检索结果-内蒙古大学图书馆

Constrained Diffusion Kurtosis Imaging Using Ternary Quartics & MLE

MAGNETIC RESONANCE IN MEDICINE 2014年第4期71卷 1581-1591页

作者： Ghosh, Aurobrata Milne, Tristan Deriche, Rachid INRIA Sophia Antipolis Athena Project Team Mediterranee France

PurposeDiffusion kurtosis imaging (DKI) is a recent improvement over diffusion tensor imaging that characterizes tissue by quantifying non-gaussian diffusion using a 3D fourth-order kurtosis tensor. DKI needs to consider three constraints to be physically relevant. Further, it can be improved by considering the Rician signal noise model. A DKI estimation method is proposed that considers all three constraints correctly, accounts for the signal noise and incorporates efficient gradient-based optimization to improve over existing methods. MethodsThe ternary quartic parameterization is utilized to elegantly impose the positivity of the kurtosis tensor implicitly. sequential quadratic programming with analytical gradients is employed to solve nonlinear constrained optimization efficiently. Finally, a maximum likelihood estimator based on Rician distribution is considered to account for signal noise. ResultsExtensive experiments conducted on synthetic data verify a MATLAB implementation by showing dramatically improved performance in terms of estimation time and quality. Experiments on in vivo cerebral data confirm that in practice the proposed method can obtain improved results. ConclusionThe proposed ternary quartic-based approach with a gradient-based optimization scheme and maximum likelihood estimator for constrained DKI estimation improves considerably on existing DKI methods. Magn Reson Med 71:1581-1591, 2014. (c) 2013 Wiley Periodicals, Inc.

关键词： diffusion kurtosis imaging ternary quartics constrained optimization sequential quadratic programming maximum likelihood estimator

来源：评论

学校读者我要写书评

暂无评论

Structural Optimization of Cylinder-crown Integrated Hydraulic Press with Hemispherical Hydraulic Cylinder

引用

Procedia Engineering 2014年 81卷 1663-1668页

作者： Weiwei Zhang Xiaosong Wang Zongren Wang Shijian Yuan School of Materials Science and Engineering Harbin Institute of Technology Harbin 150090 China

Cylinder-crown integrated hydraulic press is an innovative press. The hemispherical hydraulic cylinder also functions as a main portion of crown. Compared with the conventional hydraulic press in which cylinder mounted in the crown, the thickness of hemispherical hydraulic cylinder could be much thinner and the crown section modulus could be much higher under the same application condition. As a result, the material strength capacity is better utilized. Based on sequential quadratic programming, structural optimization of hemispherical hydraulic cylinder for weight reduction has been carried out within the range of constraints including strength and stiffness conditions. Compared with the initial design, a lighter structure with weight reduction 7% and acceptable stress distribution has been obtained. Considering the advantages of cylinder-crown integrated hydraulic press, according to its optimization design, a 6300KN prototype hydraulic press has been manufactured.

关键词： Cylinder-crown integrated hydraulic press Optimization design sequential quadratic programming

来源：评论

学校读者我要写书评

暂无评论

NONLINEAR PRECONDITIONING TECHNIQUES FOR FULL-SPACE LAGRANGE-NEWTON SOLUTION OF PDE-CONSTRAINED OPTIMIZATION PROBLEMS

引用

SIAM JOURNAL ON SCIENTIFIC COMPUTING 2016年第5期38卷 A2756-A2778页

作者： Yang, Haijian Hwang, Feng-Nan Cai, Xiao-Chuan Hunan Univ Coll Math & Econometr Changsha 410082 Hunan Peoples R China Natl Cent Univ Dept Math Taoyuan 32001 Taiwan Univ Colorado Dept Comp Sci Boulder CO 80309 USA

The full-space Lagrange-Newton algorithm is one of the numerical algorithms for solving problems arising from optimization problems constrained by nonlinear partial differential equations. Newton-type methods enjoy fast convergence when the nonlinearity in the system is well-balanced;however, for some problems, such as the control of incompressible flows, even linear convergence is difficult to achieve and a long stagnation period often appears in the iteration history. In this work, we introduce a nonlinearly preconditioned inexact Newton algorithm for the boundary control of incompressible flows. The system has nine field variables, and each field variable plays a different role in the nonlinearity of the system. The nonlinear preconditioner approximately removes some of the field variables, and as a result, the nonlinearity is balanced and inexact Newton converges much faster when compared to the unpreconditioned inexact Newton method or its two-grid version. Some numerical results are presented to demonstrate the robustness and efficiency of the algorithm.

