Sensitivity Of Dynamic Response Research Articles

Exact Sensitivity of Nonlinear Dynamic Response with Modal and Rayleigh Damping Formulated with the Tangent Stiffness

Exact Sensitivity of Nonlinear Dynamic Response with Modal and Rayleigh Damping Formulated with the Tangent Stiffness

Sensitivity of Dynamic Response of Truss-Type Aquaculture Platform to Floating Body Arrangement

Aquaculture equipment is moving from offshore areas to the deep sea to obtain a cleaner farming environment, but will suffer from a worse marine environment. Truss-type aquaculture floating platforms have gradually gained the favor of deep-sea and ocean aquaculture due to being resistant to corrosion, lightweight, easy to move, having modular assembly characteristics, and so on. Here, a modular aquaculture floating platform that is mainly composed of high-density polyethylene non-metallic pipes as a floating body, a truss structure support and a single-point mooring system is designed. The three-dimensional potential flow theory and Morison equation are applied to the motion and force prediction of discontinuous and open structures, and an evaluation method for analyzing the hydrodynamic performance of the platform system is proposed. Then, a sensitivity analysis of the dynamic response is conducted on the density and length of the bottom floating pipe arrangement of the truss-type aquaculture floating platform. The results show that the pitch motion of the heading direction and the roll motion of the beam direction have a remarkable effect on the hydrodynamics of the truss-type aquaculture floating platform, and the maximum amplitude is 12.9 deg and 10.8 deg, respectively. The effective tension under the heading direction is greater than that under the Beam direction. And the sparser the arrangement of the floating pipe is and the longer the length of the floating pipe is, the more improved the hydrodynamic performance of the floating platform will be, but the effective tension is greatly affected by the wavelength and period, so it is necessary to design the appropriate floating pipe length according to the actual marine environment. This study could provide an engineering reference for the design, analysis, and application of an aquaculture floating platform.

Enhanced braille recognition based on piezoresistive and piezoelectric dual-mode tactile sensors

Human Tactile perception can be divided into pressure perception and slip perception according to the mode of contact. At present, however, tactile sensors can not have the same good performance as human pressure and slip perception. In this paper, a piezoresistive and piezoelectric dual-mode tactile sensing scheme is proposed based on human finger tactile skin structure. PVDF polymer is used as the sensitive material in piezoelectric layer, which has good dynamic response and high sensitivity. Graphene and carbon black are used as the sensitive material in piezoresistive layer, the array process is simple and high resolution can be achieved. The fast response of piezoelectric signal can be used to segment the piezoresistive signal and improve the recognition accuracy when the tactile sensor is used for slip sensing. At the same time, the piezoelectric layer can also reflect the velocity information and direction information. In recognition method, according to the feature that the continuous tactile signal has both temporal and spatial features in the process of sliding, CNN-LSTM is proposed in this paper. The tactile sensors is integrated into the robot arm to detect 20 kinds of braille. At the same speed and the same force, the recognition rate of bimodal braille recognition is 90.58%. In addition, the model can be well recognized at different speeds and sliding directions, and the recognition rate is 84.2%. Finally, the tactile sensor is wore on the index finger of human hand, the average recognition rate of touch braille is 77.5%, which shows that the algorithm has good robustness, and the speed of recognition is twice as fast as that of the normal blind. In the future, it can be applied to blind reading, surface detection, texture identification and other fields.

Experimental‐based study of gear vibration characteristics incorporating the fractal topography of tooth surface

AbstractMicroscopic roughness is inevitable on the gear meshing surface, which is also a key parameter affecting the dynamic response. The surface roughness exhibits self‐affine characteristics across multiscales. To explore the influence of surface fractal topography on the vibration amplitude of the gear system under different rotational speeds and loads, an experimental setup of spur gear transmission is devised. The fractal dimension and fractal roughness of the meshing surface are calculated by the power spectral density method. The relationships between gear response and fractal parameters are revealed experimentally. Results indicate that a rougher tooth surface, that is, a smaller fractal dimension or larger fractal roughness, corresponds to an intense vibration amplitude. The sensitivity of dynamic response to the tooth surface topography varies at different rotational speeds and loads. Under low speed and light load conditions, the fractal dimension and fractal roughness have a more obvious influence on the dynamic response of the gear transmission system. With the increase of speed and load, the macroworking conditions gradually become the main factor attributed to vibration amplitude.

