Robustness of declarative modeling languages: Improvements via probability-one homotopy

Robustness issues with steady-state initialization remain a barrier in the practical use of declarative modeling languages for multi-domain modeling of large, complex, and heterogeneous technical systems. The objective of this paper is to illustrate how probability-one homotopy, an established method from topology, can solve this issue. This is achieved by establishing a framework for application-specific probability-one homotopy in declarative modeling languages. The analysis is based on domain-specific probability-one homotopy maps, which were reformulated in a declarative fashion. Additionally, a novel probability-one homotopy map and associated coercivity proof is introduced for a class of thermo-fluid dynamics problems. It was found that the approach enables robust initialization for declarative modeling languages on several test cases and leads to a concise declarative problem formulation.     

Robust model updating with insufficient data

The increasing need of many industrial fields for highly accurate predictions of performance and reliability gives rise to the need for enhanced underlying mathematical models. The thereby available test data are usually rather limited due to the high costs of experimental measurements. Therefore, decisions have to be made based on limited, incomplete information, which poses a challenging problem.Recently, an approach for coping with insufficient data has been introduced that attempts to extract the information delivered by the data and processes it using few additional assumptions. The underlying distribution is based on an appropriate confidence level providing a safeguard against severe underestimation of the variability of the measured quantities. This method has been applied within the field of statics involving the stochastic identification of one single structural parameter. The present paper shows the extension of this approach to the field of dynamics. It is shown how to deal with insufficient information by applying kernel densities on the stochastic representation of modal data. In addition, the problem of correlation of the established multi-dimensional probability density function will be addressed. As a numerical example the structural dynamics application of the Validation Challenge Workshop has been chosen.     

Robust decentralized PID-based power system stabilizer design using an ILMI approach

Thanks to its essential functionality and structure simplicity, proportional-integral-derivative (PID) controllers are commonly used by industrial utilities. A robust PID-based power system stabilizer (PSS) is proposed to properly function over a wide range of operating conditions. Uncertainties in plant parameters, due to variation in generation and load patterns, are expressed in the form of a polytopic model. The PID control problem is firstly reduced to a generalized static output feedback (SOF) synthesis. The derivative action is designed and implemented as a high-pass filter based on a low-pass block to reduce its sensitivity to sensor noise. The proposed design algorithm adopts a quadratic Lyapunov approach to guarantee α-decay rate for the entire polytope. A constrained structure of Lyapunov function and SOF gain matrix is considered to enforce a decentralized scheme. Setting of controller parameters is carried out via an iterative linear matrix inequality (ILMI). Simulation results, based on a benchmark model of a two-area four-machine test system, are presented to compare the proposed design to a well-tuned conventional PSS and to the standard IEEE-PSS4B stabilizer.     

大型集聚类业务预测方法探析

以实例论述了大型集会移动话务特点、分析了大型集会移动用户规模、阐述了大型集会用户业务模型,并给出了业务量预测流程及预测实例。     

Consequence-based structural design approach for black swan events

The metaphor of black swan refers to unpredictable events like 9/11, the Indian Ocean tsunami, or the Oklahoma City Federal Building bombing, that cause catastrophic consequences for structural system safety. The likelihood of occurrence for such unforeseen events cannot be estimated from the observed data or prognosticated by experts. The absence of event and likelihood information renders futile the application of usual risk-based methods for design. Therefore, a shift from the probabilistic approach to consequence-based structural design is necessary for coping with the unexpected demands. This is accomplished through the conceptual development of a system capacity oriented design approach, where structural members are designed for variable reliabilities based upon their contribution to causing adverse system consequences. Information about general structural integrity encoded in the stiffness matrix is applied, using member consequence factors ranging from 0 to 1, for determining a member’s contribution towards system response. The structural system is designed using member consequence factors as additional partial factors on the resistance side of the design equations. The consequence-based scheme does not need a triggering hazard event (or its likelihood) and is an apt structural design approach for black swan events.     

Evaluation of wind load integration in disproportionate collapse analysis of steel moment frames for column loss

The design of steel structures, in most cases, depends majorly on the level of wind loads which are prescribed by codes and regulations and are used in the structural analysis due to the fact that steel structures being light and ductile systems are strongly affected from a slight difference in the values of wind loading. During the last decades, disproportionate collapse analysis has become of major interest mainly due to the increasing number of failures occurring in that pattern. Commonly accepted guidelines and methods of analysis have been produced, the most dominating of which being the Department of Defense Facilities criteria or DoD. In the DoD, as well as in other criteria, the event of a column loss is suggested as the modeling scenario which has to be sustained by a structural system in order to be robust. However, all the guidelines so far have disconnected the column loss analysis from wind loads and have only performed it for gravity loading. This paper presents the dynamic time history disproportionate collapse analysis of steel frames, including various levels of wind loading. Interesting aspects are discussed through the parametric analysis of five different numerical examples of moment resisting frames.     

Robust maximum power point tracking method for photovoltaic cells: A sliding mode control approach

Due to nonlinear I-V characteristics of photovoltaic cells, an maximum power point tracking algorithm is adopted to maximize the output power. In this paper, an approach for peak power tracking using the sliding mode control is proposed. The proposed controller is robust to environment changes and load variations. The stability and robustness of the controller are addressed. The performance of the controller is verified through simulations and experiments. It demonstrated that the proposed approach can be implemented effectively and economically.     

Adaptive particle swarm optimization for CNN associative memories design

In this paper particle swarm optimization is used to implement a synthesis procedure for cellular neural networks autoassociative memories. The use of this optimization technique allows a global search for computing the model parameters that identify designed memories, providing a synthesis procedure that takes into account the robustness of the solution. In particular, the design parameters can be modified during the convergence in order to guarantee minimum recall performances of the network in terms of robustness to noise overlapped to input patterns. Numerical results confirm the good performances of the designed networks when patterns are affected by different kinds of noise.     

Robustness of an adaptive backstepping controller without modification

This paper examines the robustness of the adaptive controller designed using the backstepping technique proposed in Kristic et al. (Nonlinear and Adaptive Control Design, Wiley, New York, 1995). It is shown that the adaptive controller without any modification still possesses some robustness against a class of unmodeled dynamics. Moreover, the system transient performance in the presence of unmodeled dynamics can be improved to an arbitrary level by adjusting the controller design parameters.