Vibration Loads Research Articles

Road Piezoelectric Power Output Model and Experimental Study under Bidirectional Vehicle Load Excitation

Recently, piezoelectric transducers have gained significant attention for energy recovery applications in road engineering. However, in laboratory tests, vehicle loads are often simplified using vertical vibration loads, thus ignoring the role of vehicle tangential loads. In this study, a power output model of a piezoelectric transducer under vertical and tangential loads was proposed through theoretical analysis. A bidirectional cyclic dynamic load test was conducted on the piezoelectric-concrete specimens in combination with a large dynamic and static straight shear instrument, and the power output law of the piezoelectric transducer under vertical and horizontal shear was investigated. The results revealed that the vertical vibration load was the main factor affecting the output performance of the piezoelectric transducer; however, with the addition of the tangential load, the electric energy output of piezoelectric pavement increased with an increase in the horizontal shear rate and displacement. When vibrating vertically (200 kPa and 4 Hz), the electric energy output of piezoelectric pavement was 4.979 μW. However, under the action of vertical vibration and horizontal shear with the working conditions of 200 kPa and 4 Hz, and 0.1 mm and 1 Hz, the electric energy output of piezoelectric pavement was 21.04 μW, which was 3.2 times that of the vertical vibration load alone. Therefore, by considering the influence of vehicle tangential loads, the power output of piezoelectric transducers can be calculated more accurately, which provides a reference for actual installed capacities in real engineering applications.

The cohesive zone crack analogue for incomplete contacts under mild wear conditions

Fretting fatigue may appear in mechanical components that are in contact under vibrational loading, inducing oscillatory frictional stresses, often combined with alternating bulk stresses. Fretting fatigue cracking is important, with its initiation being difficult to estimate. This work extends a well-known fretting fatigue model, the crack analogue model that examines fretting fatigue induced by incomplete contacts of metallic surfaces. This is done by inserting a mode II type cohesive zone at the contact edges. In our previous work on fretting fatigue of complete contacts, we proposed mixed mode I and II cohesive zones because of the nature of the stress fields around the contact edges. The proposed cohesive zones address several issues related to the mechanics of friction and wear, by combining them in the case of mild wear where asperity plastic shakedown is the dominant inelastic mechanism. Thus, the micromechanical behaviour of the surface topology and its evolution are naturally introduced into the analysis. The surface roughness becomes an internal variable that evolves with the cyclic loading, establishing a steady state friction coefficient. Alternatively, friction evolution can be established pointwise by monitoring the accumulated micro-slip. The work of friction dissipates the mechanical work and at the same time becomes the precursor of large scale wear. A predictive methodology for fretting crack nucleation is proposed through the fatigue threshold stress intensity factor used in ordinary fatigue.

Current situation and development trend of design methods for subgrade structure of high speed railways

PurposeThis method will become a new development trend in subgrade structure design for high speed railways.Design/methodology/approachThis paper summarizes the structural types and design methods of subgrade bed for high speed railways in China, Japan, France, Germany, the United States and other countries based on the study and analysis of existing literature and combined with the research results and practices of high speed railway subgrade engineering at home and abroad.FindingsIt is found that in foreign countries, the layered reinforced structure is generally adopted for the subgrade bed of high speed railways, and the unified double-layer or multi-layer structure is adopted for the surface layer of subgrade bed, while the simple structure is adopted in China; in foreign countries, different inspection parameters are adopted to evaluate the compaction state of fillers according to their respective understanding and practice, while in China, compaction coefficient, subsoil coefficient and dynamic deformation modulus are adopted for such evaluation; in foreign countries, the subgrade top deformation control method, the subgrade bottom deformation control method, the subsurface fill strength control method are mainly adopted in subgrade bed structure design of high speed railways, while in China, dynamic deformation control of subgrade surface and dynamic strain control of subgrade bed bottom layer is adopted in the design. However, the cumulative deformation of subgrade caused by train cyclic vibration load is not considered in the existing design methods.Originality/valueThis paper introduces a new subgrade structure design method based on whole-process dynamics analysis that meets subgrade functional requirements and is established on the basis of the existing research at home and abroad on prediction methods for cumulative deformation of subgrade soil.

