A Normalized Terzaghi Model and Time-Step FEA for Predicting the Adsorption of a Cylindrical Object in Subsea Salvage

This paper proposes a normalized Terzaghi model modified based on finite element analysis to predict the adsorption force of a cylindrical object for salvage from the seabed. The maximum relative error is less than 5% compared with finite element analysis. Furthermore, the time-step finite element method is adopted to analyze the effects of the lifting force and bury depth. With increased lifting force, the critical displacement is reduced slightly, soil separation on the bottom of the object occurs earlier, and the velocity increases more quickly at the same burial depth. In addition, the soil displacement on the bottom stops increasing earlier, and the off-mud process is completed earlier. With increased burial depth, soil separation takes considerably longer, velocity increases more slowly, the maximum soil displacement is increased, and the off-mud process takes longer to complete

Mechanical Analysis of a Scraping Method to Remove Attached Barnacles

In order to clean the marine fouling attached to marine steel piles, a scraping method is proposed in this paper. Barnacles were used to represent a typical object needing removal, in order to estimate the maximum force required in the equipment designed for use in this method. On the basis of the orthogonal cutting theory and the peel zone method, a scraping method and its cutting force model are proposed in this paper for the surface cleaning of marine steel piles. The finite element method was used to verify the analytical model errors. The comparison showed that the relative errors of the cutting force are less than 10%. Our model can be used for cutting force estimation in cleaning equipment design. Our analysis shows that the blade rake angle has a large effect on the cutting force and that the optimum blade rake angle design is a compromise between blade strength and cutting force. We conclude that increasing the blade rake angle can reduce the cutting force in this scraping process; a medium blade rake angle [30°, 60°] is recommended, considering both cutting force and blade strength

Scaled Model Simulation and Experimental Verification of Submarine Flexible Pipeline Laying System

In order to adapt to the complex and changeable marine environment such as wind, wave, and current, the physical simulation experiment is usually needed in the design of a deep-sea flexible pipeline-laying system. In reality, the flexible pipeline-laying system is very large, and the experimental cost is huge. Therefore, when analyzing this system, it is necessary to carry out scaled model experiments to verify the rationality of it. Taking the flexible pipeline-laying system working under four-level sea conditions as an example, this paper deduces the similarity criteria of the scaled model according to the similarity theory. According to the required experimental site, the sizes and materials of the model are selected, and then the physical quantities of the model and their similarity ratio corresponding to the prototype are determined. According to the physical quantities of the experimental model, the similarity of dynamic characteristics and structural strength between the model and the prototype are verified by Adams and ANSYS Workbench. The research shows that the scaled model and prototype based on similarity theory can meet the established similarity relationship, and the scaled model experiment is an effective way to verify the rationality of the design of a flexible pipeline-laying system

A Normalized Terzaghi Model and Time-Step FEA for Predicting the Adsorption of a Cylindrical Object in Subsea Salvage

This paper proposes a normalized Terzaghi model modified based on finite element analysis to predict the adsorption force of a cylindrical object for salvage from the seabed. The maximum relative error is less than 5% compared with finite element analysis. Furthermore, the time-step finite element method is adopted to analyze the effects of the lifting force and bury depth. With increased lifting force, the critical displacement is reduced slightly, soil separation on the bottom of the object occurs earlier, and the velocity increases more quickly at the same burial depth. In addition, the soil displacement on the bottom stops increasing earlier, and the off-mud process is completed earlier. With increased burial depth, soil separation takes considerably longer, velocity increases more slowly, the maximum soil displacement is increased, and the off-mud process takes longer to complete

Simulation and Optimization of the Nozzle Section Geometry for a Suspension Abrasive Water Jet

In order to improve the life cycle and cutting ability of a suspension abrasive water jet nozzle at the same time, hydrodynamics technology, an enumeration method and multiparameter orthogonal optimization are used to optimize the nozzle section geometry, taking the inlet diameter coefficient of the nozzle, the axial length coefficient of the contraction section and the contraction section curve as optimization variables, and selecting the peak velocity and the unit flow erosion rate as the indicators, it is concluded that the optimal contraction section curve is a Widosinski curve, the optimal inlet diameter coefficient of the nozzle is 0.333 and the optimal axial length coefficient of the contraction section is 2.857. Compared with the commercial product single cone nozzle, the performance of the optimal section nozzle improves by 5.64% and the life cycle increases by 43.2%. On this basis, the effects of operating parameters, including inlet pressure, abrasive particle flow rate and abrasive particle size, are further studied. It is determined that the optimal section nozzle has the best performance under the above operating parameters. It is demonstrated that by optimizing the nozzle section geometry, the cutting capacity and life cycle of the nozzle are improved, the performance of the nozzle can be significantly improved and the optimization of the performance of the nozzle is realized

Numerical Simulations and Experimental Study on the Reeling Process of Submarine Pipeline by R-Lay Method

