| 1. |
- Benckert, Lars
(författare)
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Wood drying studies using white light speckle photography
- 1992
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Ingår i: Measurement. - : Elsevier BV. - 0263-2241 .- 1873-412X. ; 10:1, s. 24-30
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Tidskriftsartikel (refereegranskat)abstract
- White light speckle photography is a powerful tool for measuring displacement fields in the sub-millimetre range. Here it has been utilised to study deformation and crack development in a block of wood during drying. The use of a series of single exposures made it possible to monitor the changes of the wood's surface with time. By combining two of the negatives the displacements over a given time interval were obtained for, at least in principle, all points on the surface.
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| 2. |
- Holm, Martin, et al.
(författare)
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Simulation of flow meter calibration factors for various installation effects
- 1995
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Ingår i: Measurement. - : Elsevier BV. - 0263-2241 .- 1873-412X. ; 15:4, s. 235-244
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Tidskriftsartikel (refereegranskat)abstract
- The determination of flow meter calibration factors has been made using a computer simulation approach. The proposed technique is based on computational fluid dynamics (CFD). The CFD tools were used to determine the flow field in a flow meter as developed by three different pipe configurations. These flow fields were used to determine the calibration factor for an ultrasonic flow meter. The results have been compared with calibration factors obtained by CFD using detailed LDV input boundary data, analytical calculations and experimental data. Tests were made for reference conditions of 100D straight-pipe and for single- and double-elbow pipe configurations using Reynolds numbers from 100 to 100,000. For reference conditions good agreement is shown. For disturbed flow conditions the simulations well resembled the experimental data. However we find differences for transitional and swirl flows.
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| 3. |
- Alizadeh, Mahmoud, et al.
(författare)
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A two-tone test for characterizing nonlinear dynamic effects of radio frequency amplifiers in different amplitude regions
- 2016
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Ingår i: Measurement. - : Elsevier BV. - 0263-2241 .- 1873-412X. ; 89, s. 273-279
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Tidskriftsartikel (refereegranskat)abstract
- A new two-tone test method for radio frequency power amplifiers is presented. The test signal is a two-tone probing-signal superimposed on large-signals of different amplitude. The amplifier is, thus, excited in different amplitude regions. The amplitude and phase of the 3rd order intermodulation (IM) products are measured vs. frequency spacing and probing-signal amplitude in each region. The IM magnitude is a measure of the nonlinearity, while the frequency dependence and asymmetry are measures of the memory effects in the different regions. A Doherty and a class-AB amplifier were tested. For both amplifiers the IM magnitude increased by ∼15 dB from the lowest to the highest amplitude region. For the Doherty amplifier the behavior of the IM products vs. frequency spacing was similar in all regions, indicating similar memory effects. For the class-AB amplifier the IM vs. frequency spacing was significantly different in the different regions, which indicates different memory effects.
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| 4. |
- Andersson, Henrik, et al.
(författare)
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Principle of FT Spectrometer based on a Lateral Effect Position Sensitive Detector and Multi Channel Fabry-Perot Interferometer
- 2009
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Ingår i: Measurement. - : Elsevier BV. - 0263-2241 .- 1873-412X. ; 42:5, s. 668-671
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Tidskriftsartikel (refereegranskat)abstract
- The principle of a new type of multi channel Fourier-Transform spectrometer based on a multi channel wedge Fabry-Perot interferometer using a one dimensional lateral effect Position Sensitive Detector and a scanning slit for interferogram readout have been shown. The design of this spectrometer is very compact and the readout electronics very simple. The drawback of using a scanning slit system is minimized by the use of a position sensitive detector where the position is inherently known for each measurement. Experiments show that the position can be resolved with high accuracy and the summation of the two photocurrents gives the interferogram after scanning the slit between the wedge interferometer and the position sensitive detector. The spectral resolution obtained with a 25mm wedge interferometer together with a 45mm position sensitive detector and a 25µm slit is about 5nm around 600nm wavelength range, which is close to the theoretically anticipated resolution. The evaluated spectrometer setup show promising results and could be used in applications where compact and low cost spectrometers are required.
