Damage detection of plate-like structures using intelligent surrogate model

Peyman Torkzadeh,Hamed Fathnejat,Ramin Ghiasi 국제구조공학회 2016 Smart Structures and Systems, An International Jou Vol.18 No.6

Cracks in plate-like structures are some of the main reasons for destruction of the entire structure. In this study, a novel two-stage methodology is proposed for damage detection of flexural plates using an optimized artificial neural network. In the first stage, location of damages in plates is investigated using curvature-moment and curvature-moment derivative concepts. After detecting the damaged areas, the equations for damage severity detection are solved via Bat Algorithm (BA). In the second stage, in order to efficiently reduce the computational cost of model updating during the optimization process of damage severity detection, multiple damage location assurance criterion index based on the frequency change vector of structures are evaluated using properly trained cascade feed-forward neural network (CFNN) as a surrogate model. In order to achieve the most generalized neural network as a surrogate model, its structure is optimized using binary version of BA. To validate this proposed solution method, two examples are presented. The results indicate that after determining the damage location based on curvature-moment derivative concept, the proposed solution method for damage severity detection leads to significant reduction of computational time compared with direct finite element method. Furthermore, integrating BA with the efficient approximation mechanism of finite element model, maintains the acceptable accuracy of damage severity detection.

Multi-scale coherent structures and their role in the energy cascade in homogeneous isotropic turbulence

Susumu Goto 한국전산유체공학회 2008 한국전산유체공학회 학술대회논문집 Vol.2008 No.-

In order to investigate the physical mechanism of the energy cascade in homogeneous isotropic turbulence, we introduce Galilean-invariant energy and its transfer rate in the real space as a function of position, time and scale. By using a database of direct numerical simulations (DNS) of homogeneous isotropic turbulence, it is shown that (i) fully developed turbulence consists of multi-scale coherent vortices of tubular shapes, (ii) the energy at each scale is mainly confined in vortex tubes with the radii of the same order of the length scale, and (iii) the energy transfer takes place around pairs (especially, anti-parallel pairs) of such vortex tubes. Based on these observations, it is suggested that the energy cascade can be caused, in the real space, by the process of the stretching and creation of smaller (i.e. thinner) vortex tubes by the straining field around pairs of larger (i.e. fatter) vortex tubes Indeed, it is quite easy to find such events (in our DNS fields) which strongly support this scenario of the energy cascade.

저지대역의 중첩을 이용한 캐스캐이드 저역통과 여파기의 설계

김경훈,김상인,박익모,임한조 한국전자파학회 2004 한국전자파학회논문지 Vol.15 No.7

본 논문에서는 급전면의 개방스터브와 접지면의 슬롯으로 구성되어 있는 초광대역의 저지대역을 갖는 저역통과 여파기 단위 구조를 캐스캐이드한 저역통과 여파기를 설계하였다. 초광대역의 저지대역을 갖는 저역통과 여파기 단위 구조는 급전면 개방 스터브에 의해 통과대역 특성을 결정하는 여파기 구조와 이러한 여파기의 dual 구조로 접지면 슬롯에 의해 통과대역 특성을 결정하는 여파기 구조가 있으며, 각각의 단위구조를 캐스캐이드함으로써 단일 여파기보다 더욱 향상된 저지대역과 skirt 특성을 얻을 수 있었다. 개방 스터브에 의해 통과대역 특성이 결정되는 구조와 dual 구조의 캐스캐이드 여파기는 각각 1.035㎓와 1.286㎓에서 -3㏈ 차단 주파수를 가지며 저지대역은 두 구조 모두 -20㏈ 기준으로 20㎓ 이상의 광대역을 이루었다. In this paper, we designed a cascaded microstrip lowpass filter using the lowpass filters previously proposed. The previously proposed lowpass filters have a ultra-wide stopband and prominent cutoff sharpness using the combined characteristics of slot and microstrip open stub, respectively, and they are catagorized into 2 types by the method that determining their passband characteristics. The first type is determined its passband characteristics by open stub characteristics and the second is by slot characteristics. By cascading these structures with impedance adjustment of each element, the deeper out-of-band rejection and the sharper skirt response were achieved. The fabricated cascaded lowpass filters have -3㏈ cutoff frequencies at 1.035㎓ and 1.286㎓ respectively and -20㏈ stopband is over 20㎓ for both structures.

