Modal Testing Research Articles

Development of a Deployable Reflector Antenna for the Synthetic Aperture Radar Satellite, Part 2: Manufacturing and Qualification of the Main Reflector Using a Honeycomb Sandwich Composite Structure

A deployable reflector antenna (DR-A) is a structure that can be stored in a large-diameter Synthetic Aperture Radar (SAR) antenna and be mounted onto a launch vehicle. Considering the performance of the launch vehicle, it is necessary to develop a lightweight, high-performance antenna structure. The solid-type deployable reflector antenna is composed of a number of unit main reflectors. To reduce the weight of the antenna, a lightweight main reflector must be developed. In this paper, following “Development of Deployable Reflector Antenna for the SAR Satellite (Part 1)”, the manufacturing and qualification of the main reflector using honeycomb sandwich composites are described. Four types of composite main reflectors were manufactured with variables in the manufacturing process. The manufacturing variables include the curing process of the structure, the application of an adhesive film between the sheet and the core, and the venting path inside of the sandwich core. After manufacturing the main reflector, we performed weight measurements, non-destructive testing (NDT), surface error measurement using a Coordinate Measurement Machine (CMM), and modal testing for each type of composite main reflector. Through the research and development process, we found that a perforated hole is necessary when excluding the adhesive film during bonding of an aramid core and a CFRP sheet, and a lightweight composite reflector could be developed through this process. We selected the main reflector with the best performance and developed a composite main reflector that can be applied to satellites.

A scaled derivative-based DMDc method for modelling multiple-input multiple-output mechanical systems

Dynamic mode decomposition with control (DMDc) is a powerful data-driven method for modelling dynamical systems with inputs and outputs. However, the inability to identify oscillations and the high sensitivity to noise limit the application of standard DMDc in structural dynamics. To address this challenge, this paper proposes a novel method called scaled derivative-based DMDc (sd-DMDc) to construct a discrete state-space model for mechanical systems using noisy data. This method requires only the displacement and excitation data, computes the scaled derivatives of displacement to extend the system states, and integrates the extended forward-backward strategy. Two crucial parameters are defined and optimized by minimizing the response error. The sd-DMDc algorithm is first verified through numerical simulations of a multiple-input multiple-output (MIMO) cantilever plate. The results indicate that sd-DMDc exhibits superior modelling accuracy across various noise levels and measurement points compared to the delay-DMDc method. It has also been proved that sd-DMDc can accurately identify dynamical systems from partial observations. Subsequently, vibration experiments are conducted on a MIMO cantilever plate. The sd-DMDc method is further verified using experimental data, and the conclusions align with those drawn from simulation studies. The sd-DMDc algorithm demonstrates great modelling accuracy, surpassing that of delay-DMDc, especially for partial observations. In addition, the model given by sd-DMDc can extract the modal parameters of the plate, which are consistent with the modal test results.

Relationship Between Severity of Ischemia and Coronary Artery Disease for Different Stress Test Modalities in the ISCHEMIA Trial

BACKGROUND: The relationship between the extent and severity of stress-induced ischemia and the extent and severity of anatomic coronary artery disease (CAD) in patients with obstructive CAD is multifactorial and includes the intensity of stress achieved, type of testing used, presence and extent of prior infarction, collateral blood flow, plaque characteristics, microvascular disease, coronary vasomotor tone, and genetic factors. Among chronic coronary disease participants with site-determined moderate or severe ischemia, we investigated associations between ischemia severity on stress testing and the extent of CAD on coronary computed tomography angiography. METHODS: Clinically indicated stress testing included nuclear imaging, echocardiography, cardiac magnetic resonance imaging, or nonimaging exercise tolerance test. Among those with preserved renal function who underwent coronary computed tomography angiography, we examined relationships between ischemia and CAD by coronary computed tomography angiography, overall, and by stress test modality, regardless of subsequent randomization. Core laboratories categorized ischemia as severe, moderate, mild, or none, while the extent and severity of anatomic CAD were categorized based on the modified Duke prognostic index. RESULTS: Among 3601 participants with interpretable stress tests and coronary computed tomography angiography, ischemia severity was weakly associated with CAD extent/severity (r=0.27), with modest variability in strength of association by modality: nuclear (n=1532; r=0.40), echocardiography (n=827; r=0.15), cardiac magnetic resonance imaging (n=108; r=0.31), and exercise tolerance test (n=1134; r=0.18). The extent of infarction on nuclear imaging and echocardiography was weakly associated with CAD extent/severity. CONCLUSIONS: Overall, ischemia severity on stress testing showed weak to moderate associations with the anatomic extent of CAD in this cohort with moderate or severe ischemia on local interpretation and controlled symptoms. REGISTRATION: URL: https://www.clinicaltrials.gov ; Unique identifier: NCT01471522.

