Modal Testing Research Articles

Experimental and Theoretical Studies on the Vibration Serviceability of Composite HCS Floors with RC Topping

Composite hollow–core slab floor with reinforced concrete topping (i.e. CHFT) is relatively new, which can be applied to various long-span structures. However, these systems are typically lightweight and exhibit low damping, posing potential serviceability concerns related to human vibrations. This paper presents a comprehensive vibration test on a 9[Formula: see text]m-long CHFT system. Natural frequencies, damping ratios, and mode shapes of the floor system were obtained through modal tests. The peak acceleration, root–mean–square acceleration, maximum transient vibration value, and perception factor of the floor under heel-drop excitation were obtained through the perceived vibration test and were checked against the available design codes and standards. Sensitivity studies using the finite element method were made to investigate the vibration performance of the CHFT system. Analytical formulas for the fundamental frequency and peak acceleration were derived, which are therefore suggested for practical use. Additionally, an approach for evaluating the vibration serviceability of CHFTs is described.

Investigation on chatter stability of thin-walled parts milling considering the effects of fixture support force and tool position

The chatter stability of thin-walled parts milling has garnered widespread attention in recent years, leading to numerous important findings. However, the effects of tool position and the fixture support force applied to the workpiece on the chatter stability have yet to be adequately studied. Therefore, this paper aims to explore the mechanisms by which these two factors affect the chatter stability of thin-walled parts milling. First, based on the structural characteristics of the milling system, a three-degree-of-freedom dynamic model for thin-walled parts milling is developed. Subsequently, modal impact tests are conducted to obtain the dynamic parameters under different fixture support forces and tool positions, and the evolution of these dynamic parameters under different fixture support forces and tool positions is explored in depth. Next, the semi-discrete method is employed to solve the dynamic model, analyzing the effects of fixture support force and tool position on the chatter stability of thin-walled parts milling. Finally, milling experiments are carried out to validate the accuracy of the model. The experimental results indicate that the stability prediction results from the established dynamic model are in agreement with the experimental results, demonstrating its effectiveness in assessing the chatter stability of thin-walled parts milling.

Modal analysis of key components of crusher based on digital simulation technology

The modal characteristics of the crusher rotor and shell constitute the crucial factors influencing vibration and noise. Based on the principle of simplification, the rotor component model was established. Through mesh optimization, the model accuracy and calculation efficiency can be ensured, and the calculation of natural frequency and modal shapes was completed based on ANSYS. To verify the accuracy of the finite element model, the modal test was carried out by the hammering method. Sensors were set in three different directions to obtain the frequency response function and the modal assurance criterion matrix mode confidence criterion. Using the same research method, the modal characteristics of the shell model were simulated and analyzed. The research results show that the modal parameters identified by the modal test are basically consistent with the simulation model. The natural frequencies of the rotor and the shell are quite different from the excitation frequency of the motor, and resonance problems will not occur when the crusher is proper functioning.

Analysis of vibration characteristics of ship propeller spindle

In order to obtain the vibration response characteristics of the propeller spindle system effectively and accurately, and provide the basis for the subsequent fault diagnosis, the modal simulation and test of the spindle model were carried out. With the propeller set as eccentric mass, the amplitude and torsion angle of the spindle model were simulated under the condition of excited vibration and unexcited vibration respectively, and the frequency response of bending and torsion under the coupled condition was obtained. The newmark-β method was used to solve the transient response of the bent-torsional coupling model. The results shows that when the propeller spindle system undergoes rotation at a specific frequency and experiences bending vibration excitation force, the latter will induce torsional vibration response. Moreover, the amplitude of the torsional vibration response varies with changes in the frequency of the bending vibration excitation force.

