检索结果-内蒙古大学图书馆

作者： Mekala, Venkata Texas A&M University

Clock mesh is widely used in microprocessor designs for achieving low clock skew and high process variation tolerance. Clock mesh optimization is a very diffcult problem to solve because it has a highly connected structure and requires accurate delay models which are computationally expensive. Existing methods on clock network optimization are either restricted to clock trees, which are easy to be separated into smaller problems, or naive heuristics based on crude delay models. A clock mesh sizing algorithm, which is aimed to minimize total mesh wire area with consideration of clock skew constraints, has been proposed in this research work. This algorithm is a systematic solution search through rigorous sequential quadratic programming (SQP). The SQP is guided by an efficient adjoint sensitivity analysis which has near-SPICE(Simulation Program for Integrated Circuits Emphasis)-level accuracy and faster-than-SPICE speed. Experimental results on various benchmark circuits indicate that this algorithm leads to substantial wire area reduction while maintaining low clock skew in the clock mesh. The reduction in mesh area achieved is about 33%.

关键词： Optimization Clock Distribution Network sequential quadratic programming Book Thesis

来源：评论

学校读者我要写书评

暂无评论

Multidisciplinary Considerations in the Design of Wings and Wing Tip Devices

引用

JOURNAL OF AIRCRAFT 2010年第2期47卷 534-543页

作者： Ning, S. Andrew Kroo, Ilan Stanford Univ Dept Aeronaut & Astronaut Stanford CA 94305 USA

Conceptual wing design analysis methods are combined with numerical optimization to find minimum-drag wings subject to constraints on lift, weight, pitching moment, and stall speed. Tip extensions and winglets designed for minimum drag achieve similar performance, with the optimal solution depending on the ratio of the maneuver lift coefficient to the cruise lift coefficient. The results highlight the importance of accounting for the depth of the wing structural box in the weight model and including constraints on stall speed. For tailless aircraft, C-wings show a slight performance advantage over wings with winglets when longitudinal trim and stability constraints are considered. This performance advantage is more significant for span-constrained or low-sweep designs. Finally, to demonstrate other possible applications of the method, planar wings with active load alleviation are optimized, showing drag savings on the order of 15%.

关键词： Wing Tip Aerodynamic Center High Lift Device Lift Coefficient Lift to Drag Ratio Numerical Optimization Structural Load High Aspect Ratio Sweep Angle sequential quadratic programming

来源：评论

学校读者我要写书评

暂无评论

Rapid Generation of Accurate Entry Landing Footprints

引用

JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2010年第3期33卷 756-767页

作者： Lu, Ping Xue, Songbai Iowa State Univ Dept Aerosp Engn Ames IA 50011 USA

Rapid and reliable generation of the landing footprint of an entry vehicle is the key capability required for onboard determination of landing options. Under the conventional formulation of the maximum-crossrange problem at specified downranges, the footprint problem is difficult to numerically solve. When inequality trajectory constraints are imposed, accurate determination of footprints becomes even more challenging. Using the quasi-equilibrium glide condition in entry flight, a near-optimal closed-form bank angle control law is first developed for the class of problems, including the maximum-crossrange problem. Then, it is shown that the footprint problem is equivalent to seeking the solutions of a series of much simpler problems of the closest approach to a moving virtual target. The closest-approach problem is a univariate root-finding problem using the near-optimal control law. Common inequality entry trajectory constraints are enforced, without any additional difficulty, with appropriate velocity-dependent bounds of the bank angle by using the quasi-equilibrium glide condition. As a result, an accurate and fully constrained landing footprint from any feasible initial condition can be obtained rapidly and very reliably. The validity of the method is verified with independent trajectory optimization software. Footprints for an entry vehicle in several different mission scenarios and constraint settings are generated to demonstrate the method.

关键词： Aerodynamic Coefficients Transversality Condition Earth Flight Path Angle Angle of Attack Flight Control System Newton Raphson Method Dynamic Pressure sequential quadratic programming International Space Station

来源：评论

学校读者我要写书评

暂无评论

A Filter-Based Sample Average SQP for Optimization Problems With Highly Nonlinear Probabilistic Constraints

