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For direct time integrations: A comparison of the Newmark and <sub> ρ ∞ </sub> -Bathe schemes
Noh, Gunwoo,Bathe, Klaus-Jü,rgen Elsevier 2019 Computers & structures Vol.225 No.-
<P><B>Abstract</B></P> <P>We consider the unconditionally stable Newmark and <SUB> ρ ∞ </SUB> <B>-</B>Bathe methods for the direct time integration of the finite element equations in structural dynamics and wave propagations. In our evaluation of the Newmark method we consider the parameters δ and α , and in the <SUB> ρ ∞ </SUB> <B>-</B>Bathe method we consider the parameters γ and <SUB> ρ ∞ </SUB> <B>,</B> with 0 < γ < ∞ , γ ≠ 1 and <SUB> ρ ∞ </SUB> ∈ [ - 1 , + 1 ] . We show that the Newmark method as usually used with its δ and α parameters, α = 0.25 <SUP> ( δ + 0.5 ) 2 </SUP> and δ ⩾ 0.5 , is a special case of the <SUB> ρ ∞ </SUB> <B>-</B>Bathe method. We also show that the <SUB> β 1 </SUB> / <SUB> β 2 </SUB> -Bathe method is a special case of the <SUB> ρ ∞ </SUB> <B>-</B>Bathe scheme. The study of the curves of numerical dissipation and dispersion shows that the <SUB> ρ ∞ </SUB> -Bathe method provides effective dissipation and dispersion whereas the Newmark method lacks in that regard. To illustrate our theoretical findings we give the results of some example solutions of structural dynamics and wave propagations. Our study also shows that further research is needed to identify the optimal use of the <SUB> ρ ∞ </SUB> <B>-</B>Bathe scheme and other implicit methods in wave propagation analyses.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We consider the Newmark and <SUB> ρ ∞ </SUB> -Bathe time integrations for dynamic solutions. </LI> <LI> New insights into the Newmark and <SUB> ρ ∞ </SUB> -Bathe methods are presented. </LI> <LI> We show that the Newmark method with α = 0.25 <SUP> ( δ + 0.5 ) 2 </SUP> and δ ⩾ 0.5 is a special case of the <SUB> ρ ∞ </SUB> -Bathe method. </LI> <LI> Some example solutions of structural dynamics and wave propagations are presented to illustrate the theoretical findings. </LI> </UL> </P>
Preliminary Study of Utilizing Plastic Tubes as a Component of Continuum Robots
Denys Makarets,Gunwoo Noh,Keri Kim,Deukhee Lee 제어로봇시스템학회 2014 제어로봇시스템학회 국제학술대회 논문집 Vol.2014 No.10
Continuum robots, new class of dexterous and thin robots, can be applied in great variety of minimal invasive surgical operations. These robots consist of two parts: manipulator, also called active cannula, and control unit. Manipulators, which are composed of concentric precurved tubes(usually 2-3), commonly made from nitinol, can enter human body through small incisions or natural orifices and, after reconfiguration into more complex structure, guide surgical instruments to the target regions avoiding obstacles. In this paper, we propose to use plastic as the material for innermost tube. Variations in the shape of lab-made concentric precurved plastic tube prototypes after numerous extension-retractions are investigated. We also use kinematic model, based on beam mechanics, for capturing the end-effector tip position and the shape of the two manipulators (I ? manipulator is composed of one nitinol tube and one plastic tube prototype; II ? manipulator is composed of two nitinol tubes and one plastic tube prototype). The model predictions are compared with the experimental results. Preliminary results show that plastic tubes may have small radii of precurvature, and sustain extension-retraction without self-damage thus potentially can be used as a component of continuum robots.
