Jet formation and penetration performance of a double-layer charge liner with chemically-deposited tungsten as the inner liner

This paper proposes a type of double-layer charge liner fabricated using chemical vapor deposition(CVD)that has tungsten as its inner liner.The feasibility of this design was evaluated through penetration tests.Double-layer charge liners were fabricated by using CVD to deposit tungsten layers on the inner surfaces of pure T2 copper liners.The microstructures of the tungsten layers were analyzed using a scanning electron microscope(SEM).The feasibility analysis was carried out by pulsed X-rays,slug-retrieval test and static penetration tests.The shaped charge jet forming and penetration law of inner tungsten-coated double-layer liner were studied by numerical simulation method.The results showed that the double-layer liners could form well-shaped jets.The errors between the X-ray test results and the numerical results were within 11.07%.A slug-retrieval test was found that the retrieved slug was similar to a numerically simulated slug.Compared with the traditional pure copper shaped charge jet,the penetration depth of the double-layer shaped charge liner increased by 11.4% and>10.8% respectively.In summary,the test results are good,and the numerical simulation is in good agreement with the test,which verified the feasibility of using the CVD method to fabricate double-layer charge liners with a high-density and high-strength refractory metal as the inner liner.

Discovery and Significance of the Triassic–Late Paleozoic Double-layered Basement in the Songliao Basin:Based on the Complete Coring Data from ICDP Borehole SK2

The Songliao Basin(SLB)covers an area of approximately 260,000 km2in northeastern Asia and preserves a continuous and complete Cretaceous terrestrial record(Wang et al.,2021).The region is the most important petroliferous sedimentary basin in China because of its continual annual oil and gas equivalent production of tens of millions of tons(ca.220–440 million barrels per year)since 1959.The SLB was previously thought to have developed on Hercynian basement and accumulated continuous sedimentary deposits during the Late Jurassic and Cretaceous(Wan et al.,2013;Wang et al.,2016).

Performance and Application of Double-layered Microcapsule Corrosion Inhibitors

Double-layered microcapsule corrosion inhibitors were developed by sodium monofluorophosphate as the core material,polymethyl methacrylate as the inner wall material,and polyvinyl alcohol as the outer wall material combining the solvent evaporation method and spray drying method.The protection by the outer capsule wall was used to prolong the service life of the corrosion inhibitor.The dispersion,encapsulation,thermal stability of microcapsules,and the degradation rate of capsule wall in concrete pore solution were analyzed by ultra-deep field microscopy,scanning electron microscopy,thermal analyzer,and sodium ion release rate analysis.The microcapsules were incorporated into mortar samples containing steel reinforcement,and the effects of double-layered microcapsule corrosion inhibitors on the performance of the cement matrix and the actual corrosion-inhibiting effect were analyzed.The experimental results show that the double-layered microcapsules have a moderate particle size and uniform distribution,and the capsules were completely wrapped.The microcapsules as a whole have good thermal stability below 230 ℃.The monolayer membrane structure microcapsules completely broke within 1 day in the simulated concrete pore solution,and the double-layer membrane structure prolonged the service life of the microcapsules to 80 days in the simulated concrete pore solution before the core material was completely released.The mortar samples containing steel reinforcement incorporated with the double-layered microcapsule corrosion inhibitors still maintained a higher corrosion potential than the monolayer microcapsule corrosion inhibitors control group at 60 days.The incorporation of double-layered microcapsules into the cement matrix has no significant adverse effect on the setting time and early strength.

