• 한국환경과학회지
• /
• 제3권3호
• /
• pp.285-296
• /
• 1994

The objective of this study was to examine and compare to transient response to quantitative and hydraulic shocks which produce equal changes in mass rate of organic feed in aerobic fixed-film process. The general experimental approach was to operate the system at several growth rates under steady-state(pre-shock) conditions, then to apply step changes during day 3 in dilution rate(hydraulic shock) , or feed concentration(Quantitative shock) at the same organic mass loading rate. Performance was assessed in both the transient state and the new steady-state (post- shock). Shock load of different type did not produced equivalent disruptions of effluent quality for equal increases in mass loading rate. Based on effluent concentrations, a hydraulic and a Quantitative shock at the same mass loading caused equal increase in total effluent COD, but the increase was primarily a result of suspended solids the hydraulic shock and COD in the quantitative shock. The time which effluent COD came to peak values were about 32~48 hours at the low organic loads and 52 ~ 72 hours at the high organic loads, respectively A quantitative shock produced a much greater increase in effluent COD than did a hydraulic shock at the same mass loading. Mean and peak values of effluent concentration weve increased in 2.8~4.2 times at low organic loading rate, 5.2~6.6 times at the high organic loading rate, respectively. Key words : Aerobic fixed-film reactor, Quantitative shock, hydraulic shock, mass loading rate.

• Structural Engineering and Mechanics
• /
• 제78권4호
• /
• pp.473-484
• /
• 2021

Similar to other structures, ultimate strength values showing the maximum load that the structure can resist without damaging has great importance on ships. Therefore, increasing the ultimate strength values will be an important benefit for the structure. Low carbon steels used in ships due to their low cost and good weldability. Improving the ultimate strength values without interfering with the chemical composition to prevent of the weldability properties of these steels would be very beneficial for ships. Grain refinement via severe plastic deformation (SPD) is an essential strengthening mechanism without changing the chemical composition of metallic materials. Among SPD methods, equal channel angular pressing (ECAP) is one of the most commonly used one due to its capacity for achieving bulk ultrafine-grained (UFG) materials. When the literature is examined, it is seen that there is no study about ultimate strength calculation in ships after ECAP. Therefore, the mean purpose of this study is to apply ECAP to a shipbuilding low carbon steel to be able to achieve mechanical properties and investigate the alteration of ship hull girder grillage system's ultimate strength via finite element analysis approach. A fine-grained (FG) microstructure with a mean grain size of 6 ㎛ (initial grain size was 25 ㎛) was after ECAP. This microstructural evolution brought about a considerable increase in strength values. Both yield and tensile strength values increased from 280 MPa and 425 MPa to about 420 MPa and 785 MPa, respectively. This improvement in the strength values reflected a finite element method to determine the ultimate strength of ship hull girder grillage system. As a result of calculations, it was reached significantly higher ultimate strength values (237,876 MPa) compared the non-processed situation (192,986 MPa) on ship hull girder grillage system.

• 산업경영시스템학회지
• /
• 제35권3호
• /
• pp.103-109
• /
• 2012

The purpose of this paper is to suggest the strategical lifting postures able to alleviate imbalanced EMG amplitude leading to an increase in low back muscle fatigue while lifting asymmetric load dynamically. Eleven male subjects are required to lift symmetrically an external load with 15.8kg and load center of gravity (LCG) deviated 10cm to the right from the floor to the waist height at the speed of about 25cm/sec. The EMG amplitudes on bilateral low back muscles (Longissimus, Iliocostalis, and Multifidus) are recorded during 2sec and analyzed. Independent variables are trunk postures (No bending vs. Bending to the LCG) and feet placements (Parallel vs. Right foot in front of the other vs. Right foot behind the other). Dependent variables are EMG amplitude average on six muscles and the EMG amplitude difference between right and left muscle group. Results indicate the phenomenon showing an amplitude increase in the left muscle group is equal to an decrease in the right one is observed in dynamic as well as static lifts, bending the trunk to the LCG increases amplitude discrepancy more than no trunk bending, and the amplitude discrepancy in one foot ipsilateral to LCG in front of the other foot is lowest among other foot postures. As bilateral EMG amplitude discrepancy increases total low back muscle fatigue, the strategical combination of no trunk bending and one foot close to LCG in front of the other is recommended for preventing elevated incidence of low back pain (LBP).

