Pub Date : 2022-07-25DOI: 10.3390/vibration5030026
K. Van Nimmen, B. Vanwanseele, Peter Van den Broeck
In view of in-field applications, this paper introduces a methodology that uses the registered body motion to reconstruct the vertical dynamic running load. The principle of the reconstruction methodology is to use the time-variant pacing rate that is identified from the body motion together with a generalized single-step load model available in the literature. The methodology is reasonably robust against measurement noise. The performance of the methodology is evaluated by application to an experimental dataset where the running load and the body motion were registered simultaneously. The results show that a very good fit is found with the measured forces, with coefficients of determination of 95% in the time domain and 98% for the amplitude spectrum. Considering a 90% confidence interval, the fundamental harmonic is shown to be reconstructed with a maximum error of 12%. With nearly 90% of the energy concentrated around the fundamental harmonic, this harmonic is the dominant component of the running load. Due to the large inter-person variability in the single-step load pattern, a generalized single-step load model does not arrive at a good fit for the higher harmonics: the reproduction errors easily exceed 50% for a 90% confidence interval. Finally, the methodology is applied to reproduce the dynamic running load induced during full-scale tests on a flexible footbridge. The tests are designed such that the structural response is governed by the (near-)resonant contribution of the fundamental harmonic of the running load. The results show that even when a 12% uncertainty bound is taken into account, the structural response is significantly over-estimated by the numerical simulations (up to 50%). These results suggest a non-negligible impact of other phenomena, such as human–structure interaction, that are not accounted for in current load models.
{"title":"Reconstruction of the Vertical Dynamic Running Load from the Registered Body Motion","authors":"K. Van Nimmen, B. Vanwanseele, Peter Van den Broeck","doi":"10.3390/vibration5030026","DOIUrl":"https://doi.org/10.3390/vibration5030026","url":null,"abstract":"In view of in-field applications, this paper introduces a methodology that uses the registered body motion to reconstruct the vertical dynamic running load. The principle of the reconstruction methodology is to use the time-variant pacing rate that is identified from the body motion together with a generalized single-step load model available in the literature. The methodology is reasonably robust against measurement noise. The performance of the methodology is evaluated by application to an experimental dataset where the running load and the body motion were registered simultaneously. The results show that a very good fit is found with the measured forces, with coefficients of determination of 95% in the time domain and 98% for the amplitude spectrum. Considering a 90% confidence interval, the fundamental harmonic is shown to be reconstructed with a maximum error of 12%. With nearly 90% of the energy concentrated around the fundamental harmonic, this harmonic is the dominant component of the running load. Due to the large inter-person variability in the single-step load pattern, a generalized single-step load model does not arrive at a good fit for the higher harmonics: the reproduction errors easily exceed 50% for a 90% confidence interval. Finally, the methodology is applied to reproduce the dynamic running load induced during full-scale tests on a flexible footbridge. The tests are designed such that the structural response is governed by the (near-)resonant contribution of the fundamental harmonic of the running load. The results show that even when a 12% uncertainty bound is taken into account, the structural response is significantly over-estimated by the numerical simulations (up to 50%). These results suggest a non-negligible impact of other phenomena, such as human–structure interaction, that are not accounted for in current load models.","PeriodicalId":75301,"journal":{"name":"Vibration","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42335567","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-07-21DOI: 10.3390/vibration5030025
O. Larivière, D. Chadefaux, C. Sauret, Layla Kordulas, P. Thoreux
Manual wheelchair (MWC) users are exposed to whole-body vibrations (WBVs) during propulsion. Vibrations enter the MWC structure through the wheels’ hub, propagate according to the MWC dynamical response, and finally reach the user’s body by the footrest, seat, backrest, and handrims. Such exposure is likely to be detrimental to the user’s health and a source of discomfort and fatigue which could, in daily life, impact users’ social participation and performance in sports. To reduce WBV exposure, a solution relies on MWC dynamical response modelling and simulation, where the model could indeed be used to identify parameters that improve the MWC dynamic. As a result, it is necessary to first assess the MWC dynamical response. In this approach, experimental modal analyses were conducted on eleven MWCs, including daily and sport MWCs (tennis, basketball, and racing). Through this procedure, modal properties (i.e., modal frequencies, damping parameters, and modal shapes) were identified for each MWC part. The results pointed out that each MWC investigated, even within the same group, revealed specific vibration properties, underlining the difficulty of developing a single vibration-reducing system for all MWCs. Nevertheless, several common dynamical properties related to MWC comfort and design were identified.