Accelerated verification method for the reliability of the motor drive mechanism of the corn precision seed-metering device

The current reliability analysis of the motor drive mechanism of the corn precision seed-metering device has yet to be validated by accelerated testing. Furthermore, the bench test used for verification does not consider the effect of vibration loads on the seeder during field operation. Therefore, this paper proposes an accelerated reliability verification method for the motor drive mechanism of the corn precision seed-metering device. Firstly, reliability theory is used to analyze the importance degree of motor drive system subcomponents. Then, various field tests were carried out to collect vibration and temperature rise data, to analyze the effect of field vibration on the motor drive mechanism, and to propose the vibration influence parameter k. Finally, an indoor test bench was set up, the formula of the acceleration factor A was modified, and accelerated verification tests on 96 motors were carried out to verify the method's accuracy. Reliability analysis showed that the motor’s importance degree was 79.31%, and the Hall switch was 19.78%. The field tests showed that the mean values of the vibration influence parameter k for the four seeding conditions (different seeding speeds) were 0.155, 0.186, 0.207 and 0.228. The accelerated tests showed that the absolute error between the accelerated verification test and the reliability analysis was 1.1% and 3.3% in importance degree and average life, respectively. This paper provided a solution for the reliability study and accelerated verification of the corn electric drive seed discharge mechanism.

Study on Force Characteristics and Safety of Segment Structure and Bolts with and without Cavity behind Lining with Multi-Field Coupling

In this study, a refined three-dimensional stratigraphic–structural model is established based on ABAQUS finite element software, and the basis for determining pneumatic and vibration loads is explained in detail. From this, the force characteristics of the segment and bolts with and without a cavity behind the lining under the action of multi-field coupling were analyzed, and the force law and corresponding safety of the segment structure and high-strength bolts were determined. The results show that the peak value of the maximum principal stress on the segment structure caused by the surrounding rock pressure was 92.7 times greater than the variation in the peak value of the maximum principal stress caused by additional loads (pneumatic and vibration loads). Despite this, the safety factor of the segment structure satisfied the code requirements. Compared to the situation with no cavity behind the lining, when the cavity behind the lining was small the stresses of the segment structure were large and concentrated, which increased the possibility of crack development in the segment structure. The nodal stresses and strains on the straight and bending bolts exhibited an approximately “W”-shaped distribution with a cavity behind the lining. In addition to the effect of the preload near the nut, the stress and strain at the central measurement point of the bolt rod at the joint face were larger owing to the coupling effect of multiple fields. The high-strength bolt remained in an elastic state and did not yield with damage.

Triboelectric Film Sensor for Integrity Monitoring of Bolted Joints

In this study, a concept and design of a self-powered sensor that utilizes a triboelectric effect to evaluate the condition of tensile bolted joints was proposed. Based on the fact that the triboelectric charge yields electrostatic voltage induced by the separation of the contacting rough surfaces, the proposed sensor is a film-shaped triboelectric sensor made of inexpensive materials being installed between the objects to be fastened. The principle of the sensor is that it detects microscale relative motions between the contacting surfaces against an external vibratory load when the integrity of the fastened joint is compromised due to a decrease in the bolt’s fastening force. In this study, we designed and fabricated triboelectric sensor and tested it on a tensile bolted joint specimen subjected to inertial vibratory loading, and it was experimentally shown that the output voltage amplitude of the sensor increased as the bolt’s fastening force decreased. In addition, a modeling study was performed to explain the unexpected decrease in voltage amplitude observed at medium preloads, by combining the triboelectric and mechanical models with the experimental results of two different external circuit configurations. Estimation of the triboelectric charge density at the contacting surfaces was performed, which was found to be consistent with the contact mechanics model assumed. Finally, the calculation of the sensor output voltage based on the presented mechanical/triboelectric model was provided, confirming the validity of the modeling study.

Vibration Analysis of an On-Board Charger Assembly for Electrical Mobility

This article deals with the vibration analysis of an On-Board Charger assembly to check the strength of its components with respect to vibrational load. On-Board Charger (OBC) is a system which is built for electrical vehicles to charge high-voltage battery packs by converting AC power from an external charging source into a DC voltage. The primary role of an onboard charger is to manage the flow of electricity from the grid to the battery. This means that the OBC should fit the necessities of the grid in locations wherever it will be used. Onboard chargers enable plug-in hybrid and battery electric vehicles (BEV) to charge anywhere, not just at designated charging locations, wherever there is AC power. The OBC which is studied in this article is used in three-wheeler vehicles and the weight of this assembly is quite more because of the heat sink and other electronic components; so it is important to check its strength through a vibrational point of view, as induced vibrational load in the vehicle is more while driving the vehicle. Here, the focus will be on all housing and its internal components such as PCB (Printed Circuit Board) and its electrical components. Electrical components connect with PCB with solder joints which provide mechanical and electrical connections between components and PCB. Simulation of an OBC assembly is done by using the ANSYS tool in which modal and harmonic analysis is carried out to check assembly’s strength. The main focus will be on the natural frequencies of the assembly; the aim is to increase the natural frequencies of the assembly above 150 Hz to avoid the resonating condition. The frequency response analysis was done for the range of 50-150 Hz for the acceleration of 15g and stresses and deformation of OBC assembly components are observed after frequency response analysis.
 Keywords: On-Board Charger; Solder joint; Frequency; Vibration, Harmonic analysis, Electrical Mobility, Materials, NVH, Simulation

