Accurate Prediction of Casing Collapse Resistance by 3D Finite Element Modeling

Summary 3D outside diameter (OD) and wall thickness mapping of a casing joint consists of synchronized OD laser scanning and ultrasonic testing (UT) wall thickness measurement at a resolution of every 1 in. along the length and every 1° or 2° around the circumference. This full-length mapping data can then be used to construct a 3D finite element analysis (FEA) model that captures the geometric attributes, including OD, wall thickness, OD ovality, and wall eccentricity, of a casing joint. Together with the actual nonlinear material plasticity model and the measured as-manufactured residual stress, the 3D FEA model can predict the casing collapse strength with good accuracy. Also, the Klever-Tamano ultimate limit-state (KT ULS) collapse equation per API TR 5C3 (2018) together with a moving-average (MA) scheme can calculate the joint’s collapse strength. Results predicted by 3D FEA and KT ULS collapse models are compared to the actual full-scale collapse test results. A 3D FEA model generally produces more accurate results than the KT collapse equation. In addition, both 3D FEA and KT collapse models predict a collapse pressure slightly lower than the actual collapse pressure, which is therefore on the conservative side. The prediction of casing collapse strength can be beneficial to the end user in sorting and ranking the casing joints by collapse resistance, and therefore provides valuable information that can be used in the end user’s risk assessment. Furthermore, the end user may potentially select the joints with the highest predicted collapse strength for the portion of the casing string where the highest collapse resistance is desired. In addition, the OD and wall mapping data together with the actual material tensile properties (yield strength, ultimate tensile strength, and strain hardening parameters) can be used in estimating the internal yield, ductile rupture pressures, and other performance properties. This is outside the scope of this paper and can be pursued in future work. These predicted casing performance properties may then be used in sorting and ranking the joints based on a specific performance property of interest or a combination of performance properties.

Microbubbles provide the basis for perfusion measurement, early detection of molecular signatures of disease and as a vehicle for drug, or gene, delivery. Although the response of a single microbubble to ultrasound has been characterized by radially symmetric 1D models and high speed camera-based experiments, a plethora of mechanisms, such as bubble-bubble interaction, and adherent bubble response are poorly understood. With few exceptions, 1D model are generally valid at moderate acoustic pressures, but are incapable of predicting phenomena such as higher order mode oscillations or onset of bubble shell rupture. It has been hypothesized that second or higher order mode oscillations are a precursor to bubble shell rupture and subsequent cavitation. In addition, parameters, such as shell stress and shell strain may have threshold values related to bubble shell fracture. In this work, we propose a full 3D FEA (finite element analysis) model that can simulate temporal variations in asymmetric 3D radial, translational bubble motion, various shell parameters such as regional stress /strain, and bubble pulse echo response. Preliminary simulations were conducted to assess the performance of the model for broadband cases, including: 1) single cycle pulse excitation, 2) single cycle of free and wall-bound bubble, 3) predicting translational displacements in response to primary radiation force, and 4) tracking variations in shell stresses and strain for low (180 KPa) and high (330 KPa) peak negative pressure acoustic waveforms. For the acoustic and bubble parameters published by Dayton, the maximum displacement predicted using the 3D FEA model was within 10% of the previously published experimental data. For approximately similar bubble and acoustic parameters (using inverted pulses), the spectrum of the backscattered data from a free bubble was found to be similar to the experimental and simulated results The spectrum of the adherent bubble response was found to be downshifted with respect to that of a free bubble; similar results have been reported by Payne et al . The adherent bubble was found to oscillate asymmetrically in the planes orthogonal to the azimuth-elevation plane or the plane perpendicular to the face of the transducer (edge of the model where an external pulse is applied).