The link between digital gaming and creativity: a meta analysis

ABSTRACT This study explored the relationship between digital gaming and creativity by conducting a meta-analysis of effect sizes using data from 78 effect sizes in 19 studies encompassing 3,172 samples. We employed a two-level multivariate model with a robust variance estimator and conducted separate analyses for between-subject and within-subject designs. For the between-subject designs, the mean effect size was r = .109, 95% [−0.036, 0.249], indicating non-significance. We conducted moderator analyses to explore potential sources of variation in the observed effects, including creativity test modality, creativity test type, divergent thinking index, analytical approach, age, gender, and year of publication. None of the examined moderators were found to be statistically significant. In contrast, we observed a significant mean effect size for within-subject designs based on 29 effects from seven studies (r = .772, 95% CI [0.595, 0.878]). Variation in mean effects by study design warrants caution when making inferences about the impact of digital gaming on creativity. The implications and limitations of the findings are discussed.

A design method of large-scale partial similar model test for cementing casing string system

When the cementing casing string system (CCSS) is subjected to a large-scale equal-scale model test, the huge aspect ratio of the system makes the wall thickness of the model casing string too thin to be manufactured. Therefore, this paper proposes a design method for model test with unequal scale of axial size and radial size of the CCSS. Firstly, the dynamic model of the CCSS is established and solved by the transfer matrix method (TMM), and the modal test is carried out and the results show that the numerical calculation error of the first five natural frequencies of the system is less than 4 %. Then, based on the dynamic model, the similarity laws of the complete similarity model and the partial similarity model of the CCSS are derived by equation analysis method, and the design process of the similarity model test is given. The advantages of the research are elaborated in details through examples. To verify the correctness of the similarity model’s similarity laws of the CCSS, similarity models with different parameters are designed, and the prediction errors of prototype response are analyzed based on numerical calculations. The results show that the maximum prediction error of the first eight natural frequencies of the prototype system is less than 3 %, and the response prediction results of the system are also accurate. Finally, considering uncertain factors of the partial similarity test, the similarity model test with the axial size of double scale is designed, and the results show that the maximum prediction error of the first three natural frequencies is 7.06 %, which meets the engineering requirements. This study can provide useful theoretical guidance for the large-scale model test design of the CCSS.

Development of planar 9-DOF dynamic model with small damping and natural characteristics sensitivity analysis for a double-deck vibrating flip-flow screen

The current double-deck vibrating flip-flow screen (DDVFFS) exhibits swing motion due to an unreasonable structural design, which compromises vibration stability and impacts screen frame displacement response. Therefore, it is essential to investigate the dynamic characteristics of the DDVFFS. For this reason, a 9-degree-of-freedom (DOF) dynamic model of the DDVFFS is established, and a corresponding testbed for the DDVFFS is designed. A sensitivity analysis is conducted to examine the impact of design parameters on the natural frequency and vibration mode, thereby serving as valuable guidance for the design of DDVFFS. The damping matrix in the dynamic model is determined through modal testing, while the displacement response of the testbed is obtained by solving the dynamic model. The test results from the vibration testbed demonstrate that the actual amplitude of each sieve frame closely matches the theoretical amplitude.

Development of linear bearing equipment for modal testing of low-frequency weakly damped spacecraft structures