Development of shock absorber with quasi-zero stiffness effect to reduce dynamic effects on pump unit

The article is devoted to the improvement of the vibration isolation and shockproof properties of the shock absorber used in the vibration isolation compensator system of the pumping unit (PU). The set task is to create an elastic damping system with the desired low (quasi-zero) stiffness, which makes it possible to reduce the detrimental effect of pumping unit vibrations both on human health and on the equipment itself. High internal dynamic (vibration) loads are the main causes of early failure of pumping units, which are transmitted to the equipment through pipelines and foundations, mainly due to various operational factors. A promising trend in increasing the operating reliability and efficiency of pumping and power equipment is the use of a vibration-isolating compensator system (VICS). To obtain greater efficiency of vibration isolation, it is proposed to apply a modern method of vibration damping – the use of elastic mechanical systems with quasi-zero stiffness. The damping devices with a quasi-zero stiffness effect were studied. An assessment of the operability and effectiveness of these dampers at oil and gas facilities was given. Based on the information studied, a new concept of a quasi-zero stiffness damping device is proposed. The method of mathematical analysis determined its power curve. A 3D model of the damper device was built using a simulation software. The functional check of the damper was performed with mathematical modeling carried out on the computing device with the help of a specialized Ansys software that allows performing a system analysis of an object using the finite element method. The following results were obtained: the design of the damper with the effect of quasi-zero stiffness allows to widen the range of basement load transmission coefficient reduction towards low frequencies. The low rigidity of the system at the operating point ensures low values of the frequency of natural oscillations, and, consequently, high vibration isolation qualities.

Prediction of the biomechanical behaviour of the lumbar spine under multi-axis whole-body vibration using a whole-body finite element model.

Low back pain has been reported to have a high prevalence among occupational drivers. Whole-body vibration during the driving environment has been found to be a possible factor leading to low back pain. Vibration loads might lead to degeneration and herniation of the intervertebral disc, which would increase incidence of low back problems among drivers. Some previous studies have reported the effects of whole-body vibration on the human body, but studies on the internal dynamic responses of the lumbar spine under multi-axis vibration are limited. In this study, the internal biomechanical response of the intervertebral disc was extracted to investigate the biomechanical behaviour of the lumbar spine under a multi-axial vibration in a whole-body environment. A whole-body finite element model, including skin, soft tissues, the bone skeleton, internal organs and a detailed ligamentous lumbar spine, was used to provide a whole-body condition for analyses. The results showed that both vibrations close to vertical and fore-and-aft resonance frequencies would increase the transmission of vibrations in the intervertebral disc, and vertical vibration might have a greater effect on the lumbar spine than fore-and-aft vibration. The larger deformation of the posterior region of the intervertebral disc in a multi-axis vibration environment might contribute to the higher susceptibility of the posterior region of the intervertebral disc to injury. The findings of this study revealed the dynamic behaviours of the lumbar spine in multi-axis vehicle vibration conditions, and suggested that both vertical and fore-and-aft vibration should be considered for protecting the lumbar health of occupational drivers.

Fatigue performance of cracked diaphragm cutouts in steel bridge reinforced employing CFRP/SMA

Under long-term service conditions, fatigue cracking occurs at the diaphragm arc-shape cutouts in the orthotropic steel deck (OSD) bridges subjected to vehicle-induced vibration and cyclical wheel load. To repair cracks of the diaphragm cutouts, this study proposes two repair methods of the carbon fiber reinforced polymer (CFRP) sheets and shape memory alloys (SMA)/CFRP composite patches on the basis of crack-stop holes. The crack-stop hole eliminates the obvious source of fatigue propagation at the crack tip, but it weakens the section and harms the entirety of the diaphragm. The edge of the crack-stop hole in the cracked section becomes a new stress concentration site and the potential crack initiation point. The CFRP sheets can effectively improve the stiffness and reduce the stress amplitude of the cracked part. Moreover, the SMA/CFRP composite patches can further introduce precompression by activating SMA to reduce the stress level. Relative to the reinforcement by the crack-stop hole only, the fatigue notch factor is reduced by 12.28% and 30.76% after bonding CFRP sheets and SMA/CFRP composite patches, respectively. The fatigue tests show that the bonding of CFRP sheets and SMA/CFRP composite patches can effectively postpone the initiation of fatigue cracks and inhibit crack propagation, so they are ideal repair methods for strengthening fatigue cracks of the diaphragm cutouts in the OSD bridges.

