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1

Sensitivity Analysis of the Estimation of the Single-Number Sound Absorption Evaluation Index DLα

Batko W., Pawlik P., Wszołek G.

Archives of Acoustics

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2017

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Vol. 42, No. 4

689--696

EN

Acoustic barriers are assigned to the respective categories of sound absorbing properties on the basis of a single-number sound absorption evaluation index. Categories of absorbing properties play a significant role in selecting the barrier type for the given localisation. The estimation of the single-number sound absorption evaluation index is performed, among others, by means of measuring the sound absorption coefficient of the analysed acoustic barrier sample in the reverberation chamber. The sensitivity analysis of the determination of the single-number sound absorption evaluation index was performed in this work. The estimation of the input parameters uncertainty contribution to the expanded uncertainty of the sound absorption evaluation index, was done first. The Monte Carlo method and the reduction interval arithmetic were used for this aim. The relative sensitivity coefficients were determined by means of the author’s method based on the interval arithmetic. These coefficients contain information concerning the quantitative influence of the given input value on the final result.

2

Multi-objective model-based design optimization of hydraulic shock absorbers

Wszołek G.

Computer Assisted Methods in Engineering and Science

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2016

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Vol. 23, no. 2/3

147--166

EN

This paper presents the multi-objective optimization process of a hydraulic damper design based on its interdisciplinary meta-model considering both the properties of a damper and of the testing equipment used for the purpose of design criteria verification, and in particular the tolerance band criterion of damping force characteristics, the criterion of maximum permissible vibration level expressed with the piston rod acceleration and the criterion of fatigue durability for the damper’s hydraulic valve system. The meta-model of a damper and a testing bench include the following models: mechanical model, hydraulic model, electro-hydraulic model and valve system fatigue durability model. The multi-objective optimization method provides an optimal solution by means of Pareto frontier. Furthermore, all potential feasible solutions are ranked according to additional customer preferences to select the most suitable ones. The proposed method is intended to be used to determine the best starting point in a new shock absorber design process.

3

Experimental demonstration of Measurement System Analysis

Król A., Czaja W., Kost G., Czop P., Wszołek G., Jakubowski D.

Pomiary Automatyka Robotyka

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2013

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R. 17, nr 1

92-96

EN

This work presents the application of Measurement System Analysis (MSA) and the advantages of the Six Sigma approach in the validation of a servo-hydraulic tester. The diagnosis of repeatability and reproducibility by using repeatability (R) and reproducibility (R) gage analysis (so called Gage R&R Type II tool) which shows the correct operation of the measuring system including uncertainty of staff and measuring instrumentation. The Gage R&R Type II tool is based on the analysis of variance, called ANOVA. The structural approach to the subject has also provided knowledge of the error of the measurement system.

PL

W artykule zaprezentowano zastosowanie analizy systemu pomiarowego (MSA) oraz zalety Six Sigma w podejściu walidacji testera serwohydraulicznego. Ustalenie stopnia powtarzalności i odtwarzalności przez użycie analizy powtarzalności (repeatability - R) i odtwarzalności (reproducibility - R) zwanej Gage R&R Type II, która pokazuje prawidłową pracę systemu pomiarowego, w tym niepewność pracowników oraz narzędzi pomiarowych. Narzędzie Gage R&R Type II bazuje na analizie wariancji zwanej ANOVA. Podstawowym podejściem do wiedzy na temat badanego obiektu jest poznanie błędu samego systemu pomiarowego.

4

Model-based design approach to reducing mechanical vibrations

Czop P., Wszołek G.