Collapse performance of a casing string subjected to external hydraulic pressure is one of the most important parameters in the deep water well casing design. It often becomes one of the governing factors in a casing design program. This paper investigates the quantitative effect of inherent circumferential residual stress (RS) on casing collapse resistane to external pressure through parametric Finite Element Analysis (FEA). Nonlinear elastic-plastic FEA study on casing collapse calculations have been performed. Different magnitudes and orientations of the initial circumferential residual stress were considered. Modified Riks method was used to predict the casing onsite collapse pressure as well as the post-collapse response. Parameters considered in the analysis include: (i) two material grades (L80 and Grade 135); (ii) for each material grade, ratio of outside diameter to wall thickness (i.e. D/t) ranging from 10 to 50; (iii) for each D/t ratio, initial circumferential residual stress at casing inner diameter (ID) ranging from -40% to +50% of the material yield strength (YS). Analysis results indicate that there is a highly nonlinear, parabolic-like dependence of collapse strength on the initial circumferential residual stress. Comparison of the FEA results to the predictions by Klever-Tamano Ultimate Limit-State (KT ULS) equation indicates that the KT ULS equation in the current API Technical Report 5C3 (API TR 5C3) does not capture this nonlinear relationship. This is probably due to the limitation of the API historical collapse test data upon which the KT ULS equation was calibrated to. The majority of the API historical collapse tests had the compressive residual stress at the casing ID. Moreover, the relationship between casing collapse strength and residual stress may be used as a guideline for potentially developing new high collapse casing by full-length residual stress control in mill production.

Offshore pipeline on-bottom roughness analysis is generally performed to understand pipe stress and areas of free spanning. In this paper, the predicted pipeline profiles, by finite element analysis (FEA) modeling, are compared with survey data. Several case studies are presented and parametric effects are assessed. The FEA modeling procedures are presented in this paper along with several project experiences. The pipeline on-bottom roughness analysis is conducted to determine the pipe stress and the associated fatigue damage due to internal pressure and temperature fluctuation and vortex-induced vibration (VIV) of free span sections due to seabed unevenness. The analysis presented in this paper can aid the design of pipeline free spans and mitigation, if required. The parametric effects of higher and lower bound soil stiffness, friction resistance, pipeline bottom tension, external / internal pressure, and content density are considered. The predicted pipeline profiles by FEA modeling are compared with surveyed profiles under several loading conditions. A strong correlation between survey data and finite element analysis (FEA) is achieved. This paper shows that the FEA stress prediction is adequate, and the FEA modeling is suitable as an advanced design tool for pipeline on-bottom roughness assessment and free span behavior analysis. A commonly used mitigation method for VIV fatigue is to install VIV suppression strakes. For overstresses due to pipeline bending effect, the common mitigation methods are to install mechanical supports, use heavy wall pipe and correct the seabed unevenness among others. It is important to reliably predict the pipeline profiles in order to precisely assess the pipeline free span response and to provide guidance to determine a proper free span mitigation strategy. The FEA method can be utilized to realistically simulate the pipeline on-bottom roughness behavior affected by the pipe properties, pipe-soil interaction including penetration and soil friction resistance, the internal and external pressure, product content, temperature profile, and the bottom tension from pipe-lay. An accurately built FEA model can provide a reliable prediction for the pipeline profile, free spanning length and gap under all conditions, which are crucial for the stress and fatigue assessment as well as for the design of free span mitigation.

A finite element analysis (FEA) model is established to investigate the concrete-encased concrete-filled steel tubular (CFST) column to reinforced concrete (RC) beam joints under cyclic loading. The feasibility of the FEA model is verified by a set of test results, consisting of the failure modes, the exposed view of connections, the crack distributions and development, and the hysteretic relationships. The full-range analysis is conducted to investigate the stress and strain development process in the composite joint by using this FEA model. The internal force distributions of different components, as well as the deformation distributions, are analyzed under different failure modes. The proposed connections are investigated under dimensional and material parameters, and the proper constructional details of the connections are recommended. Parameters of the beam-column joints, including material strength, confinement factor, reinforcement ratio, diameter of steel tube to sectional width ratio, beam to column linear bending stiffness ratio and beam shear span ratio are evaluated. Furthermore, the key parameters affecting the failure modes and the corresponding parameters ranges are proposed in this paper.

