We present a dual-horizon peridynamics (DH-PD) formulation for fracture in granular and rock-like materials. In contrast to discrete crack methods such as XFEM, DH-PD does not require any ...representation of the crack surface and criteria to treat complex fracture patterns such as crack branching and coalescence. The crack path is the natural outcome of the simulation. In this manuscript, a new penalty method to model the contact for compressive fractures and constraining the penetration conditions is developed. The new method is applied to several benchmark problems in geomechanics including the four-point shear test, the indirect tensile (Brazilian) test of rock disks with one or multiple initial cracks. By using an appropriate damping coefficient, the quasi-static solution for rock failure is obtained when the dynamic formulation is used. A good agreement is obtained between the results given by DH-PD and those by the experiments.
•Novel dual-horizon peridynamics formulation•The method accounts for crack opening as well as crack closure.•The method is validated through several numerical examples.
Wave-induced ship motion and load responses are usually investigated on the assumption that the incident waves are long-crested. The realistic sea waves are however short-crested irregular waves. ...Real practice reveals that the ship motion and load responses induced by short-crested waves are different from those induced by long-crested waves. This paper aims to conduct a comprehensive study on ship motions and loads in different wave fields. For this purpose, comparative studies by small-scale model towing tank test and large-scale model sea trial are conducted to experimentally identify the difference between ship motions and loads in long-crested and short-crested irregular waves. Moreover, the influences of directional spreading function of short-crested waves on ship motions and loads are analyzed by numerical seakeeping calculation. The results and conclusions obtained from this study are of great significance for the further extrapolation and estimation of ship motions and loads in short-crested waves based on long-crested wave response results.
This paper investigates the nonlinear hydroelastic motion and load responses on a large flexible ship advancing in harsh irregular waves. A 3D time-domain nonlinear hydroelasticity theory for the ...prediction of ship motions, deformations and wave loads in long-crested irregular waves is presented. The nonlinear Froude–Krylov force and hydrostatic restoring force are calculated on the instantaneous wetted hull surface while the linear diffraction force and radiation force are estimated on the static mean wetted surface. The radiation forces are estimated by retardation function method to take account of the wave memory effects and forward speed effects. The slamming loads that were derived by momentum impact theory are also included in the ship motion equation to investigate the whipping responses. The hydrodynamic and structural responses are fully coupled by modal superposition principle to consider the hydroelastic effects including springing and whipping responses. The numerical results are well validated by the experimental data of a segmented model with large flare-bow tested in an ultra-long laboratory tank. The numerical and experimental data of ship responses in different irregular wave conditions are systemically analyzed and compared by time series analysis, spectral analysis, and probability statistics analysis methods.
Load carrying capacity is of importance in the evaluation of the stability of submarine pressure shell structure. During the buckling process of cylindrical shell under hydrostatic pressure, the ...total potential energy of ring-stiffened cylindrical shell can be divided into constant component, linear component and square nonlinear component. Based on the derivations of buckling loads of smooth cylindrical shell and ring-stiffened cylindrical shell, the reduced stiffness method (RSM) is applied to assess the role of different stiffness reductions in the evaluation of stable load carrying capacity of cylindrical shell. This study shows: (1) the circumferential membrane stiffness is influence the stability of cylindrical shell largest; (2) the ring ribs have a significant effect on the overall stability of ring-stiffened cylindrical shells under hydrostatic pressure; (3) the circumferential buckling wave number of ring-stiffened cylindrical shell may not depend on the membrane stiffness reduction of shell, but it increases with the bending stiffness reduction of ring ribs.
•Stiffness reduction on the load carrying capacity of ring-stiffened cylindrical shell.•Investigation of different stiffness effects on the stability of cylindrical shell.•Derivation of buckling loads of smooth and ring-stiffened cylindrical shell.•Stability of ring-stiffened cylindrical shells under hydrostatic pressure.
