for estimating the cost and time required in tunnel construction using tunnel boring machines (TBMs). This study focuses on investigating the impact of rock strength on PR and Pe through full-scale experiments. By conducting controlled tests on rock-like specimens, the study aims to understand the contributions of various ground parameters and machine-operating conditions to TBM excavation performance. An earth pressure balanced (EPB) TBM with a sectional diameter of 3.54 m was utilized in the experiments. The TBM excavated rocklike specimens with varying uniaxial compressive strength (UCS), while the thrust and cutterhead rotational speed were controlled. The results highlight the significance of the interplay between thrust, cutterhead speed, and rock strength (UCS) in determining Pe. In high UCS conditions exceeding 70 MPa, thrust plays a vital role in enhancing Pe as hard rock requires a greater thrust force for excavation. Conversely, in medium-to-low UCS conditions less than 50 MPa, thrust has a weak relationship with Pe, and Pe becomes directly proportional to the cutterhead rotational speed. Furthermore, a strong correlation was observed between Pe and cutterhead torque with a determination coefficient of 0.84. Based on these findings, a predictive model for Pe is proposed, incorporating thrust, TBM diameter, number of disc cutters, and UCS. This model offers a practical tool for estimating Pe in different excavation scenarios. The study presents unprecedented full-scale TBM excavation results, with well-controlled experiments, shedding light on the interplay between rock strength, TBM operational variables, and excavation performance. These insights are valuable for optimizing TBM excavation in grounds with varying strengths and operational conditions.

• 한국응용과학기술학회지
• /
• 제40권6호
• /
• pp.1340-1349
• /
• 2023

Despite its profound impact on athletic performance, the significance of heart rate recovery (HRR) has been insufficiently addressed in the filed of sports science, particularly in the context of weightlifting characterized by brief and intense exertions involving heavy weights. Serving as a valuable indicator of autonomic nervous system and cardiovascular function, HRR assumes a pivotal role in weightlifting. This comprehensive review aims to delineate the specific demands for HRR in weightlifting, shedding light on the often overlooked cardiovascular considerations within training regimes focused on strength and power. The investigation scrutinizes the repercussions of HRR on weightlifting performance, seeking to elucidate how inadequate recovery intervals may result in physiological and psychological consequences. These consequences encompass a distorted perception of effort, disruption of coordination, compromised posture due to irregular breathing, and an overall decline in lifting capacity. The review systematically presents compelling evidence pertaining to heart rate response and recovery patterns during weightlifting, underscoring the critical importance of well-structured rest periods. Furthermore, the review delves into a comprehensive discussion of factors influencing HRR in weightlifting, encompassing variables such as sex, age, cardiovascular function, hydration, nutrition, and psychological aspects. Finally, a key emphasis is placed on the integration of effective HRR techniques into the training regimens of weightlifters, thereby ensuring sustained and optimized performance outcomes.

• 한국산학기술학회논문지
• /
• 제21권4호
• /
• pp.446-451
• /
• 2020

전열관군으로 이루어진 열교환기에서 유동에 따른 진동은 전열 관군 배관의 파손을 유발할 수 있어서 열교환기에서 유동 유발 진동 특성을 규명할 필요가 있다. 본 연구는 전열 관군의 원관에서 입구의 유속이 일정한 경우와 주기적인 변동이 있는 경우에 대하여 시간에 따라 전열 관군 원관 1, 10 그리고 마지막 19번 원관에서 와류의 시간 변동 특성을 살펴보고 양력의 시간 변화 특성과 PSD 특성을 분석하여 전열 관군 원관에서 전방류의 주기적인 속도 변동에 따른 유동 특성을 규명하였다. 일정 입구 유속의 경우는 칼만 와류가 후류에 있는 원관의 유동에 영향을 미치고 있고 후류의 전열관군과 전방의 전열관군에서의 와류는 다소 시간적인 차이를 보여주지만 같은 주기의 칼만 와류를 발생하고 있음을 관찰할 수 있었다. 주기적인 입구 유속의 경우는 전열 관군에서 와류가 강한 유동이 흐르다가 유속이 줄어들 때는 와류가 약한 유동이 흐르는 것이 반복됨을 알 수 있다. 일정 입구 유속의 경우는 양력의 PSD로 살펴본 결과 주파수는 37.25Hz이며 19번 원관의 경우는 18.63Hz와 50Hz 근방에서 주파수가 관찰 되었다. 주기적인 입구 유속의 경우는 37.25Hz와 속도 주기인 18.63Hz에서 주된 주파수 특성을 보여주었다. 마지막 원관인 19번 원관은 20Hz에서 50Hz 사이에서 많은 피크 주파수를 관찰할 수 있었다.