Warpage is a major reliability concern for IC packages. Package structure, material property and assembly process will all impact warpage behavior, which can be characterized by 3D Finite Element Analysis (FEA). Traditionally, the FEA simulation will only analyze warpage of a free standing package with thermo-mechanical stress induced by Coefficient of Thermal Expansion (CTE) mismatch during cooling process of Epoxy Molding Compound (EMC) from cure temperature to room temperature. In this paper, a dedicated FEA model has been developed to simulate a strip type Fine-Pitch Ball Grid Array (FBGA) package. Different from conventional simulation, effect of both EMC chemical shrinkage due to polymerization conversion during post molding cure and actual measurement operation on warpage have been taken into consideration in the FEA model. Parametric study with different package layout, die area and die thickness has been performed. Result showed package layout of the strip can significantly impact warpage; and die area had more influence on warpage than die thickness. Warpage performance can be improved by optimizing these parameters. Compare to measurement, the simulation result is in good agreement with actual package warpage.

Most wellbore strengthening (WBS) techniques require an understanding of the width on an induced fracture to design the size and concentration of appropriate mud additives to mitigate the fracture growth. Current methods to estimate fracture width primarily consider stress and rock properties but neglect the effect of the thermal contrast between the drilling fluid and the formation. This paper reports the results of the modeling of the thermal effect on fracture width and proposes a practical method to integrate the thermal effect into current WBS design workflows. The proposed process uses both analytical and numerical methods to investigate the thermal effect. A finite element analysis (FEA) model simulates the coupled stress and temperature field around the borehole, which allows the width of the fracture to be derived at any point along the length. The Abaqus FEA model uses 2-D plane strain elements to allow either steady-state or transient thermal-mechanical analysis. The results of FEA modeling are compared to the semi-analytical solution which only addresses the mechanical effect. Both models use field data to verify and validate results. An equivalent tensile stress is used to derive an analytical solution for fracture width for the case of ‘long-term’ cooling. The results provide a good match to the steady-state thermal elastic FEA results. In the case of transient heat transfer, an approximate analytical solution is derived to describe temperature distribution around the borehole as function of time. Then the analytical solution for thermal stresses is derived based on intact circular borehole. The analytical results are compared and verified with the FEA. Currently, the fracture width in response to a transient thermal event can only be calculated using the FEA model. The change in fracture width due to the temperature disturbance can be superimposed over the elastic fracture width to provide a more accurate estimate of width due to both mechanical and thermal influences for planning WBS formulations. The model demonstrates that the cooling of the borehole with drilling mud results in a wider fracture than that which is predicted by the purely elastic models. If drilling mud temperature is not considered or managed effectively, the failure of the WBS application could result, leading to a lost circulation event. A field case where wellbore cooling occurs and leads to lost circulation is presented.

Watch circles are established by operators to ensure a dynamically positioned vessel does not induce loads that exceed wellhead system equipment capacities. In the event the vessel moves off station, beyond the boundary of the watch circle, loads could be transmitted that may approach or exceed the equipment ratings and possibly cause failure. A whole system weak point analysis approach is required to determine and identify the likely failure modes and locations throughout the system. This paper presents a system weak point analysis using a 3D finite element analysis (FEA) of an API Studded BOP Flange, Hydraulic Wellhead Connector, and Subsea Wellhead System. The FEA models include the first 200 ft below the mudline and are used to evaluate the capabilities of the entire system to failure. To ensure accurate load transfer between the components the actual field installation sequence was modeled, which included contact between components, all preloads, soil resistance, casing string weights, and cements. Subsequently, the global external loads from the rig were incrementally increased beyond the rated load capacities of the entire system to determine failure points. Loads, stresses, and strains in each component were determined as a function of the global external loads. Each component of the system was modeled using elastic-plastic material properties per ASME BPVC, Section VIII, Division 3, Paragraph KD-231.4. Critical points throughout the wellhead system were monitored for failure which was defined as either through wall plastic strain or through wall stress above yield across the entire wall of a component. A sequential order of limiting locations, or weak points, was determined (first limiting location, second limiting location, etc.). The weak point analysis performed provided valuable information to assess and help mitigate risk. The analysis results also provided valuable insight and context to the equipment manufacturer to develop more robust and reliable system designs. The insights gathered by doing a weak point analysis using large 3D FEA models of the entire system, inclusive of the wellhead system, wellhead connector, and flanged connection, are presented and provide a better understanding of the system behavior and failure mechanisms.