Journal of Achievements in Materials and Manufacturing Engineering

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2013

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Vol. 60, nr 1

39--47

EN

Purpose: The paper presents a sensitivity analysis method based on a first-principle model in order to reduce mechanical vibrations of a hydraulic damper. Design/methodology/approach: The first-principle model is formulated using a system of continuous ordinary differential equations capturing usually nonlinear relations among variables of the hydraulic damper model. The model applies three categories of parameters: geometrical, physical and phenomenological. Geometrical and physical parameters are deduced from construction and operational documentation. The phenomenological parameters are the adjustable ones, which are estimated or adjusted based on their roughly known values, e.g. friction/damping coefficients. Findings: The sensitivity analysis method provides major contributors and their magnitude that cause vibrations Research limitations/implications: The method accuracy is limited by the model accuracy and inherited nonlinear effects. Practical implications: The proposed model-based sensitivity method can be used to optimize prototypes of hydraulic dampers. Originality/value: The proposed sensitivity-analysis method minimizes a risk that a hydraulic damper does not meet the customer specification.

5

Educational Implementation of a Sound Level Meter in the LabVIEW Environment

Barański R., Wszołek G.

Archives of Acoustics

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2013

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Vol. 38, No. 1

19--26

EN

As a consequence of recent implementations of EU Directives related to noise protection more and more students of various AGH-UST programs are introduced to the basics of acoustic measurements. Students at various levels of theoretical background in the field of acoustic measurements are offered practical training in measurements using digital sound analyzers. The situation would be optimal if each student could have a device at his/her own disposal. Unfortunately, such a situation is not possible at the moment because of various reasons. With the above problem in mind, a dedicated software package has been developed, implemented in the LabVIEW environment, which allows detailed studies of problems related to the acoustic signal measurement using sound level meters, as well as tasks in spectral analysis (1/1 and 1/3 band filters) and narrow-band (FFT) analysis. With such organization during the introductory laboratory classes each student is offered a direct individual contact with a virtual device that is properly pre-programmed for realization of a well-constructed learning process. It definitely facilitates understanding of the essence of acoustic signal measurements and provides a good basis for further laboratory work carried out as a team-activity.

6

Rapid design of a hydraulic damper valve system

Wszołek G., Czop P., Skrobol A., Sławik D.

Systems : journal of transdisciplinary systems science

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2012

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Vol. 16, nr 1

45-56

EN

This paper proposes an analytical tool that supports the design process of a disc spring valve system used in hydraulic car dampers. The proposed analytical tool obtains a key design characteristic of a valve, which is the flow rate and the corresponding maximum stress level in the stack of plates. The tool is prepared based on the cases produced by a first-principle model using a finite element approach. The finite element model was calibrated based on experimental results to provide accurate results in the entire range of input parameters.

7

Automatic shape identification by data-driven algorithms with applications to design optimizing in hydraulics

Włodarczyk T. H., Czop P., Sławik D., Wszołek G.

Systems : journal of transdisciplinary systems science

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2012

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Vol. 16, nr 1

35-43

EN

A measurement methodology based on differential-geometric properties of certain characteristic curves frequently used in hydraulics is presented. An iterative process that underlies construction of the methodology and its fully automatic application is universally applicable to identifying, and ultimately optimizing, behavior of any device which can be characterized by a 2D, nonlinear curve. Illustrative examples are used to clarify the topic and its usefulness in optimizing performance of a design with respect to oil aeration effects.

PL

Prezentowany artykuł przedstawia metodę pomiarową stosowalną do automatycznego wyznaczania opisu ilościowego kształtów krzywych charakterystyk typowych dla urządzeń hydraulicznych. Proces iteracyjny dzięki któremu możliwe jest osiągnięcie założonego celu jest uniwersalnie stosowalny do optymalizacji zachowania dowolnego urządzenia posiadającego dwuwymiarową, nieliniową krzywą charakterystyki. Praca niniejsza koncentruje się na ilościowym opisaniu tak zwanego efektu aeracji - niekorzystnego zjawiska obserwowanego w urządzeniach w których olej hydrauliczny pozostaje w bezpośrednim kontakcie z rozpuszczalnym w nim gazem. Iteracyjne, lub adaptacyjne, zastosowanie filtrów wygładzających Savitzky'ego i Golay'a (S-G) leży u podstaw przedstawionej tu metodologii wyznaczania dominującego kształtu zaszumionej funkcji skalarnej jednej zmiennej. Dzięki szczególnym własnościom filtrów S-G możliwe jest dokładne rozpoznanie kształtu danej krzywej nawet w obecności znaczącego szumu. Przykładem takiego szumu są, mające dużą amplitudę, wysokoczęstotliwościowe oscylacje sygnału siły, które obserwujemy w trakcie otwierania się zaworów dyskowych.