The Question of Thermoelectric Devices (TEDs) In/Efficiency—A Practical Investigation Considering Thermoelectric Heaters (TEHs)

ABSTRACTThermoelectricity is a promising technology; however, though clean and versatile, its efficiency has been questionable and consequently limiting its extensive utilization. Many published research on thermoelectricity have been on power generation and cooling applications, with few publications on heating, especially practically. Thus, this article practically focuses on thermoelectric devices (TEDs) when used as thermoelectric heaters (TEHs). Sixteen identical TEDs (TEC‐12706) were operated as TEHs under similar test modalities and powered in succession with 12, 10, 8, 6, and 4 V, to practically examine TEHs energy dynamics and in/efficiency. It was found that all the TEHs used in the research performed relatively inconsistent with each other with the worst‐performed TEH (TEH0) having a mean hot‐side temperature of 30.276°C with a mean power consumption of 13.826 W; whereas the best‐performed TEH (TEH3) had a mean hot‐side temperature of 40.4°C with a mean power consumption of 20.822 W. Furthermore, all the TEHs hot‐side temperature increased proportionately with the input voltage; though at the specified voltages, the TEHs hot‐side temperature increased while its input power decreased over time. The concepts of TEH hot‐side mean temperature and TEH mean input power were also introduced.

Free vibration optimization of 2D tri-axial braided composite fan blade with ANN-Anal-FEM-GA integrated model

This research aimed to increase the natural frequencies of a non-rotating 2D tri-axial braided composite (2DTBC) fan blade. The investigation utilized a multidisciplinary approach, integrating Artificial Neural Network (ANN) modeling, analytical method, Finite Element (FE) analysis, optimization techniques, and experimental validation. The ANN captured the complex relationship between the braiding machine and structure parameters. The mechanical properties of the 2DTBC were determined through the micromechanical modeling, and the thin-shell analysis was applied to describe the blade’s displacement and strain characteristics. Micromechanical modeling examines material behavior at the microscopic level, and thin shell analysis focuses on modeling and analyzing thin, curved structures using simplified equations. The FE method facilitated the formulation of the equation of motion and the calculation of natural frequencies. A genetic algorithm, focused on a single-objective optimization, was employed to refine the braiding structure parameters and the number of composite layers, thereby enhancing the blade’s natural frequencies. The optimized 2DTBC blade was subsequently fabricated and validated through impact hammer modal testing, showing strong agreement with the predictions from the combined ANN-analytical-FEM-GA model. The optimization of the braiding parameters led to a significant increase in the blade’s natural frequencies.

Directional DIC method with automatic feature selection

Using displacement identification via high-speed cameras is a non-contact, full-field technique for characterizing the dynamic properties of engineered structures. Achieving reliable measurements of structural deformation through conventional Digital Image Correlation (DIC) requires a well-defined spatial gradient in two orthogonal directions within an image subset of pixels. However, DIC is susceptible to the aperture problem, which leads to an ill-conditioned optimization problem. An example of such a case is cable systems on which no speckle patterns can be applied. This study proposes Directional DIC (D-DIC) as an alternative technique to overcome the limitations posed by the aperture problem in conventional DIC methods. Directional DIC assumes the local direction of motion, which is often a valid assumption in structural vibration tests, as individual vibration shapes are often unidirectional at localized parts of the structure. This alleviates some restrictions on trackable image subsets, enabling more trackable locations. A parameter for quantifying expected tracking performance for D-DIC is introduced. The parameter enables automatic feature selection for D-DIC, making optical methods more accessible for displacement identification on structures where no speckle patterns can be applied. Experimental modal tests are conducted using a flexible spider web-like structure to validate the D-DIC method and compare it to conventional DIC. The experimental findings show that the Directional DIC method allows for measuring displacements at significantly more locations than conventional DIC. Additionally, D-DIC provided less noisy frequency response functions, more retrieved stable poles, and more fitted vibrational modes. Lastly, the findings show that D-DIC is especially superior to DIC when using small subsets since D-DIC is less inhibited by the aperture problem.

