Letteratura scientifica selezionata sul tema "Optimisation fiabiliste (RBDO)"
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Articoli di riviste sul tema "Optimisation fiabiliste (RBDO)":
Abid, Fatma, Abdelkhalak El Hami, Tarek Merzouki, Hassen Trabelsi, Lassaad Walha e Mohamed Haddar. "Optimisation fiabiliste d’une structure en alliage à mémoire de forme". MATEC Web of Conferences 261 (2019): 02001. http://dx.doi.org/10.1051/matecconf/201926102001.
Tesi sul tema "Optimisation fiabiliste (RBDO)":
Bendaou, Omar. "Caractérisation thermomécanique, modélisation et optimisation fiabiliste des packages électroniques". Thesis, Normandie, 2017. http://www.theses.fr/2017NORMIR20/document.
During operation, electronic packages are exposed to various thermal and mechanical solicitations. These solicitations combined are the source for most of electronic package failures. To ensure electronic packages robustness, manufacturers perform reliability testing and failure analysis prior to any commercialization. However, experimental tests, during design phase and prototypes development, are known to be constraining in terms of time and material resources. This research aims to develop four finite element models in 3D, validated/calibrated by experimental tests, integrating JEDEC recommendations to : - Perform electronic packages thermal and thermomechanical characterization ; - Predict the thermal fatigue life of solder joints in place of the standardized experimental characterization.However, implementation of the finite element model has some disadvantages related to uncertainties at the geometry, material properties, boundary conditions or loads. These uncertainties influence thermal and electronic systems thermomechanical behavior. Hence the need to formulate the problem in probabilistic terms, in order to conduct a reliability study and a electronic packages reliability based design optimization.To remedy the enormous computation time generated by classical reliability analysis methods, we developed methodologies specific to this problem, using approximation methods based on advanced kriging, which allowed us to build a substitution model, combining efficiency and precision. Therefore reliability analysis can be performed accurately and in a very short time with Monte Carlo simulation (MCS) and FORM / SORM methods coupled with the advanced model of kriging. Reliability analysis was associated in the optimization process, to improve the performance and electronic packages structural design reliability. In the end, we applied the reliability analysis methodologies to the four finite element models developed. As a result, reliability analysis proved to be very useful in predicting uncertainties effects related to material properties. Similarly, reliability optimization analysis performed out has enabled us to improve the electronic packages structural design performance and reliability. In the end, we applied the reliability analysis methodologies to the four finite element models developed. As a result, reliability analysis proved to be very useful in predicting uncertainties effects related to material properties. Similarly, reliability optimization analysis performed out has enabled us to improve the electronic packages structural design performance and reliability
Mtibaa, Mohamed. "Οptimisatiοn de cοuplage Ρrοcédé/Ρrοpriétés/Fiabilité des Structures en Μatériaux Cοmpοsites Fοnctiοnnels". Electronic Thesis or Diss., Normandie, 2024. http://www.theses.fr/2024NORMLH03.
This research focuses on the challenges and interactions between the manufacturing processes (Resin Transfer Molding ‘RTM’ and Compression Resin Transfer Molding ‘CRTM’), the mechanical properties, and the reliability of composite material structures; more specifically the functional composites. A number of numerical models have been developed for simulating the suspension (resin + particles) impregnation through the fibrous medium (fibers) in the RTM and CRTM processes. These models are validated by comparing their results with experimental, semi-analytical, and analytical ones from the literature. A parametric study is carried out to demonstrate the impact of various process parameters on particles’ distribution in the final composite. Moreover, a comparison between the injection and compression modes is done. The results of this part show that the distribution of particles in the final part depends on the initial concentration, the distance travelled, and the initial fibers’ volume fraction. However, it is independent of the parameters values of injection and compression. It is also observed that the CRTM process with imposed pressure injection and imposed force compression represents the most favorable scenario for producing composite parts.For the purpose of controlling the final particles’ distribution in the composite material, manufactured by the RTM process, two key steps have been identified. The first step consists in a sensitivity analysis that examines three parameters: the temporal evolution of the initial injected particles’ concentration, the injection pressure field and the initial fibers’ porosity. The conclusions indicate a minimal impact of the initial porosity and the injection pressure field; while the evolution of the initial concentration of the injected particles has a dominant effect. In a second step, an optimization algorithm is implemented in the numerical model of the RTM process. It is used to determine the optimal configuration of the initial injected particles’ concentration’s evolution; in order to approximate the particles’ distribution in the final composite to the desired profiles. The obtained results from the genetic algorithm provide a very satisfactory control of this distribution. To complete this section, a model, estimating the mechanical properties of the manufactured part, is developed. It is found that there is a positive correlation between the particles’ fraction and certain mechanical properties, namely the elastic modulus E11 and E22, and the shear modulus G12 and G23. Nevertheless, the Poisson’s ratio (Nu12) is inversely proportional to the particles’ fraction. Also, the shear module G12 is the most significantly influenced by this fraction.Following this, the control of the mechanical properties of the composite parts, manufactured by the CRTM process, is targeted, and compared to the results of the RTM process. The conclusions reveal that the RTM process offers a better control of these properties. Whereas, the CRTM process improves considerably the mechanical properties of the parts due to its compression phase, which increases the fibers’ volume fraction and consequently enhances these properties.Finally, a static analysis is conducted based on the developed numerical model that uses the finite element method (Ansys APDL). This model is combined with those of the CRTM process and the mechanical properties calculation. An optimization algorithm is integrated in our global model to adapt the mechanical properties of the composite part according to the configuration (cantilever or simply supported) and the load distribution. Moreover, it minimizes the composite part’s weight and ensures the respect of the predetermined mechanical constraints such as the maximum deformation limit. The obtained results correspond perfectly to these objectives
Price, Nathaniel Bouton. "Conception sous incertitudes de modèles avec prise en compte des tests futurs et des re-conceptions". Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEM012/document.