8

Fluid-structure simulation of a valve system used in hydraulic dampers

Czop P., Gąsiorek D., Gniłka J., Sławik D., Wszołek G.

Modelowanie Inżynierskie

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2012

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T. 14, nr 45

197--205

EN

The aim of this paper is to develop a method for optimizing the design of a disc spring valve system by reducing the aeration and cavitation effect which negatively influences the performance of a shock absorber. A fluid structure interaction (FSI) model is used in order to modify the geometry of the valve interior and, in turn, to achieve better performance of a shock absorber. The paper analyzes the pressure distribution along theflow paths inside the valve cavity to reduce the risk of aeration and cavitation, while other important engineering aspects are omitted, e.g. durability of disc-spring valve systems as discussed in [1]. A key measure of valve improvement was chosen as deterioration of the damping force level generated by a shock absorber vs. the number of cycles during continuous cycling of the damper . The objectives of this work are as follows: (i) to present a process for reducing the complexity of the geometry of a disc spring valve system in order to perform a combined fluid-structure simulation, (ii) to show keysteps of the simulation process focusing on interactions between fluid and structure domain and to review relevant simulation results, (iii) to describe practical aspects of the simulation process, including basic parameters and boundary conditions related to the applied commercial software, (iv) to make an optimization case study to show the application scope for the simulation methodology proposed in the paper, and to confront the simulation results with experimental investigations.

9

Off-line displacement error correction method for servo-hydraulic testers

Braska D., Huchla M., Czop P., Wszołek G.

Journal of Achievements in Materials and Manufacturing Engineering

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2012

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Vol. 55, nr 2

431--438

EN

Purpose: This paper presents an approach towards improving the test rig performance in reproduction of random excitation to which a prototype hydraulic damper is subjected. The method is intended to be implemented as a software solution without modifications either in hardware or the settings of the servo-hydraulic tester. These are the conditions of fatigue tests when a specific signal sequence (block) is repeated until failure of the sample. Design/methodology/approach: Experimental validation of the proposed correction method was conducted using a servo-hydraulic test rig and a transfer function inverse model which was identified based on the operational data. Findings: The proposed method, both in the frequency and time domain, improves the tracking of the test signal and allows an accuracy of more than 95% to be gained using the best fit measure in the case of reproduction of coloured noise signals. Research limitations/implications: It is possible to consider more advanced model-based methods for performing off-line error correction, e.g. state-space models. Practical implications: The proposed method was validated and implemented in the LabVIEW® software to automatically perform the correction of the test signal before the test. The method was validated for the test rig with and without the tested object. Originality/value: The paper proposes an off-line control strategy that improves the reproduction of the load signal in case of repeatable test sequences achieving more than 99% agreement between the applied and measured load.

10

Adjustment method of parameters intended for first-principle models

Czop P., Kost G., Sławik D., Wszołek G., Jakubowski D.

Journal of Achievements in Materials and Manufacturing Engineering

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2012

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Vol. 55, nr 2

446--453

EN

Purpose: This paper demonstrates a process of estimation phenomenological parameters of a first-principle nonlinear model based on the hydraulic damper system. Design/methodology/approach: First-principle (FP) models are formulated using a system of continuous ordinary differential equations capturing usually nonlinear relations among variables of the model. The considering model applies three categories of parameters: geometrical, physical and phenomenological. Geometrical and physical parameters are deduced from construction or operational documentation. The phenomenological parameters are the adjustable ones, which are estimated or adjusted based on their roughly known values, e.g. friction/damping coefficients. Findings: A phenomenological parameter, friction coefficient, was successfully estimated based on the experimental data. The error between the model response and experimental data is not greater than 10%. Research limitations/implications: Adjusting a model to data is, in most cases, a non-convex optimization problem and the criterion function may have several local minima. This is a case when multiple parameters are simultaneously estimated. Practical implications: First-principle models are fundamental tools for understanding, optimizing, designing, and diagnosing technical systems since they are updatable using operational measurements. Originality/value: First-principle models are frequently adjusted by trial-and-error, which can lead to nonoptimal results. In order to avoid deficiencies of the trial-and-error approach, a formalized mathematical method using optimization techniques to minimize the error criterion, and find optimal values of tunable model parameters, was proposed and demonstrated in this work.

