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- Andersson, Magnus
(author)
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Experimental Design and Updating of Finite Element Models
- 1997
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Licentiate thesis (other academic/artistic)abstract
- This thesis deals with two partly related topics: model updating and actuator/sensor placement concerning finite element (FE) models of large, flexible mechanical structures.The importance of accurate dynamical FE models of mechanical structures in, e.g., aviation/aerospace applications are steadily increasing. For instance, a sufficient accurate model may reduce the expenses for ground vibration testing and wind-tunnel experiments substantially. It is therefore of high industrial interest to obtain accurate models of flexible structures. One approach is to improve a parameterized, initial FE model using measurements of the real structure, so-called model updating. For a fast, successful model updating, three requirements must be fulfilled. The model updating must be computationally cheap, which requires an efficient model reduction technique. The cost function describing the deviation between the model output and the measurements must have good convexity properties so that an estimation of the parameters corresponding to the global optimum is likely to be obtained. Finally, the optimization methods must be reliable. A novel mode-pairing free cost function is presented, and together with a proposed general procedure for model updating, a cheap model updating formulation with good parameter estimation properties is obtained.Actuator and sensor placement is a part of the experimental design. It is performed in advance of the vibrational experiment in order to ensure high quality measurements. Using a nominal FE model of the structure, an actuator/sensor placement can be made. Actuator/sensor placement tasks are generally discrete, non-convex optimization problems of high complexity. One is therefore restricted to the use of sub-optimal algorithms in order to fulfill time and memory storage requirements. A computationally cheap algorithm for general actuator/sensor placement objectives are proposed. A generalization of an actuator/sensor placement criterion for model updating, and a novel noise-robust actuator placement criterion for experimental modal analysis are proposed.
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| 4. |
- Jansson, Magnus, et al.
(author)
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Efficient Implementation of a Submodel for Composite Materials to be Combined with the FDTD-Algorithm
- 1994
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In: IEEE Transactions on Magnetics. - : IEEE Magnetics Society. - 0018-9464 .- 1941-0069. ; 30:5, s. 3188-3191
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Journal article (peer-reviewed)abstract
- A submodel to be used for thin sheets of semiconducting materials in combination with the finite difference time domain algorithm for solving Maxwell's equations is derived. Emphasis is concentrated on accomplishing an efficient and robust algorithm. Stability properties of the combined model are also investigated
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| 5. |
- Larsson, Magnus
(author)
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Behavioral and Structural Model Based Approaches to Discrete Diagnosis
- 1999
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Doctoral thesis (other academic/artistic)abstract
- The basic motivation for this thesis is the fact that things go wrong. With the growing complexity of todays engineering systems, the need has arisen for systematic approaches to failure diagnosis, i.e., fault detection and isolation.In the first part of this thesis an approach for modeling and diagnosis of systems that fall in the area of discrete event dynamic systems is proposed. The approach is applicable to systems that at some level of abstraction have an interesting discrete event dynamics that can display faulty behavior. The systems suitable for this approach typically consist of several interacting components where abrupt, butnon-catastrophic, faults can occur in the components.We use a relational framework for discrete event dynamic systems focusing on a conceptually simple representation of the relationship between inputs, outputs and states of a discrete event system. Faults and faulty behavior are modeled locally using the state variables, and the diagnosis problem basically is to infer the possible states of the system using the system model and observations of the real system, i.e., an observer problem. Detectability and isolatability properties are defined and algorithms for analysis are proposed. The transitions necessary and sufficient for detection can automatically be computed from the system model under certain conditions. We also show how to compute the nest possible fault partition.The second part of this thesis addresses the problem of fault propagation between software modules in a large-scale control system with object oriented architecture. There exists a conflict between object-oriented design goals such as encapsulation and modularity, and the possibility to suppress propagating error conditions. When an object detects an error condition, it is not desirable to perform the extensive querying of other objects that would be necessary to decide how close to the real fault the object is and hence whether it should report to the user.The fault propagation manifests itself as many irrelevant error messages and hence causes problems for system operators and service personnel trying to quickly isolate the real fault. A system developer with insight in the internal system design, can, of course, often easily interpret the multitude of error messages from a fault scenario and isolate the root cause. The key observation is that it can often be done using mental high-level models of the system and the mechanics of the fault propagation. We have made an effort to automate this procedure, and propose a fault isolation scheme as an extra layer between the operator and the core control system. In the fault isolation layer, post-processing of the fault information from the system is performed, to achieve clear and concise fault information to the operator without violating encapsulation and modularity.A high-level and informal explanation model for the fault propagation is presented and a taxonomy for error conditions in an object oriented system is proposed. We present algorithms and methods that use the explanation model and the error condition taxonomy together with a structural system model to form a cause-effect relation on the error messages, that can be used to find the most significant error message(s) in a fault scenario.
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| 6. |
- Larsson, Magnus
(author)
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On Modeling and Diagnosis of Discrete Event Dynamic Systems
- 1997
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Licentiate thesis (other academic/artistic)abstract
- The basic motivation for this thesis is the fact that things go wrong. With the growing complexity of todays engineering systems, the need has arisen for systematic approaches to failure diagnosis. In this thesis an approach for modeling and diagnosis of systems that fall in the area of discrete event dynamic systems is proposed. The approach is applicable to all systems that at some level of abstraction have an interesting discrete event dynamics that can display faulty behavior. The systems suitable for this approach typically consist of several interacting components where abrupt, but non-catastrophic, faults can occur in the components.We use a relational framework for discrete event dynamic systems focusing on a conceptually simple representation of the relationships between inputs, outputs and states of a discrete event system.The modeling philosophy promoted here is to model faults locally, using special fault inputs or fault states only for that purpose. The diagnosis problem then basically is to infer the possible values of the unobservable fault inputs and states using the system model and observations of the real system.A fault is said to be detectable if there exists a transition in the system model that leads to a detection in a finite number of steps. The transition necessary for detection can automatically be computed from the system model under certain conditions. We also show how to compute the finest possible fault partition.
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| 10. |
- Ljung, Magnus, 1935-
(author)
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Conversion
- 1994
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In: The Encyclopedia of Language and Linguistics. - Oxford : Pergamon Press. - 0080359434 ; , s. 758-759
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Book chapter (other academic/artistic)
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