Local Vibration Research Articles

Efficiency enhancement of CZTSe solar cells based on in situ K-doped precursor

High FF: in situ K-doped precursors make large-grain and void-free absorbers. The doping-enhanced Sn diffusion eliminates the local content vibration, suppresses deep level defects, and to higher cell efficiency with greatly improved FF.

Wireless batteryless soft sensors for ambulatory cardiovascular health monitoring

Seismocardiography (SCG) is the measure of local vibrations in the chest due to heartbeats. Typically, SCG signals are measured using rigid integrated circuit (IC) accelerometers and bulky electronics. However, as alternatives, recent studies of emerging flexible sensors show promise. Here, we introduce the development of wireless soft capacitive sensors that require no battery or rigid IC components for measuring SCG signals for cardiovascular health monitoring. Both the capacitive and inductive components of the circuit are patterned with laser micromachining of a polyimide-coated copper and are encapsulated with an elastomer. The wearable soft sensor can detect small strain changes on the skin, which is wirelessly measured by examining the power reflected from the antenna at a stimulating frequency. The performance of the device is verified by comparing the fiducial points to SCG measured by a commercial accelerometer and electromyograms from a commercial electrode. Overall, the human subject study demonstrates that the fiducial points are consistent with data from commercial devices, showing the potential of the ultrathin soft sensors for ambulatory cardiovascular monitoring without bulky electronics and rigid components.

Structural and vibrational properties of wurtzite ZnO with oxygen-deficient defects: ab initio and potential-based calculations.

The structural and vibrational properties of the ZnO wurtzite phase with oxygen vacancies in different charged states are studied using first-principles and potential-based methods. The calculations based on density-functional theory are performed to determine the atomic configurations around defects. The DFT results are discussed and compared with those obtained using the static lattice method in the traditional shell model. Both computational approaches predict the same character of crystal lattice relaxation around oxygen vacancies. The phonon local symmetrized densities of states are calculated using the Green function method. The frequencies of localized vibrations of various symmetry types induced by oxygen vacancies in neutral and positively charged states are determined. The calculation results allow estimating the effect of oxygen vacancies on the formation of the intense Raman peak.

Topology Optimization for Harmonic Excitation Structures with Minimum Length Scale Control Using the Discrete Variable Method

Continuum topology optimization considering the vibration response is of great value in the engineering structure design. The aim of this study is to address the topological design optimization of harmonic excitation structures with minimum length scale control to facilitate structural manufacturing. A structural topology design based on discrete variables is proposed to avoid localized vibration modes, gray regions and fuzzy boundaries in harmonic excitation topology optimization. The topological design model and sensitivity formulation are derived. The requirement of minimum size control is transformed into a geometric constraint using the discrete variables. Consequently, thin bars, small holes, and sharp corners, which are not conducive to the manufacturing process, can be eliminated from the design results. The present optimization design can efficiently achieve a 0–1 topology configuration with a significantly improved resonance frequency in a wide range of excitation frequencies. Additionally, the optimal solution for harmonic excitation topology optimization is not necessarily symmetric when the load and support are symmetric, which is a distinct difference from the static optimization design. Hence, one-half of the design domain cannot be selected according to the load and support symmetry. Numerical examples are presented to demonstrate the effectiveness of the discrete variable design for excitation frequency topology optimization, and to improve the design manufacturability

Development of a reliability model for crack growth occurrence for a secondary hull component