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| 5. |
- Arrhenius, Karine, et al.
(författare)
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An inter-laboratory comparison between 13 international laboratories for eight components relevant for hydrogen fuel quality assessment
- 2024
-
Ingår i: Measurement. - : Elsevier B.V.. - 0263-2241 .- 1873-412X. ; 230
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Tidskriftsartikel (refereegranskat)abstract
- The quality of the hydrogen delivered by refuelling stations is critical for end-users and society. The purity of the hydrogen dispensed at hydrogen refuelling points should comply with the technical specifications included in the ISO 14687:2019 and EN 17124:2022 standards. Once laboratories have set up methods, they need to verify their performances, for example through participation in interlaboratory comparisons. Due to the challenge associated with the production of stable reference materials and transport of these which are produced in hydrogen at high pressure (>10 bar), interlaboratory comparisons have been organized in different steps, with increasing extent. This study describes an inter-laboratory comparison exercise for hydrogen fuel involving a large number of participants (13 laboratories), completed in less than a year and included eight key contaminants of hydrogen fuel at level close to the ISO14687 threshold. These compounds were selected based on their high probability of occurrence or because they have been found in hydrogen fuel samples. For the results of the intercomparison, it appeared that fully complying with ISO 21087:2019 is still challenging for many participants and highlighted the importance of organising these types of exercises. Many laboratories performed corrective actions based on their results, which in turn significantly improved their performances. © 2024 The Author(s)
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| 6. |
- Avoci Ugwiri, M., et al.
(författare)
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Benefits of enhanced techniques combining negentropy, spectral correlation and kurtogram for bearing fault diagnosis
- 2021
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Ingår i: Measurement. - : Elsevier B.V.. - 0263-2241 .- 1873-412X. ; 185
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Tidskriftsartikel (refereegranskat)abstract
- In condition monitoring based on vibrations for rotating machines fault detection, one of the typical symptoms is the presence of repetitive transients, which are characterized by impulsive and cyclostationarity signature. The approach quite popular nowadays in the industry for their detection is time–frequency techniques. Those techniques are mainly analysis tools instead of processing tools, and in any case, they are unable to offer a versatile methodology that applies to all mechanical signals in all circumstances. On the one hand, the paper is motivated by ideas borrowed from thermodynamics, where transients are seen as departures from a state of equilibrium; it is proposed to measure the negentropy of the squared envelope (SE) and the squared envelope spectrum (SES) of the signal. On the other hand, the paper proposes an adequate approach to exploit methods such as spectral correlation and kurtogram. The work's main objective is to investigate connections in those approaches to capture the signature of this repetitive behavior. The methodology used in this paper proposes to display as images all three proposed techniques. The impulsive events are then detected and localized in frequency by high values of the squared envelope spectrum (SES) infogram in some frequency bands. In order to analyze the signal in the frequency domain, the Short-Time Fourier Transform (STFT) is then used. The STFT is suggested in this study due to its simplicity and high flexibility. For fault, such as bearings, Kurtogram was demonstrated to be efficient. However, kurtosis based on temporal signals is effective under some conditions; its performance is low in the presence of a low signal-to-noise ratio. The paper analyzed the case of Ball Pass Frequency Inner Race (BPFI), where bearings are housed in a casing allowing the shaft to rotate while driven by a variable speed electric motor. A radial load is applied using a hydraulic cylinder, and different sizes of defects are realized. For fault like BPFI, the negentropy gives more information even for a shallow size of fault and allows a prompt fault detection, and it can also be used for fault localization. The paper demonstrated that results obtained from negentropy through infograms combining with spectral correlation could significantly extend the domain of the applicability of the Kurtogram. © 2021 Elsevier Ltd
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| 7. |
- Bernstone, Christian, et al.