11

A computational fluid flow analysis of a disc valve system

Czop P., Śliwa P., Gniłka J., Gąsiorek D., Wszołek G.

Journal of KONES

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2011

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Vol. 18, No. 1

117-122

EN

Noise concerns in shock absorbers can be divided into two categories. The first is fluid flow noise, or “swish noise”, caused by the oil being forced through openings in the valves. The type and temperature of the oil, its velocity and the orifice geometry all have an effect on this. In addition, the structural design of the shock absorber shell may either reduce or amplify the noise. The second type of shock absorber noise is often described as regular operational noise or “chuckle noise”. It can be observed in vehicles during low-displacement, higher-frequency events, such as driving over a slightly rough road. This effect measurable as a force discontinuity into the vehicle and can come from a number of sources in the shock absorber, e.g. hydraulic transitions. It is often traceable to the valve discs closing and opening, but can also be caused by cavitation/aeration in the oil and air being pulled through the valves. The work on noise improvement reported in this paper has been started using conventional shock absorbers to be extended and will cover in the future variable damping shock systems as well. The paper gives an overview about the configurations of a typical valve system including three basic regimes of operation, which correspond to the amount of oil flowing through a valve cavity. The aim of this work was to propose a finite element fluid flow model, which can be used in order to reduce the velocity of fluid flow through a cavity of a shock absorber valve. High flow velocity can cause high-content frequency vibrations and, in turn, audible noise. The model will be used for initial screening of new valve concepts and on the other hand to improve the currently use ones.

12

Six Sigma methodology applied to minimizing damping lag in hydraulic shock absorbers

Czop P., Sławik D., Włodarczyk T. H., Wojtyczka M., Wszołek G.

Journal of Achievements in Materials and Manufacturing Engineering

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2011

|

Vol. 49, nr 2

243--250

EN

Purpose: The aim of this paper is to identify the root cause of the temporary decrease of the damping force during the early stage of the compression phase of the stroking cycle, the so called damping lag, to describe measures of the phenomenon and to present methods for optimizing the design towards minimizing this (negative) effect. Design/methodology/approach: Theoretical background is presented in a constructive and computable manner with emphasis on measurement data analysis and MATLAB/Simulink modeling. Six Sigma tools were used to validate the model statistically and, more importantly, to propose a method of data-driven optimization of the design. Findings: Root cause of the occurrence of the damping lag was confirmed during model validation to be caused by oil aeration. The dependence of the damping lag on parameters is nonlinear. Six Sigma methodology proved to be useful in achieving design optimality. Research limitations/implications: Statistical model and conclusions drawn from it are only valid in the interior of the investigated region of the parameter space. Additionally, it might not be possible to find a local minimum of the aeration measure (damping lag) inside the selected region of the parameter space; global minimum located at the boundary might be the only possible solution. Practical implications: Optimal value of parameters is not unique and thus additional sub-criteria (cost/ durability) can be imposed. Conducting tests in an organized manner and according to the Six Sigma methodology allows for expediting the design optimization process and eliminating unnecessary costs. Originality/value: : Improvements in understanding and measuring aeration effects constitute a clear foundation for further product optimization. Signal post-processing algorithms are essential for the statistical analysis and are the original contribution of this work.

13

Optimization of pneumatic actuators with the use of design for Six Sigma methodology

Król A., Wszołek G., Czop P.

