다이내믹 토픽 모델링의 의미적 시각화 방법론

연진욱(Jinwook Yeon),부현경(Hyunkyung Boo),김남규(Namgyu Kim) 한국지능정보시스템학회 2022 지능정보연구 Vol.28 No.1

Recently, researches on unstructured data analysis have been actively conducted with the development of information and communication technology. In particular, topic modeling is a representative technique for discovering core topics from massive text data. In the early stages of topic modeling, most studies focused only on topic discovery. As the topic modeling field matured, studies on the change of the topic according to the change of time began to be carried out. Accordingly, interest in dynamic topic modeling that handle changes in keywords constituting the topic is also increasing. Dynamic topic modeling identifies major topics from the data of the initial period and manages the change and flow of topics in a way that utilizes topic information of the previous period to derive further topics in subsequent periods. However, it is very difficult to understand and interpret the results of dynamic topic modeling. The results of traditional dynamic topic modeling simply reveal changes in keywords and their rankings. However, this information is insufficient to represent how the meaning of the topic has changed. Therefore, in this study, we propose a method to visualize topics by period by reflecting the meaning of keywords in each topic. In addition, we propose a method that can intuitively interpret changes in topics and relationships between or among topics. The detailed method of visualizing topics by period is as follows. In the first step, dynamic topic modeling is implemented to derive the top keywords of each period and their weight from text data. In the second step, we derive vectors of top keywords of each topic from the pre-trained word embedding model. Then, we perform dimension reduction for the extracted vectors. Then, we formulate a semantic vector of each topic by calculating weight sum of keywords in each vector using topic weight of each keyword. In the third step, we visualize the semantic vector of each topic using matplotlib, and analyze the relationship between or among the topics based on the visualized result. The change of topic can be interpreted in the following manners. From the result of dynamic topic modeling, we identify rising top 5 keywords and descending top 5 keywords for each period to show the change of the topic. Existing many topic visualization studies usually visualize keywords of each topic, but our approach proposed in this study differs from previous studies in that it attempts to visualize each topic itself. To evaluate the practical applicability of the proposed methodology, we performed an experiment on 1,847 abstracts of artificial intelligence-related papers. The experiment was performed by dividing abstracts of artificial intelligence-related papers into three periods (2016-2017, 2018-2019, 2020-2021). We selected seven topics based on the consistency score, and utilized the pre-trained word embedding model of Word2vec trained with ‘Wikipedia’, an Internet encyclopedia. Based on the proposed methodology, we generated a semantic vector for each topic. Through this, by reflecting the meaning of keywords, we visualized and interpreted the themes by period. Through these experiments, we confirmed that the rising and descending of the topic weight of a keyword can be usefully used to interpret the semantic change of the corresponding topic and to grasp the relationship among topics. In this study, to overcome the limitations of dynamic topic modeling results, we used word embedding and dimension reduction techniques to visualize topics by era. The results of this study are meaningful in that they broadened the scope of topic understanding through the visualization of dynamic topic modeling results. In addition, the academic contribution can be acknowledged in that it laid the foundation for follow-up studies using various word embeddings and dimensionality reduction techniques to improve the performance of the proposed methodology.

A Flexible Multi-body Dynamic Model for Analyzing the Hysteretic Characteristics and the Dynamic Stress of a Taper Leaf Spring

Il-Dong Moon,Ho-Sang Yoon,Chae-Youn Oh 대한기계학회 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.10

This paper proposes a modeling technique which is able to not only reliably and easily represent the hysteretic characteristics but also analyze the dynamic stress of a taper leaf spring. The flexible multi-body dynamic model of the taper leaf spring is developed by interfacing the finite element model and computation model of the taper leaf spring. Rigid dummy parts are attached at the places where a finite element leaf model is in contact with an adjacent one in order to apply contact model. Friction is defined in the contact model to represent the hysteretic phenomenon of the taper leaf spring. The test of the taper leaf spring is conducted for the validation of the reliability of the flexible multi-body dynamic model of the taper leaf spring developed in this paper. The test is started at an unloaded state with the excitation amplitude of 1~2 ㎜/sec and frequency of 132 ㎜. First, the simulation is conducted with the same condition as the test. Then, the simulations are conducted with various amplitudes in a loaded state. The hysteretic diagram from the test is compared with the ones from the simulation for the validation of the reliability of the model. The dynamic stress analysis of the taper leaf spring is also conducted with the developed flexible multi-body dynamic model under a dynamic loading condition.

