Coupled Eulerian-Lagrangian Analysis Research Articles

Incorporation of the riser-seabed-seawater interaction effects into the trench formation and fatigue response of steel catenary risers in the touchdown zone

The existing Steel Catenary Riser (SCR)-seabed interaction models do not account for the contribution of seawater as a key influential factor. The present study has examined the effect of SCR-seabed-seawater interaction on the trench enlargement and consequently on the fatigue performance of the SCR in the touchdown zone (TDZ). Coupled Eulerian-Lagrangian (CEL) analysis with three domains of SCR, seabed soil, and seawater were performed using ABAQUS. A parametric study was conducted to investigate the impact of seawater interaction along with incorporation of the shear strain rate and softening effects. The conventional bearing capacity approach for analysing pipe penetration into the seabed was also reviewed, and modifications were proposed to account for the effects of water entrainment into the trench. The results obtained from CEL analysis were integrated with a global SCR model to incorporate the SCR-seabed-seawater interaction effects into the fatigue analysis. The study showed that the entrainment of seawater into the trench can be coupled with SCR oscillations to further soften the seabed and erode the trench resulting in an enlarged trench profile affecting the fatigue damage in the TDZ.

Numerical study on vibratory extraction of offshore wind turbine monopile foundations under sandy seabed condition

The wind industry has experienced a rapid growth in Europe over the last decades. The early generation turbines were designed for a life of 20–25 years. Decommissioning of offshore wind turbines is becoming more important since many of these installed assets are approaching their end of lifetime. In this study, using vibratory extraction of monopile foundations instead of current practice of cutting them is investigated numerically. Correct estimation of extraction force helps operators to choose suitable vibro-hammer and vessel (or crane-barge), which leads to reduction of decommissioning costs. A Coupled Eulerian-Lagrangian (CEL) approach of ABAQUS/Explicit combined with a modified Mohr-Coulomb (MMC) model are used to find the pile shaft resistance during total removal operation under saturated dense sand condition. The MMC model captures the nonlinear pre-peak hardening and post-peak softening of the dense sand which is not modelled by conventional Mohr-Coulomb model. The VUSDFLD subroutine, which is a user-defined framework, has been used to implement the MMC model into CEL analysis. A parametric study is conducted to analyze how the characteristics of the vibro-hammer, such as its frequency, eccentric moment, and the extraction rate influence the results. The present numerical results show that using proper frequency results in reduction of soil resistance to less than 25% of the initial resistance. However, appropriate hammer with enough eccentric moment and suitable extraction rate, are vital to ensure soil degradation. The results show that the proposed methodology is both robust and straightforward and it has the potential to reduce computational time which is efficient for engineering applications.

Research on the Initial Settlement Depth of Artificial Reef on the Clay Seabed

The artificial reef is an artificial structure that simulates some characteristics of a natural reef. Its penetration depth in the seabed soil affects the stability of the reef on the seabed. In this paper, based on the CEL (Coupled Eulerian-Lagrangian analysis) method, a finite element model is established for the process of artificial reef entry and penetration, which simulates the speed change law of the artificial reef in the water and the penetration depth in the clay seabed, and The study analyzed the influence of different reef weights, penetration speeds, and seabed soil properties on the penetration depth of artificial reefs.

Coupled Eulerian-Lagrangian finite element analysis of penetration processes in silty clay for bucket foundation

ABSTRACT Bucket foundations, as an innovative type of offshore wind turbine foundation, have been widely adopted for their cost competitiveness and time effectiveness in construction and installation. For a successful installation, the penetration process prediction is crucial. This paper investigates the penetration process of both thin-walled and thick-walled bucket foundations in silty clay through small-scale experiments. Based on the experimental results, empirical formulas of penetration resistance are modified. Next, a Coupled Eulerian-Lagrangian (CEL) numerical method is validated and used to simulate the sinking process of engineering prototypes. The penetration resistance obtained by the calculated and numerical methods is in good agreement. Additionally, through the 3D CEL analysis, the disturbance of bulkheads and skirts on soil plugs is gained. The Eulerian volume fraction shows that the soil surface within the outer compartments is prone to rise to form a soil plug, which will bring out a sudden sharp increase in the penetration resistance due to the contact of lid and soil, and consequently affect the ultimate installation depth.

The Coupled Eulerian-Lagrangian Analysis of the KOBO Extrusion Process

The Coupled Eulerian-Lagrangian Analysis of the KOBO Extrusion Process

Dynamic characteristics of deposit fracture and impacts of operating pressure during sootblowing in the radiant syngas cooler

AbstractDuring the operation of entrained‐flow gasifiers, the ash deposits located on the wall tubes in the radiant syngas coolers (RSC) reduce the heat transfer efficiency. Syngas sootblowing is an effective method to remove the slag deposits in the RSC. In this study, a 3D numerical model was developed by combining the cohesive zone method (CZM) and the coupled Eulerian–Lagrangian analysis to investigate the deposit fracture process in RSC during sootblowing. The quasi‐static analysis using ABAQUS obtained the stress–strain curve of the slag sample, which agreed well with the experimental tests and provided the detailed mechanical parameters to the CZM model. The dynamic characteristics of deposit fracture were discovered. The main fracture occurred between 1.0 and 1.5 ms, and the shape of the fracture area was not round but elliptical. The RSC operating pressure (P) was also investigated. The study found that higher pressure led to lower fracture speed, longer sootblowing time, and more syngas consumption. Based on the same extent of deposit fracture, syngas consumption increased when P < 3.5 MPa, and the density of syngas (ρsyngas) has a more significant influence on the syngas consumption than the velocity of sootblowing syngas flow (vavg), especially when the sootblowing time is small.