{"title":"Modal Characterization of Manual Wheelchairs","authors":"O. Larivière, D. Chadefaux, C. Sauret, Layla Kordulas, P. Thoreux","doi":"10.3390/vibration5030025","DOIUrl":"https://doi.org/10.3390/vibration5030025","url":null,"abstract":"Manual wheelchair (MWC) users are exposed to whole-body vibrations (WBVs) during propulsion. Vibrations enter the MWC structure through the wheels’ hub, propagate according to the MWC dynamical response, and finally reach the user’s body by the footrest, seat, backrest, and handrims. Such exposure is likely to be detrimental to the user’s health and a source of discomfort and fatigue which could, in daily life, impact users’ social participation and performance in sports. To reduce WBV exposure, a solution relies on MWC dynamical response modelling and simulation, where the model could indeed be used to identify parameters that improve the MWC dynamic. As a result, it is necessary to first assess the MWC dynamical response. In this approach, experimental modal analyses were conducted on eleven MWCs, including daily and sport MWCs (tennis, basketball, and racing). Through this procedure, modal properties (i.e., modal frequencies, damping parameters, and modal shapes) were identified for each MWC part. The results pointed out that each MWC investigated, even within the same group, revealed specific vibration properties, underlining the difficulty of developing a single vibration-reducing system for all MWCs. Nevertheless, several common dynamical properties related to MWC comfort and design were identified.","PeriodicalId":75301,"journal":{"name":"Vibration","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-07-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42835165","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-07-16DOI: 10.3390/vibration5030024
M. Kucher, M. Dannemann, R. Böhm, N. Modler
Structures made of the thermoplastic polymer polyether ether ketone (PEEK) are widely used in dynamically-loaded applications due to their high-temperature resistance and high mechanical properties. To design these dynamic applications, in addition to the well-known stiffness and strength properties the vibration-damping properties at the given frequencies are required. Depending on the application, frequencies from a few hertz to the ultrasonic range are of interest here. To characterize the frequency-dependent behavior, an experimental approach was chosen and applied to a sample polymer PEEK. The test setup consists of a piezoelectrically driven base excitation of the polymeric specimen and the non-contact measurement of the velocity as well as the surface temperature. The beam’s bending vibrations were analyzed by means of the Timoshenko theory to determine the polymer’s storage modulus. The mechanical loss factor was calculated using the half-power bandwidth method. For PEEK and a considered frequency range of 1 kHz to 16 kHz, a storage modulus between 3.9 GPa and 4.2 GPa and a loss factor between 9 × 10−3 and 17 × 10−3 were determined. For the used experimental parameters, the resulting mechanical properties were not essentially influenced by the amplitude of excitation, the duration of excitation, or thermal degrad.ation due to self-heating, but rather slightly by the clamping force within the fixation area.
