1,720,979 research outputs found
Diesel After-Treatment Systems Modeling Optimization Techniques
Full text linkL'abstract è presente nell'allegato / the abstract is in the attachmen
Quasistatic Limit of a Dynamic Viscoelastic Model with Memory
No full textWe study the behaviour of the solutions to a dynamic evolution problem for a viscoelastic model with long memory, when the rate of change of the data tends to zero. We prove that a suitably rescaled version of the solutions converges to the solution of the corresponding stationary problem
The viscoelastic paradox in a nonlinear Kelvin-Voigt type model of dynamic fracture
No full textIn this paper, we consider a dynamic model of fracture for viscoelastic materials, in which the constitutive relation, involving the Cauchy stress and the strain tensors, is given in an implicit nonlinear form. We prove the existence of a solution to the associated viscoelastic dynamic system on a prescribed time-dependent cracked domain via a discretization-in-time argument. Moreover, we show that such a solution satisfies an energy-dissipation balance in which the energy used to increase the crack does not appear. As a consequence, in analogy to the linear case this nonlinear model exhibits the so-called viscoelastic paradox
An existence result for the fractional Kelvin–Voigt’s model on time-dependent cracked domains
Full text linkWe prove an existence result for the fractional Kelvin–Voigt’s model involving Caputo’s derivative on time-dependent cracked domains. We first show the existence of a solution to a regularized version of this problem. Then, we use a compactness argument to derive that the fractional Kelvin–Voigt’s model admits a solution which satisfies an energy-dissipation inequality. Finally, we prove that when the crack is not moving, the solution is unique
A dynamic model for viscoelastic materials with prescribed growing cracks
Full text linkIn this paper, we prove the existence of solutions for a class of viscoelastic dynamic systems on time-dependent cracked domains, with possibly degenerate viscosity coefficients. Under stronger regularity assumptions, we also show a uniqueness result. Finally, we exhibit an example where the energy-dissipation balance is not satisfied, showing there is an additional dissipation due to the crack growth
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Multi-Objective optimization of fuel injection pattern for a Light Duty Diesel engine through numerical simulation
No full textDevelopment trends in modern common rail fuel injection systems (FIS) show dramatically increasing capabilities in terms of optimization of the fuel injection strategy through a constantly increasing number of injection events per engine cycle as well as through the modulation and shaping of the injection rate. In order to fully exploit the potential of the abovementioned fuel injection strategy optimization, numerical simulation can play a fundamental role by allowing the creation of a kind of a virtual test rig, where the input is the fuel injection rate and the optimization targets are the combustion outputs, such as the burn rate, the pollutant emissions, and the combustion noise (CN). Starting from a previously developed 1D-CFD (Computational Fluid Dynamics) virtual test rig, obtained coupling a 1.6L, 4-cylinder turbocharged diesel engine model with a 1D-CFD injector model, this article presents a methodology for optimizing the fuel injection strategy aiming to minimize brake-specific fuel consumption (BSFC) and CN without exceeding the brake-specific NOx (BSNOx) baseline value. The Non-dominated Sorting Genetic Algorithm (NSGA-III) was used in GT-SUITE environment for Pareto optimization in the BSFC-CN space, for three different engine operating conditions in the low-medium speed and low-medium load range. The proposed approach highlighted that significant improvements in terms of BSFC and CN can be achieved by adopting digitalized close pilot events with respect to the Design of Experiments (DoE) analysis previously presented in [1], also highlighting relevant computational time savings for the optimization process
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