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A sensibility analysis to geometric and cutting conditions using the particle finite element method (PFEM)
Get PDFThe (PFEM) is employed to simulate orthogonal metal cutting of 42CD4 steel. The objectives of this work are mainly three: The first one is to validate PFEM strategies as an efficient tool for numerical simulation of metal cutting processes by a detailed comparison (forces, stresses, strains, temperature, etc.) with results provided by commercial finite element software (Abaqus, AdvantEdge, Deform) and experimental results. The second is to carry out a sensibility analysis to geometric and cutting conditions using PFEM by means of a Design of Experiments (DoE) methodology. And the third one is to identify the advantages and drawbacks of PFEM over FEM and meshless strategies.
Also, this work identifies some advantages of PFEM that directly apply to the numerical simulation of machining processes: (i) allows the separation of chip and workpiece without using a physical or geometrical criterion (ii) presents negligible numerical diffusion of state variables due to continuous triangulation, (iii) is an efficient numerical scheme in comparison with FEM
Simulation of distortion due to machining of thin-walled components
Get PDFThe distortion of components is strongly related to the residual stress state induced by manufacturing processes like heat treatment, forming or machining. Each process step affects the initial stress state of the following process step. When removing material during machining, the component establishes a new stress equilibrium. Stresses are redistributed causing the component geometry to adjust. Especially for thin-walled components distortion potential is high. Gaining knowledge about the influence of initial loads and the release of distortion during machining processes helps to increase product quality and efficiency. The influences of different initial stress states and different machining parameters on the amount of distortion are examined using both FEM simulations and experiments. A thin-walled T-profile made of aluminum alloy Al 7075-T6 serves as test specimen. A bending process applies a load to initialize a repeatable and defined residual stress state. A groove was machined afterwards into the plastically deformed work piece to trigger stress redistribution and a release of distortion. Different loads with 35 to 45 kN and two different geometries of a groove were used. The amount of initial stress has a significant effect on the distortion potential which could be quantified in the study. Simulations show the same behavior as the experiments and the results match very well especially for a high load
Comprehensive analysis of voltage balancing techniques for 5L NPC converters
Get PDFThe reduced capability of the 5L-NPC Inverter to balance the voltages of the four DC-bus capacitors makes this converter unattractive for real power applications. This is especially true if the load demands active power. The Back-to-Back (B2B) configuration of two 5L-NPC converters and the use of a Space Vector Modulation (SVM) that exploits the voltage balancing capabilities of the redundant switching vectors, extend the operating conditions range in which a proper voltage balance can be achieved. However, if practical modulation restrictions are considered (limitation of voltage steps, dead times, switching losses, etc.) the voltage balance cannot be achieved for all operation conditions. This paper introduces the main restrictions that should be considered for the 5L-NPC modulation strategy. The voltage balancing limits of the proposed SVM scheme are shown and additional considerations to improve the voltage balancing capability are proposed and evaluated
DC versus AC in residential buildings: efficiency comparison
Get PDFDC energy solutions are gaining interest in recent years, due to improvements in power electronics. Some companies have developed solutions for the domestic implementation of DC power systems. This article analyzes the state of the art about domestic DC applications and compares the efficiency of these systems in comparison to conventional AC systems. Different loads of a building as lighting, elevator or heating and renewable energies as PV panels or small wind generator are modeled for both AC and DC connections. With these models the power consumption of the building is simulated to compare the performance of both systems
Multi revolution finite element model to predict machining induced residual stresses in Inconel 718
Get PDFInconel 718 is commonly used in structural critical components of aircraft engines due to its mechanical thermal properties at high temperatures, which makes it to be considered as a difficult to machine material. In these critical parts, such as disk turbines, surface integrity should be assured in order to ensure the expected fatigue life. In order to determine the influence of feed and depth of cut in residual stresses a finite element facing model has been developed. This model takes into account the complex thermo mechanical phenomena that take place during chip formation process as well as the effect of cyclic loading phenomena due to the successive revolutions. Firstly, full stress, strain and temperature fields are obtained with a Deform 3D v10.2 nose turning model. Those fields are introduced in a multi revolution Abaqus/Standard v6.12 machining model. Finally the residual stresses of the model are extracted as an approach of Hole Drilling measurement technique. The results are in good agreement with empirical measurements
Fully pipelined implementation of tree-search algorithms for vector precoding
