Gaussian mixture model for automated tracking of modal parameters of long-span bridge

Jian-Xiao Mao,Hao Wang,Billie F. Spencer Jr. 국제구조공학회 2019 Smart Structures and Systems, An International Jou Vol.24 No.2

Determination of the most meaningful structural modes and gaining insight into how these modes evolve are important issues for long-term structural health monitoring of the long-span bridges. To address this issue, modal parameters identified throughout the life of the bridge need to be compared and linked with each other, which is the process of mode tracking. The modal frequencies for a long-span bridge are typically closely-spaced, sensitive to the environment (e.g., temperature, wind, traffic, etc.), which makes the automated tracking of modal parameters a difficult process, often requiring human intervention. Machine learning methods are well-suited for uncovering complex underlying relationships between processes and thus have the potential to realize accurate and automated modal tracking. In this study, Gaussian mixture model (GMM), a popular unsupervised machine learning method, is employed to automatically determine and update baseline modal properties from the identified unlabeled modal parameters. On this foundation, a new mode tracking method is proposed for automated mode tracking for long-span bridges. Firstly, a numerical example for a three-degree-of-freedom system is employed to validate the feasibility of using GMM to automatically determine the baseline modal properties. Subsequently, the field monitoring data of a long-span bridge are utilized to illustrate the practical usage of GMM for automated determination of the baseline list. Finally, the continuously monitoring bridge acceleration data during strong typhoon events are employed to validate the reliability of proposed method in tracking the changing modal parameters. Results show that the proposed method can automatically track the modal parameters in disastrous scenarios and provide valuable references for condition assessment of the bridge structure.

허구적 대상에 대한 양상 문장의 해석

이종희 ( Jong Hee Lee ) 한국미학회 2012 美學 Vol.69 No.-

본고는 허구적 이름이 추상적 대상을 지칭한다는 허구적 실재론의 관점에서 허구적 이름이 등장하는 양상문장에 대한 해석을 시도한다. 양상문장의 참/거짓이 양상성이 부여되는 대상의 정체성에 의해 결정된다고 볼 때, 이런 문장들에 대한 직관적 이해를 지지하는 해석을 줄 수 있느냐는 문제는 이론의 타당성을 가늠하는 중요한 의미를 지닌다. 먼저 존재술어가 들어있는 양상문들을 다룬 뒤 그 외의 양상문들을 해석한다. 홈즈의 정체성을 이루는 성격이나 주요한 줄거리에 속하는 사건의 경우 그가 그것을 가지지 않거나 그런 사건을 겪지 않았을 수 있다고 말할 수는 없다. 그렇다고 소설 속에서 언급된 모든 속성들을 허구적 대상이 본질적 속성으로서 가진다는 말은 아니다. 본고는 허구적 대상의 속성들 전부가 필연적이라는, 혹은 전부 우연적이라는 양 극단의 주장에 치우치지 않는 해석을 제시할 것이다. ``홈즈가 존재할 수 있었다``거나 ``홈즈가 소설 속에 기술된 일 모두를 하지 않았을 수 있다``처럼 본고의 주장과 원칙적으로 부딪치는 양상문에 대해서도, 그것들을 참으로 여기는 직관을 설명할 방법을 모색한다. 이러한 과정에서 이차원적 의미론의 해법이 소개되고 반박될 것이다. This paper tries to interpret the modal sentences in which fictional names occur within a framework of fictional realism which argues that fictional names refer to abstract objects. Whether a theory of fictional object can give us the interpretation to ground the intuitive understanding about the modal sentences is a matter of crucial importance for the validity of the theory. For the truth values of those sentences are determined by what it is of the thing to which the modality is given. After treating the modal sentences which include existential predicates, I will interpret the other ones. Of the personality comprising the Holmes`s identity or the main events of the story, we cannot say that Holmes can have failed to have that personality nor say that he may have avoided those events. However, I don`t mean to say that fictional object has all of the properties that are attributed to it in the story, as its essential properties. This paper will present the moderate interpretation which is not slanted in the extremes. That is to say, I am not in the position that the all properties of fictional object are necessary nor in the one that all of them are contingent. And I will try to find out the way to explain the intuitions by which people allow the modal sentences which contradict my view in principle, the sentences like ``Holmes might have existed`` or ``Holmes might have done nothing described in the story``. In the process of that, the solution of two-dimensional semantics is introduced and refuted.