{"title":"An Experimental Approach for the Determination of the Mechanical Properties of Base-Excited Polymeric Specimens at Higher Frequency Modes","authors":"M. Kucher, M. Dannemann, R. Böhm, N. Modler","doi":"10.3390/vibration5030024","DOIUrl":"https://doi.org/10.3390/vibration5030024","url":null,"abstract":"Structures made of the thermoplastic polymer polyether ether ketone (PEEK) are widely used in dynamically-loaded applications due to their high-temperature resistance and high mechanical properties. To design these dynamic applications, in addition to the well-known stiffness and strength properties the vibration-damping properties at the given frequencies are required. Depending on the application, frequencies from a few hertz to the ultrasonic range are of interest here. To characterize the frequency-dependent behavior, an experimental approach was chosen and applied to a sample polymer PEEK. The test setup consists of a piezoelectrically driven base excitation of the polymeric specimen and the non-contact measurement of the velocity as well as the surface temperature. The beam’s bending vibrations were analyzed by means of the Timoshenko theory to determine the polymer’s storage modulus. The mechanical loss factor was calculated using the half-power bandwidth method. For PEEK and a considered frequency range of 1 kHz to 16 kHz, a storage modulus between 3.9 GPa and 4.2 GPa and a loss factor between 9 × 10−3 and 17 × 10−3 were determined. For the used experimental parameters, the resulting mechanical properties were not essentially influenced by the amplitude of excitation, the duration of excitation, or thermal degrad.ation due to self-heating, but rather slightly by the clamping force within the fixation area.","PeriodicalId":75301,"journal":{"name":"Vibration","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45203001","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-07-02DOI: 10.3390/vibration5030023
H. Khorrami, R. Sedaghati, S. Rakheja
The crack-induced changes in the vertical transient response of a rotating shaft–disc system, Jeffcott rotor, are investigated for transverse crack detection. The crack is considered as a breathing crack. A novel breathing function is proposed, in which the partially open–closed crack breathing behavior is interpolated between the fully open and closed crack behaviors. The breathing crack excites superharmonic response components of the transient as well as the subharmonic components. A Hilbert–Huang transform based on an improved empirical mode decomposition algorithm is subsequently formulated to evaluate the time–frequency representation of the vertical transient response of the rotor to detect the crack. The results show that the proposed breathing function can effectively reduce the computational effort without sacrificing the accuracy of the crack breathing behavior in the presence of small cracks. It is shown that time–frequency representations based on an improved empirical mode decomposition algorithm can lead to the detection of smaller cracks compared with those based on the empirical mode decomposition algorithm.
{"title":"Vertical Transient Response Analysis of a Cracked Jeffcott Rotor Based on Improved Empirical Mode Decomposition","authors":"H. Khorrami, R. Sedaghati, S. Rakheja","doi":"10.3390/vibration5030023","DOIUrl":"https://doi.org/10.3390/vibration5030023","url":null,"abstract":"The crack-induced changes in the vertical transient response of a rotating shaft–disc system, Jeffcott rotor, are investigated for transverse crack detection. The crack is considered as a breathing crack. A novel breathing function is proposed, in which the partially open–closed crack breathing behavior is interpolated between the fully open and closed crack behaviors. The breathing crack excites superharmonic response components of the transient as well as the subharmonic components. A Hilbert–Huang transform based on an improved empirical mode decomposition algorithm is subsequently formulated to evaluate the time–frequency representation of the vertical transient response of the rotor to detect the crack. The results show that the proposed breathing function can effectively reduce the computational effort without sacrificing the accuracy of the crack breathing behavior in the presence of small cracks. It is shown that time–frequency representations based on an improved empirical mode decomposition algorithm can lead to the detection of smaller cracks compared with those based on the empirical mode decomposition algorithm.","PeriodicalId":75301,"journal":{"name":"Vibration","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47192346","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-06-22DOI: 10.3390/vibration5030022
M. Yuan, Youzuo Jin, Kefu Liu, A. Sadhu
This paper investigates the optimization of a non-traditional vibration absorber for simultaneous vibration suppression and energy harvesting. Unlike a traditional vibration absorber, the non-traditional vibration absorber has its damper connected between the absorber mass and the base. An electromagnetic energy harvester is used as a tunable absorber damper. This non-traditional vibration absorber is attached to a primary system that is subjected to random base excitation. An analytical study is conducted by assuming that the base excitation is white noise. In terms of vibration suppression, the objective of the optimization is to minimize the power dissipated by the primary damper and maximize the power dissipated by the absorber damper. It is found that when the primary system is undamped, the power dissipated by the absorber damper remains a constant that is related to the mass ratio. The higher the mass ratio, the higher the power dissipated. When the primary system is damped, the minimization of the power dissipated by the primary damping is equivalent to the maximization of the power dissipated by the absorber damper. The existence of the optimum solutions depends on both the mass ratio and the primary damping ratio. In terms of energy harvesting, the objective of optimization is to maximize the power harvested by the load resistor. It is found that for a given mass ratio and primary damping ratio, the optimum frequency tuning ratio required to maximize vibration suppression is slightly higher than that required to maximize the harvested power. The trade-off issue between vibration suppression and energy harvesting is investigated. An apparatus is developed to allow frequency tuning and damping tuning. Both the numerical simulation and experimental study with band-limited white noise validate the general trends revealed in the analytical study.
