Shaker Tests Research Articles

Low-frequency bandgap characteristics and vibration attenuation performance of metamaterial-tailored concrete-filled steel tube columns

Low-frequency vibrations, such as earthquakes and wind loads, may negatively affect the proper operation of buildings and bridges and even lead to structural failure. Even though, in the past two decades, metamaterial-based structures have been utilized in structure vibration suppression, they are mainly used in the mitigation of high-frequency vibrations, and it has been an open challenge to suppress low-frequency vibrations below 100Hz and ensure adequate bearing capacity in engineering structures. In this work, we present metamaterial composite column structures with built-in local resonators to achieve the low-frequency vibration mitigation effect. Compared to ordinary concrete-filled steel tube (CFST) columns, the metamaterial columns (meta-columns) can utilize the rubber shear modulus to create a low-frequency flexural bandgap in 30–50 Hz. Dynamic stiffness is introduced in the Timoshenko beam and Bloch's theorem, the metamaterial analytical model is established, and the bandgap generation mechanism and vibration reduction effect are analyzed in conjunction with numerical simulations. Then, the bandgap effect and vibration attenuation law of the meta-columns are investigated by shaker tests at different acceleration amplitudes. Guided by theory and simulations, we have successfully fabricated several meta-composite columns with low-frequency bandgaps, which attenuate up to half of the vibrational energy near the bandgap center. The bandgap ranges derived from the theoretical and numerical models show a high degree of consistency with the experimental results, with deviations generally within 10 %, all indicating that a bandgap exists near the resonator self-oscillation frequency. Additionally, the bandgap is significantly affected by the number of unit cells and resonators, especially the meta-column with fewer resonators fails to form a bandgap where the top response is smaller than the bottom response. As the number of resonators and metamaterial units increases, the meta-columns exhibit wider bandgap and stronger vibration reduction performance.

Quasi-zero stiffness interval optimization design and dynamics analysis of a new bi-directional horizontal isolation system

The quasi-Zero Stiffness (QZS) isolation system is a typical nonlinear isolation system, which has high static stiffness characteristics to improve the bearing capacity and deformation resistance, and its low dynamic stiffness characteristics can reduce the inherent frequency of the system to realize a wider vibration isolation frequency band, so it has a more excellent low-frequency vibration isolation performance compared with the linear system. In this paper, a horizontal QZS isolator is constructed based on a pre-compressed oblique spring system, and two sets of the horizontal QZS isolators are mechanically assembled to work together to achieve a bi-directional horizontal QZS isolation system. Considering that the construction of two sets of horizontal vibration isolators is approximately the same, we focus on one of the isolators for the static analysis and derive the parameter conditions to be satisfied for achieving quasi-zero stiffness characteristics. We considered the effect of each adjustable parameter of the horizontal vibration isolator on the mechanical performance of the QZS system, and sought to optimize the QZS interval to improve the vibration isolation performance. A comparative study of the dynamical properties between the QZS system with ordinary and optimized parameters, as well as the equivalent linear system, is further carried out by means of nonlinear approximate analysis. Finally, the dynamic characteristics of the bi-directional horizontal QZS system and the equivalent linear system are compared by shaker tests on the prototype device, which proved the excellent vibration isolation performance of the proposed QZS isolation system.

Research on Vibration Damping Analysis of UHV Suspended Converter Valve Model

The UHV (ultra high voltage) suspended converter valve is hinged to the top of the valve hall, so the equipment has a long structural period, the suspended converter valve is displaced under the action of earthquakes, and the valve tower is susceptible to damage due to interaction with the important equipment connected to it. The high cost, large size, and weight of the real type of UHV suspended converter valve make it difficult to carry out shaking table test studies of the real type of equipment. In this paper, a numerical model of a UHV-suspended converter valve scaling device and its damping structure model are established, and a damping analysis study with damping at the top of the converter valve model is carried out. The analysis showed that the maximum displacement of the converter tower was 136.3 mm under the action of a 0.4 g El-Centro earthquake. With horizontal damping at the top, the maximum displacement of the converter tower is 62.9 mm, a reduction of 53.9% compared to the undamped case. This study proposes a vibration damping design for UHV suspended converter valve, laying the foundation for subsequent shaker test studies of the scaled-down model vibration damping structure of the UHV suspended converter valve and the productization of vibration dampers for the equipment.