EQUIVALENT MATERIAL PROPERTIES OF PERFORATED PLATE WITH TRIANGULAR OR SQUARE PENETRATION PATTERN FOR DYNAMIC ANALYSIS

Jhung, Myung-Jo,Jo, Jong-Chull Korean Nuclear Society 2006 Nuclear Engineering and Technology Vol.38 No.7

For a perforated plate, it is challenging to develop a finite element model due to the necessity of the fine meshing of the plate, especially if it is submerged in fluid. This necessitates the use of a solid plate with equivalent material properties. Unfortunately, the effective elastic constants suggested by the ASME code are deemed not valid for a modal analysis. Therefore, in this study the equivalent material properties of a perforated plate are suggested by performing several finite element analyses with respect to the ligament efficiencies.

A Study on Aging Fracture Behavior of Sintered Joint by Bi-Modal Cu Paste

손준혁,이창우,유동열,변동진,방정환 대한용접접합학회 2022 대한용접·접합학회지 Vol.40 No.6

Power semiconductors for automobiles were joined by high Pb soldering to joint properties at high temperatures during operations. However, this process is being replaced by low-temperature sintering. In the low-temperature sin- tering bonding method, Cu powder is low-cost and exhibits high-performance material and excellent bonding properties. In this study, the effect of high-temperature aging on Cu paste sintered joints and the failure mechanism of the shear test were investigated. Cu monomodal and bimodal pastes were manufactured, and electroless nickel immersion gold (ENIG) surface treatment was applied on the Cu chip side. In the ENIG-treated joints, a significant number of Kirkendall voids were observed at the interface under Au after 2,000 h at 200 °C, and Cu2O was also formed. This is attributed to the difference between the interdiffusion coefficients of Au and Cu, which decreases the shear strength of the junction and rapidly increases the electrical resistance. After the shear strength tests, the crack propagation pattern at the interface of the ENIG-treated joint was confirmed via cross-section scanning electron microscopy. Future studies on surface treatment are required to clarify the long-term stability of the joints.

고층건물의 자연 진동실험 및 시스템판별

조순호 한국지진공학회 2012 한국지진공학회논문집 Vol.16 No.3

구조물의 특성치를 결정하기 위하여 18층 규모의 사무용 건물 3동에 대하여 자연진동 조건하에서 동적계측실험을 수행하였다. 대상건물은 기본적으로 보-기둥 골조시스템에 횡하중을 보다 효율적으로 지지하기 위하여 추가적으로 코아가 배치된 혼합 구조형식을 나타낸다. 매층 마다 측정한 일련의 진동기록으로부터 고유진동수, 모드형태 및 감쇠율 등과 같은 모달계수를 추출하기 위하여 최신주파수- 및 시간영역-기반 응답의존 시스템판별법인 FDD, pLSCF 및 SSI를 적용하였다. 3방법에 의하여 추출한 결과는 대체로 일치하였으나, 초기 FE 해석결과와 비교하여 저차 3개 고유진동수는 대략 1.2~1.7배나 되는 단단한 거동을 나타냈다. 진동응답으로부터 추출된값, 기준에서 제시하는 약산식 및 FE해석에 의하여 산정된 고유주기를 비교하여 보면, FE결과가 가장 유연한 거동을 예측하였으며, 높이를 변수로 하는 약산식이 추출된 값에 가장 근접한 결과를 나타냈다. 이러한 차이는 현재의 실험 추출치에는 콘크리트 균열 등과 같은강성저감 요인을 포함하고 있지 않으며, 또한 FE 해석치는 비구조체 및 사용된 재료의 실제성능 등과 관련된 강성증가 요소를 포함하고있지 않기 때문이다. Dynamic response measurements from natural excitation were carried out for three 18-story office buildings to determine their inherent properties. The beam-column frame system was adopted as a typical structural form, but a core wall was added to resist the lateral force more effectively, resulting in a mixed configuration. To extract modal parameters such as natural frequencies, mode shapes and damping ratios from a series of vibration records at each floor, the most advanced operational system identification methods based on frequency- and time-domain like FDD, pLSCF and SSI were applied. Extracted frequencies and mode shapes from the different identification methods showed a greater consistency for three buildings, however the three lower frequencies extracted were 1.2 to 1.7 times as stiff as those obtained using the initial FE models. Comparing the extracted fundamental periods with those estimated from the code equations and FE analysis, the FE analysis results showed the most flexible behavior, and the most simple equation that considers the building height as the only parameter correlated fairly well with test results. It is recognized that such a discrepancy arises from the fact that the present tests exclude the stiffness decreasing factors like concrete cracking, while the FE models ignore the stiffness increasing factors, such as the contribution of non-structural elements and the actual material properties used.

