Efficient Multirate Simulation of Complex Multibody Systems Based on Free Software

2011 ◽  
Author(s):  
Tommaso Solcia ◽  
Pierangelo Masarati
Keyword(s):  
Time Scales ◽  
Block Diagram ◽  
Computational Cost ◽  
Solution Process ◽  
General Purpose ◽  
Loop Analysis ◽  
Horizontal Axis Wind Turbine ◽  
Mechatronic Systems ◽  
Electric Generator ◽  
Analysis And Design

Complex aeroservoelastic and mechatronic systems imply interaction between multidisciplinary or multifield subcomponents, whose dynamics are characterized by problem- and field-specific time scales and frequency ranges. As opposed to what is usually termed monolithic approach to the simulation of coupled problems, where a single formulation (and software solver) directly models the entire problems, the co-simulation approach allows to exploit state-of-art formulations for specific fields by coupling them as appropriate to establish the required interaction between the subcomponents. The interaction problem between the different and even incompatible interfaces of subcomponent domains can be split in spatial and temporal. This work focuses on the latter aspect. In fact, when subdomains require different time scales to achieve the desired trade-off between accuracy and computational cost, multirate methods can be used to avoid the need of a subdomain solver to comply with excessively stringent requirements resulting from another one. Many multirate methods are designed for monoblock systems and used in single-disciplinary simulations (e.g. electric networks). Their application to co-simulation setups may be not straightforward. A key problem in co-simulation, especially when stability and free response of a system are addressed, as in aeroservoelasticity, is related to the numerical stability of the coupled solution process. This work investigates the linear stability properties of a multirate formulation called ‘Double Extrapolation’ (DE) consisting in integrating each subproblem using second-order accurate, L-stable Backward Difference Formulas (BDF) while each subdomain extrapolates the behavior of the other one. It has been chosen because it allows to eliminate most of the idle time of each subdomain solver. The resulting performance gains are illustrated by applying the proposed method to the simulation of a complex aeroservoelastic system consisting in the aeroelastic model of a Horizontal Axis Wind Turbine (HAWT), developed using the general-purpose multibody formulation implemented in the free solver MBDyn, and a dynamic model of the electric generator, modeled in the free general-purpose block-diagram simulation environment ScicosLab. Both modeling environments are real-time capable; thus the proposed system represents an affordable and versatile solution for the hardware-in-the-loop analysis and design of complex multidisciplinary systems.

An Alternate Algorithm for (3x3) Median Filtering of Digital Images

2012 ◽  
Vol 2 (1) ◽  
pp. 7-9 ◽  
Author(s):  
Satinderjit Singh
Keyword(s):  
Median Filter ◽  
Computational Cost ◽  
Spatial Coherence ◽  
General Purpose ◽  
Median Filtering ◽  
Basic Algorithm ◽  
Temporal Complexity ◽  
Filter Kernel ◽  
One Step ◽  
High Computational Cost

Median filtering is a commonly used technique in image processing. The main problem of the median filter is its high computational cost (for sorting N pixels, the temporal complexity is O(N·log N), even with the most efficient sorting algorithms). When the median filter must be carried out in real time, the software implementation in general-purpose processorsdoes not usually give good results. This Paper presents an efficient algorithm for median filtering with a 3x3 filter kernel with only about 9 comparisons per pixel using spatial coherence between neighboring filter computations. The basic algorithm calculates two medians in one step and reuses sorted slices of three vertical neighboring pixels. An extension of this algorithm for 2D spatial coherence is also examined, which calculates four medians per step.

Multirow Intersection Cuts Based on the Infinity Norm

2021 ◽  
Author(s):  
Álinson S. Xavier ◽  
Ricardo Fukasawa ◽  
Laurent Poirrier
Keyword(s):  
Optimization Problems ◽  
Valid Inequalities ◽  
Linear Optimization ◽  
Computational Cost ◽  
General Purpose ◽  
Mixed Integer ◽  
Infinity Norm ◽  
Intersection Cuts ◽  
Linear Optimization Problems ◽  
Mixed Integer Linear Optimization

When generating multirow intersection cuts for mixed-integer linear optimization problems, an important practical question is deciding which intersection cuts to use. Even when restricted to cuts that are facet defining for the corner relaxation, the number of potential candidates is still very large, especially for instances of large size. In this paper, we introduce a subset of intersection cuts based on the infinity norm that is very small, works for relaxations having arbitrary number of rows and, unlike many subclasses studied in the literature, takes into account the entire data from the simplex tableau. We describe an algorithm for generating these inequalities and run extensive computational experiments in order to evaluate their practical effectiveness in real-world instances. We conclude that this subset of inequalities yields, in terms of gap closure, around 50% of the benefits of using all valid inequalities for the corner relaxation simultaneously, but at a small fraction of the computational cost, and with a very small number of cuts. Summary of Contribution: Cutting planes are one of the most important techniques used by modern mixed-integer linear programming solvers when solving a variety of challenging operations research problems. The paper advances the state of the art on general-purpose multirow intersection cuts by proposing a practical and computationally friendly method to generate them.

