Calibration Of Numerical Model Research Articles

Comparison of Local and Global Optimization Methods for Calibration of a 3D Morphodynamic Model of a Curved Channel

In curved channels, the flow characteristics, sediment transport mechanisms, and bed evolution are more complex than in straight channels, owing to the interaction between the centrifugal force and the pressure gradient, which results in the formation of secondary currents. Therefore, using an appropriate numerical model that considers this fully three-dimensional effect, and subsequently, the model calibration are substantial tasks for achieving reliable simulation results. The calibration of numerical models as a subjective approach can become challenging and highly time-consuming, especially for inexperienced modelers, due to dealing with a large number of input parameters with respect to hydraulics and sediment transport. Using optimization methods can notably facilitate and expedite the calibration procedure by reducing the user intervention, which results in a more objective selection of parameters. This study focuses on the application of four different optimization algorithms for calibration of a 3D morphodynamic numerical model of a curved channel. The performance of a local gradient-based method is compared with three global optimization algorithms in terms of accuracy and computational time (model runs). The outputs of the optimization methods demonstrate similar sets of calibrated parameters and almost the same degree of accuracy according to the achieved minimum of the objective function. Accordingly, the most efficient method concerning the number of model runs (i.e., local optimization method) is selected for further investigation by setting up additional numerical models using different sediment transport formulae and various discharge rates. The comparisons of bed topography changes in several longitudinal and cross-sections between the measured data and the results of the calibrated numerical models are presented. The outcomes show an acceptable degree of accuracy for the automatically calibrated models.

Fatigue Prediction for Extended Riser Life and Improved Vessel-Response Analysis

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper OTC 29531, “Flexible-Riser Fatigue Counter Developed From Field Measurements and Machine-Learning Techniques,” by Christoffer Nilsen-Aas, Jan Muren, and Håvard Skjerve, 4Subsea, et al., prepared for the 2019 Offshore Technology Conference, Houston, 6–9 May. The paper has not been peer reviewed. Copyright 2019 Offshore Technology Conference. Reproduced by permission. This paper presents a fatigue-prediction methodology designed to extend the life of unbonded flexible risers and improve the accuracy of floating production, storage, and offloading (FPSO) vessel response analysis. The methodology combines measured-motion-response, maritime-environment, and process data to improve traditional time-domain dynamic analysis models, along with machine-learning (ML) techniques to develop a heading model for the FPSO. Introduction Life extension of unbonded flexible risers is a challenge because of uncertainties associated with key parameters driving deterioration, such as how the riser was designed, manufactured, and installed and how it is operated. Fatigue service life is calculated during the design phase using models based on field-specific environmental data derived for the area and loads for the required design conditions per project specifications and international standards. Using real measured data from the riser motions and from environmental sources can reduce uncertainties significantly, improving life-extension analysis for fatigue and other failure drivers. These data, when combined with high-end engineering assessments and considerations on data reliability, provide better insight and contribute to continued operations with acceptable risk for the risers. The complete paper presents a methodology that uses measured environmental data and FPSO and riser response data in an ML environment to build more-realistic riser-response and fatigue-prediction models. A case example is presented for the risers suspended from the FPSO Fluminense producing from the BijupirÁ and Salema fields offshore Brazil. Because FPSO heading is important for vessel dynamics, especially roll, and the vessel dynamics are a key factor in the riser dynamics at this field, initial focus was on predicting vessel heading relative to swell. The heading model developed by ML showed good agreement and was used as a key tool in a traditional fatigue analysis. This analysis was based on historical sea states from the last 2 years. The results show that the fatigue analysis from the design phase is conservative and lifetime extension is achievable. Because the fully instrumented measurement campaign ended after 4 months, the work focused on using all captured data to provide improved insight and develop both traditional simulation and ML models. For future fatigue predictions based on the developed fatigue counter, the objective is to maintain accuracy with less instrumentation. In the present phase, FPSO and riser-response data from the 4-month campaign have been used to establish a correlation between riser behavior, environmental data, and FPSO heading and motion. Calibration of a traditional numerical model is performed using measurement data along with a direct waves-to-fatigue prediction based on modern ML techniques. The ongoing work illustrates how real environmental data and response monitoring can reduce uncertainties and improve and extend flexible-riser life.