Boosting output performance of tri-hybrid vibration-based generator via quin-stable nonlinearity and speed amplification

A high-performance tri-hybrid vibration-driven generator with quin-stability and speed amplification characteristics is presented. This design integrates three different mechanisms in a compact and interactive working mode to enhance power density. Exploiting the quin-stable nonlinear behavior to the dynamic system creates a shallow potential well that can be triggered under broadband, low-level, and random ambient sources. In addition, the implementation of the rack and pinion steering system not only doubles the relative motion of the translators’ moving components in the electromagnetic and triboelectric units, and also increases the number of operations per cycle of the frequency up-conversion piezoelectric units. Consequently, the output performance of this tri-hybrid generator is significantly enhanced. To examine the working efficiency of this design, an experimental model is assembled and tested. In the shaker test, the peak output power of the prototype can be boosted to ∼822 mW, and the maximum power density is 7.74 mW cm−3 g−2 subjected to low excitation levels (5 Hz and 1-g acceleration). Experimental demonstrations are also carried out to exhibit the exceptional performance of this design that can support various power levels of electronic devices under human-induced motions.

Vibrational comfort improvement for a passenger car driver seat

Abstract This paper presents an experimental study aimed at providing new insights into passenger vehicle driver seat vibration. The study investigates the effects of various driver seat components on the damping coefficient. By employing a design for six sigma method, an optimized seating solution is proposed to enhance seat comfort levels. The control factors used in this study include seat cushion upholstery, topper foam, cushion foam, pulmaflex, torsion bar and seat structure. Seat position, foam thickness and body mass are considered as potential noise factors. Subjective evaluation of seat comfort is conducted using the SAE J 1441-2016, comparing three different passenger car driver seats. The seats are disassembled from the vehicles and mounted on a six-degree-of-freedom shaker test bench. Vertical vibration data are filtered, and transmissibility curves are experimentally obtained from the seat rail to the seat cushion via a pad. Uncomfortable seat prototypes are then manufactured, and alternative configurations are tested on the shaker. The objective and subjective evaluations of the seat prototypes reveal that lower foam hardness, higher foam density, and flexible upholstery contribute to improved comfort levels. Moreover, the prototype seat with optimum parameters receives a subjective evaluation SAE score of +0.75, indicating an enhancement in comfort.

A comparison of modal parameter identification tests in laboratory conditions

AbstractModal parameter evaluation is widely used for structural health monitoring, damage detection, and numerical model calibration. This study benchmarks two methods for modal identification under controlled laboratory conditions using operational modal analysis to compare dynamic parameters from ambient vibrations and shaker tests. A 2‐storey 3D spatial steel frame equipped with 3‐axial accelerometers is used as a case study. The identified dynamic parameters are benchmarked against a preliminary finite element model by computing Auto‐MAC and MAC matrices. It can be concluded that the preliminary FEM approach performs better in the prediction of modes shapes than natural frequencies. It was found that analysing the structural response to both ambient and artificially induced excitations provide a more complete understanding of a structure's dynamic characteristics. An additional mode shape was identified from the artificially induced excitation that was not previously captured from the ambient excitation.

Seismic response analysis of double-trough aqueduct considering fluid-structure interaction effect.

At present, the crude fluid-structure interaction analysis model cannot accurately characterize the interaction mechanism between aqueduct and water under earthquake action. In order to solve this problem, this paper analyzes the seismic response of the double-tank aqueduct under the action of earthquake by using the shaker test and the VOF (Volume of Fluid) method considering the free liquid level from the perspective of fluid-solid bidirectional coupling, explores whether the liquid movement in the double tank is consistent and the shock absorption effect of different water levels on the aqueduct, and analyzes the amplitude of free liquid level sloshing and the change of horizontal dynamic pressure caused by water level change from the generation mechanism of TLD (Liquid tuning dampers). The results show that the liquid movement in the two tanks in the double-channel aqueduct is basically the same under the action of earthquake, and the TLD effect of the liquid gradually increases with the increase of the water level in the aqueduct, and the maximum peak shock absorption rate is 63.4% at the maximum peak and 50.4% in numerical simulation. The shaking amplitude of the liquid is positively correlated with the water level height, and the magnitude of the shaking amplitude also reflects the magnitude of the moving water pressure.

