Vibration Magnitude Research Articles

The Damage and Impulse Transfer Characteristics of Flexible Steel V-Structures with Large Bend Radii

This paper reports results from an experimental and computational study on the influence of bend radius and internal angle on the damage and impulse transfer characteristics of flexible steel V-structures subjected to localized explosion loading. This issue has bearing on the manufacturing of V-hulls used for Mine Resistant Ambush Protected vehicles used around the world. Global impulse transfer, damage and transient deformation were measured during small-scale explosive detonations on 1:8-scale V-structures. The work found that increasing the bend radius to values that can be used in practical manufacturing generated damage that was less localized than the damage observed in V-structures with tighter bend radii. High-speed imaging was able to measure transient deformation that was maximal in the centre, and lower elastic post-peak vibration magnitudes at high charge masses. The impulse transfer increased as the bend radius increased and the internal V-angle increased. Since V-structures with tighter bend radii exhibit less permanent deformation and higher deformation gradients, they will be more prone to localized ruptures when deployed for blast protection, whereas structures with larger tip radii will need a larger region of the V-structure repaired after a blast event but may be less prone to rupturing when the blast loading is localized.

Design and Implementation of Permanent and Electromagnet Composite Vibration Isolation System Based on Negative Stiffness Theory

In order to decrease the transmission of vibration and achieve the attenuation of the vibration magnitude of an isolated object, a new type of permanent and electromagnet composite vibration isolation system is designed based on negative stiffness theory. Firstly, according to the characteristic analysis, the design of a permanent and electromagnet hybrid actuator is accomplished; secondly, the vibration isolation system model is established, and the active control strategy based on the fuzzy PID algorithm is designed. Finally, a test platform is built to verify the vibration isolation effect. The results indicate that the developed permanent and electromagnet composite vibration isolation system renders the sharp attenuation of external vibration in multiple frequency bands. When the external vibration frequency is within the frequency range of 20 Hz to 100 Hz, the vibration attenuation is greater than 80%; when the external vibration frequency is within the frequency range of 100 Hz to 500 Hz, the vibration attenuation rate is greater than 90%.

Vortex-induced vibrations of a cantilevered blunt plate: POD of TR-PIV measurements and structural modal analysis

Vortex-induced vibrations sustained by immersed bodies may induce early structural fatigue and acoustic noise radiation. The present study consists of an experimental characterization of the vortex shedding and induced vibrations of a cantilevered blunt rectangular aluminium plate of chord to thickness ratio 16.7, immersed in a uniform water flow in the hydrodynamic tunnel of the French Naval Academy Research Institute. Experiences have been conducted at zero degrees incidence for Reynolds numbers Rec (based on chord length) ranging from 2.5×105 to 9.5×105, leading to turbulent wake conditions. The hydrodynamic properties of the wake have been evaluated by statistical analysis, Proper Orthogonal Decomposition (POD) and vortex core identification of Time Resolved Particle Image Velocimetry fields. The structural response of the plate has been examined by laser vibrometry through modal analysis. The fluid–structure interactions have been analysed for three different vibration regimes: out of resonance, lock-off resonance and lock-in resonance with the 1st twisting mode. The features of the first nine POD modes were analysed according to the different vibration regimes to understand the physics proper to the near wake. In the out of resonance regime, the strength of the primary Karman vortices is preferentially controlled by the Strouhal and Reynolds numbers. The thickness based Strouhal number is 0.195. A secondary hydrodynamic excitation source of characteristic Strouhal number 0.227 coexists with the primary Karman vortex shedding mode. At the lock-off resonance, this secondary excitation source is identified as a second Karman vortex shedding mode which is coupled with the natural frequency. A local maximum of vibration magnitude is attained for this regime. The coexistence of these two Karman modes is responsible for the early occurrence of resonance. The lock-in resonance occurs when the primary vortex shedding mode locks with the natural frequency. It is characterized by an enlargement of the wake and by a reinforcement of the primary Karman vortices strength.

