Gravity Anchor Research Articles

Evolutionarily conserved brainstem architecture enables gravity-guided vertical navigation.

The sensation of gravity anchors our perception of the environment and is important for navigation. However, the neural circuits that transform gravity into commands for navigation are undefined. We first determined that larval zebrafish (Danio rerio) navigate vertically by maintaining a consistent heading across a series of upward climb or downward dive bouts. Gravity-blind mutant fish swim with more variable heading and excessive veering, leading to less effective vertical navigation. After targeted photoablation of ascending vestibular neurons and spinal projecting midbrain neurons, but not vestibulospinal neurons, vertical navigation was impaired. These data define a sensorimotor circuit that uses evolutionarily conserved brainstem architecture to transform gravitational signals into persistent heading for vertical navigation. The work lays a foundation to understand how vestibular inputs allow animals to move effectively through their environment.

Analytical and numerical investigation of gravity anchors for floating photovoltaic systems

Gravity anchors are a widely used anchoring solution for floating photovoltaic systems but can be costly and difficult to transport and install. To address this issue, 3D printed concrete gravity anchors can be fabricated offsite into a custom shape that optimizes the bearing resistance then filled with ballast onsite. This study evaluates the performance of gravity anchors with novel geometries enabled by 3D printing in representative sandy (drained) and clayey (undrained) soil layers for mooring angles ranging from 0 to 70°. The failure modes of gravity anchors were explored using numerical simulations with the goal of validating simpler analytical methods suitable for design. Results indicate that sliding primarily affects anchor efficiency (pullout capacity divided by buoyant weight) at small mooring angles, while overturning and plowing become dominant at larger mooring angles. Greater anchor efficiency is gained when using a skirt to enhance the passive bearing resistance, but difficulties may arise in the penetration of the skirt into sand. A C-shaped anchor with a padeye close to the center of gravity promoted plowing at high mooring angles. Analytical models are suitable fat lower mooring angles, but numerical simulations are recommended when evaluating anchor performance at mooring angles greater than 30°.

Bearing performance of a novel caisson–plate gravity anchor

To provide a more reliable shared anchor for floating wind farms, a novel caisson–plate gravity anchor (CGA) is proposed. This design merges the benefits of both gravity anchors and suction caissons. Centrifuge model tests adopting only half of each anchor were carried out to study their bearing performance in sand. In addition, particle image velocimetry analyses were performed to monitor anchor movement and soil displacement. As supplementary data, numerical simulations with an advanced hypoplasticity model were also conducted to reveal the anchor capacity mobilisation mechanism. Findings indicate that the novel CGA possesses a significantly higher bearing capacity compared to standalone caisson or plate designs. By adding a plate above the caisson and increasing its weight, the anchor failure modes may shift from forward rotation to translational movement. In addition, this adjustment may transition the brittle failure to a more reliable ductile failure. This augmented capacity of the CGA stems from the expanded soil mobilisation region and increased soil stress level in front of the caisson. The proposed CGA provides a promising solution for shared anchors in floating wind farms.

Теоретическое обоснование держащей силы мобильной опоры для крепления лесосплавных объектов

Exploitation of small and medium-sized rivers for wood transportation ensures the economic availability of wood raw materials located at a great distance from consumers. Short-term operation of timber rafting facilities and their movement from one place to another is typical for these rivers. At such facilities, the use of mobile fillable anchors is considered to be the most appropriate. The article provides a brief description of their design, installation and dismantling. The fabrication and effective application of such anchors requires appropriate justification of their parameters (the holding power, in particular). The purpose of this study is to develop the scientific basis for determining the holding power and effective application of these anchors. A theoretical justification for the process of interaction of the proposed anchor with the soil mass has been carried out. On the basis of this justification, two alternative formulas were obtained to determine the holding power provided by one section of the grouser. Calculations using these formulas give similar results. The dependences of the holding power on the determinants, such as the vertical load on one section of the grouser transmitted from the containers being filled, the coefficient of friction of the anchor material on the soil, the density of the soil, the coefficient of its internal friction and the depth of penetration of the grousers into the soil are approximately the same. Similar properties of these formulas allow to consider them reliable. The total holding power of the anchor is calculated according to the weight of the filled containers, the holding power of one section of the grouser and their number. The degree and nature of the influence of the determinants on the holding power of a mobile fillable gravity anchor have been established. An increase in any of them leads to an increase in the holding power. The most significant determinant is the vertical load on one section of the grouser. The dependence of the holding power on it is linear. To a lesser extent, in descending order, the angle of the internal friction of the soil, the coefficient of friction of the anchor material on the soil, and the density of the soil influence the holding power. The dimensions of the grouser and their change have little effect, but the very fact of their presence provides a sizeable proportion of the holding power of the anchor.