At the initial design stage, engineers often rely on low-fidelity models that have high uncertainty. In a deterministic safety-margin-based design approach, uncertainty is implicitly compensated for by using fixed conservative values in place of aleatory variables and ensuring the design satisfies a safety-margin with respect to design constraints. After an initial design is selected, high-fidelity modeling is performed to reduce epistemic uncertainty and ensure the design achieves the targeted levels of safety. High-fidelity modeling is used to calibrate low-fidelity models and prescribe redesign when tests are not passed. After calibration, reduced epistemic model uncertainty can be leveraged through redesign to restore safety or improve design performance; however, redesign may be associated with substantial costs or delays. In this work, the possible effects of a future test and redesign are considered while the initial design is optimized using only a low-fidelity model. The context of the work and a literature review make Chapters 1 and 2 of this manuscript. Chapter 3 analyzes the dilemma of whether to start with a more conservative initial design and possibly redesign for performance or to start with a less conservative initial design and risk redesigning to restore safety. Chapter 4 develops a generalized method for simulating a future test and possible redesign that accounts for spatial correlations in the epistemic model error. Chapter 5 discusses the application of the method to the design of a sounding rocket under mixed epistemic model uncertainty and aleatory parameter uncertainty. Chapter 6 concludes the work
Zhang, Peipei. "Diffuse response surface model based on advancing latin hypercube patterns for reliability-based design optimization of ultrahigh strength steel NC milling parameters". Compiègne, 2011. http://www.theses.fr/2011COMP1949.
Since variances in the input parameters of engineering systems cause subsequent variations in the product performance, and deterministic optimum designs that are obtained without taking uncertainties into consideration could lead to unreliable designs. Reliability-Based Design Optimization (RBDO) is getting a lot of attention recently. However, RBDO is computationally expensive. Therefore, the Response Surface Methodology (RSM) is often used to improve the computational efficiency in the solution of problems in RBDO. In this work, we focus on a Response Surface Methodology (RSM) adapted to the Reliability-Based Design Optimization (RBDO). The Diffuse Approximation (DA), a variant of the well-known Moving Least Squares (MLS) approximation based on a progressive sampling pattern is used within a variant of the First Order Reliability Method (FORM). The proposed method simultaneously uses points in the standard normal space (U-space) as well as the physical space (X-space). The two grids form a “virtual design of experiments” defined by two sets of points in the two design spaces, that are evaluated only when needed in order to minimize the number of ‘exact’ thus computationally expensive function evaluations. In each new iteration, the pattern of points is updated with points appropriately selected from the “virtual design of experiments”, in order to perform the approximation. As an original contribution, we introduce the concept of « advancing Latin Hypercube Sampling (LHS) » which extends the idea of Latin Hypercube Sampling (LHS) to maximally reuse previously computed points while adding a minimal number of new neighboring points at each step, necessary for the approximation in the vicinity of the current design. We propose panning, expanding and shrinking Latin hypercube patterns of sampling points and we analyze the influence of this specific kind of patterns on the quality of the approximation. Next we calculate the minimal number of data points required in order to get a well-conditioned approximation system. In the application part of this work, we investigate the optimization of the process parameters for Numerical Control (NC) milling of ultrahigh strength steel. The success of the machining operation depends on the selection of machining parameters such as the feed rate, cutting speed, and the axial and radial depths of cut. A variant of the First Order Reliability Method (FORM) is chosen to calculate the reliability index. The optimization constraints are expressed as functions of the computed reliability indices