Noise Reduction in Spur Gear Systems.

This article lists some tips for reducing gear case noise. With this aim, a static analysis was carried out in order to describe how stresses resulting from meshing gears affect the acoustic emissions. Different parameters were taken into account, such as the friction, material, and lubrication, in order to validate ideas from the literature and to make several comparisons. Furthermore, a coupled Eulerian–Lagrangian (CEL) analysis was performed, which was an innovative way of evaluating the sound pressure level of the aforementioned gears. Different parameters were considered again, such as the friction, lubrication, material, and rotational speed, in order to make different research comparisons. The analytical results agreed with those in the literature, both for the static analysis and CEL analysis—for example, it was shown that changing the material from steel to ductile iron improved the gear noise, while increasing the rotational speed or the friction increased the acoustic emissions. Regarding the CEL analysis, air was considered a perfect gas, but its viscosity or another state equation could have also been taken into account. Therefore, the above allowed us to state that research into these scientific fields will bring about reliable results.

Investigations of granular material behaviors using coupled Eulerian-Lagrangian technique: From granular collapse to fluid-structure interaction

Abstract In this study, a coupled Eulerian-Lagrangian (CEL) technique was used to investigate the dynamic behaviors of granular material, including the collapse of a granular column and the interaction between granular flow and a rigid barrier. The CEL technique, combining Eulerian and Lagrangian algorithms, is capable of overcoming mesh distortions of conventional finite element approaches. By validating well-established experiments, the development of progressive failure in the granular column can be accurately simulated using the equations of state (EOS) and Bingham plastic constitutive models, and the granular flow impact force on the rigid barrier based on the small-scale CEL model shows good agreement with the data measured in flume tests. The impact force simulated by the CEL technique was compared with the predictions of empirical hydrostatic and hydrodynamic models, which are the approaches generally used to estimate the granular flow impact force in engineering practice. In addition, a normalized parameter S Velocity was proposed to obtain a representative velocity and height of the granular flow from the CEL analysis to improve the accuracy of empirical approaches. The proposed parameter could benefit the in-situ monitoring of potential granular flow disasters and demonstrates the applicability of the CEL technique in practical engineering.

Structural Safety Analyses for Offshore Platforms Under Explosion Loadings

Abstract A gas explosion in an offshore platform may result in loss of life, pollution, and critical damage to facilities. Safety critical structural elements of these facilities have to be designed to withstand high explosion loads. The present study discusses methodologies for explosion risk assessment (ERA) of safety critical structural elements and introduces a coupled Eulerian–Lagrangian (CEL) method to improve the accuracy of the dynamic structural response under explosion loading. The design accidental load is defined by explosion risk analyses in terms of drag pressure, differential pressure, and overpressure. In current practice, an explosion pressure-time history is simplified into a triangular shape and uniformly applied to the surface of the impacted structures. This approach cannot account for the interaction between elastic waves (normally solved by the Lagrangian method) in the structure and compression waves (normally solved by the Eulerian method) in air. The CEL method which accounts for fluid–structure interaction has been experimentally validated and leads to more realistic predictions of the dynamic response of structures when compared to other analysis methods. The plastic strains derived from the CEL analysis can be approximately 50% lower than those predicted by Lagrangian analysis. Therefore, significant potential weight reduction can be achieved using the CEL method for gas explosion analysis.

Effects of wrinkling prevention forming method using paraffin on forming accuracy for 1060 aluminum sheet metal

Paraffin wax is a viscoelastic material that is prone to flow under pressure. In this paper, paraffin wax is used as the pressure medium to transfer the punch force to form 1060 aluminum plate. Paraffin wax can effectively suppress the instability and wrinkling occurrence for the sheet metal during the forming process. The finite element modeling (FEM) was employed to study the effects of different forming radii, paraffin particle size, paraffin layer thickness and forming pressure on the forming accuracy of the formed part. The proposed method was simulated by Coupled Eulerian-Lagrangian analysis. The effects of paraffin layer thickness and forming pressure on the average error of the formed part was analyzed by measuring the actual formed part. The experimental results show that increasing the forming pressure and the thickness of the paraffin layer can reduce the shape deviation of the formed part.