The effect of dome properties on design of the axial symmetric cylindrical wall

2021 ◽  
Vol 7 (1) ◽  
pp. 11
Author(s):  
Aylin Ece Kayabekir
Keyword(s):  
Reinforced Concrete ◽  
Computer Program ◽  
Numerical Investigation ◽  
Computer Software ◽  
General Purpose ◽  
Design Stage ◽  
Cylindrical Wall ◽  
Support Condition ◽  
Structural Concrete ◽  
Analysis And Design

The usage of computer software in civil engineering has expanded in last decades. Many general-purpose and special-purpose commercial programs perform a very important function, especially at the design stage. In this study, a computer program is introduced for the analysis and design of the axial symmetric cylindrical wall considering the dome effects. Analysis processes are carried out according to Flexibility theory with long wall assumption and during the reinforced concrete (RC) design of the wall, ACI 318-Building code requirements for structural concrete are considered. In numerical investigation, the effects of the dome properties (thickness and height) on the analysis and design of the wall are investigated by performing a totally 72 case analyzes. These cases include different support condition at bottom of the wall, wall heights, dome thicknesses and heights. According to analysis results, it is concluded that effects of dome thickness and heights on the wall on the wall are very limited.

Applications of Symbolic Computing for Numerical Analysis of Mechanical Systems

1989 ◽  
Author(s):  
H. Ashrafiuon ◽  
N. K. Mani
Keyword(s):  
Numerical Analysis ◽  
Optimal Design ◽  
System Dynamics ◽  
Multibody System ◽  
Computing System ◽  
General Purpose ◽  
Kinematic Constraints ◽  
Symbolic Computing ◽  
Analysis And Design ◽  
Construct System

Abstract The symbolic computing system MACSYMA is used to automatically generate the explicit equations necessary to represent the kinematic constraints and system dynamics and to compute the design sensitivities for optimal design of any multibody system. The logic to construct system matrices and vectors involved in the analysis and design equations is implemented as general purpose MACSYMA programs. All necessary manipulations are performed by MACSYMA and the equations are output as FORTRAN statements that can be compiled and executed. This approach results in a computational saving of up to 95% compared to using a general purpose programs. The approach is general in nature and is applicable to any multibody system. Examples are presented to demonstrate the effectiveness of the approach.

Analysis and Optimal Design of Spatial Mechanical Systems

1987 ◽  
Author(s):  
H. Ashrafeiuon ◽  
N. K. Mani
Keyword(s):  
Sensitivity Analysis ◽  
Optimal Design ◽  
Dynamic Analysis ◽  
Equations Of Motion ◽  
Mechanical Systems ◽  
Design Sensitivity ◽  
General Purpose ◽  
Design Sensitivity Analysis ◽  
Analysis And Design ◽  
Spatial Systems

Abstract This paper presents a new approach to optimal design of large multibody spatial mechanical systems. This approach uses symbolic computing to generate the necessary equations for dynamic analysis and design sensitivity analysis. Identification of system topology is carried out using graph theory. The equations of motion are formulated in terms of relative joint coordinates through the use of velocity transformation matrix. Design sensitivity analysis is carried out using the Direct Differentiation method applied to the relative joint coordinate formulation for spatial systems. Symbolic manipulation programs are used to develop subroutines which provide information for dynamic and design sensitivity analysis. These subroutines are linked to a general purpose computer program which performs dynamic analysis, design sensitivity analysis, and optimization. An example is presented to demonstrate the efficiency of the approach.

Sequential Simulation Used in the Computer Aided Design of Airfoils for Horizontal Axis Wind Turbine Rotors

2005 ◽  
Author(s):  
Sarim N. Al-Zubaidy ◽  
Alwyn Johnson ◽  
Jacqueline Bridge
Keyword(s):  
Growth Rate ◽  
Wind Turbine ◽  
Computer Aided Design ◽  
Fluid Dynamic ◽  
Numerical Procedure ◽  
Design Procedure ◽  
Horizontal Axis ◽  
Horizontal Axis Wind Turbine ◽  
Analysis And Design ◽  
Turbine Rotors

In the past twenty years wind energy remerged on the world scene with a very healthy growth rate, it has outstripped photovoltaics as the world’s fastest growing energy source, with a growth rate in excess of 30 percent per annum. The proposed paper presents a numerical procedure for the analysis and design of Horizontal Axis Wind Turbine rotors for fabrication in countries with limited manufacturing base and limited design expertise. To ascertain the accuracy and to determine where further improvements could be initiated; numerical findings were then compared with published experimental test data, the compression showed an average deviation of less than 3%. Once the approach was validated and standardized an airfoil design was produced. A computational fluid dynamic code coupled with a simple numerical algorithm aided the inverse design procedure. The final design is well proportioned and theoretically able to meet the stated objective and satisfied the constraints. The generated geometrical data is in a form suitable for manufacture using local manufacturing capabilities, the primary objective of this work.

