Numerical Simulation on Variation Characteristics of Wave Field around Submerged Breakwater and Low-Crested Structure

본 연구는 2차원 혹은 3차원해역에서 규칙파 혹은 불규칙파와 흐름(조류)의 공존장에 표사제어구조물(littoral drift control structure) 혹은 해역제어구조물(offshore structure for control of wave and current)중에 대표적인 잠제(submerged breakwater)나 저천단구조물(이후 LCS로 칭함 ; Low-Crested Structure)의 설치에 따른 파고와 해빈류의 변동특성을 2차원 혹은 3차원수치해석으로 규명하고자한 것이다. 여기서, 천단고가 정수면보다 낮아 수중에 설치되는 잠제는 연안의 자연경관을 유지하는 친환경적인 효과와 더불어 공학적으로는 잠제 배후에 양빈된 저질의 침식을 방지하거나 혹은 침식성 해빈에서 저질이동을 방지하여 해빈의 현상유지ㆍ회복을 도모할 수 있어 자연발생적인 형태와 유사한 해빈을 조성할 수 있는 것으로 알려져 있다. 그러나, 우리나라 남ㆍ동해안을 비롯한 다수의 해역에 침식방지대책으로 잠제를 계획ㆍ설치하여 왔지만, 광폭에 따른 비경제성이 또한 많이 지적되고 있고, 의도한 침식방지 역할이 충실히 수행되는 현장은 그다지 많지 않은 것으로도 알려져 있다. 이러한 이유로는 잠제의 천단폭, 개구폭, 길이 및 해안선에서 이격거리 등이 현장조건에 부합되지 않게 설치된 것, 그리고 평상파랑과 이상파랑의 두 파랑조건에 동시에는 부합되지 않게 설치된 것 등을 들 수 있을 것이다. 따라서, 일본 및 유럽에서는 전술한 잠제의 기능에서 단점을 보완할 수 있는 해안구조물로 LCS에 오래 전부터 관심을 집중하여왔다. 여기서, LCS는 일반적으로 해빈을 보호하기 위해 해안에 평행한 낮은 천단의 구조물로, 전술한 잠제와 이안제(detached breakwater)의 중간적인 역할을 수행하는 것으로 알려져 있으며, LCS의 형상은 잠제나 이안제와 유사하지만, 천단고가 이안제보다 상대적으로 낮은 저천단이므로 고파랑의 경우는 월파가 허용되는 구조이고, 따라서 종래의 이안제보다 작용수평파력이 적어진다. 그리고, 광폭에 의한 마찰저항을 향상시키고 천단수심을 적게 하여 천단상에서 강제쇄파를 유도하는 잠제의 파랑제어기구와는 달리, LCS는 잠제에 비해 천단폭이 좁고, 천단이 공기중으로 돌출되어 천단고가 높기 때문에 반사와 월파 및 마찰저항에 의한 파랑제어기능이 우수하므로 잠제보다는 훨씬 경제적이다. LCS와 잠제 모두 해빈에 작용되는 파에너지를 소멸시키지 않고 어느 정도로 줄이지만, LCS의 경우가 더 많은 전달파에너지를 감소시킨다. 이상과 같은 LCS의 장점에 주목하여 유럽에서는 많은 이론 및 실험연구를 수행하여왔고, 결과의 현장적용으로 설계기술이 많이 향상되었으며, 또한 집대성되었다. 일반적으로, 해역에서 파고 혹은 해빈류(nearshore current)를 산정하는 경우는 수심방향으로 적분된 형태의 평면 2차원해석수법(완경사방정식류 및 Boussinesq방정식류)을 적용하는 경우가 거의 대부분이다. 그러나, 이의 경우, 파고와 같은 수위변동은 어느 정도 정확성을 가진 결과가 도출되지만, 해빈류는 수심방향으로 평균류가 얻어지기 때문에 수심의 영향을 크게 받는 천해역과 해빈류에 기반하는 해빈변형해석(소류사와 부유사)에 정도상 문제가 발생할 수 있고, 특히 잠제와 같은 수중투과성구조물의 경우 파동장은 구조물이 존재하는 영역과 구조물이 존재하지 않는 영역으로 나누어지기 때문에 수심방향의 연직적분은 많은 오차를 발생시킬 수 있다. 따라서, 본 연구에서는 전술한 평면 2차원해석법이 가지는 결점을 해결하고, 더불어 고정도의 결과를 도출하기 위하여 3차원수치해석을 수행하며, 이에 최근 세계적으로 각광을 받고 있는 olaFlow 모델을 적용하였다. 이 모델은 원래 OpenFOAMⓇ(Open source Field Operation And Manipulation) 모델을 근간으로 개발되었으며, 액체와 기체의 혼상류해석, 난류해석 및 쇄파해석이 가능한 유한체적법의 강비선형해석법으로, 3차원 VARANS(Volume-Averaged Reynolds-Averaged Navier-Stokes) 방정식에 기초한다. 최근, 다양한 모듈을 이용하여 파와 구조물의 상호작용, 투과성구조물에서 혼상류의 거동, 파와 구조물 및 지반의 상호작용, 고립파의 발생, 선체운동과 항주파 및 추진 등에 관한 연구들이 수행되고 있다. 그러나, 소스코드 개발을 주도한 유럽을 중심으로 활발히 사용ㆍ개발되고 있지만, 국내 특히 해안공학분야에서의 적용사례는 매우 미진한 실정에 있다. 따라서, 본 연구의 잠제 혹은 LCS가 설치된 3차원해역에서 구조물에 의한 파고 및 해빈류 등의 변동특성을 규명하기 위하여 전술한 olaFlow 모델을 적용함에 있어서 먼저 그의 정당성을 확인한다. 이를 위하여 1) 다공질매질을 통과하는 단파의 수위변동, 2) 투과성잠제 주변에서 파랑변동과 잠제내 및 지반내에서 과잉간극수압변동, 3) 파랑과 흐름의 공존장내 평균유속의 변화, 4) 3차원투과성직립벽 주변에서 수위 및 파압변동, 5) 3차원불투과성잠제 주변에서 수위와 유속변동 및 6) 불규칙파의 조파파형과 주파수스펙트럼 등에 관해 얻어진 기존의 실험결과와 본 수치해석을 비교ㆍ검토하였다. 이상과 같은 olaFlow 모델에 의한 결과의 고정도 및 타당성에 근거하여 1) 투과성잠제 주변에서 규칙파와 흐름의 공존장내 2차원파동장의 수치해석, 2) 투과성잠제 주변에서 불규칙파와 흐름의 공존장내 2차원파동장의 수치해석, 3) 투과성잠제 주변에서 규칙파 입사조건하 3차원파동장의 수치해석, 4) 투과성잠제 주변에서 불규칙파 입사조건하 3차원파동장의 수치해석, 5) 투과성잠제 주변에서 규칙파 혹은 불규칙파와 흐름의 공존장내 3차원파동장의 수치해석 및 6) 저천단구조물 주변에서 규칙파 입사조건하 3차원파동장의 수치해석을 각각 실시하였다. 이로부터 입사파랑과 흐름조건 및 구조물의 배치조건에 따른 수위변동, 파고변화, 주파수스펙트럼의 변동, 평균유속(해빈류)과 평균난류운동에너지의 변동특성 등을 면밀히 논의하였다. 특히, LCS 주변에서 파고와 유속변화 및 난류운동에너지 등을 도출하고, 구조물의 개구폭, 천단수심과 같은 배치형상의 변화 및 입사파고와 주기와 같은 입사파랑조건의 변화에 따른 결과를 잠제의 경우와 비교ㆍ검토하여 LCS와 잠제의 각각에 대한 특성의 차이 등을 면밀히 분석ㆍ논의하였다. 마지막으로, 이상의 각 장에서 도출된 중요한 결과를 말미에 결언으로 제시하였고, 각 결언을 종합하여 본 논문의 결론을 최종적으로 기술하였다.목 차 목차 ······················································································································(i) LIST OF FIGURES ··································································································(v) LIST OF TABLES ···································································································(x) LIST OF PHOTOS ··································································································(xi) ABSTRACT ········································································································ (xii) 요약 ·················································································································· (xvi) 제 1 장 서론 ·············································································································(1) 1.1 본 연구의 배경과 목적···············································································(1) 1.2 본 연구의 내용························································································· (6) References ····································································································(9) 제 2 장 olaFlow 모델의 수치해석이론 및 검증·····································································(11) 2.1 서언 ······································································································(11) 2.2 olaFlow 모델의 기초방정식······································································· (11) 2.3 불규칙파의 조파이론···············································································(13) 2.4 olaFlow 모델의 검증··············································································(14) 2.4.1 다공질매질을 통과하는 단파의 수위변동···································(14) 2.4.2 투과성잠제 주변에서 파랑변동과 잠제내 및 지반내에서 과잉간극수압변동 ·································································(16) 2.4.3 파랑과 흐름의 공존장내 평균유속·············································(19) 2.4.4 3차원투과성직립벽 주변에서 수위 및 파압·································(20) 2.4.5 3차원불투과성잠제 주변에서 수위 및 유속·································(26) 2.4.6 불규칙파의 조파검증······························································(29) 2.5 결언······································································································(31) References ···································································································(32) 제 3 장 투과성잠제 주변에서 규칙파와 흐름의 공존장내 2차원파동장의 수치해석······························(35) 3.1 서언 ······································································································(35) 3.2 수치해석결과··························································································(37) 3.2.1 파랑변형···············································································(37) 3.2.2 파고의 분포···········································································(44) 3.2.3 평균유속 및 평균난류운동에너지의 분포···································(46) 3.3 결언······································································································(48) References ···································································································(49) 제 4 장 투과성잠제 주변에서 불규칙파와 흐름의 공존장내 2차원파동장의 수치해석···························(54) 4.1 서언 ······································································································(54) 4.2 수치해석결과························································································· (55) 4.2.1 파랑변형···············································································(55) 4.2.2 파고분포···············································································(62) 4.2.3 평균유속 및 평균난류운동에너지의 분포···································(63) 4.3 결론······································································································(66) References ···································································································(67) 제 5 장 투과성잠제 주변에서 규칙파 입사조건하 3차원파동장의 수치해석······································(70) 5.1 서언 ······································································································(70) 5.2 수치해석 결과·························································································(70) 5.2.1 계산조건···············································································(70) 5.2.2 잠제 주변의 파고분포에 대한 고찰············································(72) 5.2.3 평균수위분포········································································(78) 5.2.4 평균유속의 공간분포······························································(81) 5.2.5 연안류의 분포········································································(84) 5.2.6 평균난류운동에너지의 분포·····················································(87) 5.3 