Design and experiment of a large-scale space micro-vibration simulator

To solve the problems of difficult vibration sources simulation in the ground test of the on-orbit optical load, a multi-dimensional micro-vibration simulator based on the improved Gough–Stewart platform was designed, which can effectively reproduce the characteristics of wide frequency distribution and small vibration magnitude of space micro-vibration. The analytical formula was derived by using the virtual frequent principle and the Newton–Euler equation for the natural frequency of the system, and the simulator’s configuration was optimized. The structure of legs was designed and optimized according to the optimal configuration parameters. Finally, the micro-vibration simulator was tested, and the test results showed that the output bandwidth of the simulator was 5–300 Hz and the maximum magnitude error was 8%, thus demonstrating the multi-dimensional micro-vibration simulation platform has the characteristics of large frequent bandwidth, high load carrying capacity, and small vibration magnitude.

Effect of Driver Mass Loading on Bone Conduction Transfer in an Implantable Bone Conduction Transducer

This paper focuses on transducers, which are the most important components of bone conduction implants. To improve vibration magnitude, we develop a coil vibration transducer in which the driver mass loading is reduced by about 3.25-fold compared to magnet vibration transducers. We use finite element analysis to derive and implement the maximum Lorentz force and frequency characteristics. We compare the effect of driver mass loading on the vibration magnitude to that of an older transducer. The new transducer vibrates about 4.4-fold more strongly. To compare force magnitude between the two transducers, output force is measured using an artificial mastoid. The force imparted by the new transducer is higher than that of the older transducer only below 1.4 kHz, and tends to be lower at high frequencies. Nevertheless, the improved force in the low-frequency region will improve conductive hearing loss.

Investigations of hand transmitted vibrations and associated health risks in load haul dumper operators based on different components of a work cycle

Load Haul Dumpers (LHDs) are operated in underground mines to transport ore/waste rock under extreme conditions. The operating conditions of the LHDs make the operators susceptible to occupational vibration exposure, including Hand Transmitted Vibrations (HTVs). To date, no research literature is available concerning the evaluation of HTVs based on different components of the LHD work cycle. In the present research study, HTV data were collected by mounting a hand strap on tri-axial accelerometer to the operator's hand in contact with the steering device of the LHDs. Frequency-weighted root mean square (WRMs) acceleration values for all the three measurement axes were collected during different components of the LHD work cycle, namely mucking, loaded travel, unloading, and empty travel. High vibration responses were recorded during the mucking operations, followed by empty hauling. Out of the eight LHDs considered for the study, three LHDs had total daily vibration values A(8) more than that of the stipulated Exposure Action Values (EAV) of 2.5 m/s2, the highest recorded being 2.9 m/s2 in the LHD designated L-6. Health risk assessment was carried out based on EU Directive 2002 and ISO 5349:2001, which showed that operators of three LHDs were at risk of developing health issues such as finger blanching within 12 years of their work life. Strategies to mitigate HTVs should focus on the component of the work cycle and the dominant axis of vibration along with the total daily vibration magnitudes. Operating the LHDs using remote controls during mucking can significantly reduce the total vibration magnitude within daily exposure limits.

ОПРЕДЕЛЕНИЕ РАДИАЛЬНОГО БИЕНИЯ ТОРМОЗНЫХ БАРАБАНОВ МЕТОДОМ ПРОЕКЦИЙ

The literature sources were analyzed, on the basis of the analysis of which the purpose of the study was formulated – the development of a mathematical model for calculating the radial beating of the rim of the brake drum, taking into account the deviations of geometry. The developed mathematical model for calculating the radial runout of the brake drum rim allows determining the maximum value of the protrusions on the inner surface of the metal friction element in order to minimize the magnitude of forced vibrations of transverse and angular displacements of the brake pads of power devices during the interaction of friction pairs. This model is suitable for quan-tifying the machining of the working surface of the brake drum rims with minimizing the resulting eccentricity during long-term operation.

