The long-term response of adhesively bonded composite joints is governed by the coupled effects of bonded-layer rheology, adherend viscoelasticity, and interfacial damage. In many joint-level studies, however, these mechanisms are treated separately, which weakens both the physical consistency of parameter identification and the reliability of long-term response interpretation. This study develops a unified multiscale framework for composite single-lap joints under tensile-hold loading by integrating RVE-based homogenization of the orthotropic viscoelastic behavior of unidirectional and plain-woven composite adherends, a viscoelastic cohesive-zone formulation for the bonded layer, and a surrogate-assisted inverse-identification strategy combining a CNNbased forward model with particle swarm optimization. Tensile-hold relaxation tests were conducted under displacement control, and the force-time response during a 1200 s hold period was used as the inversion target. On the independent test subset, the proposed inverse framework achieved a mean response-level R2 above 0.9998, while constitutive-consistency validation remained above 0.9999. The calibrated model further indicates that the hold-stage response is governed by the coupled evolution of interfacial displacement readjustment, local strain accumulation, traction attenuation, and progressive damage growth, rather than by viscoelastic stress decay alone. Acoustic emission measurements provide independent temporal corroboration of persistent irreversible internal activity during relaxation. The proposed framework offers an efficient route for identifying viscoelastic cohesive parameters and a physically grounded basis for interpreting relaxation-damage coupling in bonded composite joints under sustained loading.

Power take-off (PTO) mechanisms are key devices that convert ocean wave energy into mechanical energy for triboelectric nanogenerators (TENGs)-based wave energy converter. However, conventional PTO mechanisms, including gears and screws, are structurally complex, require high assembly precision, and are difficult to maintain, which limits their potential for large-scale engineering applications. Moreover, the PTO mechanism parameter optimization typically depends on numerous single-variable experiments, leading to high costs and limiting the potential for globally optimal designs. Here, we propose a novel wave energy converter (WEC) whose core is a planar four-bar linkage that converts the heaving motion of a wave-driven buoy into the reciprocating rotation of a main shaft, and then drives the TENG rotor into unidirectional rotation via one-way bearings for continuous electricity generation. This design not only simplifies the PTO structure but also enhances energy harvesting efficiency during both upward and downward motions. We establish a kinematic model of the PTO mechanism to predict the angular velocity of the TENG rotor, and verify the model through theoretical calculation and experimental testing of the short-circuit current of the TENG unit. Next, we propose an AI-assisted mechanism optimization method that uses the kinematic model to generate a dataset, combined with artificial neural network training and intelligent algorithm search, with the TENG rotor kinetic energy as the optimization objective, to optimize the mechanism parameters. This enables PTO parameters to be tailored for specific marine environments without extensive physical testing. The optimized device achieves peak and average power densities of 3.83 W/m3 and 0.746 W/m3, respectively, and after power management demonstrates the ability to power small electronic devices. This work provides a timely and cost-effective strategy for optimizing PTO mechanisms in TENG-based WECs, accelerating the transition from laboratory research to practical applications.

This study develops a coupled theoretical framework for predicting interfacial failure in fusion-bonded reinforcement joints (FRJs) in reinforced thermoplastic pipes (RTPs) under internal pressure or axial tension. The framework integrates a stress-transfer formulation, a helically armored stiffness representation, thick-walled cylinder theory and a cohesive traction-separation law into a unified scheme that explicitly models the reinforcement fibers and polymer matrix as separate constituents. This modeling strategy reduces the amount of experimental material characterization required, compared with homogenized approaches and offers clear advantages for scenarios involving material nonlinearity or temperature-dependent behavior. The model's accuracy is validated against finite element simulations, blast tests, and tensile experiments, with errors in adhesive shear stress distributions and failure loads remaining within 10 %. The adhesive layer exhibits a pronounced U-shaped shear stress profile, with peak values at the joint ends. Effective shear-transfer lengths of approximately 30 mm under internal pressure and 20 mm under axial tension establish a minimum bonded length requirement of 60 mm. Fiber orientation shows a clear monotonic influence: the peak shear stress at the joint ends decreases with the joint fiber angle but increases with the pipe reinforcement angle, yielding an optimal configuration at a 45 degrees joint angle and a +/- 55 degrees pipe reinforcement angle under practical pipe-manufacturing constraints. These findings also provide actionable engineering guidance, indicating that a 100 mm bonded length with this fiber angle architecture supports safe operation up to 2 MPa internal pressure or 5 kN axial tension, with a safety factor exceeding 3. Overall, the proposed framework offers a new analytical pathway that improves stress-transfer fidelity while simplifying material parameter calibration, thereby enhancing the reliability of RTP bondedjoint design in demanding service environments.

