Search Results (51)

Asymmetric friction, that is, different friction forces resisting sliding in opposing directions, works as a rectifier, transferring the applied oscillations into unidirectional motion. Locomotion of devices based on asymmetric friction is investigated by considering a model system consisting of an asymmetric friction block connected to a symmetric friction block by a spring. The symmetric friction block models the resistance to the movement by the environment. It is found that under harmonic oscillation, the system displays two distinct types of motion: Recurrent Movement (stick-slip-type movement) and Sub-Frictional Movement. The Recurrent Movement occurs when the inertia force is sufficient to overcome the frictional force. In this case, the system with asymmetric friction exhibits unidirectional locomotion, while the system with only symmetric friction oscillates about a fixed point. The Sub-Frictional Movement occurs when the inertia is insufficient to overcome the frictional force. Then the symmetric friction block moves against the asymmetric friction block and sufficiently loads the spring to enable some movement of the system. Thus, motion is generated even when the external forces are below the static friction threshold. These types of motion have been found to exhibit different types of spectral fallout: while the Recurrent Movement produces a typically observed frictional fallout 1/ω, where ω is the frequency, the Sub-Frictional Movement produces a stronger 1/ω² fallout, only observed in the development of an oblique fracture in rocks under compression. This discovery can shed light on mechanisms of rock failure in compression. Understanding of the unidirectional movement induced by asymmetric friction can be instrumental in designing novel locomotion devices that can move in narrow channels or fractures in the Earth’s crust or in extraterrestrial bodies utilising the (renewable) energy of external vibrations. Full article

This study investigates the development of axial force in micro anti-slide piles under soil movement during slope stabilization. Axial force arises from two primary mechanisms: axial soil displacement ($z_{\mathrm{s}}$) and pile kinematics. The former plays a dominant role, producing either tensile or compressive axial force depending on the direction of $z_{\mathrm{s}}$, while the kinematically induced component remains consistently tensile. A sliding angle of $\alpha =5°$ represents an approximate transition point where these two effects balance each other. Furthermore, the two mechanisms exhibit distinct mobilization behaviors: $z_{\mathrm{s}}$-induced axial force mobilizes earlier than both bending moment and shear force, whereas kinematically induced axial force mobilizes significantly later. The study reveals two distinct pile–soil interaction mechanisms depending on proximity to the slip surface: away from the slip surface, axial soil resistance is governed by rigid cross-section translation, whereas near the slip surface, rotation-dominated displacement accompanied by soil–pile separation introduces significant complexity in predicting both the magnitude and direction of axial friction. A hyperbolic formulation was adopted to model both the lateral soil resistance relative to lateral pile–soil displacement (p-y behavior) and the axial frictional resistance relative to axial pile–soil displacement (t-z behavior). Soil resistance equations were derived to explicitly incorporate the effects of cross-sectional rotation and pile–soil separation. A novel beam-spring finite element method (BSFEM) that incorporates both geometric and material nonlinearities of the pile behavior was developed, using a soil displacement-driven solution algorithm. Validation against both numerical simulations and field monitoring data from an engineering application demonstrates the model’s effectiveness in capturing the distribution and evolution of axial deformation and axial force in micropiles under varying soil movement conditions. Full article

This paper presents an enhanced pseudo-rigid body model (PRBM) integrated with the LuGre friction law to analyze the dynamic behavior of flexure-hinge-based piezoelectric stick–slip actuators (PSSAs). The PRBM captures flexure compliance through Lagrangian dynamics, while Newtonian mechanics describe the piezoelectric stack and slider motion. Non-linear contact effects, including stick–slip transitions, are modeled using the LuGre formulation. A mass–spring–damper model (MSDM) is also implemented as a baseline for comparison. The models are solved in MATLAB Simulink version R2021a and validated against experimental data from a published prototype. The enhanced PRBM achieves strong agreement with experiments, with a root mean square error of 20.19%, compared to 51.65% for the MSDM. By reformulating the equations into closed-form expressions, it removes symbolic evaluations required in the standard PRBM, resulting in one to two orders of magnitude faster simulation time while preserving accuracy. Stable transient simulations are achieved at fine time steps ($\Delta t={10}^{-8}$ s). A systematic parametric study highlights preload force, flexure stiffness, friction coefficients, and tangential stiffness as dominant factors in extending the linear frequency–velocity regime. Overall, the PRBM–LuGre framework bridges the gap between computationally intensive finite element analysis and oversimplified lumped models, providing an accurate and efficient tool for design-oriented optimization of compliant piezoelectric actuators. Full article