{"title":"Optimization of a Non-Traditional Vibration Absorber for Vibration Suppression and Energy Harvesting","authors":"M. Yuan, Youzuo Jin, Kefu Liu, A. Sadhu","doi":"10.3390/vibration5030022","DOIUrl":"https://doi.org/10.3390/vibration5030022","url":null,"abstract":"This paper investigates the optimization of a non-traditional vibration absorber for simultaneous vibration suppression and energy harvesting. Unlike a traditional vibration absorber, the non-traditional vibration absorber has its damper connected between the absorber mass and the base. An electromagnetic energy harvester is used as a tunable absorber damper. This non-traditional vibration absorber is attached to a primary system that is subjected to random base excitation. An analytical study is conducted by assuming that the base excitation is white noise. In terms of vibration suppression, the objective of the optimization is to minimize the power dissipated by the primary damper and maximize the power dissipated by the absorber damper. It is found that when the primary system is undamped, the power dissipated by the absorber damper remains a constant that is related to the mass ratio. The higher the mass ratio, the higher the power dissipated. When the primary system is damped, the minimization of the power dissipated by the primary damping is equivalent to the maximization of the power dissipated by the absorber damper. The existence of the optimum solutions depends on both the mass ratio and the primary damping ratio. In terms of energy harvesting, the objective of optimization is to maximize the power harvested by the load resistor. It is found that for a given mass ratio and primary damping ratio, the optimum frequency tuning ratio required to maximize vibration suppression is slightly higher than that required to maximize the harvested power. The trade-off issue between vibration suppression and energy harvesting is investigated. An apparatus is developed to allow frequency tuning and damping tuning. Both the numerical simulation and experimental study with band-limited white noise validate the general trends revealed in the analytical study.","PeriodicalId":75301,"journal":{"name":"Vibration","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-06-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45843289","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-06-16DOI: 10.3390/vibration5020021
Lili Bykerk, Jaime Valls Miro
Leaks in Water Distribution Networks (WDNs) account for a large proportion of Non-Revenue Water (NRW) for utilities worldwide. Typically, a leak is only confirmed once water surfaces, allowing the leak to be traced; however, a high percentage of leaks may never surface, incurring large water losses and costs for utilities. Active Leak Detection (ALD) methods can be used to detect hidden leaks; however, the success of such methods is highly dependent on the available detection instrumentation and the experience of the operator. To aid in the detection of both hidden and surfacing leaks, deployment of vibro-acoustic sensors is being increasingly explored by water utilities for temporary structural health monitoring. In this paper, data were collected and curated from a range of temporary Lift and Shift (L&S) vibro-acoustic sensor deployments across suburban Sydney. Time-frequency and frequency-domain features were generated to assess the performance and suitability of two state-of-the-art binary classification models for water leak detection. The results drawn from the extensive field data sets are shown to provide reliable leak detection outcomes, with accuracies of at least 97% and low false positive rates. Through the use of such a reliable leak detection system, utilities can streamline their leak detection and repair processes, effectively mitigating NRW and reducing customer disruptions.