Asymmetric input motion for accumulation of lateral ground deformation in laminar container shake table testing

Due to seismic response, accumulation of permanent ground deformation (lateral spreading) is an important mechanism of much practical significance. Such deformations typically occur near a ground slope, behind retaining structures such as sheet-pile and quay walls, and in mildly sloping ground. In conducting a shake table test, the generation of permanent deformations further elucidates the underlying mechanisms and allows for related ground–foundation–structure response insights. In this paper, an approach for development of accumulated ground deformations is presented, in which asymmetric inertial loading results in a biased dynamic one-dimensional shear state of stress. As such, the proposed approach allows for further insights into the soil cyclic response and pore pressure build-up, with deformations accumulating in a preferred direction. To permit a virtually unlimited number of such loading cycles, focus is placed on motions that do not cause the shake-table actuator to accumulate displacement, in view of its possible limited stroke. Using this approach, representative experimental response is outlined and discussed. This experimental response can be used for calibration of numerical models to emulate the observed permanent strain accumulation profile and associated mechanisms. In addition to liquefaction-induced lateral spreading, this asymmetric shaking approach might be beneficial for a wide class of earthquake engineering shake table testing applications.

Effect of Mining Geometry on Natural Stress Field in Underground Ore Mining with Conventional and Nature-Like Technologies

The authors study the process of the induced stress field formation in mining with the conventional and nature-like geotechnical systems, including frame and honeycomb mine structures. The rate of change in the natural stress field during mining is estimated using a new index—coefficient of influence. Based on the data of experimental mine research, as well as physical and numerical models, with regard to the numerical model calibration, the diagram of influence exerted on the rate of change in the natural stress field by the geometry of stopes in underground ore mining with the conventional and naturelike geotechnologies is plotted. It is found that the highest effect on the size of the induced tensile strain zones is exerted by the mining systems with caving of ore and enclosing rocks. The optimum coefficient of influence is a characteristic of the frame mine structure.

Evaluation of terrestrial carbonaceous matter aromatization by Raman spectroscopy and its application to C chondrites

AbstractA Raman method to estimate the aromatization degree of carbonaceous matter (CM) was established, and calibrated by literature data respecting differences in acquisition procedures. The generated equations allowed a comparison of the G‐band width to vitrinite reflectance, and to additional structural organization parameter extracted from X‐ray powder diffraction. The relations between aromatization degree and peak temperatures from literature were then propagated to G‐band width parameter. The applicability of these geothermometers is demonstrated by the consistency of data obtained for carbonaceous chondrites with previous estimations. Since the CM aromatization is controlled by peak temperature and time span, it is possible to estimate the duration of chondrite’s heating events. The G‐band width relation to elemental ratio trends of organic matter in chondrites, interplanetary dust particles, glucose, and saccharose‐based semi‐coke favors synthesis by formose route. These findings provide new approaches for the future development of chemical kinetic models for organic matter of chondrites. A reliable chemical model may allow the external calibration of numerical models for accurately evaluating the peak temperatures and cooling durations of chondrites.

Railway ballast anisotropy testing via true triaxial apparatus

Abstract This paper aims to demonstrate the anisotropic behaviour of railway ballast via true-triaxial tests. To do so, a novel, large-scale, true-triaxial testing apparatus (GeoTT) is designed and constructed. It consists of six hydraulic actuators, designed to apply a distributed stress to large granular cubic test specimens with dimensions: 500 mm × 500 m × 500 mm. To show the capability of the new facility, crushed granite railway ballast with d50 = 43 mm is tested. Three different confining stresses are applied to determine the Poisson’s ratio and modulus in three dimensions. Anisotropic behaviour is clearly evident, with horizontal directions showing a lower modulus compared to the vertical direction. It is also found that confining stress has an important effect on both Poisson’s ratio and modulus when the primary loading is applied in three orthogonal directions. These results are useful for understanding the behaviour of railway ballast and for the calibration of railroad numerical models.