The torsional, lateral, and axial vibrations that occur during drilling operations have negative effects on the drilling equipment. These negative effects can cause huge economic impacts, as the failure of drilling tools results in wasted materials, non-productive time, and substantial expenses for equipment repairs. Many researchers have tried to reduce these vibrations and have tested several models in their studies. In most of these models, the drill string used in oil wells behaves like a rotating torsion pendulum (mass spring), represented by different discs. The top drive (with the rotary table) and the BHA (with the drill pipes) have been considered together as a linear spring with constant torsional stiffness and torsional damping coefficients. In this article, three models with different degrees of freedom are considered, with the aim of analyzing the effect of variations in the stiffness and damping coefficients on the severity of torsional vibrations. A comparative study has been conducted between the three models for dynamic responses to parametric variation effects. To ensure the relevance of the considered models, the field data of torsional vibrations while drilling were used to support the modeling assumption and the designed simulation scenarios. The main novelty of this work is its rigorous comparative analysis of how the stiffness and damping coefficients influence the severity of torsional vibrations based on field measurements, which has a direct application in operational energy efficiency and equipment reliability. The results demonstrated that the variation of the damping coefficient does not significantly affect the severity of the torsional vibrations. However, it is highly recommended to consider all existing frictions in the tool string to obtain a reliable torsional vibration model that can reproduce the physical phenomenon of stick–slip. Furthermore, this study contributes to the improvement of operational energy efficiency and equipment reliability in fossil energy extraction processes. Full article

The locking mechanism is crucial for the reliable connection and disconnection of electrical connectors. Aiming at the lack of theoretical support for the reliability evaluation in long-term storage, a comprehensive multi-theory modeling method is proposed to solve unlocking failure and related performance-evaluation problems. An analysis reveals that metal-crystal dislocation glide, causing pull-rod deformation and spring stress relaxation, is the main cause of unlocking failure. Based on Hertz’s contact theory, a locking-state mechanical model is established. Integrating the crystal dislocation-slip theory, an accelerated degradation trajectory model considering design parameters is developed to characterize the friction between the pull rod and steel ball and the spring’s elastic-force degradation. Finally, the model is verified using the unlocking-force accelerated test data. It offers a theoretical basis for the reliability evaluation and design of locking mechanisms in long-term storage environments. Full article

Jumping is a fundamental capability for wheeled-bipedal robots (WBRs) navigating unstructured terrains, with jump height and stability serving as indicators of the robot’s environmental adaptability. However, existing trajectory planning methods demand high output capacity from the joints and fail to balance computational load with trajectory tracking performance. This limitation hinders most robots from experimental validation. To address these challenges, this study presents an optimized virtual model, trajectory planning strategy, and control method. These solutions enhance both the height and stability of jumps while ensuring real-time execution on physical robots. Firstly, inspired by the human jumping mechanism, a Nonlinear Wheel-Spring-Loaded Inverted Pendulum (NW-SLIP) model was originally proposed as the virtual model for trajectory planning. The jump height is increased by 3.4 times compared to the linear spring model. Then, cost functions are established based on this virtual model, and the trajectory for each stage is iteratively optimized using Quadratic Programming (QP) and a bisection method. This leads to a 21.5% increase in the maximum jump height while reducing the peak joint torque by 14% at the same height. This significantly eases execution and enhances the robot’s trajectory-tracking ability. Subsequently, a leg statics model is introduced alongside the kinematics model to map the relationship between the virtual model and joint space. This approach improves trajectory tracking performance while circumventing the intricate calculation of the dynamics model, thereby enhancing jump consistency and stability. Finally, the proposed trajectory planning and jump control method is validated through both simulations and real-world experiments, demonstrating its feasibility and effectiveness in practical robotic applications. Full article

This work continues the study of a mathematical model for the motion of a mass–spring–damper system with friction. There, a two-mass model was constructed, its solvability established, the steady states investigated, and numerical simulations presented. The main interest here is in the modeling, analysis of the steady states, and simulation of a three-mass system—in particular, in the propagation of detachment or slip waves, which happen when the system transits from a stick state to a slip motion. The introduction of friction changes the problem into systems of three differential set-valued inclusions, which are mathematically and computationally very challenging. The analysis of the steady states shows the regions of stick, where there is enough frictional resistance that prevents motion. The proposed numerical methods are implemented, and the simulations show some representative types of system behavior, especially the cases of detachment waves. Some of the numerical simulations specifically support the theoretical analysis of slip initiation, reachability, and energy balance. Full article