Limits of permissible vibrations of vehicles for different driving conditions and norms of vibration load

A method for constructing regulatory boundaries for the amplitude-frequency characteristics of sprung vehicles is presented using the parameters of the road micro-profile and the regulations of vibration load. Formulas are given for calculating the standard spectral dispersion densities for the boundaries of labor productivity decrease, comfort boundaries and boundaries that ensure safety and health, with a duration of vibration exposure of 8 hours, 4, and 1 hour. The graphs of the regulatory spectral densities of dispersions for the boundaries of the decrease in labor productivity for the same duration of exposure are given. The method for calculating the spectral density of the dispersion of the road profile based on its correlation function is presented. Formulas for calculating spectral dispersion densities for 8 types of road profile are given. The examples of the regulatory boundaries of the amplitude-frequency characteristics obtained on the basis of the presented method are given. Keywords: vehicle suspension, road micro-profile, spectral density of road micro-profile, correlation function of road microprofile, regulatory boundaries, amplitude-frequency characteristics

The Quality Assessment of Timber Structural Joints Using the Coaxial Correlation Method

With the growing popularity of timber structures, the requirement for reliable and non-destructive methods to assess the quality and condition of structural joints becomes increasingly essential. A novel coaxial correlations method is investigated to assess the degradation of panel-to-panel moment joints in timber structures. The method involves analysing the response data obtained from accelerometers placed on both sides of the joint and comparing the readings to evaluate the joint’s condition. A specific joint solution to simulate the degradation of the moment joint in laboratory conditions is selected based on its simplicity and the ease with which its degradation can be simulated. The joint consists of angle brackets joined with timber screws and bolts to plywood panels. Gradually unscrewing the timber screws reduces the joint’s stiffness to simulate wear and tear over time. The experimental setup includes static loading and finite element modelling (FEM) to determine the rotational stiffness of the investigated joint at each degradation level. A dynamic experiment using vibration loading with sweep signal in the frequency range of 10 Hz to 2000 Hz is conducted to assess the quality of the joint. The conducted research provides valuable insights into the behaviour of timber panel-to-panel connections. The findings highlight the relationship between joint stiffness, vertical displacements, and the proposed dimensionless parameter, volume root mean square value (RMSvol), which offers a more comprehensive assessment of the joint’s condition in three spatial directions. As a result of the research, it has been established that, in the case of linear-type connections, unlike point-type joints, there is a possibility of signal scattering, so it is recommended that power comparisons and evaluations of the response signals from both accelerometers at the initial stage of applying the coaxial correlations method are performed.

A numerical investigation on the influence of full vs perimeter arrays on the mechanical reliability of electronic assemblies under vibration

PurposeThis paper aims to compare and evaluate the influence of package designs and characteristics on the mechanical reliability of electronic assemblies when subjected to harmonic vibrations.Design/methodology/approachUsing finite element analysis (FEA), the effect of package design-related parameters, including the interconnect array configuration, i.e. full vs perimeter, and package size, on solder mechanical stresses are fully addressed.FindingsThe results of FEA simulations revealed that the number of solder rows or columns available in the array, could significantly affect solder stresses. In addition, smaller packages result in lower solder stresses and differing distributions.Originality/valueIn literature, there are no papers that discuss the effect of solder array layout on electronic packages vibration reliability. In addition, general rules for designing electronic assemblies subjected to harmonic vibration loadings are proposed in this paper.