Gear dynamic modelling based on the concept of dynamic mesh stiffness: theoretical study and experimental verification

Chongyang Xie,Wei Yu 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.10

Gear mesh stiffness (GMS) is considered as one of the most important internal excitations affecting the dynamic response of the gear transmission system. In most gear dynamic model established by the lumped parameter method, the GMS is pre-calculated under static condition, and treated as a kind of known input of the gear dynamic model. However, the actual tooth contact state under dynamic operation condition is rather different from that under static condition, which means the variation of GMS should also be evaluated dynamically. In this paper, a new gear dynamic model is established based on the lumped parameter method, where the real-time GMS is used. To validate the proposed gear dynamic model, simulated result has been compared with the experiment result that reported in the literature, and it shows that the proposed gear dynamic model is more reasonable for gear dynamic response prediction.

유연 다물체 동역학 모델을 이용한 판스프링의 이력현상 및 동응력해석

문일동(Ildong Moon),김기태(Gitae Kim),임정환(Junghwan Lim),오재윤(Chaeyoun Oh) 한국자동차공학회 2006 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-

This paper proposes a modeling technique which is able to not only reliably and easily represent the hysteretic characteristic but also analyze the dynamic stress of a taper leaf spring. The flexible multi-body dynamic model of the taper leaf spring is developed by interfacing the finite element model and computation model of the taper leaf spring. Rigid dummy parts are attached at the places where a finite element leaf model is in contact with an adjacent one in order to apply contact model. Friction is defined in the contact model to represent the hysteretic phenomenon of the taper leaf spring. The test of the taper leaf spring is conducted for the validation of the reliability of the flexible multi-body dynamic model of the taper leaf spring developed in this paper. The test is started at an unloaded state with the excitation amplitude of 1-2㎜/sec and frequency of 132㎜. First, the simulation is conducted with the same condition as the test. Then, the simulations are conducted with various amplitudes in a loaded state. The hysteretic diagram from the test is compared with the ones from the simulation for the validation of the reliability of the model. The dynamic stress analysis of the taper leaf spring is also conducted with the developed flexible multi-body dynamic model under a dynamic loading condition.

Integration of an individual-oriented model into a system dynamics model: An application to a multi-species system

Kim, Yongeun,Son, Jino,Lee, Yun-Sik,Lee, Minyoung,Hong, Jinsol,Cho, Kijong Elsevier 2019 Environmental modelling & software Vol.112 No.-

<P><B>Abstract</B></P> <P>Although the system dynamics (SD) modeling approach has been used frequently to model various systems, there is little research on the development of hybrid SD–individual-oriented (IO) modeling. The aim of this study is to demonstrate the use of an array variable for the hybrid SD–IO modeling approach using the SD platform, and to provide a detailed modeling process of an algae–daphnid system consisting of two freshwater algal species and <I>Daphnia</I>. Our study showed that the array variable in the SD approach is useful for modeling multiple individuals and as a function to control the switch and integration variable for the hybrid modeling approach. The proposed method can improve the usability of hybrid modeling by enabling hybrid SD–IO modeling without requiring extensive knowledge of programming. Given the ongoing development and advancement of the SD modeling approach, this modeling technique will be a useful method to study complex systems.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The method for hybrid system dynamics (SD)–individual-oriented (IO) approach using the SD platform was demonstrated. </LI> <LI> For IO modeling in the SD approach, multiple individuals were modeled using array variables. </LI> <LI> To implement the proposed method, the algae–daphnid system was chosen as the subject of the case study. </LI> <LI> The results showed that the method can be a useful approach for combining SD and IO models in a single modeling platform. </LI> </UL> </P>

