LMI-based robust admissible control for uncertain singular delta operator systems

This paper investigates the problem of state feedback robust admissible control for singular delta operator systems with norm-bounded coefficient matrix uncertainties. A necessary and sufficient condition is derived to ensure the admissibility of the closed-loop singular delta operator system for all allowable uncertainties. Then, by specifying the structure of some matrix variables, the existence condition and explicit expression of a robust admissible controller are obtained in terms of strict linear matrix inequalities. Moreover, from the relation between singular discrete systems and singular delta operator systems, the corresponding results are also presented for uncertain singular discrete systems. Finally, some numerical examples are provided to demonstrate the effectiveness of the results in this paper.     

A new calibration method for ductile fracture models as chip separation criteria in machining

Several leading commercial FEM codes offer a number of fracture options without giving any guidance to the users in determining the fracture parameters for different materials. A modification is implemented to Johnson and Cook’s calibration method to provide simultaneous consideration of both active failure mechanisms in actual domain of the field variables. Application of FE simulation of machining to accumulate damage is the key point to solve problems of available calibration method. As a result, a new set of fracture constants is presented for AISI 1045 steel. It is demonstrated that due to different failure mechanism a unique fracture model cannot be the representative of crack generation in all machining zone. Then the classical Lagrangian simulation is modified based on this concept.     

Numerical simulation of low stress triaxiality ductile fracture

One of the main shortcoming of existing damage models when applied to the simulation of metal forming operations is their limited validity under low stress triaxiality conditions. An extended Gurson model incorporating the effect of void shape and relative void spacing on the growth and coalescence has been developed in order to encompass both low and large stress triaxiality regimes. The constitutive model has been implemented into an implicit finite element code within a finite strain set up. Identification procedures from experimental data are proposed and illustrated in an application on copper bars exhibiting different strain hardening capacity. A parametric analysis of the damage evolution in specimens deformed under uniaxial tension with necking demonstrates the importance of properly accounting for void shape and void coalescence in the case of large strains problems.     

Delta算子系统动态输出反馈D-稳定鲁棒协方差控制

研究Delta算子描述的线性不确定系统基于动态输出反馈的D-稳定鲁棒协方差控制问题.设计动态输出反馈控制器,使Delta算子不确定系统鲁棒D-稳定,且稳态输出协方差矩阵具有给定上界.利用线性矩阵不等式(LMI)方法,给出D-稳定鲁棒协方差控制器存在的充分条件.在此基础上,提出相应控制器的设计算法.数值算例表明了该设计方法的可行性.     

Delta算子不确定系统的多目标鲁棒 H∞控制

研究Delta算子描述的线性不确定离散系统在区域极点配置约束下的鲁棒H∞控制问题。目的是设计状态反馈控制器，使得闭环极点位于预先指定的圆形区域，且闭环系统传递函数的H∞范数小于给定的正常数。基于Delta算子系统具有H∞范数界二次D可镇定的概念，导出状态矩阵和输入矩阵均存在不确定性时，Delta算子系统具有H∞范数界的鲁棒区域极点配置的充要条件及其状态反馈设计。研究结果表明，可将现有结果推广到更为一般的情形，并可统一处理连续与离散系统的相关问题。     

Massively parallel adaptive mesh refinement and coarsening for dynamic fracture simulations

We use the graphical processing unit (GPU) to perform dynamic fracture simulation using adaptively refined and coarsened finite elements and the inter-element cohesive zone model. Due to the limited memory available on the GPU, we created a specialized data structure for efficient representation of the evolving mesh given. To achieve maximum efficiency, we perform finite element calculation on a nodal basis (i.e., by launching one thread per node and collecting contributions from neighboring elements) rather than by launching threads per element, which requires expensive graph coloring schemes to avoid concurrency issues. These developments made possible the parallel adaptive mesh refinement and coarsening schemes to systematically change the topology of the mesh. We investigate aspects of the parallel implementation through microbranching examples, which has been explored experimentally and numerically in the literature. First, we use a reduced-scale version of the experimental specimen to demonstrate the impact of variation in floating point operations on the final fracture pattern. Interestingly, the parallel approach adds some randomness into the finite element simulation on the structured mesh in a similar way as would be expected from a random mesh. Next, we take advantage of the speedup of the implementation over a similar serial implementation to simulate a specimen whose size matches that of the actual experiment. At this scale, we are able to make more direct comparisons to the original experiment and find excellent agreement with those results.     