Current observation and analysis based on mooring systems in the Andaman Sea

The basic structure and intraseasonal evolution of currents in the southeastern Andaman Sea was analyzed based on data collected in 2017 from two subsurface moorings(C1 and C5).Periodic variation in the upper ocean currents of the Andaman Sea was investigated by combining observational and satellite data.Mooring observations show that rapid changes of current speed and direction occurred in May and June,with a significant increase in current velocity at the C1 mooring.In the second half of the year,southward flow dominated at the C1 mooring,and alternating northward and southward flows were evident at the C5 mooring during the same period but the northward flow prevailed in boreal winter.In addition,analysis of the power spectra of the upper currents revealed that the tidal period at both moorings is primarily semidiurnal with weaker energy than that of the low-frequency currents.The upper ocean currents at the C1 and C5 moorings exhibited intraseasonal variation of 30-60 d and 120 d,while the zonal current at the C1 mooring exhibited a notable period of approximately 180 d.Further analysis indicated that the variability of currents in the Andaman Sea is influenced primarily by equatorial Kelvin waves and Rossby wave packets.Moreover,our results suggest that equatorial Kelvin waves from the eastern Indian Ocean entered the Andaman Sea in the form of Wyrtki Jets and propagated primarily along two distinct pathways during the observation period.In addition to coastal boundary Kelvin waves,it was found that a branch of the Wyrtki Jet that directly enters the Andaman Sea and flows northward along the slope of the continental shelf,and reflected Rossby wave packets by topography.

Intraseasonal variability of the Kuroshio observed via mooring at 18°N

Insufficient observations near the origin of the Kuroshio have led to incomplete understanding of the intraseasonal variability(ISV)of the Kuroshio.Direct measurements of the Kuroshio velocity were performed with an array of three profiler moorings(122.7°E,123°E,and 123.3°E)along 18°N from January 2018 to February 2020.The ISV of the Kuroshio at 18°N was investigated based on a combination of mooring observations and global high-resolution HYbrid Coordinate Ocean Model reanalysis data.The estimated time-averaged transport in the upper 350 m across the observation transect was 6.5±2.6 Sv(1.0 Sv=10^(6)m^(3)/s).Two significant ISV peaks at 50-60 and~100 d were recognized in the power spectra of the meridional velocity and transport.Further analysis indicated that the ISV at 50-60 d was caused by westward-propagating eddies at average propagation speed of~13 cm/s and wavelength of~635 km.Another ISV peak at~100 d was mainly caused by northward-propagating eddies generated in the North Equatorial Current region.Further investigation indicated that the ISV of the Kuroshio at 18°N is dominated by meridional transport,rather than by the zonal migration of the Kuroshio main axis.Our findings provide a better understanding of the ISV of the Kuroshio east of Luzon Island.

Double-layer model updating for steel-concrete composite beam cable-stayed bridge based on GPS

In order to establish the relationship between the measured dynamic response and the health status of long-span bridges, a double-layer model updating method for steel-concrete composite beam cable-stayed bridges is proposed. Measured frequencies are selected as the first-layer reference data, and the mass of the bridge deck, the grid density, the modulus of concrete and the ballast on the side span are modified by using a manual tuning technique. Measured global positioning system （GPS） data is selected as the second-layer reference data, and the degradation of the integral structure stiffness EI of the whole bridge is taken into account for the second-layer model updating by using the finite element iteration algorithm. The Nanpu Bridge in Shanghai is taken as a case to verify the applicability of the proposed model updating method. After the first-layer model updating, the standard deviation of modal frequencies is smaller than 7%. After the second-layer model updating, the error of the deflection of the mid-span is smaller than 10%. The integral structure stiffness of the whole bridge decreases about 20%. The research results show a good agreement between the calculated response and the measured response.

Computation of the Fatigue Life of Road Wheel with Double-Layer Rubber Flange

In order to increase the fatigue life (FL) of road wheels (RW), a kind of double layer rubber flange (DLRF) is put forward. It consists of two layers of rubber, where metal wires are laid in the inner layer and the outer layer has no inlaid metal wires. Stress, strain and temperature field of DLRF were calculated with ANSYS finite element analysis (FEA) software, FL of DLRF RW was also computed with fracture mechanics fatigue theory. The results of computation indicate that the heat generated in RW's rubber flange (RF) can be reduced by the use of DLRF, and the FL of RW can be increased without affecting the mechanical intensity of RW.

