Flexural Deformation Research Articles

Study on the mechanism of flexible deformation affecting the hydrodynamic performance of oscillating hydrofoil

The declining natural environment and rising energy demand have led to increased interest in oscillating hydrofoil structures for their high energy extraction efficiency and environmental benefits. In this study, the numerical simulation method is used to study the mechanism of flexible deformation affecting the hydrodynamic performance of hydrofoil. The results show that the flexible deformation can increase the average power coefficient (CP) by increasing the lift, but it will also aggravate the dynamic stall of the hydrofoil, which has many effects on the hydrodynamic performance of the hydrofoil. Then, the double flexible hydrofoil structure coupled with flexible deformation and dynamic wing-in-ground effect is studied, its hydrodynamic performance is obviously better than other types of hydrofoils. the average power coefficient is 2.51 % higher than that of single flexible hydrofoil and 25.03 % higher than that of double rigid hydrofoil. This shows the superiority of the double flexible hydrofoil structure.

Test rig for validating the integrated motion measurement of flexible beams

AbstractThe fundamental principle of integrated motion measurement (IMM) is integrated navigation with inertial sensors combined with, for example, a satellite navigation receiver. Accordingly, IMM makes use of the specific advantages of complementary sensors and blends them in a filter algorithm. To meet requirements in advanced motion measurements, for instance, for structural health monitoring or for structural control purposes, the approach of a single rigid body like in classical navigation no longer holds for IMM. As a solution, additional degrees of freedom (DOFs) for the moving structure are introduced, which represent deformations and allow the navigated body to be treated as a flexible structure. To cover a variety of flexible deformation shapes, a sufficient number of distributed inertial sensors is required. To restrict accumulating errors of these sensors, additional structural measurements for aiding are necessary. The signals of the inertial sensors and the aiding measurements are fused by an extended Kalman filter (EKF) to obtain an optimal estimation of the usual navigation states, extended by the deformation variables. The contribution presents the preparation of the experimental validation of an IMM system for a flexible structure, which represents an idealization of a wing or rotor blade by a movable beam. The mechanical and electrical setup of a test rig is described. Furthermore, the simulation of the test configuration, that is the model of a test beam with a variety of distributed sensors for generating artificial measurements as a test reference, is discussed. Finally, for an optimal sensor placement, the two methods of effective independence and maximization of modal energy are compared and experimentally tested for different amounts of additional flexible DOFs.

An improved quasi-steady model capable of calculating flexible deformation for bird-sized flapping wings

An improved quasi-steady model capable of calculating flexible deformation for bird-sized flapping wings

Morphy: A Compliant and Morphologically Aware Flying Robot

This study introduces a novel compliant and morphologically aware aerial robot called Morphy. The system is small (primary dimension 25.2 cm), lightweight (260 g), and agile (thrust‐to‐weight ratio of 3.3) while simultaneously integrating sensorized flexible joints in its arms. These elastic joints unlock the potential of experiencing flexible deformations, thus enabling the robot to resiliently withstand collisions at high speeds and squeeze through openings more narrow than its nominal dimensions. Extensive analysis of the flexible joints’ behavior under static loads and in free flight is conducted. Driven by the deformations that the robot can experience, adaptive control allocation exploiting real‐time angle deflection feedback from Hall‐effect sensors embedded in the joints is proposed and combined with fixed‐gain control. To demonstrate Morphy's performance, multiple experiments are conducted, including free flight trajectory tracking, impacts with the environment, and flying through narrow passages. As shown, the system can withstand collisions up to 7.6 m s−1 in drop tests and 3 m s−1 midflight while recovering back to hover. Finally, Morphy's capability to passively change its shape and squeeze through openings smaller than its nominal size is showcased both in the horizontal and in the vertical directions.

Pore-Scale Visualized Transport and Retention of Fibrous and Fragmental Microplastics in Porous Media under Various Surfactant Conditions.

