Dynamic Modal Analysis Research Articles

Effect of vehicular vibrations on L-4 lumbar vertebrae – A finite element study

Lower Back Pain (LBP) is a global health issue, with increasing prevalence, partly attributed to vehicular vibrations experienced by motorcyclists. The L4 lumbar vertebra is responsible for greater mobility and flexibility of the body, but also is the most crucial body element affected by vehicular vibrations. Anthropometric properties, types of speed humps, and vehicle types are the critical variables that impact bone health during riding, need to be studied. To understand the potential zones of injury, computational simulation can be performed under the influence of vehicle vibrations while crossing different types of speed humps at varying speeds. In the present study, finite element method (FEM) is used to evaluate stress and deformation in the bone. The L4 cortical bone is modelled by considering the CT-Scan data and assumed to be homogeneous and isotropic material. Vibration data is collected using two vehicle types (Type I and Type II) on four different humps (Trapezoidal, Bitumen Semi-circular, Rubber Semi-circular, and Rumble strip). The bone's dynamic behavior is studied using FEM simulation, which involved static structural, modal and transient dynamic analyses. The findings from static analysis indicate that the most concentrated stress is located in the lower pedicle region and is an expected commonplace for injuries because of vibrations. In transient dynamic analysis, Type I vehicle showed a 25 % higher stress than Type II.

Wind turbine foundation ring fatigue reliability analysis under wind-load using SCADA system

Under the action of wind load, the foundation ring of the fan will generate stress concentration and alternating stress, leading to fatigue failure. Based on the average wind speed obtained from the supervisory control and data acquisition (SCADA) system, the orthogonal expansion method of random pulsating wind field and the number theory point selection method are used to calculate and simulate the corresponding pulsating wind speed time series, and then calculate the wind speed time series and wind load time series. Based on the ABAQUS finite element software, a model of a 5 MW wind turbine is established. The modal analysis is used to obtain the modal vibration pattern and the intrinsic frequency to verify the reasonableness of the structural modeling. Subsequently, the wind load time series is applied to the wind turbine model to obtain the stress time series using instantaneous modal dynamic analysis (Modal dynamics). The stress time series at the location of maximum stress concentration in the foundation ring is extracted, and the stress time series with the same stress amplitude is obtained through conversion, which has Wiener characteristics. After obtaining the stress amplitude using the rainflow counting method, the fatigue reliability is calculated based on the structural fatigue reliability analysis method considering the threshold crossing duration of the random process. This research holds reference significance for the calculation of fatigue reliability under approximate working conditions.

Dynamic Failure Mode Analysis for a Transmission Tower-Line System Induced by Strong Winds

Dynamic Failure Mode Analysis for a Transmission Tower-Line System Induced by Strong Winds

Fatigue damage assessment of a large rail-cum-road steel truss-arch bridge using structural health monitoring dynamic data

Structural health monitoring (SHM) system provides valuable information for the fatigue assessment of existing rail-cum-road bridges. This paper aims to develop an effective fatigue assessment approach for the rail-cum-road bridge, Jiujiang Yangtze River Bridge, by utilising the SHM data, focusing on dynamic modal analysis, finite element model updating and fatigue assessment. First, the traffic load spectrum and modal characteristics of the bridge are investigated from the SHM data. A three-dimensional finite element model is constructed and then updated by using the measured modal data through the proposed regularised model updating method. Then, the updated numerical model is verified with the measured dynamic response data, which can be utilised for calculating stress response at critical structural components of the rail-cum-road bridge. Finally, an improved Corten-Dolan’s model is proposed to analyse the fatigue damage and structural reliability of the critical structural components of the bridge, taking into account the combined effects of train and highway vehicle loads. The results demonstrate that the proposed fatigue assessment method provides more reliable results for the rail-cum-road bridge by considering the combined effect of multi-level traffic loads and the non-linear fatigue damage accumulation. It is concluded that the short H-shaped suspender is identified as the most vulnerable structural member of the rail-cum-road bridge, and the remaining fatigue service life of the typical components of the bridge should meet the design requirement.

Cognitive activity significantly affects the dynamic cerebral autoregulation, but not the dynamic vasoreactivity, in healthy adults.