고층건물의 자연진동 실험 및 FE 해석모델 향상

조순호 대한건축학회지회연합회 2017 대한건축학회연합논문집 Vol.19 No.1

18층 사무실용도 건물(SIB)의 동적성능을 결정하기 위하여 자연 진동계측 실험을 수행하였다. 해당건물은 기본적으로 철골골조 형식이나, 보다 효율적으로 수평하중을 지지하기 위하여 콘크리트 코아가 추가된 복합 구조형식을 취하고 있다. 계측된 일련의 진동기록에 최신 주파수- 및 시간영역-기반 응답의존 시스템판별법인 FDD, pLSCF 및 SSI를 적용하여 모달계수를 추출하였다. 3방법에 의하여 추출한 결과는 대체로 일치하였으나, 초기 3D-FE 해석결과와 비교하여 저차 3개 고유진동수는 대략 1.1~1.6배 정도의 단단한 거동을 나타냈다. 진동실험 및 FE 해석으로 부터 획득한 고유진동수 및 모드형태와 같은 모달계수의 일치를 위하여 최적화이론에 근거한 자동모델향상을 시도하였다. 자세한 3D-FE모델의 해석결과로부터 매 층 마다 3개의 강성 및 3개의 질량을 변수로 갖는 단순 FE모델을 유도하여 모델향상의 시작모델로 사용하였다. 일치를 시도한 6개의 모드 중 저차 3차 모드까지만 고려한 향상된 FE모델은 자연진동수 및 모드형태에 대하여 우수한 일치를 나타냈다. 모델향상을 수행한 결과에 의하면, 현재의 국내 FE 구조해석 실무는 층강성 및 층질량을 각각 다소 과소 및 과다하게 고려하고 있는 것으로 판단된다. Dynamic response measurements from natural excitation were carried out for a 18-story office building(SIB) to determine its inherent properties. A steel beam-column frame system was adopted as a typical structural form, but a concrete core wall was added to resist the lateral force more effectively, resulting in a mixed configuration. The most advanced operational system identification methods based on frequency- and time-domain like FDD, pLSCF and SSI were used to extract modal parameters form a series of vibration records. The frequencies and mode shapes extracted from different identification methods showed a greater consistency, however the three lower frequencies exhibited 1.1 to 1.6 times as stiff as those obtained using a detailed 3D-FE model. Automatic FE model updating adopting optimization theory was applied to correlate experimental and analytical modal parameters such as natural frequencies and mode shapes. The simplified FE model containing 3 stiffnesses and 3 masses at each story as structural parameters derived from a detailed 3D-FE model was used as a starting one for updating. The excellent match between test and analytical modal parameters was made for the lower three modes out of the six. Based on the updating results, it can be judged that the domestic design practice for FE analysis somewhat underestimates the story stiffness, while overestimating the story mass.