Journal of Achievements in Materials and Manufacturing Engineering

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2011

|

Vol. 47, nr 2

205--210

EN

Purpose: The first aim of this paper is to optimize pneumatic actuator behavior using a structured approach to define and control system factors in order to achieve targeted output values. The second aim is to present a structured optimization process supported by Measurement System Analysis (MSA) and Design of Experiment (DOE) tools in practical applications. Design/methodology/approach: A complete approach for optimizing an unknown system with a structured approach known from DFSS methodology is used in the practical example of pneumatic actuators. DFSS methodology requires a detailed project definition, but ensures good quality of measurement data and a well-prepared optimization process supported by known DOE tools. Findings: The structural approach for system optimization known from DFSS methodology provides a good fit for the optimization of a pneumatic actuator to achieve specified targets. Teams working on system optimization not only set the parameters but also gather a large amount of valuable information about how the mentioned system works, and what the main factors influencing the final results are. The gathered knowledge can be used to create a robust design with the lowest possible cost. Research limitations/implications: The results obtained from Measurement System Analysis and Design of Experiment are valid only for chosen factors and, importantly, only in the range used in both statistical methods. Extrapolation outside the statistical model boundaries is forbidden. Therefore a critical aspect is to agree within the project team on the correct factors and their levels. Practical implications: The optimization of pneumatic actuators can be achieved by a structured approach consisting mainly of project definition, measurement system analysis and final optimization through DOE tools to achieve given targets for displacement and time simultaneously. Originality/value: First Time Through optimization of a pneumatic actuator system as an example of any system treated as a black box, meaning a system with an unknown relationship between input and output. Design for Six Sigma methodology presented in a practical approach.

14

Formulation and identification of First-Principle Data-Driven models

Czop P., Kost G., Sławik D., Wszołek G.

Journal of Achievements in Materials and Manufacturing Engineering

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2011

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Vol. 44, nr 2

179--186

EN

Purpose The paper consists of two parts. The first part presents and discusses a process of formulation and identification of First-Principle Data-Driven (FPDD) models, while the second part demonstrates numerical examples of identification of FPDD models. Design/methodology/approach: First-Principle (FP) model is formulated using a system of continuous ordinary differential equations capturing usually nonlinear relations among variables of the model. The considering model applies three categories of parameters: geometrical, physical and phenomenological. Geometrical and physical parameters are deduced from construction or operational documentation. The phenomenological parameters are the adjustable ones, which are estimated or adjusted based on their roughly known values, e.g. friction/damping coefficients. Findings A few phenomenological parameters were successfully estimated from numerically generated data. The error between the true and estimated value of the parameter occurred, however its magnitude is low at level below 2%. Research limitations/implications Adjusting a model to data is, in most cases, a non-convex optimization problem and the criterion function may have several local minima. This is a case when multiple parameters are simultaneously estimated. Practical implications: FPDD models are an excellent tool for understanding, optimizing, designing, and diagnosing technical systems since they are updatable using operational measurements. This opens application area, for example, for model-based design and early warning diagnostics. Originality/value: First-Principle (FP) models are frequently adjusted by trial-and-error, which can lead to non-optimal results. In order to avoid deficiencies of the trial-and-error approach, a formalized mathematical method using optimization techniques to minimize the error criterion, and find optimal values of tunable model parameters, was proposed and demonstrated in this work.

15

Demonstration of First-Principle Data-Driven models using numerical case studies

Czop P., Sławik D., Wszołek G.

Journal of Achievements in Materials and Manufacturing Engineering

|

2011

|

Vol. 45, nr 2

170--177

EN

Purpose: The paper consists of two parts. The first part presents and discusses a process of formulation and identification of First-Principle Data-Driven (FPDD) models, while the second part demonstrates numerical examples of identification of FPDD models. Design/methodology/approach: First-Principle (FP) model is formulated using a system of continuous ordinary differential equations capturing usually nonlinear relations among variables of the model. The considering model applies three categories of parameters: geometrical, physical and phenomenological. Geometrical and physical parameters are deduced from construction or operational documentation. The phenomenological parameters are the adjustable ones, which are estimated or adjusted based on their roughly known values, e.g. friction/damping coefficients. Findings: A few phenomenological parameters were successfully estimated from numerically generated data. The error between the true and estimated value of the parameter occurred, however its magnitude is low at level below 2%. Research limitations/implications: Adjusting a model to data is, in most cases, a non-convex optimization problem and the criterion function may have several local minima. This is a case when multiple parameters are simultaneously estimated. Practical implications: FPDD models are an excellent tool for understanding, optimizing, designing, and diagnosing technical systems since they are updatable using operational measurements. This opens application area, for example, for model-based design and early warning diagnostics. Originality/value: First-Principle (FP) models are frequently adjusted by trial-and-error, which can lead to non-optimal results. In order to avoid deficiencies of the trial-and-error approach, a formalized mathematical method using optimization techniques to minimize the error criterion, and find optimal values of tunable model parameters, was proposed and demonstrated in this work.

