Rotor-stator rub interactions are a significant area of interest in rotordynamics because they can generate backward whirling, often causing malfunctions. This paper extends the analytical solution for rotor-stator rub dynamics to include friction at the rotor-stator contact. A simple two-degrees-of-freedom Jeffcott rotor model is used, and the contact mechanics follows a piecewise-smooth model with Coulomb friction. The rotor can be in the contact or non-contact regime, introducing motion-dependent discontinuities and strong nonlinear behaviour due to contact forces. To obtain an analytical solution, these nonlinear forces are approximated using the first-order Taylor expansion. Eigenvalue and nonlinear dynamics analyses of the model are also undertaken. The analytical solution is validated against fourth/fifth order Runge-Kutta integration. Effects of varying friction, rotor damping, and stator stiffness are investigated. The main contribution is an analytical solution applicable to wide range of problems from rotordynamics including drill-string whirling, offering faster computation while maintaining accuracy, and contributing to improved rotor dynamics modelling.

Ball-end cutters are widely used for high precision machining of complex surfaces. However, cutter deflection significantly affects machining accuracy and surface quality, making accurate modelling of deflection essential. To address this, an iterative predictive model for cutter deflection in ball-end milling is proposed. The model employs the subcomponent method to efficiently compute static deflection of cutter and establishes the multivariate deflection-cutting geometry feedback mechanism based on the cutter centre point position, cutting depth and width, and tool attitude angles. The experimental validation shows that the model has an average error of 6.815% in predicting peak milling force. It was found that deflection narrows the entry and exit angle ranges, changes the axial span of cutting elements, decreases the cutter-workpiece engagement zones, and concentrates instantaneous loads. This method addresses the issues of insufficient accuracy and high computational complexity in existing models, providing a theoretical basic for process optimization and accurate predictions in ball-end milling.

The forming and sizing processes of longitudinal submerged arc welded (LSAW) pipes for deep-sea energy transportation influence their geometric accuracy and mechanical characteristics, thereby governing their collapse resistance and bending capacity. In this study, a full-process theoretical model and numerical simulations were developed to investigate the forming, sizing and buckling failure behaviour of the LSAW pipes, filling the limitations of existing studies. The results indicate that compression-sized pipes exhibit superior dimensional accuracy, higher compressive yield strength, and lower residual stresses compared with expansion-sized pipes. By utilizing the stress-strain history from the forming process and considering plastic buckling, the developed analytical model can reduce prediction error of collapse pressure for thick-walled pipes to within ±2 MPa. The anisotropy induced by different sizing processes and ratios has a negligible effect on the ultimate bending moment. The pressure and bending loading paths alter the collapse pressure and propagation behaviour. The pressure–bending sequences accelerates plastic strain accumulation, thereby reducing the ultimate collapse resistance of the pipe. As the pressure increased from 0 to 5.42 MPa, the normalized bending capacity decreased from 0.94 to 0.81 for the -1.22% sized pipe, whereas a more pronounced reduction from 0.96 to 0.74 was observed for the 0.75% sized pipe. This study provides valuable guidance for forming processes and evaluation of buckling resistance for pipes serving in deep-sea environments.

This study proposes SINDy-PI-SWR, a parameter identification framework for nonlinear frictional systems that integrates Parallel Implicit Sparse Identification (SINDy-PI) with sliding window resampling (SWR). To our knowledge, this is the first application of an implicit sparse identification framework combined with SWR for frictional dynamics. The proposed framework employs a hybrid regularisation strategy, incorporating L0 regularisation to promote sparsity and L2 regularisation to suppress parameter outliers, thereby improving robustness against measurement noise. The identification performance of the proposed method is benchmarked against numerical integration results. Results demonstrate the SWR technique effectively overcomes the original SINDyPI method's challenge with high noise. Beyond conventional root mean square error (RMSE), this study introduces a coefficient offset as the critical evaluation criterion. For instance, in single degree-of-freedom (SDOF) systems at a noise level of 0.3, SWR reduces the Coulomb model RMSE by 93.78% and suppresses the Stribeck model coefficient offset by 87.3% at a noise level of 0.2. For Stribeck and steady-state Dieterich-Ruina models, the method prioritizes minimizing coefficient offsets over RMSE, enhancing model identifiability. The effectiveness of this SINDy-PI-SWR method is experimentally verified. For the tested cases with excitations at 15, 17, 19 and 25 Hz, it is found that the Coulomb friction provided the best agreement in the tested cases up to 19 Hz, whereas the steady-state Dieterich-Ruina law gave a comparatively better empirical fit in the tested 25 Hz case within the candidate model library. The proposed SINDy-PI framework significantly improves parameter identification performance in frictional systems, offering a novel paradigm for constructing precise nonlinear dynamic models in engineering applications.