关键词： PDE-constrained optimizations flow control nonlinear elimination preconditioner inexact Newton method sequential quadratic programming

来源：评论

学校读者我要写书评

暂无评论

Collision Avoidance in Cooperative Missions: Bezier Surfaces for Circumnavigating Uncertain Speed Profiles

引用

JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2019年第8期42卷 1779-1796页

作者： Mehdi, Syed Bilal Choe, Ronald Hovakimyan, Naira Univ Illinois Dept Mech Sci & Engn 1206 West Green St Urbana IL 61801 USA Univ Illinois Dept Aerosp Engn 104 South Wright St Urbana IL 61801 USA

This paper presents a collision-prediction and avoidance algorithm for multivehicle cooperative missions. Using Bezier surfaces, the algorithm avoids time discretization of trajectories and is capable of considering uncertainties in speed profiles. The algorithm runs independently onboard each vehicle and, upon detection of a possible collision, replans its trajectory. Under a few assumptions, the modified trajectory is guaranteed to avoid the predicted collision as well as satisfy mission specific constraints. The deviations in position, velocity, and acceleration caused by the avoidance maneuver are small and respect bounds that can be computed offline. These bounds can be used during the mission-planning phase to guarantee satisfaction of vehicle dynamic constraints and intervehicle safety distances even during collision-avoidance maneuvers.

关键词： Vehicle Trajectories Multirotor Automatic Dependent Surveillance Broadcast National Airspace System Mixed Integer Linear programming Optimal Control Ground Station sequential quadratic programming Unmanned Aerial Vehicle Model Predictive Control

来源：评论

学校读者我要写书评

暂无评论

A novel application of integrated grasshopper optimization heuristics for attenuation of noise interferences

引用

AIN SHAMS ENGINEERING JOURNAL 2022年第2期13卷

作者： Khan, Wasim Ullah Raja, Muhammad Asif Zahoor He, Yigang Chaudhary, Naveed Ishtiaq Wuhan Univ Sch Elect Engn & Automat Wuhan 430072 Peoples R China Natl Yunlin Univ Sci & Technol Future Technol Res Ctr 123 Univ RdSect 3 Touliu 64002 Yunlin Taiwan COMSATS Univ Islamabad Dept Elect & Comp Engn Attock Campus Attock 43600 Pakistan Int Islamic Univ Dept Elect Engn Islamabad Pakistan

Novel application of integrated swarming intelligence computing paradigm is exploited for reliable treatment of nonlinear active noise control (ANC) systems using global search capacity of grasshopper optimization algorithm (GOA) combined with local search efficacy of sequential quadratic programming (SQP), i.e., GOA-SQP. The designed optimization mechanism GOA-SQP is applied to minimize the cost function of ANC controller incorporating the nonlinear Volterra filtering having linear/nonlinear primary/secondary paths in case of different noise interferences of sinusoidal, random, and complex random type signals. The comparison of the results through statistical observations in terms of accuracy, convergence and complexity indices reveals that the GOA-SQP based ANC controllers are operative, resilient and viable.(c) 2021 The Authors. Production and hosting by Elsevier B.V. on behalf of Ain Shams University. This is an open access article under the CC BY-NC-ND license (http://***/licenses/by-nc-nd/4.0/).

关键词： Active noise control Grasshopper optimization algorithm sequential quadratic programming System identification Volterra filtering

来源：评论

学校读者我要写书评

暂无评论

Task-Constrained Trajectory Planning of Free-Floating Space-Robotic Systems Using Convex Optimization

引用

JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2017年第11期40卷 2857-2870页

作者： Misra, Gaurav Bai, Xiaoli Rutgers State Univ Dept Mech & Aerosp Engn Piscataway NJ 08854 USA

This paper addresses the trajectory-planning problem for a free-floating space-robotic system for which there are no actuations on the base spacecraft. The mission considered is that the end effector is subject to task compliance constraints and the whole system is kinematically redundant such that it can incorporate various objects such as collision avoidance. Based on the conservation of the system moment, trajectory planning is formulated as a convex quadratic programming problem in the joint space. The attitude disturbance on the base spacecraft due to the dynamic coupling between the manipulator and the base is shown to be a convex function of the design variables and is incorporated in the objective function to be minimized. Physical constraints including obstacle avoidance and the bounds on the joint angles, joint velocities, and joint accelerations are directly included in the developed framework. The proposed quadratic programming formulation allows for rapid generation of optimal trajectories, which brings robustness to the planning. Numerical simulations for a 10-degree-of-freedom space manipulator validate the efficacy of the proposed approach and demonstrate the method's potential for real-time applications.

关键词： Space Robotic Systems Nonlinear programming Obstacle Avoidance Manipulators sequential quadratic programming Free Floating Space Manipulators Numerical Simulation Robots Pfaffian Constraint Forward Kinematics

来源：评论

学校读者我要写书评

暂无评论

Optimal coordinated maneuvers for three-dimensional aircraft conflict resolution

引用

JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2002年第5期25卷 888-900页

作者： Hu, JH Prandini, M Sastry, S Univ Calif Berkeley Dept Elect Engn & Comp Sci Berkeley CA 94720 USA Univ Brescia Dept Elect Automat I-25123 Brescia Italy

The problem of designing optimal conflict-free maneuvers for multiple aircraft encounters is studied. The candidate maneuvers may involve changes not only of heading and speed but also of altitude. The goal is to determine, among all of the conflict-free maneuvers, the one that minimizes a certain energy cost function. A priority mechanism is incorporated into the energy function so that optimal resolution maneuvers are such that aircraft with lower priorities assume more responsibility in resolving the conflicts. Moreover, vertical maneuvers are penalized with respect to horizontal ones for the sake of passenger comfort. A geometric construction and a numerical algorithm for computing the optimal resolution maneuvers are given in the two-aircraft case. As for the multiple-aircraft case, an approximation scheme is proposed to compute a suboptimal two-legged solution. Extensive simulation results are presented to illustrate the effectiveness of the proposed algorithms.