Robotic Camera Calibration to Maintain Consistent Percision of 3D Trackers
Junmin Baek,Gunwoo Noh,Joonho Seo 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.22 No.11
Camera calibration is essential for calculating camera parameters, and the parameters should be constant whenever the position tracker needs to be recalibrated. Manual camera calibration obtains a checkerboard image by tilting or positioning the checkerboard by hand. However, it makes difficult to obtain the same checkerboard images in every calibration, resulting in different camera parameters. Therefore, this study proposes robotic camera calibration to produce the constant camera parameters whenever the tracker needs to be calibrated. The robot arm moves the checkerboard according to the programmed positions and orientations so that the position tracker can obtain the same checkerboard image every calibration. Experiments were conducted to compare results of the manual and robotic camera calibrations. First, we compared the standard deviations of the intrinsic parameters and extrinsic parameters; the results show that robotic camera calibration produced the parameters with smaller standard deviations. We also compared the tracking precision of the cubic marker using manual and robotic camera calibration. As a result, the standard deviations of the tracking precision of cubic marker by the manual and the robotic camera calibration were 1.65 mm and only 0.35 mm, respectively. It reveals that the robotic camera calibration enables more precise and consistent tracking than the manual calibration.
백준민(Junmin Baek),노건우(Gunwoo Noh),서준호(Joonho Seo) 제어로봇시스템학회 2019 제어·로봇·시스템학회 논문지 Vol.25 No.12
Position-tracking devices have been used in various fields, including medical surgery and augmented reality. In this paper, a wireless optical position-tracking module with a processor that can perform self-3D tracking is developed, and the position coordinates of the cube marker are obtained using a position-tracking algorithm. Software is developed to send position coordinate data to the host computer using a wireless UDP network and make it visible at the host computer. To verify the networking system speed and evaluate the accuracy of the position coordinate data, we conducted experiments using the host computer and a two-axis electronic stage. The results demonstrate a speed of 26.81 ㎳ on average with a frequency of 37.3 ㎐. The difference between the moving distance of the actual cube marker and measuring cube marker is 0.764 ㎜ on average, with an RMSE of 0.973 ㎜. This system enables the installation of the device in any space and permits the use of a wireless network, eliminating the data transmission line and simplifying the configuration. Furthermore, many optical position-tracking modules can be installed to solve the problem where the obstacle blocks the cube marker.
유민철(Minchul Yu),노건우(Gunwoo Noh) 대한기계학회 2020 大韓機械學會論文集A Vol.44 No.4
유한구체법은 신뢰성 높은 해석 기법으로, 유한요소법과 다르게 격자를 구성할 필요가 없으므로 매우 쉽고 편리하지만 해석 시간이 오래 걸리기 때문에 상용화에 어려움을 겪고 있다. 이 때문에 유한구체법에 특화된 가우스 구적법의 연구가 진행됐지만 해석 시간 단축에 대한 근본적인 해결책을 제시하지는 못하였다. 이와 관련하여 본 연구에서 인공신경망을 사용하여 가우스 구적법의 가중치를 최적화하는 알고리즘을 제시하고, 이를 통해 얻어낸 가중치를 실제 문제에 적용하였다. 적용한 문제는 총 두 개이며, 정적 문제와 동적 문제를 통해 향상된 가우스 구적법의 성능을 평가하였다. 결과적으로 가우스 구적법에 사용되는 적분 점 개수를 줄일 수 있었으며 해석 시간을 대폭 감소시켰다. The method of finite spheres is a novel and reliable numerical scheme. It is easy to use since it does not require a mesh, in contrast with the finite element method. However, the method of finite spheres uses rational interpolation functions based on the Shepard functions. Thus, it requires more integration points to integrate the element matrices accurately, resulting in poor computational efficiency. In this regard, research on Gaussian quadrature for the method of finite spheres has been conducted, however, it still implies a large computational cost. Therefore, we propose an algorithm for optimizing the weights of Gaussian quadrature using supervised learning. We evaluated the performance of enhanced Gaussian quadrature using the solutions of static and dynamic problems. The results establish that the number of integration points used in the Gaussian quadrature can be reduced, thereby significantly reducing the computational cost.