(författare)
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Image analysis for monitoring of crack growth in hydropower concrete structures
- 2009
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Ingår i: Measurement. - : Elsevier BV. - 0263-2241 .- 1873-412X. ; 42:6, s. 878-893
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Tidskriftsartikel (refereegranskat)abstract
- A digital image analysis technique for crack monitoring using a standard web-camera has been further developed to acquire continuous data sets on crack development in concrete dams. The method is based on an existing robust and straightforward non-contact method for experimental deformation analysis. It allows for the measurement of suspected serious cracks, identified from inspections, through a sequence of images captured at intervals. The crack opening displacements at the surface of investigated objects are obtained by an algorithm that makes it possible to automatically track the motions of discrete markers painted on the object surface markers and compute their centre of mass in a sequence of images. The data acquisition process is straightforward and is well suited for this type of environment. Results from laboratory experiments and a field-test on a commuter bridge in Sweden are presented. The study implies that the technique can be useful for hydropower concrete structure applications. (C) 2009 Elsevier Ltd. All rights reserved.
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| 8. |
- Björsell, Niclas, 1964-, et al.
(författare)
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A waveform digitizer-based automatic modulation classifier for a flexible spectrum management
- 2011
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Ingår i: Measurement. - : Elsevier BV. - 0263-2241 .- 1873-412X. ; 44:6, s. 1007-1017
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Tidskriftsartikel (refereegranskat)abstract
- The paper presents the development and validation of an automatic digital modulation classifier based on a waveform digitizer architecture. The proposed automatic digital modulation classifier can be used for signal recognition in the next generation telecommunication systems, characterized by a flexible and dynamic management of the radio spectrum. It has been implemented on a PC architecture, connected with two different types of waveform digitizers. The experimental validation has been carried out by means of actual telecommunication signals, even in presence of narrowband and wideband interference. (C) 2011 Elsevier Ltd. All rights reserved.
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| 9. |
- Björsell, Niclas, et al.
(författare)
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Truncated Gaussian Noise in ADC Histogram Tests
- 2007
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Ingår i: Measurement. - : Elsevier BV. - 0263-2241 .- 1873-412X. ; 40:1, s. 36-42
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Tidskriftsartikel (refereegranskat)abstract
- One method to characterize analogue to digital converters (ADCs) is to use a histogram, where Gaussian noise may be used as stimulus signal. However, a Gaussian noise signal that excites all transition levels also generates input values outside working range of the ADC. Modern signal generators can generate arbitrary signals. Hence, excluding undesired values outside the ADC full scale can minimize test sequences. Truncating the signal to the working range gives further advantages, which are explored in this paper. The Cramer-Rao lower bound and a minimum variance estimator for histogram tests with an arbitrary stimulus are derived. These are applied for truncated Gaussian noise and the result is theoretically evaluated and compared to untruncated noise. It is shown that accuracy increases for a fixed sample length and that variation over transition levels decrease.
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| 10. |
- Brandt, Anders, et al.
(författare)
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Integrating time signals in frequency domain : comparison with time domain integration
- 2014
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Ingår i: Measurement. - : Elsevier. - 0263-2241 .- 1873-412X. ; 58, s. 511-519
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Tidskriftsartikel (refereegranskat)abstract
- Integrating sampled time signals is a common task in signal processing. In this paper we investigate the performance of two straightforward integration methods: (i) integration in the frequency domain by a discrete Fourier transform (DFT), division by jω followed by inverse DFT (IDFT) back to the time domain, and (ii) a method using a weighted overlap-add (WOLA) technique which is developed in the paper. These two methods are compared with two time domain methods: (a) the trapezoidal rule, and (b) an optimized IIR filter. It is shown that the intuitive method of a straightforward DFT/IDFT is a very good method which is recommended for data lengths exceeding 16 K samples, provided data are short enough to allow a single DFT. The IIR filter integration is shown to have very similar accuracy and can also be recommended. The WOLA integration method is shown to perform well in most cases for steady-state conditions. For cases with short transients it should, however, be avoided. A signal integrated by the WOLA method is further shown to be incoherent with the signal before integration. This suggests that the WOLA method should be avoided in cases where coherence between the signals before and after integration is important. It is also demonstrated by a simulation example that integration by the trapezoidal rule should be avoided, as it gives biased results, particularly for higher frequencies.