Ship hull vibration is a major contributor to fatigue crack growth and main engine excitation is identified as an important vibration source. A general method to solve any vibration problem arising onboard a ship does not exist, which encourages the use of a reliability-based framework for assessing ship vibration and its consequences. A stochastic model of vibration response is developed for the probabilistic formulation of the failure probability of the occurrence of crack propagation of a secondary structural hull component. The secondary structural component considered is a pipe stack support. The pipe stack support connects a cargo pump pipe stack to the wall inside the cargo tank, and the support is welded directly onto this wall. First, a generic cargo hold model is analysed with engine speed and the relative distance between the engine and the structural component under consideration as stochastic variables. Then, submodels are used to investigate the local vibration of the support and the stress response is evaluated for a combination of different engine speeds and relative distances. A surface is fitted to the vibration response and used for probabilistic analysis by Monte Carlo (MC/DSPS) and FORM/SORM reliability methods. The limit state is formulated as the possibility of fatigue crack growth based on a threshold stress intensity factor. This threshold factor depends on the initial crack size and different initial sizes are investigated. The adequacy of the functional representation for the stochastic model, which is fitted to discrete data points, is also assessed. It is seen that a functional representation using a sum of sine terms give an adequate fit for describing the stress response induced by engine speed, while a polynomial representation was adequate for the relative distance variable. The failure probability estimated by Monte Carlo simulations and SORM indicates that the pipe stack support is not critical for the occurrence of fatigue crack growth. A main observation from the analysis is that the reliability-based design of secondary structural components, also looking at the interaction with the global structure, may help to improve the vibration-induced stresses in local hull details by application of proper design measures.

Effect of electromechanical coupling on locally resonant quasiperiodic metamaterials

Electromechanical metamaterials have been the focus of many recent studies for use in simultaneous energy harvesting and vibration control. Metamaterials with quasiperiodic patterns possess many useful topological properties that make them a good candidate for study. However, it is currently unknown what effect electromechanical coupling may have on the topological bandgaps and localized edge modes of a quasiperiodic metamaterial. In this paper, we study a quasiperiodic metamaterial with electromechanical resonators to investigate the effect on its bandgaps and localized vibration modes. We derive here the analytical dispersion surfaces of the proposed metamaterial. A semi-infinite system is also simulated numerically to validate the analytical results and show the band structure for different quasiperiodic patterns, load resistors, and electromechanical coupling coefficients. The topological nature of the bandgaps is detailed through an estimation of the integrated density of states. Furthermore, the presence of topological edge modes is determined through numerical simulation of the energy harvested from the system. The results indicate that quasiperiodic metamaterials with electromechanical resonators can be used for effective energy harvesting without changes in the bandgap topology for weak electromechanical coupling.

Efficacy of Novafon Local Vibration Voice Therapy and Water Resistance Therapy: a meta-analysis

Treatment approaches for voice therapy are diverse and two treatment approaches in voice therapy with assistive devices will be evaluated and compared for efficacy. Evaluations of the treatment effects of different approaches are important for clinical consultation and evidence-based practice. To evaluate the efficacy of Novafon Local Vibration Voice Therapy (NLVVT) and Water Resistance Therapy (WRT) using Voice Handicap Index (VHI). Systematic literature search and meta-analysis with random effects model. The analysis of two databases (MEDLINE and CENTRAL) and a manual search from inception to September 19th 2021. Any clinical trial with case series in a pre-post design written in English or German that tested the efficacy of NLVVT or WRT using VHI (functional [F], physical [P], and emotional [E] aspects, and total score [T]) in adult voice patients with an organic or functional voice disorder was considered. Five eligible studies were identified (NLVVT n= 22; WRT n= 42). Both treatment approaches showed highly significant improvement in all aspects of the VHI (p-values< 0.01). In direct comparison, NLVVT achieved significantly higher improvements in VHI-T, VHI-F and VHI-E than WRT (p-values< 0.01). Comparable improvement was received in VHI-P (p= 0.28). NLVVT and WRT are effective treatments for voice disorders related to the subjective evaluation of a voice disorder. In direct comparison, NLVVT achieved higher improvements than WRT in most VHI aspects.

The relationship of electroencephalography (EEG) and neuroenergocarting indicators in vibration disease