Neurovascular coupling (NVC) is an important mechanism for the regulation of cerebral perfusion during intensive cognitive activity. Thus, it should be examined in terms of its effects on the regulation dynamics of cerebral perfusion and its possible alterations during cognitive impairment. The dynamic dependence of continuous changes in cerebral blood velocity (CBv), which can be measured noninvasively using transcranial Doppler upon fluctuations in arterial blood pressure (ABP) and CO2 tension, using end-tidal CO2 (EtCO2) as a proxy, can be quantified via data-based dynamic modeling to yield insights into two key regulatory mechanisms: the dynamic cerebral autoregulation (dCA) and dynamic vasomotor reactivity (DVR), respectively. Using the Laguerre Expansion Technique (LET), this study extracted such models from data in supine resting vs cognitively active conditions (during attention, fluency, and memory tasks from the Addenbrooke's Cognitive Examination III, ACE-III) to elucidate possible changes in dCA and DVR due to cognitive stimulation of NVC. Healthy volunteers (n = 39) were recruited at the University of Leicester and continuous measurements of CBv, ABP, and EtCO2 were recorded. Modeling analysis of the dynamic ABP-to-CBv and CO2-to-CBv relationships showed significant changes in dCA, but not DVR, under cognitively active conditions compared to resting state. Interpretation of these changes through Principal Dynamic Mode (PDM) analysis is discussed in terms of possible associations between stronger NVC stimulation during cognitive tasks and enhanced sympathetic activation.

The α-generalized implicit method associated with Potra–Pták iteration for solving non-linear dynamic problems

Generally, direct time integration procedures are used for solving the equations of motion in transient analysis of structures with large displacements. In this context, we propose an algorithm that combines the α-Generalized implicit integration method with the Potra–Pták two-step iterative scheme. The free Scilab program develops a computer code for the non-linear dynamic analysis of plane frames with large displacements and rotations. The FEM corotational formulation discretizes the structures considering the Euler-Bernoulli beam theory. The null-length connection element described by the axial, translational and rotational stiffnesses simulate the behavior of the beam-column connection. Jacobi’s method and the Scilab’s spec function determine the natural frequencies. The developed program is used for modal and transient dynamic analyses of frame problems available in the literature. The numerical results show that the Potra-Pták scheme obtains approximate solutions with fewer cumulative iterations until convergence and shorter processing time compared to the standard Newton-Raphson scheme. Further-more, the results show that the type of beam-column connection affects the vibratory behavior of the structure as well as the values of its natural frequencies.

Response spectrum and modal dynamic analyses of gravity dams using ground motion accelerations modified to account for hydrodynamic effects

This research proposes simplified methods for response spectrum and modal dynamic analyses of gravity dams using time-history and spectral seismic accelerations modified to directly account for hydrodynamic effects. The developed methods waive the need for specialized fluid-structure interaction software. They also lead to more accurate assessment of coupled structural flexibility and hydrodynamic effects due to each vibration mode than the static correction method commonly used in traditional simplified methods. The methodology utilizes analytical formulations of hydrodynamic pressure or simplified added masses to obtain the contributions of the selected vibration modes to the total seismic response. A hydrodynamic modification factor characterizing the amplification/de-amplification of acceleration seismic demands due to earthquake-induced hydrodynamic effects is also introduced. The application of the proposed methods is illustrated numerically through examples of two typical gravity dam-reservoir systems subjected to four earthquakes. The obtained results are in excellent agreement with the classical reference solutions. Time-history and spectral seismic acceleration demands modified by hydrodynamic effects as well as selected key response indicators, such as relative displacements and stresses within the studied gravity dams, are discussed.

Human–structure interaction effects on lightweight footbridges with tuned mass dampers

The aim of the work is to explore how the interaction between pedestrians and a bridge deck could affect the effectiveness of tuned mass dampers (TMD) in suppressing the vibrations of lightweight footbridges. To this end, a human–structure interaction (HSI) model is built in a modal dynamic analysis framework, and it is applied to a lightweight footbridge subject to a large number of pedestrian arrangements with near-resonant walking frequencies. Compared with the response ignoring HSI, the results show that the interaction between the dynamic response of the pedestrians and the structure can reduce the vibrations in the deck, but they exceed comfort limits based on peak and root mean square (RMS) acceleration criteria. In order to reduce the oscillations to a comfortable level, a TMD located at midspan has been designed following classical optimisation methods that neglect HSI. The efficiency of the damper in resonant conditions is demonstrated in the time and frequency domains, even under a large number of synchronised pedestrians interacting with the structure, suggesting that crowds do not introduce important detuning effects in the TMD.