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| 11. |
- Böckler, H B, et al.
(författare)
-
Metrology infrastructure for high-pressure gas and liquified hydrogen flows. A brief outline of the MetHyInfra project, measurement challenges, and first results
- 2024
-
Ingår i: Measurement. - : Elsevier B.V.. - 0263-2241 .- 1873-412X. ; 232
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Tidskriftsartikel (refereegranskat)abstract
- This paper gives an overview of the ongoing Joint Research Project (JRP) 20IND11 “Metrology infrastructure for high pressure gas and liquefied hydrogen flows” (MetHyInfra), which will ensure traceability in the hydrogen distribution chain. For this purpose, very precise nozzles with well-defined geometries have been produced. In this project, Critical Flow Venturi Nozzles (CFVNs) will be traceably calibrated for the first time with hydrogen and pressures up to 100 MPa using a Coriolis Flow Meter (CFM) as a secondary standard. A CFM has been successfully calibrated with hydrogen against a gravimetric primary standard. Equations of State (EoS) are important for the high-pressure calibration of the nozzles, but also for Computational Fluid Dynamics (CFD) simulations. With regard to CFD, a numerical model has been developed to simulate high pressure hydrogen flow in the CFVN. In a parameter study, non-ideal nozzle shapes are investigated using a shape variation parameter. New Speed of Sound (SoS) measurements were conducted at temperatures from 273 to 323 K and pressures from 1 to 100 MPa. These new data were then used to develop a new EoS for normal hydrogen, optimized for gas phase calculations. In addition to gaseous hydrogen, the project has a strong focus on liquefied hydrogen. Here a three-pronged approach allows traceable measurements. Each of the approaches presented is based on a unique flow calibration principle and relies on independent traceability schemes. The results of the project will ensure traceable measurements and thus a higher level of confidence among end users. © 2024 The Authors
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| 12. |
- Capriglione, D., et al.
(författare)
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Development of a test plan and a testbed for performance analysis of MEMS-based IMUs under vibration conditions
- 2020
-
Ingår i: Measurement. - : Elsevier B.V.. - 0263-2241 .- 1873-412X. ; 158
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Tidskriftsartikel (refereegranskat)abstract
- Micro-Electro-Mechanical Systems (MEMS) are today widespread in many industrial and consumer applications. In the field of terrestrial transportation, cellular, wearable devices, robotics, drone, to cite a few, MEMS-based Inertial Measurement Units (IMUs) are widely employed for assuring several tasks as for the object tracking, self-driving vehicles, human motion and so on. Expected performance of such systems and also recent literature and technical standards miss considering both a context-awareness reliability analysis and metrological performance analyses of MEMS-based IMUs when operating in real scenarios characterized by the presence of significant temperature excursions, humidity, vibrations, mechanical shocks and so on. In particular, standard procedures to be applied for testing MEMS-based IMUs are not still available. Trying to fill these needs, this paper proposes both a suitable testbed and test plans for performance analysis of such kinds of devices under vibration conditions. The application to a real IMUs has confirmed that the proposed tests allow identifying the effects of mechanical stress on both the reliability and metrological performance of such devices. These results could be useful also for the international committees involved in the definition of technical standards to be adopted for testing these kinds of devices. © 2020 Elsevier Ltd
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| 13. |
- Carratù, M., et al.