아리스토텔레스에 있어서의 필연성과 소위 아리스토텔레스적 본질주의

이영환(Yungwhan Lee) 한국서양고전학회 2010 西洋古典學硏究 Vol.39 No.-

아리스토텔레스의 필연성 개념과 관련하여 필자는 크게 두 가지 문제를 다룬다. 첫째는 아리스토텔레스가 양상 실재론자인지 그리고 그가 양상 실재 론자라면 어떤 의미에서 그런 지이고, 또 하나는 콰인(W. V. O. Quine)이 de re 필연성을 부정하고 반(反)본질주의를 주장하면서 타겟으로 삼은 소위 ‘아리스토텔레스적 본질주의 (Aristotelian essentialism)’가 정말로 아리스토텔레스적인가 하는 것이다. 아리스토텔레스가 근본적으로 양상 실재론자라는 것은 많은 연구자들이 동의할 만한 주장이나, 구체적으로 그의 양상 이해가 어떤 의미에서 실재 론적인지에 대해서는 충분한 논의가 이루어지지 않았다. 이것은 많은 아리스토텔레스 연구자들이 콰인의 공격으로부터 방어하고자 한 소위 아리스토텔레스적 본질주의가 (필자가 이해하기에) 중요한 점에서 아리스토텔레스의 실체/본질 이해에서 벗어나 있다는 것에도 잘 드러난다. 필자는 아리스토텔레스의 실체/본질에 대한 하나의 이해를 바탕으로 양상성에 대한 아리스토텔레스의 입장이 물론 콰인식의 반본질주의가 아니지만, 마찬가지로 콰인이 비판하고 일군의 학자들이 콰인의 비판으로부터 옹호하는 소위 아리스토텔레스적 본질주의도 아닌 제 삼의 입장이라고 주장한다. 이 논의를 통해 또한 필자는 아리스토텔레스의 철학을 이해함에 있어서 현대 술어 논리를 끌어들이는 것이 부적절함을 주장하고, 이러한 논의를 바탕으로 형이상학적으로 중립적이라고 주장되어왔던 현대 술어 논리가 어떤 의미에서 근본적으로 아리스토텔레스의 형이상학과는 다른 존재론적 가정을 끌어들이고 있는 것은 아닌지 조심스럽게 문제제기를 할 것이다. 필자는 마지막으로 아리스토텔레스가 이해하는 필연성 개념이 현대적인 이해와는 근본적으로 다른 것이라고 주장하고 그러한 필연성 개념을 이해하는 한 시도로서 ‘능력으로서의 필연성’ (dynamic necessity) 개념을 소개할 것이다. I address two issues regarding Aristotelian modality. One issue concerns whether Aristotle is a modal realist. Is modality in Aristotle part of the objective world or is it somehow dependent on how we use our language or concepts? My answer is that Aristotle is a modal realist all right, but a peculiar kind, peculiar because his metaphysical stance is fundamentally different from ours. Another issue is whether Quine’s so-called Aristotelian essentialism is really Aristotelian. My answer is negative. When I explain why so-called Aristotelian essentialism is not Aristotelian, I will have a chance to discuss Aristotle’s metaphysical stance. The picture emerging out of my discussion of Aristotelian substances shows that there is a third alternative beside anti-essentialism of Quine and what he and other scholars have characterized as Aristotelian essentialism. During the course, the difference between Aristotelian metaphysics and the metaphysics that dominates the modern mind is noted and the applicability of modern logical notions/devices to Aristotle’s philosophy questioned. I suggest that we should be very careful in approaching Aristotle’s philosophy with the modern logical notions/devices since modern philosophy and logic are, I believe, on a quite different metaphysical footing from that on which Aristotle’s philosophy stands. I suggest at the end the notion of dynamic necessity as a basic framework to understand Aristotelian necessity.