Polymer flooding is an enhanced oil recovery (EOR) technique that improves oil extraction by injecting polymer solutions into reservoirs. However, the disposal and treatment of polymer flooding waste liquids (PFWL) present significant challenges due to their high viscosity, complex molecular structure, and environmental impact. This study investigates the shear-induced degradation of polymer solutions, focusing on rheological properties, particle size distribution, and morphological changes under controlled shear conditions. Experimental results show that shear forces significantly reduce the viscosity of polymer solutions, with shear rates of 4285.36 s−1 in the rotating domain and 3505.21 s−1 in the fixed domain. The particle size analysis reveals a significant reduction in average particle size, indicating polymer aggregate breakup. SEM images confirm these morphological changes. Additionally, numerical simulations using a power-law model highlight the correlation between shear rate, wall shear stress, and polymer degradation efficiency. This study suggests that optimizing rotor–stator configurations with high shear forces is essential for efficient polymer degradation, offering insights for designing more effective polymer waste liquid treatment systems in oilfields.

The axial movement of tools in the wellbore caused by the heave of drilling vessels or operation platforms and the resultant sand production in the annulus are particularly prominent. Currently， there is also a lack of computational analysis methods specifically addressing these issues. For the sand control packing completion string structure in deepwater （water depth > 1 000 m） shallow （burial depth < 300 m） horizontal wells， a string vibration model considering the dynamic friction effect of the pipe wall was built. Then， the finite difference method was used to analyze the string vibration process under wave excitation to reveal the axial movement behavior of the packing tool in the wellbore under different conditions. Finally， a structural improvement scheme for the packing tool was proposed. The research results show that the reciprocating movement of the pipe string caused by the heave of drilling vessels can be regarded as a low-frequency vibration. Considering the string-wall friction and the variations in movement characteristics at different wellbore locations， the corresponding displacement-time relationship can be obtained using the vibration model. The conversion of dynamic-static friction causes the displacement⁃time curve of the tool in the wellbore to have a “platform section” with zero displacement. Affected by the packing seal bore and the “platform section”， the axial displacement of the packing tool at the top packer in the middle section of the wellbore is the smallest. By extending the top packer distance， increasing the seal bore length and utilizing twice the number of seal stacks during the packing operation， the achievable distance for packing to the backwash position is significantly increased. Concurrently， the seal friction resistance is raised by approximately 1.5 times. This effectively mitigates issues of packing tool position variation and seal bore disengagement caused by the heave of drilling vessels. The test results show that the scheme effectively solves the problem of annular sand production.

Liquid sloshiness refers to the movement of liquid in a container due to external force or its own gravity, and there is a free surface that can move freely and has strong nonlinear and random characteristics. With the development of oil, gas, and Marine mining and Marine aquaculture in offshore engineering, more and more floating production and storage tankers, liquefied natural gas carriers (LNG) and other liquid-carrying vessels are used to store offshore oil and transport natural gas. In order to ensure the transportation of oil and natural gas at sea, people pay more attention to the movement of multiphase flow and the fluid-solid coupling with the transport structure. In this paper, the numerical simulation of liquid sloshing under different baffles is carried out based on the smoothed particle hydrodynamics (SPH) method. Based on the governing equations of continuum mechanics, a model for calculating the sloshing motion of gas-liquid two-phase flow in a tank is established and discretized by SPH kernel approximation and particle approximation techniques. A physical experiment platform is used to verify the feasibility and effectiveness of the numerical model. The influence of the physical parameters of the baffle on the liquid swaying is studied, including the flexibility, height, width and shape of the baffle, which provides a reference for the selection of baffle parameters. The effects of different baffles on the motion of oil-gas interface and the load on bulkhead under the condition of 20% liquid loading rate are calculated and compared.