(författare)
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A Sound Level Meter featured with automatic estimation of the measurement uncertainty
- 2022
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Ingår i: Measurement. - : Elsevier BV. - 0263-2241 .- 1873-412X. ; 188
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Tidskriftsartikel (refereegranskat)abstract
- In the area of measuring the environmental noise the equivalent sound pressure level LA,eq is adopted and compared with legal thresholds in order to characterize the site of interest. The paper describes an innovative Sound Level Meter (SLM) able to provide information about the measurand contribution to the measurement uncertainty estimation. This measurement technology is made possible thanks to an approach based on bootstrap method for selecting the suitable measurement episode for an estimation of LAeq. The firmware implementation of the developed SLM is disclosed with reference to a low-cost platform for real-time execution of the proposed methodology. Finally, a metrological characterization of the prototype performed in laboratory is reported as well as the performance comparison with a class 1 SLM in a real scenario. As a result, the smart features of the new SLM may be easily implemented by including commercial devices into the instrument schematics.
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| 14. |
- Cervantes, Michel, et al.
(författare)
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Reformulation of the pressure-time method for application without flow rate cut-off
- 2022
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Ingår i: Measurement. - : Elsevier. - 0263-2241 .- 1873-412X. ; 188
-
Tidskriftsartikel (refereegranskat)abstract
- The paper presents a reformulation of the standard pressure-time method for flow rate measurement in closed conduits. According to the IEC 60041 standard, the method is used with turbines flow rate cut-off. Its current formulation requires complete closure of the turbine shut-off device, generally guide vanes for reaction turbines and valves for impulse turbines, which may cause wear and tear on the machine. Any leakage through the closed shut-off device also needs to be measured. In the present work, a new formulation of the pressure-time method is derived, extending the actual use. The newly formulated method allows the determination of the flow rate at any instant of time from a load variation and, thus, the initial, incremental, and final flow rate. The load variation may be positive or negative. Measurements of any leakage flow are eliminated. Numerical and experimental cases are used to assess the validity and applicability of the proposed formulation. The numerical results demonstrate the correctness of the derivation. The experimental results exemplify the applicability of the method. Limitations of the derived methodology are discussed.
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| 15. |
- Chelgani, Saeed Chehreh, et al.
(författare)
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Modeling of Free Swelling Index Based on Variable Importance Measurements of Parent Coal Properties by Random Forest Method
- 2016
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Ingår i: Measurement. - : Elsevier. - 0263-2241 .- 1873-412X. ; 94, s. 416-422
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Tidskriftsartikel (refereegranskat)abstract
- Coke quality has a critical role in the steelmaking industry. The aim of this study is to examine the complex relationships between various conventional coal analyses using coke making index “free swelling index (FSI)”. Random forest (RF) associated with variable importance measurements (VIMs), which is a new powerful statistical data mining approach, is utilized in this study to analyze a high-dimensional database (3961 samples) to rank variables, and to develop an accurate FSI predictive model based on the most important variables. VIMs was performed on various types of analyses which indicated that volatile matter, carbon, moisture (coal rank parameters) and organic sulfur are the most effective coal properties for the prediction of FSI. These variables have been used as an input set of RF model for the FSI modeling and prediction. Results of FSI model indicated that RF can provide a satisfactory prediction of FSI with the correlation of determination R2 = 0.96 and mean square error of 0.16 from laboratory FSIs (which is smaller than the interval unit of FSI; 0.5). Based on this result, RF can be used to rank and select effective variables by evaluating nonlinear relationships among parameters. Moreover, it can be further employed as a non-parametric reliable predictive method for modeling, controlling, and optimizing complex variables; which to our knowledge has never been utilized in the fuel and energy sectors.
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| 16. |
- Chelgani, Saeed Chehreh, et al.