결언······································································································(91) References ···································································································(92) 제 6 장 투과성잠제 주변에서 불규칙파 입사조건하 3차원파동장의 수치해석····································(95) 6.1 서언 ······································································································(95) 6.2 수치해석결과··························································································(95) 6.2.1 계산조건···············································································(95) 6.2.2 의 분포········································································(97) 6.2.3 평균유속의 공간분포·····························································(100) 6.2.4 연안류분포··········································································(104) 6.2.5 평균난류운동에너지의 분포···················································(108) 6.3 결언·····································································································(109) References ·································································································(110) 제 7 장 투과성잠제 주변에서 규칙파 혹은 불규칙파와 흐름의 공존장내 3차원파동장의 수치해석···········(112) 7.1 서언 ····································································································(112) 7.2 수치해석결과························································································(113) 7.2.1 계산조건·············································································(113) 7.2.2 파고분포·············································································(114) 7.2.3 평균유속의 공간분포·····························································(119) 7.2.4 연안류분포··········································································(122) 7.2.5 평균난류운동에너지의 분포···················································(126) 7.3 결언·····································································································(130) References ·································································································(131) 제 8 장 저천단구조물 주변에서 규칙파 입사조건하 3차원파동장의 수치해석··································(133) 8.1 서언 ····································································································(133) 8.2 수치해석결과························································································(134) 8.2.1 계산조건·············································································(134) 8.2.2 정상상태의 판단···································································(134) 8.2.3 파고분포와 파의 전파····························································(136) 8.2.4 평균유속·············································································(141) 8.2.5 평균난류운동에너지·····························································(142) 8.3 결언·····································································································(148) References ·································································································(149) 제 9 장 결론···········································································································(152) 9.1 제 2장에서 결언·····················································································(152) 9.2 제 3장에서 결언·····················································································(152) 9.3 제 4장에서 결언·····················································································(153) 9.4 제 5장에서 결언·····················································································(154) 9.5 제 6장에서 결언·····················································································(155) 9.6 제 7장에서 결언·····················································································(156) 9.7 제 8장에서 결언·····················································································(157) References ·································································································(158)Docto