Methodology to calculate mooring and anchoring costs of floating offshore wind devices

The aim of this article is defining a methodology which allows us to evaluate the main mooring and anchoring costs of floating offshore wind farms. In this sense, costs of most important phases of life cycle will be analysed: manufacturing, installation, exploitation and dismantling. For this purpose several models will be defined taking into account the type of floating offshore wind platform (semisubmersible, Tensioned Leg Platform or spar), mooring disposition (transitional no tensioned, slack no tensioned, tensioned with 90º or tensioned with 45º), mooring material (chain, cable and synthetic fibre) and type of anchor (drag embedment anchor, suction pile, gravity anchor and plate anchor). Finally the proposed method will be applied to know mooring costs of a substructure located in the region of Galicia (North-West of Spain). Results show how each of these costs depend on the model considered, which help investors to decide what the best model is.

Performance Analysis of an Improved Gravity Anchor Bolt Expanded Foundation

With the continuous utilization of renewable energy, the number of onshore wind turbines is increasing. Small design improvements can save costs and facilitate the maintenance and repair of the wind turbine foundation. In this paper, an existing gravity expansion foundation with an anchor cage is improved. Our improvements further expand the space inside the foundation and reduce the length of the anchor bolt, which could reduce the costs and facilitate construction. To study the performance of the new foundation, a three-dimensional finite element model of the foundation–soil–anchor bolt was established via a finite element simulation. The damage evolution of the foundation was simulated with the concrete damage plasticity model (CDP). The separation ratio, foundation settlement, inclination ratio, reinforcement stress, foundation stress, and foundation damage of the new foundation under ultimate load conditions were analyzed. The influence of parameters h1 and b3 on the performance of the foundation was further studied. The finite element analysis results show that the tensile stress of concrete can be effectively reduced by appropriately increasing the corbel height and ring beam width of the foundation. The results also show that the improved wind turbine foundation force is reasonable and can meet the use of the actual project requirements on the level of finite element analysis.

Hybrid Power-Generation Concept Incorporates Offshore Wind

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 204901, “Hybrid Offshore Power Generation,” by Izleena Md. Iqbar, SPE, Fauzi O.B. Othman, and Hasmi Taib, Petronas, et al. The paper has not been peer reviewed. _ The operator has developed an offshore hybrid power-generation concept to leverage and optimize wind-turbine systems for power generation in weak-wind areas such as Malaysia. In this concept, one gas-turbine generator is replaced by an offshore wind turbine adapted to low wind speeds. This lowers maintenance costs and carbon exposure. Additionally, the fuel gas will be diverted to sales gas, thereby improving economics and making offshore renewable power generation feasible for oil and gas platforms. Background Malaysia is situated in a weak-wind area. Most of the operator’s oil and gas platforms are in water depths of more than 60 m, which are considered deep water for offshore wind-turbine systems. Offshore wind-turbine systems generally are expensive and not cost-effective for low-wind-speed areas where the annual average wind speed at hub height is less than 6.5 m/s. For economic reasons, offshore wind turbines are multimegawatt turbines designed for sites of International Electrotechnical Commission Class I or II only. However, a need exists to install CO2-effective, renewable electrical generators with high power density to support industrial plants that cannot follow the wind but are bound to local offshore oil and gas resources. In view of these challenges, specific criteria have been identified for this project, namely specific rated power, maintenance costs, risk of hazards, capability of a black start (the ability of generation to recover from a blackout), and offshore capability. Hybrid Offshore Power-Generation Project From preliminary studies, it was concluded that a reasonable value for specific power is less than 200 W/m² to achieve high-capacity factors in a weak-wind region. The need for low maintenance costs calls for a solution with little technical complexity and a minimum of components. Capability for a black start in an island situation requires storage and parameters for the generator or invertor system of the wind power plant. At the time of writing, no wind turbine can be bought off the shelf for the purposes mentioned. A wind turbine found closest to these criteria is provided by a European manufacturer based in Estonia. The offshore wind-turbine system consists of a customized wind turbine adapted to harness the energy from the weak-wind area and a microgrid system to integrate the wind turbine with the turbine generators, which are housed on a tension-leg-platform (TLP) floating structure. This floating platform is held by a gravity anchor.

