15 research outputs found
Variable selection with LASSO regression for complex survey data
Variable selection is an important step to end up with good prediction models. LASSO regression
models are one of the most commonly used methods for this purpose, for which
cross-validation is the most widely applied validation technique to choose the tuning parameter
(λ). Validation techniques in a complex survey framework are closely related to
“replicate weights”. However, to our knowledge, they have never been used in a LASSO
regression context. Applying LASSO regression models to complex survey data could be
challenging. The goal of this paper is two-fold. On the one hand, we analyze the performance
of replicate weights methods to select the tuning parameter for fitting LASSO regression
models to complex survey data. On the other hand, we propose new replicate weights methods
for the same purpose. In particular, we propose a new design-based cross-validation
method as a combination of the traditional cross-validation and replicate weights. The performance
of all these methods has been analyzed and compared by means of an extensive
simulation study to the traditional cross-validation technique to select the tuning parameter
for LASSO regression models. The results suggest a considerable improvement when
the new proposal design-based cross-validation is used instead of the traditional crossvalidation.IT1456-22
PIF18/21
An application of tomographic PIV to investigate the spray-induced turbulence in a direct-injection engine
Fuel sprays produce high-velocity, jet-like flows that impart turbulence onto
the ambient flow field. The spray-induced turbulence augments fuel-air mixing,
which has a primary role in controlling pollutant formation and cyclic
variability in engines. This paper presents tomographic particle image
velocimetry (TPIV) measurements to analyse the 3D spray-induced turbulence
during the intake stroke of a direct-injection engine. The spray produces a
strong spray-induced jet in the far field, which travels through the cylinder
and imparts turbulence onto the surrounding flow. Planar high-speed PIV
measurements at 4.8 kHz are combined with TPIV at 3.3 Hz to evaluate spray
particle distributions and validate TPIV measurements in the particle-laden
flow. An uncertainty analysis is performed to assess the uncertainty associated
with vorticity and strain rate components. TPIV analyses quantify the spatial
domain of the turbulence in relation to the SIJ and describe how turbulent flow
features such as turbulent kinetic energy, strain rate and vorticity evolve
into the surrounding flow field. Access to the full tensors facilitate the
evaluation of turbulence for individual spray events. TPIV images reveal the
presence of strong shear layers (visualized by high S magnitudes) and pockets
of elevated vorticity along the immediate boundary of the SIJ. Values are
extracted from spatial domains extending in 1mm increments from the SIJ.
Turbulence levels are greatest within the 0-1mm region from the SIJ boarder and
dissipate with radial distance. Individual strain rate and vorticity components
are analyzed in detail to describe the relationship between local strain rates
and 3D vortical structures produced within strong shear layers of the SIJ.
Analyses are intended to understand the flow features responsible for rapid
fuel-air mixing and provide valuable data for the development of numerical
models