Intersubband Transitions in Nonpolar GaN-based Resonant Phonon Depopulation Multiple-Quantum Wells for Terahertz Emissions

Ya-Feng Song,Xiong-Xiong Kong,Wei-Bin Tang,Zhong-Qiang Suo,Huan Zhang,Chen-Yang Li,Qian Jia,Cai-Xia Xue,Yan-Wu Lu,Chao-Pu Yang 한국물리학회 2019 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.74 No.11

We investigate the polarization effect in intersubband transitions in polar and nonpolar GaN-based multiple-quantum well (MQW) structures for terahertz (THz) emissions by using systematic comparisons and design a nonpolar GaN/Al$_{0.2}$Ga$_{0.8}$N two-well-based MQW structure with an emitting photon of 7.27 THz (30.07 meV). Its lower energy separation (92.7 meV) matches the resonant phonon depopulation condition for better population inversion. It shows a lower threshold current density $J\rm_{th}$ at all temperatures (1.548 kA/cm$^2$ at 90 K) and a higher output power of up to 86.1 mW at 5.8 K and 33.6 mW at 100 K. Our results for the polar GaN MQW are very close to the experimental data in the literature. We find that the $J\rm_{th}$ of the nonpolar GaN MQW increases more slowly than that of the polar GaN MQW as temperature increases, indicating the nonpolar GaN MQW may be a worth-trying direction for improving the operation temperature. These results can provide meaningful references for the design and fabrication of nonpolar GaN-based THz MQW or quantum cascade structures.

의사 가속도와 백스텝핑 제어를 이용한 TVC 기반 유도탄의 자동조종장치 설계

서민국,탁민제,전병을 한국항공우주학회 2015 한국항공우주학회 학술발표회 논문집 Vol.2015 No.11

본 논문에서는 중저고도 환경에서 운용되는 TVC 기반 유도탄의 자동조종장치 설계에 대하여 다룬다. 제안된 자동조종장치는 종속 제어 구조를 가진다. 내부 루프는 의사 가속도라는 상태변수를 새로이 정의하고 이를 추종하는 제어기를 백스텝핑 제어 기법을 적용함으로써 설계된다. 외부 루프는 PI(Proportional and Integral, 비례적분) 제어기법을 이용하여 측방향 가속도 명령을 추종하기 위한 의사가속도 명령을 생성한다. 설계된 자동조종장치의 성능은 시뮬레이션을 통하여 살펴본다. This paper deals with the autopilot design for missile with TVC operated in middle and low altitude environment. The proposed autopilot system has a cascade control structure. The inner-loop is an approximate acceleration controller designed by applying a backstepping control law. The outer-loop derives the approximate acceleration command required to track the normal acceleration command. Simulation results are addressed to analyze the performance of the suggested autopilot system.

다계층 구조를 가진 산업용 스위치드 이더넷에서의 실시간 전송 특성

이경창,이석,Lee, Kyung-Chang,Lee, Seok 제어로봇시스템학회 2004 제어·로봇·시스템학회 논문지 Vol.10 No.8

The real-time industrial network, often referred to as fieldbus, is an important element for intelligent manufacturing systems. Thus, in order to satisfy the real-time requirements of field devices, numerous fieldbus protocols have been announced. But, the application of fieldbus has been limited due to the high cost of hardware and the difficulty in interfacing with multi-vendor products. Therefore, as an alternative to fieldbus, the computer network technology, especially Ethernet (IEEE 802.3), is being adapted to the industrial environment. However, the crucial technical obstacle for Ethernet is its non-deterministic behavior that makes it inadequate for industrial applications where real-time data have to be delivered within a certain time limit. Recently, the development of switched Ethernet shows a very promising prospect for industrial application due to the elimination of uncertainties in the network operation resulting in much improved performance. This paper focuses on the application of the switched Ethernet with cascade structure for industrial communications. More specifically, this paper presents an analytical performance evaluation of switched Ethernet with cascade structure, and a case study about networked control system.

The Influence of Structural Dynamics on Cascaded Joint Position Control of a Flexible Beam with a Compliant Gear

Tobias F. C. Berninger,Chenhong Huang,Marvin A. Ochsenius,Daniel J. Rixen 제어로봇시스템학회 2019 제어로봇시스템학회 국제학술대회 논문집 Vol.2019 No.10

The structural dynamics of a robot manipulator can have a large influence on its overall dynamic behavior. They can cause unwanted resonances, limit the control bandwidth and lead to instability. For this reason, a significant amount of research has focused on the development of advanced control methods which consider the structural dynamics of a robot. These techniques are, however, still rarely employed in practice due to their complex nature and reliance on accurate models. A popular decentralized control scheme for robot joints is cascaded position, velocity and current control of the motor. The goal of this paper is to visualize the influence of the structural dynamics of a flexible beam and flexible harmonic drive gear on this type of joint controller. The derived effects are explained by mainly relying on simulated and measured transfer functions, without the use of the typical equations. The difference between closing the control loop with position feedback from the motor side or on the joint side after the flexible gear is also investigated. The results are first generated using a flexible multibody simulation and later verified on a robot joint test rig.