For advancing current knowledge on the transport of microplastics (MPs) in the environment, this study used a real-time pore-scale visualization and quantitative system to examine the motions and mobility of fibrous and fragmental MPs under various surfactant (AEO, CTAC, and AES) and electrolyte conditions. The videos showed that fibrous MPs formed tangles through entanglement, which moved in an axial direction aligned with the flow streamline. Both fibrous and fragmental MPs showed suspended movement as well as surface movement (e.g., sliding, rolling, and saltating) in the porous media. Some deposited fibrous MPs showed flexible deformation due to shear flow. Compared to fragmental MPs, fibrous MPs showed lower mobility due to the tendency to deposit and clog the porous media. The mobility of fragmental MPs was enhanced in the presence of AEO but remained relatively unchanged with AES. In the presence of CTAC, the mobility of fragmental MPs was slightly inhibited under low ionic strength (IS) conditions but remarkably enhanced under high IS conditions. However, the mobility of fibrous MPs was largely unaffected by the surfactants. Both the numerical model and FDLVO calculations effectively described the transport and deposition of MPs in porous media.

Seismic behavior analysis of control rod dropping by vector form Intrinsic Finite-Element method

Control rod drive mechanism (CDRM) play a major role in ensuring safe operation of nuclear reactor during the earthquake, under which the dropping time of control rod is crucial for safe shutdown. Under the earthquake, Rod Cluster Control Assembly (RCCA) has contact collision with the guide tube, resulting in an increase of friction and a decrease of the speed of the falling rod. In addition, in view of the slender structure of the falling rod, the flexible deformation vibration will occur under the impact excitation, which will aggravate the collision and friction. In order to solve the nonlinear problem caused by contact collision between control rod and guide tube, we proposed a dynamic behavior analysis program of rod dropping based on vector finite element method. In order to simulate contact collision force more accurately, we proposed a conformal contact law to simulate the contact force between control rod and guide tube. The vector finite element model and simulation program are validated by comparing with a rod drop experiment. Based on the developed program, the rod dropping behavior, including rod dropping time, contact force, friction force and control rod deformation under several earthquake condition were discussed in this work.

Development of a Novel Tailless X-Type Flapping-Wing Micro Air Vehicle with Independent Electric Drive.

A novel tailless X-type flapping-wing micro air vehicle with two pairs of independent drive wings is designed and fabricated in this paper. Due to the complexity and unsteady of the flapping wing mechanism, the geometric and kinematic parameters of flapping wings significantly influence the aerodynamic characteristics of the bio-inspired flying robot. The wings of the vehicle are vector-controlled independently on both sides, enhancing the maneuverability and robustness of the system. Unique flight control strategy enables the aircraft to have multiple flight modes such as fast forward flight, sharp turn and hovering. The aerodynamics of the prototype is analyzed via the lattice Boltzmann method of computational fluid dynamics. The chordwise flexible deformation of the wing is implemented via designing a segmented rigid model. The clap-and-peel mechanism to improve the aerodynamic lift is revealed, and two air jets in one cycle are shown. Moreover, the dynamics experiment for the novel vehicle is implemented to investigate the kinematic parameters that affect the generation of thrust and maneuver moment via a 6-axis load cell. Optimized parameters of the flapping wing motion and structure are obtained to improve flight dynamics. Finally, the prototype realizes controllable take-off and flight from the ground.

A strong bioceramic microtube and its use in the fabrication of bioceramic implants through flexible deformation and pressure-assisted forming

Bioceramic implants with complex structures, controllable pore size, and excellent mechanical property are hardly manufactured due to high hardness and brittleness of bioceramics. To address the challenge, the study developed a different way to facilitate the fabrication of a strong and tough hydroxyaptite (HA) microtube (HAMT) and ceramic implants. Ceramic implants such as HA bone cage and screw containing microtube were manufactured through flexible deformation and pressure-assisted forming. The compressive strength of HAMT formed by HA filament with 70 carbon fiber(CF) was 132.4 ± 8.4 MPa, which was 73.68 % higher compared to that of HA filament. Furthermore, the HA cage was closely stacked to form dense and uniform structure and had a better mechanical property. The HA bone screw based on the microtube had a compressive strength of 24.5 ± 1.3 MPa and a pullout force of 83.5 ± 1.4 N, which can be used as a bioabsorbable cancellous-bone screw.