Non-linear dynamic behaviour of spiral bevel gear by considering the torsional shaft stiffness

Spiral bevel gears (SBGs) play a crucial role in developing silent power transmissions for non-parallel shaft applications, offering advantages such as improved motor allocation flexibility and space reduction. While SBGs have been recognized for reducing vibration magnitude in high-speed gearboxes compared to straight bevel gears, complete vibration suppression remains elusive, leading to potential challenges such as teeth contact loss and complex dynamic scenarios. To construct the dynamical model of SBG, time-dependent mesh stiffness and non-smooth nonlinearity caused by backlash is considered. The employed dynamical system is a three-degree-of-freedom model, integrating rotational shaft stiffness, to investigate the dynamic behavior of SBGs. Through the utilization of various analysis tools such as bifurcation diagram, Fourier spectrum, 3D-phase diagram, Poincaré map, and amplitude-frequency diagram are generated, revealing the presence of periodic, quasiperiodic, and chaotic responses in specific regimes. This research provides an in-deep understanding of the dynamic behavior of SBG system, contributing to the characterization and prediction of nonlinear phenomena, which is vital for the optimization and design of gear mechanisms across various engineering applications.

In-Situ Estimation of Bolt Clamping Force by Utilization of Its Effects on Flexural Vibration Propagation

After a bolt assembling process, non-destructive identification of the clamping force is important to minimize unexpected failure of the assembled joint structures. For in-situ inspection for every parts, a detachable device which allows generation and detection of vibration propagation was proposed in this study. Tone burst excitation was transmitted through the bolted-joint structure. The vibration propagation characteristics depended on the clamping force. With an increase in the clamping force, the surface vibration propagation speed increased. The vibration magnitude decreased due to increasing constraint. A band-pass filter was used to remove noise component. The filtered vibration propagation responses were used in convolutional long short-term memory (CLSTM) training. The performance of CLSTM model was verified through comparison with actual clamping force. With minimal physical influence on the assembled parts, the clamping force of bolted-joint was measured using the surface vibration propagation characteristics.

Computational Design of Antimicrobial Active Surfaces via Automated Bayesian Optimization.

Biofilms pose significant problems for engineers in diverse fields, such as marine science, bioenergy, and biomedicine, where effective biofilm control is a long-term goal. The adhesion and surface mechanics of biofilms play crucial roles in generating and removing biofilm. Designing customized nanosurfaces with different surface topologies can alter the adhesive properties to remove biofilms more easily and greatly improve long-term biofilm control. To rapidly design such topologies, we employ individual-based modeling and Bayesian optimization to automate the design process and generate different active surfaces for effective biofilm removal. Our framework successfully generated optimized functional nanosurfaces for improved biofilm removal through applied shear and vibration. Densely distributed short pillar topography is the optimal geometry to prevent biofilm formation. Under fluidic shearing, the optimal topography is to sparsely distribute tall, slim, pillar-like structures. When subjected to either vertical or lateral vibrations, thick trapezoidal cones are found to be optimal. Optimizing the vibrational loading indicates a small vibration magnitude with relatively low frequencies is more efficient in removing biofilm. Our results provide insights into various engineering fields that require surface-mediated biofilm control. Our framework can also be applied to more general materials design and optimization.

Equivalent magnitude-dependent discomfort under vertical vibration up to 100 Hz

The effect of vibration magnitude on frequency-dependence of discomfort of human body is always overlooked with respect to the comfort equivalence contours, particularly for high-magnitude vibration in wideband frequency. In this study, the magnitude effect of vertical vibration on discomfort of human body is investigated experimentally. Nineteen male subjects are involved in the jury test of vibration discomfort in the vertical direction with 2–5 m/s2 in magnitude up to 100 Hz. It is shown that the growth rate of discomfort may exceed 1 due to the high-magnitude vibration employed. In this condition that the rate varies around 1, the Stevens’ power law is not capable to properly represent the relationship between the subjective discomfort and the vibration magnitude. It means the equivalent comfort contours are not only dependent on the frequency range but also related to the vibration magnitude. Frequency weightings of vibration discomfort are influenced by the excitation magnitude. Practitioner summary: The occupant comfort to vertical whole-body vibration is affected by vibration magnitude. This study provides the effect of vibration magnitude on frequency-dependence of discomfort to whole-body vibration. It is suggested to propose variable frequency weightings for vibration discomfort evaluation under different magnitudes to achieve better comfort design.