Monitoring and early warning systems for cross-fault buried pipelines are critical measures to ensure the safe operation of oil and gas pipelines. Accurately acquiring pipeline strain response serves as the fundamental basis for achieving this objective. This study proposes a comprehensive analytical methodology combining finite element analysis (FEA) and experimental verification to investigate strain responses in cross-fault buried pipelines. Firstly, a finite element modeling approach with equivalent-spring boundaries was established for cross-fault pipeline systems. Secondly, based on the similarity ratio theory, an experimental platform was designed using Φ89 mm X42 steel pipes and in situ soil materials. Subsequently, the finite element model of the experimental conditions was constructed using the proposed FEA. Guided by simulation results, strain sensors were strategically deployed on test pipelines to capture strain response data under mechanical loading. Finally, prototype-scale strain responses were obtained through similarity ratio inverse modeling, and a comparative analysis with full-scale FEA results was performed. The results demonstrate that strike-slip fault displacement induces characteristic “S”-shaped antisymmetric deformation in pipelines, with maximum strain concentrations occurring near the fault plane. Both the magnitude and location of maximum strain derived from similarity ratio inverse modeling show close agreement with FEA predictions, with relative discrepancies within 18%. This consistency validates the reliability of the experimental design and confirms the accuracy of the finite element model. The proposed methodology provides valuable technical guidance for implementing strain-based monitoring and early warning systems in cross-fault buried pipeline applications. Full article

This study investigates the modeling and dynamic analysis of three coupled electromechanical systems, emphasizing interactions between a magnetic linear drive and frictional contact with flat springs. The experimental setup includes a table driven by a three-phase permanent magnet linear synchronous motor (PMLSM) using an LMCA4 inductor, LMCAS3 magnetic track, and Xenus XTL controller. Mechanical phenomena such as stick-slip friction and impulsive loads are observed, particularly due to the rapid buckling of flat springs. These springs transition between sliding friction and fixation, impacting the motor’s operation during reciprocating velocity trajectories and generating acoustic emissions. Numerical simulations using COMSOL Multiphysics evaluate the magnetic field and system geometry in two- and three-dimensional spaces. Key findings include mechanical stick-slip vibrations, numerical modeling of the linear drive, and comparative analysis of experimental and simulated inductor current variations. Additionally, energy loss mechanisms under irregular loading conditions are assessed. The results highlight the coupling between friction-induced current changes and magnetic field variations, elucidating their impact on motor efficiency, vibration propagation, and acoustic emissions. The study provides insights into optimizing the design and reliability of coreless linear motors for precision applications under discontinuous loading. Full article

Models used to study the fracture process of concrete are often considered 2D, ignoring the influence of specimen width. However, during the fracture process in pre-cracked concrete beams, the crack length varies along the thickness direction, especially in reinforced concrete. To study the influence of specimen width on reinforced concrete fracture behavior, a 3D numerical method was used to simulate the crack propagation processes of lightly reinforced concrete beams based on Fracture Mechanics. Nonlinear spring elements with different stress-displacement constitutive laws were employed to characterize the softening behavior of concrete and the bond-slip behavior between the steel bars and concrete, respectively. It is assumed that the crack begins to propagate when the maximum stress intensity factor at the crack tip along the beam width reaches the initial fracture toughness of concrete. To verify the validity of the proposed method, the completed crack propagation processes of lightly reinforced concrete three-point bending notched beams were simulated, and the calculated load-crack mouth opening displacement curves showed a reasonable agreement with the experimental data. Moreover, the impact of the 2D reinforced concrete beam model on the crack propagation process was analyzed. The results indicate that at the initial loading stage, the external load P obtained from the 2D model is significantly larger than the result from the presented 3D model. Full article

Over the past few years, there has been an increased focus on offshore pipeline safety due to the development of offshore oil and gas resources. Both onshore and offshore pipelines may face significant geological hazards resulting from active faults. Pre-excavated soil can be used as backfill for trenches to prevent major pipeline deformations. Since these backfill materials have been heavily remolded, they are softer than the native soil. Therefore, the difference in shear strength between the backfill and native ground may have an effect on the interaction between the pipeline and the backfill. In this paper, the pipeline–backfill–trench interaction is investigated using a hybrid beam–spring model. The P-Y curves obtained from CEL analysis are incorporated into a 3D beam–spring model to analyze the pipeline’s response to lateral strike-slip faults. Additionally, the nonlinearity of pipeline materials is considered to study pipeline failure modes under strike-slip fault movements. A series of parametric studies were conducted to explore the effects of fault intersection angle, pipe diameter, buried depth of the pipe, and soil conditions on the failure modes of buckling pipelines. The developed method can be used to analyze and assess pipeline–backfill–trench interaction when subjected to strike-slip fault displacements. Full article

