Wenkai Wang

Bio: Wenkai Wang is an academic researcher from Shanghai Jiao Tong University. The author has contributed to research in topics: Penetration depth. The author has an hindex of 2, co-authored 2 publications receiving 24 citations. Previous affiliations of Wenkai Wang include Transport Research Institute.

Penetration depth of torpedo anchor in cohesive soil by free fall

Abstract: Developing deep sea technologies, many marine novel facilities have been introduced; and mooring systems, however, have become more expensive, complex, and hard cooperative in deep-water marine industry. The torpedo anchor is regarded as a modern technology benefits from easy installation, cost efficiency, and high level of anchor force. In this study, the penetration depth of a free falling torpedo anchor into cohesive soil has been laboratory investigated. 128 Sets of tests have been conducted with nine different torpedo anchors not only in shape, but also in size. Three anchor aspect ratios and three different types of muds were tested while mud rheological properties such as the yield stress and flow curves were also measured. Finally, a formula calculating the penetration depth of the anchor, regardless of soil separation has been proposed based on energy conservation principle and experimental measurements. Results indicate that the predicted penetration depth has a good conformity with the measured penetration depths in laboratory and field tests. Static undrained shear strength values should be reduced in formula when the impact velocity exceeds a critical value. Soil separation occurs depending on the anchor nose angle and surface roughness, and also soil properties. Nevertheless, the critical impact velocity resulting into soil separation and its degree require further study in the future.

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.

Installation of dynamically embedded plate anchors as assessed through field tests

Abstract: A dynamically embedded plate anchor (DEPLA) is a rocket-shaped anchor that comprises a removable central shaft and a set of four flukes. The DEPLA penetrates to a target depth in the seabed by the kinetic energy obtained through free-fall in water. After embedment the central shaft is retrieved leaving the anchor flukes vertically embedded in the seabed. The flukes constitute the load-bearing element as a plate anchor. This paper focuses on the dynamic installation of the DEPLA. Net resistance and velocity profiles are derived from acceleration data measured by an inertial measurement unit during DEPLA field tests, which are compared with corresponding theoretical profiles based on strain rate–enhanced shear resistance and fluid mechanics drag resistance. Comparison of the measured net resistance force profiles with the model predictions shows fair agreement at 1:12 scale and good agreement at 1:7.2 and 1:4.5 scales. For all scales the embedment model predicts the final anchor embedment depth to a high de...

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.

Pull-out capacity of an inclined embedded torpedo anchor subjected to combined vertical and horizontal loading

Abstract: Whilst the installed torpedo anchors in offshore practice are often characterized with off-verticality, the effect of inclination on the anchor pull-out capacity has seemingly received little attention in the research literature. This paper presents a numerical study on the pullout capacities and failure envelopes of inclined embedded torpedo anchors subjected to combined vertical and horizontal loading. Using Coupled Eulerian–Lagrangian finite element method, effects of load inclination, azimuthal angle of pull-out plane and anchor inclination were sequentially evaluated. It was found the most critical pull-out plane is the one that coincides with anchor plane towards the anchor inclination direction. Its corresponding failure envelope, which can be well fitted by a closed form expression, gives the conservative estimation of anchor pull-out capacities. The comprehensive parametric investigation indicated this conservative failure envelope is mainly affected by anchor inclination and soil’s strength gradient. A series of tables with fitting constant values appropriate for different strength and inclination conditions were furnished. On these bases, a simple design procedure was developed for estimating the ultimate pull-out capacities of inclined embedded torpedo anchors. The outcomes of this work are likely of help for engineers to factor the anchor inclination into the design practice of torpedo anchors.

Visualizing the effect of Fin length on torpedo anchor penetration and pullout using a transparent soil

Abstract: The effect of torpedo shape on its penetration depth and pull out capacity is explored using laboratory-scale experiments. The study offers a number of useful practical implications for the design of full-scale torpedo anchors. Results demonstrate that the resistance to penetration and extraction of torpedo anchors is strongly affected by their fin design. A transparent soil surrogate made of Magnesium Lithium Phyllosilicate (MLPS), was employed to simulate soft marine clay. Three torpedo models having a length to diameter (L/D) ratio of eight and a similar weight (W), but different fin length to diameter ratios (LF/D) of zero (no fins), 2.6, and 5.2, were penetrated, vertically, at an impact velocity of 4.5 m/s. It was found that fin length correlated negatively with penetration depth (P) and positively with the maximum resistance to extraction. However, the maximum extraction resistance, normalized by weight (W), increased from 2.3 for the case of no fins to 3.1 for short fins and to 3.6 for long fins. Transparent soils enabled measurement of in situ displacements within the target during penetration and pullout and correlating them to the torpedo behavior. Soil displacement increases with the increase of penetration depth till full embedment, after that displacements remain constant.

A novel thermal stimulation approach for natural gas hydrate exploitation —— the application of the self-entry energy compensation device in the Shenhu sea

Abstract: Thermal stimulation is a common measure used to improve the decomposition efficiency of natural gas hydrate. However, the conventional thermal stimulation methods require considerable investments in wellbore construction. According to the penetration mechanism of the torpedo anchor, the self-entry energy compensation device (ECD) is innovatively proposed to replace the existing wellbore platform. The principle and critical technologies of the ECD are described and analyzed in detail. Then, a penetration model and an exploitation model are developed using the reservoir data from the W17 station in the Shenhu sea area, and the main conclusions are: It takes about 4 s for the ECD to penetrate from the overburden layer to the reservoir, and its penetration depth is about 50.1–370.4 m, which covers the buried depth of most marine reservoirs. Nevertheless, the combined depressurization + thermal stimulation method is unsuitable for the Shenhu reservoir due to the low permeability, low thermal conductivity, and high initial temperature. Overall, the ECD can provide a new idea for developing the NGH thermal stimulation method to solve the Joule-Thomson effect and seawater freezing problems during the depressurization production.