A speed-amplified tri-stable piezoelectric-electromagnetic-triboelectric hybrid energy harvester for low-frequency applications

This work proposes a new speed-amplified multi-stable tri-hybrid energy harvesting technique via the multi-stable nonlinearity enhanced frequency up-conversion and rack-pinion mechanisms to efficiently harness structural and biomechanical vibration energy. In the present design, two frequency up-conversion piezoelectric generators, an array-type electromagnetic generator and a sliding-mode triboelectric nanogenerator are integrated together to form a compact and interactive system. By utilizing the rack-pinion mechanism, the relative speed between the stators and the translators of the electromagnetic and triboelectric generators are both doubled. Meanwhile, the process of frequency up-conversion in the piezoelectric generators is also doubled per each cycle. This results in better performance under wideband and low-frequency vibration sources. For verification, a prototype of this design is tested by mechanical excitations and body-induced motions. In the shaker test, the prototype can generate a peak output power of 446.16 mW under an optimal resistance load, resulting in a normalized power density of 4.20 mW cm–3 g–2 at 5 Hz under 1 g. The prototype also exhibits exceptional performance under various human motion tests, it can drive 600 commercial light-emitting diodes simultaneously. Using a commercial DC/DC voltage regulator circuit, the proposed harvester can serve as a universal power source to charge commercial electronic devices, including smartphones and GPS sensors. The present design shows great potential as a sustainable power source for wearable/portable electronics as well as wireless monitoring systems.

Euclid Spacecraft Sine Vibration Test Prediction Through the Virtual Shaker Testing Technique

In the space industry, the sine vibration test prediction of a spacecraft is approached numerically by exploiting the spacecraft finite element model (FEM). A frequency response analysis is run for this purpose, and the spacecraft is assumed in hard-mounted boundary conditions, thus neglecting the shaker compliance. Consequently, unrepresentative structural predictions may lead to test article under- or overtesting, as well as incorrect FEM mathematical model updating, and affect the proper fulfilment of the launcher frequency requirements. Virtual shaker testing (VST) solves these issues by including the shaker FEM within the computational framework and exploiting a coupled transient analysis inclusive of the vibration control system. In this study, VST is applied as a pioneering predictive tool to study spacecraft–shaker dynamic coupling of the Euclid spacecraft, before mechanical qualification tests. Experimental measurements such as test control accelerations, lateral bending moments, cross talk, and notching were effectively predicted and compared to the classical approach. Compression factor effects were investigated through a sensitivity analysis, and test predictions were strongly influenced by this parameter. VST has been shown to be a valid methodology to faithfully simulate the sinusoidal test and extract data otherwise unavailable.

Vibrations of joined conical-cylindrical shells with bolt connections: Theory and experiment

This paper investigated the vibration characteristics of joined conical-cylindrical shells (JCCSs) with bolt loosening boundary conditions both theoretically and experimentally. The non-uniform arc constraint model is established to simulate the bolt loosening boundary conditions by the artificial spring technology, which can describe the actual bolt contact pressure distribution. Continuously distributed artificial springs are introduced to realize the connection of the conical and cylindrical shells. Donnell's shell theory and Chebyshev polynomials are adopted to establish the theoretical model, and the dynamic equation is derived from the Lagrange equation. The validity of the present model is verified by the available literature, hammer test and vibration shaker test. The results indicate that the maximum errors of natural frequencies and resonant displacements are less than 4.41% and 18.6%, respectively. It is found that bolt loosening has a significant effect on the fundamental frequency, but it gradually weakens with the increase of the mode order. Increasing bolt loosening degree can lead to an increment of resonant displacement. The developed model is reliable in estimating the dynamic behaviors of bolted JCCSs with different loosening degrees, and it contributes to providing guidance in the design and service process of combined shell structures.

