Control of Unstable Ship Motions Using Anti-Rolling Tanks: Erosion of Safe Basins

The objective of the paper is to apply modern numerical techniques of nonlinear dynamics to the problem of control of the roll motion employing U-shaped anti rolling tanks (ART). Parametric rolling in head seas is the focus of the paper. A transom stern small vessel, well known for her tendency to develop strong parametric excitation is investigated. Nonlinear equations are employed to describe the liquid motion inside the tank, the forces and moments generated by the tank on the ship and the coupled ship motions (heave, roll and pitch). These are numerically solved for different initial conditions. An analysis of the dynamical behavior of the vessel with stabilization is presented in the form of numerical limits of stability, safe basins, integrity curves and integrity surfaces. Finally, curves of critical amplitude for different wave tunings are computed. A design procedure for quantitative assessment of the level of parametric rolling mitigation by means of ART’s is discussed.

Supporting New Insight in Pipeline Hydrodynamics Using Stochastic Approaches on External Corrosion Damage

Several recent discoveries in the fluid-structure interactions between the external flows and circular cylinders placed close to the wall have added new values to the hydrodynamics of unburied marine pipelines on a seabed. The hydrodynamics of waves and/or currents introduced vortex flows surrounding the pipeline. External corrosions formed in marine pipelines were assumed to be partly contributed by such fluid-structure interactions. The spatial consequences of such interactions were of interest of this study. This paper summarized some experimental and numerical works carried out by previous researchers on these new discoveries. Actual field data were utilized in this study to support this hypothesis. The characteristics of corrosion orientations in the pipelines were studied comprehensively using stochastic approaches and results were discussed. Results adopted from the field data acknowledged well to the hypothesis from the reported literature. The updated knowledge from this fluid-structure interaction is hoped to be given more attention by the industry and perhaps to be incorporated into the current subsea pipeline designs.

FourStar™ Dry-Tree Semisubmersible Development

This paper discusses the development of a dry-tree semisubmersible (DTS) platform concept appropriate for deployment in non-hurricane/non-cyclonic environments worldwide, and the verification of the concept through wave basin model tests. An example configuration is presented for an application in 2,100 m water depth offshore Brazil.

An Innovative Synthetic Mooring Solution for an Octagonal FPSO in Shallow Waters

An octagonal FPSO has been proposed for marginal oil and gas development in shallow waters. A shuttle tanker will be deployed near the FPSO during offloading operations. This new concept simplifies the design and manufacturing processes, yet maintains full production, storage, and offloading functions of a conventional ship-shaped FPSO. However, design of the mooring system for this floating unit imposes technical challenges due to: 1) high environmental loads expected on this unit, 2) large dynamic offsets of the unit in shallow waters, and 3) inadequate performance of catenary mooring systems in shallow waters. Thus, development of a viable station keeping solution becomes a key issue to the new concept FPSO design. In this paper, an innovative mooring system is designed to meet the challenges. The FPSO mooring system consists of pile anchors, bridle chains, anchorage buoys, and polyester ropes. Nine mooring lines are grouped into three bundles which evenly spread around the FPSO. The shuttle tanker is attached to the FPSO with a nylon rope hawser at the bow and secured to pre-installed anchorage buoys at the stern with two other nylon ropes. Analyses have been performed for the FPSO mooring system. It is concluded that the proposed mooring system is fully functional and effective.

Measurement of Soil Suction and Soil-Water Characteristics of Bentonite-Sand Mixtures

The soil-water characteristic curve (SWCC) is a widely used experimental means for assessing fundamental properties of unsaturated soils for a wide range of soil suction values. The study of SWCC is helpful because some properties of unsaturated soils can be predicted from it. Nowadays, much attention has been paid to the behaviours of highly compacted bentonite-sand mixtures used in engineering barriers for high level radioactive nuclear waste disposal. It is very important to study the various performances of bentonite-sand mixtures in order to insure the safety of high-level radioactive waste (HLW) repository. After an introduction to vapor phase method and osmotic technique, a laboratory study has been carried out on compacted bentonite-sand mixtures. The SWCC of bentonite-sand mixtures has been obtained and analyzed. The results show that the vapor phase method and osmotic technique is suitable to the unsaturated soils with high and low suction.

