• Title, Summary, Keyword: Time Integration

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Explicit time integration algorithm for fully flexible cell simulation (외연적 적분 기법을 적용한 Fully Flexible Cell 분자 동영학 시뮬레이션)

  • Park Shi-Dong;Cho Maeng-Hyo
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • pp.389-394
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    • 2006
  • Fully flexible cell preserves Hamiltonian in structure, so the symplectic time integrator is applied to the equations of motion. Primarily, generalized leapfrog time integration (GLF) is applicable, but the equations of motion by GLF have some of implicit formulas. The implicit formulas give rise to a complicate calculation for coding and need an iteration process. In this paper, the time integration formulas are obtained for the fully flexible cell molecular dynamics simulation by using the splitting time integration. It separates flexible cell Hamiltonian into terms corresponding to each of Hamiltonian term, so the simple and completely explicit recursion formula was obtained. The explicit formulas are easy to implementation for coding and may be reduced the integration time because they are not need iteration process. We are going to compare the resulting splitting time integration with the implicit generalized leapfrog time integration.

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A Splitting Time Integrator for Fully Flexible Cell Molecular Dynamics (분할 적분 기법을 적용한 N-sigma-T 분자동역학 전산모사)

  • Park, Shi-Dong;Cho, Maeng-Hyo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.31 no.8
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    • pp.826-832
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    • 2007
  • Fully flexible cell preserves Hamiltonian in structure so that the symplectic time integrator is applicable to the equations of motion. In the direct formulation of fully flexible cell N-Sigma-T ensemble, a generalized leapfrog time integration (GLF) is applicable for fully flexible cell simulation, but the equations of motion by GLF has structure of implicit algorithm. In this paper, the time integration formula is derived for the fully flexible cell molecular dynamics simulation by using the splitting time integration. It separates flexible cell Hamiltonian into terms corresponding to each of Hamiltonian term. Thus the simple and completely explicit recursion formula was obtained. We compare the performance and the result of present splitting time integration with those of the implicit generalized leapfrog time integration.

Accuracy Analysis of GLONASS Orbit Determination Strategies for GLONASS Positioning (GLONASS 측위를 위한 위성좌표 산출 정확도 향상 방안)

  • Lee, Ho-Seok;Park, Kwan-Dong;Kim, Hye-In
    • Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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    • v.28 no.6
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    • pp.573-578
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    • 2010
  • Precise determination of satellite positions is necessary to improve positioning accuracy in GNSS. In this study, GLONASS orbits were predicted from broadcast ephemeris using the 4th-order Runge-Kutta numerical integration method and their accuracy dependence on the integration step and the integration time was analyzed. The 3D RMS (Root Mean Square) differences between the results from I-second integration step and 300-second integration step was about 3 cm, but the processing time was one hundred times less for the I-second integration time case. For trials of different integration times, the 3D RMS errors were 8.3 m, 187.3 m, and 661.5 m for 30-, 150-, and 300-minutes of integration time, respectively. Though this integration-time analysis, we concluded that the accuracy gets higher with a shorter integration time. Thus we suggest forward and backward integration methods to improve GLONASS positioning accuracy, and with this method we can achieve a 5-meter level of 3-D orbit accuracy.

Performance Characteristics for the Variation of Altitude and Tilt Angle in the Satellite Imager Using Time Delay and Integration(TDI) (Time Delay and Integration(TDI)을 사용하는 위성 영상 기기의 고도 및 촬영각 변화에 대한 성능 특성)

  • 조영민
    • Korean Journal of Remote Sensing
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    • v.18 no.2
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    • pp.91-96
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    • 2002
  • The performance characteristics of a satellite imager using a Time Delay and Integration(TDI) Charge Coupled Device (CCD) with fixed integration time is investigated for the variation of satellite altitude and tilt angle. In consequence of the investigation TDI synchronization using tilt imaging is proposed as a solution to compensate geometric performance degradation due to altitude decrease. The tilt angle optimized for the TDI synchronization at decreased altitude is presented. This result can be used for a TDI CCD imager with variable integration time in a certain range as well.

A novel two sub-stepping implicit time integration algorithm for structural dynamics

  • Yasamani, K.;Mohammadzadeh, S.
    • Earthquakes and Structures
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    • v.13 no.3
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    • pp.279-288
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    • 2017
  • Having the ability to keep on yielding stable solutions in problems involving high potential of instability, composite time integration methods have become very popular among scientists. These methods try to split a time step into multiple sub-steps so that each sub-step can be solved using different time integration methods with different behaviors. This paper proposes a new composite time integration in which a time step is divided into two sub-steps; the first sub-step is solved using the well-known Newmark method and the second sub-step is solved using Simpson's Rule of integration. An unconditional stability region is determined for the constant parameters to be chosen from. Also accuracy analysis is perform on the proposed method and proved that minor period elongation as well as a reasonable amount of numerical dissipation is produced in the responses obtained by the proposed method. Finally, in order to provide a practical assessment of the method, several benchmark problems are solved using the proposed method.