During the reeling process of the reel-lay method, the pipe will be subjected to combined loading of tension and bending. Excessive ovalization of the pipe will affect the structural performance and even lead to structural instability of the pipe. In this paper, a numerical simulation model of the pipe-reeling process is established by finite element tools. The Ramberg–Osgood material model is used to study the ovalization and bending moment of the pipe cross-section during the pipe-reeling process based on the Von Mises plasticity and nonlinear kinematic hardening rules. The results show that the ovalization and bending moment of the pipe section will change significantly during the pipe-reeling process. Subsequently, one set of 6-inch pipe-reeling experimental setups was designed to conduct a full-scale experiment. Compared with the experimental results, the feasibility of the finite element model is verified. Finally, the effects of diameter-to-thickness ratio, the material parameters of the pipe, and the pipe axial tension on the ovalization and bending moment changes are studied. Research shows that each parameter has a certain influence on the pipe of the reeling process, and the diameter-to-thickness ratio of the pipe has the most obvious effect. When the diameter-to-thickness ratio decreases, the bearing capacity for bending moments and the ability to resist ovalization of pipe are enhanced. At the same time, each parameter has a significant impact on the reeling process of the pipeline

Numerical Simulation for Elasto-Plastic Contact of Novel Ti-(SiC_f/Al₃Ti)-Laminated Composite with Double-Layered SiC Fiber Reinforcements

An innovative, high-strength metal⁻intermetallic-laminate (MIL) composite Ti-(SiCf/Al3Ti), reinforced by double or even several SiC fiber rows, was fabricated. A high-efficiency, semi-analytical model with a numerical equivalent inclusion method (NEIM) was employed to investigate the deformation behaviors, microscopic strengthening, and failure mechanisms of the composite during elasto-plastic sphere⁻plane contact. The microstructure and interface features were characterized by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The contact model for the Ti-(SiCf/Al3Ti) composite was validated via quasi-static compressive indentation tests with a spherical indenter. A series of in-depth parametric studies were conducted to quantify the effect of the microstructure. The results indicate that the as-fabricated laminated composite has a well-organized microstructure and a higher volume fraction of fibers. The SiC fiber rows effectively enhance the strength and toughness of the composite. The optimal diameter of the SiC fibers is 32 μm when the horizontal center distance between the adjacent fibers is 2.5 times that of the fiber diameter. The hole defects occurring above the fibers would damage the material strength most compared with those occurring in other positions. The optimal quantity of the SiC fiber rows is four when the thickness of the SiCf/Al3Ti layer is 400 μm and the fiber diameter is 8 μm

Research on Dynamic Response of Pipeline under the Reeling Process and Laying Process

During the process of laying submarine pipelines using the R-lay (short for reel-lay) method, the interaction between the pipeline and the laying equipment undergoes continual fluctuations, leading to bending in the pipeline induced by the stochastic dynamics of various external loads. Considering the challenge in forecasting the dynamic behavior of pipeline bending moments and ovality throughout this procedure, we constructed a finite element-based shell element model for a 6-inch pipeline. In this paper, a multi-step simulation approach was used to replicate the pipeline laying process, and the dynamic response in pipeline bending moments and ovality during the winding, unwinding, and straightening processes was analyzed. Additionally, the effects of the pipeline’s diameter–thickness ratio and material properties on the dynamic response process were also studied. The results show that the dynamic response in bending moments and ovality is closely related to the curvature of the pipeline; a brief peak will appear at the critical point where the pipeline deforms, and the peak is related to the different bending stages of the pipeline, with the winding stage having a greater impact on the peak than the unwinding stage. During the unwinding process, a reverse bending moment will occur. The dynamic response of pipeline bending moments and ovality is influenced to some extent by the pipeline’s diameter–thickness ratio and material properties, with the diameter–thickness ratio demonstrating a more conspicuous impact

Parameter Analysis and Optimization of Annular Jet Pump Based on Kriging Model

Jet pump efficiency heavily relies on the geometrical parameters of the pump design and parameter global optimization in the full variable space is still a big challenge. This paper proposed a global optimization method for annular jet pump design combining computational fluid dynamics (CFD) simulation, the Kriging approximate model and experimental data. The suction angle, the flow ratio, the diffusion angle, and the area ratio are selected as the design variables for optimization. The optimal space filling design (OSF) method is used to generate sampling points from the design space of the four design variables. The optimization method solves the constrained optimization problem with a given head ratio by building the functional relationship established by the Kriging model between efficiency and design parameters, which makes the method more applicable. The design result shows that the annular jet pump efficiency is predicted well by the Kriging model; m is a key variable affecting the annular jet pump efficiency. As the area ratio m decreases, the mixing effect at the suction chamber outlet can be improved, but the frictional resistance increases

A FBG and Magnetostrictive Alloy based Magnetic Field Sensor with the Demodulation realized by Optoelectronic Oscillator

A FBG and magnetostrictive alloy based magnetic field optical sensor is realized with the demodulation by a new dual-loop optoelectronic oscillator (OEO). Unlike the previously reported OED-based sensing schemes, the stability of this proposed scheme is enhanced by using the combination of a fiber ring laser (FRL) cavity and a dual-loop OEO structure. The sensitivity of −48.40476 Hz/mT is obtained. The stability is up to 0.194 ppm