• 한국지역지리학회지
• /
• 제23권2호
• /
• pp.239-256
• /
• 2017

본 연구는 지난 16년간(1997~2013) 우리나라 지역 테크노파크 기능의 변화과정을 역사적 제도주의 시각에서 분석함으로써 지역산업정책에 대한 정책적 함의를 도출하고자 하였다. 중앙정부 행위자와 지역 행위자 간 영향력의 정도를 분석하기 위하여 대구와 경북 테크노파크를 중심으로 사례연구를 하였다. 분석결과 지역 테크노파크의 기능은 크게 3단계의 변화과정을 경험하였다. 초기 지역 테크노파크의 6대 기능은 중앙정부의 기획에 의하여 확정되었으며, 참여정부에서는 6대 기능에 지역혁신사업의 거점기관이라는 기능이 추가되었고, 이후 이명박 정부에서는 중소기업 지원의 종합 창구로 발전시키는데 중점을 두었다. 지역 테크노파크의 변화과정에서 포착되는 특징은 첫째, 테크노파크가 태동하던 시기에 형성된 중앙정부와 지역 행위자 상호관계가 그 이후에도 지속되는 경로의존적 속성이 발견되었다. 둘째는 지역 테크노파크 기능이라는 '제도' 자체에서 가겹(layering)과 재정향(reorientation) 현상이 발견되었다. 셋째는 중앙정부 행위자의 강한 영향력에도 불구하고 지역에 내재한 환경적 특수성이 지역 간 기능의 차별화를 초래하였다는 것이다. 이러한 결론을 바탕으로 향후 지역 테크노파크 관련 정책은 중앙정부와 지역 행위자 간 이미 형성된 관계의 경로의존을 탈피(path breaking)하는 것이 필요하다는 시사점을 도출하였다.

• 시스템엔지니어링학술지
• /
• 제20권spc1호
• /
• pp.12-29
• /
• 2024

The purpose of this study is to identify the social issues discussed in Korea regarding Maritime Autonomous Surface Ships (MASS), the most advanced ICT field in the shipbuilding industry, and to suggest policy implications. In recent years, it has become important to reflect social issues of public interest in the policymaking process. For this reason, an increasing number of studies use media data and social media to identify public opinion. In this study, we collected 2,843 domestic media articles related to MASS from 2017 to 2022, when MASS was officially discussed at the International Maritime Organization, and analyzed them using text mining techniques. Through term frequency-inverse document frequency (TF-IDF) analysis, major keywords such as 'shipbuilding,' 'shipping,' 'US,' and 'HD Hyundai' were derived. For LDA topic modeling, we selected eight topics with the highest coherence score (-2.2) and analyzed the main news for each topic. According to the combined analysis of five years, the topics '1. Technology integration of the shipbuilding industry' and '3. Shipping industry in the post-COVID-19 era' received the most media attention, each accounting for 16%. Conversely, the topic '5. MASS pilotage areas' received the least media attention, accounting for 8 percent. Based on the results of the study, the implications for policy, society, and international security are as follows. First, from a policy perspective, the government should consider the current situation of each industry sector and introduce MASS in stages and carefully, as they will affect the shipbuilding, port, and shipping industries, and a radical introduction may cause various adverse effects. Second, from a social perspective, while the positive aspects of MASS are often reported, there are also negative issues such as cybersecurity issues and the loss of seafarer jobs, which require institutional development and strategic commercialization timing. Third, from a security perspective, MASS are expected to change the paradigm of future maritime warfare, and South Korea is promoting the construction of a maritime unmanned system-based power, but it emphasizes the need for a clear plan and military leadership to secure and develop the technology. This study has academic and policy implications by shedding light on the multidimensional political and social issues of MASS through news data analysis, and suggesting implications from national, regional, strategic, and security perspectives beyond legal and institutional discussions.

• 분석과 대안
• /
• 제6권1호
• /
• pp.115-162
• /
• 2022

2021년 8차 당대회에서 개정된 조선노동당 규약은 김정은 정권의 북한의 사회주의·공산주의에 대한 이데올로기 규정변화, 새로운 전략적 노선 및 최근 정세변화를 반영하는 한편, 중앙과 지방을 포괄하는 당 조직체계 상 주요 변화를 포괄한다. 본 연구는 9차례 개정된 조선노동당 규약 전체를 대상으로, 2021년 1월 개정 당규약이 명시한 '당중앙의 유일적 영도체계'의 조직적 변화를 분석함으로써 김정은 정권의 권력구조, 즉 수령제 및 당·정·군관계를 평가한다. 2010년 3차 당대표자회 후계구도를 거쳐 2012년 4차 당대표자회 이후 공식출범한 김정은 정권은 2022년 4월 집권 10년을 앞두고 당 수반이자 국가 수반인 김정은을 중심으로 한 유일영도체계를 제도화하고 새로운 당·정·군 조직 재편을 통해 일원적 지도·집행체계를 확립했다. '당중앙의 유일적 영도체계'는 당 수반-총비서의 당중앙위원회 기구를 통한 '조직영도'의 체계로 구축되며 김정은 시대 당-국가체제의 제도화와 일원화를 동시에 보여준다. 이러한 조직적 개편은 2020년 코로나19 팬데믹 이후 '삼중고'를 겪고 있는 김정은 시대 북한의 위기관리체제 확립의 특성을 보이며 향후 김정은 정권의 통치구조를 이해, 전망하는 데 중요한 함의를 가진다.