This article presents the results of a study of the bearing capacity and dissipative properties of an aerostatic linear bearing developed at JSC RESHETNEV for modal testing of complex structures. When selecting equipment for modal testing, the main condition is the requirement to minimize the distortions introduced into the determined dynamic characteristics: frequencies of natural vibration modes, the vibration modes themselves, as well as modal masses and damping coefficients. In other words, all equipment used for ground-based modal testing should ideally have zero added mass, stiffness and friction. The main systems containing elements that create dissipative forces that affect the determination of damping coefficients are systems for weight compensation and vibration excitation on natural modes. The weight compensation system usually contains either elastic elements or a system of guides with rolling or sliding bearings. If the former bring additional rigidity and mass to the test object, the latter bring mass and friction (dry or viscous), which increases the error in determining the dynamic characteristics. The excitation of vibrations on natural modes, in most cases, is carried out by electrodynamic vibrators consisting of a magnetization coil (or permanent magnet) and a movable coil moving in a magnetic gap. The movable coil is oriented in the magnetic gap using a special system containing either elastic elements or a linear guide bearing. Vibrators with elastic coil suspension elements cannot be used for modal tests of extended structures with low rigidity. The problem of creating an ideal bearing to replace classic linear (sliding or roller) ones arose during preparation for modal tests of the wing of a solar battery of a spacecraft (SC). Aerostatic bearings (supports) have virtually zero friction and sufficient load-bearing capacity, in which compressed air acts as a lubricant, eliminating physical contacts of the interacting surfaces. To confirm the possibility of using aerostatic bearings in equipment for conducting modal tests of extended structures with low frequencies of natural oscillations, comparative tests of a roller and aerostatic bearing were carried out. During the tests, optimal air flow parameters (nozzle diameter, operating pressure and gap) were selected, which ensure the required load-bearing capacity for radial forces and torques (bending and torsion). A comparative assessment of dissipative properties was carried out when measuring the attenuation parameters of single-mass harmonic oscillators, which include aerostatic and roller linear bearings. With a nozzle diameter of 0.6 mm, a working gap of 40 μm and a bearing input pressure of 1.0 bar, the logarithmic decrement of oscillations of the harmonic oscillator with an aerostatic bearing was 0.084, which is more than 28 times lower than the logarithmic decrement of oscillations of an oscillator with a roller bearing. The conducted studies confirmed the possibility of using the developed aerostatic bearing in test systems used in modal tests of large-sized transformable spacecraft structures.

Research on flow-induced radiated noise of twin-screw pumps based on the Lighthill acoustic analogue theory

Abstract To optimize the control of twin-screw pumps (TSP), it is essential to ensure performance while simultaneously preventing noise levels from exceeding specified limits. In order to investigate the flow characteristics and the mechanism of flow-induced radiated noise under various operating conditions, a coupled numerical simulation approach using Computational Fluid Dynamics (CFD) and Computational Acoustics (CA) was employed, and the findings were validated through experiments. The study reveals that the highest sound pressure levels of radiated noise occur near the rotor outlet surface, and the dynamic-static interference at the rotor-boundary interface is the primary cause of flow-induced noise in TSP. The flow-induced noise in TSP exhibits dipole characteristics, with the overall sound pressure level gradually increasing and then sharply rising with the increase in rotational speed (or flow rate). It stabilizes near the design operating point and continues to increase steadily with further increases in rotational speed (or flow rate). Modal testing using a dual-distributed measurement technique highlights significant interference effects between the rotor inlet and the dynamic rotor for the first two Blade Passing Frequencies (BPF) in TSP. The results of this study provide a theoretical foundation for the low-vibration and low-noise design and operation of TSP.

Static and Dynamic Stress of the Combined Rotor with Curvic Couplings Considering the Rough Three-Dimensional Interface at Extreme Operating Conditions

The curvic coupling, as one of the common connecting structures for gas turbine combined rotors, is more susceptible to various dynamic and static loads at extreme operating conditions. But, traditional combined rotor models tend to neglect the influence of the connection structure, especially failing to consider the contribution of the curvic coupling interfaces. To address this problem, this paper establishes a solid geometric model of the combined rotor with curvic couplings considering the rough three-dimensional interfaces. The effectiveness of the proposed model method is indirectly verified through the compression tests and modal tests. Subsequently, combined with finite element calculations, the mechanical properties of the rotor with curvic couplings considering the rough interface are analyzed under static and dynamic load conditions. The results indicate that the roughness of the interface significantly affects the deformation of the contact surface under static load, but its impact on the overall deformation of the rotor is relatively insignificant. The dynamic stress at the interface exhibits periodic variations at the resonance speed. At the maximum operating speed, the dynamic stress is influenced by the magnitude of imbalance. The aforementioned methods and conclusions provide a reference for the design research and engineering application of combined rotors.

Vibration modal analysis of adaptive grinding and polishing tools

Abstract Adaptive grinding and polishing tools have a compact structure, fast response, and stable performance, and they can improve the efficiency of polishing and grinding large welded parts. The vibration frequency of the AGP600 adaptive grinding and polishing tool is abnormal after switching from the blade grinding head to the nylon grinding head, and the vibration is noticeable when the rotational speed is more significant than 4, 000 r/min, which seriously affects the quality of grinding. To analyze the cause of its vibration, this paper adopts HyperWorks to analyze the modal frequency of AGP600, carries out the vibration modal test, and analyses the reasons for the different vibration harmonic frequencies of AGP600. Finally, improvement measures for AGP600 are proposed, through which the vibration of AGP600 grinding tools can be reduced.