A library for constraint consistent learning

This paper introduces the first, open source software library for Constraint Consistent Learning (CCL). It implements a family of data-driven methods that are capable of (i) learning state-independent and -dependent constraints, (ii) decomposing the behaviour of redundant systems into task- and null-space parts, and (iii) uncovering the underlying null space control policy. It is a tool to analyse and decompose many everyday tasks, such as wiping, reaching and drawing. The library also includes several tutorials that demonstrate its use with both simulated and real world data in a systematic way. This paper documents the methods contained within the library, including the implementations of said methods in tutorials and associated helper methods. The software is made freely available to the community, to enable code reuse and allow users to gain in-depth experience in statistical learning in this area.     

Integrating adaptive neuro-fuzzy inference system and local binary pattern operator for robust retinal blood vessels segmentation

Automatic extraction of blood vessels is an important step in computer-aided diagnosis in ophthalmology. The blood vessels have different widths, orientations, and structures. Therefore, the extracting of the proper feature vector is a critical step especially in the classifier-based vessel segmentation methods. In this paper, a new multi-scale rotation-invariant local binary pattern operator is employed to extract efficient feature vector for different types of vessels in the retinal images. To estimate the vesselness value of each pixel, the obtained multi-scale feature vector is applied to an adaptive neuro-fuzzy inference system. Then by applying proper top-hat transform, thresholding, and length filtering, the thick and thin vessels are highlighted separately. The performance of the proposed method is measured on the publicly available DRIVE and STARE databases. The average accuracy 0.942 along with true positive rate (TPR) 0.752 and false positive rate (FPR) 0.041 is very close to the manual segmentation rates obtained by the second observer. The proposed method is also compared with several state-of-the-art methods. The proposed method shows higher average TPR in the same range of FPR and accuracy.

     

Parallel adaptive simulations of dynamic fracture events

Finite element simulations of dynamic fracture problems usually require very fine discretizations in the vicinity of the propagating stress waves and advancing crack fronts, while coarser meshes can be used in the remainder of the domain. This need for a constantly evolving discretization poses several challenges, especially when the simulation is performed on a parallel computing platform. To address this issue, we present a parallel computational framework developed specifically for unstructured meshes. This framework allows dynamic adaptive refinement and coarsening of finite element meshes and also performs load balancing between processors. We demonstrate the capability of this framework, called ParFUM, using two-dimensional structural dynamic problems involving the propagation of elastodynamic waves and the spontaneous initiation and propagation of cracks through a domain discretized with triangular finite elements.     

A method for consistent fault coverage reporting

Procedure 5012 of Mil-Std-883, which describes requirements for the logic model, the assumed fault model and universe, fault classing, fault simulation and reporting of test results for digital microcircuits is described. The procedure provides a consistent means of measuring fault coverage regardless of the specific logic and fault simulator used. Procedure 5012 addresses complex, embedded structures such as random-access memories (RAMs), read-only memories (ROMs), and programmable logic arrays (PLAs) weighting gate-level and non-gate-level structures by transistor counts to arrive at overall fault coverage     

Sequential robust optimization of a V-bending process using numerical simulations

The coupling of finite element simulations to mathematical optimization techniques has contributed significantly to product improvements and cost reductions in the metal forming industries. The next challenge is to bridge the gap between deterministic optimization techniques and the industrial need for robustness. This paper introduces a generally applicable strategy for modeling and efficiently solving robust optimization problems based on time consuming simulations. Noise variables and their effect on the responses are taken into account explicitly. The robust optimization strategy consists of four main stages: modeling, sensitivity analysis, robust optimization and sequential robust optimization. Use is made of a metamodel-based optimization approach to couple the computationally expensive finite element simulations with the robust optimization procedure. The initial metamodel approximation will only serve to find a first estimate of the robust optimum. Sequential optimization steps are subsequently applied to efficiently increase the accuracy of the response prediction at regions of interest containing the optimal robust design. The applicability of the proposed robust optimization strategy is demonstrated by the sequential robust optimization of an analytical test function and an industrial V-bending process. For the industrial application, several production trial runs have been performed to investigate and validate the robustness of the production process. For both applications, it is shown that the robust optimization strategy accounts for the effect of different sources of uncertainty onto the process responses in a very efficient manner. Moreover, application of the methodology to the industrial V-bending process results in valuable process insights and an improved robust process design.     