A Framework for Mooring and Anchor Design in Sand Considering Seabed Trenches Based on Floater Hydrodynamics

Seabed trenches reduce anchor capacity. However, the adverse influence is not considered in the current design, and no guideline is found in engineering practice. This paper presents a framework for mooring and anchor design in sand considering seabed trenches based on floater hydrodynamics. First, a hydrodynamic calculation of the studied floater coupled with the mooring system was conducted. Then, the potential trench profile was assessed using a mooring line–seabed dynamic model. Third, after assessing the suction anchor performance based on its installation and capacity, a refined anchor, caisson–plate gravity anchor (CPGA), was proposed, and the capacity mechanisms were analyzed. It was found that the tensions of mooring lines l1 and l2 resist maximum loads under a 45° load condition. Due to the sand’s high strength, a trench is difficult to form in this mooring type. The suction anchor is not suitable as an anchor for the carbonate sand, considering its installation and capacity. The analyses indicate that the increase in soil stress and soil mobilized range in front of the caisson promotes the capacity of CPGA. This paper provides a framework/example to design moorings and anchors considering potential trenches and provides a solution to the anchor design in carbonate sand.

Study on safety assessment methods of gravity anchors based on a simplified mechanical model

Gravity anchor blocks are a common type of ground anchor used for suspension bridges, whose bearing depends on its large body and gravity. As there is no stratum requirement, the safety of the anchor block is important for bridge stability. This study summarizes all available estimation indexes, calculating methods, and evaluation criteria for gravity anchor block safety for the Ruili bank of the Banjin Dam grand suspension bridge. The anti-overturning, anti-sliding, base stress, and deformation safeties were comprehensively evaluated using methods including the suggested specification method (SM), simplified mechanical method (SMM), and finite element method (FEM), the results of which were compared and analyzed. The reasons for errors and improved formulas and working conditions were presented. The main conclusions were as follows. 1) The methods for calculating different evaluation indexes according to specifications lack consistency. Moreover, FEM requires that designers have good computer skills and has low feasibility in practice. 2) The SMM for gravity anchor block safety estimation as described in this study, whose indexes cover systematic and overall, the computational formula is simple and speedy, with relatively conservative results and good practicability. 3) SM, SMM, and FEM were all used for the safety estimation of gravity anchor blocks in Ruili bank. The anti-overturning and anti-sliding stability coefficients must all meet the specification requirements of 2.0. SM cannot be used to estimate the base tensile stress under limited conditions. SMM denoted tensile stress at 2.5 times the main cable design force, compared to 3.2 P for FEM. Deformation calculation methods are not given by SM, but can be suggested by SMM based on the elastic mechanics. The horizontal displacements under design load conditions were 122 mm (SMM), 108 mm (FEM), and 44 mm (composite foundation treated by root piles), with a safety standard of <80 mm. The vertical displacements were 338 mm (SMM), 110 mm (FEM), and 123 mm (composite foundation treated by root piles), with a safety standard of <160 mm. These findings proved the feasibility of SMM for the safety design of gravity anchor blocks in cases lacking regional experience.

Stability analysis of gravity anchor foundation of layered argillaceous sandstone under dry-wet cycles

Stability analysis of gravity anchor foundation of layered argillaceous sandstone under dry-wet cycles

Research on Bearing Characteristics of Gravity Anchor in Clay

The applications and studies of gravity anchors in the ocean are becoming more and more extensive. Most of the research, however, has been directed toward the bearing properties of sand. Relatively less attention has been paid to the bearing properties of gravity anchors in clay. Clay is widely distributed on the seabed. The research on the bearing capacity of gravity anchors in clay is of great significance for offshore oil exploitation. Therefore, the gravity anchor was investigated by conducting reduced-scale model tests, and the bearing process of gravity anchors in clay was simulated through a 3D finite element method. Model tests and numerical simulations were used to determine the capacity curve and the V-H failure envelope of gravity anchors in clay. The simulation results and the test results are in good agreement. The failure form of the gravity anchor in clay was revealed by 3D finite element analysis. The effect of cohesion, internal friction angle, and mooring point height on bearing capacity have been studied. The influence of the height of the mooring point on the V-H failure envelope curve was explored by changing the height of the mooring point. The formula of the V-H failure envelope curve suitable for different mooring point heights was obtained.