Hydrodynamics investigation of a three-dimensional fish swimming in oblique flows by a ghost cell method

Fish in nature can encounter various flow environments. This paper numerically simulated a 3D (three-dimensional) carangiform fish swimming in oblique flow. The numerical model adopts a robust ghost cell method with graphics processing unit acceleration. The dynamic performance and the 3D wake evolutions are discussed under different Strouhal numbers and attack angles. It is found that the thrust along the swimming direction would get enhanced with more energy consumption as the Strouhal number (St) rises. The attack angle can get the similar but less significant effect. Also, the stall angle of θ = 40° is approximately determined, which is independent of the Strouhal number. However, the flexible deformation can reduce the adverse effects of the stall. In terms of the wake structures, they are transitioned from the two rows of vortex streets at St = 0.2 to the three rows at St = 0.6, and even to the four rows at St = 1. The connected oblique vortex ring rows induced by the undulating caudal fin contributes to the thrust and lateral forces dominantly. As the St rises, the vortex ring rows is transformed from the typical von Karman vortex streets to the reverse one, indicating the generation of thrust. The slender, parallel vortex contrails are caused by the detachment of leading-edge vortices (LEVs), and they induce the high-order harmonic components in force coefficients. The oblique angle of the vortex rings grows with the Strouhal number, while it is hardly affected by the attack angle. As the attack angle grows, the wake is turned from the disconnected hairpin vortices to the intertwined vortex rings and losses the spanwise symmetry. Moreover, the reattachment of the LEV is not observed after the stall angle.

Impact of Geometric Forms on the Effectiveness and Physical Features of POD-based Geometric Parameterization

Effective geometric parameterization is crucial in aerodynamic shape optimization for enabling flexible surface deformation while maximizing design space coverage. This paper studies the impact of different geometric forms (closed and open curves) on the effectiveness of Proper Orthogonal Decomposition (POD) geometric parameterization and explores the information of physical features contained in the POD bases. The efficiency and design space coverage which are the main indicators of effectiveness. These indicators of two POD-based parameterization methods are tested on a hybrid database and four typical airfoils. The convergence of aerodynamic properties is also investigated in typical airfoils. In addition, a modified application criterion for POD bases is established by the recursive feature elimination method. A feature importance-based explainable AI (xAI) method is also developed, combining Shapley additive explanations (SHAP) and modified application criterion to explore the physical information contained in POD bases. The results indicate that the POD-based parameterization method constructed from open curves can reconstruct database with better efficiency and design space coverage. Additionally, compared to geometric errors, more POD bases may be required to cover the airfoil design space in order to achieve superior aerodynamic accuracy. Significant differences exist in the importance and correlation of POD bases derived from different geometric forms, with those from closed curves providing better reconstruction efficiency for geometric parameters.

Manuscript title: Experimental investigations of concrete-filled double skin steel tube column-column grouted connection under axial compression

This paper presents a novel grouted connection joint for prefabricated CFDST columns. In order to ascertain the reliability of this grouted connection, axial compression tests were conducted on 24 CFDST columns with grouted connections and 3 CFDST columns without grouted connections. The test parameters were grout strength, casing tube length, and length-to-diameter ratio. The results showed that the stub columns failed due to local buckling and the slender columns failed due to global buckling with significant lateral flexural deformation. CFDST columns with grouted connections exhibited a similar or even higher ultimate bearing capacity and much higher later bearing capacity than conventional CFDST columns. The ultimate bearing capacity of CFDST columns with grouted connections is influenced by the casing tube length and the length-to-diameter ratio. The increase in casing tube length leads to an increase in bearing capacity, while an increase in length-to-diameter ratio results in a decrease. Enhancing the grout strength does not significantly improve the ultimate bearing capacity. Furthermore, the effects of each test parameter on the stiffness, strength and ductility of the CFDST column-column grouted connections were evaluated. Finally, by considering the interaction between components and the impact of casing tube length on bearing capacity, a prediction equation for the ultimate bearing capacity of CFDST column-column grouting connections was developed. This equation can offer accurate predictions with an average error of less than 1 % to provide a reference for the joint design.