Fluid-Structure Interaction Analysis Using Finite Element Methods for IRWST of Reactor Building

Fluid-structure interaction analysis of in-containment refuelling water storage tank (IRWST) of HPR1000, the Chinese 3rd-generation nuclear reactor type, was performed. During analysis simulation of water was made using three well established methods:1) Dispersed-Mass-Method; 2)Coupled Eulerian-Lagrangian(CEL) method; 3)Smoothed Particle Hydrodynamics(SPH) method. The member forces and required reinforcement of the IRWST walls from different methods were compared and the following conclusions were drawn: 1) CEL is accurate but time-costing when the analysis target has a complex configuration. Also, CEL analysis is often terminated due to intrinsic algorithm. 2) SPH method provides same results accuracy with that of CEL method when SPH method and CEL method have similar mesh size. It can effectively avoid the problem of unexpected termination in CEL method; 3) the stress and required reinforcement obtained from CEL and SPH method are obviously less than those from Dispersed-Mass-Method, which proves that Dispersed-Mass-Method can be used in preliminary design stage for reinforcement amount evaluation.

Dynamic Analysis of Tunnel in Soil Subjected to Internal Blast Loading

The present work deals with the three-dimensional nonlinear finite element (FE) analyses of the tunnel in soil subjected to internal blast loading. The analyses are performed using the coupled Eulerian–Lagrangian analysis tool in FE software Abaqus/Explicit. The soil and reinforced concrete lining are modeled using the Lagrangian elements. The explosive Trinitrotoluene (TNT) is modeled using the Eulerian elements. The stress–strain response of soil, concrete, and reinforcement are simulated using strain rate dependent Drucker–Prager plasticity, concrete damaged plasticity and Johnson–Cook (J–C) plasticity models, respectively. The pressure–volume relationship of the TNT explosive is simulated using the Jones-Wilkins-Lee equation of state. Parametric sensitivity studies have been performed for different (1) tunnel lining thicknesses, (2) explosive charge weights and (3) angles of internal friction of soil. It is observed from the results that blast induced pressure on the tunnel lining increases with the increase in charge weight. Both the lining and the surrounding soil undergo significant deformation. The deformation of the tunnel lining increases with increasing charge weight and decreases with increasing lining thickness and increasing the angle of internal friction of soil. Blast-induced velocity in soil attenuates with increasing distance from the source of the blast.

Dynamic Analysis of Tunnel in Weathered Rock Subjected to Internal Blast Loading

The present study deals with three-dimensional nonlinear finite element (FE) analyses of a tunnel in rock with reinforced concrete (RC) lining subjected to internal blast loading. The analyses have been performed using the coupled Eulerian–Lagrangian analysis tool available in FE software Abaqus/Explicit. Rock and RC lining are modeled using three-dimensional Lagrangian elements. Beam elements have been used to model reinforcement in RC lining. Three different rock types with different weathering conditions have been used to understand the response of rock when subjected to blast load. The trinitrotoluene (TNT) explosive and surrounding air have been modeled using the Eulerian elements. The Drucker–Prager plasticity model with strain rate-dependent material properties has been used to simulate the stress–strain response of rock. The concrete damaged plasticity model and Johnson–Cook plasticity model have been used for the simulation of stress–strain response of concrete and steel, respectively. The explosive (TNT) has been modeled using Jones–Wilkins–Lee (JWL) equation of state. The analysis results have been studied for stresses, deformation and damage of RC lining and the surrounding rock. It is observed that damage in RC lining results in higher stress in rock. Rocks with low modulus and high weathering conditions show higher attenuation of shock wave. Higher amount of ground shock wave propagation is observed in case of less weathered rock. Ground heave is observed under blast loading for tunnel close to ground surface.

An efficient approach to incorporate anchor line effects into the coupled Eulerian–Lagrangian analysis of comprehensive anchor behaviors

With the application of innovative anchor concepts and advanced technologies in deepwater moorings, anchor behaviors in the seabed are becoming more complicated and significantly affected by the anchor line. Based on the coupled Eulerian–Lagrangian (CEL) method, a numerical approach incorporating anchor line effects is developed to investigate comprehensive anchor behaviors in the soil, including penetration of drag anchors, keying of suction embedded plate anchors and diving of gravity installed anchors. Compared to the method directly incorporating the anchor line into the CEL analysis, the proposed method is computationally efficient. To examine the robustness and accuracy of the proposed method, numerical probe tests and then comparative studies are carried out. It is found that the penetration (or diving) and keying behaviors of anchors can be well simulated. A parametric study is also undertaken to quantify the effects of various factors on the behavior of OMNI-Max anchors, whose mechanisms are not yet fully understood. The maximum embedment loss of OMNI-Max anchors during keying is not influenced by the initial anchor embedment depth, whereas significantly increases with increasing drag angle at the embedment point. With decreasing initial anchor embedment depth or increasing soil strength gradient, drag angle at the embedment point and diameter of the anchor line, the behavior of OMNI-Max anchors could change from diving to pullout, which is undesirable in offshore engineering practice. If the drag angle increases over a certain limit, the anchor will fail similar to a suction anchor.