Analysis of seismic time-history effect of single corroded pipeline in seasonally frozen soil region

Based on the pipe-soil thermal-solid coupling analysis method, the single corrosion defect pipeline, insulation layer and seasonally frozen soil were taken as the research object in this paper. Under the specific working conditions of differential frost heave, the seismic time history seismic time history effects were analyzed. The study focused on the axial and vertical velocity responses at the center of the corroded zone of buried pipelines with different corrosion defect characteristics, and then their variations were summarized. The result indicates that the corrosion depth has a greater influence on the axial velocity response than the vertical velocity response. Moreover, the corrosion depth has a larger impact on the maximum vertical and axial displacements at the center of the corroded zone than the corrosion length. The response sensitivity of the corrosion depth to vibratory loading is twice that of the length. When the corrosion length is fixed, the maximum growth rate of axial strain in the corroded zone typically occurs at a corrosion depth ratio between 50% and 75%. Additionally, when the same peak ground motion is considered for pipelines in the same type of site, different seismic wave spectra have significant effects on the dynamic response of buried defective pipelines.

Comparison of Different Standard Test Methods for Evaluating Greases for Rolling Bearings under Vibration Load or at Small Oscillation Angles

Rolling bearings operated at small oscillation angles or exposed to vibrations during standstill show typical damage after only a short period of operation. This can be false brinelling damage, so-called standstill marks or classic fretting damage (fretting corrosion, tribo-oxidation). It is important to differentiate here according to the amplitude-ratio x/2b, which indicates the ratio between the rolling element Motion (x) and the Hertzian contact half-axis (b). Depending on this ratio, suitable laboratory test methods must be used to test the lubricating grease practically for the particular application. For this purpose, the Fafnir wear test, according to the standard of the American Society for Testing and Materials ASTM D4170, is also listed in the current high-performance multi-use specification of the National Lubricating Grease Institute (NLGI) as a release test for lubricating greases. In Europe, the SNR-FEB2 test is frequently used, which is also required to release greases in the blade bearings of wind turbines, among other things. In the case of standstill marks due to very small oscillation angles or vibrations, the Mannheim Tribology Competence Center (KTM) has developed a special test now established in the industry. The oscillating angles vary in these three different standard tests in the range from ±6° in the Fafnir test to ±3° in the SNR-FEB2 test to ±0.5° in the KTM standstill marking test; the x-to-2b ratios range from 5.5 (Fafnir) to 3.4 (SNR) to 0.5 (KTM). This paper will explain the scientific basis for these special operating and test conditions and compare test results of specially prepared model greases in these three standard rolling bearing tests, two test variations and a classical fretting test under oscillating sliding friction (ASTM D7594). The paper’s main objective is to show that the suitability of grease for such an application depends strongly on the prevailing operating conditions. Different tests in this field are, therefore, not interchangeable. Good results in one test do not automatically mean good results in a similar test at first glance. Therefore, selecting the right test for the application is important.

An Investigation of the Anisotropic Fatigue Properties of Laser Additively Manufactured Ti-6Al-4V under Vibration Loading.

Laser additively manufactured (LAM) Ti-6Al-4V alloy has huge application potential in aerospace structural parts such as turbine blades. However, there are few studies on the fatigue properties of such LAM parts under vibration loading, particularly with regard to anisotropy. In this paper, vibration fatigue properties of LAM Ti-6Al-4V by laser melted deposition were investigated along the transversely deposited (TD) and parallelly deposited (PD) directions. Through the first-order bending vibration experiments, the LAM Ti-6Al-4V alloy exhibits obvious anisotropic fatigue properties and significant dispersion in fracture position. The fracture morphology analysis reveals that the vibration fatigue failure was mainly dominated by process-induced defects and microstructure. The fatigue strength at 106 cycles of the samples with defect-free failure features (DFF) at initiation sites is 470.9 MPa in PD and 434.2 Mpa in TD, while that of the samples with defect-related failure features (DRF) at initiation sites is 364.2 Mpa in PD and 381.0 Mpa in TD. For the DFF group, the fatigue behavior is controlled by the prior β columnar grains with preferential orientation, which leads to enhanced fatigue crack propagation resistance for the PD samples. For the DRF group, which has lower fatigue lives, the fatigue anisotropy strongly depends on the projection area of the lack-of-fusion defects relative to the loading direction, resulting in better fatigue performance for the TD samples.

Determination of Blast Vibration Safety Criteria for Buried Polyethylene Pipelines Adjacent to Blast Areas, Using Vibration Velocity and Strain Data.

