László Róbert Hári

57235136500

Publications - 7

Calibration of Two Novel Segmentation Approaches by Synthetic Road Vehicle Vibrations

P. Földesi László Róbert Hári

Publication Name: Tehnicki Vjesnik

Publication Date: 2024-01-01

Volume: 31

Issue: 6

Page Range: 2094-2101

Description:

Simulation of non-stationary random vibrations has motivated Packaging vibration testing for decades. Often, an event-detection algorithm decomposes Road vehicle vibrations when analyzing the recorded series. However, heuristics and subjective justifications are often in the papers, whereby the foremost concern is the validation of the non-stationarity of simulated signals. Furthermore, if a changepoint detection is inherent to the procedure, it is recommended to calibrate the detector. The current paper concerns the Receiver operating characteristics (ROC) of two novel algorithms and provides contextual support by Segment length distributions (SLD).

Open Access: Yes

DOI: 10.17559/TV-20220114115149

Evaluation of a CUSUM-Type Changepoint Detector Applied in the Time-Frequency Domain of Synthetic Road Vehicle Vibrations

P. Földesi László Róbert Hári

Publication Name: Lecture Notes in Mechanical Engineering

Publication Date: 2023-01-01

Volume: Unknown

Issue: Unknown

Page Range: 812-823

Description:

Non-stationary random vibrations gained increasing interest in vibration testing. Often, a changepoint detection procedure handles the decomposition of Road vehicle vibrations (RVV) when analysing the recorded series. Unfortunately, only subjective justifications support the proposed methods, and mainly the validation of the non-stationarity of simulated signals is concerned. Thus, if a detector is inherent to the procedure, it is also recommended to calibrate it. The current paper concerns the Receiver operating characteristics (ROC) of a CUSUM-type algorithm and supplies contextual support by Segment length distributions (SLD).

Open Access: Yes

DOI: 10.1007/978-3-031-15211-5_67

Spectral Non-Stationarity in Road Vehicle Vibrations

László Róbert Hári

Publication Name: Periodica Polytechnica Transportation Engineering

Publication Date: 2023-01-01

Volume: 51

Issue: 1

Page Range: 79-88

Description:

Road-induced vibrations are in the scope of various environmental testing protocols, e.g., for packaging vibration testing (PVT) purposes. This field matures with well-understood methods for analyzing amplitude-type non-stationarity (NS) in road vehicle vibrations (RVV). Albeit frequency-type NS is well known, only suggestions are provided for processing the phenomenon in PVT. Both types of NS can be jointly investigated in the time-frequency domain; thus, the current study initiates the investigation of spectral non-stationarities (SNS) in RVV. Three vibration series were recorded from 118 km traveled distance supplying an empirical insight.

Open Access: Yes

DOI: 10.3311/PPtr.18318

An Approach for Hierarchical Clustering of Road Vehicle Vibration Spectrums

P. Földesi László Róbert Hári

Publication Name: Lecture Notes in Mechanical Engineering

Publication Date: 2023-01-01

Volume: Unknown

Issue: Unknown

Page Range: 799-811

Description:

Research on the non-stationary nature of road vehicle vibrations (RVV) led to advances in simulating such processes. Contemporary methods introduced for the analysis of RVV primarily aimed at partitioning the signal in the time- or time − frequency domain, providing differing segments of a signal. However, a degree of dissimilarity, or conversely similarity, is still challenging to find. Hereunder we argue that in some cases, merely a statement of dissimilarity between neighbouring segments within a signal might be well-enough, though from a broader perspective, the assessment of the similarity of discrete Fourier transforms (DFT) may be the next practical step forward. For this reason, the current paper presents the hierarchical clustering of elements of the short-time Fourier transform (STFT) plane from an RVV measurement; secondly, it introduces a clustering validation metric to arrive at an optimum distance metric and a threshold to use in binary hierarchical clusters.

Open Access: Yes

DOI: 10.1007/978-3-031-15211-5_66

Spectral moment segmentation and spectrogram synthesis for simulation of road vehicle vibrations

László Róbert Hári

Publication Name: Mechanical Systems and Signal Processing

Publication Date: 2022-11-15

Volume: 180

Issue: Unknown

Page Range: Unknown

Description:

Vibration testing procedures relying solely on a Fourier profile can introduce only stationary random vibrations. It is in contrast with the non-stationary and non-Gaussian nature of the Road vehicle vibrations (RVV). The following procedure segments the first four spectral moments of the time–frequency domain of RVV, constructs probability density arrays per frequency bins, and perform simulations according to random segment lengths and -root mean squares, yielding more realistic representations of RVV. The distribution of time- and frequency domain moments and normalized spectral entropies are confronted. The Probability-based spectrogram synthesis (PBSS) offers a data-driven stochastic modelling framework for simulating non-stationary RVV.

Open Access: Yes

DOI: 10.1016/j.ymssp.2022.109408

Segmentation of a road vehicle vibration signal using multiple comparison procedures between paired samples

László Róbert Hári

Publication Name: Tehnicki Vjesnik

Publication Date: 2021-08-01

Volume: 28

Issue: 5

Page Range: 1597-1604

Description:

Segmentation of road vehicle vibration (RVV) signals can occur by the need to analyse or synthesise vibrations obtained in passenger cars or on the stowage of vans, trucks. A general and widely used measure to quantify RVV signals is its description via power spectral density (PSD). From a given PSD a Gaussian signal can be generated in a shaker testing laboratory. However, actual RVVs tend to have a non-Gaussian and nonstationary nature, which can be modelled as a composition of different segments, each with a different length and RMS content. For simulation purposes of nonstationary vibration signals, different approaches have been introduced yet each with its unique signal segmentation approaches. The current paper proposes a signal segmentation method implemented in the time-frequency domain in order to find segments within an RVV signal, where each segment has similarity in-between and is dissimilar to neighbouring segments. For this purpose, multiple comparison tests had been utilised between the Short-time Fourier transforms (STFT) applied on given fractions of an RVV. Different countermeasures had been applied against the Type I. error inflation.

Open Access: Yes

DOI: 10.17559/TV-20200122112551

Multiple hypothesis testing by unpaired samples for indexing changepoints in a road-induced vibration signal

László Róbert Hári

Publication Name: UPB Scientific Bulletin Series D Mechanical Engineering

Publication Date: 2021-01-01

Volume: 83

Issue: 3

Page Range: 17-28

Description:

Several methods have been developed for simulating non-stationary and non-Gaussian processes in packaging vibration testing, encompassing unique methods for the segmentation of road vehicle vibrations. However, only a limited number of those consider spectral characteristics. Thus, the current paper introduces a novel segmentation algorithm conducted in the time-frequency domain. The spectral characteristics obtained by short-time Fourier transform are compared by multiple hypothesis tests to find changepoints in a wheeled vehicle vibration sample. Different post hoc procedures are introduced against the inflating Type I. error.

Open Access: Yes

DOI: DOI not available