The Effect of Preload, Density and Thickness on Seat Dynamic Stiffness

The vibration transferred to the car floor transmits to the human body through the seat structure, and the typical design of the seat structure consists of several components such as seat frame and seat cushion. The material widely used as seat cushion is open-cell polyurethane (PUR) foam; when under vibration, it will behave dynamically. Factors such as mechanical properties and material thickness of PUR can affect its behaviour and performance and the amount of vibration transmits to the human body. This work measures the PUR dynamic stiffness for different material densities and thicknesses. The test was conducted using an indenter head with a flat surface since it was a less expensive method, and quicker measurement could be done. The force sensor was placed within the indenter structure to measure the load transmitted to the seat and acceleration data acquired by the accelerometer, which was mounted on a shaker test plate. Foam materials with 30 kg/m3 and 44 kg/m3 with 30 mm and 50mm thickness are used in the experiment with the amount of preload applied of 20 N,30 N and 40 N. Seat stiffness increased when the preload increased from 20 N to 40 N, and a similar trend occurred when foam thickness decreased. The lower density of PUR resulted in a greater increase of seat stiffness and damping across the frequency 0-30 Hz compared to a higher density of PUR. This study concluded that thickness, preload, and density significantly affect seat dynamic stiffness.

Power Generation by a Limestone-Contained Putty.

A novel contact-separation triboelectric generator concept is proposed in this paper, which consists of a limestone-based mounting putty and a metallized polyester (PET/Al) sheet. This is an attempt to explore tacky materials for power generation and extend the operational frequency bandwidth compared to existing TriboElectric NanoGenerators (TENGs). Moreover, the proposed design is very cost-effective and easy to build. Unlike traditional TENGs, which generate power solely due to a charge developing on the surface, the putty also replies on charge developed inside the material. Parametric study was conducted to determine the optimal putty thickness in a shaker test at 40 Hz. It was found that a putty layer at 0.6 mm thick yielded maximum power generation. During the separation phase, the electrical breakdown between triboelectric layers allows most existing electrons to flow back from the ground due to rapid charge removal at the interface. We are able to achieve a peak power of 16 mW in a shaker test at 40 Hz with an electrical load of 8 MΩ, which corresponds to a power density of 25.6 W/m2. A peak power of 120 mW in a manual prototype generator is achieved, which operates at approximately 2 Hz. Since putty material has less tackiness than double-sided tape, we are able to expand the frequency bandwidth up to 80 Hz, which is significantly higher than a TENG (typically <10 Hz). The mounting putty material contains limestone with approximate 31 nm of mean grain size mixed with synthetic rubber materials. Elasticity from rubber and the nanohardness of calcite crystallites allow us to operate a putty generator repeatedly without the concern of grain fracture. Also, a durability test was conducted with up to 250,000 contact-separation cycles. In summary, comparable performance is achieved in the proposed putty generator to benefit energy harvesting and sensor applications.

Analysis of Seismic Damage Modes of Landslides Containing Tunnels under Horizontal Earthquake Action

With the vigorous development of railway and highway construction, tunnel construction often follows the mountains and rivers, crossing high-intensity landslide areas, and potential earthquakes triggering damage in areas including tunnel landslides have become a hot issue today. Based on this, this paper performs a shaker test on the tunnel-containing landslide body, inputs horizontal seismic waves, and tests the acceleration response data of different bits in the landslide body. By analyzing the temporal and frequency domain transformations of the acceleration response at different positions in the slope body combined with the deformation characteristics of the slope, and then analyzing the seismic response of the slope under the action of the front and back seismic sequences, the results show that (1) the existence of the tunnel has the effect of energy dissipation and vibration reduction, making the energy input at T8, and the measuring point on the upper part of the tunnel at the lowest. (2) When the seismic wave is transmitted, it will cause reflection around the tunnel, forming complex seismic wave field, resulting in the irregular distribution of acceleration amplification coefficient. (3) There is a high correlation between seismic responses of different levels. When the acceleration response of the preseismic response to the landslide-containing tunnel is not considered, the acceleration response of the postseismic response to the slope and the structure will be lower than the real value. (4) The sequence of failure at different locations of landslide mass containing tunnel is found through marginal spectrum analysis. It is concluded that the failure mode of landslide mass with tunnel is extrusion and sliding out of the middle slope. The research results can provide some reference for the reinforcement design of landslide with tunnel in high-intensity area.