Development and surrogate-based calibration of a CO2 reservoir model

Simulation-optimization framework is a widely used approach for numerical model calibrations, though its primary difficulty is its high-demand of computational efforts. In this study, Bagging MARS (BMARS) adapted from Multivariate Adaptive Regression Splines (MARS) algorithm, is used to construct the surrogate of a three-dimensional CO2 reservoir model, which is developed to simulate CO2 injection and migration in a fault-compartmentalized underground reservoir. The BMARS surrogate model is then used in model calibration to estimate specified reservoir model input parameters efficiently. The results demonstrate that the BMARS model can improve fitting stability and predictive accuracy against the ordinary MARS model. Parameter sensitivity analysis, which is efficiently conducted using the BMARS model, suggest that permeability of Fault#10 and caprock dominate the pressure buildup in this fault-compartmentalized reservoir. Hence priority should be given to investment in estimating these two reservoir properties. Overpressure propagation and CO2 migration in the reservoir responding to three years of CO2 injection are also analyzed using the calibrated model. The calibrated water-CO2 flow model could be a useful tool to evaluate the future operation and risk assessment of the reservoir. The results comparison and sensitivity analysis demonstrated the proposed BMARS-based simulation–optimization framework is an efficient and accurate model calibration approach.

STARx Hottpad for smoldering treatment of waste oil sludge: Proof of concept and sensitivity to key design parameters.

Growing stockpiles of waste oil sludge (WOS) are an outstanding problem worldwide. Self-sustaining Treatment for Active Remediation applied ex situ (STARx) is a treatment technology based on smoldering combustion. Pilot-scale experiments for the STARx Hottpad prove this new concept for the mobile treatment of WOS mixed intentionally with sand or contaminated soil. The experiments also allowed for the calibration and validation of a smoldering propagation numerical model. The model was used to systematically explore the sensitivity of Hottpad performance to system design, operational parameters, and environmental factors. Pilot-scale (~1.5 m width) simulations investigated sensitivity to injected air flux, WOS saturation, heterogeneity of intrinsic permeability, and heterogeneity of WOS saturation. Results reveal that Hottpad design is predicted to be successful for WOS treatment across a wide range of scenarios. The operator can control the rate of WOS destruction and extent of treatment by increasing the air flux injected into the bed. The potential for smoldering channeling to develop was demonstrated for the first time. Under certain conditions, such as WOS saturations of 80%, high heterogeneity of WOS saturations, or moderate to high heterogeneity of soil permeability, smoldering channeling was predicted to accelerate to the point that remedial performance was degraded. Field-scale simulations (~10 m width) predicted successful treatment, with WOS destruction rates an order of magnitude higher than the pilot-scale and treatment times increasing only linearly with bed height. This work is a key step toward the design and effective operation of field STARx Hottpad systems for eliminating WOS.

Rib Presence, Anterior Rib Cage Integrity, and Segmental Length Affect the Stability of the Human Thoracic Spine: An in vitro Study.

The effects of segmental length as well as anterior rib cage and costovertebral joint integrity on thoracic spinal stability have not been extensively investigated, but are essential for the calibration and validation of numerical models of the thoracic spine and rib cage. The aim of the study was to quantify these effects by in vitro experiments. Eight human thoracic spine specimens (C7-L1) including the rib cage were loaded with pure moments of 5 Nm in flexion/extension, lateral bending, and axial rotation while tracking the motions of all functional spinal units. Specimens were tested stepwise in four different conditions: (1) In the intact condition, (2) after cutting all anterior rib-to-rib connections, (3) after partitioning the polysegmental specimens into monosegmental specimens, and (4) after removing the ribs in the monosegmental condition. Significant increases of the range of motion (p < 0.05) were especially found at the segmental levels of the upper half of the thoracic spine in all motion planes and for all resection steps, particularly in axial rotation, while the stabilizing effects of the structures decreased in inferior direction. Partitioning of polysegmental specimens into monosegmental specimens primarily affected the stability in lateral bending, while the effects of resection were generally lowest in flexion/extension. Presence of the ribs, anterior rib cage integrity, and segmental length all affect the thoracic spinal stability and have therefore to be considered in the calibration process of numerical models of the thoracic spine and rib cage.

Calibration of estuary numerical model by the Powell’s optimization method

In this paper, we attempt to optimize the parameters related to estuarine salt intrusion in Delft3D model. BOBYQA algorithm by Powell, a constrained optimization algorithm was applied to the &#57583;？？ ？？ model of Delft3D to calibrate the vertical salinity profiles. The optimization was first demonstrated with the flume data of Ippen and Harleman (1961), then was applied to the observation data of the Seomjin River in Korea. A total of 11 or 15 parameters were optimized with the objective function of salinity RMS error. The observation data were totally 28 sets of the vertical salinity distribution at 14 different stations, obtained by Korea Institute of Ocean Science & Technology. The results showed that the turbulence generation and viscous dissipation terms, and turbulent Prandtl number were relatively more important among the parameters employed in the optimization. It could also be assured that the accuracy of the vertical salinity profile was much improved through the optimization.

