Hai Gu

Bio: Hai Gu is an academic researcher from American Bureau of Shipping. The author has contributed to research in topics: Centrifuge & Pore water pressure. The author has an hindex of 4, co-authored 8 publications receiving 40 citations.

Holding capacity of dynamically installed anchors in normally consolidated clay under inclined loading

Abstract: This paper describes a design framework for inclined tensile loading capacity (holding capacity) of dynamically installed anchors in soft clay. Centrifuge model test and numerical results indicate ...

A 3D RITSS approach for total stress and coupled-flow large deformation problems using ABAQUS

Abstract: A large deformation finite element (LDFE) method is implemented in a commercially available finite element software in three dimensions using a re-meshing and interpolation technique. The method allows fully coupled pore fluid effective stress analysis as well as decoupled total stress analysis to be performed. The method is described step by step following its application to offshore pipeline penetration analysis in full 3D. The results indicate versatility of the approach, showing reasonable agreement with existing solutions.

Technique for Modeling Installation and Pullout of DIAs on a Beam Centrifuge

Abstract: This paper describes a technique for modeling the installation and pullout of a dynamically installed anchor (DIA) using specifically designed equipment on a beam centrifuge. The equipment consists of three subassemblies, an X-Y table, an anchor installation system, and a pullout system. The X-Y table allows the location of anchor installation and pullout direction and pullout angle to be adjusted within a relatively short time without stopping the centrifuge. This permits the pullout angle with respect to vertical and the azimuthal angle of the pullout direction relative to the fins to be adjusted under high-g conditions. Inclined anchor penetration could also be preset by changing the lateral offset of the top of the guide tube. Finally, a very short transition time of several seconds between installation and pullout can be achieved, thereby allowing nearly short-term conditions to be achieved during pullout. The centrifuge model test results show that vertical pullout of non-vertically installed anchors and non-vertical pullout of vertically installed anchors both give a higher holding capacity than vertical pullout of vertically installed anchors. This indicates that the transverse pullout resistance of an anchor may contribute measurably to the anchor capacity and raises the possibility that, when appropriately installed, even higher pullout capacity may be obtainable from inclined pullout of non-vertically installed anchors. The findings also suggest that the ratio of short-term to long-term capacity may differ for different soils, thereby underlining the importance of being able to conduct tests at sufficiently shorter reconsolidation times.

Physical and Numerical Modeling of the Performance of Dynamically Installed Anchors in Clay

Abstract: Depletion of shallow-water hydrocarbons is increasingly forcing the oil and gas industry to explore in deeper water. Dynamically installed anchors (i.e. torpedo anchors and deep penetrating anchor) are increasingly used as a cost-effective solution for floating offshore structures in deep water environments because their installation cost is largely independent of water depth. In addition, dynamically installed anchors can be deployed accurately, and their performance is less dependent on accurate assessment of the soil shear strength since lower seabed strengths permit greater penetration depths. Despite of the economic advantages afforded by dynamically installed anchors, there remain significant uncertainties in the prediction of the embedment depth and verticality, which is likely to affect their long-term holding capacity. Currently, the holding capacity of the dynamically installed anchors is assessed using conventional pile capacity techniques, which neglect discrepancies in the rate of installation and failure mechanism between them.This paper presents a series of model tests simulating dynamic installation and monotonic pull-out of dynamically installed anchors in normally consolidated clay. The model tests are carried out in a beam centrifuge at 100g, with varying penetration angles, extraction angles and model masses. A special designed apparatus allows model anchors to be penetrated and extracted with different penetration angles. The test results show that for models without fins, no matter by which angle the model penetrated the soil, the smallest value of holding capacity is obtained when the pullout and penetration directions are the same. Results also indicate that the penetration depth linearly increases with the anchor mass. This study also reported the results from finite element (FE) analyses. The Coupled Eulerian-Lagrangian (CEL) approach in the commercial FE package Abaqus/Explicit is carried out to simulate dynamic anchor installation.The findings of this study points to a method of assessing the minimum holding capacity of the anchor and its depth of penetration. Further study is now on-going to study the behavior of finned anchors.Copyright © 2014 by ASME

An effective stress theoretical model for shear resistance and adhesion factor of dynamically installed anchors

Abstract: This paper proposes a theoretical effective stress model for estimating the shear resistance and the time-dependent adhesion factor of dynamically installed anchors. The anchor installation process...