Combining the real world with simulations for a robust testing of Ambient Intelligence services

This paper proposes a general architecture for testing, validating and verifying Ambient Intelligence (AmI) environments: AmISim. The development of AmI is a very complex task because this technology must often adapt to contextual information as well as unpredictable behaviours and environmental features. The architecture presented deals with AmI applications in order to cover the different components of these kinds of systems: environment, users, context and adaptation. This architecture is the first one that is able to cover all these features, which are needed in a full AmI system. The paper shows that AmISim is able to cover a complete AmI system and to provide a framework which can test scenarios that would be impossible to test in real environments or even with previous simulation approaches. Simulated and real elements coexist in AmISim for a robust testing, validation and verification of the AmI systems, which provide an easier and less costly deployment.     

A collection operator for graph transformation

Algebraic graph transformation has a wellestablished theory and associated tools that can be used to perform model transformations. However, the lack of a construct to match and transform collections of similar subgraphs makes graph transformation complex or even impractical to use in a number of transformation cases. This is addressed in this paper, by defining a collection operator which is powerful, yet simple to model and understand. A rule can contain multiple collection operators, each with lower and upper bound cardinalities, and the collection operators can be nested. An associated matching process dynamically builds a collection free rule that enables us to reuse the existing graph transformation apparatus. We present model transformation examples from different modeling domains to illustrate the benefit of the approach.     

A lipschitz operator for function strips

For function strips defined by an arithmetic interval expression, Lipschitz operators are constructed.

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Ein Lipschitz-Operator für Funktionsstreifen

Zusammenfassung Für Funktionsstreifen, welche durch einen arithmetischen Intervallausdruck definiert sind, werden zugeordnete Lipschitzoperatoren konstruiert.

     

A new consistent estimator for linear errors-in-variables models

A new estimator for linear errors-in-variables models is considered that is based on the Fourier transform of a weight function. The consistency of the estimator is verified. Examples and simulation results are also presented.     

A common operator for FFT and FEC decoding

In the Software Radio context, the parametrization is becoming an important topic especially when it comes to multi-standard designs. This paper capitalizes on the common operator technique to present new common structures for the FFT and FEC decoding algorithms. A key benefit of exhibiting common operators is the regular architecture it brings when implemented in a Common Operator Bank (COB). This regularity makes the architecture open to future function mapping and adapted to accommodated silicon technology variability through dependable design.     

A consistent discrete elements technique for curved members

A general solution method of a system of coupled differential equations governing the elastic behavior of curved members is presented. The finite element displacement method is formulated based on a variational principle. The stiffness, stability and mass matrices of the discrete finite element are consistent and are obtained within the bounds of linearized displacement theories. Examination of a convergence test indicated an extremely fast converging upper bound solutions, as expected, due to the utilization of the variational procedure. Critical loads and natural frequencies were obtained using computer programs developed. A measure of warping contribution to torsional behavior is assessed and the effects of antisymmetry of the cross sections are examined. An excellent correlation has been observed in comparative studies.     

An efficient and robust method for Lagrangian magnetic particle tracking in fluid flow simulations on unstructured grids

In this paper we report on a newly developed particle tracking scheme for fluid flow simulations on 3D unstructured grids, aiming to provide detailed insights in the particle behaviour in complex geometries. A possible field of applications is the magnetic drug targeting (MDT) technique, on which this paper will be focused. MDT is a promising medical technique that uses locally applied magnetic fields to capture magnetic drug carriers at the desired locations in the human body, strongly increasing the efficiency of medical drugs. The new particle tracking scheme combines the advantages of existing methods and is easy for implementation in a generic numerical code. The scheme is tested and validated for simple MDT cases that include effects of a non-homogeneous magnetic field on deposition of magnetic particles in laminar flow. The first test case is a validation study of the magnetic particle trajectories released in a horizontal circular pipe flow with a current-carrying wire parallel to the flow, for which analytical solutions are reported in literature. The second test case involves particle capture efficiencies in a 90° bent tube for different configurations of the imposed magnetic field. This configuration corresponds more closely to the conditions inside blood vessels, because of the presence of secondary motions. These results are compared with numerical studies from literature too. The obtained results demonstrate that the developed particle tracking scheme is a very robust, efficient and accurate method, which can give detailed insights in particle behaviour in complex geometries. As such it is a good candidate for future applications and optimisations of MDT technique for loco-regional cancer treatment or treatment of cardiovascular diseases.     

鲁棒稳定后推控制设计

研究严格反馈形式系统的鲁棒稳定控制问题.考虑输入噪声、测量噪声以及控制对象扰动的情况,通过非线性距离度量框架结构,建立了鲁棒稳定后推控制设计方法.作为应用,考虑一个时滞的二维系统,得到了闭环系统对时滞的鲁棒稳定性.