scholarly journals Robustness Can Be Cheap: A Highly Efficient Approach to Discover Outliers under High Outlier Ratios

2019 ◽  
Vol 33 ◽  
pp. 5313-5320
Author(s):  
Siqi Wang ◽  
En Zhu ◽  
Xiping Hu ◽  
Xinwang Liu ◽  
Qiang Liu ◽  
...  
Keyword(s):  
Computational Cost ◽  
Solution Process ◽  
Closed Form Solution ◽  
Form Solution ◽  
Low Rank ◽  
Alternative Formulation ◽  
Efficient Detection ◽  
Comparable Performance ◽  
High Space ◽  
High Outlier

Efficient detection of outliers from massive data with a high outlier ratio is challenging but not explicitly discussed yet. In such a case, existing methods either suffer from poor robustness or require expensive computations. This paper proposes a Low-rank based Efficient Outlier Detection (LEOD) framework to achieve favorable robustness against high outlier ratios with much cheaper computations. Specifically, it is worth highlighting the following aspects of LEOD: (1) Our framework exploits the low-rank structure embedded in the similarity matrix and considers inliers/outliers equally based on this low-rank structure, which facilitates us to encourage satisfying robustness with low computational cost later; (2) A novel re-weighting algorithm is derived as a new general solution to the constrained eigenvalue problem, which is a major bottleneck for the optimization process. Instead of the high space and time complexity (O((2n)2)/O((2n)3)) required by the classic solution, our algorithm enjoys O(n) space complexity and a faster optimization speed in the experiments; (3) A new alternative formulation is proposed for further acceleration of the solution process, where a cheap closed-form solution can be obtained. Experiments show that LEOD achieves strong robustness under an outlier ratio from 20% to 60%, while it is at most 100 times more memory efficient and 1000 times faster than its previous counterpart that attains comparable performance. The codes of LEOD are publicly available at https://github.com/demonzyj56/LEOD.

Numerical Prediction of Poly-Dispersed Condensation Using Quadrature Method of Moments and Multi-Fluid Model

2017 ◽  
Author(s):  
Anjaneyulu Lankadasu ◽  
Laurent Krumenacker ◽  
Anil Kumar ◽  
Amita Tripathi
Keyword(s):  
Method Of Moments ◽  
Laval Nozzle ◽  
High Efficiency ◽  
Fluid Model ◽  
Computational Cost ◽  
Droplet Size Distribution ◽  
General Purpose ◽  
Navier Stokes ◽  
Quadrature Method ◽  
Quadrature Method Of Moments

Accurate prediction of condensation plays an important role in the development of high efficiency turbo-machines working on condensable fluid. Therefore it demands modeling of poly-disperse characteristic of number distribution function while modeling condensation. Two such kind of models are considered in this work and they are namely, quadrature method of moments (QMOM) and multi-fluid method (MFM) models. The vital difference between these two models lies in the method of discretisation of the droplet size distribution. Further, their numerical aspects like ease of implementation in general purpose computational fluid dynamics solvers, accuracy and associated computational cost are discussed. In order to obtain accurate thermodynamic properties, the real gas formulations defined in IAPWS-IF97 are used. These algorithms are applied to the compressible Navier-Stokes solver of Fluidyn MP and tests are carried on Laval nozzle and compared with the experimental measurements.

Development of a Pressure-Based Coupled CFD Solver for Turbulent and Compressible Flows in Turbomachinery Applications

2014 ◽  
Author(s):  
Luca Mangani ◽  
Marwan Darwish ◽  
Fadl Moukalled
Keyword(s):  
Compressible Flows ◽  
Stokes Equations ◽  
Computational Cost ◽  
Simple Algorithm ◽  
Numerical Data ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Analysis And Design ◽  
Flow Problems ◽  
Matrix Coefficients

In this paper we present a fully coupled algorithm for the resolution of compressible flows at all speed. The pressure-velocity coupling at the heart of the Navier Stokes equations is accomplished by deriving a pressure equation in similar fashion to what is done in the segregated SIMPLE algorithm except that the influence of the velocity fields is treated implicitly. In a similar way, the assembly of the momentum equations is modified to treat the pressure gradient implicitly. The resulting extended system of equations, now formed of matrix coefficients that couples the momentum and pressure equations, is solved using an algebraic multigrid solver. The performance of the coupled approach and the improved efficiency of the novel developed code was validated comparing results with experimental and numerical data available from reference literature test cases as well as with segregated solver as exemplified by the SIMPLE algorithm. Moreover the reference geometries considered in the validation process cover the typical aerodynamics applications in gas turbine analysis and design, considering Euler to turbulent flow problems and clearly indicating the substantial improvements in terms of computational cost and robustness.

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