The article presents a novel non-linear multivariate and multiscale statistical process monitoring and signal denoising method which combines the strengths of the Kernel Principal Component Analysis (KPCA) non-linear multivariate monitoring approach with the benefits of Ensemble Empirical Mode Decomposition (EEMD) to handle multiscale system dynamics. The proposed method which enables us to cope with complex even severe non-linear systems with a wide dynamic range was named the EEMD-based multiscale KPCA (EEMD-MSKPCA). The method is quite general in nature and could be used in different areas for various tasks even without any really deep understanding of the nature of the system under consideration. Its efficiency was first demonstrated by an illustrative example, after which the applicability for the task of bearing fault detection, diagnosis and signal denosing was tested on simulated as well as actual vibration and acoustic emission (AE) signals measured on purpose-built large-size low-speed bearing test stand. The positive results obtained indicate that the proposed EEMD-MSKPCA method provides a promising tool for tackling non-linear multiscale data which present a convolved picture of many events occupying different regions in the time-frequency plane.
COBISS.SI-ID: 11953179
With a view to detecting incipient failures in large-size low-speed rolling bearings, a new multivariate and multiscale statistical monitoring method was developed. The developed method, which combines the Principal Component Analysis (PCA) and the Ensemble Empirical Mode Decomposition (EEMD) method, was called EEMD-MSPCA. The efficiency of the developed method was verified on a purpose-built laboratory test stand. The fact that the developed method is able to identify local bearing defect of a very small size indicates that the method ensures high-reliability bearing fault detection.
COBISS.SI-ID: 11450395
Due to the increasing number of traffic accidents involving the collisions of vehicles with the emergency-stop-area head walls in tunnels, a comparative numerical analysis in accordance with the EN 1317 standard has been performed in order to assess the quality of the available protective safety barriers. Based on the simulation results, the values of the relevant injury criteria the Acceleration Severity Index (ASI), the Theoretical Head Impact Velocity (THIV) and the Post-Impact Head Deceleration (PHD) were computed for several collision scenarios involving two different passenger vehicles colliding with two different safety barriers in various ways. The results show that due to the geometrical restrictions in the tunnels emergency stop area none of the barriers can provide total protection for the occupants of the vehicle in the event of a collision. The installation of a steel-sheet-tube crash cushion was, however, found to provide the best possible protection within the given limitations. The results of the analysis were the basis for selecting a safety-barrier design for existing tunnel installations and for the proposed changes in regulations governing the geometry of the tunnels emergency stop area.
COBISS.SI-ID: 13216027
Cervical spine ligaments have an important role in providing spinal cord stability and restricting excessive movements. Therefore, it is of great importance to study mechanical properties and model the response of these ligaments. The aim of this study is to characterize ageing effects on failure properties and model damage of three cervical spine ligaments: the anterior and the posterior longitudinal ligament and the ligamentum flavum. A total of 46 samples of human cadaveric ligaments removed within 2448 hours after death have been tested. Uniaxial tension tests along fibre direction were performed in physiological conditions. The results showed that ageing decreased failure properties of all three ligaments (failure load, failure elongation). Furthermore, the reported non-linear response of cervical ligaments has been modelled with a combination of the previously reported hyperelastic and damage model. The model predicted a non-linear response and damage region. Material parameters are in agreement with experimental data, and the quality of agreement is represented with very low RMS error values and the values of coefficient of determination close to 1.
COBISS.SI-ID: 13356827
In this article, the process of deep rolling of the torsion bar for heavy armored vehicles is investigated. Deep rolling is a mechanical process of introducing compressive stresses into near surface regions of the working piece. The main objective of deep rolling of the torsion bar is to increase fatigue strength and life time of the torsion bar. The investigated specimen (quenched and tempered before deep rolling) was deep rolled according to the producer's standard technology procedure. The material used in this study was the TORKA steel, which is a low-alloy steel with high strength and toughness. The material was characterized through a series of monotonic and cyclic tension compression experiments. Parameters used in the process were changed during deep rolling of the specimen and their influence was measured. Residual stresses resulting from the deep rolling process were measured with an X-ray diffraction (XRD) device and evaluated with the use of commercial finite element method software. An isotropic and kinematic hardening material model based on the cyclic characteristics of the material was used in three dimensional simulation of deep rolling. Numerical simulation results agree very well with the results obtained from XRD measurements.