Internal tides in the northern South China Sea from 20-day in-situ mooring observations in 1998

20-day in-situ ADCP current and CTD data are used to investigate the characteristics and energy of the internal tides in the northern South China Sea （NSCS）. The results show that the O1, K1, M2 and S2 constituents of internal tides are energetic and diurnal constituents （O1 and K1） are dominating. In the observational period, the current vectors of these four constituents all rotate clockwise and the maximum semi-major axe of internal tidal ellipses is more than 14 cm/s. The variation of ocean temperature shows that the internal tides present obvious quasi-diurnal oscillation and the average amplitude reaches 50 m. Furthermore, these internal tides carry high energy and appear to be intermittent. The maximum values of KE （PE） during the observational period are up to 2 （3.5） k J/m^2 for diurnal internal tides, and up to 1 （1.5） k J/m^2 for semidiurnal internal tides.

Fully Coupled Effects of Hull,Mooring and Risers Model in Time Domain Based on An Innovative Deep Draft Multi-Spar

The coupled hull, mooring and riser analysis techniques in time domain are widely recognized as the unique approach to predict the accurate global motions. However, these complex issues have not been perfectly solved due to a large number of nonlinear factors, e.g. forces nonlinearity, mooring nonlinearity, motion nonlinearity and so on. This paper investigates the coupled effects through the numerical uncoupled model, mooring coupled model and fully coupled model accounting mooring and risers based on a novel deep draft multi-spar which is especially designed for deepwater in 2009. The numerical static-offset, free-decay, wind-action tests are executed, and finally three hours simulations are conducted under 100-year return period of GOM conditions involving wave, wind and current actions. The damping contributions, response characteristics and mooring line tensions are emphatically studied.

Static and Dynamic Analysis of Mooring Lines by Nonlinear Finite Element Method

This study has focused on developing numerical procedures for the static and dynamic nonlinear analysis of mooring lines. A geometrically nonlinear finite element method using isoparametric cable element with two nodes is briefly presented on the basis of the total Lagrangian formulation. The static and dynamic equilibrium equations of mooring lines are established. An incremental-iterative method is used to determine the initial static equilibrium state of cable systems under the action of self weights, buoyancy and current. Also the Newmark method is used for dynamic nonlinear analysis of ocean cables. Numerical examples are presented to validate the present numerical method, and examine the effect of various parameters.

Study on A New Mooring System Integrating Catenary with Taut Mooring

Analyzed are the merits and demerits of catenary mooring system and taut mooring system, which are commonly used nowadays. As falling somewhere between these two systems, a new mooring system integrating catenary with taut mooring is proposed. In order to expound and prove the advantages of this new system, the motion performance of a semi-submersible platform is simulated by employing full time domain coupled analysis method. A comparison of the result of new mooting system with that of taut mooring system shows that the movement of the platform using the new type mooting system is smaller than that using the taut mooring system, which ensures a better working condition. Furthermore, the new mooring system is also compatible with the characteristics of catenary mooting system, which eliminates the requirement of anti-uplift capacity of the anchors.

Fatigue Analysis of the Taut-Wire Mooring System Applied for Deep Waters

Precisely predicting the fatigue life of taut-wire mooring systems has become an interesting and important problem for scientists and engineers since there are still difficulties in the inspection and maintenance of mooring lines in a rough sea environment especially in deep waters. In this paper, a comprehensive fatigue analysis is performed for a polyester taut-wire mooring system of an FPSO based on the time domain dynamic theory, rainflow cycle counting method and linear damage accumulation rule of Palmgren-Miner. Three influential factors in the fatigue analysis including the pre-tension, dynamic stiffness and T-N curve are investigated in detail. Two polyester T-N curves, one is from the DNV- 0S-E301 and the other is from the API-RP-2SM, are adopted in the calculation. The fatigue analysis of the mooting system after one-line failure is also carried out. The calculation results indicate that the fatigue life is significantly affected by the T-N curve. The fatigue life decreases with increasing pre-tension, and is largely reduced if taking into account the dynamic stiffness caused by cyclic loading. The analysis also proves that one-line failure has remarkable effects on the fatigue lives of other mooting lines. The present parametric and comparative study is believed to be meaningful to further understanding of the taut-wire mooting system for deepwater applications.