Development and testing of a novel vibratory compaction instrument considering its natural frequency.

This study aims to develop a novel vibratory compaction instrument designed for the preparation of large triaxial soil specimens, offering an efficient alternative to the traditional manual specimen preparation process. However, when the motor frequency closely aligns with the natural frequency of the structure, severe resonance phenomena may occur. This paper employed finite element modal analysis, experimental modal analysis, and operational modal analysis techniques to conduct a multi-objective optimization of the structure, aiming to improve the dynamic characteristics. First, the natural frequency and mode shapes of the vibratory compaction instrument were determined via finite element technology. Subsequently, the optimization of this instrument was conducted by integrating the Kriging surrogate model with the Non-dominated Sorting Genetic Algorithm II (NSGA-II). Finally, the steel column underwent a modal test using impulse stimulation to ascertain its natural frequency, and the stochastic subspace identification (SSI) approach was employed to conduct an operational modal analysis of the vibratory compaction instrument to determine its modal characteristics. The experimental findings corroborated the conclusions obtained from the finite element analysis, validating the precision of the finite element modal analysis and the rationality of the optimized structure. The research results are of significant importance for improving the preparation efficiency of large triaxial specimen, contributing to advancements in soil mechanics testing.

Design and Experimental Research of a Non-Destructive Detection Device for High-Precision Cylindrical Roller Dynamic Unbalance

Due to their small size and light mass, small precision cylindrical rollers present challenges in dynamic unbalance detection, including difficulties in measurement and the risk of surface damage. This paper proposes a non-destructive detection device for assessing the dynamic unbalance of small precision cylindrical rollers. The device utilizes an air flotation support method combined with resonance amplification to indirectly measure the dynamic unbalance. A dynamic model of the air flotation tooling-cylindrical roller vibration system was developed to explore the relationship between the vibration parameters of the air flotation tooling and the dynamic unbalance of the cylindrical roller. Modal analysis and harmonic response analysis were performed, revealing that the amplitude of the vibration system at resonance could be detected using the sensor. Additionally, modal testing was conducted to determine the natural frequency of the system. A non-destructive detection platform was constructed for testing the dynamic unbalance of cylindrical rollers. Microscopic observation of the roller surface before and after testing confirmed that the device successfully performs non-destructive detection of dynamic unbalance.

Modal parameters and damage evaluation of steel fiber reinforced concrete under flexural cyclic loadings

Structures may be subjected to static and dynamic loads during their service life. When it comes to the dynamic spectrum, wind action, ocean waves and seismic loads are key examples and are responsible for cracking evolution and material degradation along their lifespan. Therefore, the fatigue behavior of cementitious materials has been receiving great attention due to cyclic loading that can be of natural occurrence or induced by human activity lately. The present research aims to investigate the evolution of the modal parameters of steel fiber reinforced concretes under flexural cyclic load and to evaluate how the mechanical degradation can be monitored from a non-destructive impact modal testing over the cycles. The dynamic properties of the material, including natural frequencies, vibration modes and damping ratios, were tracked to assess the level of fatigue damage using modal testing techniques. Hence, it was possible to evaluate the material mechanical degradation as a function of the dynamic parameters. From the dynamic test, it was possible to evaluate the presence of damage, which was corroborated by the observed stiffness degradation. The first flexural mode and the following second, third and sixth vibration modes were more affected along the cycles. Finally, the proposed non-destructive methodology was effective in assessing the mechanical decay of cementitious composites.