COBISS.SI-ID: 13818651
The vehicle simulator models systems on the vehicle, including suspension, powertrain, braking and steering system. The models are incorporated into a software application with visualization in virtual 3D, which can simulate a wheeled vehicle of various configurations with up to eight wheels in real time. The simulation models also control actuators of a haptic interface to provide motion and force feedback. The system was verified by measurements on real vehicles. The results correspond well, making the system usable for studying different aspects of vehicle performance.
COBISS.SI-ID: 11310875
This paper discusses the flow and fracture properties of high-strength armor steel PROTAC 500. Based on combination of both experimental and numerical studies, material parameters for the Johnson-Cook (JC) strength and fracture model were determined. For that purpose, experimental tensile tests were conducted at elevated temperatures (20/400 °C), various strain rates (0.001/1 s[sup]-1) and triaxialities of axisymmetric notched specimens (0.333/1.431). Some test specimens were photographed during the testing, and by means of image processing, input data for calculation of true stresses and strains up to the point of fracture were extracted. After determination of strength material parameters, tensile axisymmetric tests with different triaxialities were numerically simulated and triaxiality data from the simulations were taken for evaluation of the material parameters of the damage model. Validation study was also performed successfully. The results of this paper will enable numerical prediction of large deformation processes as well as possible fracture occurrence, its development and final size, for structures made of high strength armor steel, PROTAC 500.
COBISS.SI-ID: 13766939
The main goal of this study was an experimental comparison of six different active magnetic regenerators (AMRs) with gadolinium as the magnetocaloric material. The analysis was carried out for three different parallel-plate AMRs (with different porosities and different orientations of the plates in the magnetic field) and three different packed-bed AMRs (filled with spheres, powders and cylinders). Since the operation of an AMR is strongly affected by the operating conditions, the experiments were performed at different mass-flow rates and at different operating frequencies. These were required in order to define the optimum corresponding operating conditions for the analyzed AMRs. As comparative criteria the maximum temperature span, the cooling capacity and the experimentally predicted COP were taken into consideration. The experimental analysis was performed on a new prototype of magnetic refrigerator designed as an experimental device. Its operation is based on the linear movement of a permanent-magnet assembly over a static AMR. The magnet assembly provides a measured magnetic field of about 1.15 T. The results reveal that the geometry of the AMR (the form of the magnetocaloric material) has a crucial impact on the performance of the magnetic refrigerator. The best overall cooling characteristics (temperature span, cooling capacity and COP) were obtained for the parallel-plate AMR with the smallest porosity (25%) and the orientation of the plates parallel to the magnetic field. This particular AMR generated a temperature span of 20 K, which is also the largest, so-far measured and published temperature span with a parallel-plate AMR for a given magnetic field change generated by permanent magnets. With respect to the comparison of the experimentally predicted COP values, the parallel-plate AMRs show higher efficiencies than the packed-bed AMRs.
COBISS.SI-ID: 12647707
Driving with too short of a safety distance is a common problem in road traffic, often with traffic accidents as a consequence. Research has identified a lack of vehicle-mountable devices for alerting the drivers of trailing vehicles about keeping a sufficient safe distance. The principal requirements for such a device were defined. A conceptual study was performed in order to select the components for the integration of the device. Based on the results of this study, a working prototype of a flexible, self-contained device was designed, built and tested. The device is intended to be mounted on the rear of a vehicle. It uses radar as the primary distance sensor, assisted with a GPS receiver for velocity measurement. A Raspberry Pi single-board computer is used for data acquisition and processing. The alerts are shown on an LED-matrix display mounted on the rear of the host vehicle. The device software is written in Python and provides automatic operation without requiring any user intervention. The tests have shown that the device is usable on almost any motor vehicle and performs reliably in simulated and real traffic. The open issues and possibilities for future improvements are presented in the Discussion.
COBISS.SI-ID: 14714139
An interactive wheeled vehicle simulator is described, consisting of a software application for simulating vehicle dynamics and presenting the results in virtual 3D environment, and a haptic interface. The latter consists of a hydraulically actuated active seat and an electrically activated active steering wheel. The system makes it possible to simulate wheeled vehicles of various configurations on arbitrary terrains. The design of the system is presented and the specific considerations are discussed. The system was experimentally verified by measurements on a real off-road vehicle. The kinematic values measured on the real vehicle and those, measured on the haptic interface were compared. The results are discussed and are generally found to correspond well, making the system usable for studying vehicle performance and training its operators.
COBISS.SI-ID: 12122139