The rapid development of wearable technologies is increasing research interest in on-body robotics, where relocatable robots can serve as haptic interfaces, support healthcare measurements, or assist with daily activities. However, on-body mobile robotics poses challenges in aspects such as stable locomotion and control. This article proposes a novel small robot design for moving on human limbs that consists of an open grasping mechanism with a spring linkage, where one side holds a pivoting differential drive base (PDDB) with two spherical rollers, and the other side holds an actuated roller for grasping and stabilization. The spherical rollers maintain contact at three points on the limb, optimizing stability with a minimal number of rollers and integrating DC motors within. The PDDB wheels (spherical rollers) enable directional changes on limb surfaces. The combination of the open mechanism, the PDDB, and the spherical rollers allows adaptability to diameter variations along the limb. Furthermore, the mechanism can be easily put on or removed at any point along the limb, eliminating the need to slip the robot over the hand or foot. The kinematic model for the proposed mechanism has been developed. A cascade control strategy is proposed with an outer loop for stable grasping and an inner loop for trajectory adjustments using PDDB roller velocities. An on-limb robot prototype has been built to test its applicability to human arms. Simulation and experimental results validate the design. Full article

The modeling method of unbonded effects is a challenging and hot topic for the structural performance analysis of unbonded and partially bonded post-tensioned concrete beams. The main concerns accounting for the unbonded effects are the longitudinal free-slip behaviors and the vertical deformation compatibility relationship between the unbonded tendon and concrete beam. Three modeling schemes, namely, the beam–truss element model, the slipping cable element model, and the slack spring model, are presented in this paper. These modeling schemes are, for the first time, systematically compared regarding applicability, convenience, and accuracy. Then, these modeling schemes are applied to experimental beams with different tendon layouts and bonding conditions, including external tendons, internal unbonded tendons, and partially bonded tendons. The beam–truss element model and the slipping cable element model are only applicable to the fully bonded and unbonded members, respectively. The slack spring model is recommended as the generally applicable model for analyzing post-tensioned concrete beams with different bonding conditions. Crucial suggestions are put forward as to the zero-length slack spring element, which have the potential to improve the prediction accuracy for tendon stress. In addition, parametrical analysis is conducted to determine the influence of unbonded length on flexural performance. With the increase of unbonded length, the flexural capacity of the beam will decrease, but the self-centering performance can be improved. Interestingly, the effects of unbonded length on the structural deformability are not monotonic, and the reasons for this are clarified. Full article

The integration of steel fibers into high-strength concrete (HSC) offers a solution to address the brittleness and limited ductility typically associated with conventional HSC structures. To investigate the bonding properties between shaped steel and high-strength concrete with steel fiber (SFRC), thirteen tests of the shaped steel/SFRC specimens are conducted to explore the effects of various factors such as steel fiber volume ratio, concrete strength grade, reinforcement ratio, steel embedment depth, and cover thickness on bond–slip behavior. Three distinct failure modes, such as pushout failure, bond splitting, and yielding failure of steel, are identified during the pushout tests. Three different types of bond strength, such as the initial bond strength, the ultimate bond strength, and the residual bond strength, are observed from the load–slip curves between the shaped steel and concrete. By incorporating nonlinear spring elements, a numerical model for accurately simulating the bond performance between the shaped steel and SFRC specimens is developed. The bond strength between the shaped steel and concrete increase as the concrete strength, cover thickness, steel fiber volume ratio, and stirrup ratio increase, while it decreases as the steel embedment depth increases. A model for the bond strength between shaped steel and SFRC is developed, and it agrees well with the test data. Full article

Overrunning spring clutches are widely used as essential transmission devices, and the occurrence of abnormal noise can lead to a decline in their performance. This study investigates the dynamic aspects of abnormal noise in engineering applications, including its causes, influencing factors, and suppression methods. Audio processing algorithms are employed to analyze the audio associated with abnormal noise, and the Fourier Motion Blur algorithm is applied to process video images of the springs. By combining the motion blur curve with the noise spectrum curve, the source of the abnormal noise is identified as friction-induced vibrations in the spring. Theoretical modeling and calculations are carried out from a dynamic perspective to validate that the phenomenon of abnormal noise in the clutch is a result of self-excited friction vibration caused by the stick–slip phenomenon. Based on theoretical analysis and practical engineering, surface texturing is added to the center shaft of the spring seat, optimizing the system as an overdamped system to suppress self-vibration. Utilizing CFD simulation analysis, the simulation results are used to improve the texturing parameters and further optimize the texturing shape, resulting in an optimal parallelogram surface texture structure. Experimental validation confirms that the improved overrunning spring clutch completely eliminates abnormal noise during overrunning operation. Therefore, this paper contributes to the understanding of the dynamic issues associated with abnormal noise in overrunning spring clutches, confirming that the mechanism for abnormal noise generation is friction-induced self-excitation vibration, and demonstrating that surface texture optimization methods effectively suppress the occurrence of abnormal noise. Full article