In order to ensure the safe operation of buried polyethylene pipelines adjacent to blasting excavations, controlling the effects of blasting vibration loads on the pipelines is a key concern. Model tests on buried polyethylene pipelines under blasting loads were designed and implemented, the vibration velocity and dynamic strain response of the pipelines were obtained using a TC-4850 blast vibrometer and a UT-3408 dynamic strain tester, and the distribution characteristics of blast vibration velocity and dynamic strain were analyzed based on the experimental data. The results show that the blast load has the greatest effect on the circumferential strain of the polyethylene pipe, and the dynamic strain response is greatest at the section of the pipe nearest to the blast source. Pipe peak vibration velocity (PPVV), ground peak particle velocity (GPPV), and the peak dynamic strain of the pipe were highly positively correlated, which verifies the feasibility of using GPPV to characterize pipeline vibration and strain level. According to the failure criteria and relevant codes, combined with the analysis of experimental results, the safety threshold of additional circumferential stress on the pipeline is 1.52 MPa, and the safety control vibration speed of the ground surface is 21.6 cm/s.

Fuzzy Neural Network PID Control Used in Individual Blade Control

In order to further reduce the vibration level of helicopters, the active vibration control technology of helicopters has been extensively studied. Among them, individual blade control (IBC) independently applies high-order harmonics to each blade with an actuator, which can improve the aerodynamic environment of the blade and effectively reduce the vibration load of the hub. The rotor structural dynamics model based on the Hamilton energy variation principle and the medium deformation beam theory were established firstly, and the aerodynamic model based on the dynamic inflow model and the Leishman–Beddoes unsteady aerodynamic model were also established. The structural finite element method and the direct numerical integration method were used to calculate the vibration response of the rotor to determine the vibration load of the hub. After these, the steepest descent-golden section combinatorial optimization algorithm was used to find the optimization parameters of IBC. Based on this, the input parameters of fuzzy neural network PID control were determined, and the rotor hub vibration load control simulation was conducted. Under the effect of IBC, the vibration loads of the hub could be reduced by about 60%. The article gives the best control laws of individual harmonic pitch control and their combinations. These results can theoretically be applied to the design of control law to reduce helicopter vibration loads.

Dynamic Response Analysis of Soil around Curve Section Tunnel under Train Vibration Load

To investigate the changes in soil dynamic response around the tunnel periphery under the vibration loads generated by train operation on curved sections, field measurements were carried out to observe void water pressure, water level, and settlement on the ground. Additionally, simulation modeling using MIDAS was employed to simulate and analyze the soil’s dynamic response under the impact of train loads. Based on the track stress diagram combined with the axle weight of the train, the transverse and vertical loads of the track are calculated. The corresponding parameters are entered into the train dynamic load table in the MIDAS/GTS NX dynamic analysis module, so as to simulate the vibration loads of the tunnel. The results show that the application of vibration load is an important reason for the change in pore water pressure during train operation. During the initial stages of train operation, the pore water pressure exhibits a significant increase, followed by a gradual decrease over time. The overall variation follows a seasonal pattern, with the pore pressure increasing as the depth of burial increases. The response of the soil around the tunnel to the vibration of the train is closely related to the location. The closer to the tunnel, the more sensitive the soil is to the vibration of the train, and the greater the amplitude and rate of pore pressure change and vertical deformation in the soil. The variation trend of groundwater level in soil is basically consistent with that of pore pressure, and the groundwater level is proportional to the depth. The dynamic response of the soil at the bottom of the curved tunnel decreases with the increase in the turning radius. The main influence range of the dynamic response is 0~15 m at the bottom of the tunnel. The excess pore water pressure generated by the soil gradually dissipates, and it can be predicted that the vibration of the train will not cause deformation damage to the surrounding soil.

Wind Tunnel Testing and Analysis of a Rigid, Variable Speed Rotor for eVTOL Applications

Many electric vertical take-off and landing (eVTOL) aircraft intended for the urban air mobility (UAM) market are currently being designed with multirotor configurations using variable speed fixed-pitch, rigid rotors for lift. These types of rotors, which are similar in construction to general aviation airplane propellers, are simpler than helicopter rotors and have no moving parts in the rotating frame. This paper discusses wind-tunnel testing of a full-scale, UAM multirotor size, fixed-pitch, rigid rotor with a focus on vibratory blade loads and on the ability to predict these loads with comprehensive analysis. Test results show that vibratory loads are very high, with peak-to-peak magnitudes up to three times greater than the steady component. Correlation of test data to comprehensive analysis using geometrically exact composite beam structural elements and dynamic inflow wake modeling captures the trends in the steady and vibratory loads though it underpredicts the magnitudes; an expected result with the level of wake modeling fidelity used. The paper also discusses the physical sources of the observed vibratory loads and suggests potential options for mitigating their magnitude.