Introduction. This article presents the results of a study of the relationship of phenomena characterizing the state of regulation of neurophysiological and energy processes in vibration disease (VD). The study aims to identify the relationships characterizing the state of regulation of neurophysiological and energy processes, according to the parameters of EEG and the level of constant potential (LCP) in patients with vibration disease. Materials and methods. We have examined thirty seven patients with VB caused by the combined effects of local and general vibration, thirty healthy men (comparison group). The researchers used electroencephalography and neurogenetic mapping techniques. Results. In the group of patients with VB, the nature of EEG activity was manifested by a change in the topical organization of the main normal EEG rhythms: the alpha rhythm, when compared with the comparison group, is more represented in the parietal leads (alpha rhythm index 30.7(15.8-53.5) and 45.3(34.9-59.5)% at p=0.010, respectively), beta1-rhythm - in a small, approximately the same amount, in all leads (in the right frontal from 3.7(2.8-5.6) and 6(3.8-8.2)% at p=0.020, in the left central leads up to 5.9(4.8-7.7) and 8.3(5.9-12.1)% at p=0.018, respectively). The delta rhythm index prevailed in the right frontal region 57.3(47.1-74.8) and 17(12-19)% at p=0.013, respectively. We have revealed a negative correlation of the delta rhythm index in the left frontal (Fp1), left central (C3), left parietal (P3), left occipital (O3), left temporal (T3) regions and LCP in the central (Cz) (r=-0.34; -0.32; -0.35; -0.39; -0.44; p=0.036; 0.048; 0.033; 0.016; 0.006, respectively). An increase in the theta rhythm index in the anterior frontal left lead (Fp1) can be associated with an increase in SCP in the occipital lobe of the right hemisphere (Pd-Ps, r=0.50; p=0.001). Limitations. Limitations are presented in the form of a small number of individuals in groups, insufficient depth of study of foreign literature materials on the issue under study. Conclusion. Interdependent disorders of neurofunctional activity in VB are: an increase in the theta rhythm index in the frontal, central regions of the left hemisphere with a right-hemisphere increase in neuroenergy exchange in the frontal, temporal, parietal regions; an increase in the delta rhythm index of the rhythm in the left hemisphere with a decrease in the LCP in the central parietal region. The strengthening of interhemispheric interaction with compensatory activation of the subdominant hemisphere is probably associated with the strain of adaptive potential, mechanisms for maintaining homeostasis, allowing to reduce neurological deficit by neuroplasticity.

A novel mathematical model for the design of the resonance mechanism of an intentional mistuning bladed disk system

Abstract. Bladed disk systems with advanced functions are widely used in turbo-machineries. However, there are always deviations in physical dynamic properties between blades and blades due to the tolerance and wear in operation. The deviations will lead to vibration localization, which will result in high cycle fatigue and accelerate the damage of the bladed disk system. Therefore, many intentional mistuning patterns are proposed to overcome this larger local vibration. Previous studies show that intentional mistuning patterns can be used to reduce the vibration localization of the bladed disk. However, the determination of the resonance mechanism of the intentional mistuning bladed disk system is still an unsolved issue. In this paper, a novel mathematical model of resonance of an intentional mistuning bladed disk system is established. Mistuning of blades and energy resonance are included in this theoretical model. The method of the mechanical power of the rotating blade for one cycle is applied to obtain the resonance condition. By using this theoretical model, the resonance mechanism of an intentional mistuning bladed disk is demonstrated. The results suggest that the ideal results can be obtained by adjusting the intentional mistuning parameter. This paper will guide the design of the dynamic characteristics of the intentional mistuning bladed disk.

A novel nondestructive testing method for honeycomb structure using acoustic band gap

Honeycomb structure is increasingly applied in various fields due to its high strength-to-weight ratios. However, due to the complex wave field in the structure, how to detect the defect accurately and efficiently is always an important problem. In this article, the honeycomb core, instead of being an obstacle to obtain the dispersion characteristic for traditional guided wave method, provides a way to calculate the wave propagation by being taken advantage of its space periodicity. By analyzing, simulating, and experimental testing, it is exhibited that there is a gap in the dispersion relation of the honeycomb structure which caused by the interaction between the local resonant vibration of the skins and the bending vibration of the structure. This gap disappears in the debonding area. Then a nondestructive testing method is proposed to detect the debonding defects based on this feature. The detection results of this proposed method are accord with that of ultrasonic C-scan. The results indicate that this method is suitable for detecting and locating the debonding defects in honeycomb structure with quite high sensitivity and efficiency, and it has a great potential to be widely used in filed test of honeycomb structure for its high feasibility.