Natural gas hydrates are considered a promising clean energy resource with significant development potential. This study focuses on the research and application of energy supplementation tools in natural gas hydrate extraction. First, a methane combustion heating process is proposed, and a methane combustion heating tool is designed to heat hydrate reservoirs through methane combustion. The tool includes key components such as a pressure-bearing pipe and an igniter, with the primary goal of promoting hydrate dissociation by increasing the reservoir temperature. To assess the tool's ignition and heating capabilities in a water-immersed environment, surface experiments are conducted, and the tool's actual value for reservoir development is verified using a gas production model. Next, a flow field model of the tool in the downhole environment is established using Computational Fluid Dynamics (CFD), and the flow field characteristics and heat transfer performance of the tool are systematically studied. The results show that the tool can increase the reservoir temperature by 10 degrees C. Further analysis of the impact of various operational parameters on the internal flow field and heating efficiency reveals that a higher inlet gas flow rate (methane at 6 m/s) and optimized gas ratio (e.g., 1:5) significantly improve heating efficiency. Additionally, the influence of key structural parameters, such as the number of combustion ports and combustion channel dimensions, on the tool's heating performance is analyzed. Based on these findings, recommendations for optimizing the tool's design are proposed.

This study proposes a microwave heating energy supplement technology for gas hydrate reservoir. The microwave radiation simulation model of the leaky coaxial antenna is established by HFSS. Based on the simulation results of microwave antenna structure parameters on the radiation performance, the optimized shape, angle, length, width and fillet of the slot are rectangle, 80 degrees, 38 mm, 12 mm and 2 mm, respectively. To compare the heating performance of microwave antenna before and after optimization, a microwave heating simulation model for hydrate reservoir is developed, which is validated by experimental results. The comparison results illustrate that, after microwave heating 10 h with the optimized antenna structure, the average temperature within a 1-m radius of natural gas hydrate reservoir increases to 10.613 degrees C, which is about 5.5 degrees C higher than that before the optimization. The aforementioned results suggest that the optimized microwave antenna structure significantly increases the temperature of the hydrate reservoir, providing the necessary energy to drive hydrate decomposition. The proposed microwave energy supplementation technique holds promise for advancing the efficient development of natural gas hydrates, the further investigation of effect of which on gas production within hydrate reservoirs is needed for future application.

As deep-sea oil and gas extraction technologies advance, the demand for high-performance joints in reinforced thermoplastic pipes (RTPs) has increased. This study introduces a novel fusion-reinforced joint for RTPs and analyzes its tensile failure mechanism. Two user-defined material (VUMAT) subroutines were developed for unidirectional fiber composites and plain fabric composites to analyze the damage of RTPs and joints. The tensile damage mechanisms were evaluated using the 3D Hashin failure criterion, the maximum strain failure criterion, the residual stiffness model, and the cohesive zone model (CZM). To validate the numerical model, fusion-reinforced joints were designed, machined, and subjected to uniaxial tensile tests. Findings suggest that matrix damage in RTPs is the primary factor contributing to stiffness degradation. The shear stress in the adhesive layer at both ends of the joint reaches the shear strength, resulting in the failure of the adhesive. The tensile process can be divided into four distinct stages: the no-damage stage, the bonding damage stage, the matrix damage stage, and the failure stage. Initially, damage in the adhesive layer leads to a minor decrease in tensile stiffness, followed by significant matrix damage in the RTPs. Failure of the adhesive layer at both ends of the joint gradually propagates to the middle, culminating in the failure of the fusion zone. The time required to reach maximum strain in the central joint region is longer than at the ends.