{"title":"Detection of Water Leaks in Suburban Distribution Mains with Lift and Shift Vibro-Acoustic Sensors","authors":"Lili Bykerk, Jaime Valls Miro","doi":"10.3390/vibration5020021","DOIUrl":"https://doi.org/10.3390/vibration5020021","url":null,"abstract":"Leaks in Water Distribution Networks (WDNs) account for a large proportion of Non-Revenue Water (NRW) for utilities worldwide. Typically, a leak is only confirmed once water surfaces, allowing the leak to be traced; however, a high percentage of leaks may never surface, incurring large water losses and costs for utilities. Active Leak Detection (ALD) methods can be used to detect hidden leaks; however, the success of such methods is highly dependent on the available detection instrumentation and the experience of the operator. To aid in the detection of both hidden and surfacing leaks, deployment of vibro-acoustic sensors is being increasingly explored by water utilities for temporary structural health monitoring. In this paper, data were collected and curated from a range of temporary Lift and Shift (L&S) vibro-acoustic sensor deployments across suburban Sydney. Time-frequency and frequency-domain features were generated to assess the performance and suitability of two state-of-the-art binary classification models for water leak detection. The results drawn from the extensive field data sets are shown to provide reliable leak detection outcomes, with accuracies of at least 97% and low false positive rates. Through the use of such a reliable leak detection system, utilities can streamline their leak detection and repair processes, effectively mitigating NRW and reducing customer disruptions.","PeriodicalId":75301,"journal":{"name":"Vibration","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46433460","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-06-10DOI: 10.3390/vibration5020020
J. Sadet, F. Massa, T. Tison, E. Talbi, I. Turpin
Despite numerous works over the past two decades, friction-induced vibrations, especially braking noises, are a major issue for transportation manufacturers as well as for the scientific community. To study these fugitive phenomena, the engineers need numerical methods to efficiently predict the mode coupling instabilities in a multiparametric context. The objective of this paper is to approximate the unstable frequencies and the associated damping rates extracted from a complex eigenvalue analysis under variability. To achieve this, a deep Gaussian process is considered to fit the non-linear and non-stationary evolutions of the real and imaginary parts of complex eigenvalues. The current challenge is to build an efficient surrogate modelling, considering a small training set. A discussion about the sample distribution density effect, the training set size and the kernel function choice is proposed. The results are compared to those of a Gaussian process and a deep neural network. A focus is made on several deceptive predictions of surrogate models, although the better settings were well chosen in theory. Finally, the deep Gaussian process is investigated in a multiparametric analysis to identify the best number of hidden layers and neurons, allowing a precise approximation of the behaviours of complex eigensolutions.
{"title":"Deep Gaussian Process for the Approximation of a Quadratic Eigenvalue Problem: Application to Friction-Induced Vibration","authors":"J. Sadet, F. Massa, T. Tison, E. Talbi, I. Turpin","doi":"10.3390/vibration5020020","DOIUrl":"https://doi.org/10.3390/vibration5020020","url":null,"abstract":"Despite numerous works over the past two decades, friction-induced vibrations, especially braking noises, are a major issue for transportation manufacturers as well as for the scientific community. To study these fugitive phenomena, the engineers need numerical methods to efficiently predict the mode coupling instabilities in a multiparametric context. The objective of this paper is to approximate the unstable frequencies and the associated damping rates extracted from a complex eigenvalue analysis under variability. To achieve this, a deep Gaussian process is considered to fit the non-linear and non-stationary evolutions of the real and imaginary parts of complex eigenvalues. The current challenge is to build an efficient surrogate modelling, considering a small training set. A discussion about the sample distribution density effect, the training set size and the kernel function choice is proposed. The results are compared to those of a Gaussian process and a deep neural network. A focus is made on several deceptive predictions of surrogate models, although the better settings were well chosen in theory. Finally, the deep Gaussian process is investigated in a multiparametric analysis to identify the best number of hidden layers and neurons, allowing a precise approximation of the behaviours of complex eigensolutions.","PeriodicalId":75301,"journal":{"name":"Vibration","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41865521","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-05-24DOI: 10.3390/vibration5020019