Experimental and numerical investigation on the dynamic response and damage of large-scale multi-box structure under internal blast loading

Internal blast is different from external or air blast for the reason of internal blast load is much more complicated and more destructive to target structures. The present work presents a large-scale experiment on multiple steel box structure under confined blast loading. A multi-box structure specimen with a dimension of 7.5 m × 2.9 m × 2.2 m was designed and field blast test with 1.782 kg TNT detonated inside this model was carried out. The damage features and dynamic response of the specimen were analyzed. The plates near the explosive suffer from strong impact and result in some fragments with high velocity which are destructive to other structural members. Meanwhile, the dynamic response processes were recorded by using the high-speed photography system. The response process of the whole model can be divided into two different stages, namely, localized damage response stage and integral vibration stage. In addition, numerical model considering both double-sided and single-sided fillet welding of this large-scale experiment were built, the dynamic response and the propagation of internal blast wave were analyzed. The numerical studies show that, to achieve a good consistency with the experiment, the failure strain for double-sided and single-sided fillet welding should be set to 0.1 and 0.08 respectively for such large-scale structure under explosive load. Finally, several suggestions for the design of multi-box structure are put forward based on the experimental and numerical investigations.

Neuropsychological criteria for diagnosing cognitive impairment in patients with occupational diseases caused by physical factors

The aim. To identify neuropsychological signs of a decrease in higher mental functions associated with professional exposure to physical factors.Materials and methods. The study involved 40 patients with vibration disease caused by local vibration (Group 1), 50 patients with vibration disease caused by combined exposure to local and general vibration (Group 2), 71 civil aviation pilots with an established diagnosis of occupational sensorineural hearing loss (Group 3), and 38 healthy men (Group 4, control group). Methods of neuropsychological testing were used.Results. In Groups 1–3 the state of functioning of the cognitive sphere is represented by a mildly pronounced nature of impairments. The results of MMSE and FAB tests in patients of Groups 1–2, when compared with Group 4, determine a decrease in the functional activity of the frontal lobes and subcortical structures (25 (24–27), 25 (22–26), 15 (14–16) and 15 (13–16) points respectively). The most informative feature associated with the fact of occupational exposure to local vibration is the indicator of long-term memory (F = 9.41; р = 0.003); with combined impact of local and general vibration – short-term memory (F = 11.0; р = 0.001); with aircraft noise – objective gnosis (F = 8.48; р = 0.001). The obtained features make it possible to track with a high degree of accuracy the development of a decrease in cognitive functions in this contingent (86.1 %, 84.8 % and 72.1 % respectively).Conclusion. Common signs of changes in the cognitive sphere and lesions of the brain structures in patients with vibration disease are a decrease in praxis, impressive speech, for occupational sensorineural hearing loss – the lack of analytical-synthetic and conceptual thinking, object and finger gnosis, characterizing the inferiority of the functioning of the frontal and parietal regions of the left hemisphere.

Compact phase-modulated metasurface for vibration encoding and localization by single-sensor

Sensing and locating multi-source vibrations has been an attractive theme in various fields. The conventional methods of vibration localization rely on numerous sensors and complicated hardware. Aiming at such flaw, in this paper, a coding metasurface based on wavefront phase random modulation is designed. The designed metasurface can encode the vibration response in a direction-dependent manner through a disordered coupling network to realize highly uncorrelated vibration transmission. Combining the designed coding metasurface with the computational sensing technology, a metasurface-based single-sensor vibration sensing system (MSVS) is proposed. Deploying this metasurface sensing system, multi-source vibrations can be located and identified using only one sensor. A series of random, multiple vibration excitation tests with high-precision verify the effectiveness and robustness of the proposed MSVS. Compared with the bulky coding metamaterials with negative index, the proposed coding metasurface has the absolute advantages of single-material, simple-paradigm and easy-fabrication, which is more conducive to practical application. The proposed metasurface sensing system paves a promising avenue to simplify the vibration sensing system, which shows potential applications in various fields, such as structural health monitoring, fault diagnosis and intelligent devices.