16

A numerical calculations of fluid flow of a shock absorber valve

Gniłka J., Gąsiorek D., Czop P., Śliwa P., Wszołek G.

Modelling and Optimization of Physical Systems

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2010

|

z. 9

29--36

EN

Noise concerns in shock absorbers can be divided into two categories. The first is fluid flow noise, or “swish noise”, caused by the oil being forced through openings in the valves. The type and temperature of the oil, its velocity and the orifice geometry all have an effect on this. In addition, the structural design of the shock absorber shell may either reduce or amplify the noise. The second type of shock absorber noise is often described as regular operational noise or “chuckle noise”. It can be observed in vehicles during low-displacement, higher-frequency events, such as driving over a slightly rough road. This effect measurable as a force discontinuity into the vehicle and can come from a number of sources in the shock absorber, e.g. hydraulic transitions. It is often traceable to the valve discs closing and opening, but can also be caused by cavitation/aeration in the oil and air being pulled through the valves. The work on noise improvement reported in this paper has been started using conventional shock absorbers to be extended and will cover in the future variable damping shock systems as well. The paper gives an overview about the configurations of a typical valve system including three basic regimes of operation which correspond to the amount of oil flowing through a valve cavity. The aim of this work was to propose a finite element fluid flow model which can be used in order to reduce the velocity of fluid flow through a cavity of a shock absorber valve. High flow velocity can cause high-content frequency vibrations and, in turn, audible noise. The model will be used for initial screening of new valve concepts and on the other hand to improve the currently use ones.

17

Optimization of hydraulic dampers with the use of Design For Six Sigma methodology

Sławik D., Czop P., Król A., Wszołek G.

Journal of Achievements in Materials and Manufacturing Engineering

|

2010

|

Vol. 43, nr 2

676--683

EN

Purpose: The aims of this paper are to identify the root cause of the temporary decrease in the damping force which occurs during the early stage of the stroking cycle’s compression phase, the so-called damping lag, to describe measures of the phenomenon and to present methods for optimizing the design towards minimizing this (negative) effect. Design/methodology/approach: A theoretical background is presented in a constructive and computable manner with emphasis on data-driven modeling. The Design For Six Sigma (DFFS) approach and tools were used to validate the model statistically and, more importantly, to propose a method for data-driven optimization of the design. Findings: The root cause of the damping lag was confirmed during model validation as being a result of oil aeration. DFFS methodology proved to be useful in achieving design optimality. Research limitations/implications: The statistical model and conclusions drawn from it are only valid in the interior of the investigated region of the parameter space. Additionally, it might not be possible to find a local minimum of the aeration measure (damping lag) inside the selected region of the parameter space; a/the (depending on the context) global minimum located at the boundary might be the only possible solution. Practical implications: The optimal value of parameters is not unique and thus additional sub-criteria (cost/durability) can be imposed. Conducting tests in an organized manner and according to the Six Sigma methodology allows the design optimization process to be expedited and unnecessary costs to be eliminated. Originality/value: Improvements in understanding and measuring aeration effects constitute a clear foundation for further product optimization. Signal post-processing algorithms are essential for the statistical analysis and are the original contribution of this work.