Finite element method-based study for spinal vibration characteristics of the scoliosis and kyphosis lumbar spine to whole-body vibration under a compressive follower preload

Purpose To analyze the dynamic response of the lumbosacral vertebrae structure of a scoliosis spine and a kyphosis spine under whole-body vibration. Methods Typical Lenke4 (kyphosis) and Lenke3 (scoliosis) spinal columns were used as research objects. A finite element model of the lumbosacral vertebrae segment was established and validated based on CT scanning images. Modal, harmonic response, and transient dynamic analyses were performed on the lumbar-sacral scoliosis model using the finite element software abaqus. Results The first four resonance frequencies of kyphosis spine extracted from modal analysis were 0.86, 1.45, 8.51, and 55.71 Hz. The first four resonance frequencies of scoliosis spine extracted from modal analysis were 0.76, 1.45, 10.51, and 63.82 Hz. The scoliosis spine had the maximum resonance amplitude in the transverse direction, while the kyphosis spine had the maximum resonance amplitude in the anteroposterior direction. The dynamic response in transient analysis exhibited periodic response over time at all levels. Conclusion The scoliosis and kyphosis deformity of the spine significantly complicates the vibration response in the scoliosis and kyphosis areas at the top of the spine. Scoliosis and kyphosis patients are more likely to experience vibrational spinal diseases than healthy people. Besides, applying vertical cyclic loads on a malformed spine may cause further rotation of scoliosis and kyphosis deformities.

Dynamic behavior modelling of the silicone-ethanol actuator based on principal dynamic modes of the Laguerre model

The silicone-ethanol actuator is an emerging artificial muscle gaining attention because of its simple construction/stimulation and high-force generation. Most related researches are focused on structural modification methods, while behavior modeling has received less attention. Although the previous models are highly accurate, they suffer from the lack of ethanol content as an input, highly feedback dependency, and fixed output range. In this research, to address the mentioned concerns, the actuator was made according to the conventional procedure and subjected to stimulation, and displacement/blocked-force recording by special custom hardware. The displacement/blocked-force was not limited to a fix amount in order to evaluate ethanol leakage. To predict displacement/blocked-force, a non-autoregressive model was developed with the applied energy, temperature, and ethanol content as inputs. The Laguerre functions was applied to ensure dynamic matching between input-output. Finally, Principal Dynamic Mode analysis was used to optimize the number of filter banks in the model. The results showed that the proposed model provide a reasonable balance between accuracy, interpretability, and simplicity. Also, we found that the prediction of displacement/blocked-force is mainly influenced by the core-temperature/applied-energy, respectively. The proposed model focuses on the effect of stimulation signal and disregards the structural parameters due to their variety in different applications. By considering the both structural parameters and excitation signal, a more comprehensive model can be developed to predict actuator dynamic behavior.

Equivalent converter method for analyzing complex DC–DC converting systems

AbstractThis paper introduces a new approach for analyzing the dynamics of DC–DC converters. Currently, the primary widely accepted method for examining dynamic processes is the Small Signal Analysis technique. However, when applied to modern complex converters, this method poses additional challenges in formulating and solving systems of differential equations. The method proposed in this paper is based on its application to the analysis of dynamic modes of energy functions—Lagrangians. These functions make it possible to define simple criteria to describe the course of dynamic processes, and in the end define an equivalent (approximating) conventional converter identical to the original one with respect to the course of dynamics. If the magnetic and electrical energies in the Lagrangians of both the converters are equal, the outcome is practically identical transient processes. These findings were confirmed by both theoretical analysis and experimentally modelling the dynamics of the initial converter and an equivalent to it in the Matlab–Simscape program. An additional possibility of using the transfer functions of a conventional boost converter for the theoretical analysis of the converters of much greater orders is also discussed. The authors’ experiments confirm the correctness of their theoretical conclusions.

Validation of numerical results of complex seismic analysis through simple analytics

The paper analyzes the application of the numerical findings of the program, which is becoming increasingly difficult for civil and structural design. Since, as in many other countries, the verification of design using a software model is now required by current Italian codes as well. Given this, the structural engineer must provide a technical report using a licensed software tool, attached to other project documents to get the Seismic Authorization at the local Civil Engineering Department offices. Following a brief explanation of structural analysis methodologies, this study presents a criterion for assessing the applicability of numerical findings obtained using any structural software. Three case studies of this criterion are shown to demonstrate how to check them using simple manual calculations: (i) the normal stress in RC columns subjected to gravity loads; (ii) the periods of vibration, participating masses, and seismic base shear derived from dynamic modal analysis; and (iii) the main parameters characterizing the pushover curves of existing buildings. Finally, this work underlines the significance of confirming the application of numerical results obtained by software in civil and structural design. The offered criteria and scenarios exhibit realistic techniques to ensure accuracy and reliability in structural performance assessment, according to the structural requirements imposed by current codes in Italy and similar countries.