Tailored Bioengineering and Nanomedicine Strategies for Sex-Specific Healing of Chronic Wounds.

Chronic wounds, defined by their prolonged healing process, significantly impair patient quality of life and impose a hefty financial burden on healthcare systems worldwide. Sex/gender-specific mechanisms regulate inflammation and infection, angiogenesis, matrix synthesis, and cell recruitment contribute to cutaneous wound healing, but remain largely understudied. This review is aimed to spotlight the innovative realm of bioengineering and nanomedicine, which is at the helm of revolutionizing complex chronic wound care. It underscores the significance of integrating patient sex into the development and (pre)clinical testing of these avant-garde treatment modalities, in order to enhance healing prospects for both women and men. Moreover, we explore the representation of both sexes in clinical trials of bioengineered and nanomedicine products. Finally, we examine the primary reasons for the historical neglect in translating sex-specific wound healing research into clinical practice and propose strategic solutions. By tackling these issues, the article advocates for advanced treatment frameworks that could significantly improve healing outcomes for individuals of all sexes, thereby optimizing both efficacy and inclusivity in chronic wound management.

Innovative Vibration Control of Triply Periodic Minimum Surfaces Lattice Structures: A Hybrid Approach with Constrained Layer Damping Silicone–Viscoelastic Layer Integration

This article introduces a novel method to enhance the damping performance of triply periodic minimal surface (TPMS) structures by integrating metamaterials with constrained layer damping (CLD) applications. This objective is accomplished by combining a viscoelastic silicone polymer layer with a primitive TPMS structure fabricated through laser powder bed fusion using aluminum alloy powder. Finite‐element method (FEM) models using voxel elements, due to their high accuracy and computational efficiency, are developed to analyze the damping behavior of the TPMS‐based CLD structure across various frequencies. Experimental modal test results validate the FEM model with high accuracy. Two distinct damping characterization methods, both time‐domain and frequency‐based, are employed to quantify the damping performance. The results reveal a fivefold improvement in damping performance in the time domain compared to the metal TPMS structure. In the frequency domain, the structure demonstrates 76% lower cumulative vibration compared to the metallic reference using the integral of frequency response method.

Vibration Measurement and Numerical Simulation of the Effect of Non-Structural Elements on Dynamic Properties of Large-Span Structures

Non-structural elements have been demonstrated to be essential for the dynamic performance of large-span structures. However, how to quantify their effect has not yet been fully understood. In this study, the contribution of non-structural elements to dynamic properties of large-span structures is systematically investigated via both field measurement and numerical simulation methods. Modal testing of an indoor stadium and an elevated highway bridge was conducted during different construction phases, and the corresponding modal characteristics were identified. Results show that the traditional capacity-based models are incapable of reflecting the actual dynamic characteristics of in-service structures since neglecting the effect of non-structural elements would result in remarkable discrepancies in modal properties. A general modeling framework incorporating the contribution of slab/deck pavement, infill walls (or crash barriers), and joints/connections for large-span structures is developed to quantitatively consider the effect of non-structural elements based on the principle of equivalence of stiffness and mass to the actual structure. The effectiveness of the method is validated by vibration measurement results.

Contact Stiffness Identification Method for Joint Surface and the Effect of Contact Stiffness on the Dynamic Response of the Cable Bracket

The cable bracket is one of the crucial components of high-speed Electric Multiple Units (EMUs), which is fixed to the axle box by bolts to support the cable. As an important parameter of the joint surface, contact stiffness significantly affects the dynamic response and service life of the cable bracket. However, it is difficult to directly measure the contact stiffness of the joint surface. As a result, an identification method is proposed in this investigation to identify the contact stiffness. A finite element model incorporating both normal and tangential stiffness parameters is developed. According to the finite element model and modal testing results, an improved particle swarm optimization algorithm is employed to identify the contact stiffness of the joint surface. The effect of the contact stiffness on the vibrations of the cable bracket is investigated. The findings indicate that pre-tightening torque significantly influences the contact stiffness of the cable bracket. The contact stiffness has a great effect on the vibrations of the cable bracket. Optimal contact stiffness notably reduces vibrations of the cable bracket, thereby extending its service life.