Experimental and computational investigations of flexible membrane nano rotors in hover

With reduced size, the flight Reynolds number of the nano rotor decreases, leading to a sharp drop in the aerodynamic efficiency of the nano rotor. Therefore, improving the aerodynamic performance of the nano rotor at low Reynolds numbers through flow control methods becomes imperative. In this study, from the perspective of bionics, flexible materials are employed in nano rotor design. Seven different layouts of flexible membrane rotor blades are designed and fabricated. The influence of leading and trailing edge flexibility, as well as membrane occupancy ratio on rotor blade propulsion characteristics, is explored through propulsion performance tests in hover.Results show that among several layouts proposed in this study, the layout with both reinforced leading and trailing edges of the flexible membrane nano rotor blade exhibits excellent propulsive performance. However, the propulsion performance of the flexible membrane rotors doesn't vary linearly with the ratio of membrane area to the whole rotor area. The appropriate ratio or flexibility can increase the propulsive performance of the rotor, especially at medium and high collective angles. At 7000 RPM and a 20° collective angle, the Figure of Merit of the flexible membrane nano rotor increases up to 4.2% when comparing with the nano rotor without membrane. This improvement becomes more significant with higher collective angles. The structural natural vibration characteristics of each flexible membrane with different layouts are analyzed through modal tests, ensuring the accuracy of the finite element model for flexible membrane rotors. Numerical analysis of the fluid-structure coupling of a flexible membrane rotor with different layouts indicates that rotor structural vibrations is highly consistent with fluctuation of aerodynamic parameters. The deformation of the flexible membrane under aerodynamic forces enhances local blade camber, but reduces angles of attack. This, subsequently, minimizes the size of laminar separation bubbles and the intensity of the blade tip vortices at high collective angles. Consequently, rotor power coefficients decrease, and overall aerodynamic performance improves.

Characterization of inter-panel connections in CLT floors using finite element model updating

Large cross-laminated timber (CLT) floors are inevitably composed of multiple CLT panels assembled on the construction site. Due to the sheer lack of adequate numerical characterization of the inter-panel connections, CLT floors are normally modelled as monolithic structures or independent “piano keyboards”, yielding errors between simulated and the actual vibration response. This paper presents a benchmark study for a deterministic finite element (FE) model updating of so called “an equivalent elastic strip” representation of the inter-panel connections. Fitting modelling parameters of the strip, i.e. its width and material properties, featured FE modelling and modal testing of two full-scale CLT floors composed of one and two panels connected with a half-lapped joint. The floors were made of (almost) identical panels and placed on elastic mats along their shorter edges. First, the single-panel floor was used to fit material properties of the timber and the boundary conditions. Then, the FE model updating (FEMU) of two-panel floor yielded the actual values of the strip modelling parameters. Finally, these were successfully verified by direct comparison between numerically calculated and experimentally measured modal properties of a full-scale model of a simply supported three-panel floor. The results implied that the rotational stiffness of the inter-panel connection depends strongly on its vertical vibration displacement. Consequently, values of the rotational stiffness derived from rare static tests published so far cannot be used reliably in a much subtler vibration response analysis. Future studies should feature other types of the inter-panel connections in various floor layouts and a probabilistic FEMU.

Opportunities for Microphysiological Systems in Toxicity Testing of New Drug Modalities.

New drug modalities offer life-saving benefits for patients through access to previously undruggable targets. Yet these modalities pose a challenge for the pharmaceutical industry, as side effects are complex, unpredictable, and often uniquely human. With animal studies having limited predictive value due to translatability challenges, the pharmaceutical industry seeks out new approach methodologies. Microphysiological systems (MPS) offer important features that enable complex toxicological processes to be modeled in vitro such as (a) an adjustable complexity of cellular components, including immune components; (b) a modifiable tissue architecture; (c) integration and monitoring of dynamic mechanisms; and (d) a multiorgan connection. Here we review MPS studies in the context of four clinical adverse events triggered by new drug modalities: peripheral neuropathy, thrombocytopenia, immune-mediated hepatotoxicity, and cytokine release syndrome. We conclude that while the use of MPS for testing new drug modality-induced toxicities is still in its infancy, we see strong potential going forward.