Seismic Vulnerability of Segmental Bridges with Drop-In Span by Pushover Analysis

Insight into the application of pushover analysis to prestressed concrete segmental bridges built in the 1950s–1970s by cantilevering with medium-large span length is provided. Seismic assessment must be carried out considering the whole structural response and, in particular, the task of tall piers, bearings, and drop-in spans with Gerber saddles, which are likely to be subjected to girder pounding and/or unseating. In this paper, the assessment of seismic vulnerability is initially performed by linear modal dynamic analysis; then, the efficiency in assessing the seismic response of different methods of pushover analyses is compared, assuming as a benchmark the results of non-linear time history analysis. The outcomes show that, for the bridge with the drop-in span, criteria for selecting the load pattern considered in pushover analysis, the reliable modeling of the bearings, and tall piers play a dominant role in the assessment of the seismic vulnerability, particularly in longitudinal motion.

Mode transition mechanisms in semi-passive flapping-wing propulsion or energy extraction

To facilitate the smooth transition of operational modes in self-sustaining micro-thrusters, this study focuses on a device employing semi-passive flapping wings. Transient numerical methods are used to analyze the variation of flap energy acquisition and propulsion characteristics with pitching frequency, and the relationship between the dominant vortex structure and the force characteristics is analyzed by using the integral momentum theorem and the dynamic mode decomposition (DMD) method. The results indicate that, under the investigated operational conditions, with an increase in the pitching frequency, distinct wake evolution characteristics were observed. In the energy harvesting operational regime, the wake patterns manifest as 2P + mS, 2S + mS, and mS types. During the transitional phase from energy harvesting to propulsion, the wake patterns shift from 2S + mS to 2S transitional types, eventually leading to the manifestation of a reverse Karman vortex street (2S RBVK). In the propulsion operational regime, the wake patterns consist of a reverse Karman vortex street and asymmetric reverse Karman vortex street phenomena. Simultaneously, it was observed that the transition of flapping-wing performance from energy harvesting to propulsion conditions delays behind the transformation of vortex street structures. This delay is attributed to the necessity for the flapping-wing device to overcome its own resistance before generating a net effective propulsive force. The contributions of unsteady wake to thrust primarily encompass vortex thrust, thrust due to localized fluid acceleration, induced momentum force, and induced pressure force. As the pitching frequency increases, the influence of wake vortices on propulsion also intensifies. The contribution of wake vortices to flapping-wing propulsion is determined by the spatial distribution of Lamb vectors and localized fluid accelerations. The conclusions drawn from the dynamic modal analysis and reconstructed flow field analysis of wake vortices align with the findings of the investigation of wake vortices based on the integral momentum theorem.

Dynamic modal analysis of pristine single-walled carbon nanotubes

Carbon nanotubes (CNTs) exhibit exceptional mechanical properties, making them highly promising for various applications. This study conducts dynamic modal analysis on single-walled carbon nanotubes (SWNTs) to explore their vibrational behavior and natural frequencies. Findings indicate a consistent decrease in natural frequencies with increasing nanotube length under cantilever and bridge boundary conditions, attributed to increased mass requiring more vibrational energy. In contrast, nanotube diameter shows inconsistent effects on natural frequency. Results suggest that SWNT natural frequency is more influenced by length than diameter. The study provides valuable insights for designing devices and structures using SWNTs, proposing short SWNTs for high-frequency resonators and long SWNTs for high-performance applications. Overall, this research enhances our understanding of SWNT dynamic characteristics, offering crucial information for the development of innovative nanoscale technologies.