Study of concentrated anchoring, siting, system layout and preliminary cost analysis for a large scale Kuroshio power plant by the cross-stream active mooring

The development of large scale ocean current power generally encounters difficulties associated with water depth, seafloor engineering, storms and current meanders. The Cross-stream Active Mooring (CSAM) is a recently proposed new concept to overcome these issues. It features serial mooring of multiple turbines on a common tether as a linear array, single point anchoring and applying hydro sails to position the linear array across current streams over deep seafloor or seabed not suitable for anchoring construction. The CSAM can change the linear array's horizontal position to track meandering velocity core to increase system power capacity and adjust its depth to avoid storms. This paper proposes and studies a new concentrated anchoring concept of high capacity based on slope enhancement and assembled anchors to resolve issues of anchoring on rocky undersea ridges in many areas along the Kuroshio. Two new gravity anchor designs making use of seafloor landforms are devised and analyzed. Efficiency of assembled anchor blocks is analyzed and tested using models. Anchoring sites, anchor implementation and large scale deployment with an example 1 GW power plant in the Kuroshio southeast of Taiwan are discussed. A preliminary cost analysis of the anchors and of the CSAM-based example power plant is also presented.

Slope stability analysis and protection of deep accumulation excavation foundation pit in the Sichuan Bank of the Kahalo Jinsha River Bridge

The Kahalo Jinsha River Super Large Bridge of the Sichuan Riverside Expressway spans the deep canyon of the Jinsha River and is situated in a high-intensity, complex, and dangerous mountainous area. Long-term deformation and stability of the gravity anchor slope are the main controlling factors affecting bridge safety. The maximum slope height formed by the excavation of the gravity anchor foundation pit on the Sichuan Bank of the Kahalo Jinsha River Bridge is 110m, and the anchorage area is located on the Q3h thick accumulation with a thickness of more than 170 m. First, the important soil mechanical parameters, such as shear strength, deformation modulus and bearing capacity eigenvalues of rock and soil were obtained by conducting field shear tests, deformation tests, and load tests. On this basis, the pseudo-static method was used to simulate the seismic conditions, and a three-dimensional numerical analysis and calculations of the potential instability range of the high slope of the gravity anchor foundation pit excavation were conducted. The results reveal that the slope of the super-deep foundation pit with a huge thick mixed accumulation layer will deform and become unstable under the influence of an earthquake, with a maximum deformation of about 20 m in the slope body. A two-level earthquake prevention and disaster-reduction target for the bridge foundation pit and slope engineering protection is proposed based on the two-level seismic fortification requirements of super-long-span suspension bridges. An active reinforcement scheme of excavation pre-reinforcement, step-by-step excavation, and zoning protection is designed and proposed based on this target and the deformation and stability analysis results of the field test and three-dimensional numerical calculation.

Study on the penetration process of torpedo anchor into layer soils

Wing torpedo anchor is a new type of gravity anchor which is installed by self weight and anchored by gravity and seabed resistance. Based on the T98 torpedo anchor, the penetration process of torpedo anchor in layer soils is numerically simulated, and the change laws of penetration resistance, acceleration, velocity and penetration energy with depth is analyzed. The results showed that the end resistance and the friction resistance broke at the interface of soil layers, and the friction resistance increased with increasing of depth, while the end resistance first increased and then decreased. With the increasing of depth, the acceleration increased and the velocity decreased. In the early stage of penetration, the work is mainly done by the end resistance, whereas the work is mainly done by the side friction resistance in the later stage, suggesting that the side friction resistance consumed more anchor energy than the end resistance.

Design of Mooring Solutions and Array Systems for Point Absorbing Wave Energy Devices—Methodology and Application

Abstract Most of the ocean energy technologies are considered to be in a pre-commercial phase and need technical development. This study focuses on the design of mooring solutions and compares array systems of a specific floating point-absorbing wave energy converter (WEC) developed by the company Waves4Power. A full-scale prototype of the WEC is installed in Runde (Norway) where it is moored with three polyester mooring lines, each having one floater and one gravity anchor. Based on this reference installation, the method of systems engineering was used to propose 22 conceptual mooring solutions for different array systems. They were compared and reduced to four top concepts in a systematic elimination procedure using Pugh and Kesselring matrices. The top concepts were assessed in detail by means of levelized cost of energy (LCOE), life cycle analysis (LCA), and risk analyses. The fatigue life of the mooring lines and the energy capture were calculated using results obtained from coupled hydrodynamic and structure response analyses in the dnv-gl deepc software. Two final concepts were proposed for the water depths 75 and 200 m.

Recent centrifuge modelling of offshore geotechnical problems at IWHR

Centrifuge modelling has been proven to be an efficient and reliable approach for examining offshore geotechnical problems. This study reports the two series of centrifuge tests to understand the behaviour of spudcan penetration in a “soft-stiff-soft clay” stratigraphy and the behaviour of gravity anchor subjected to a lateral loading. A hydraulic system has been adopted to apply the large compressive and tensional load on the spudcan and gravity anchor, respectively. Load cells were installed on the base of the spudcan to directly measure the stress acting on the spudcan base. A 2D laser scanner was adopted to monitor the horizontal, vertical movement and tilting of the gravity anchor. The influence of the relative soil stiffness on the spudcan pentration behaviour and the soil deformation and interaction with the gravity anchor are discussed based on the centrifuge test results.