Maryam El Moueddeb, F. Louf, P. Boucard, Franck Dadié, G. Saussine, Danilo Sorrentino
With railway interoperability, new trains are allowed to move on the French railway network. These trains may present different designs from standard trains. This work aims to complete the current approach for vehicle admission on the railway network, which is defined in technical baselines. Historically, computation rules for traffic conditions are based on simplified analytical works, which are considerably qualitative. They have evolved through feedback and experimental campaigns to comply with the track structure evolution. An efficient methodology based on numerical simulation is needed to evaluate railway vehicle admission to answer this issue. A perspective to update these computation rules is to evaluate the structural fatigue in the rail. That is to say, fatigue is caused by bending and shear stresses. The complexity of the railway system has led to an investigation at first of the vertical response of the railway track and quantifying its contribution to the rail’s stress response. In that sense, this paper investigates the vertical track response to a moving railway vehicle at low frequencies. For this purpose, a lightweight numerical model for the track, a multi-body model for the vehicle, and a random vertical track irregularity are proposed. More explicitly, the track model consists of a two-layer discrete support model in which the rail is considered as a beam and sleepers are point masses. The rail pads and ballast layer are modelled as spring/damper couples. Numerical results show a negligible effect of track inertia forces due to high track stiffness and damping. Nevertheless, this assumption is valid for normal rail stresses but not for ballast loading, especially in the case of sleeper voids or unsupported sleepers. Hence, the prediction of the mechanical stress state in the rail for fatigue issues is achieved through a static track model where the equivalent loading is obtained from a dynamic study of a simplified vehicle model. A statistical analysis shows that the variability of the vertical track irregularity does not influence the output variabilities like the maximum in time and space of the normal and shear stress.
{"title":"An Efficient Numerical Model to Predict the Mechanical Response of a Railway Track in the Low-Frequency Range","authors":"Maryam El Moueddeb, F. Louf, P. Boucard, Franck Dadié, G. Saussine, Danilo Sorrentino","doi":"10.3390/vibration5020019","DOIUrl":"https://doi.org/10.3390/vibration5020019","url":null,"abstract":"With railway interoperability, new trains are allowed to move on the French railway network. These trains may present different designs from standard trains. This work aims to complete the current approach for vehicle admission on the railway network, which is defined in technical baselines. Historically, computation rules for traffic conditions are based on simplified analytical works, which are considerably qualitative. They have evolved through feedback and experimental campaigns to comply with the track structure evolution. An efficient methodology based on numerical simulation is needed to evaluate railway vehicle admission to answer this issue. A perspective to update these computation rules is to evaluate the structural fatigue in the rail. That is to say, fatigue is caused by bending and shear stresses. The complexity of the railway system has led to an investigation at first of the vertical response of the railway track and quantifying its contribution to the rail’s stress response. In that sense, this paper investigates the vertical track response to a moving railway vehicle at low frequencies. For this purpose, a lightweight numerical model for the track, a multi-body model for the vehicle, and a random vertical track irregularity are proposed. More explicitly, the track model consists of a two-layer discrete support model in which the rail is considered as a beam and sleepers are point masses. The rail pads and ballast layer are modelled as spring/damper couples. Numerical results show a negligible effect of track inertia forces due to high track stiffness and damping. Nevertheless, this assumption is valid for normal rail stresses but not for ballast loading, especially in the case of sleeper voids or unsupported sleepers. Hence, the prediction of the mechanical stress state in the rail for fatigue issues is achieved through a static track model where the equivalent loading is obtained from a dynamic study of a simplified vehicle model. A statistical analysis shows that the variability of the vertical track irregularity does not influence the output variabilities like the maximum in time and space of the normal and shear stress.","PeriodicalId":75301,"journal":{"name":"Vibration","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44135567","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-05-16DOI: 10.3390/vibration5020018