Thermodynamic property of sandwich cylindrical shell structure with metallic wire mesh: Numerical modeling and experimental analysis

As a new addition to lightweight composite structures, the sandwich cylindrical shell with a metallic wire mesh core has emerged as a promising solution for thermodynamic performance analysis at elevated temperatures. The intricate interwoven cellular formations within the metallic wire mesh pose difficulties for thermo-mechanical modeling and property evaluation. First, the constitutive models employed to characterize hysteresis phenomena were presented, comprising isotropic elasticity, Bergstrom-Boyce model, Ogden hyper-elasticity, and parameter identification through mechanical examinations at varying temperatures. Second, the finite element modeling of cylindrical shell structures was determined for modal and steady-state dynamic analyses. Third, the experimental procedures were carried out, including the preparation of the sandwich cylindrical shell and the dynamic testing platform. The first-order natural frequency of the cylindrical shell structure is close to the resonance frequency of the dynamic test results, with a maximum error of 6.5%, demonstrating the accuracy of the simulation model. When compared to the solid-core cylindrical shell, the average insertion loss of the sandwich cylindrical shell structure within the frequency range of 10–1000 Hz at room temperature is up to 11.09 dB. Furthermore, at elevated temperatures, the average insertion loss of the sandwich cylindrical shell decreases but fluctuates as the temperature changes.

Resolvent and dynamic mode analysis of flow past a square cylinder at subcritical Reynolds numbers

Flow-induced vibration (FIV) of bluff bodies can occur at subcritical Reynolds numbers (i.e., below the Re of the vortex shedding from fixed bodies). To analyze the mechanism of this subcritical FIV phenomenon, resolvent and dynamic mode analyses are introduced in this work. For laminar flow past a square cylinder, both resolvent and dynamic modes are extracted and investigated. The results indicate that the dominant dynamic mode decomposition mode and the leading response mode are similar. Both modes lead to vortex shedding at supercritical Reynolds numbers, and they vanish below Re = 19 along with the dominant forcing mode. In addition, the first and second resolvent gains separate near the characteristic flow frequency and overlap at Re = 19, indicating the disappearance of the first-order resolvent mode. The disappearance of these critical modes indicates the lowest Reynolds number of FIV instability for flow past a square cylinder.

Dynamic Modeling of Helicopter Aerogun System Based on Transfer Matrix Method

The aerogun system is an indispensable automatic shooting weapon on the armed helicopter. The system is a complex mechanical system with large motion and small deformation, in which multiple rigid bodies and flexible bodies are connected in a certain way. In this study, the system dynamics model of the armed helicopter aerogun was established by using the multi-body system transfer matrix method. The finite element model for dynamic analysis of helicopter aerial gun is established, and the modal calculation and dynamic response analysis of key connection parts are carried out. t lays a foundation for adjusting the vibration frequency by changing the state parameters. So as to reduce vibration and improve shooting accuracy.

A dynamic failure mode and effect analysis (FMEA) method for CNC machine tool in service

To solve the problems such as uncertain evaluation information, high dependence on experts, and no consideration of the degradation of machine operating performance to failure risk in the practical application of FMEA in CNC machine tool operation and maintenance, a dynamic failure mode and effect analysis (FMEA) method for CNC machine tool in service is proposed, operation and maintenance data is introduced to the traditional failure risk analysis, which makes semantics criteria and data-driven method are systematically integrated, resulting in better performance of quantitative assessment and risk ranking of dynamic fault risk. Afterward, the fault classification and maintenance strategy of the CNC machine tool based on risk priority number (RPN) is proposed, which provides decision support for efficient operation and maintenance of the CNC machine tool. Finally, a machining center is taken as an example to verify the feasibility and effectiveness of the method.

Development and Validation of a LabVIEW Automated Software System for Displacement and Dynamic Modal Parameters Analysis Purposes

The structural health monitoring (SHM) technique is a highly competent operative process dedicated to improving the resilience of an infrastructure by evaluating its system state. SHM is performed to identify any modification in the dynamic properties of an infrastructure by evaluating the acceleration, natural frequencies, and damping ratios. Apart from the vibrational measurements, SHM is employed to assess the displacement. Consequently, sensors are mounted on the investigated framework aiming to collect frequent readings at regularly spaced time intervals during and after being induced. In this study, a LabVIEW program was developed for vibrational monitoring and system evaluation. In a case study reported herein, it calculates the natural frequencies as well as the damping and displacement parameters of a cantilever steel beam after being subjected to excitation at its free end. For that purpose, a Bridge Diagnostic Inc. (BDI) accelerometer and a displacement transducer were parallelly mounted on the free end of the beam. The developed program was capable of detecting the eigenfrequencies, the damping properties, and the displacements from the acceleration data. The evaluated parameters were estimated with the ARTeMIS modal analysis software for comparison purposes. The reported response confirmed that the proposed system strongly conducted the desired performance as it successfully identified the system state and modal parameters.