Modelling and vibration evaluations of rotational mistuning-connecting disk-drum coupling structures with partial hard-coating damping treatment

Mistuning connections between drums and disks are very common in engineering. However, this point has not been mentioned in previous studies. This work develops discontinuous arc connections with different connecting stiffness to simulate actual mistuning connections by modifying the traditional spring method with continuous distributions. The admission functions are represented by good-convergence orthogonal polynomials. Through considering the rotation-generated gyroscopic and centrifugal effects and utilizing Kirchhoff's plate theory and Sanders’ shell theory, the dynamic model of rotational mistuning-connecting disk-drum coupling structures with partial hard-coating damping treatment (PHDT) is derived through Lagrange equations and verified by utilizing FEA and existing literature, in which the partial-coating model is more suitable for practical vibration suppression than the existing whole coating model. Moreover, further mistuned vibration evaluations show that the mistuning connections induce the change of mode order, frequency division, and vibration localization. The veering phenomenon caused by mistuning is also revealed, and the modal coupling and dominant mode exchange during veering are explained by the change of mode shape and MAC. Furthermore, the mistuning will also seriously affect the key information (critical speeds, instability positions, and veering positions) in Campbell diagrams. The present model provides key technical references for the vibration prediction, connection fault diagnosis, and coating parameter optimization of rotational disk-drum coupling structures with PHDT.

Evaluation of the interrelationships of indicators characterizing neurofunctional activity in vibration disease

Introduction. The results of studying the relationship between the bioelectrical activity of the brain, neuroenergetic exchange, the state of extracranial vessels, cognitive functions, in case of vibration disease caused by the effect of combined local and general vibration (CLGV) are presented. Materials and methods. Constant potential levels (CPP), characteristics of somatosensory evoked potentials (SSEPs), doppler ultrasound (USDG) and electroencephalography (EEG), neuropsychological features were studied in thirty eight patients exposed to CLGV, 32 persons of the comparison group. Results. Under CLGV topical disorganization and inhibition of alpha and beta activity, an increase in pathological delta activity, in the level of constant potential (DC-potential level) in the left frontal, right temporal and posterior parts of the brain, an increase in the latency of the N13, N20 components, the duration of the N18 interval -N20 are associated with an increase in the tone of the main extracranial arteries, a decrease in associative-logical thinking, short-term and long-term memory, dynamic praxis, and reciprocal coordination. Indicators of impaired neurofunctional activity (NFA) are an increase in the linear blood flow velocity (LBFV) in the internal carotid artery (ICA), the circulatory resistance index of the ICA, the DC-potential level of the occipital, central right, and parietal left leads; decrease in indices of theta - rhythm in the anterofrontal and parietal right, occipital left leads, indices of beta1, beta2 - rhythms in the occipital left lead. Limitations. The limitations of the work are presented in the form of a small number of individuals in groups, insufficient depth of the study of foreign literature materials on the issue under study. Conclusion. The interdependence of indicators characterizing the decrease in the tone of the cerebral cortex, cognitive functions, the state of the hypothalamic-stem connections, the increase in the tone of the extracranial arteries, as well as diagnostic signs that make it possible to detect changes in NFA in CLGV.

ACL Reconstruction: Which Additional Physiotherapy Interventions Improve Early-Stage Rehabilitation? A Systematic Review

Despite the restoration of the mechanical stability of the knee joint after ACL reconstruction (ACLR), patients often experience postoperative limitations. To our knowledge, there are no systematic reviews analyzing additional physiotherapy interventions implementing standard rehabilitation programs in the early postoperative phase after ACLR. The objective of this study was to analyze the additional physiotherapy interventions implemented in standard rehabilitation programs that improve early-stage ACLR rehabilitation. For this systematic review, we followed the PRISMA guidelines. In March 2022 we conducted a literature review using electronic databases. Primary outcomes were pain, edema, muscle strength, ROM, and knee function. The risk of bias and scientific quality of included studies were assessed with the RoB 2, ROBINS-I and PEDro scale. For the review, we included 10 studies that met the inclusion criteria (total n = 3271). The included studies evaluated the effectiveness of Kinesio Taping, Whole-body vibration, Local Vibration Training, Trigger Point Dry Needling, High Tone Power Therapy, alternating magnetic field, and App-Based Active Muscle Training Program. Most of the additional physiotherapy interventions improved pain, edema, ROM, knee muscle strength, or knee function in early-stage postoperative ACL rehabilitation. Except for one study, no adverse events occurred in the included studies, which demonstrates the safety of the discussed physiotherapy interventions. Further in-depth research is needed in this area.