IntroductionSelective posterior rhizotomy (SPR) is a preferred procedure for relieving spastic children with cerebral palsy, but it is associated with severe pain and significant emergence agitation ...(EA). The thoracolumbar interfascial plane (TLIP) block provides an effective blockade to the dorsal branch of the spinal nerve. We hypothesise that the TLIP block may be an effective tool to alleviate EA and postoperative pain scores in children with cerebral palsy undergoing SPR.Methods and analysisThis study is a single-centre, randomised, parallel-controlled trial being conducted in Beijing, China. A total of 50 paediatric patients with cerebral palsy scheduled for SPR are randomised in a 1:1 ratio to receive bilateral TLIP block with 0.2% ropivacaine 0.5 mL/kg or control. Patients in the TLIP group receive general anaesthesia combined with TLIP block, while patients in the control group receive only general anaesthesia, without a TLIP block. The primary outcome is the Paediatric Anaesthesia Emergence Delirium Score. The secondary outcomes are the incidence of EA, the Wong-Baker Faces Pain-rating Scale, the perioperative haemodynamics, the intraoperative remifentanil and propofol dosage, the extubation time and recovery time, and adverse reactions.Ethics and disseminationThis study was approved by the Ethics Committee of Dongzhimen Hospital, Beijing University of Chinese Medicine on 21 September 2023 (2023DZMEC-379–02). Written informed consent is obtained from the legal guardian of each patient. The results of this study will be published in peer-reviewed international journals.Trial registration numberChiCTR2300076397
Springing and whipping play an important role in determining the fatigue damages of ultra-large container ships in waves, and it is widely acknowledged that the separation of the contributions of ...springing and whipping on fatigue damages is difficult. In this paper, the effects of springing and whipping on a targeted 21,000 TEU container ship are numerically investigated. The springing responses are calculated based on the linear 3D frequency domain hydroelasticity theory, while a 3D nonlinear time domain hydroelasticity formulation which couples the 3D hydrodynamic theory, 1D Timoshenko beam theory, 2D generalized Wagner method and 1D green water theory, is adopted to obtain the slamming-induced whipping response. Spectral analysis method is analyzed and compared with an indirect time domain method. Through investigating the characteristics of the accumulated fatigue damages with respect to the significant wave heights and characteristic wave periods of short-term sea states, the contributions from springing and whipping to the accumulated fatigue damages are generally separated for most short-term sea states. In addition, several short-term sea states are chosen to present detailed information on the extents to which springing and whipping increase the fatigue damages relative to the low-frequency structural responses counterpart.
The so-called large multi-body floating offshore structure is a new type of offshore structure with a huge and extremely flat deck area, which has a promising prospect as a floating port and also in ...applications in the area of marine space exploitation. Due to its unique structural form, the hydrodynamic and structural response characteristics are very complex. Specifically, due to the instantaneous position variation in the body surface, the nonlinearity of the free surface, the interactions between floating bodies, and the elastic deformation of floating bodies, the nonlinear factors are significant and cannot be neglected. For these kinds of problems, methods based on CFD-FEA (computation fluid dynamics–finite element analysis) coupling simulation have significant advantages over traditional methods. In the present paper, the hydrodynamic and structural response characteristics of a large multi-body floating offshore structure are studied using a CFD-FEA method, and the results are compared with those obtained by the potential-flow-based commercial code SESAM/WADAM, and a three-dimensional nonlinear hydroelastic analysis commercial code COMPASS-WALCS-NE. The comparison and the analysis of the results show that the CFD-FEA method presented in this study can well simulate the behavior of the hydroelastic responses of flexible floating structures and has the potential to capture complex nonlinear behaviors.
Due to the complex fluid interference between outrigger and main hull, it is difficult to predict the trimaran load fluctuation accurately in different marine environments. Therefore, a time-domain ...Rankine method is developed to improve the accuracy of trimaran load prediction. This method successfully adds the nonlinear load components in time-domain load simulation by taking into account the factors such as instantaneous hull wetted surface, steady ship waves, green wave and slamming. Additionally, the nonlinear growth of green wave and slamming is also observed at outrigger and wet deck, with the increasing of speeds and wave heights. Finally, the relatively smaller errors in the Rankine method are confirmed by comparison with the values from a trimaran model test and linear time-domain load prediction method. Furthermore, the weakly nonlinear Rankine method is considered to be more suitable for trimaran load prediction under harsh marine environment.
In this paper, we present a dual-horizon peridynamics formulation which allows for simulations with dual-horizon with minimal spurious wave reflection. We prove the general dual property for ...dual-horizon peridynamics, based on which the balance of momentum and angular momentum in PD are naturally satisfied. We also analyze the crack pattern of random point distribution and the multiple materials issue in peridynamics. For selected benchmark problems, we show that DH-PD is less sensitive to the spatial than the original PD formulation.
•Stable crack paths with variable horizon and particle sizes.•Dual-horizon peridynamics for multiple materials/material interfaces.•Fulfillment of balance of momentum and balance of angular momentum.
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