Reduction of Bump Vibration of an Agricultural Front-End Loader by an Improved Hydraulic Circuit of Accumulator

학위논문 (석사)-- 서울대학교 대학원 : 바이오시스템·소재학부, 2014. 8. 김학진.프론트 로더의 버켓에 무거운 하중을 적재하면 트랙터의 무게중심이 이동하면서 피치진동이 발생하게 된다. 이는 안전성 및 조작성에 문제를 야기할 수 있으며, 서스펜션을 이용하여 주행 안전성 및 편안함을 높이는 것이 필요하다. 선진사의 프론트 로더의 경우, 이미 붐 서스펜션 시스템이 갖추어져 판매가 되고 있으나, 국내 프론트 로더는 어큐뮬레이터를 장착하여 충격을 저감하도록 되어 있으나 선진사 대비 충격 저감 정도가 낮아 개선이 필요하다. 본 논문에서는 유압 회로 시뮬레이션과 실험적 분석을 통하여 국내 프론트 로더의 유압회로를 개선하고자 하였다. 현 국내 프론트 로더의 요철 주행 시험 결과, 어큐뮬레이터 미장착시, 붐 실린더의 압력 RMS는 29.3 bar, 버켓의 수직 가속도 RMS는 0.04 였으며, 어큐뮬레이터 장착 시 붐 실린더의 압력 RMS는 13.8 bar로 감소하였으나 수직 가속도 RMS는 0.13 로 증가하는 모습을 보였다. 증가된 가속도를 줄이기 위하여, 유압 회로에 유량제어밸브를 추가하고 서스펜션 동작이 원활히 되도록 설계T하였다. 개선된 서스펜션 유압회로를 시뮬레이션을 이용하여 분석하였으며, 그 결과, 다양한 주파수와 진폭을 가진 사인파에 대하여 감쇠력을 보여주었고 측정된 압력 값을 이용한 회로의 민감도를 분석하여, 압력과 가속도가 개선됨을 보였다. 이를 바탕으로 제작한 개선된 서스펜션 회로는 기존과 같은 프론트 로더에 장착하여 요철 충격 시험을 하였다. 새로 개선된 서스펜션 유압회로의 미적용 시, 붐 실린더의 압력 RMS는 31.1 bar, 버켓의 수직 가속도 RMS는 0.06 이었으며, 적용 시에는 붐 실린더의 압력 RMS는 16.5 bar, 버켓의 수직 가속도 RMS는 0.04 으로 압력과 수직 가속도가 감소되었다. 이는 개선된 서스펜션 유압회로가 요철 진동의 감소에 효과가 있는 것으로 나타났다.목 차 List of Tables ⅲ List of Figures ⅳ 1. 서론 1 2. 연구목적 3 3. 연구사 4 4. 관련 이론 7 4.1 스프링 특성 7 4.2 감쇠 특성 13 5. 재료 및 방법 18 5.1 기존 프론트 로더 장착 트랙터 주행 충격 요인 실험 18 5.1.1 실험 조건 18 5.1.2 평가 방법 21 5.2 시뮬레이션에 의한 프론트 로더 유압시스템 요인 해석 22 5.2.1 단품 모델 해석 23 5.2.2 요인해석 방법 25 5.3 붐 서스펜션 유압회로 설계 27 5.4 시뮬레이션에 의한 붐 서스펜션 회로 검증 29 5.4.1 단품 모델 해석 29 5.4.2 붐 서스펜션 회로의 검증 35 5.5 붐 서스펜션 시스템 장착 트랙터 주행 충격 시험 40 6. 결과 및 고찰 45 6.1 기존 프론트 로더 장착 프랙터 주행 충격 실험 결과 45 6.2 시뮬레이션에 의한 유압시스템 요인 해석 결과 57 6.3 시뮬레이션에 의한 붐 서스펜션 회로 검증 결과 61 6.4 붐 서스펜션 시스템 장착 트랙터 주행 충격 시험 결과 66 7. 요약 및 결론 76 8. 참고문헌 77 AbstractMaste