Study on multi-clearance nonlinear dynamic characteristics of herringbone gear transmission system under optimal 3d modification

The tooth surface 3d modification technology is the most effective method to realize the reduction of vibration and noise of gear system (GS) by comprehensively considering tooth profile modification and axial modification. Moreover, the system nonlinear factors such as backlash and bearing clearance will make the motion of GS have complex variability. Therefore, we will combine 3d modification technology with contact performance and dynamic characteristics to optimize the meshing characteristics of herringbone gear pair through tooth contact analysis technology, loaded tooth contact analysis technology and antlion optimizer with error minimum amplitude as optimization objective, determine three nonlinear dynamic model of herringbone gear for numerical solution. Finally, this paper studies the influence of different system parameters on the system nonlinear dynamic characteristics under 3d modification and non-modification from both local vibration characteristics on the diagrams of time history, phase, spectrum and Poincare map and global vibration characteristics on the diagrams of system bifurcation and maximum Lyapunov exponent. The results show: After optimizing modification, the system vibration is obviously reduced. With the increase of input power, input speed, backlash and static transmission error (STE), the system has jump, while there is no jump with the change of bearing clearance and damping ratio. Compared with other parameters, the changes of input speed and STE make system have complex bifurcation characteristics. The 3d modification can eliminate the jump and make system motion more regular.

Numerical simulation of unsteady hydrodynamic performance of CRP

Strong hydrodynamic interference between forward and aft contra-rotating propellers (CRP) can result in load fluctuations, local blade vibrations, and noise. This study adopts a Reynolds-averaged Navier–Stokes solver (RANS) and a shear stress transport (SST) k−ω turbulence model to investigate the unsteady hydrodynamic performance of CRPs during uniform flow. The influences of time step and grid scale on the numerical simulation are discussed first. The numerical results of the open-water hydrodynamic performances of the CRPs agree well with experimental data. The fluctuation patterns of the hydrodynamic loads (i.e., force and torque) and propulsion efficiency of CRPs having different advance coefficients induced by the mutual hydrodynamic interference between the forward and aft propeller are investigated. A series of probes that rotate with the propellers are set upon the surface of the blades to analyze the unsteady local pressures under the hydrodynamic interference between the forward and aft propellers.

Low-frequency vibrational states in ideal glasses with random pinning.

Glasses exhibit spatially localized vibrations in the low-frequency regime. These localized modes emerge below the boson peak frequency ω_{BP}, and their vibrational densities of state follow g(ω)∝ω^{4} (ω is frequency). Here, we attempt to address how the localized vibrations behave through the ideal glass transition. To do this, we employ a random pinning method, which enables us to study the thermodynamic glass transition. We find that the localized vibrations survive even in equilibrium glass states. Remarkably, the localized vibrations still maintain the properties of appearance below ω_{BP} and g(ω)∝ω^{4}. Our results provide important insight into the material properties of ideal glasses.

Segmental molecular dynamics boosts Li-ion conduction in metal-organic solid electrolytes for Li-metal batteries

Metal-organic frameworks have emerged as a promising class of solid electrolytes for Li batteries. However, previous efforts to enhance Li-ion conductivity exclusively rely on the incorporation of solvents/salts and modifications of the rigid frameworks. In this study, we demonstrate metal-organic solid electrolytes with superionic conductivity by grafting hemilabile anionic chains with segmental motions in the pore channels of an Al-based metal-organic framework. High room-temperature ionic conductivity of 1.4×10–5 and 1.1×10−3 S cm–1 have been achieved under solvent-free and lean-solvent conditions, respectively. Solid-state nuclear magnetic resonance analysis reveals the localized molecular rotation and vibration of the anionic chains within in the rigid framework. Such segmental molecular dynamics would build Li transport highways and facilitate the Li-ion transport even without solvent. The metal-organic solid electrolyte shows excellent stability against Li metal anode, and the as-developed Li-metal batteries exhibit remarkable rate performance up to 4 C and long lifespan over 300 cycles. This work sheds light on the design principles of advanced metal-organic solid electrolytes for solid-state Li batteries.