18

First-principle and data-driven model-based approach in rotating machinery failure mode detection

Wszołek G., Czop P.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

|

Vol. 43, nr 2

692--701

EN

Purpose: A major concern of modern diagnostics is the use of vibration or acoustic signals generated by a machine to reveal its operating conditions. This paper presents a method which allows to periodically obtain estimates of model eigenvalues represented by complex numbers. The method is intended to diagnose rotating machinery under transient conditions. Design/methodology/approach: The method uses a parametric data-driven model, the parameters of which are estimated using operational data. Findings: Experimental results were obtained with the use of a laboratory single-disc rotor system equipped with both sliding and hydrodynamic bearings. The test rig used allows measurements of data under normal, or reference, and malfunctioning operation, including oil instabilities, rub, looseness and unbalance, to be collected. Research limitations/implications: Numerical and experimental studies performed in order to validate the method are presented in the paper. Moreover, literature and industrial case studies are analyzed to better understand vibration modes of the rotor under abnormal operating conditions. Practical implications: A model of the test rig has been developed to verify the method proposed herein and to understand the results of the experiments. Hardware realization of the proposed method was implemented as a standalone operating module developed using the Texas Instruments TMS3200LF2407 Starter Kit. Originality/value: The parametric approach was proposed instead of nonparametric one towards diagnosing of rotating machinery.

19

Application of off-line error correction method software to reproduce random signals on servo-hydraulic testers

Braska D., Czop P., Sławik D., Wszołek G.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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Vol. 40, nr 1

41-49

EN

Purpose: This paper presents an approach towards improving the test rig performance for road signals used in automotive shock absorber tests. The goal is to develop a method for correction of the test signal profile in the off-line mode. The method is intended to be implemented as a software solution without any changes either in hardware or the settings of the servo-hydraulic tester. Design/methodology/approach: A two-stage validation of the proposed correction method was conducted using a servo-hydraulic test rig and its first-principles model. The model is capable of capturing key dynamical properties over a wide operating range while being only moderately complex. Both simulation and experimental performance results are presented and discussed. Findings: The proposed method, both in the frequency and time domain, improves the tracking of the test signal by 10-20% and allows an accuracy of more than 90% to be gained using the best fit measure in the case of reproduction of white noise signals. Research limitations/implications: It is possible to consider more advanced model-based methods for performing off-line error correction. These methods can be used if an accuracy close to 100% is expected. Practical implications: The result of the investigations is the algorithm implemented in the LabView software to automatically perform the correction of the test signal before the test. Originality/value: The paper proposes a modern approach towards the validation process by applying a simulation environment. This ensures the involvement of arbitrary disturbance models to investigate key parameters of the correction method without expensive and time-consuming experimental validation. The developed model can be extended to a model of a shock absorber to simulate full interaction between the servo-hydraulic test rig and the tested product.

20

Advanced model structures applied to system identification of a servohydraulic test rig

Czop P., Wszołek G.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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Vol. 41, nr 1-2

96-103

EN

Purpose: This paper deals with a method for the parametric system identification of a nonlinear system to obtain its parametric representation using a linear transfer function. Such representation is applicable in off-line profile correction methods minimizing the error between a reference input signal and a signal performed by the test rig. In turn, a test signal can be perfectly tracked by a servo-hydraulic test rig. This is the requirement in massive production where short test sequences are repeated to validate the products. Design/methodology/approach: A numerical and experimental case studies are presented in the paper. The numerical study presents a system identification process of a nonlinear system consisting of a linear transfer function and a nonlinear output component, being a static function. The experimental study presents a system identification process of a nonlinear system which is a servo-hydraulic test rig. The simulation data has been used to illustrate the feasibility study of the proposed approach, while the experimental data have been used to validate advanced model structures under operational conditions. Findings: The advanced model structures confirmed their better performance by means of the model fit in the time domain. Research limitations/implications: The method applies to analysis of such mechanical and hydraulic systems for which measurements are corrupted by residual harmonic disturbances resulting from system nonlinearities. Practical implications: The advanced model structures are intended to be used as inverse models in off-line signal profile correction. Originality/value: The results state the foundation for the off-line parametric error cancellation method which aims in improving tracking of load signals on servo-hydraulic test rigs.