(författare)
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Support vector regression modeling of coal flotation based on variable importance measurements by mutual information method
- 2018
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Ingår i: Measurement. - : Elsevier. - 0263-2241 .- 1873-412X. ; 114, s. 102-108
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Tidskriftsartikel (refereegranskat)abstract
- Support vector regression (SVR) modeling was used to predict the coal flotation responses (recovery (R∗) and flotation rate constant (k)) as a function of measured particle properties and hydrodynamic flotation variables. Coal flotation is a complicated multifaceted separation process and many measurable and unmeasurable variables can be considered for its modeling. Therefore, feature selection can be used to save time and cost of measuring irrelevant parameters. Mutual information (MI) as a powerful variable selection tool was used through laboratory measured variables to assess interactions and choose the most effective ones for predictions of R∗ and k. Feature selection by MI through variables indicated that the best arrangements for the R∗ and k predictions are the sets of particle Reynolds number-energy dissipation and particle size-bubble Reynolds number, respectively. Correlation of determination (R2) and difference between laboratory measured and SVR predicted values based on MI selected variables indicated that the SVR can model R∗ and k quite accurately with R2 = 0.93 and R2 = 0.72, respectively. These results demonstrated that the MI-SVR combination can quite satisfactorily measure the importance of variables, increase interpretability, reduce the risk of overfitting, decrease complexity and generate predictive models for high dimension of variables based on selected features for complicated processing systems.
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| 17. |
- Chen, Dingfu, et al.
(författare)
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Bayesian uncertainty evaluation of stitching interferometry for cylindrical surface
- 2020
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Ingår i: Measurement. - : ELSEVIER SCI LTD. - 0263-2241 .- 1873-412X. ; 157
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Tidskriftsartikel (refereegranskat)abstract
- Uncertainty evaluation is one of the most important concepts in metrological characterizations. This paper proposes a method for uncertainty evaluation of measurements of cylindrical surfaces by means of stitching interferometry. The proposed method is based on the Bayesian statistical analysis. The prior deviation for a tested surface is determined by both calculation of standard deviation through multiple measurements of a single sub-aperture and calibration of the optical system error. The probability distribution functions (PDF) of the prior and real misalignment error and measured data of the aperture are derived according to the stitching model. Simulated observations are approximated with the Gibbs Sampler using the Markov Chain Monte Carlo (MCMC) method. Our proposed method is a promising alternative to the ordinary least square technique (LST) with the maximum likelihood estimation (MLE) for obtaining the uncertainty of the misalignment and measurement error in the stitching results. Moreover, it can take the inevitable environment errors into account. The prediction of the uncertainty interval makes our method more attractive in industrial applications. (C) 2020 Elsevier Ltd. All rights reserved.
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| 18. |
- Chi, Zhexiang, et al.
(författare)
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Data-driven approach to study the polygonization of high-speed railway train wheel-sets using field data of China’s HSR train
- 2020
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Ingår i: Measurement. - : Elsevier. - 0263-2241 .- 1873-412X. ; 149
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Tidskriftsartikel (refereegranskat)abstract
- Environmental factors, like seasonality, have been proved to exert significant impact on reliability of China high-speed rail train wheels in this article. Most studies on polygonization of train wheels are based on physical models, mathematical models or simulation systems. Normally, characteristics and mechanisms of wheel polygonization are studied under ideal conditions without considering the impact of the environment. However, in practical use, there are many irregular wear wheels and irregular wear cannot be explained by theoretical models with assumptions of ideal conditions. We look at two possible factors in polygonization: seasonality and proximity to engines. Our analysis of field data shows the environmental factor has more impact on wheel polygonization than the mechanical factor. Based on the Bayesian models, the mean time to failure of the wheels under different operation conditions is conducted. A case study of China’s HSR train wheels is conducted to confirm the finding. The case study shows the degree of polygonal wear is much more severe in summer than other seasons. The finding may give a totally new research perspective on polygonization of train wheels. We use Bayesian analysis because this method is useful for small and incomplete data sets. We propose three Bayesian data-driven models.
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| 19. |
- Costa, Marcelo Azevedo, et al.