Downhole stuck tools are a significant source of downtime during drilling, and jarring tools can remedy such problems. In a typical jarring operation, axial impact releases a stuck tool during drilling. Innovative jarring tool designs generate multiple, high-frequency impacts, but existing models of jarring operations focus on conventional jarring with a single impact. In this work, we developed two low-dimensional models to describe a multi-impact jarring system to investigate nonlinear behaviour during multi-impact jarring. A simplified strongly nonlinear one degree-of-freedom model with a realistic dynamic loading scenario was selected for investigation through a direct numerical simulation. Typical nonlinear dynamics characteristics, such as time–history evolutions, phase portraits, and bifurcation diagrams, are presented. In addition, novel steady-state force equilibrium diagrams are constructed. Results of the numerical simulations indicate the system behaviour is sensitive to some operational parameters, namely the excitation frequency. We present examples of the system dynamic responses ranging from periodic to chaotic solutions, strongly affecting the transmitted force onto a stuck pipe. Our analysis shows that the external excitation frequency has a major effect on system operation and can be used to improve tool performance.

In this article, in terms of the first and second laws of thermodynamics, as well as the principle of maximum energy dissipation rate, a continuum elastic-plastic theory for porous materials is proposed. Unlike the Prandtl-Reuss equation, the influence of plastic volumetric strain is fully taken into account. An incremental elastic-plastic constitutive law is derived, and a series of yield criteria is proposed. Its implementation is demonstrated with a simple example. This study offers a new perspective for modeling the elastic-plastic deformation of porous materials.

Conventional acoustic metamaterials possess a rigid configuration, precluding modulation of their sound absorption properties to adapt to complex, variable low-frequency noise environments. This study proposes an origami-inspired acoustic metamaterial (OriAM), featuring broadband, real-time tunable, and tailored bandgaps with low-frequency sound attenuation capabilities. The unit cell of the OriAM is derived from an accordion origami structure, endowed with flexible deformability, and integrated with a Helmholtz resonator. The accordion origami height of each unit cell can be real-time and dynamically regulated via pneumatic control to further manipulate the band structures and sound attenuation performance. The band structure and transmission loss of the OriAM are systematically investigated using the Bloch’s theorem, transfer matrix theory, and finite element analysis. It is demonstrated that the sound attenuation can be synergistically enhanced by both local resonance and Bragg reflection bandgaps. For a seven-unit-cell configuration, the effective noise attenuation bandwidth (sound energy attenuation greater than 90 %) can reach 1.85 octaves, enabling broadband mitigation. Bandgap properties and effective attenuation capacity can be also readily tailored by adjusting the 2D crease pattern parameters. Further investigation of the OriAM with gradient arrangement of unit cells reveals diverse acoustic phenomena, including spatial frequency division and wave field energy enhancement.

Uncontrolled wellbore temperature in ultra-high-temperature wells is one of the critical engineering bottlenecks restricting the safe and efficient development of unconventional energy resources. As a novel wellbore temperature-control technique, the optimization of engineering parameters for the insulating mud cake (IMC) still lacks systematic theoretical support. In this study, a transient temperature field model in ultra-high-temperature wells under coupled drilling–production conditions is established. By integrating a Gaussian process regression (GPR) surrogate model with the Non-dominated Sorting Genetic Algorithm II (NSGA-II), a thermo-economic collaborative optimization of the thermal conductivity (kIMC) and the covered well section length (LIMC) of the IMC is conducted. The results show that wellbore-wall insulation can significantly suppress heat transfer between the wellbore and the formation, extending the thermal equilibrium time under drilling and production conditions to approximately six and five times that of the original conditions, respectively. Under drilling conditions, the bottomhole temperature (BHT) is mainly governed by LIMC; under production conditions, the tubing outlet temperature (TOT) exhibits a markedly amplified high sensitivity to kIMC. Both BHT and TOT display pronounced nonlinear responses to kIMC. When balancing insulation performance and engineering cost, the reasonable range of kIMC is 0.1–0.5 W/(m·℃). The Pareto front obtained from the multi-objective optimization quantitatively reveals the inevitable trade-offs among BHT reduction, TOT enhancement, and cost increase, providing a quantifiable decision-making basis for the engineering selection of wellbore-wall insulation parameters in ultra-high-temperature wells.