Get PDFThe nonlinear vector precoding (VP) technique has been proven to achieve close-to-capacity performance in multiuser multipleinput multiple-output (MIMO) downlink channels. The performance benefit with respect to its linear counterparts stems from the incorporation of a perturbation signal that reduces the power of the precoded signal. The computation of this perturbation element, which is known to belong in the class of NP-hard problems, is the main aspect that hinders the hardware implementation of VP systems. To this respect, several tree-search algorithms have been proposed for the closest-point lattice search problem in VP systems hitherto. Nevertheless, the optimality of these algorithms has been assessed mainly in terms of error-rate performance and computational complexity, leaving the hardware cost of their implementation an open issue.The parallel data-processing capabilities of field-programmable gate arrays (FPGA) and the loopless nature of the proposed tree-search algorithms have enabled an efficient hardware implementation of a VP system that provides a very high data-processing throughput
Methodology for thermal modelling of lithium-ion batteries
Get PDFTemperature is a determinant parameter in terms of performance, lifespan and safety working with li-ion batteries. Working above 45°C, in hot climates, has direct influence in the cycle life of the battery and can cause a dangerous failure if higher temperatures are reached; besides, performance of li-ion batteries in cold climates is very poor due to the high internal resistance they present under these ambient conditions. Being able to predict the temperature of a li-ion cell or the temperature distribution in a module for any working condition without testing the device is considered important when designing energy storage systems based on li-ion batteries. Thus, this paper presents a methodology to achieve the equivalent thermal parameters governing the behavior of a single li-ion cell and the power losses within it; different experimental tests are combined with an analytical expression of the power losses inside a cell to reach this target. The parameters obtained are used to develop a model in matlab/simulink and another model solved with CFD software. Simulation results show good agreement with experimental results with a maximum error of 2°C committed during the validation of the methodology
Model/framework for addressing continuous improvement projects effectively and efficiently using Six Sigma methodology. Case study of automotive auxialiry company
Get PDFThe purpose of this work is to develop a model for implementing an effective and efficient Continuous Improvement projects, aimed at increasing the performance of production processes. In particular, it aims to innovate in the way of deploying a Program Improvement in the company to make this process run as efficiently as possible. Although continuous improvement programs are some of the tools that are commonly used in industrial environments to increase the performance of their processes, it has become clear that there is a need to develop a continuous improvement model that will be implemented efficiently, and its results will remain over time. Also, it has been found that the model mentioned previously should serve to develop the foundations of an Organization which learns quickly and continuously
Reuse in safety critical systems: educational use case
Get PDFThe last decades, the electromechanical control systems are being replaced by Programmable Electronic Control Systems. The challenge is that these new systems have to be at least as safe as the replaced ones. Any company that want to compete in the Safety Embedded Systems related market and have success in business, have to develop competent systems reducing the time to market and the cost of the development and certification. The reusability of SW components is one of the solutions in this way. It is clear that the industry needs new graduates with this knowledge. In this paper we are going to explain a use case that the University of Mondragon is developing in order to use it in the Master of Embedded Systems with the objective to transfer the knowledge about how to develop safety critical and certifiable systems in an efficient way
Numerical study of the pressure drop phenomena in wound woven wire matrix of a Stirling regenerator
Get PDFFriction pressure drop correlation equations are derived from a numerical study by characterizing the pressure drop phenomena through porous medium of both types namely stacked and wound woven wire matrices of a Stirling engine regenerator over a specified range of Reynolds number, diameter and porosity. First, a finite volume method (FVM) based numerical approach is used and validated against well known experimentally obtained empirical correlations for a misaligned stacked woven wire matrix, the most widely used due to fabrication issues, for Reynolds number up to 400. The friction pressure drop correlation equation derived from the numerical results corresponds well with the experimentally obtained correlations with less than 5% deviation. Once the numerical approach is validated, the study is further extended to characterize the pressure drop phenomena in a wound woven wire matrix model of a Stirling engine regenerator for a diameter range from 0.080 to 0.110 mm and a porosity range from 0.472 to 0.638 within the same Reynolds number range. Thus, the new correlation equations are derived from this numerical study for different flow configurations of the Stirling engine regenerator. The results indicate flow nature and complex geometry dependent friction pressure drop characteristics within the present Stirling engine regenerator system. It is believed that the developed correlations can be applied with confidence as a cost effective solution to characterize and hence to optimize stacked and woven Stirling engine efficiency in the above specified ranges