• 콘크리트학회논문집
• /
• 제14권3호
• /
• pp.365-372
• /
• 2002

본 연구는 700kgf/$\textrm{cm}^2$ 고강도 콘크리트에서 횡보강근 형태, 체적비 그리고 횡보강근 항복강도에 따른 고강도 콘크리트기둥의 거동을 규명하기 위한 실험연구이다. 기둥은 중심축내력의 30%에 해당하는 일정축력과 수평방향의 반복 휨모멘트를 받는다. 본 연구에서 사용된 변수는 횡보강근 체적비(Ps=1.58, 2.25%), 횡보강근 형태(hoop-type, cross-type, diagonal-type) 그리고 횡보강근 항복강도(fy=5,600, 7,950 kgf/$\textrm{cm}^2$)이다. 실험결과로 모든 기둥의 휨강도는 현행규준의 등가응력블럭에 근거하여 산정된 휨강도보다 낮게 나타났다. 횡보강근을 ACI 규준 요구량보다 42%증가시킨 기둥 시험체는 연성적인 거동을 보였다. 그리고, 본 연구에서 적용한 축력비 0.3 P/PO하에서 고강도급 횡보강근을 사용한 시험체의 연성이 저강도급 횡보강근을 사용한 시험체의 경우보다 같거나 다소 큰 경향을 보이고 있었다.

• 한국태양에너지학회 논문집
• /
• 제32권1호
• /
• pp.15-24
• /
• 2012

IEC 61400-1 requires design lifetime of wind turbines at least 20 years, thus wind turbine should be assured for structural safety through load assessment. DLCs have been defined with respect to the load assessment in IEC 61400-1. In addition, if the extreme design values for DLC1.3 are equal or exceed the extreme design value for DLC1.1, DLC1.1 may be omitted. To omit DLC1.1, scale factor (c) will be increased in DLC1.3. However, this particular adjustment is not specified guidelines. Thus, this study was conducted. DLC1.1 was calculated for extrapolation of 50 years-extreme events using several probability distribution functions and fitting methods. And DLC1.3 was calculated for up to seven different values of scale factor (c) with $2{\leq}c{\leq}5$ in steps of 0.5. Finally, in this study, scale factor (c) that was the value of 4.51 was determined.

• Steel and Composite Structures
• /
• 제44권3호
• /
• pp.295-307
• /
• 2022

The objective of this research is to study experimentally the behavior of stiffened steel tubes (CFSTs). Considered parameters are stiffening methods by through-bolts or shear connectors with different configurations. In addition, the effect of global (ratio between length to diameter) and local (proportion between diameter to thickness) slenderness ratios are investigated. Load application either applied on steel only or both steel and concrete is studied as well. Case of loading on steel only happens when concrete inside the column shrinks. The purpose of the research is to improve the behavior of CFSTs by load transfer between them and different stiffening methods. A parametric experimental study that incorporates thirty-three specimens is carried out to highlight the impact of those parameters. Different outputs are recorded for every specimen such as load capacities, vertical deflections, longitudinal strains, and hoop strains. Two modes of failure occur, yielding and global buckling. Shear connectors and through-bolts improve the ultimate load by up to 5% for sections loaded at steel with different studied global slenderness and local slenderness equal 63.5. Meanwhile, shear connectors or through bolts increase the ultimate load by up to 6% for global slenderness up to 15.75 for sections loaded on composite with local slenderness equals 63.50. Recommendations for future design code development are outlined.

• Structural Monitoring and Maintenance
• /
• 제9권1호
• /
• pp.43-57
• /
• 2022

One of the instances which demand structural engineer's greatest attention and upgradation is the changing live load requirement in bridge design code. The challenge increases in developing countries as the pace of infrastructural growth is being catered by the respective country codes with bigger and heavier vehicles to be considered in the design. This paper presents the case study of India where Indian Roads Congress (IRC) codes in its revised version from 2014 to 2017 introduced massive Special vehicle (SV) around 40 m long and weighing 3850 kN to be considered in the design of road bridges. The code does not specify the minimum distance between successive special vehicles unlike other loading classes and hence the consequences of it form the motivation for this study. The effect of SV in comparison with Class 70R, Class AA, Class A, and Class B loading is studied based on the maximum bending moment with moving load applied in Autodesk Robot Structural Analysis. The spans considered in the analysis varied from 10 m to 1991 m corresponding to the span of Akashi Kaikyo Bridge (longest bridge span in the world). A total of 182 analyses for 7 types of vehicles (class B, class A, class 70R tracked, class 70R wheeled, class AA tracked, AA wheeled, and Special vehicle) on 26 different span lengths is carried out. The span corresponding to other vehicles which would equal the bending moment of a single SV is presented along with a comparison relative to Standard Uniformly Distributed Load. Further, the results are presented by introducing a new parameter named Intensity Factor which is proven to relate the effect of axle spacing of vehicle on the normalized bending moment developed.

