FCT: UNIDEMI - Documentos de conferências internacionais
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- Stiffness and strength-based lightweight design of truss structures using multi-material topology optimizationPublication . Almeida, Cláudia J.; Conde, Fábio M.; Coelho, Pedro G.; Pratas, Tiago L.; UNIDEMI - Unidade de Investigação e Desenvolvimento em Engenharia Mecânica e IndustrialStiffness and strength are important structural design criteria. However, most contributions to Topology Optimization (TO) deal with the compliance minimization problem. Controlling stresses in a structure is very important to avoid material failure, but that raises complications in TO, such as: nonlinearity, singularity and high computational cost. The total weight of a structure is also another important criterion in optimal design. The multi-material setting is considered in the present work as it opens the possibility to improve structural performance even further allowing extra weight reduction. Recursive SIMP is used as the material interpolation scheme and design solutions are sought using the ground structure approach. This means that truss-like (lattice) designs are obtained here. The problem is relaxed to the continuum by introducing an artificial density variable and it is solved by a gradientbased algorithm (MMA). A stress-constraint relaxation technique (qp-approach) is applied to overcome the stress singularity phenomenon. A continuation approach is used to guarantee discrete solutions, i.e., only the presence or absence of bars is identified. Therefore, design uniformity in terms of bars cross section areas is ensured. Hence, this work proposes a methodology to perform Multi-Material Topology Optimization (MMTO) of truss structures, with density-based design variables, and subject to stress constraints. To discuss the differences between stiffness and strength-oriented optimal designs, a compliance minimization problem subject to mass constraint is also considered. The example chosen demonstrates the viability of the proposed design methodology and it also reveals differences between the strongest and the stiffest designs.
- Control of Grid-Tied Converters for Integration of Renewable Energy Sources into the Weak GridsPublication . Sepehr, Amir; Pouresmaeil, Edris; Saeedian, Meysam; Routimo, Mikko; Godina, Radu; Yousefi-Talouki, Arzhang; UNIDEMI - Unidade de Investigação e Desenvolvimento em Engenharia Mecânica e IndustrialThis paper proposes a developed control technique for integration of renewable energy sources into the weak grids. The developed controller alleviates the negative impact of weak grid operating condition on the stability of interface converters by mean of impedance reshaping technique. Furthermore, the proposed controller provides virtual inertia to support the power grid stability. Satisfactory and stable operation of the interface converter as well as providing virtual inertia under weak grid condition with high penetration level of RESs, are the main contributions of this paper. Comparative simulation results are presented to demonstrate and verify the effectiveness of the proposed control technique.
- Resilient Supply ChainsPublication . Machado, Virgílio António Cruz; Carvalho, Helena Maria Lourenço; UNIDEMI - Unidade de Investigação e Desenvolvimento em Engenharia Mecânica e IndustrialThis paper explores the designing principlesto create resilient Supply Chains (SC's) with the ability toreturn, rapidly, to the initial stage or to an improved oneafter a disturbance occurrence. SC disturbances and failuremodes are identified and discussed. The concept of SCresilience is defined and explored; a conceptual SCResilience Index and a SC Resilience Indicator areproposed. A framework for the design of resilient SC's isintroduced, identifying main SC characteristic that can bemodified to increase SC resilience and to mitigate itsvulnerability.