This paper investigates the dynamics of a two-coupled pendula system subjected to non-ideal vertical harmonic excitation generated by an electromagnetic shaker. The novelty of this study lies in establishing the dynamic bases for coupled pendula systems capable of sustaining stable rotational motions under non-ideal harmonic excitations, such as those characterising ocean wave conditions. This approach broadens the operational frequency range of pendulum-based wave energy converters (WECs) and enhances their robustness for efficient energy harvesting in harsh marine environments. The study aims to identify different types of dynamic responses for a wide range of parametric excitation, with particular emphasis on the effects of a parameter mismatch. The investigation focuses on the existence, stability, and robustness of phase-synchronised rotational motions, motivated by potential applications in wave energy harvesting devices. A four mechanical and half electrical degrees-of-freedom model incorporating interactions between the pendula and an electromagnetic shaker is developed. System responses are analysed with time histories, phase portraits, and Poincar & eacute;-based maps to determine the ranges of excitation amplitude and frequency supporting stable synchronised rotations. Results show that small asymmetries in pendulum lengths can shift the system response between co-existing attractors, inducing transitions from oscillatory to rotational regimes, in cases of non-identical pendula. These findings highlight the potential of using parameter asymmetry to extend the operational range of synchronised rotations in practical applications. Finally, the numerical model is validated experimentally, showing a good agreement with the observed qualitative dynamics and the boundaries of rotational responses.

This study proposes a multiscale slip-line field model for predicting cutting forces in chamfered tool machining of 42CrMo steel. By integrating slip-line field theory with unequal division shear-zone theory, a five-zone model incorporating the Dead Metal Zone (DMZ) effect is established. The Johnson-Cook constitutive model enables multiscale coupling by linking flow stress to shear angle, while the Schulz friction model establishes a velocity-dependent tool-chip friction relationship. The DMZ angle and chamfer friction angle, which are empirical in existing models, are quantitatively determined through DEFORM-2D simulations and embedded into the theoretical framework. These coupled relationships form the foundation for an energy minimization-based solution. Through iterative application of the minimum energy principle, the optimal shear angle is determined, yielding a closed-loop predictive model. Turning experiments on 42CrMo steel demonstrate that the model predicts cutting forces with errors consistently below 10

We investigate the vibrational energy transmission and dissipation of energy in mechanical jointed systems using single degree-of-freedom (DOF) and 2DOF impact oscillators incorporating dry friction. Analytical and semianalytical harmonic balance methods (HBM) are employed to evaluate dynamic responses, transmissibility, and power flow indices, with results validated via numerical integration. In the single-DOF system, friction increases force transmissibility and input energy in the non-impact regime, while enhancing dissipation and reducing transmission in the impact regime. In the 2DOF coupled system, dry friction at the interface induces stick-slip behaviour and energy transfer fluctuations, especially at low frequencies. A distinct superharmonic resonance peak emerges when impact oscillators begin to engage. The interactions between dry friction and the elastic impact constraint are frequency-dependent and competitive: lower friction facilitates constraint engagement and energy transfer at low frequencies, whereas higher friction reduces transmission and promotes localized energy dissipation near resonance. Non-monotonic features in the power-flow indices reveal that optimal combinations of dry friction and impact constraint parameters exist for minimal energy transfer or dissipation across the coupled non-smooth interface. The study reveals vibration transmission mechanisms in jointed systems with frictional sliding and intermittent impacts. It demonstrates that well tuned dry friction and elastic constraints can serve as effective passive vibration control elements in systems with clearance and frictional nonlinearities.