引用

JOURNAL OF MECHANICAL DESIGN 2010年第11期132卷 111002-111002页

作者： Hsu, Kai-Shian Chan, Kuei-Yuan Natl Cheng Kung Univ Tainan 70101 Taiwan

In this work, we develop a filter-based sequential quadratic programming (SQP) algorithm for solving reliability-based design optimization (RBDO) problems with highly nonlinear constraints. The proposed filter-based SQP uses the approach of average importance sampling (AAIS) in calculating the values and gradients of probabilistic constraints. AAIS allocates samples at the limit state boundaries such that relatively few samples are required in calculating constraint probability values to achieve high accuracy and low variance. The accuracy of probabilistic constraint gradients using AAIS is improved by a sample filter that eliminates sample outliers that have low probability of occurrence and high gradient values. To ensure convergence, the algorithm uses an iteration filter in place of the penalty function to avoid the ill-conditioning problems of the penalty parameters in the acceptance of a design update. A sample reuse mechanism that improves the efficiency of the algorithm by avoiding redundant samples is introduced. The "unsampled" region, the region not covered by previous samples, is identified using iteration step lengths, the trust region, and constraint reliability levels. As a result, the filter-based sampling SQP efficiently handles highly nonlinear probabilistic constraints with multiple most probable points or functions without analytical forms. Several examples are demonstrated, and the results are compared with those from first order reliability method/second order reliability method and Monte Carlo simulations. Results show that by integrating the modified AAIS with the filter-based SQP, the overall computation cost of solving RBDO problems can be significantly reduced. [DOI: 10.1115/1.4002560]

关键词： sequential quadratic programming approach of average importance sampling reliability-based design optimization gradient of probability function

来源：评论

学校读者我要写书评

暂无评论

On Gradient Computation in Single-shooting Nonlinear Model Predictive Control

引用

IFAC Proceedings Volumes 2010年第5期43卷 613-618页

作者： Ruben Ringset Lars Imsland Bjarne Foss Cybernetica AS Leirfossveien 27 N-7038 Trondheim Norway Department of Engineering Cybernetics NTNU N-7038 Trondheim Norway

This paper gives an overview of methods for computing derivative information in dynamic optimization with path constraints. Efficiency of forward and adjoint techniques are discussed in a discrete-time setting and some algorithms are derived. Next, the discussion is extended to also include continuous-discrete systems. Dimensions in the model, signal parameterization, horizon length and sampling interval affect each of the methods differently. The key contributions of this paper is to give an overview of these methods, how they can be combined, and how different parameters affect efficiency.

关键词： dynamic optimization nonlinear model predictive control adjoint method sensitivity analysis sequential quadratic programming

来源：评论

学校读者我要写书评

暂无评论

Comparison of Surrogate Models in a Multidisciplinary Optimization Framework for Wing Design

引用

AIAA JOURNAL 2010年第5期48卷 995-1006页

作者： Paiva, Ricardo M. Carvalho, Andre R. D. Crawford, Curran Suleman, Afzal Univ Victoria Dept Mech Engn Victoria BC V8W 2Y2 Canada

The replacement of the analysis portion of an optimization problem by its equivalent metamodel usually results in a lower computational cost. In this paper, a conventional nonapproximative approach is compared against three different metamodels: quadratic-interpolation-based response surfaces, Kriging, and artificial neural networks. The results obtained from the solution of four different case studies based on aircraft design problems reinforces the idea that quadratic interpolation is only well-suited to very simple problems. At higher dimensionality, the usage of the more complex Kriging and artificial neural networks models may result in considerable performance benefits.

关键词： Surrogate Model Multilayer Perceptron Aircraft Design Aerodynamic Shape Optimization Cumulative Distribution Function MDO Lift to Drag Ratio sequential quadratic programming Reynolds Averaged Navier Stokes Thickness Ratio

来源：评论

学校读者我要写书评

暂无评论

Two-dimensional Trajectory Optimization of a Soft Lunar Landing from a Parking Orbit Considering a Landing Site

引用

IFAC Proceedings Volumes 2010年第15期43卷 178-183页

作者： Jong-Sun Ahn Bong-Gyun Park Min-Jea Tahk Space Exploration Engineering Department Korea Advanced Institute of Science and Technology Daejeon Korea Aerospace Engineering Department Korea Advanced Institute of Science and Technology Daejeon Korea (Tel:82-42-350-5758) Aerospace Engineering Department Korea Advanced Institute of Science and Technology Daejeon Korea

Abstract In this paper, minimum-fuel, two-dimensional trajectory optimization from a parking orbit to the desired landing site is presented. The landing site is usually not considered when performing the trajectory optimization. However, to design the precise trajectories to land at the desired site, the landing site has to be considered as the terminal constraint. To convert the trajectory optimization problem into a parameter optimization problem, a pseudospcetral (PS) method is used, and CFSQP is used as a numerical solver. To check that the results obtained are good solutions, the feasibility check is performed.