P-ultimate for undrained analysis of laterally loaded piles. discussion and closure

Abstract: A discussion of a paper with the aforementioned title by Murff and Hamilton, published in this journal (Volume 119, Number 1, January 1993), is presented The discussion focuses on laterally loaded piles in layered soils Maugeri, Castelli, and Motta assert that the authors' method overpredicts the ultimate lateral resistance on the pile Discussion is followed by closure from the authors

Particle finite element method implementation for large deformation analysis using Abaqus

Abstract: In this study, a simple PFEM approach for analyzing large deformation problems in geotechnical practice is implemented in the commercial FEM package Abaqus. The main feature of the proposed Abaqus-PFEM approach lies in its capability to absorb the advantages of the functionality available in Abaqus and integrate them into PFEM with a single Python script, which leads to a considerable reduction in coding work. By utilizing the built-in functions in Abaqus to fulfil the standard incremental FEM analysis, as well as the powerful mesh-to-mesh solution mapping technique, the proposed Abaqus-PFEM approach allows for the large deformation analysis automatically running with a single Python script and requires no intervention from the user. The accuracy of the proposed Abaqus-PFEM approach is firstly validated through a simple elastic cantilever beam bending problem. Then, the performance and robustness of the proposed Abaqus-PFEM approach are further examined by three illustrative numerical examples: penetration of rigid footing, penetration of T-bar and pipeline–soil interaction problem. The numerical results demonstrate that the proposed Abaqus-PFEM approach as a powerful and easily extensible numerical tool is capable of handling large deformation and soil–structure interaction problems in geotechnical engineering, and consequently, it offers an alternative way to tackle such problems.

Holding capacity of dynamically installed anchors in normally consolidated clay under inclined loading

Abstract: This paper describes a design framework for inclined tensile loading capacity (holding capacity) of dynamically installed anchors in soft clay. Centrifuge model test and numerical results indicate ...

Numerical simulation of a free fall penetrometer deployment using the material point method

Abstract: Free Fall Penetrometer (FFP) testing consist of a torpedo-shaped body freefalling into a soil target. The use of this type of device is becoming popular for the characterization of shallow sediments in near-shore and off-shore environments because it is a fast, versatile, and non-expensive test capable of recording acceleration and pore pressures. In recent years, the data analysis advanced considerably, but the soil behavior during fast penetration is still uncertain. Hence, there is a need to develop numerical models capable of simulating this process to improve its understanding. This paper proposes a numerical framework to simulate the deployment of an FFP device in dry sands using the Material Point Method (MPM). A moving mesh technique is used to ensure the accurate geometry of the FFP device throughout the calculation, and the soil-FFP interaction is modelled with a frictional contact algorithm. Moreover, a rigid body algorithm is proposed to model the FFP device, which enhances the performance of the computation and reduces its computational cost. The sand is simulated by using two constitutive models, a non-associate Mohr-Coulomb (MC) and a Strain-Softening Mohr-Coulomb (SSMC) that reduces, exponentially, the strength parameters with the accumulated plastic deviatoric deformation ( Yerro et al., 2016 ). Variable dilatancy, which reduces as a function of the plastic strain, is also taken into account, and the strain-rate effects have been evaluated in terms of peak friction angle. In general, the behavior predicted by the MPM simulations is consistent with the experimental test. The results indicate that the soil stiffness has a big impact on the deceleration time-history and the development of a failure mechanism, but less influence on the magnitude of the peak deceleration and the penetration depth; the soil dilatancy reduces the FFP rebound, and the FFP-soil contact friction angle and the peak friction angle are highly linked to the peak deceleration.

Vertical holding capacity of torpedo anchors in underwater cohesive soils

Abstract: Torpedo anchors are regarded as one of the most efficient mooring solutions for taut mooring systems and can withstand vertical loads. The estimation of the undrained pullout capacity of the anchors is vital for the design of offshore floating facilities. There have been some achievements obtained for the calculation of the holding capacity of a torpedo anchor via field tests, conventional model tests under one gravity, centrifuge tests with a high value of gravity acceleration and numerical tests. However, a simple and reliable formula is still required to calculate the holding capacity of a torpedo anchor. In this study, 240 sets of laboratory tests were performed, and 11 differently shaped model anchors, vertically embedded in a soft sedimentary bed, were pulled out vertically from different types of cohesive soils and different embedment depths. The characteristics of the loading curves were analyzed, and the relationship between the pullout capacities and properties of the anchors and types of soils were investigated. Based on force analysis and the laboratory data, a formula was proposed for the calculation of the undrained monotonic holding capacity of a torpedo anchor, which mainly depends on the embedded depth of the anchor, net weight, geometry, and in situ soil properties. The calculated vertical holding capacities were consistent with the laboratory and field data obtained by the authors and other scientists.