Determination of stress concentration factors in offshore wind welded structures through a hybrid experimental and numerical approach

The interfacial stress and its distribution affect directly the mechanical properties of polymeric blends and composites. Polymers are usually modified with rubber to improve their toughness. The three-dimensional (3D) finite element analysis (FEA) of the interfacial stress distribution between the particulate and the matrix during tensile of a rubber-modified polypropylene (PP) blend is made by means of an ANSYS software in this article, and the results are compared with those of the two-dimensional (2D) FEA simulation published earlier. The results show that the shear effect subjected in the pole zone of the rubber particle is maximal, the equator zone of the rubber particle is strongly pressed and pulled, and the tensile stress reaches the maximum. Comparatively, the stress distribution of 3D FEA is more gentle than that of 2D FEA.

Typically, axial flux permanent magnet machines require 3-dimensional (3D) finite element analysis, increasing the amount of time required to complete a machine design. To overcome the drawback of 3D finite element analysis, several authors have proposed 2-dimensional (2D) finite element (FE) modeling and analysis techniques. This paper expands upon previous work, investigating quasi-boundary conditions to address end-effects and expands upon existing knowledge of discretizing the 3D problem into multiple 2D models for axial flux permanent magnet (AFPM) machines. The results of 2D finite element method are verified by a prototype which has single rotor, dual stator (SRDS) configuration. The results presented in this paper reaffirm that the less conventional SRDS AFPM can be effectively modeled in 2D, and that quasi-boundary condition can offer increased model accuracy, relative to conventional 2D FE modeling of AFPM machines.

ObjectiveThis study aimed to compare the hemodynamic differences among no sac (NOS), porous media (POM) and finite element analysis (FEA) models to investigate the recurrence-related risks for coiled intracranial aneurysms...

The aim of this in vitro study was to determine the load and deflection at failure of different lingual retainers bonded with composite to enamel in a standardized three-point bending test. The results were rationalized with finite element analysis (FEA) models. Four types of multistranded wires, Dead Soft Respond, Twisted ligature, Penta-One, Gold-plated Penta-One, and two glass fibre-reinforced composite retainers, Fibre 07 and Fibre 09, were bonded to enamel with composite and submitted to a three-point bending test. The load and deflection at failure and the mode of debonding were recorded. The stiffness of the wires was determined and all experimental data were used in FEA models to rationalize the observed values and mode of debonding. Significant higher load and deflection were found for the most flexible retainers Twisted ligature and Dead Soft Respond. All retainers failed between the wire and composite, which was confirmed by FEA showing the highest stress in the composite around the retainer. The FEA models showed that the amount of composite used for bonding the retainers should be 2-4mm. Based on the in vitro results, optimal bonding of lingual retainers can be achieved by flexible retainers, bonded with intrinsically strong composites. According to the FEA models the retainer should be bonded with 2-4mm composite, leaving the critical 'free-wire' length for the success of the retainer system.

Contamination of roadside soils by runoff pollutants: A numerical study

This study was designed to test the hypothesis that: "A properly designed implant that harnesses the principle of the incompressibility of fluids can improve the weight carrying ability of an amputee's residual femur and reduce the frictional forces at the stump external socket interface." The hypothesis was tested both mechanically on an Amputee Simulation Device (ASD) and through Finite Element Analysis (FEA) modeling software. With the implant attached to the femur, the FEA and ASD demonstrated that the femur carried 90% and 93% respectively of the force of walking. Without the implant, the FEA model and ASD femur carried only 35% and 77%, respectively, of the force of walking. Statistical calculations reveal three (3) degrees of separation (99% probability of non-random significant difference) between with and without implant data points. FEA modeling demonstrates that the normal contact forces and shear forces are pushed the distal weight-bearing area of the amputee stump, relieving the lateral stump of frictional forces. The ASD mechanical and FEA modeling data validate each other with both systems supporting the hypotheses with confidence intervals of three degrees of separation between with implant and without implant models.