关键词： Soft landing trajectory optimization legendre pseudospectral method pseudospectral knotting method sequential quadratic programming

来源：评论

学校读者我要写书评

暂无评论

A ROBUST MINIMUM VOLUME ENCLOSING SIMPLEX ALGORITHM FOR HYPERSPECTRAL UNMIXING

A ROBUST MINIMUM VOLUME ENCLOSING SIMPLEX ALGORITHM FOR HYPE...

引用

IEEE International Conference on Acoustics, Speech, and Signal Processing

作者： ArulMurugan Ambikapathi Tsung-Han Chan Wing-Kin Ma Chong-Yung Chi Inst. Commun. Eng. National Tsing Hua Univ. Hsinchu Taiwan Dept. Electronic Eng. Chinese Univ. Hong Kong Shatin N.T. Hong Kong

ISBN: (纸本)9781424442959

Hyperspectral unmixing is a process of extracting hidden spectral signatures (or endmembers) and the corresponding proportions (or abundances) of a scene, from its hyperspectral observations. Motivated by Craig's belief, we recently proposed an alternating linear programming based hyperspectral unmixing algorithm called minimum volume enclosing simplex (MVES) algorithm, which can yield good unmixing performance even for instances of highly mixed data. In this paper, we propose a robust MVES algorithm called RMVES algorithm, which involves probabilistic reformulation of the MVES algorithm, so as to account for the presence of noise in the observations. The problem formulation for RMVES algorithm is manifested as a chance constrained program, which can be suitably implemented using sequential quadratic programming (SQP) solvers in an alternating fashion. Monte Carlo simulations are presented to demonstrate the efficacy of the proposed RMVES algorithm over several existing benchmark hyperspectral unmixing methods, including the original MVES algorithm.

关键词： Convex analysis Hyperspectral unmixing Minimum-volume enclosing simplex Chance constrained program sequential quadratic programming

来源：评论

学校读者我要写书评

暂无评论

Second-Order DMOC Using Projection

Second-Order DMOC Using Projection

引用

2010 49th IEEE Conference on Decision and Control

作者： Kristine L. Snyder Todd D. Murphey Department of Applied Mathematics 526 UCB University of Colorado Boulder CO 80309 Department of Mechanical Engineering Northwestern University 2145 Sheridan Road Evanston IL 60208 USA

ISBN: (纸本)9781424477456

Discrete mechanics and optimal control (DMOC) is a recent development in optimal control of mechanical systems that takes advantage of the variational structure of mechanics when discretizing the optimal control problem. Typically, the discrete Euler-Lagrange equations are used as constraints on the feasible set of solutions, and then the objective function is minimized using a constrained optimization algorithm, such as sequential quadratic programming (SQP). In contrast, this paper illustrates that by reducing dimensionality by projecting onto the feasible subspace and then performing optimization, one can obtain significant improvements in convergence, going from superlinear to quadratic convergence. Moreover, whereas numerical SQP can run into machine precision problems before terminating, the projection-based technique converges easily. Double and single pendulum examples are used to illustrate the technique.

关键词： Optimal control mechanic Mechanics Supralinearity Mechanical systems Optimization algorithms Objective function Machine Precision quadratic Convergence Converge sequential quadratic programming

来源：评论

学校读者我要写书评

暂无评论

Probabilistic limit and shakedown analysis of thin plates and shells

引用

STRUCTURAL SAFETY 2009年第1期31卷 1-18页

作者： Tran, Thanh Ngoc Kreissig, R. Staat, M. Aachen Univ Appl Sci D-52428 Julich Germany Tech Univ Chemnitz Fac Mech Engn D-09107 Chemnitz Germany

The reliability analysis of plates and shells with respect to plastic collapse or to inadaptation is formulated on the basis of limit and shakedown theorems. Based on a direct definition of file limit state function, the non-linear problems may be efficiently solved by using the first and second-order reliability methods (FORM/SORM). In order to get the design point, it non-linear optimisation was implemented. Sensitivity analyses are obtained numerically from a mathematical problem. This direct approach reduces considerably the necessary knowledge of uncertain technological input data, computing costs and the numerical error. Numerical examples are presented to show the validity and effectiveness of the present method. (C) 2007 Elsevier Ltd. All rights reserved.

关键词： Limit analysis Shakedown analysis sequential quadratic programming First-order reliability method Second-order reliability method Design point

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：