Evaluation of dynamic hardening models for BCC, FCC, and HCP metals at a wide range of strain rates

Huh, H.,Ahn, K.,Lim, J.H.,Kim, H.W.,Park, L.J. Elsevier 2014 Journal of materials processing technology Vol.214 No.7

This paper is concerned with dynamic hardening models of metallic materials for various crystalline structures. The dynamic response of metallic materials is indispensable for the analysis of deformation in the high-speed condition. The description of the dynamic behavior, however, can be hardly suggested with a unique model that is capable of representing the dynamic hardening characteristics of all types of materials because the dynamic hardening behavior of a material is inherent characteristics which are different in materials. It is important to select the most adequate model that is capable of representing the dynamic hardening characteristics of a material accurately. In this paper, the fitting characteristics of several well-known models are investigated and verified by experiments at a wide range of strain rates. By comparing the characteristics of the models with experimental results, the effective selecting of the most adequate model has been carried out to apply experimental stress-strain curves to the numerical analysis accurately and effectively. Several hardening models reported have been investigated and evaluated using the dynamic hardening characteristics of three kinds of materials: 4340Steel (BCC); OFHC (FCC); and Ti6Al4V (HCP). Three well-known models have been constructed and evaluated for the Johnson-Cook model, the Zerilli-Armstrong model, and the Preston-Tonks-Wallace model using the test results of three materials. Several models suggested by the authors have also been compared for the modified Johnson-Cook model and the modified Khan-Huang model. Another novel dynamic hardening model is newly proposed and compared to the other models. The changes in the strain rate and the temperature during the deformation process were considered for the accurate application of the hardening models. The most applicable model for each material has been suggested by comparison of results investigated.

구조물의 진동 제어를 위한 압착식 MR 감쇠기의 동적 모델링

허광희,전준용 한국구조물진단유지관리공학회 2009 한국구조물진단유지관리공학회 논문집 Vol.13 No.2

일반적으로 MR 감쇠기를 이용한 준능동 제어 시스템을 구축하기 위해서는 감쇠장치의 동적모델이 요구된다. 여기서, 동적모델링은 감쇠장치의 발생 감쇠력 및 거동 성향 등을 수치적으로 예측하는 것이다. 따라서 본 연구에서는 이러한 MR 감쇠기의 동적거동을 실무적인 관점에서 합리적으로 모델링하기 위하여 다양한 동적모델 중 Power 모델 및 Bingham 모델을 적용해 MR 감쇠기의 동적거동특성을 예측․평가하였다. 이때 활용한 MR 감쇠기의 실험결과는 압착식 형태로 개발된 MR 감쇠기를 대상으로 동하중 실험을 수행하여 획득하였으며, 힘-변위 이력곡선으로부터 준능동 제어장치로의 타당성을 확인하였다. 또한, 각 동적모델의 예측성능을 평가하기 위하여 우선 실험결과를 이용해 각 동적모델 별 모델변수를 규명하였고, 이를 바탕으로 힘-속도 관계곡선 및 예측된 발생 감쇠력의 오차율을 산출하여 개발된 압착식 MR 감쇠기의 실험결과와 상호 비교․평가하였다. 최종적으로 본 연구에서 개발한 압착식 MR 감쇠기는 준능동 제어장치로 활용 가능함을 확인하였고, 평가된 두 가지 동적모델은 모두 우수한 예측성능을 보임으로써 본 연구에서 개발한 압착식 MR 감쇠기는 물론 MR유체를 이용한 다양한 형태의 감쇠장치의 거동특성을 수치적으로 예측하기 위하여 간단히 활용될 수 있는 가능성을 제시하였다. Normally in order to build a semi-active control system equipped with MR damper, the dynamic modeling of the damper is required to numerically predict its dynamic damping force and also its behavioral characteristics. For the dynamic modeling of the MR damper, this paper attempts to predict and evaluate its dynamic behavior by applying specifically both a power model and a Bingham model. Dynamic loading tests were performed on the squeeze type of damper specially designed for this research, and force-displacement hysteresis loops confirmed the effectiveness of the damper as a semi-active control device. In the meantime, in order to evaluate the effectiveness of each model applied, the model parameter for each model was identified. On the basis of the parameter, we derived the error ratio of the force-velocity relationship curve and the dynamic damping force, which was contrasted and compared with the experimental results of the squeeze type of damper. Finally, the squeeze type of MR damper developed in this research was proved to be valid as a semi-active control device, and also the evaluation of the two dynamic models showed they were working fine so that they were likely to be easily utilized to numerically predict the dynamic characteristics of any dampers with MR fluid as well as the squeeze type of MR damper.