K. Goggins, Elizabeth A. Kelly, Taryn J. Thompson, T. Eger
Adopting non-neutral sitting postures while exposed to whole-body vibration (WBV) can put heavy equipment operators at an increased risk for lower back pain and may cause damage to the spinal tissue. A laboratory experiment involving 11 participants (5 females, 6 males) completing four 45-min test sessions incorporating different seated conditions (vibration versus no vibration, and rotation versus no rotation) was used to assess seat-to-head transmissibility (STHT) and self-reported discomfort while in four rotated neck and trunk postures. The vibration exposure profile was a constant vertical sinusoidal signal with a frequency of 3 Hz and 0.7 m/s2 acceleration. Vibration measured at the head was greater than at the seat under all conditions, with a statistically significant effect of time (F1,10 = 101.73, p < 0.001, Eta2 = 0.910) and posture (F3,8 = 5.64, p = 0.023, Eta2 = 0.679). Mean self-reported discomfort ratings revealed increased participant discomfort in rotated neck and trunk positions in both vibration and non-vibration conditions. Increasing time also had a significant (F(1,10) = 15.53, p = 0.003) impact on higher rates of participant discomfort. Overall, it was found that increasing the degree of rotated neck and trunk position from neutral amplified the STHT and self-reported discomfort.
{"title":"Examining the Impact of Rotated Neck and Trunk Postures on Vertical Seat-to-Head Vibration Transmissibility and Self-Reported Discomfort","authors":"K. Goggins, Elizabeth A. Kelly, Taryn J. Thompson, T. Eger","doi":"10.3390/vibration5020018","DOIUrl":"https://doi.org/10.3390/vibration5020018","url":null,"abstract":"Adopting non-neutral sitting postures while exposed to whole-body vibration (WBV) can put heavy equipment operators at an increased risk for lower back pain and may cause damage to the spinal tissue. A laboratory experiment involving 11 participants (5 females, 6 males) completing four 45-min test sessions incorporating different seated conditions (vibration versus no vibration, and rotation versus no rotation) was used to assess seat-to-head transmissibility (STHT) and self-reported discomfort while in four rotated neck and trunk postures. The vibration exposure profile was a constant vertical sinusoidal signal with a frequency of 3 Hz and 0.7 m/s2 acceleration. Vibration measured at the head was greater than at the seat under all conditions, with a statistically significant effect of time (F1,10 = 101.73, p < 0.001, Eta2 = 0.910) and posture (F3,8 = 5.64, p = 0.023, Eta2 = 0.679). Mean self-reported discomfort ratings revealed increased participant discomfort in rotated neck and trunk positions in both vibration and non-vibration conditions. Increasing time also had a significant (F(1,10) = 15.53, p = 0.003) impact on higher rates of participant discomfort. Overall, it was found that increasing the degree of rotated neck and trunk position from neutral amplified the STHT and self-reported discomfort.","PeriodicalId":75301,"journal":{"name":"Vibration","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-05-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46555900","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-05-03DOI: 10.3390/vibration5020017
M. Furinghetti
The research on traditional and innovative seismic isolation techniques has grown significantly in recent years, thanks to both experimental and numerical campaigns. As a consequence, practitioners have also started to apply such techniques in real applications, and nowadays, seismic isolation is widespread in regions characterized by a high level of seismic hazard. The present work aims at providing practitioners with very simple procedures for the first design of the isolation devices of a building, according to the most common typologies of isolators: Rubber Bearings, Lead Rubber Bearings and Curved Surface Sliders. Such Fast Design Procedures are based on simplified approaches, and the mechanical properties of the implemented devices can be obtained by assuming a performance point of the overall structural system, namely effective period and equivalent viscous damping. Furthermore, some important parameters are defined, according to the outcomes of a statistical analysis of the test database of the EUCENTRE Foundation in Italy. Finally, results of a validation study have been provided by analyzing a case-study structure through a Multi Degree of Freedom oscillator and a full 3D Finite Element model.
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