关键词： Commercial Aircraft sequential quadratic programming Computing Aircraft Systems Aircraft Trajectory Airspace Flight Planning MATLAB Traffic Alert and Collision Avoidance System Closely Spaced Parallel Runways

来源：评论

学校读者我要写书评

暂无评论

A velocity tracking approach for the data assimilation problem in blood flow simulations

引用

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2017年第10期33卷 2017 Oct;33(10)页

作者： Tiago, J. Guerra, T. Sequeira, A. ULisboa Dept Math Lisbon Portugal ULisboa CEMAT IST Lisbon Portugal Inst Politecnico Setubal ESTBarreiro Setubal Portugal

Several advances have been made in data assimilation techniques applied to blood flow modeling. Typically, idealized boundary conditions, only verified in straight parts of the vessel, are assumed. We present a general approach, on the basis of a Dirichlet boundary control problem, that may potentially be used in different parts of the arterial system. The relevance of this method appears when computational reconstructions of the 3D domains, prone to be considered sufficiently extended, are either not possible, or desirable, because of computational costs. On the basis of taking a fully unknown velocity profile as the control, the approach uses a discretize then optimize methodology to solve the control problem numerically. The methodology is applied to a realistic 3D geometry representing a brain aneurysm. The results show that this data assimilation approach may be preferable to a pressure control strategy and that it can significantly improve the accuracy associated to typical solutions obtained using idealized velocity profiles.

关键词： blood flow boundary control data assimilation sequential quadratic programming

来源：评论

学校读者我要写书评

暂无评论

Adjustment Method of Coupled Dual-Surface Accuracy for Antennas Using Interval Model Updating

引用

JOURNAL OF SPACECRAFT AND ROCKETS 2023年第2期60卷 556-567页

作者： Li, Tuanjie Wen, Jiangbo Shi, Zhiyang Zeng, Zijie Xidian Univ Sch Mechanoelect Engn Xian 710071 Peoples R China

Affected by the uncertainties caused by cable cutting and assembly errors, material performance dispersion, and truss deformation, the dual-surface accuracy of a mesh antenna cannot satisfy the design requirements. However, the existing methods can only adjust the accuracy of a single surface. This paper studies a method for adjusting coupled dual-surface mesh antennas considering uncertainties. Dual-reflector mesh antennas use both the front and rear reflectors for sensing, and both surfaces have shape accuracy requirements. First, an interval model updating method based on sensitivity analysis is proposed to obtain an updated interval parameters model group, which can accurately represent the relationship between adjustment cable length and surface accuracy. Then, an interval optimization function for the coupled dual-surface accuracy is established to get optimal adjustment amounts, which is solved by using the fast elitist nondominated sorting genetic algorithm (NSGA-II). Meanwhile, a kriging model is introduced to improve the optimization efficiency. Finally, the AstroMesh antenna is taken as an example to verify the validity of the proposed method. The results show that both the front and back net accuracies can be improved after adjustment, proving the proposed method's feasibility.

关键词： Kriging Model Sensitivity Analysis Trusses Genetic Algorithm Finite Element Analysis sequential quadratic programming Numerical Simulation Surrogate Model Finite Element Software

来源：评论

学校读者我要写书评

暂无评论

Evaluation of multidisciplinary optimization techniques applied to a reusable launch vehicle

引用

JOURNAL OF SPACECRAFT AND ROCKETS 2006年第6期43卷 1289-1300页

作者： Brown, Nichols F. Olds, John R. Northrop Grumman Corp Mission Syst Fairfax VA 22033 USA Georgia Inst Technol Sch Aerosp Engn Space Syst Design Lab Atlanta GA 30332 USA

Three multilevel multidisciplinary optimization techniques, Bi-Level Integrated System Synthesis, Collaborative Optimization, and Modified Collaborative Optimization, are applied to the design of a reusable launch vehicle, evaluated, and compared in this study. In addition to comparing the techniques against each other, they are also compared with designs reached via fixed-point iteration of disciplines with local optimization and the industry accepted multidisciplinary optimization technique, All-at-Once. The new multidisciplinary optimization techniques, particularly Bi-Level Integrated System Synthesis, showed greater ability than fixed-point iteration to design for a global objective and were more applicable to complex systems than All-at-Once. This study was the first time that the novel multidisciplinary optimization methods were compared qualitatively and quantitatively under controlled experimentation practices. It is still impossible to statistically determine whether any one of the novel multidisciplinary optimization techniques is better than another, because more studies using different test problems corroborating the conclusions made here are needed.

关键词： Reusable Launch Vehicle MDO Orbital Maneuvering System ISS Aerospace System sequential quadratic programming sequential Linear programming Numerical Integration Aerospace Industry Propulsion System

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：