(författare)
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Failure detection in robotic arms using statistical modeling, machine learning and hybrid gradient boosting
- 2019
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Ingår i: Measurement. - : ELSEVIER SCI LTD. - 0263-2241 .- 1873-412X. ; 146, s. 425-436
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Tidskriftsartikel (refereegranskat)abstract
- Modeling and failure prediction are important tasks in many engineering systems. For these tasks, the machine learning literature presents a large variety of models such as classification trees, random forest, artificial neural networks, among others. Standard statistical models such as the logistic regression, linear discriminant analysis, k-nearest neighbors, among others, can be applied. This work evaluates advantages and limitations of statistical and machine learning methods to predict failures in industrial robots. The work is based on data from more than five thousand robots in industrial use. Furthermore, a new approach combining standard statistical and machine learning models, named hybrid gradient boosting, is proposed. Results show that the hybrid gradient boosting achieves significant improvement as compared to statistical and machine learning methods. Furthermore, local joint information has been identified as the main driver for failure detection, whereas failure classification can be improved using additional information from different joints and hybrid models. (C) 2019 Elsevier Ltd. All rights reserved.
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| 20. |
- Dróżdż, Artur, et al.
(författare)
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Hot-wire spatial resolution issues in adverse pressure gradient turbulent boundary layers
- 2024
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Ingår i: Measurement. - : Elsevier BV. - 0263-2241 .- 1873-412X. ; 237
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Tidskriftsartikel (refereegranskat)abstract
- The effect of a finite length of hot-wire probe sensor length on the measured streamwise velocity fluctuations is well understood in canonical wall-bounded flow, where the small-scale energy has been found to be universal and invariant with Reynolds number. A straightforward application of that assumption to non-canonical flows such as strong adverse pressure gradient (APG) flows has, however, been hampered since the effect of Re and APG could not conclusively be studied separately due to the lack of data with a clear scale separation. The present experimental investigation at Reτ≈4000 in weak, moderate and strong APGs with different wire length shows that spatial averaging effects are not only limited to the inner layer. A note of caution is hence warranted for measurements that seemingly try to take the bias effect of spatial attenuation into account by performing measurements with albeit long but fixed viscous-scaled wire length.
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| 21. |
- Endrias, Dawit H., et al.
(författare)
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A combinatorial optimization approach for evaluating minimum-zone spatial straightness errors
- 2012
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Ingår i: Measurement. - : Elsevier. - 0263-2241 .- 1873-412X. ; 45:5, s. 1170-1179
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a new and robust approach for the accurate evaluation of minimumzone spatial straightness error from a set of coordinate measurement data points. The algorithm iteratively searches for the specific data points that define the minimum bound of the spatial straightness zone using combinatorial optimization. It is based on the fact that the minimum circumscribed cylinder of a point set, which is equivalent to the minimum spatial straightness zone of the measurement data, will pass through three, four, or five of the data points that constitute the convex hull vertices of the entire data set. Computed results have shown that although the presented approach may lead to increased computational time, it is robust and able to construct the exact minimum circumscribed cylinder for a given point set. The minimum-zone spatial straightness error can thus be evaluated with the best possible accuracy. The advantage of the presented algorithm is demonstrated via comparison with published computed results of existing algorithms.
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| 22. |
- Galar, Diego, et al.
(författare)
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Context awareness for maintenance decision making : A diagnosis and prognosis approach
- 2015
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Ingår i: Measurement. - : Elsevier BV. - 0263-2241 .- 1873-412X. ; 67, s. 137-150
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Tidskriftsartikel (refereegranskat)abstract
- All assets necessarily suffer wear and tear during operation. Prognostics can assess the current health of a system and predict its remaining life based on features capturing the gradual degradation of its operational capabilities. Prognostics are critical to improve safety, plan successful work, schedule maintenance, and reduce maintenance costs and down time. Prognosis is a relatively new area but has become an important part of Condition-based Maintenance (CBM) of systems. Broadly stated, prognostic methods are either data-driven, rule based, or model-based. Each approach has advantages and disadvantages; consequently, they are often combined in hybrid applications. A hybrid model can combine some or all model types; thus, more complete information can be gathered, leading to more accurate recognition of the fault state. In this context, it is important to evaluate the consistency and reliability of the measurement data obtained during laboratory testing and the prognostic/diagnostic monitoring of the system under examination.This approach is especially relevant in systems where the maintainer and operator know some of the failure mechanisms with a sufficient amount of data, but the sheer complexity of the assets precludes the development of a complete model-based approach. This paper addresses the process of data aggregation into a contextual awareness hybrid model to get Residual Useful Life (RUL) values within logical confidence intervals so that the life cycle of assets can be managed and optimised.