Random analysis of train-bridge coupled system under non-uniform ground motion

The increasing prevalence of simply supported bridges in high-speed railway (HSR) lines has raised concerns about the safety of trains crossing these bridges during an earthquake. As these bridges are typically continuous and long, it is essential to consider the effects of traveling seismic waves on the random vibration of the train-bridge coupled (TBC) system. To address this issue, the new point estimate method (NPEM) is used to analyze the dynamic response and parametric sensitivity of a three-dimensional TBC system subjected to non-uniform ground motion with multiple random parameters. The motion equations of the TBC system are derived using bridge seismic theory under multi-support excitations. The analysis incorporates random variables such as the damping ratio, density, Young’s modulus, and seismic magnitude to capture the influence of traveling seismic waves on the random vibration of the TBC system. Simulation results show that the traveling seismic wave effect can cause changes in the first vibration frequencies of the train and bridge, potentially leading to the first few frequencies reordering. Additionally, considering the traveling wave effect will make the TBC system’s response less apparent than without considering the traveling wave effect. The uncertainty of bridge and seismic parameters can seriously affect the train’s running safety. The sensitivity of the bridge density and seismic magnitude is particularly prominent for bridge responses when the traveling seismic waves effect is strong. This methodology can be used for random and sensitivity analysis of a train running over a long bridge under non-uniform earthquake conditions. Overall, the NPEM can provide valuable insights into the dynamic behavior and safety of TBC systems, enabling more effective design and maintenance of HSR bridges.

Design and Optimization of Interdigital Capacitive Humidity Sensor with Highly Sensitive and Dynamic Response Time

Humidity sensors are widely used in various fields of life. In meteorological detection, the sensor must have high sensitivity and fast dynamic response time due to extreme environmental interference. However, the sensitive mechanism of the humidity sensor determines that the dynamic response time will inevitably be increased while improving the sensitivity, which undoubtedly creates difficulties for sensor design. This article takes the interdigitated capacitive humidity sensor as the research object and proposes an optimal design scheme for the sensor that considers high dynamic response time and sensitivity. By constructing the sensor’s theoretical mathematical model, the influence of each structure is analyzed. The theoretical model has been verified by finite element simulation to have an accuracy higher than 95%. The article constructs the sensor optimization objective equation based on this model. Through analysis, within the range of structural parameters set in the article, to improve the sensitivity and reduce the dynamic response time of the sensor, the width and spacing of the interdigital electrodes should have a minimum value of 3 μm and a maximum value of 14 μm, respectively. The thickness of the electrode layer and the moisture-sensitive layer should be flexibly adjusted according to the application to ensure the lowest value of the optimization objective function. To further improve the sensor’s performance, the article optimizes the electrode structure and heating strategy of the sensor heating layer, which not only enhances the uniformity of heat transfer but also increases the optimal heat transfer area by 6% compared with the traditional scheme.

Substructure damage identification based on sensitivity of Power Spectral Density

In this paper, a new method for substructure damage identification under random excitation is proposed, which is based on the sensitivity of the power spectral density (PSD) analysis. The finite element model is divided into different substructures and combined with the improved reduced system (IRS) method to achieve model condensation. When the system is subjected to excitations, the sensitivity of dynamic response of power spectral density function to structural damage parameters is obtained. The substructure is regarded as an independent structure, and the structural damage identification is realized by using the method of model updating. By increasing the number of frequency points used for damage identification to reduce the selection of measuring points. The identified results are obtained by updating the damaged parameters using sensitivity of PSD with few measurement points. The assembled finite element model is obtained by condensation and the number of elements is greatly reduced. The substructure damage identification method based on the PSD sensitivity is proposed in this paper, it not only reduces the size of analytical model involved in model updating but also decreases the uncertain parameters that need updating, thus resulting in a rapid convergence of the iterative process. The numerical and experimental model of a six-story steel frame structure with different damage conditions demonstrates the satisfactory identification results from the proposed method.