ANCF-based modelling of rigid-flexible coupling of helicopter flexible rotor blades

Abstract A high-precision rotor structure dynamic model applicable to a variety of helicopter blade hub structures is established considering rotor blade flexible deformation. The absolute nodal coordinate method is applied to the traditional rotor blade rigid-flexible coupling dynamics model, making the new model applicable to both fully articulated rotor blades and other advanced blade hub structures. No small-volume assumptions were made in the modelling process. Both Green’s strain expression under finite deformation and the geometrical relation of elastic deformation motion based on the absolute nodal coordinate method are used to derive the blade strain energy, kinetic energy, and the external load virtual work. The rotation angle at the articulation constraint at the root of the blade coupled with the elastic deformation degrees of freedom of the blade in three independent rigid body degrees of freedom, respectively. The rotor blade rigid-flexible coupling dynamics equations were established according to the Hamilton action principle. The time-domain simulation is carried out under a free single pendulum and fixed rotational speed/fixed torque for the established flexible blade model, which verifies the validity and high accuracy of the rigid-flexible coupling articulation model of the flexible rotor blade and the blade hub.

A rapid and accurate transfer alignment method using inertial instrument measurement information

The rapidity and precision of transfer alignment impacts the response speed and working precision of inertial navigation system (INS) directly, and flexural deformation is a critical constraint on transfer alignment performance. However, transfer alignment performance of the traditional modeling estimation method is easily degraded by the effect of model mismatch. Therefore, a rapid and accurate transfer alignment method using inertial instrument measurements is proposed in this paper. The relative attitude of main/sub INSs is roughly estimated by angular velocity measurements. Then, a novel transfer alignment filter model is established by relative attitude error model, and measurements of inertial instrument are used to construct angular increment matching and specific force matching quantities. This approach improves both the rapidity and precision of sub INS’s alignment. The performance validation results indicate that compared with traditional methods, the proposed method can improve alignment accuracy by more than 70% and significantly shorten alignment time, thus realizing rapid and accurate alignment.

Enhancing output characteristics of semi-active flapping airfoil energy capture device via flexible deformation strategy

ABSTRACT A concentrated-torsion flexible airfoil model is established to enhance the output characteristics of the flapping airfoil energy capture device in this work. The effect of the damping ratio C 2*, spring ratio K 2* of the torsion spring, and mass ratio M A * of the tail airfoil on the dynamic characteristics is investigated systematically. The numerical simulation results show that compared with the rigid airfoil, the time-averaged power coefficient and output efficiency of the optimized flexible airfoil (C 2* = 4, K 2* = 0.5, and M A * = 0.7) are increased by 91.85% and 63.45%, respectively. Remarkably, the output efficiency of the optimized flexible airfoil is 32.15%. The reason for the enhanced performance is that the passive deformation can ensure the airfoil generates a stronger vortex and delays the shedding of the vortex. In addition, the experimental test results (with a 36.29% performance enhancement) further demonstrate the effectiveness of using the concentrated-torsional flexible deformation strategy in enhancing the energy output characteristics of the flapping airfoil.