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| 23. |
- González-González, Asier, et al.
(författare)
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Condition Monitoring of Wind Turbine Pitch Controller : A Maintenance Approach
- 2018
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Ingår i: Measurement. - : Elsevier. - 0263-2241 .- 1873-412X. ; 123, s. 80-93
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Tidskriftsartikel (refereegranskat)abstract
- With the increase of wind power capacity worldwide, researchers are focusing their attention on the operation and maintenance of wind turbines. A proper pitch controller must be designed to extend the life cycle of a wind turbine’s blades and tower. The pitch control system has two main, but conflicting, objectives: to maximize the wind energy captured and converted into electrical energy and to minimize fatigue and mechanical load. Four metrics have been proposed to balance these two objectives. Also, diverse pitch controller strategies are proposed in this paper to evaluate these objectives. This paper proposes a novel metrics approach to achieve the conflicting objectives with a maintenance focus. It uses a 100 kW wind turbine as a case study to simulate the proposed pitch control strategies and evaluate with the metrics proposed. The results are showed in two tables due to two different wind models are used.
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| 24. |
- Hadavandi, E., et al.
(författare)
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Estimation of coking indexes based on parental coal properties by variable importance measurement and boosted-support vector regression method
- 2019
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Ingår i: Measurement. - : Elsevier. - 0263-2241 .- 1873-412X. ; 135, s. 306-311
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Tidskriftsartikel (refereegranskat)abstract
- Coke as a fuel has a critical role for steel making industries. Since coke is a product of blended coals, it is essential to study relationships between parental coal components with quality of their coke products. Free swelling index (FSI) and maximum fluidity (MF) are standard coking indexes that widely used for blending coals and measuring quality of products. This study has been explored interdependencies between measured coal components by mutual information (MI) method and evaluated their importance in the prediction of coking indexes for a wide range of Illinois coal samples. MI results indicated that the set of moisture-organic sulfur and moisture-nitrogen-sulfate sulfur were the best variables for predictions of log(MF) and FSI, respectively. Adaptive Boosting method based on support vector regression (SVR), called Boosted-SVR, was used the selected variable sets for predictions of coking indexes. In testing stage of models, correlation of determination (R2) between actual and predicted values for the log(MF) and FSI were 0.89 and 0.90, respectively. These results indicated that Boosted-SVR model could quite satisfactory predict coking indexes. In general, outcomes of this investigation demonstrated an appropriate potential of coking quality prediction with limited numbers of input variables and suggested that a combination of MI with Boosted-SVR model as a new powerful tool which can be used for the computation of other complex fuel and processing problems based on measurement of conventional properties.
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| 25. |
- Hagqvist, Petter, 1986-, et al.
(författare)
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Emissivity estimation for high temperature radiation pyrometry on Ti–6Al–4V
- 2013
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Ingår i: Measurement. - : Elsevier BV. - 0263-2241 .- 1873-412X. ; 46:2, s. 871-880
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Tidskriftsartikel (refereegranskat)abstract
- The paper demonstrates a versatile procedure suitable for industrial implementation of temperature measurement on a hot titanium alloy. The driving force has been the need for an accurate temperature measurement during additive manufacturing using laser welding technology where Ti–6Al–4V-wire is melted. The challenges consider both industrial constraints and the varying emissivity of the surface. Measurements makes use of a narrow bandwidth spot radiation pyrometer and a calibration procedure for estimation of the surface temperature through spectral emissivity estimation. The theoretical results are validated through experiments. A number of difficulties in radiation temperature measurements for metals with varying surface properties are discussed; especially the case of surface oxidation. The uncertainty in temperature reading due to the uncertainty in the emissivity estimate is established along with a model that qualitatively describes surface oxidation. The procedure is expected to be useful for several manufacturing applications where it is important to control high temperatures.
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