Parametric Studies on Dynamic Analysis of Blast-Loaded Retrofitted RC Columns

The majority of public and private facilities, existing today, were not originally designed to withstand blast loads rising from terrorist attacks. Hence, such facilities require effective countermeasures to minimize losses inflicted on property and people in the event of terrorist bombing. Retrofitting of main structural elements is very effective to increase blast resistance. In this paper, comprehensive parametric studies for the dynamic response of blast-loaded RC columns are performed using the proposed nonlinear coupled model and AUTODYN software. Many material and reinforcement parameters are considered in the paper such as concrete compressive strength, steel yield stress, longitudinal steel ratio and transverse stirrups ratio. Blast-loading parameters such as using different explosive weights, changing the stand-off distance of explosion, are also studied. Finally, the retrofitting parameters for blast-loaded columns, such as using different retrofit material types like the Carbon Fiber Reinforcing Polymers (CFRP), Glass Fiber Reinforcing Polymers (GFRP) and Steel Reinforcing Polymers (SRP) with different thicknesses for each material type, are considered. Important conclusions are drawn for the sensitivity of dynamic response and failure modes of RC columns under blast loading.

Topology optimization of multi-story buildings under fully non-stationary stochastic seismic ground motion

Topology optimization has been mainly addressed for structures under static loads using a deterministic setting. Nonetheless, many structural systems are subjected to uncertain dynamic loads, and thus efficient approaches are required to evaluate the optimal topology in such kind of applications. Within this framework, the present paper deals with the topology optimization of multi-story buildings subjected to seismic ground motion. Because of the inherent randomness of the earthquakes, the uncertain system response is determined through a random vibration-based approach in which the seismic ground motion is described as filtered white Gaussian noise with time-varying amplitude and frequency content (i.e., fully non-stationary seismic ground motion). The paper is especially concerned with the assessment of the dynamic response sensitivity for the gradient-based numerical solution of the optimization problem. To this end, an approximated construction of the gradient is proposed in which explicit, exact derivatives with respect to the design variables are computed analytically through direct differentiation for a sub-assembly of elements (up to a single element) resulting from the discretization of the optimizable domain. The proposed strategy is first validated for the simpler case of stationary base excitation by comparing the results with those obtained using an exact approach based on the adjoint method, and its correctness is ultimately verified for the more general case of non-stationary seismic ground motion. Overall, this validation demonstrates that the proposed approach leads to accurate results at low computational effort. Further numerical investigations are finally presented to highlight to what extent the features of the non-stationary seismic ground motion influence the optimal topology.

Vibration attenuation of beam structure with intermediate support under harmonic excitation

The optimal position design of viscoelastic supports is studied for vibration attenuation of a beam under a harmonic excitation. By attaching the supports properly to the structure, the dynamic deflection of the steady-state response can be significantly suppressed. In this work, the derivative analysis of the dynamic deflection is first investigated with respect to the attachment location of a viscoelastic support. A closed-form formulation for the dynamic response sensitivity is gained readily by use of the discrete methodology. Then, a heuristic optimization algorithm is applied on the design sensitivity analysis to achieve the optimal solution of the supporting points to minimize the maximal steady-state displacement vibration of a beam structure. Finally, two typical examples are presented to demonstrate the validity and accuracy of the design sensitivity formulation developed. Numerical results show that the structural vibration deflections can be substantially reduced with optimization of the intermediate support positions.