First principle predictions for screening low stacking fault energy of SiVCrMn0.3Fe0.5CoNi

2

Influence of Manila clam (Ruditapes philippinarum) aquaculture on the partitioning of organic carbon oxidation coupled to sulfate- and iron reduction in the sediments of the Keunso Bay, Yellow Sea

Although it represents the third highest production (4,228,594 tonnes in 2016) in global shellfish aquaculture, little is known about the effects of Manila clam (Ruditapes philippinarum) aquaculture on the sediment biogeochemistry. We investigated the rates and pathways of anaerobic organic carbon (Corg) oxidation in highly bioturbated (HB) sediments by the R. philippinarum aquaculture and poorly bioturbated (PB) sediments in the Keunso Bay, Yellow Sea. As a result of increasing solute exchange through reworking and irrigation activities, anaerobic Corg oxidation rates at HB (38.8 mmol m-2 d-1) were about twice as high as that at PB (26.8 mmol m-2 d-1). Microbial Fe(III) reduction pre-dominated Corg oxidationpathway at HB, comprising 551

Rates and Controls of Organic Matter Mineralization and Benthic Nutrient Release in the Coastal Sediment Near Lake Shihwa

시화호 인근 연안 퇴적물에서 유기물 분해 특성, 퇴적물로부터의 영양염 용출 및 주요 조절요인을 파악하기 위해 공극수와 퇴적물내 지화학 성분, 혐기성 유기물 분해율, 황산염 환원율 및 저층 영양염 용출률을 측정하였다. 연구정점은 소래포구 인근 정점(E0), 송도갯벌 정점(E1), 오이도 선착장 부근 정점(E3), 시화 조력발전소 수문 앞 정점(E5)으로 선정하였다. 유기탄소와 공극수 내 암모니아, 인산염 농도는 정점 E0에서 가장 높게 나타났으며, 외측 해역(정점 E1, E3, E5)으로 갈수록 점진적으로 감소하였다. 혐기성유기물 분해율과 황산염 환원율은 정점 E0에서 각각 260.6 mmol C m-2 d-1와 91.4 mmol S m-2 d-1로 외측 정점들보다 각각 4–9배, 6 –54배 높게 나타났다. 혐기성 유기물 분해에서 황산염 환원이 차지하는 비율은 정점 E3, E5에서 11–23%로 미미한 것으로 나타났으나, 정점 E0, E1에서는 47-70%로 황산염 환원에 의해 혐기성 유기물 분해가 주도되는 것으로 나타났다. 또한, 혐기성 유기물분해율과 황산염 환원율은 용존 유기탄소와 상관성이 매우 높은 것으로 나타났다(r2 = 0.795, 0.777). 한편, 정점 E0, E1, E3에서 퇴적물로부터 용출된 무기질소와 무기인은 각각 일차생산자가 요구하는 무기질소와 무기인의 120–510%와 26–178%를 공급하는것으로 나타났다. 이상의 결과들은, 시화호 인근 연안 퇴적물 내 유기물 분해는 이용 가능한 용존 유기탄소의 공급에 의해 조절되고있으며, 과도한 유기물 분해는 저층 영양염 용출을 촉진시켜 부영양화를 야기할 수 있음을 의미한다22Nkc