Forced vibration analysis model for pumped storage power station based on the 1D–3D coupling and pipe walls vibration

AbstractHydraulic vibration is a common phenomenon in pumped storage power stations (PSPS) and hydropower plants. Evaluating the performance of the PSPS and water conveyance system under the hydraulic vibration condition is significant for the safety of the electric power and the PSPS system. In this study, the one‐dimensional (1D) and three‐dimensional (3D) coupling model for the entire PSPS system is established based on the open‐source software OpenFOAM and in‐house C++ codes. The coupling data exchange is realized by writing and reading files. The coupling model is validated by comparing the results with the pure 1D method under small load disturbance conditions. The forced vibration source is modeled by the pipe walls vibration method in the 3D region, and the 1D method takes charge of other parts in the PSPS system. The combination of the pipe walls vibration and 1D–3D coupling could fully consider the incident and reflected characteristics of the pressure waves. The established model could evaluate the overall performance of the PSPS system under forced vibration. Sensitive analysis of the vibration magnitude is carried out, and the results are consistent with the theoretical analysis, demonstrating that the established model is applicable for the forced vibration analysis.

Multi-axis vibration test technology of satellite based on vector-fixture’s design and applications

Aiming at the problems that the three-direction uniaxial sequential vibration test cannot effectively simulate the real launch environment of the satellite, and the high cost of the multi-axis shaker and the limitation of engineering application, the multi-axis vibration test scheme based on vector-fixture is proposed. Taking the vibration magnitude of uniaxial vibration test on the satellite mounting surface as equivalent reference, the appropriate vector direction is determined to carry out vector-fixture design. By analyzing the multi-axial vibration test data of the real structure of a satellite, it can be seen that: The “satellite-fixture” mounting surface can reach the set vibration magnitude at low frequencies, and undertest occurs at high frequency due to structural resonance and other factors; By optimizing the control strategy, the degree of over-test and under-test in the three directions can be balanced. According to the mission characteristics and development cycle of micro-nano satellites, this paper provides an efficient vibration test scheme.

Development of Empirical Relations to Predict Ground Vibrations due to Underground Metro Trains

The vibration caused due to underground metro trains in densely populated urban areas and its adverse effect on the nearby structures and occupants is a growing concern for the policymakers and government bodies, demanding its rapid and correct assessment. Metro bodies in India use Research Designs and Standards Organisation guidelines similar to Federal Transit Administration guidelines for vibration assessment. However, in the guidelines, there is limited discussion on soil geotechnical properties, tunnel depth and axle load, which considerably affect the magnitude of train-induced ground vibration. This study focuses on developing easily comprehendible empirical relations to predict metro train-induced ground vibrations considering the effect of these parameters. Multiple non-linear regression is used to establish the empirical relations utilising the datasets generated from a two-dimensional train-track-tunnel-soil dynamic interaction (TTTSDI) finite element model. The TTTSDI model is based on the two-step methodology available in the literature and is validated with field measurement results of the Delhi metro sites. The developed empirical relations predicted the ground vibrations with maximum and minimum errors of 2.66% and 0.84%, respectively.

Fault injection and diagnosis of the centrifugal fan

Centrifugal fan is widely used in industry, vehicle and ship application to provide air cycle power. To detect the fan fault at early stage, this paper explores the fault feature in the vibration signal and fault diagnosis method through the fault injection test, where impeller unbalance, rotor unbalance, and bearing fault are involved. Firstly, the fault mechanism is introduced; then, the fault injection methods of the three faults are introduced to obtain the faulty fans; finally, health and fault tests are performed, where the vibration sensors are employed and distributed on the fan in the axial and radial direction. Moreover, the acquired vibration data is analyzed by using time-domain and frequency-domain methods, and further the fault features between health and fault are compared and discussed. The analysis results indicate that the three faults can be detected through the vibration intensity and magnitude comparison at their individual characteristic frequencies in the spectrum.