Application of Current Mode Signal Processing: ADC

박소연,김형민,이다니엘,김성권 한국과학기술원 반도체설계교육센터 2020 IDEC Journal of Integrated Circuits and Systems Vol.6 No.3

In this paper, a low power current mode 12-bit ADC (Analog to Digital Converter) is proposed to mix digital circuits and analog circuits with the advantages of low power consumption and high speed operation. The proposed 12 bit ADC is implemented by using 4-bit ADC in a cascade structure, so its power consumption can be reduced, and the chip area can be reduced by using a conversion current transfer circuit. Error of the reference current, which is caused by the current mismatch in the reference current transfer and the conversion current transfer is about 4.19 μA. The proposed 12-bit ADC is implemented with SK Hynix 350nm 5metal 1poly process, and post-layout simulation is performed using Cadence MMSIM. It operates at a supply voltage of 3.3V and the area of the proposed circuit is 318μm × 514μm. In addition, the ADC shows the possibility of operating with low power consumption of 3.4mW average power consumption in this paper.

Complementary Absorbing Star‐Shaped Small Molecules for the Preparation of Ternary Cascade Energy Structures in Organic Photovoltaic Cells

Cha, Hyojung,Chung, Dae Sung,Bae, Suk Young,Lee, Min‐,Jung,An, Tae Kyu,Hwang, Jihun,Kim, Kyung Hwan,Kim, Yun‐,Hi,Choi, Dong Hoon,Park, Chan Eon WILEY‐VCH Verlag 2013 Advanced functional materials Vol.23 No.12

<P><B>Abstract</B></P><P>Two anthracene‐based star‐shaped conjugated small molecules, 5′,5″‐(9,10‐bis((4‐hexylphenyl)ethynyl)anthracene‐2,6‐diyl)bis(5‐hexyl‐2,2′‐bithiophene), HBantHBT, and 5′,5″‐(9,10‐bis(phenylethynyl)anthracene‐2,6‐diyl)bis(5‐hexyl‐2,2′‐bithiophene), BantHBT, are used as electron‐cascade donor materials by incorporating them into organic photovoltaic cells prepared using a poly((5,5‐E‐alpha‐((2‐thienyl)methylene)‐2‐thiopheneacetonitrile)‐alt‐2,6‐[(1,5‐didecyloxy)naphthalene])) (PBTADN):[6,6]‐phenyl‐C71‐butyric acid methyl ester (PC<SUB>71</SUB>BM) blend. The small molecules penetrate the PBTADN:PC<SUB>71</SUB>BM blend layer to yield complementary absorption spectra through appropriate energy level alignment and optimal domain sizes for charge carrier transfer. A high short‐circuit current (<I>J</I><SUB>SC</SUB>) and fill factor (FF) are obtained using solar cells prepared with the ternary blend. The highest photovoltaic performance of the PBTADN:<B>BantHBT</B>:PC<SUB>71</SUB>BM blend solar cells is characterized by a <I>J</I><SUB>SC</SUB> of 11.0 mA cm<SUP>−2</SUP>, an open circuit voltage (<I>V</I><SUB>OC</SUB>) of 0.91 V, a FF of 56.4%, and a power conversion efficiency (PCE) of 5.6% under AM1.5G illumination (with a high intensity of 100 mW<SUP>−2</SUP>). The effects of the small molecules on the ternary blend are investigated by comparison with the traditional poly(3‐hexylthiophene) (P3HT):[6,6]‐phenyl‐C61‐butyric acid methyl ester (PC<SUB>61</SUB>BM) system.</P>

Video Expression Recognition Method Based on Spatiotemporal Recurrent Neural Network and Feature Fusion

( Xuan Zhou ) 한국정보처리학회 2021 Journal of information processing systems Vol.17 No.2

Automatically recognizing facial expressions in video sequences is a challenging task because there is little direct correlation between facial features and subjective emotions in video. To overcome the problem, a video facial expression recognition method using spatiotemporal recurrent neural network and feature fusion is proposed. Firstly, the video is preprocessed. Then, the double-layer cascade structure is used to detect a face in a video image. In addition, two deep convolutional neural networks are used to extract the time-domain and airspace facial features in the video. The spatial convolutional neural network is used to extract the spatial information features from each frame of the static expression images in the video. The temporal convolutional neural network is used to extract the dynamic information features from the optical flow information from multiple frames of expression images in the video. A multiplication fusion is performed with the spatiotemporal features learned by the two deep convolutional neural networks. Finally, the fused features are input to the support vector machine to realize the facial expression classification task. The experimental results on cNTERFACE, RML, and AFEW6.0 datasets show that the recognition rates obtained by the proposed method are as high as 88.67%, 70.32%, and 63.84%, respectively. Comparative experiments show that the proposed method obtains higher recognition accuracy than other recently reported methods.