Dynamic crushing response of novel re-entrant circular auxetic honeycombs: Numerical simulation and theoretical analysis

Auxetic honeycombs have a variety of potential applications in aerospace engineering due to their excellent mechanical and multidisciplinary properties. A novel class of auxetic honeycombs have been invented recently named as Re-entrant circular (REC) honeycombs. The REC honeycombs can be obtained by replacing the sloped cell walls of the well-known re-entrant (RE) unit honeycombs with double circular arc walls to dissipate more energy. This study aims to investigate the in-plane dynamic crushing responses of the novel REC honeycombs through numerical simulations and theoretical analyses. LS-DYNA based numerical simulations revealed the “X” and “I” combined deformation mode of the REC honeycomb under low velocity crushing, and the “I” mode under high velocity loading. The geometric parameters of unit cell and the crushing velocity were both found to have great effects on the proximal end crushing stress of the REC honeycomb. It was also shown that the REC honeycomb presents obvious negative Poisson's ratio (NPR) effect, attributed to its re-entrant characteristic. Based on the meso-scale deformation mechanisms of the representative unit cell, theoretical models have been established to predict the plateau stress of the REC honeycomb under different crushing velocities. The theoretical predictions were in good agreement with the numerical simulation results. Moreover, the dynamic sensitivity index and the deformation mode map of the REC honeycomb were obtained to evaluate its dynamic response sensitivity to the loading velocity. Finally, the in-plane crushing characteristics of the REC and the RE honeycombs were compared. The REC honeycomb was found to show higher specific energy absorption (SEA) and penetration resistance than its RE counterpart, due to the more plastic hinges formed during the dynamic crushing process.

Prognostics of Gear Manufacturing Errors for Planetary Gear Systems Based on Power Flow Theory

Abstract Gear manufacturing errors are key parameters in planetary gear trains and have effects on load sharing, tooth stress, and so on. Accurate estimation of manufacturing errors can help monitor the conditions of planetary gear systems. This study investigates the dynamic response sensitivity to model parameters for a nonlinear single-stage planetary gear set with coupled lateral and torsional motions. Power flow theory is introduced to assess the gear vibration and the parameter sensitivity. The response sensitivity equations are deduced with the direct method (DM). The influence of the rotating speed is considered in the sensitivity analysis. Then, the identifiability of the parameter estimation is investigated based on the sensitivity results. The Gauss-Newton method is applied to estimate the manufacturing errors. Gear meshing is a primary factor in gear vibration, so the sensitivities of its vibration power to the parameters are analyzed in this paper. The estimated results are accurate when the collected data contain a lower noise signal. The sensitivity and parameter estimation make it possible to provide support for the design and diagnosis of a planetary gear set.

The Influence of Track Structure Parameters on the Dynamic Response Sensitivity of Heavy Haul Train-LVT System

Background: In order to study the applicability of Low Vibration Track (LVT) in heavy-haul railway tunnels, this paper carried out research on the dynamic effects of LVT heavy-haul railway wheels and rails and provided a technical reference for the structural design of heavy-haul railway track structures. Methods: Based on system dynamics response sensitivity and vehicle-track coupling dynamics, the stability of the upper heavy-haul train, the track deformation tendency, and the dynamic response sensitivity of the vehicle-track system under the influence of random track irregularity and different track structure parameters were calculated, compared and analyzed. Results: Larger under-rail lateral and vertical structural stiffness can reduce the dynamic response of the rail system. The vertical and lateral stiffness under the block should be set within a reasonable range to achieve the purpose of reducing the dynamic response of the system, and beyond a certain range, the dynamic response of the rail system will increase significantly, which will affect the safety and stability of train operation. Conclusions: Considering the changes of track vehicle body stability coefficients, the change of deformation control coefficients, and the sensitivity indexes of dynamic performance coefficients to track structure stiffness change, the recommended values of the vertical stiffness under rail, the lateral stiffness under rail, the vertical stiffness under block, and the lateral stiffness under block are, respectively 160 kN/mm, 200 kN/mm, 100 kN/mm, and 200 kN/mm.

Structural damage identification based on dynamic deflection sensitivity of bridge under vehicle loading

Based on the concept of dynamic response sensitivity, a method of identifying bridge structural damage by using the dynamic deflection response of bridge under vehicle load is proposed. Firstly, the dynamic equation of vehicle-bridge coupling dynamic system is established. And then, the basic principle and iterative identification process of bridge damage identification based on dynamic deflection response sensitivity are derived. Finally, the effectiveness of the algorithm is verified with a numerical example of three-span continuous beam vehicle-bridge coupling system. The research results show that the proposed algorithm can overcome the influence of measurement noise and initial model error, and realize the damage location and quantification of bridge from dynamic deflections of a few measuring points.