A failure of classical seal bore production packers for packer challenging wells, may lead inefficient, expensive operations, and also significant environmental risk. In response to these challenges, a low-cost and highefficiency ball plugging injection process has been proposed and developed, which primarily utilizes the motion and plugging capabilities of custom made balls to control the flow control of injected fluids across different formations, and its key technologies involved in the pitching, plugging-selection, and recovery process. The plugging balls were subjected to a rigorous manufacturing and performance inspection to ensure high strength and no deformation for the downhole operational environment. Motion characteristics and plugging mechanism of the plugging balls were revealed through calibrated mathematical modelling. Dimensionless analysis based on the Stokes number and Elasticity number was introduced to distinguish plugging, competition, and offside. An experimental rig has been developed and experimental studies have been conducted to determine process parameters and verifying mathematical predictions. Temperature sensitivity analysis was performed to assess the effect of elastic modulus reduction on plugging stability. The research findings from the modelling calibrated by the laboratory experiments were implemented successfully in the oilfield setting showing potentials in Enhanced Oil Recovery (EOR) of this technology.

Rub-impacts and local damages of the supercritical tail drive shaft system can cause dangerous dynamic responses, thereby affecting helicopters flight safety. At present, the dynamic behaviour of this type of shaft system with rub-impacts and local damages is not known. Hence, this study is focused on modelling and experimental verification of such system. For the rub-impact caused by dry a friction damper and local damages caused by impacts, we established the dynamic model and analyzed effects of local damages. Then we proposed the local damage identification method based on vibration response analysis. The tail drive shafts with local damages were manufactured and an experimental rig to investigate the supercritical tail drive shaft systems with rub-impact and local damage was developed. Dynamics experiments of the tail drive shaft system with rub-impact and local damage verify the mathematical predictions. This paper can provide theoretical underpinning for improvement of helicopters safety.

This article presents a generic methodology to investigate dynamics and bifurcation scenarios of multi degrees-of-freedom piecewise linear systems. The method takes advantage of the analytical solutions for linear regimes to define mapping transformations, which in turn allow to determine all periodic orbits. The methodology is applied to analyse dynamic interactions between two oscillators connected via an elastic link. A rich variety and complexity of solutions are obtained close to the first grazing frequency. Zones with isolated solutions and co-existence of three to five orbits were found. The in-phase and out-phase modes are sensitive to the phase shift between the forces and the ratio between the natural frequencies of the individual oscillators.

For low-frequency vibration control (<5 Hz), the unique advantages of bistable dynamic vibration absorbers (DVAs) are demonstrated through detailed theoretical explorations and mechanism analyses. Existing research has primarily focused on single-degrees-of-freedom (SDOF) systems, whereas the structural design and performance evaluation of multi-degrees-of-freedom (MDOF) configurations that incorporate bistable mechanisms remain underexplored. To address this gap, this paper presents a compact nonlinear dynamic vibration absorber (DVA) that employs a series-connected magnet structure, referred to as the SM-NDVA. The proposed system not only utilizes the bistable mechanism to achieve low-frequency resonance but also enhances absorption efficiency through a serial configuration. A long cantilever beam with a lump mass attached serves as the primary structure to simulate low-frequency vibration characteristics; an equivalent dynamic model incorporating the SM-NDVA is developed accordingly. The magnetic force of the triple-magnet structure is calculated using the equivalent magnetic charge method. Subsequently, transient vibration tests are conducted to identify key structural parameters, including energy dissipation coefficients, followed by an experimental validation and detailed discussion of the system response under harmonic excitations. While comparing the SM-NDVA, under the premise of the same total added mass, with the traditional SDOF magnetic nonlinear DVA (SDOF M-NDVA), the results show that the SM-NDVA achieves a significant improvement in the overall vibration absorption performance. Furthermore, the effect of magnet spacing on absorption efficiency is investigated, and an optimization strategy using a genetic algorithm is applied to identify optimal spacing configurations. Experimental validation demonstrates that the optimized SM-NDVA maintains a remarkable absorption efficiency across a wide excitation range. Finally, comparative tests under realistic working conditions show that the SM-NDVA outperforms conventional absorbers, which validates its potential for practical low-frequency vibration mitigation.

The fatigue performance of offshore structures in the oil and gas industry is vital to the reliability and integrity during service life, and there are very few studies on fatigue cracks induced dynamically to tubulars. Capability of a unique experimental fatigue rig designed to test single-edge notched beams [1] was in this work expanded allowing to obtain for new insights into fatigue crack growth in tubular specimens. Fatigue cracks were initiated in pre-cut grooves in aluminium tubular specimens and then under dynamic loading propagated in the direction of the groove. The alternating current potential difference (ACPD) method was adopted to monitor the crack propagation in time histories. Three specimen types featuring different groove depths were made and tested in fifteen individual experiments. And for each specimen type, a three-dimensional finite element model was created to calculate the stress concentration factor (SCF). Experimental measurements of specimen accelerations and forces generated were used to develop a novel calibrated dynamic model, for which dynamic responses were computed. The predictions obtained from a mathematical model were compared with the experimental results and a close correlation was observed.