• 한국정보처리학회논문지
• /
• 제1권4호
• /
• pp.427-437
• /
• 1994

스타형 컴퓨터 네트워크의 최적 부하균형 문제를 생각한다. 스타형 모델에서는 세가지 부하균형방향정책을 생각할 수 있다. 첫 번째는, 주변노드로 도착한 작업들은 자노드에서 처리되거나 자노드가 과부하인 경우 중앙노드에 보내져 처리될 수 있다. 두 번째는, 중앙노드에 도착한 작업만이 자노드에서 처리되거나 중앙노드가 과부하인 경우 저부하의 주변노드로 작업이 전송되어 처리될 수 있다. 본 연구에서는 두 번째 정책에 대하여 비선형 최적화 문제를 만들고, 최적해를 이용하여 최적 부가균형 알고 리즘을 제안한다. 세 번째는, 중앙노드 혹은 주변노드를 가리지 않고 도착한 작업들은 자노드에서 처리되거나 자노드가 과부하인 경우 저부하의 타노드로 작업이 전송되어 처리된다. 이 세 번째 부하균형 정책을 위한 부하분산 알고리즘도 제안한다. 본 논문 에서 대상으로 하고 있는 세가지 부하균형 정책을 수치실험을 통하여 비교분석 하였다. 수치실험 결과중 다음과 같은 몇 가지 재미있는 실험결과가 발견되었다. 세 번째 부하 균형 정책은 대부분의 경우 다른 두 정책보다 시스템 성능을 크게 향상시킨다. 두 번 째 부하균형 정책은 대부분의 경우 미약한 성능향상 밖에 보이지 않는다. 마지막으로 중앙노드의 처리능력이 주변노드보다 훨씬 큰 경우에는 첫 번째와 세 번째의 부하균 형 정책은 동일한 성능향상을 보인다.

• 대한치과보철학회지
• /
• 제32권2호
• /
• pp.327-353
• /
• 1994

This study was performed to evaluate the effects of number and alignment of implant fixture and various bar designs on the retention of denture and the stress distribution. Six kinds of photoelastic mandibular models and nine kinds of overdenture specimens were designed. A unilateral vertical load was gradually applied on the right first molar to calculate the maximal dislodgement load of each specimen. A unilateral vertical load of 17 Kgf was applied on the right first molar and a vertical load of 10 Kgf was applied on the interincisal edge region. The stress pattern which developed in each photoelastic model was analyzed by the reflection polariscope. The results obtained were as follows: 1. The maximal dislodgement load reversely increased with the distance from the loading point to the implant fixture, while it linearly increased with that from the most posterior implant fixture to the mesial clip. The maximal dislodgement load also increased with the use of a cantilever bar. 2. Under the posterior vertical load, the stress to the supporting tissue of the denture base increased with the distance from the loading point to the implant future. The stress concentration on the apical area of the implant future reversely increased with the distance from the loading point to the implant future. 3. In the overdentures supported by two implant fixtures under the posterior vertical load. the specimen implanted on lateral incisor areas with a cantilever bar exhibited more favorable stress distribution than that without a cantilever bar. The specimen implanted on the canine areas without a cantilever bar, however, exhibited more favorable stress distribution. 4. In the overdentures supported by three implant fixtures. the specimen implanted ell the midline and canine areas exhibited more favorable stress distribution than that implanted oil the midline and the first premolar areas. 5. In the overdentures supported by four implant fixtures. the specimen implanted with two adjacent implant fixtures exhibited more favorable stress distribution than that implanted at equal distance under the posterior vertical load. 6. Under the anterior vertical load, the overdentures supported by three implant fixtures exhibited stress concentration on the supporting structure of the middle implant future. In overdentures supported by two or four implant futures, no significant difference was noted in stress distribution between the types of bars. These results indicate that the greater the number of implant fixtures, the better the stress distribution is. A favorable stress distribution may be obtained in the overdentures supported by two or three implant fixtures, if the location and the design of the bar are appropriate.

• 조명전기설비학회논문지
• /
• 제15권6호
• /
• pp.65-72
• /
• 2001

본 논문에서는 UPS용 인버터의 강인한 디지털제어를 위하여 인버터 출력측 LC필터의 커패시터 전압과 전류의 2중 제어루프로 구성된 새로운 제어기법을 제안한다. 제안된 전압·전류의 2중 제어루프는 전압 제어루프의 커패시터 전압을 전류 제어루프의 커패시터 전류의 위상중심으로 두고, 2중 데드비트 제어를 수행함으로써 커패시터 전류의 위상지연이 보상된 완전한 진상전류 제어가 가능하게 된다. 전류 제어루프는 디지털 제어기의 시간 지연요소를 시스템의 고유한 파라미터로 가정한 2차 데드비트 제어기로 설계하여 디지털 제어기의 고유한 연산 지연시간에 의한 성능저하를 개선한다. 또한, 외란에 의한 데드비트 제어의 영향을 제거하기 위하여 부하전류 예측기법을 전류 제어루프에 부가하여 외란을 피드포워드 보상함으로써 외란에 강인한 전류제어를 수행한다.