针对目前压裂泵液力端阀箱裂纹检测依靠工人经验判断,随机性大、可靠性差的问题,本文提出采用声发射技术对压裂泵裂纹信号进行分析诊断,并设计研发相应的裂纹实时监测系统.通过模拟试验的方法,确定出本监测系统裂纹起裂的振铃计数阈值,门槛值为,并在文件传输间隔为3s时获得系统的最高监测准确度,并对试验转速对系统的影响进行了分析.模拟试验结果表明,该监测系统可在复杂工况条件下保持稳定运行,具有一定的工程应用价值.

Sucker rod constructed of FRP (fiber-reinforced plastic) is currently used in offshore oil and gas industries due to its high tensile strength, lightweight, and resistance to corrosion. Due to the fact that the surface of FRP sucker rod cannot be threaded, it is often attached to steel joints via adhesive technology, and the bonded joint of FRP sucker rod is particularly prone to breaking and coming off. The current research is primarily concerned with the mechanical properties of FRP sucker rods, with little emphasis on the adhesive performance of bonded connections. This research developed a numerical model with a novel bonded joint structure based on the cohesion failure criteria. An indoor test was used to determine and confirm the expected bonded joint failure load. Additionally, an orthogonal test was conducted to maximize the adhesion performance. The findings indicated that a) theaccuracy of numerical model was within 10% and b) when the groove angle was 30 degrees, the length ratio was 2/23, each groove was 14 mm in length based on a triangular groove, and the anticipated failure stress of the bonded joint was around 443 kN, an increase of 10%.

Droplet impacts on super-hydrophobic surfaces play an important role in many fields. Previous studies have focused on rigid substrates and ignored the effect of substrate deformation. Simulating droplet impacts on a flexible substrate is a challenge to numerical methods due to the coupling of free surface, elasticity, large deformation and surface tension. In this study, a fully meshfree model of fluid–solid interaction is developed based on the smoothed particle hydrodynamics (SPH) method. The liquid droplet is modeled by the weakly compressible (WC) SPH method, and the flexible substrate is modeled by the total Lagrangian (TL) SPH method. Liquid surface tension is modeled by the continuum surface force (CSF) method through reconstructing the free surface of the droplet. The surface geometry reconstruction process is given for both 2D and 3D cases, enabling the model to simulate the bouncing of droplets in both 2D and 3D cases. Furthermore, in order to reduce the computational cost of 3D simulation, the TL-SPH model combined with shell theory established the TL-SPH-shell model, thus achieving the simulation of 3D droplet impact on thin plates. For verification and testing, the established WC-TL SPH model is used to simulate the process of droplet impact on various substrates, including fixed-fixed and curved beams, micro-pillar substrates, and cantilever beams. The results show that the spreading, retraction and bouncing processes of the droplets interact with the deformation and recovery of the flexible substrate, accompanied by large deformation and dynamic characteristics, which can be effectively simulated by the model.

The research on the injection production string (IPS) system mechanics was limited to theoretical derivation and numerical simulation due to the lack of a mechanical detection system (MDS) for IPS. This made it difficult to further optimize string design and reduce accidents during injection and production operations. The three-dimensional (3-D) equivalent axial force model (3-D EAF model) of IPS was established using the 3-D vector method, and MDS based on the 3-D EAF model was designed. The calculation and detection of the DXX-162-X20 example of the Shengli Oilfield well showed that both the 3-D EAF model and MDS met the actual working conditions of IPS. The root-mean-square error between the calculated value of the 3-D EAF model and the downhole-measured data was less than 6.25 kN. MDS met the mechanical detection requirements under the injection production operation environment, such as a well-depth of 3000 m, well fluid pressure of 30 MPa, and downhole temperature of 80 °C. The MDS effectively detected the axial force of 0–300 kN using the strain gauge matrix detection method, and the standard deviation was less than 3.13 kN during each experimental point. The 3-D EAF model was used in more wells of the Bohai oilfield in China to predict the axial force in the process of IPS running down. The relative error was no more than 5%. The above results showed that the 3-D EAF model and MDS could effectively solve the mechanical detection problems of IPS in oil and gas wells having high temperature and high pressure and provided a theoretical basis and method support for the research of string mechanics.