A Flexible Multi-body Dynamic Model for Analyzing the Hysteretic Characteristics and the Dynamic Stress of a Taper Leaf Spring

Moon Il-Dong,Yoon Ho-Sang,Oh Chae-Youn The Korean Society of Mechanical Engineers 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.10

This paper proposes a modeling technique which is able to not only reliably and easily represent the hysteretic characteristics but also analyze the dynamic stress of a taper leaf spring. The flexible multi-body dynamic model of the taper leaf spring is developed by interfacing the finite element model and computation model of the taper leaf spring. Rigid dummy parts are attached at the places where a finite element leaf model is in contact with an adjacent one in order to apply contact model. Friction is defined in the contact model to represent the hysteretic phenomenon of the taper leaf spring. The test of the taper leaf spring is conducted for the validation of the reliability of the flexible multi-body dynamic model of the taper leaf spring developed in this paper. The test is started at an unloaded state with the excitation amplitude of $1{\sim}2mm/sec$ and frequency of 132 mm. First, the simulation is conducted with the same condition as the test. Then, the simulations are conducted with various amplitudes in a loaded state. The hysteretic diagram from the test is compared with the ones from the simulation for the validation of the reliability of the model. The dynamic stress analysis of the taper leaf spring is also conducted with the developed flexible multi-body dynamic model under a dynamic loading condition.

