Factorial experiment

In statistics, a full factorial experiment is an experiment whose design consists of two or more factors, each with discrete possible values or "levels", and whose experimental units take on all possible combinations of these levels across all such factors. A full factorial design may also be called a fully crossed design. Such an experiment allows the investigator to study the effect of each factor on the response variable, as well as the effects of interactions between factors on the response variable. For the vast majority of factorial experiments, each factor has only two levels. For example, with two factors each taking two levels, a factorial experiment would have four treatment combinations in total, and is usually called a 2×2 factorial design. In such a design, the interaction between the variables is often the most important. This applies even to scenarios where a main effect and an interaction are present. If the number of combinations in a full factorial design is too h

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Discretization Uncertainties of Flow and Fatigue Damage Simulations of a Reversible Francis Pump-Turbine at Off-Design Operation in Turbine Mode

Daniel Biner, Philippe Alexandre Bontemps, Drazen Dujic

In the framework of the XFLEX HYDRO H2020 European Project, a 5 MW reversible Francis pump-turbine prototype, equipped with an industrial full size frequency converter, is investigated to demonstrate enhanced grid regulation capacities of variable speed hydropower units. The targeted high flexibility operation modes imply increased numbers of start and stop cycles, frequent off-design operation and even power reversions. Thereby, the understanding of fatigue mechanisms at off-design conditions and during transitions is crucial to ensure safe long term flexibility operation of hydropower units. The present paper aims to investigate spatial and temporal discretization uncertainties of numerical flow and fatigue damage simulations. For a selected off-design operating point in turbine mode, unsteady CFD simulations and one way coupled FSI simulations are carried out to reveal stress fluctuations and fatigue damage on the Francis pump-turbine runner. First, a classical Grid Convergence Index (GCI) methodology is carried out. Moreover, a design of experiments methodology is applied, comprising a fractional factorial plan, to evaluate the individual effects from the guide vane, runner, and draft tube grid sizes as well as the simulation time step on the flow and fatigue damage results. The guide vane grid size is found to be the most impactful on torque, discharge, and efficiency results. The correlation of the grid sizes with the fatigue damage responses shows less pronounced statistical evidence. Nevertheless, the study reveals expectable numerical error ranges related to discretization uncertainties of runner fatigue damage simulations within practicable grid size and time step ranges.

SPRINGER INTERNATIONAL PUBLISHING AG2022

Screening of the factors influencing frictional interactions between a cylindrical tip and the cardiac wall using factorial analysis

Hannes Bleuler, Lionel Flaction, Bandar Muntazar Hakim, Giulio Rognini

Knowledge of frictional forces acting on the tips of minimally invasive medical devices is important in the design and simulation of such devices. Moreover, several studies have shown that uncontrolled frictional forces can induce damage to organs. The goal of this study is to empirically investigate the dominant factors affecting frictional forces between a bovine cardiac tissue and a catheters tip. A dedicated apparatus is developed to reproduce the sliding contact between a cylindrical element and the cardiac tissue. In this paper, we utilize the design of experiment (DOE) approach to study friction. Factorial designs (FD) are used to reduce the number of experiments without reducing the information that could be extracted. Twelve factors were selected to represent the main parameters that could potentially affect friction. These factors are of physical, geometrical, physiological and temporal nature. As a result of 4 factorial designs representing a set of 128 experiments, we studied the impact on friction of the 12 parameters as well as the interactions between them. As expected, the normal force applied on the cylindrical tip is the dominant factor affecting the friction force. The remaining significant effects are the cylinder pitch angle, tissue physiological state and the pressure applied on the cardiac tissue expressed in cylinder dimensions. This study gives some guidelines to minimize and control friction interactions between a cylindrical tip and a tissue.

Elsevier2012

Design optimization analysis of a standing wave ultrasonic linear actuator

José Fernandez Lopez, Yves Perriard, Yann Ruffieux

The design, properties and optimization of an ultrasonic actuator are presented. Numerical modeling has been carried out and simulations with the FEM Ansys software have been realized. To avoid performing a large number of simulations, input parameters like geometrical dimensions, material properties or even boundary conditions can be judiciously chosen in function of their influence on the output parameter (deformation amplitude). In this manner, sensitivity of each input parameter on the output parameter value can be achieved, in particular using design of experiments. Factorial designs and Doehlert method have been chosen. The results found show that this pre-optimization stage allows one to improve the deformation amplitude but also to reduce the input parameter variation ranges. Different optimization methods using Ansys are then applied and results show that the deformation amplitude can even be more increased compared to the initial design.

2005

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