Experimental validation of lift and drag forces on an asymmetrical hydrofoil for seafloor anchoring applications

Tidal power can be described as harnessing the kinetic energy of the in and out flows known as tides created by the changing gravitational pull of the moon and the sun on the oceans of the world. As the relative positions of the sun and moon can be accurately predicted, so can the resultant tidal movements, making tidal energy such a valuable resource and an attractive option for renewable power generation. However, the high costs and difficulties associated with the deployment of underwater turbines, which includes anchoring, are prohibitive factors in the widespread utilisation of tidal power technology. Existing turbine fixation methods are primarily based on the use of large gravity anchors or monopole structures to secure the turbine to the seabed. In an effort to reduce size, environmental impact on the seafloor and installation cost, a hydrofoil-based anchor could be considered. The objective of this study is to experimentally test the lift and drag force behaviour of a finite-span hydrofoil with endplates, whose profile was selected based on simplified two-dimensional (2D) numerical simulations using the vortex panel method. A customised lift and drag force measurement system for this prototype hydrofoil was designed, fabricated and calibrated, and subsequently installed and tested in the Dutch Tidal Testing Centre (TTC) in Den Oever, the Netherlands. A series of tests with force and flow velocity measurements are described for different angles-of-attack under realistic tidal flow conditions. Results for the lift and drag coefficients as a function of angle-of-attack are compared to numerical simulation data and revealed that the real-world lift force is predicted well, whereas the drag force is underpredicted by the numerical predictions. These findings provide useful information for the design of anchoring systems based of hydrofoil profiles.

Further investigation of the six-DOF hollow gravity anchor: Impact of the internal slant angle

Our recent study on the new type hollow gravity anchor shows that the hollow anchor can save the anchoring time and decrease the anchoring deviation, compared with the traditional solid anchor. This study aims to do further research on the internal structure of the hollow anchor using the developed motion-based zonal mesh update (MBZMU) method. However, though the validated MBZMU method is able to capture the large-scale six-DOF motion of the gravity anchor, the tested cases in the previous study did not reflect the sway-yaw-roll motion of the gravity anchor. Instead of the imperfect one camera calibration method, two orthorhombic high-speed cameras are adopted in this study to record the six-DOF anchoring process. Additionally, quaternions are introduced to quantitate the anchor rotation to avoid the singularity problem caused by Euler angles. The experimentally measured trajectory path of the six-DOF gravity anchor is consistent with the numerical simulated result. Furthermore, one optimal internal slant angle is observed, through a comparative on the six-DOF anchoring processes of the hollow anchors with different internal slant angles, which are the key factor determining the inlet flow rate through the central water channel of the hollow anchor.

Passive Vibration Control of Existing Structures by Gravity-Loaded Cables

Structures with high concentration of mass at or close to the top such as highway bridge piers are vulnerable in earthquakes or accidents. In this paper, a simple and convenient retrofit strategy is proposed for minimizing vibrations and damages, extending service life and preventing collapse of existing structures. The proposed system comprises of tension-only cables secured to the sides of the structure through gravity anchor blocks that are free to move in vertical shafts. The system is installed in such a way that the cables do not induce unnecessary stress on the main structure when there is no lateral motion or vibration. The effectiveness of controlling global structural responses is investigated for tension-only bilinear-elastic behaviour of cables. Results of a realistic case study for a reinforced concrete bridge pier show that response reduction is remarkably well under seismic excitation.

Numerical study on the six-DOF anchoring process of gravity anchor using a new mesh update strategy

Compared with the conventional solid gravity anchor, one new type hollow anchor is designed to improve the stability and maneuverability of the gravity anchor. One water channel is dug through the center line of a traditional solid anchor to decrease the rotation angle and the drift distance when anchoring. In this study, scaled models of one traditional solid gravity anchor and one new type hollow gravity anchor are released under the water, and their anchoring processes are experimentally recorded and numerically simulated. Because the large-scale six-DOF motion of the anchor may lead to the unexpected dynamic mesh distortion, a six-DOF motion-based zonal mesh update (MBZMU) strategy is developed to control the mesh quality and guarantee the convergence and accuracy of the numerical results. As expected, simulated numerical anchoring processes of the two gravity anchor models agree well with the experimental measurements. Additionally, both the anchoring time and deviation of the hollow gravity anchor model are smaller than those of the solid anchor model during anchoring, indicating better practical and economic value of the hollow gravity anchors in engineering.