적응적 이월효과를 가진 동태적 가격결정 모형의 응용가능성

차경천(Kyoung Cheon Cha),유필화(Pil Hwa Yoo) 한국마케팅학회 2009 마케팅연구 Vol.24 No.3

현재의 가격이 미래의 수요에도 영향을 미치는 동태적인 가격효과가 존재할 때, 가격결정을 위해 동태적 가격결정 모형의 사용을 고려한다. 전통적인 동태적 가격결정 모형은 이월효과를 시간에 따라 항상 일정하게 가정하고 있다. 또한 이러한 가정을 완화하기 위해 확정적인 이월효과의 감소를 가정한 변동이월효과 모형도 있었다. 본 연구에서는 전통적인 동태적 가격결정 모형이 현재효과(Current-effect)와 전기(t-1) 판매량의 선형결합(linear combination)으로 구성되어 있어 전통적인 동태적 가격결정 모형은 지수평활법과 유사한 모형으로 이해할 수 있음을 보인다. 본 연구에서는 이월효과의 변동을 보다 일반화하기 위해 적응적 지수평활법으로 잘 알려진 Trigg & Leach(1967)를 이용하여 적응적 이월효과를 가진 동태적 가격결정 모형을 제안하고, 전통적인 동태적 가격결정 모형, 시간에 따라 이월효과가 확정적으로 감소하는 변동이월효과 모형과의 비교를 통해 적응적 이월효과를 가진 모형의 응용가능성을 검증하고자 한다. 제안된 모형은 한국 담배시장의 19개 브랜드별 판매량에 응용된다. When marketing activities have influence on future sales as well as present sales, we could consider the use of typical dynamic pricing model. This model assumes the constant carry-over effect. To release this assumption, there was the dynamic pricing model with the decreasing carry-over coefficient. In this paper, we show that the typical dynamic pricing model consists of the linear combination between the current-effect and the one period lagged sales. So, it could be seen as the exponential smoothing method. For the general carry-over effect, in this paper, we propose the dynamic pricing model with adaptive carry-over effect from the well-known adaptive exponential soothing model of Trigg & Leach(1967) and compare the proposed model with the typical dynamic pricing model and the dynamic pricing model with the decreasing carry-over effect. The proposed model is applied to the sales of 19 brands in Korean cigarette market. When y(t) is the sales, Pr(t) is the price, and u(t) is the disturbance term at time t, typical dynamic pricing model could be arranged as equation 1. For comparison, we estimated the dynamic pricing model with the decreasing carry-over effect as equation 2. We proposed the dynamic pricing model with adaptive carry-over effect from the well-known adaptive exponential soothing model of Trigg & Leach(1967) as equation 3. Estimation results of three alternative models are table 1 that it shows the best model for 19 brands named from A to S. Table 2 reports the brands which have the estimation problems in three alternative models. We chosen the best model with the following four criteria; 1) the parameter of absolute price, β should have negative value, 2) the parameter r in the decreasing carry-over effect model should have the value ranged from 0 to 1, 3) all estimated parameters should be statistically significant, and 4) the fitted value of best model (Adj-R2) has to have the highest value than the last two alternative models. In table 2, there are five decision reserved brands (C, J, K, O, R in italics) because they violate one and/or more criteria above listed. From the results, we could see an applicability of the proposed model with adaptive carry-over effect. Even if it performed better only four brands in total nineteen brands, it is necessary to analyze the price response on sales using the proposed model because there were the brands (L, P) that the proposed adaptive model was the only model having no estimation problem among alternative three models.

헬리콥터 비행역학 해석프로그램 HETLAS 모델충실도 검증

김창주,양창덕,김철호 한국항공우주학회 2014 한국항공우주학회 학술발표회 논문집 Vol.2014 No.4

본 논문은 헬리콥터 비행역학 해석 프로그램인 HETLAS 의 모델 충실도 개선연구의 결과를 수록하였다. 요소기반 모델을 적용한 HETLAS 의 주요 모델링 특성과 모델충실도 개선을 위한 공기역학적인 모델링 기법을 소개하고 트림해석, 선형화 및 시뮬레이션 등 비행역학 해석에 필요한 해석 모듈을 포함한 HETLAS 의 구조를 설명하였다. 모델충실도 요구조건은 FAA AC-120-63 의 시뮬레이터에 대한 요구조건과 기존의 GENHEL 프로그램과 Boeing 사 등에서 사용한 목표 등을 참조로 선정하였다. 모델 충실도 개선을 위한 데이터베이스는 해석적인 공력성능, 비행시험에서 획득한 트림조건 및 조종입력에 대한 동적 응답특성 등으로 구성하였다. 모델 충실도는 isolated 로터에 대한 성능, 트림해석 결과 및 비행시험 조종입력에 대한 HETLAS 의 시뮬레이션 결과 등을 비교하여 충실도 요구조건과의 비교함으로써 파악하였으며 필요한 경우 모델링 개선을 통해 충실도의 향상을 꾀하였다. This paper concerns on the model refinement to improve the level of model fidelity of the HETAS, which is a flight dynamic analysis program. First, the main structure of the HETLAS is introduced, which includes the component-based modeling approaches and analysis modules such as trim, linearization, and simulation modules. The model-fidelity requirements for HETLAS are established using FAA AC-120-63 and other approaches used in the Genhel-development program and the Boeing company. The database for the model-fidelity validation is built using analytic performance predictions and flight test data for trimmed flight conditions and dynamic responses to control inputs for each channel. The fidelity validation works are started from the isolated rotor performance validation and include comparative studies on the HETLAS modeling parameter to match its results with the trim conditions and dynamic responses obtained from flight tests. The results are utilized to refine aerodynamic modeling for the HETLAS for the fidelity enhancement.