낙동강 하구 댐 시스템에서 용존 미량 금속의 분포 특성

해수에 존재하는 용존 미량 금속은 식물플랑크톤 성장에 필수적인 미량영양염으로 작용하지만, 일부 원소는 고농도에서 독성을 나타낼 수 있으며, 주로 강을 통해 해양 환경으로 유입된다. 하구역은 복잡한 생지화학적 과정이 발생하며 강에서 바다로 전달되는 다양한 물질들의 유입량 및 화학적 조성을 변화시킨다. 낙동강 하구에는 산업 및 농업용수의 안정적인 공급과 염수 유입 차단을 위해 하굿둑(estuarine barrage)이 설치되어 있다. 이러한 하굿둑의 존재는 복잡한 하구 환경에서 미량 금속의 분포에 인위적인 영향을 미칠 가능성이 있다. 따라서 본 연구에서는 2021 년 7 월에 낙동강 하구에서 용존 미량 금속의 농도 분포를 조사하여 하굿둑이 미량 금속의 거동에 미치는 영향을 분석하고자 하였다. 낙동강 하굿둑을 기준으로 상류와 하류에서 염분과 영양염 농도가 상반된 양상을 보였으며, 미량 금속 또한 원소별로 다양한 거동을 나타내는 것으로 확인되었다. 이는 하굿둑으로 인한 환경 변화가 낙동강 하구역의 물질 순환 기작에도 상당한 영향을 미치고 있음을 시사한다.2

개발도상 연안·소도서국 해양개발 인프라 구축연구 :기관임무형사업 1단계(2012-2014)

한국해양과학기술

Biogeochemical cycling and marine environmental change study

최종 목표 ○ 연안환경, 우리바다, 인도양에서 생지화학순환을 이해하고 해양환경 변화를 탐지하는 기술을 구축하여 당면한 환경문제를 해결하는 방안을 제시함 연구 내용 ○ KIOST 장기 모니터링 시스템 및 이를 통한 동해와 남해 대기/물리/화학/생물 시계열 관측자료 ○ 제주 연안 오염원 및 외래기원 환경교란물질 탐지 및 이동경향 분석 ○ 동해와 황해에서 탄소와 미량원소/동위원소 생지화학 순환 연구 ○ 해양 방사능 사고 대응 관측 및 모델 정보제공 기술지원 체계 구축 ○ 인도양 다매체 해양 프로세스 이해 연구개발성과 ○ 지역해에 최적화된 해양환경변화 탐지기술 개발 ○ 제주도 연안에서 일어나는 현안문제 해결방안 제시 ○ 인도양 쌍극진동 변동과 물질순화 기작 및 생태계 반응이해 ○ 해양 방사능 사고대응 기술지원 체계 운용 메뉴얼 연구개발성과 활용계획 및 기대 효과 ○ 광역-국지적 규모의 환경유해 인자 조기 탐지 기술 및 예보 기술 확보 ○ 유관기관에 해양환경변화 탐지 및 예측 자료를 제공하여 피해저감 활동 지원 ○ 한반도 주변해역에서 기후변화/환경변화/인위적 오염증가에 따른 해양환경 변동이해 ○ 주변해와 대양간의 상호연관성 파악 및 미래기후 변화 예측 능력 향상 ○ 일본 방사능 오염수 방출 계획 실행 시 정부차원의 대응 지원 ○ 국제인도양탐사 프로그램(IIOE-2) 참여 및 인도양 변동 특성 이해에 기여 ○ GEOTRACES 프로그램 참여를 통한 대양연구 선도 기관으로 국제 인식 개선한국해양과학기술