Calibration and assessment of process-based numerical models for beach profile evolution in southern California

Cross-shore profile response to energetic wave events is challenging to predict because the physics are poorly understood and wave and topographic data are often sparse or unknown. Six events with varying duration, wave intensity and beach slopes are used to calibrate and assess two process-based cross-shore models, CShore and XBeach, at two southern California beaches. Model performance is quantitatively evaluated using high resolution spatiotemporal survey observations along with Brier Skill Scores (BSS) and a Beach Elevation Change Error (BECE) metric that evaluates alongshore-averaged upper beach volume predictions. XBeach is tested with default and site-calibrated parameters. Calibration improved skill for all profiles and events, however XBeach skill scores often remained low and in no case correctly predicted the offshore bar formation. Notably, XBeach is sensitive to the beach profile’s calibration depth extent. Upper beach calibration produced significantly different skill than when the full profile was considered. CShore was tested using both the ’Atlantic’ and ’Pacific’ parameters. Both models predict profile change with limited skill. In their present forms, CShore and XBeach are unable to accurately predict beach profile change on these typical southern California beaches, but when calibrated may provide qualitatively useful beach face erosion estimates.

A generalised additive model to characterise dairy cows’ responses to heat stress

Heat stress is one of the most critical issues jeopardising animal welfare and productivity during the warm season in dairy cattle farms. The global trend of increase in average and peak temperatures is making the problem more and more serious. Many devices have been introduced in livestock farms to monitor and control temperature-humidity index, as well as animal behaviour and production parameters. The consequent availability of collected databases has increasingly enhanced the research aimed to understand the consequences of heat stress in cattle, in relation to genetic, reproductive, productive and behavioural features. Moreover, these investigations laid the foundations for the development, calibration, validation and test of numerical models quantifying the individual responses to heat stress conditions. In this work, a generalised additive model with mixed effects has been developed to analyse the relationship between milk production, animal behaviour and environmental parameters based on data surveyed in 2016 in an Italian dairy farm. Each cow has been characterised in terms of her response to heat conditions, and the results led to define three classes of susceptibility to heat stress within the herd. These attributes have then been related to the various phenotypic parameters collected by the precision livestock farming devices used in the farm. The study provides a model to understand the effects of heat stress conditions on individual animals in relation to the main parameters describing their rearing conditions; moreover, the results contribute to improve the herd management by lending indications to define targeted treatments according to the cow’s characteristics.

Flows of Liquefied Filtered Tailings: Laboratory-Scale Physical and Numerical Modeling

The numerical prediction of the runout and spread of liquefied-tailings flows is a complex problem that depends on many factors, including the rheological properties of the liquefied tailings. However, published benchmark problems specific to tailings flows, useful for validation and calibration of numerical models, are virtually nonexistent. This paper presents a laboratory-scale benchmark problem of liquefied-tailings flow. Gold filtered tailings were characterized via rheological measurements, geotechnical index tests, and toxicity chemical analysis. Physical flow experiments of the liquefied-tailings paste, at 70% solids concentration, were carried out in an instrumented laboratory flume with high-speed video and direct measurements of the at-rest “footprint” (lobe) dimensions. Subsequently, using the measured physical parameters, computational fluid dynamics (CFD) tools were used to solve the three-dimensional, rheology-dependent Navier–Stokes equations via the finite-volume method and a multiphase volume-of-fluid (VOF) technique. Thus, the at-rest lobe of the spilled tailings was numerically reproduced. Results show that the liquefied tailings bear nearly zero-yield stress and low viscosity, thereby practically behaving as a Newtonian fluid despite their high solid concentration. In addition, good agreement (within 14% of the main dimensions) was found between the physical and numerically simulated at-rest lobes. Hence, the use of a Navier–Stokes approach, supported on a finite-volume/VOF technique, and a Newtonian-fluid constitutive rheological model, simulates well the at-rest shape of liquefied tailings at laboratory scale. This benchmark problem will aid numerical research specific to tailings flows.