In trimming of long overhanging thin-walled plates, we observed that the cutting force along the tool axis can be bidirectional rather than unidirectional like milling of short and stiff overhanging plates. This experimental phenomenon cannot be explained by standard oblique cutting force models. Accordingly, this study systematically investigated the interaction mechanism between the tool and the workpiece during trimming. It turned out that vibration velocity and displacement of the workpiece have non-ignorable effects on the direction of cutting velocity, engagement position between tool and workpiece, resulting in state-dependent inclination angle, instantaneous rotation angle and time delay. Consequently, a dynamic cutting force model that incorporates workpiece vibration-based modulation effects was developed, which effectively captured the change in the direction of cutting force along the tool axis. Furthermore, both simulation and experimental results demonstrated that workpiece vibration can reduce the amplitude of cutting force compared to rigid trimming. Additionally, surface comparisons of the workpieces after trimming were conducted, showing no obvious difference between short and long overhanging workpieces. This indicated that long overhanging thin-walled workpieces can be a feasible choice for trimming under certain conditions. These new findings offer new insights for trimming of thin-walled structures in industry.

Slender shafts have wide application on the aerospace, automotive and medical devices. However, they are prone to bending deformation during cutting process due to their low rigidity, resulting in poor machining accuracy and efficiency. A parallel multidirectional cutting (PMC) method is proposed using two tools to simultaneously cut the workpiece in forward or reverse directions contributing to overcome the problem of large deflections of these shafts. The main concept and PMC shared and unshared cutting modes are elucidated. An analytical model for PMC is established including chip geometry model, cutting force model and workpiece deflection feedback model. Given tool geometry, feed and depth of cut, chip load is accurately calculated using cutting edge discretization. The Johnson-Cook constitutive model is used to determine shear stress and shear force on the primary shear plane, and therefore the three-dimensional cutting force is obtained. The force condition of the workpiece is analysed under two clamping methods and the deformation of the workpiece is calculated and feed back into the model. On this basis, the influencing mechanism of cutting force, cutting power, cutting temperature and machining error of PMC is explored under different cutting modes, machined shaft geometry, tool parameters and cutting parameters. The smaller-the-better characteristic of Taguchi's method and signal-to-noise ratio are used to analyse the effect of cutting parameters on the PMC performance. Furthermore, an experimental validation is conducted to verify the cutting power, temperature, and diameter errors obtained by the proposed model, and the result shows a strong correlation with simulation predictions. The proposed method significantly improves machining precision and efficiency, with promising applications in high-precision manufacturing industries such as aerospace and medical device production.

Gallium nitride (GaN) is an important third-generation semiconductor material. However, due to its high hardness, high brittleness and anisotropy, the material removal efficiency of GaN during ultraprecision machining is low, and subsurface damage easily occurs. In order to achieve high-efficiency and low-damage ultra-precision machining, the model of double nanoscratches is innovatively utilized to investigate the mechanical behavioral of GaN at the atomic scale. Specifically, double nanoscratches experiments and corresponding molecular dynamics (MD) simulations were carried out on GaN (0001) crystal plane along the [1010 ] and [1210 ] crystal directions to reveal the material removal, deformation and subsurface damage mechanisms of GaN under anisotropic conditions. The results show that the plastic removal of GaN can be realized by setting loading force and scratch spacing. Scratching along the [1210 ] crystal direction has a greater ductile-brittle transition load force than the [1010 ] crystal direction. MD analysis shows that the downward-extending prismatic slip produced by scratching along the [1010 ] crystal direction is the cause of crack extension to the subsurface during the experiment. As the load force increases, the surface cracks of the double scratches expand and intersect, inducing streak-like brittle fracture. The significant increase in the lateral force of the second scratch is the main reason for the brittle fracture in the double scratch experiment. After the double nanoscratches experiment, the damage presented on the GaN subsurface mainly includes atomic scale damage such as amorphization, stacked laminations, polycrystalline nanoscratch, and phase transition. The Stacking fault bands around the damage zone inhibit the damage extension. The second scratch generates a large number of dislocations in the overlap zone and attenuates the subsurface amorphization under the influence of dislocation strengthening effect.