Performance of Two Types of Mooring Systems in the Heave Motion of a Two-body Floating Wave Energy Converter

This work investigated the influence of two types of mooring systems on the hydrodynamic performance of a two-body floating wave energy converter(WEC). It also investigated the effects of the physical parameters of the mooring system on the amount of extractable power from incident waves in the frequency domain. The modeled converter comprised a floating body(a buoy), a submerged body with two mooring systems, and a coupling system for two bodies. The coupling system was a simplified power take-off system that was modeled by a linear spring-damper model. The tension leg mooring system could drastically affect the heave motion of the submerged body of the model and increase relative displacement between the two bodies. The effects of the stiffness parameter of the mooring system on power absorption exceeded those of the pretension tendon force.

Sensitivity Analysis of Air Gap Motion with Respect to Wind Load and Mooring System for Semi-Submersible Platform Design

A design of semi-submersible platform is mainly based on the extreme response analysis due to the forces experienced by the components during lifetime. The external loads can induce the extreme air gap response and potential deck impact to the semi-submersible platform. It is important to predict air gap response of platforms accurately in order to check the strength of local structures which withstand the wave slamming due to negative air gap. The wind load cannot be simulated easily by model test in towing tank whereas it can be simulated accurately in wind tunnel test. Furthermore, full scale simulation of the mooring system in model test is still a tuffwork especially the stiffness of the mooring system. Owing to the above mentioned problem, the model test results are not accurate enough for air gap evaluation. The aim of this paper is to present sensitivity analysis results of air gap motion with respect to the mooring system and wind load for the design of semi-submersible platform. Though the model test results are not suitable for the direct evaluation of air gap, they can be used as a good basis for tuning the radiation damping and viscous drag in numerical simulation. In the presented design example, a numerical model is tuned and validated by ANSYS AQWA based on the model test results with a simple 4 line symmetrical horizontal soft mooring system. According to the tuned numerical model, sensitivity analysis studies of air gap motion with respect to the mooring system and wind load are performed in time domain. Three mooring systems and five simulation cases about the presented platform are simulated based on the results of wind tunnel tests and sea-keeping tests. The sensitivity analysis results are valuable for the floating platform design.

Risk Assessment on A Pipeline Passing Through A Ship Mooring Area

It is very common that a submarine pipeline has to pass through a ship mooring area near a harbor zone in the Bohai Bay, China. The risk assessment of accidental events induced by the potential anchoring ships is carried out, which will lead to external interference with the pipeline. A procedure to calculate the probability for the anchoring activity in the ship mooring area to damage the underlying pipeline is proposed. The adopted methodology is based on the recommendations suggested by the DNV Codes. The same philosophy is also applied to estimate the damage probability that is concerned with sinking ships.

Analysis for the Deployment of Single-Point Mooring Buoy System Based on Multi-Body Dynamics Method

Deployment of buoy systems is one of the most important procedures for the operation of buoy system. In the present study, a single-point mooring buoy system which contains surface buoy, cable segments with components, anchor and so on is modeled by applying multi-body dynamics method. The motion equations are developed in discrete node description and fully Cartesian coordinates. Then numerical method is used to solve the ordinary differential equations and dynamics simulations are achieved while anchor is casting from board. The trajectories and velocities of different nodes without current and with current in buoy system are obtained. The transient tension force of each part of the cable is analyzed in the process of deployment. Numerical results indicate that the transient payload increases to a peak value when the anchor is touching the seabed and the maximum tension force will vary with different floating configuration. This work is helpful for design and deployment planning of buoy system.