Effectiveness of whole-body vibration on bone mineral density in postmenopausal women: a systematic review and meta-analysis of randomized controlled trials.

The present study observed significant effects of whole-body vibration (WBV) on bone mineral density (BMD) in postmenopausal women, with high-quality evidence for high-frequency, low-magnitude, and high-cumulative-dose use. The aim was to update a previous systematic review with meta-analysis to observe the effects of WBV on BMD in postmenopausal women. For the meta-analysis, the weighted mean difference between WBV and control groups, or WBV and conventional exercise, was used for the area of bone mineral density (aBMD) of the lumbar spine, femoral neck, total hip, trochanter, intertrochanter, and Ward's area, or volumetric trabecular bone mineral density (vBMDt) of the radius and tibia. Methodological quality was assessed using the PEDro scale and the quality of evidence using the GRADE system. In total, 23 studies were included in the systematic review and 20 in the meta-analysis. Thirteen studies showed high methodological quality. WBV compared with control groups showed significant effects on aBMD in the primary analysis (lumbar spine and trochanter), sensitivity (lumbar spine), side-alternating vibration (lumbar spine and trochanter), synchronous vibration (lumbar spine), low frequency and high magnitude (lumbar spine and trochanter), high frequency and low magnitude (lumbar spine), high frequency and high magnitude (lumbar spine, trochanter, and Ward's area), high cumulative dose and low magnitude (lumbar spine), low cumulative dose and high magnitude (lumbar spine and trochanter), and positioning with semi-flexed knees (trochanter). Of these results, only high frequency associated with low magnitude and high cumulative dose with low magnitude showed high-quality evidence. At this time, considering the high quality of evidence, it is possible to recommend WBV using high frequency (≈ 30Hz), low magnitude (≈ 0.3g), and high cumulative dose (≈ 7000min) to improve lumbar spine aBMD in postmenopausal women. Other parameters, although promising, need to be better investigated, considering, when applicable, the safety of the participants, especially in vibrations with higher magnitudes (≥ 1g).

Investigation of Vehicle Engine Driving Comfort Used in Vibration Dampers

In this study, it is aimed to reduce the vibration transmitted to the chassis by using vibration dampers in the connection between the vehicle engine and chassis. A theoretical and experimental study was examined. The vibration damper is an elastic material. In the structure of this material, spring and damping are combined with the suspension system. In this study, insulation ratios between the two were compared using new and old dampers. As the engine speed changes in the vehicles, the vibration size it produces also changes. This causes severe discomfort to the driver and passengers in the vehicle. It was observed that the vibration magnitude passing from the engine to the chassis decreased by 50%. When the old and new dampers are compared, it is seen that the vibration isolation of old dampers is very weak. Therefore, it was concluded that the appropriate damper should be selected according to the mass and operating conditions of the engine. Also, it was observed that vibration amplitude increases at low engine speeds, and vibration amplitude decreases at high engine speeds. It has been found that the new vibration damper is a better insulating material than the worn damper.

Evaluation of subjective discomfort of the seated human body exposed to vertical vibration using dynamic body pressure

Pressure distribution has been regarded as a crucial parameter for static comfort evaluation of the seated human body. However, the association between the pressure distribution and subjective rating, exposed to vertical vibration, is still unclear. This study devotes to characterizing the vibration discomfort of the seated human body on a foam seat using dynamic body pressure distribution and investigating the associations between them. First, the dynamic body pressure of twelve subjects seated on a foam seat exposed to vertical random excitation was measured at frequencies from 0.5 to 20 Hz with six magnitudes (0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 m/s2 r.m.s.). Meanwhile, the subjective discomfort rating of the foam seat was evaluated with the relative magnitude estimation method. Then, the influence of vibration magnitude on subjective discomfort ratings and dynamic body pressure indicators was investigated. The results show that with the increase of vibration magnitude, the mean average dynamic pressure, the mean peak dynamic pressure, the mean dynamic contact area, and the normal dynamic force had no significant change. On the contrary, the subjective discomfort ratings, normal dynamic force change rate root-mean-square, and the indicators related to pressure change rate root-mean-square increased significantly. Finally, the relation between the subjective discomfort ratings and dynamic body pressure indicators was analyzed using Stevens’ power law. The linear regression fitting accuracy of the average dynamic pressure change rate root-mean-square, peak dynamic pressure change rate root-mean-square, area pressure change rate root-mean-square, and normal dynamic force change rate root-mean-square with discomfort ratings were above 95%. The four dynamic body pressure indicators are highly correlated with the subjective discomfort ratings, which can be used as objective indicators for vibration discomfort evaluation.