Experimental mechanical analysis of traditional in-service glass windows subjected to dynamic tests and hard body impact

The large use of glass in buildings, and especially the presence of fenestrations and facade systems, represents a potential critical issue for people safety. The brittle nature of glass (with limited elastic deformation and resistance) is often enforced by its use in combination of several secondary components, whose reciprocal interaction and potential damage should be properly assessed. In the case of windows, accordingly, a special care should be spent for glass members but also for the framing system and possible adhesive or mechanical connections. This study aims at exploring the dynamic response and damage sensitivity of traditional glass window systems, based on the experimental derivation of few key material properties and mechanical parameters. To this aim the attention is focused on traditional, in-service windows that belongs to existing residential buildings and are typically sustained by timber frames, through a linear flexible connection. In doing so, major advantage is taken from experimental analysis, both in the static and dynamic field, for whole window assemblies of single components. For comparative purposes, selected window specimens including plastic (PVC) frame members and Insulated Glass Units (IGUs) are also taken into account in the paper. The static characteristics of the windows components are first preliminary derived. The dynamic performance of such a kind of systems is then experimentally explored with the support of modal analysis techniques and hard body impact procedures, including the experimental derivation of stiffness parameters for the frame members and the glass panels. Further assessment of experimental outcomes is finally achieved with the support of Finite Element numerical analyses.

Wind-induced dynamic performance of a super-large hyperbolic steel-truss cooling tower

In order to study the wind-induced performance of super-large steel structure cooling towers, a super-large hyperbolic 216.3m-high cooling tower comprising a double-layer steel-truss structure with steel-sheet cladding was taken as a case study. The dynamic characteristics of this cooling tower were analyzed and compared with those of a similar-scale reinforced concrete cooling tower. Then, fluctuating wind loads measured in wind tunnel tests were applied directly to a structural finite-element model based on proper orthogonal decomposition and reconstruction of the wind pressures. The displacement response of the cooling tower was subsequently obtained by full transient dynamic analysis, and then the distribution characteristics of mean response, the mode participation contribution of the fluctuating displacement responses, the wind-induced vibration factors and the influence of structural damping ratio were investigated and compared with those of a concrete cooling tower. The comparison results mainly show that the steel-structure cooling tower has higher natural vibration frequencies, a lower-order number of lateral overturning mode (indicating a higher risk of overturning collapse), simpler resonant modes, smaller variance ratio of resonant component and weaker sensitivity of dynamic response to structural damping. The study results could assist in wind resistance design of similar super-large steel-structure cooling towers.

Dynamic response and sensitivity analysis for mechanical systems with clearance joints and parameter uncertainties using Chebyshev polynomials method

A mechanical system with clearance joints exhibits non-linear characteristics. Even a small variation of one parameter may lead to a drastic change of the overall system response. The coupling of clearance and uncertainty would therefore significantly influence the system performance. In this paper, an analysis method for dynamic response and parameter sensitivity of mechanical systems is proposed with the consideration of both clearance joints and uncertainties. In this method, elements of a revolute clearance joint are modeled as colliding bodies, where continuous contact force model and modified friction force model are employed to describe the impact-contact behavior. The clearance joint model is then coupled with the system motion equations to obtain the system dynamic response. Furthermore, by introducing the multi-dimensional Chebyshev polynomials approach, dependence of the system dynamic response on its parameters can be established. The bounds of the dynamic response could be obtained by using the interval operations, and the parameter sensitivity is interpreted as the rate of the change of the system dynamic response with respect to the parameter variation, revealing the contribution of each parameter on the dynamic performance. Finally, dynamics of a crank-slider mechanism with clearance and uncertainties is investigated. Results show that a larger clearance would cause severe oscillation in the response bounds and larger expansion of the interval length, and clearance effect restraint zones can be obtained through the sensitivity analysis, where the expansion of the response interval length could be reduced.