Ranked Importance of Visual Function Outcome Measures in Choroideremia Clinical Trials.

Clinical trials of novel therapies for choroideremia require robust and clinically meaningful visual function outcome measures. Best-corrected visual acuity (BCVA) is mostly insensitive to changes in disease state, until late stages, and hence also to potential therapeutic gains after gene therapies. While the insensitivity of BCVA as an effective outcome measure is common wisdom, its low importance has not been rigorously demonstrated in the literature. This work uses statistical techniques to rank the relative importance of potential functional outcome measures in choroideremia. Retrospective dominance analysis was performed on data from a longitudinal interventional clinical trial performed at the Oxford Eye Hospital. Functional data from the untreated eye were analyzed and correlated with an anatomic measure of disease progression in the form of blue fundus autofluorescence area of the surviving outer retinal island. Each functional measure was then ranked in terms of variable importance. Microperimetry was the functional measure ranking first in terms of variable importance, followed by time since baseline visit, Pelli-Robson contrast sensitivity, high spatial frequency contrast sensitivity function, and low luminance visual acuity. Early Treatment Diabetic Screening chart BCVA under standard lighting conditions was ranked lowest among the panel of test modalities. Clinical trials in choroideremia for early and mid-stage disease would be justified in moving away from using standard BCVA as a clinical trial outcome measure as we have shown its sensitivity to be relatively low compared to microperimetry. We have also demonstrated how functional measures rank in terms of importance.

Investigation on the dominant mechanism of chatter in high-load robot milling process based on theoretical and experimental analysis

Chatter has always been a key problem restricting the improvement of robotic milling quality and efficiency. To avoid chatter, it is necessary to determine what is the dominant chatter mechanism (mode coupling or regenerative) of the robot milling system. Therefore, this paper focus on the dominant chatter mechanism in high-load (600kg) robot milling. The modal test results show that the dynamic flexibility of spindle-tool structure mode in high-load robot is significantly higher than that of the body structure mode, which is significantly different from the low-load robot in other studies. The mode coupling chatter stability prediction models are established based on eigenvalue method and zeroth order approximation, and the predicted stability boundaries are compared with the experimental results. The results show that only high-frequency chatter exists in the high speed region (1000-8000rpm), and no low frequency chatter occurs. The low-frequency chatter around the robot body mode is found in the low-speed region (400-1000rpm), but the mode coupling chatter theory could not explain the chatter varies periodically with the spindle speed. However, the stability boundary predicted by the regenerative chatter theory also changes periodically with the spindle speed. This indicates that the milling chatter dominant mechanism of high load robot is regenerative chatter. This study analyzes the milling chatter dominant mechanism of high-load robot through theoretical and experimental verification, which can provide theoretical support for high-load robot milling chatter control.

Modal Testing Method for Whole-Body Vibration of Large-Mass Power Equipment

Modal Testing Method for Whole-Body Vibration of Large-Mass Power Equipment

Modal testing and analysis of high-rise laminated timber building

To enhance the design and research work on dynamic characteristics of high-rise laminated timber buildings, this paper carried out a modal analysis study on one of the largest laminated timber buildings in China. The finite element calculating modal analysis was carried out using SAP2000 software, and the experimental modal analysis of the building was carried out via environmental excitation. The calculating modal results and the experimental modal results showed good agreement. The calculating modal frequency values were generally lower than the experimental modal frequency values. The natural frequencies obtained by the two methods appeared in the Y-direction first-order bending mode and had values of 2.03 and 2.5 Hz, respectively. The corresponding frequencies of the first-order torsional mode were 2.82 and 3.25 Hz, respectively. The distribution of the CLT core tube along the length direction of the building has an impact on the vibration mode. The six-story part shows the second-order bending form, while the four-story section only shows the first-order bending form. The above work provides a case study and reference for the simulation and modal analysis of high-rise laminated timber buildings, demonstrating the critical role of the core tube structure in such wooden buildings. This insight contributes to a better understanding of structural performance and design considerations in similar projects.

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.