In the beam pumping system, the broken valve cover of the oil well pump frequently leads to oil well failure. This paper examined the alternating load of the oil well pump valve cover and predicted its fatigue life. First, the fluid–structure coupling simulation model of valve ball motion was established through the fluid dynamics simulation software Fluent to investigate the velocity of the valve ball impacting the valve cover. Based on the simulation results about the impact velocity of the valve ball, the mechanical model of the valve ball impacting the valve cover was constructed through ANSYS/LS-DYNA software, and the impact stress and change rule of the valve cover were analyzed. Then, the S-N fatigue curve of the common material of the valve cover was experimentally obtained. Based on the impact stress simulation results of the valve cover and the fatigue curve of the common material of the valve cover, the modified Miner’s Rule was applied to evaluate the fatigue life of the oil well pump valve cover. The results showed that the impact stress of the valve cover was positively related to the impact velocity of the valve ball, and the fatigue life of the 17-4 PH valve cover was longer than that of other materials. The above results not only provide a theoretical basis for the performance improvement and material selection of the valve cover but also contribute to the optimization of production parameters of the oil well.

Mineral precipitation or scale formation in oil and gas wellbore is recognized as an obstacle to hydrocarbon recovery. A method using computational fluid dynamics for structure optimization of downhole descaling tools is presented in this paper. The effects of key parameters, such as the nozzle structure style, cone angle, and incidence angle on the descaling performance, are systemically investigated. Numerical results indicate that the cone nozzle has higher jet efficiency because of its smoother velocity and pressure changes, as well as less energy loss. Under the conditions considered, key parameters of the downhole descaling tool are optimized as an incidence angle of 10° and a cone angle of 14°. Furthermore, the numerical results are validated with experimental results, in which the average error between the experimental and numerical results is ∼7.1%. The proposed numerical approaches can accurately predict the jetting status, which consequently has technical guiding significance for the design of downhole descaling tools.

Aiming at the problem of prominent tear marks in the inner ring of the low-stress cropping cross-section of thick-walled metal tubes, a low-stress cropping method based on symmetric position notching is proposed. The optimal internal notch shape is determined by the XFEM method as V-shape. Combined with the orthogonal experimental method, it is concluded that the bottom corner radius of the internal notch has the greatest impact on cracking force and cracking quality, and the flare angle of the internal notch has the smallest impact. The optimal internal notch parameters of the typical tube are obtained through the optimization analysis. The cropping results of comparing the tubes with an optimal internal notch of 45# steel and 304 stainless steel with the traditional tube show that the fatigue tear marks of inner rings are significantly reduced by the proposed cross-section quality evaluation method, and the cropping time is also obviously shortened. Considering those notch parameters related to cracking force and deflection, the critical cracking force formula and discontinuous variable section deflection formula of the tube with annular notches and different parameters are established. The evaluation parameters of deflection allowable value ωi(2LB/(D-d)) are proposed. The allowable ratio of length to the wall thickness of 45# steel tube in cropping with common wall thickness is given, and the allowable deflection range which meets the cropping requirements before cracking is obtained.

During oil-well production, there are often cracks, breaks, and perforation corrosion on the screen pipe that can significantly deteriorate sand control and pipe strength. To repair damaged screen pipes, we developed a technique originating from the tube hydroforming, and the feasibility of the technique was systematically investigated. First, the elastoplastic mechanics of patch tubes during the hydroforming process was analyzed to investigate the forming mechanism. Second, tensile experiments showed that AISI 321 after cold drawn and solution had good mechanical properties. A numerical simulation model of a hydroforming patch composed of AISI 321 steel was built to investigate the effect of structural parameters such as the length, initial outer diameter, and thickness of a patch tube on hydroforming patch performance. Forming pressure did not significantly change with length, but it decreased with initial outer diameter and increased with thickness. In addition to the simulation, a hydroforming test bench was constructed to experimentally test the patch method. Test results showed that the patch tube could fit closely with the screen base pipe, and residual contact stress could be more than 139.78 kN/m2. Deformation strengthening due to the deformed martensite was conducive to improving the strength of the patch tube after hydroforming. The combination of the simulation and experiment indicates that the application of hydroforming patch technology can effectively repair damaged screen pipes.