Jingkai Chen

Summary: Drilling vibration contributes largely to the premature failure of drillstring. The vibration absorption intensifier is a downhole drilling tool that suppresses the drillstring vibration while generating a high-pressure water jet. Previous studies have demonstrated its vibration suppression effect through experiments and its high-pressure water jet generation through computational fluid dynamics. Those field tests further demonstrated a longer service life of bottomhole assemblies (BHAs) and an improvement in the rate of penetration (ROP). However, the performance of the intensifier and its influence on the drillstring dynamics have not been investigated quantitatively. In this paper, we first derive a mathematical model for the intensifier and identify three working stages. We then couple the intensifier model with the drillstring lumped mass model and implement a numerical integration based on the fourth-order Runge-Kutta method, in which we check the intensifier status and bit/rock interactions at each integration timestep. The undertaken analyses in the time and frequency domains confirm that the intensifier can suppress the drillstring vibration and stabilize the weight on bit (WOB), while the generated high-pressure water jet can reach up to 132 MPa depending on the bottomhole geometry, the drilling parameters, the intensifier structures, and the size of the high-pressure waterjet nozzle. As such, this paper casts light on the vibration suppression of the drillstring and provides theoretical support to the field application of the intensifier.

In non-ordinary state-based peridynamics, the non-local deformation gradient constructed by averaging over material point neighborhoods leads to a non-injective mapping between force and deformation states, which results in zero-energy modes. This paper proposes a new Mid-point based Bond-Level PeriDynamic (MBLPD) model. After constructing the bond-specific neighborhood centered at midpoint of the bond, a weighted least squares fit yields a unique bond-associated deformation gradient; thereby ensuring the injectivity of the deformation to force mapping. On this basis, bond-strain energy is defined, and bond-level equilibrium equations are established through the principle of virtual work. The internal virtual work is then transformed into nodal internal forces, which yields the nodal equation of motion. Theoretical analysis proves the conservation of linear momentum, angular momentum, and the objectivity of the deformation. The numerical examples verify the efficacy of the proposed model. The influence of the neighborhood radius on numerical accuracy is investigated and an adaptive radius selection strategy correlated with bond length is proposed. Numerical results demonstrate that the MBLPD model achieves accuracy comparable to existing bond-associated formulations while effectively eliminating zero-energy modes. The proposed model provides an explicit bond-level kinematic description, offering an effective approach for deformation and fracture analysis in non-ordinary state-based peridynamics.

In non‑ordinary state‑based peridynamics, the nonlocal deformation gradient constructed by averaging over material point neighborhoods leads to a non‑injective mapping between force states and deformation states, which results in zero‑energy modes and non‑physical oscillations. In this paper, a new Mid‑point based Bond‑Level PeriDynamic (MBLPD) model is proposed. After constructing the bond-specific neighborhood centered at midpoint of the bond, a weighted least squares fit is then employed to obtain a unique bond-associated deformation gradient; thereby fundamentally ensuring the injectivity of the deformation‑to‑force mapping. On this basis, the bond strain energy is defined, and the bond‑level equilibrium equations are established through the principle of virtual work. The internal virtual work at the bond level is then transformed into nodal internal forces, which yields the nodal equation of motion. Theoretical analysis proves the conservation of linear momentum, angular momentum, and the objectivity of the deformation. The numerical examples are implemented to verify the efficacy of the proposed model. The influence of the neighborhood radius on numerical accuracy is investigated and an adaptive radius selection strategy correlated with bond length is proposed. Numerical results demonstrate that the MBLPD model achieves accuracy comparable to existing bond‑associated formulations while effectively eliminating zero‑energy modes. The proposed model provides an explicit bond‑level kinematic description, offering an effective approach for deformation and fracture analysis in non‑ordinary state‑based peridynamics.

Currently, the completeness of the peridynamics (PD) contact theory is challenged, and its compatibility with classical contact mechanics is limited. This study, based on the short-range force (SRF) method and the force-based PD contact method, explores the characteristics of PD contact interaction in detail. By deriving and calculating the analytical and numerical solutions of the PD contact force on a two-dimensional surface, the influence of the curvature of the contact surface and the geometric discretization parameters on the two solutions is evaluated. Subsequently, energy conservation tests are used to systematically evaluate the performance of different contact functions. These research results provide a foundation for improving both the PD contact model and the overall PD contact theory.

This paper presents a comprehensive and hybrid control framework for the real-time regulation of drillstring systems that are subject to complex nonlinear dynamics, including torsional stick–slip oscillations, coupled axial vibrations, and intricate bit–rock interactions. The model also accounts for parametric uncertainties and external disturbances typically encountered during rotary drilling operations. A robust sliding mode controller (SMC) is designed for inner-loop regulation to ensure accurate state tracking and strong disturbance rejection. This is complemented by an outer-loop model predictive control (MPC) scheme, which optimizes control trajectories over a finite horizon while balancing performance objectives such as rate of penetration (ROP) and torque smoothness, and respecting actuator and operational constraints. To address the challenges of partial observability and noise-corrupted measurements, an Ensemble Kalman Filter (EnKF) is incorporated to provide real-time estimation of both internal states and external disturbances. Simulation studies conducted under realistic operating scenarios show that the hybrid MPC–SMC framework substantially enhances drilling performance. The controller effectively suppresses stick–slip oscillations, provides smoother and more stable bit-speed behavior, and improves the consistency of ROP compared with both open-loop operation and SMC alone. The integrated architecture maintains robust performance despite uncertainties in model parameters and downhole disturbances, demonstrating strong potential for deployment in intelligent and automated drilling systems operating under dynamic and uncertain conditions.

This paper investigates the evolution of temperature and stress during induction heating local postweld heat treatment (PWHT) of ultra-thick pressure vessels (with a thickness typically exceeding 300 mm) through electromagnetic-thermo-mechanical coupling simulations and experimental validation, aiming to develop an effective heat treatment method for ultralarge equipment. The effects of various inductive heating parameters including the cable winding width, the number of turns, the spacing, the winding method, the current density, and the current frequency on the temperature uniformity during the heat treatment holding time are studied. The results indicate that the maximum temperature difference is directly proportional to current density, but inversely proportional to frequency, winding width, and the number of turns. After local PWHT, the residual stress on the outer surface of backward-oriented pressure vessels can be effectively reduced, but the stress relief on the inner wall is relatively small. Furthermore, the influence of heated bandwidth on the reduction of residual stress is considered. If reducing residual stress on the inner wall is considered, the width of the heated band should exceed 3Rt. If aforementioned width cannot be achieved, the local PWHT by primary plus secondary heating method can be used to further reduce the residual stress. This research sheds light on the application of inductive heating in ultralarge pressure vessels.