영어, 독일어, 프랑스어, 아랍어 조동사의 유형론적 고찰

김선 ( Sun Kim ) 한국현대언어학회 2016 언어연구 Vol.32 No.1

This paper aims to trace how the auxiliaries of four languages (English, German, French and Arabic) are varied and to study what significant similarities and differences of four languages are found based on the typology. English auxiliaries have NICE property (Negative marker, Invert, Code position, Emphasis), while the other three languages show various properties. As main verbs do, auxiliaries of four languages also specify grammatical meanings such as tense, aspect, and modality. The origins of auxiliaries are universal: auxiliaries are developed from main verbs but as time goes by their original meanings have gradually faded away. (Chonnam National University)

Modal Particles and Their Projections : A Minimalist Approach

Yongzhong Yang 서울대학교 언어교육원 2013 語學硏究 Vol.49 No.1

This paper discusses the syntactic status, distribution and constraints on generation of modal particles in the framework of generative grammar. After a summary of the syntactic properties of modal particles, we argue that modal particles vary from each other in terms of syntactic distribution, but they have similar syntactic functions and base-generated positions. In the syntactic structure, modal particles of the same type occupy the same position, whereas modal particles of different types occupy different positions, which is due to the fact that they occupy different positions in the syntactic hierarchy. It is argued that declarative sentences are the basis on which other types of sentences are generated. As a result, declarative modal particles can co-occur with interrogative, imperative, and exclamatory modal particles. Based on the syntactic hierarchy, the Constraints on Modal Particle Merger/Co-occurrence, the Principle of Locality, the Principle of Prominence, the Hierarchy of Modal Types, the Hierarchy of Abstractness, and the Hierarchy of Subjectivity are proposed to account for the possible cooccurrences of modal particles, tendency to be used as topic and focus markers, linear order of modal particles, and correlation between the hierarchy of modal types, the hierarchy of abstractness, and the hierarchy of subjectivity as well as non-occurrence of interrogative, imperative, and exclamatory modal particles in embedded clauses. It is also argued that there is correlation between the degree of grammaticalization of modal particles and the complexity of sentence structure. The conclusion has been testified cross-linguistically, which is in the spirit of universal grammar.

가진기를 이용한 강제진동시험에 의한 전기 캐비닛의 실험적 모드특성 분석

조성국,소기환 한국지진공학회 2011 한국지진공학회논문집 Vol.15 No.6

원자력발전소(이하, 원전)에 설치되는 안전관련 전기기기들의 합리적인 내진검증을 위해서는 사전에 정확한 동특성분석이 필요하다. 이 연구에서는 원전에 설치되는 전기기기 캐비닛 구조를 대상으로 입력 진동의 수준에 따른 모드특성의 변화를 평가하였다. 이를 위해, 실제 전기기기 캐비닛을 시편으로 선정하고 가진 시험기를 이용하여 입력진동에너지의 크기를 변화시켜 가면서 진동시험을 수행하였다. 시험은 캐비닛의 문짝을 부착한 경우와 탈거한 경우로 구분하여 수행하였다. 진동시험을 통하여 계측된 시편의 가속도응답신호와 입력운동신호로부터 진동의 크기에 따라 진동수응답함수를 작성하였다. 다항식회귀분석기법을 이용한 모드분석기법으로 시편의 진동수응답함수를 분석하여 모드특성을 추출하고, 진동수준에 따른 시편의 동특성 변화를 검토하였다. 연구결과, 대상 기기는 입력진동의 크기가 증가할수록 모드진동수와 모드감쇠비가 비선형적으로 변화하는 것을 확인하였다. 문짝이 부착된 경우에는 문짝이 탈거된 경우에 비하여 캐비닛의 모드감쇠가 증가한다. Accurate modal identification analysis is required to reasonably perform a seismic qualification of safety-related electric equipment installed in nuclear power plants (NPPs). This study evaluates a variation of the modal properties of an electric equipment cabinet structure in NPPs according to the excitation levels. For the study, an actual electric equipment cabinet was selected as a specimen and was dynamically tested by using a portable exciter in accordance with the level of input vibration energy. Tests were classified into two sets: with-door cases, and without-door cases. Frequency response functions were computed from the signals of the acceleration responses and input motions measured from the vibration tests. A polynomial curve fitting algorithm was used to extract the modal properties from the frequency response functions. This study reviews the variation of the modal properties according to the variation of the excitation levels. The results of the study show that the modal frequencies and the modal dampings of the object specimen varies nonlinearly according to the excitation level of the test motion. Attaching the door increases the modal damping of the cabinet.