Four-parameter punching theory for reinforced concrete flat slabs without transverse reinforcement

Despite extensive scientific research, the underlying physical principles in theoretical models for understanding punching behavior remain a concern. In this paper, a four-parameter punching theory for reinforced concrete flat slabs without transverse reinforcement has been introduced and validated. The kinematic behavior of the slab was characterized by three key parameters, i.e., critical shear crack inclination, slab rotation, and slab translation. Four distinct shear transfer effects from aggregate interlocking, concrete residual tensile stress, reinforcement dowel action, and the shear-compression ring, were considered and quantified using a novel algorithm based on these three parameters, and the fourth parameter, i.e., the direction of the minimum principal stress within the shear-compression ring. The punching capacity was subsequently determined by summing the contributions from these effects. This model was evaluated through extensive comparisons with experimental data, demonstrating that it accurately captures the influence of various parameters. Across the collected 260 test data, the average ratio of experimental to predicted punching capacity was 1.01, with a coefficient of variance of 0.11 and a coefficient of determination of 0.97. The average ratio, coefficient of variation, and coefficient of determination improved by 8 %, 21 %, and 1 %, compared to the optimal results from other design and theoretical models. The developed model can also assess all shear contributions, slab deformation, and critical shear crack inclination. It is ultimately confirmed that the proposed model can elucidate the physical phenomena and underlying mechanisms involved in punching behavior. Slab deformation primarily arises from flexural deformation, whereas shear forces are predominantly transmitted through the shear-compression ring. Punching failure is attributed to the failure of the shear-compression ring under tension-compression-compression triaxial stress.

Impact behavior of the SCS panel with hybrid energy absorbing components: Experimental and analytical studies

A new steel-concrete-steel panel with front aluminum foam layer and rear energy absorbing connector (SCS-FL-EAC) was firstly developed. The dynamic behavior of SCS-FL-EAC was studied through conducting drop-weight impact tests. Three stages of impact process of SCS-FL-EAC were identified. The aluminum foam layer and energy absorbing connector were crushed under impact loading. The aluminum foam layer reached densification, and a local indention was observed beneath the projectile. Plastic hinges were also found at the corners of the pleated steel plate of the energy absorbing connector. The SCS panel exhibited the combination of bi-linear global flexural deformation and local deformation. Furthermore, the effects of aluminum foam layer on the impact resistant performances of SCS-FL-EAC were investigated. The results indicated that the inclusion of the aluminum foam layer effectively mitigated inertial effects and reduced the maximum impact force. Additionally, the SCS-FL-EAC demonstrated improved impact-resistant performances with an increased thickness of the aluminum foam layer. Furthermore, an analytical model was proposed to predict the force and displacement responses of SCS-FL-EAC subjected to impact load, and the predicted impact responses showed good agreement with experimental results.

Sunflower pith inspired dual-gradient cellular polyurethane architecture with amplified mechanical functions

Artificial cellular materials with various mechanical functions are attracting increasing attentions from aerospace, transportation, and industrialization. However, many artificial cellular materials, despite of the hierarchically ordered structures and even unique performance to some, still lag behind many natural ones in amplification of mechanical functions owing to the limitations in intrinsic mechanical performance and sophisticated structural design. Herein, inspired with lightweight and high strength of sunflower piths, we proposed a dual-gradient structure consisting of pore size gradient and wall thickness gradient to engineer cellular architectures with desirable mechanical performance by harnessing vat photopolymerization 3D printing of double crosslinking networks polyurethane elastomer. The double-gradient cellular polyurethane architecture displays more exceptional capability in load-bearing and energy absorption compared with non– and single gradient structures. Besides, the specific compressive strength and energy absorption of the dual-gradient cellular architectures are 4 times higher than those of traditional mechanical metamaterial structures such as octet-truss lattice, gyroid lattice, and porous structure prepared with the same material. Potential mechanisms such as dual-gradient cellular structures to obtain selective flexural deformation behaviour increasing their energy absorption and dissipation capacity are fully elucidated. As the potential paradigms, we demonstrated the mechanical functions of biomimetic mechanical cellular architectures for efficient impact protection and noise isolation, which offered a promising perspective toward developing soft metamaterials with excellent mechanical functions for potential soft machines and engineering applications.