Power Generation by a Double-Sided Tape.

A novel contact-separation triboelectric generator concept is proposed in this study, which is composed of a double-sided tape with acrylic adhesive material and a metalized polyester (PET/Al) film (an aluminum layer coating on one side). The proposed concept is very cost-effective and easy to fabricate compared to existing triboelectric nanogenerators (TENGs), which require special equipment and sophisticated procedure to build. The strong bonding nature of acrylic adhesive on the tape induces a significant charge when contacting. The peak power generation depends on the induced pressure at the impact. During the separation phase, the air breakdown between triboelectric layers allows most existing electrons to flow back from the ground due to rapid charge removal at the interface. A higher voltage can be generated when the PET is interfaced with the double-sided tape compared to the Al-acrylic configuration because of the effect of triboelectric series and a Schottky barrier formation for electrons at the tape-Al interface during contact. A double-electrode configuration with an assembly of Al/PET-tape-PET/Al significantly improved the performance, in which a 21.2 mW peak power is achieved compared to 7.6 mW in the single-electrode design with tape-PET/Al assembly when excited at 20 Hz in a shaker test. This double-electrode triboelectric generator can power 476 LEDs with an active area of 38 mm × 25 mm. Moreover, a direct power of a 650 nm laser diode was demonstrated. In summary, the proposed triboelectric generator concept using tacky materials shows the potential for higher-energy harvesting via triboelectrification and advances the state of the art by offering low cost and easy fabrication options. It is expected that such newly proposed triboelectric generators are able to meet power requirements in many engineering applications.

Human Comfort Assessment of Vibration Behaviour of Office Floors: Before and After Strengthening Using the Laminated Elastomeric Bearing

Vibration issues of floor areas in relation to human comfort perception in an open working space are very common. This paper discusses the results of a human comfort assessment before and after strengthening of a a post-tensioned reinforced concrete flooring structure. All floors experience structural vibration, which arises from various sources inside and outside of the building. This paper investigated the vibration issue of a problematic flooring slab area on Level 3 of a four storey building, which vibrations induced by people walking through the working station area. Two types of tests were conducted, namely a (1) shaker test and a (2) walking test. Accelerometers were attached to the floor according tothe sensor points and recorded all acceleration responses on the floor system. The highly sensitive KS 48C accelerometer was used in this study. The accelerometers were placed at the same locations for both shaker and walking tests. The floor slab which was initially reported as problematic structure on Level 3 was found that its peak acceleration exceeded the recommended human comfort limitation. A passive vibration isolation technique was used in order to tackle the vibration issue. A laminated elastomeric bearing was chosen as one of the methods in passive vibration isolation. The natural frequency for both results before and after strengthening remained as low-frequency floor classes. However, peak acceleration excitation was reduced after the strengthening work was completed.

Design, Development, and Validation of a Whole-Body Vibration Measurement Device

Abstract Measurements of whole-body vibration are fundamental to access and evaluate comfort levels and possible injury development in the human being. International standards such as ISO 2631 and ISO 10326 are dedicated to the measurement and validation of mechanical systems to access vibration levels. Nowadays, the traditional measurement devices require multiple components and so hence become highly bulky, do not allow autonomous data recording, and are expensive. Following the previously mentioned standards, the present research is focused on the design and validation of a new and economic whole-body vibration measurement device. The developed device, besides being capable to measure the whole-body vibration, allows the user to select multiple sample ratings, is capable to record data on a µSD card, is easily moved and adapted, and is autonomous and low cost. This device is composed of three main components: a tri-axial accelerometer, a protective metal case, and semi-rigid rubber disc. Shaker tests were conducted to evaluate the measurement capability of the whole system and the influence of each component on the vibration measurements. This article will introduce the design and development steps for the proposed system. Concerning the validation phase, its results will be discussed and analyzed.