Viaduct seismic response under spatial variable ground motion considering site conditions

The evaluation of the seismic hazard for a given site is to estimate the seismic ground motion at the surface. This is the result of the combination of the action of the seismic source, which generates seismic waves, the propagation of these waves between the source and the site, and site local conditions. The aim of this work is to evaluate the sensitivity of dynamic response of extended structures to spatial variable ground motions (SVGM). All factors of spatial variability of ground motion are considered, especially local site effect. In this paper, a method is presented to simulate spatially varying earthquake ground motions. The scheme for generating spatially varying ground motions is established for spatial locations on the ground surface with varying site conditions. In this proposed method, two steps are necessary. Firstly, the base rock motions are assumed to have the same intensity and are modelled with a filtered Tajimi-Kanai power spectral density function. An empirical coherency loss model is used to define spatial variable seismic ground motions at the base rock. In the second step, power spectral density function of ground motion on surface is derived by considering site amplification effect based on the one dimensional seismic wave propagation theory. Several dynamics analysis of a curved viaduct to various cases of spatially varying seismic ground motions are performed. For comparison, responses to uniform ground motion, to spatial ground motions without considering local site effect, to spatial ground motions with considering coherency loss, phase delay and local site effects are also calculated. The results showed that the generated seismic signals are strongly conditioned by the local site effect. In the same sense, the dynamic response of the viaduct is very sensitive of the variation of local geological conditions of the site. The effect of neglecting local site effect in dynamic analysis gives rise to a significant underestimation of the seismic demand of the structure.

Role of oxygen vacancies in vanadium oxide and oxygen functional groups in graphene oxide for room temperature CO2 gas sensors

The greenhouse effect is involving global heating and climate change within the world. Carbon dioxide (CO2) is one of the major gas at the origin of this effect, but also the byproduct of human activity. Therefore, monitoring the indoor/outdoor CO2 emission by gas sensors is one of the priorities for environmental preservation. In this paper, the sensing performance of CO2 towards two different O-rich films have been studied; graphene oxide (GO) and vanadium dioxide (VO2). The preparation of GO film has been carried out by spray pyrolysis on fluorine tin oxide (FTO) prepared by the modified Hummers method. While the VO2 film has been sol-gel spin-coated on a glass substrate. Both films have been characterized using XRD, SEM and electrical properties. The CO2 gas sensing mechanism and the role of oxygen vacancies in VO2 are addressing. The oxygen functional groups in GO play a main role in the CO2 gas the sensitivity level and response time. Their gas sensing performances have been investigated based on measuring the response vs recovery time, dynamic response curve analysis and sensitivity. In order to better understand the sensing mechanism, characterization has been done with different gas concentrations. Both GO and VO2 based CO2-sensors are acted as an n-type sensor. Sensing behavior of GO at RT has explained to be mainly mediated by the oxygen functional groups and a wide range of active sites. In the other hand, VO2 contains oxygen vacancies and more defect sites which play a main role in the RT sensing activity and low recovery time.

Dynamic response and material sensitivity analysis of pelvic complex numerical model under side impact.

The surrogate design and clinical diagnostic suggest that the pelvic dynamic response should be the basis of bone fracture mechanism study under side impact. Pelvic response indicators are the impact force, compression (C), viscous criterion (VC), bone stress, and bone strain. However, no evaluation of these indicators has been conducted. To evaluate pelvic response indicators under side impact. A sitting pelvic finite element (FE) complex model comprising bone, artery, ligaments, and soft tissue was constructed. The dynamic response of the model under side impact with initial velocity of 3 m/s was investigated and material sensitivity analysis was complemented by changing bone elastic modulus. The pelvic FE model could predict response under side impact. Specifically, the indicators such as artery pressure and strain, together with the ligaments axial force and strain were provided. The sensitivity analysis showed the impact force, bone stress, and axial force were sensitive to the elastic modulus, whereas, C, VC, bone strain, and artery pressure were not. The sitting FE model in this study can predict pelvic dynamic response, and C, VC, bone strain and artery pressure are proposed for pelvic tolerance instead of impact force under side impact.