A new column collapse apparatus for the characterisation of the flowability of granular materials

The packaging industry is lacking a standard methodology to characterise the granular flow of a wide range of powders and grains in actual handling conditions. We present a new fully-instrumented granular column collapse apparatus for the experimental investigation of granular flow phenomena, by a quasi-two-dimensional set-up with novel features including: a lifting gate activated by a parallelogram mechanism for material release; a reversible pneumatic circuit to impose fluidised and vacuum conditions to the initial granular column; a set of load cells to monitor the basal load distribution during flow propagation; a 3D laser line profile sensor to scan the free surface morphology of the samples at rest; and a high-speed video recording set to capture near-wall flow visualisations and relevant kinematic measures by particle image velocimetry. The selected results on dry flows of oat flakes, copper sulphate fertiliser, and talc powder samples show their distinctive flow dynamics, indicating the good flowability of fertiliser compared to the poor flowability of talc. This research has implications for the selection and design of bulk solids handling equipment, and the calibration and validation of mechanical and numerical models.

Numerical Modelling of Plate Load Tests on Unsaturated Silt Loams in Laboratory Stands

The paper summarizes the results of the numerical modelling of plate load tests on unsaturated silt loams in laboratory conditions using two different constitutive models and different software packages. The first part of the paper presents laboratory measurements on large specimens of compacted unsaturated silt loams with a constant degree of saturation during the experiments. It comments on the issues of the classical interpretations of static plate load tests including the influence zone theory and further issues with calibration of numerical models using the parameters gained from the classical approach. The second part of the paper dedicated to the problems of numerical modelling of these soils presents results of the Cam-Clay constitutive model modified for capturing the influence of the moisture content implemented in the SIFEL software package and results of the Hypoplastic constitutive model for clays implemented in the GEO 5 software package. The paper presents a comprehensive analysis of the advantages and drawbacks of both constitutive models in details and comments on the possible issues when using them for more topologically complex tasks.

Biomechanical In Vitro Test of a Novel Dynamic Spinal Stabilization System Incorporating Polycarbonate Urethane Material Under Physiological Conditions.

Posterior dynamic stabilization systems (PDSS) were developed to provide stabilization to pathologic or hypermobile spinal segments while maintaining the healthy biomechanics of the spine. Numerous novel dynamic devices incorporate the temperature and moisture dependent material polycarbonate urethane (PCU) due to its mechanical properties and biocompatibility. In this study, standardized pure moment in vitro tests were carried out on human lumbar spines to evaluate the performance of a device containing PCU. An environmental chamber with controlled moisture and temperature was included in the setup to meet the requirements of testing under physiological conditions. Three test conditions were compared: (1) native spine, (2) dynamic instrumentation, and (3) dynamic instrumentation with decompression. The ranges of motion, centers of rotation, and relative pedicle screw motions were evaluated. The device displayed significant stiffening in flexion-extension, lateral bending, and axial rotation load directions. A reduction of the native range of motion diminished the stiffening effect along the spinal column and has the potential to reduce the risk of the onset of degeneration of an adjacent segment. In combination with decompression, the implant decreased the native range of motion for flexion-extension and skew bending, but not for lateral bending and axial rotation. Curve fittings using the sigmoid function were performed to parameterize all load-deflection curves in order to enhance accurate numerical model calibrations and comparisons. The device caused a shift of the center of rotation (COR) in the posterior and caudal direction during flexion-extension loading.

Geotechnical centrifuge and numerical modelling of buried pipelines

Mechanical response of buried pipes subjected to vehicle live loads acting on the ground surface has been exhaustively studied in the past decades. However, it remains an open subject especially for cases where the load is not necessarily positioned over the centre of the crown. Simplifications regarding loading transmission based on the theory of elasticity and the lack of soil–pipe interaction in the analyses have been blamed for possible lack of adherence between the predicted and the observed behaviour of such structures. Herein, both numerical and physical modelling were used to capture the important features of the mechanical behaviour of buried pipelines under live moving surface loads. The physical models were tested under modified gravity in a centrifuge, which allowed the calibration of a three-dimensional numerical finite-element model. Three different models were tested in the geotechnical centrifuge, corresponding to three different cover heights: 1D, 1·5D and 2D, where D is the pipe diameter. The results showed that pipe deformations, caused by live vehicle loads applied at distances greater than twice the diameter of the pipe, are negligible. The diametrical deformations did not exceed the 2% limit suggested by regulation associations. The highest value found in this study was 0·2%.