Finite element analysis of ductility and flexural capacity of FRP and steel bars hybrid reinforced concrete beams

AbstractTo study the flexural behavior of hybrid reinforced concrete (hybrid‐RC) beams with FRP and steel bars, this paper used ABAQUS finite element (FE) software to model and nonlinear analyze the hybrid‐RC beams and investigate the effects of effective reinforcement ratio, concrete strength, and FRP bars type on the flexural behavior of hybrid‐RC beams. In addition, the FRP bars stress, flexural bearing capacity, and ductility formulas for hybrid‐RC beams were fitted based on the FE results, and existing literature data were used to verify their accuracy. The FE model results indicated that the effective reinforcement ratio, FRP bars type, and concrete strength significantly impacted the flexural bearing capacity and deformation performance of hybrid‐RC beams. Increasing the strength of concrete improved the flexural bearing capacity and ductility of hybrid‐RC beams; increasing the effective reinforcement ratio and the elastic modulus of FRP bars increased the flexural bearing capacity of the hybrid‐RC beams but decreased its ductility. In addition, the fitted FRP bars stress, flexural bearing capacity, and ductility calculation formulas can quickly and conveniently predict the flexural bearing capacity and ductility of hybrid‐RC beams.

Seismic design and analysis of truss‐confined buckling‐restrained braces

AbstractThe truss‐confined buckling‐restrained brace (TC‐BRB) with a varying or constant section truss confining system was proposed for applications of long span and large force capacities. Their feasibility and hysteresis behavior were examined through experimental investigations. This paper presents an original formulation of the elastic buckling resistance of the novel restraining system, considering the shear reduction effect. The findings indicate that the chord predominantly contributes to the flexural rigidity in the restraining system, while the post primarily contributes to the overall shear rigidity. Subsequently, the ultimate compressive strength of a TC‐BRB is evaluated, incorporating the effects of chord residual stress, length differences between the restrainer and entire brace, and initial in‐plane flexural deformation, based on available experimental data. A numerical procedure employing finite element model (FEM) analysis is introduced to simulate the mechanical characteristics of TC‐BRBs. The critical loads are verified through FEM analyses and test results. The failure mode observed in the numerical models is the instability of the chords near the midspan, as expected. A simplified approach for determining the ultimate compressive strength and design recommendations for TC‐BRBs are provided for engineering practice.

Model‐ versus data‐uncertainty for concrete members and connections in cyclic loading

AbstractLarge databases of cyclic tests on flexure‐ or shear‐critical concrete members and shear‐critical connections of columns to beams or slabs are used to estimate the uncertainty inherent in experimental data in literature—as read by users. To this end, the predictions of two different, presumably independent, design‐oriented models for the properties of interest are used to establish the “central tendency” of data, against which individual tests or small groups thereof are assessed. Properties considered are: (a) the cyclic ultimate chord‐rotation of flexure‐controlled members with continuous or lap‐spliced deformed bars, (b) the cyclic shear strength of shear‐critical members, (c) the chord‐rotation at yielding of rectangular columns with plain bars, and (d) the cyclic shear strength of shear‐controlled beam‐column and slab‐column joints. Results suggest that the data from each test campaign have a certain degree of bias, specific to it. Test campaigns with ratio of estimated average deviation from the “central tendency” to the standard deviation of campaign deviations (called “data uncertainty”) which is far into the tail of the Normal distribution may be excluded as questionable. This systematic bias, along with other types of “data uncertainty” addressed in this work, seem to contribute to the apparent scatter of model predictions with respect to cyclic test results the equivalent of a coefficient of variation of model‐to‐test‐ratio of at least 10% and possibly as high as 25%–30%. Model uncertainty seems to contribute to this scatter the equivalent of a coefficient of variation of at least 15% in shear‐controlled connections, or as much as 25% in the case of flexural deformation capacity of members with deformed bars; the cyclic shear resistance of members and—with the reservation of the small number of tests—the chord‐rotation at yielding of members with plain bars, are in‐between.