Application of a Viscoelastic Model for Polyester Mooring

A new practical method to simulate time-dependent material properties of polyester mooring line is proposed. The time-dependent material properties of polyester rope are modeled with a standard linear solid (SLS) model, which is one of the simplest forms of a linear viscoelastic model. The viscoelastic model simulates most of the mechanical properties of polyester rope such as creep, strain-stress hysteresis and excitation period-dependent stiffness. The strain rate-stress relation of the SLS model has been re-formulated to a stretch-tension relation, which is more suitable for implementation into global performance and mooring analyses tools for floating platforms. The new model has been implemented to a time-domain global performance analysis software and applied to simulate motion of a spar platform with chain-polyester-chain mooring system. The new model provides accurate platform offset without any approximation on the mean environmental load and can simulate the transient effect due to the loss of a mooring line during storm conditions, which has not been possible to simulate using existing dual-stiffness models.

Experimental Study on Influences of Wave Height on Liquefaction Depth of Silty Soil Bed

Storm waves tend to cause seabed liquefaction by exerting strong cyclic loads on the seabed of the Yellow River Delta. In order to study influences of different wave heights on liquefaction depth of the soil bed, silty soil taken from the Yellow River Delta is used to prepare a soil bed for flume experiments and local parts of superficial soil layer were disturbed by hand. The weakened soil tended to liquefy and slide under wave actions and the liquefaction depth increased with the increasing of wave height. Based on the experimental results, an empirical relationship was proposed between liquefaction depth of silty soil bed and wave height under experimental conditions.

Effect of Seabed Slope on Offshore Pile Lateral Behaviour Under Wave Force

Fixed offshore platforms supported by pile foundations are required to resist dynamic lateral loading due to wave forces. The response of a jacket offshore tower is affected by the flexibility and nonlinear behavior of the supporting piles. In this study, a typical fixed offshore platform is chosen, and dynamic wave analysis is performed on it. Analysis has been performed for normal environmental conditions and extreme conditions. For the foundation, the deflections and reactions at regular intervals along the vertical direction from the seabed have been found out from the dynamic analysis, and the results have been compared for normal and extreme conditions. The aim of this study is to investigate the effects of the combined lateral and vertical loads on pile group foundation of a fixed offshore structure and the effects of seabed slope on the pile responses. To provide a more accurate and effective design for offshore pile foundation systems under axial structural loads and lateral wave loads, a finite element model which is modelled in FLAC3D is employed herein to determine the soil structure interaction under similar loading conditions. Three dimensional modelling and the analyses are done using FLAC3D — a finite element package.

Vibration Isolation Using Pile Rows in a Layered Poroelastic Half-Space Against the Vibration Due to Harmonic Loads

The isolation of the vibration due to a harmonic vertical load using pile rows embedded in a layered poroelastic half-space is investigated in this study. Based on Biot’s theory, the frequency domain fundamental solution for a vertical circular patch load applied in a layered poroelastic half-space is derived via the transmission and reflection matrices (TRM) method. Utilizing Muki and Sternberg’s method, the second kind of Fredholm integral equations describing the dynamic interaction between the pile rows and the layered poroelastic half-space subjected to a harmonic vertical load is constructed. The isolation effect of piles rows for the vibration due to the harmonic vertical load is investigated via numerical solution of the integral equations. Numerical results of this study show that a stiffer upper layer overlying a softer bottom half-space will worsen the vibration isolation effect of pile rows and vice versa. Also, pile rows with large length are preferable for a better vibration isolation effect.

Dynamic Analysis of Floating Bodies Considering Multi-Body Interaction Effects

Recently, there are several problems in space, infra-structure, and facility in the contiguity of existing harbors due to the trend of enlarged container vessels. In this regard, the Mobile Harbor has been proposed conceptually as an effective solution for those problems. This concept is a kind of transfer loader of the containers from the large container ship to the harbor on land, which is a floating barge of a catamaran type. The catamaran-type vessel is well known for its advantage in maneuverability, resistance, and the effectiveness for working on board. For the safe and effective operation of the two floating bodies, a container ship and the mobile harbor in the near sea apart from the quay, robot arms, novel crane systems, and pneumatic fenders are specially devised with additional mooring facility or DP (dynamic positioning) system. The concept is to be verified through comparison and simulation studies under various environmental conditions. It is shown that the proposed concept is in general feasible but there are several areas for further investigation and improvement.