Pilot experimental and numerical studies on a novel retrofit scheme for steel joints against progressive collapse

Current design standards require that beam-column joints should withstand a minimum tie force in the case of an extreme loading event resulting in the loss of one or more columns to prevent progressive collapse of a building. However, research has shown that nominally-pinned steel beam-column joints, which are commonly used in non-seismic areas and in the gravity frames of seismically-designed frames, are not capable of providing the required tie force while undergoing significant rotations imposed by a loss of column event. This paper proposes a set of novel structural details that can be added to industry-standard nominally pinned joints to increase both their tensile resistance and rotation capacity. The proposed structural details exploit the exceptional strength and ductility of duplex stainless steel pins (SSPs) under bending. SSPs are strategically placed in a way that they do not interfere with the behaviour of the joint under gravity loads. The monotonic fracture capacity of SSPs is first experimentally evaluated and the calibration of numerical models that can capture the fracture behaviour of the SSPs follows. Using the calibrated numerical models, a parametric study was carried out to identify optimal geometries of SSPs to reliably achieve the required levels of tie force and rotation in a joint. Finally, two previously tested vulnerable fin plate joints are used as design cases to demonstrate the effectiveness of the proposed structural details to increase the resistance against progressive collapse of nominally-pinned joints.

Transient characteristics of effective porosity and specific yield in bedrock aquifers

Studies of bedrock aquifers have often treated effective porosity and specific yield as having a similar, time-invariant value. Here, we apply a series of tests of specific yield and effective porosity at multiple temporal scales to the Chalk aquifer of east Hampshire, England. These include analysis of natural water level, discharge and water quality variations, numerical model calibrations, hydrograph recession analysis, pumping tests, and tracer tests using both injected and environmental tracers. Values of both effective porosity and specific yield are shown to be transient phenomena that are dependent upon the temporal test scale, an effect which results from the dual-porosity structure of the aquifer. Over short time periods, aquifer response is dominated by preferential flow through the low-storage, high-permeability fracture network; effective porosities on a timescale of hours to days are 0.0001–0.001. Over longer time periods, aquifer response becomes increasingly dominated by the high-storage, low-permeability matrix, with the effective porosity rising to approximate total porosity (0.39) on a timescale of decades. Specific yield also increases as a function of timescale, though there is much less variability than with effective porosity. Our findings demonstrate that it is critical to use an effective porosity value appropriate to the timescale when making transport calculations. Preferential flow through fracture networks is common in bedrock aquifers. Consequently, the transient nature of both effective porosity and specific yield that has been demonstrated in the Chalk aquifer is likely to be broadly representative of most bedrock aquifers.

Non-modal vibration-based methods for bridge damage identification

Many methods of damage identification in bridge structures have focused on the use of numerical models, modal parameters or non-destructive damage tests as a means of condition assessment. These techniques can often be very effective but can also suffer from specific pitfalls such as, numerical model calibration issues for non-linear and inelastic behaviour, modal parameter sensitivity to environmental and operational conditions and bridge usage restrictions for non-destructive testing. This paper covers alternative approaches to damage identification of bridge structures using empirical parameters applied to measured vibration response data obtained from two field experiments of progressively damaged bridges subjected to ambient and vehicle-induced excitation, respectively. Numerous non-modal vibration-based damage features are detailed and selected for the assessment of either the ambient or vehicle-induced excitation data based on their inherent properties. The results of the application to two real bridges, one under ambient vibration and the other of forced vibration, demonstrate the robustness of the proposed damage features for damage identification using measurements of ambient and vehicle excitations. Moreover, this investigation has demonstrated that the novel empirical vibration parameters assessed are suitable for damage detection, localisation and quantification.AbbreviationsCAVcumulative absolute velocityCADcumulative absolute displacementDVIdistributed vibration intensityMCVImean cumulative vibration intensityIVIinstantaneous vibration intensityAIVIAmalgamated instantaneous vibration intensityEMDempirical mode decompositionICEEMDANimproved complete ensemble empirical mode decomposition with adaptive noiseHHTHilbert–Huang TransformIMFintrinsic mode functionsMCDminimum covariance determinateMSDmahalanobis squared distanceMTSMahalanobis Taguchi system