Transmissibility response analysis of a human body in semi-supine posture exposed to low-frequency vibrations

The study presents transmissibility responses of 14 male subjects exposed to vertical sinusoidal vibration (2.0–16.0 Hz) at five vibration magnitudes (0.5–1.5 m s−2 r.m.s.). The vibration magnitudes are measured at five body locations: head (at the forehead), sternum, abdomen, thigh, and leg, for which the transmissibility at each body location is statistically analyzed. The nonlinearity in the transmissibility response, that is, decrease in resonance frequency with an increase in vibration magnitude, is evident for the sternum, abdomen, thigh, and leg. The higher vibration magnitude causes greater segmental transmissibility at excitation frequency lower than the resonance frequency. The highest vibration transmissibility has been observed for the abdomen, followed by the thigh, sternum, and head. The findings indicate that the higher energy content associated with the sinusoidal waveform further softens the tissues in contact with the vibrating surface. Practitioner Summary: The present study provides transmissibility responses of the semi-supine posture of humans at the head, sternum, abdomen, thigh, and leg under vertical sinusoidal excitation (2.0–16.0 Hz). Pronounced transmissibility is obtained for the abdomen among the other body segments, followed by the thigh, as both consist of a majority of soft tissues.

Vibration Measurements of the Gerbil Eardrum Under Quasi-static Pressure Sweeps.

Tympanometry provides an objective measurement of the status of the middle ear. During tympanometry, the ear-canal pressure is varied, while the response of the ear to sound pressure is measured. The effects of the pressure on the mechanics of the middle ear are not well understood. This study is a continuation of our previous work in which the vibration response of the gerbil eardrum was measured in vivo under quasi-static pressure steps. In this study, we delivered a continuous pressure sweep to the middle ear and measured the vibration response at four locations for six gerbils. Vibrations were recorded using a single-point laser Doppler vibrometer and glass-coated reflective beads (diameter ~ 40µm) at the umbo and on the mid-manubrium, posterior pars tensa and anterior pars tensa.The vibration magnitudes were similar to those in the previous step-wise pressurization experiments. Most gerbils showed repeatability within less than 10dB for consecutive cycles. As described in the previous study, as the frequency was increased at ambient pressure, the vibration magnitude on the manubrium increased slightly to a broad peak (referred to as R1) and then decreased until a small peak appeared (referred to as R2), followed by multiple peaks and troughs as the magnitude decreased further. The low-frequency vibration magnitude (at 1kHz) decreased monotonically as the pressure became more negative except for a dip (about 500Pa wide) that occurred between - 700 and - 1800Pa. The lowest overall magnitude was recorded in the dip at mid-manubrium. The vibration magnitudes also decreased as the middle-ear pressure was made more positive and were larger than those at negative pressures. R1 was only visible at negative and small positive middle-ear pressures, while R2 was visible for both positive and negative pressures. R2 split into multiple branches after the middle-ear pressure became slightly positive. No magnitude dip was visible for positive middle-ear pressures.The low-frequency vibration magnitudes at negative middle-ear pressures on the pars tensa were higher than those on the manubrium. R1 was not visible for large negative middle-ear pressures on the pars tensa. R2 appeared as a multi-peak feature on the pars tensa as well, and a higher-frequency branch on the posterior pars tensa appeared as a trough on the anterior pars tensa. The magnitude dip was not present on the pars tensa. The largest overall magnitude was recorded at the R2 peak on the posterior pars tensa.The results of this study expand on the findings of the step-wise pressurization experiments and provide further insight into the evolution of the vibration response of the eardrum under quasi-static pressures.