Vibration response of glass fiber composite multi-layer graded corrugated sandwich panels

Based on the criteria of equal total height and relative density, a series of glass fiber composite multi-layer graded corrugated sandwich panels (MLGCSPs) with different configurations is designed and fabricated by an in-house hot-molding secondary molding method. The effects of arrangement modes, graded corrugated cores and corrugated topologies on the vibration behavior of the present MLGCSPs are comprehensively investigated by the vibration shaker tests. The results reveal that the arrangement modes, graded arrangement and topologies of the corrugated cores all have significant influences on the frequency responses, and vibration reduction of the present MLGCSPs. The arrangement mode II and III generally have significantly higher resonant frequencies and vibration attenuation performance in the low frequency range, but the arrangement mode I shows better vibration reduction and isolation performance in the higher frequency range. It is possible to simultaneously achieve higher fundamental frequency and lower amplitude of the structures by optimizing the arrangement mode and gradient configuration. Subsequently, finite element simulation is carried out to systematically analyze the vibration responses of the composite MLGCSPs with different configurations. The consistency between numerical and experimental results is quite well. Finally, the effects of structural parameters on the vibration characteristics of the present structures are also revealed. Some conclusions are obtained, which can provide some meaningful guidelines for the vibration reduction design of such type of multi-layer structures.

Forced response with shaker test and analytical approach using mode equivalent factors on a coupled catalyst muffler system

Dynamic behavior is a key factor for preventing fatigue failures of a structure or system. With fundamental specimens of simple cantilevered structures, the basic calculation methodology using equivalent factors of vibration mode was proposed and verified. With a rigid installation under bolt fastening, the vibration transmissibility of a coupled catalyst muffler system connecting in parallel was examined through a shaker system. The resonance peaks of the first, second translational modes, and the rotation mode of two units were identified in three excitations. A lumped-parameter model was built using the six-element and two mass points for modeling the muffler system. The dynamic parameters were analyzed, and their coupled vibration transmissibilities were calculated with the equivalent factors of mode. The calculated curves were in excellent agreement with the experimental curves, and the characteristic parameters were identified. When the spring and damping coefficients of the connecting pipe in the specimen were changed, the resonance frequencies and transmissibilities changed accordingly by calculation. This approach is appropriate to be used as a prediction method for vibration control and optimization including interactions and damping in a system with complicated components in engineering applications.

Modeling Rig Dynamics to Determine Dynamics of GTE Elements’ Performance under Shaker Conditions

During shaker tests to determine the strength properties of the test article, it can be difficult to shake the article to the required in the concentrator stresses. This may be due to the losses of the force transmitted from the shaker to the test article, which occur due to an improperly designed rig. Using some methods for rig designing, along with numerical modeling, provides the possibility to make an easy-to-excite rig with minimum loss of transmitted forces. This paper deals with the modeling of the “article – rig – shaker” system executing constrained oscillations under the influence of harmonic excitation. The model’s response dependencies on dynamic excitation caused by the oscillation frequency have been outlined. The excitation level’s influence on the dynamic parameters of the model have been analyzed.

In situ, real-time measurements of contact pressure internal to jointed interfaces during dynamic excitation of an assembled structure

Despite the ubiquitousness of jointed structures, the nonlinear interfacial behavior within bolted joints is still an insufficiently studied and poorly understood environment. For the development of effective simulation approaches, a deeper understanding of the salient physical effects within the contact surface is needed. This work studies the interfacial pressure distribution and pressure changes during static and dynamic loading within the contact interface of a bolted structure. An electronic pressure sensor is placed in the interface plane. After analyzing to what extent the system’s nonlinear stiffness and normal kinematics are changed by the measurement equipment, real-time measurements of the contact pressure are made for both impact hammer and sinusoidal shaker testing (both swept sine and steady-state excitations). The measurements invalidate many commonly held assumptions for contact models that were based on observations from static pressure films.