Experimentally Aided Operational Virtual Prototyping to Predict Best Clamping Conditions for Face Milling of Large-Size Structures

Vibrations occurring during milling operations are one of the main issues disturbing the pursuit of better efficiency of milling operations and product quality. Even in the case of a stable cutting process, vibration reduction is still an important goal. One of the possible solutions to obtain it is selection of the favorable conditions for clamping the workpiece to the machine table. In this paper, a method for predicting and selecting the clamping condition of a large-size workpiece for the reduction in vibrations during milling is presented. A modal test of the workpiece is performed first for a selected set of tightening screw settings. Next, one milling pass is performed to obtain reference data which are then used to tune the hybrid computational model. In the subsequent step, milling simulations are performed for a set of tightening variants, and the best one is selected, providing the lowest vibrations, assessed as the root mean square (RMS) of vibration displacements. In this paper, the description of the clamping selection procedure, key elements of the simulation model, and simulation and experimental results obtained for the milling of the test workpiece performed for a set of different clamping conditions are provided. The proposed method accurately predicts not only the best but also the worst clamping conditions.

Innovative Structural Optimization and Dynamic Performance Enhancement of High-Precision Five-Axis Machine Tools

To satisfy the requirements of five-axis processing quality, this article improves and optimizes the machine tool structure design to produce improved dynamic characteristics. This study focuses on the investigation of five-axis machine tools’ static and dynamic stiffness as well as structural integrity. We also include performance optimization and experimental verification. We use the finite element approach as a structural analysis tool to evaluate and compare the individual parts of the machine created in this study, primarily the saddle, slide table, column, spindle head, and worktable. We discuss the precision of the machine tool model and relative space distortion at each location. To meet the requirements of the actual machine, we optimize the structure of the five-axis machine tool based on the parameters and boundary conditions of each component. The machine’s weight was 15% less than in the original design model, the material it was subjected to was not strained, and the area of the structure where the force was considerably deformed was strengthened. We evaluate the AM machine’s impact resistance to compare the vibrational deformation observed in real time with the analytical findings. During modal analysis, all the order of frequencies were determined to be 97.5, 110.4, 115.6, and 129.6 Hz. The modal test yielded the following orders of frequencies: 104, 118, 125, and 133 Hz. Based on the analytical results, the top three order error percentages are +6.6%, +6.8%, +8.1%, and +2.6%. In ME’scope, the findings of the modal test were compared with the modal assurance criteria (MAC) analysis. According to the static stiffness analysis’s findings, the main shaft and screw have quite substantial major deformations, with a maximum deformation of 33.2 µm. Force flow explore provides the relative deformation amount of 26.98 µm from the rotating base (C) to the tool base, when a force of 1000 N is applied in the X-axis direction, which is more than other relative deformation amounts. We also performed cutting transient analysis, cutting spectrum analysis, steady-state thermal analysis, and analysis of different locations of the machine tool. All of these improvements may effectively increase the stiffness of the machine structure as well improve the machine’s dynamic characteristics and increases its machining accuracy. The topology optimization method checks how the saddle affects the machine’s stability and accuracy. This research will boost smart manufacturing in the machine tool sector, leading to notable advantages and technical innovations.

Localized rail third-order bending mode causes high-order polygonization of high-speed train wheels

The formation mechanism of high-order (mainly 18 ∼ 23) polygonization of high-speed train wheels has been debated for over a decade. Currently, researchers believe that the mechanisms leading to the high-order polygonization of high-speed train wheels mainly include: (A) vibration of bogie components, (B) self-excited vibration of wheel-rail friction, (C) third-order bending (B3) modal vibration of a segment of localized rail constrained by a bogie, etc. Of these, mechanism C was previously proposed by our team and has been insisted on until now, although it is highly controversial. To further prove the plausibility of mechanism C, through rail modal tests, vehicle tracking tests, and dynamics simulation analyses, this paper systematically proves that (1) the rail B3 mode can induce resonance of the wheel-rail system, which is the fundamental factor causing the high-order polygonization of high-speed train wheels, and (2) there is no significant frequency shift between the vibration frequency of the excited rail B3 mode and the passing frequency of the formed polygonal wheel, with an extreme difference being less than the wheel rotation frequency.