Analysis of delay compensation in real-time dynamic hybrid testing with large integration time-step

  • Zhu, Fei;Wang, Jin-Ting;Jin, Feng;Gui, Yao;Zhou, Meng-Xia
    • Smart Structures and Systems
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    • v.14 no.6
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    • pp.1269-1289
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    • 2014
  • With the sub-stepping technique, the numerical analysis in real-time dynamic hybrid testing is split into the response analysis and signal generation tasks. Two target computers that operate in real-time may be assigned to implement these two tasks, respectively, for fully extending the simulation scale of the numerical substructure. In this case, the integration time-step of solving the dynamic response of the numerical substructure can be dozens of times bigger than the sampling time-step of the controller. The time delay between the real and desired feedback forces becomes more striking, which challenges the well-developed delay compensation methods in real-time dynamic hybrid testing. This paper focuses on displacement prediction and force correction for delay compensation in the real-time dynamic hybrid testing with a large integration time-step. A new displacement prediction scheme is proposed based on recently-developed explicit integration algorithms and compared with several commonly-used prediction procedures. The evaluation of its prediction accuracy is carried out theoretically, numerically and experimentally. Results indicate that the accuracy and effectiveness of the proposed prediction method are of significance.

Implementation of Optical neural Netwoks Based on Parallel rank-One Interconnections and Time Integration

  • Jeon, Ho-In;Choi, Jin-San;Shin, Chang-Min;Kang, Yo-Sik;Jung, Nak-Hee
    • Proceedings of the Optical Society of Korea Conference
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    • pp.220-221
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    • 1998
  • An optical implementation of higher order neural networks based on based principal component analysis and time integration has been described. The principal component analysis combined with time integration allows larger input size than fully spatial neural networks at the cost certain amount of time consumption. This time-integration usage actually breaks down the barrier of the maximum space-bandwidth product that optical systems can offer.

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Parallel Integration for Real-Time Simulation (실시간 시뮬레이션을 위한 병렬적분)

  • Lee, W.S.;Samson, J.
    • Transactions of the Korean Society of Automotive Engineers
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    • v.2 no.1
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    • pp.106-115
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    • 1994
  • A parallel integration approach is proposed for real-time simulation of controlled mechanical systems. The proposed approach, which employs the dual-rate integration method in a parallel computing environment, is developed to deal with stiffness and high frequency characteristics of the controlled mechanical systems effectively. Numerical experiments are performed to demonstrate the effectiveness of the approach in shared memory multiprocessors, Alliant FX/8 and Alliant FX/80.

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Performance Characteristics of Time Delay and Integration(TDI) Satellite Imager for Altitude Change and Line-Of-Sight Tilt over Spherical Earth Surface

  • Cho, Young-Min
    • Proceedings of the KSRS Conference
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    • pp.216-221
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    • 2002
  • A spherical Earth surface is used fur realistic analysis of the geometrical performance characteristics about the variation of satellite altitude and 2-dimensional line-of-sight(LOS) tilt angle in a satellite imager using Time Delay and Integration(TDI) technique with fixed integration time. In the spherical Earth surface model TDI synchronization using LOS tilt is investigated as a solution to compensate geometric performance degradation due to altitude decrease. This result can be used fur a TDI CCD imager with variable integration time in a certain as well.

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Integrated equations of motion for direct integration methods

  • Chang, Shuenn-Yih
    • Structural Engineering and Mechanics
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    • v.13 no.5
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    • pp.569-589
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    • 2002
  • In performing the dynamic analysis, the step size used in a step-by-step integration method might be much smaller than that required by the accuracy consideration in order to capture the rapid chances of dynamic loading or to eliminate the linearization errors. It was first found by Chen and Robinson that these difficulties might be overcome by integrating the equations of motion with respect to time once. A further study of this technique is conducted herein. This include the theoretical evaluation and comparison of the capability to capture the rapid changes of dynamic loading if using the constant average acceleration method and its integral form and the exploration of the superiority of the time integration to reduce the linearization error. In addition, its advantage in the solution of the impact problems or the wave propagation problems is also numerically demonstrated. It seems that this time integration technique can be applicable to all the currently available direct integration methods.