Lateral Vibration Behavior Analysis and TLD Vibration Absorption Design of the Soft Yoke Single-Point Mooring System

Mooring system is the key equipment of FPSO safe operation. The soft yoke mooring system is regarded as one of the best shallow water mooring strategies and widely applied to the oil exploitation in the Bohai Bay in China and the Gulf of Mexico. Based on the analysis of numerous monitoring data obtained by the prototype monitoring system of one FPSO in the Bohai Bay, the on-site lateral vibration behaviors found on the site of the soft yoke subject to wave load were analyzed. ADAMS simulation and model experiment were utilized to analyze the soft yoke lateral vibration and it was determined that lateral vibration was resonance behaviors caused by wave excitation. On the basis of the soft yoke longitudinal restoring force being guaranteed, a TLD-based vibration damper system was constructed and the vibration reduction experiments with multi-tank space and multi-load conditions were developed. The experimental results demonstrated that the proposed TLD vibration reduction system can effectively reduce lateral vibration of soft yoke structures.

Mooring System Optimisation and Effect of Different Line Design Variables on Motions of Truss Spar Platforms in Intact and Damaged Conditions

This paper presents the effect of mooring diameters, fairlead slopes and pretensions on the dynamic responses of a truss spar platform in intact and damaged line conditions. The platform is modelled as a rigid body with three degrees-of-freedom and its motions are analysed in time-domain using the implicit Newmark Beta technique. The mooring restoring force-excursion relationship is evaluated using quasi-static approach. MATLAB codes DATSpar and QSAML, are developed to compute the dynamic responses of truss spar platform and to determine the mooring system stiffness. To eliminate the conventional trial and error approach in the mooring system design, a numerical tool is also developed and described in this paper for optimising the mooring configuration. It has a graphical user interface and includes regrouping particle swarm optimisation technique combined with DATSpar and QSAML. A case study of truss spar platform with ten mooring lines is analysed using this numerical tool. The results show that optimum mooring system design benefits the oil and gas industry to economise the project cost in terms of material, weight, structural load onto the platform as well as manpower requirements. This tool is useful especially for the preliminary design of truss spar platforms and its mooring system.

Impact Analysis of Air Gap Motion with Respect to Parameters of Mooring System for Floating Platform

In this paper, the impact analysis of air gap concerning the parameters of mooring system for the semi-submersible platform is conducted. It is challenging to simulate the wave, current and wind loads of a platform based on a model test simultaneously. Furthermore, the dynamic equivalence between the truncated and full-depth mooring system is still a tuff work. However, the wind and current loads can be tested accurately in wind tunnel model. Furthermore, the wave can be simulated accurately in wave tank test. The full-scale mooring system and the all environment loads can be simulated accurately by using the numerical model based on the model tests simultaneously. In this paper, the air gap response of a floating platform is calculated based on the results of tunnel test and wave tank. Meanwhile, full-scale mooring system, the wind, wave and current load can be considered simultaneously. In addition, a numerical model of the platform is tuned and validated by ANSYS AQWA according to the model test results. With the support of the tuned numerical model, seventeen simulation cases about the presented platform are considered to study the wave, wind, and current loads simultaneously. Then, the impact analysis studies of air gap motion regarding the length, elasticity, and type of the mooring line are performed in the time domain under the beam wave, head wave, and oblique wave conditions.

Theoretical Model and Dynamic Analysis of Soft Yoke Mooring System

As a popular solution for mooring an FPSO （Floating Production, Storage and Offloading） permanently in shallow water, the soft yoke mooring system has been widely used in ocean oil production activities in the Bohai Bay of China. In order to simulate the interaction mechanism and conduct dynamic analysis of the soft yoke mooring system, a theoretical model with basic dynamic equations is established. A numerical iteration algorithm based on error estimation is developed to solve the equations and calculate the dynanfic response of the mooring system due to FPSO motions. Validation is conducted by wave basin experimentation. It is shown that the numerical simulation takes only a few iteration times and the final errors are small. Furthermore, the calculated results of both the static and dynamic responses agree well with those ones obtained by the model test. It indicates that the efficiency, the precision, the reliability and the validity of the developed numerical algorithm and program are rather good. It is proposed to develop a real-time monitoring system to further monitor the dynamic performance of the FPSO with a soft yoke mooring system under various real sea environments.