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While matrix-assisted autologous chondrocyte implantation has emerged as a promising therapy to treat focal chondral defects, matrices that support regeneration of hyaline cartilage remain challenging. The goal of this work was to investigate the potential of a matrix metalloproteinase (MMP)-sensitive poly(ethylene glycol) (PEG) hydrogel containing the tethered growth factor, transforming growth factor β3 (TGF-β3), and compare cartilage regeneration in vitro and in vivo. The in vitro environment comprised chemically-defined medium while the in vivo environment utilized the subcutaneous implant model in athymic mice. Porcine chondrocytes were isolated and expanded in 2D culture for 10 days prior to encapsulation. The presence of tethered TGF-β3 reduced cell spreading. Chondrocyte-laden hydrogels were analyzed for total sulfated glycosaminoglycan and collagen contents, MMP activity, and spatial deposition of aggrecan, decorin, biglycan, and collagens type II and I. The total amount of extracellular matrix (ECM) deposited in the hydrogel constructs was similar in vitro and in vivo. However, the in vitro environment was not able to support long-term culture up to 64 days of the engineered cartilage leading to the eventual breakdown of aggrecan. The in vivo environment, on the other hand, led to more elaborate ECM, which correlated with higher MMP activity, and an overall higher quality of engineered tissue that was rich in aggrecan, decorin, biglycan and collagen type II with minimal collagen type I. Overall, the MMP-sensitive PEG hydrogel containing tethered TGF-β3 is a promising matrix for hyaline cartilage regeneration in vivo. Regenerating hyaline cartilage remains a significant clinical challenge. The resultant repair tissue is often fibrocartilage, which long-term cannot be sustained. The goal of this study was to investigate the potential of a synthetic hydrogel matrix containing peptide crosslinks that can be degraded by enzymes secreted by encapsulated cartilage cells (i.e., chondrocytes) and tethered growth factors, specifically TGF-β3, to provide localized chondrogenic cues to the cells. This hydrogel led to hyaline cartilage-like tissue growth in vitro and in vivo , with minimal formation of fibrocartilage. However, the tissue formed in vitro , could not be maintained long-term. In vivo this hydrogel shows great promise as a potential matrix for use in regenerating hyaline cartilage. [ABSTRACT FROM AUTHOR]

Osteoarthrosis is a debilitating disease affecting millions, yet engineering materials for cartilage regeneration has proven difficult because of the complex microstructure of this tissue. Articular cartilage, like many biological tissues, produces a time-dependent response to mechanical load that is critical to cell’s physiological function in part due to solid and fluid phase interactions and property variations across multiple length scales. Recreating the time-dependent strain and fluid flow may be critical for successfully engineering replacement tissues but thus far has largely been neglected. Here, microindentation is used to accomplish three objectives: (1) quantify a material’s time-dependent mechanical response, (2) map material properties at a cellular relevant length scale throughout zonal articular cartilage and (3) elucidate the underlying viscoelastic, poroelastic, and nonlinear poroelastic causes of deformation in articular cartilage. Untreated and trypsin-treated cartilage was sectioned perpendicular to the articular surface and indentation was used to evaluate properties throughout zonal cartilage on the cut surface. The experimental results demonstrated that within all cartilage zones, the mechanical response was well represented by a model assuming nonlinear biphasic behavior and did not follow conventional viscoelastic or linear poroelastic models. Additionally, 10% (w/w) agarose was tested and, as anticipated, behaved as a linear poroelastic material. The approach outlined here provides a method, applicable to many tissues and biomaterials, which reveals and quantifies the underlying causes of time-dependent deformation, elucidates key aspects of material structure and function, and that can be used to provide important inputs for computational models and targets for tissue engineering. Statement of Significance Elucidating the time-dependent mechanical behavior of cartilage, and other biological materials, is critical to adequately recapitulate native mechanosensory cues for cells. We used microindentation to map the time-dependent properties of untreated and trypsin treated cartilage throughout each cartilage zone. Unlike conventional approaches that combine viscoelastic and poroelastic behaviors into a single framework, we deconvoluted the mechanical response into separate contributions to time-dependent behavior. Poroelastic effects in all cartilage zones dominated the time-dependent behavior of articular cartilage, and a model that incorporates tension–compression nonlinearity best represented cartilage mechanical behavior. These results can be used to assess the success of regeneration and repair approaches, as design targets for tissue engineering, and for development of accurate computational models. [ABSTRACT FROM AUTHOR]

Pile tip damage has become of particular concern for the offshore wind industry due to the extensive use of large-diameter, thin-walled piles for monopiles and jacket structures. The potential for damage has increased in recent developments due to the occurrence of embedded boulders within the seabed sediments (e.g. glacial tills) or partially weathered soft rocks (e.g. limestones, chalk). To assess the risk of pile tip damage, this paper presents a simple schematic approach to estimate: i) whether pile tip damage might occur following impact with embedded boulders; and ii) what soil strength (e.g. as reflected in the cone tip resistance q c) might initiate progressive distortion of an initial minor dent (extrusion buckling). The methodology was developed based on results of centrifuge model tests and large displacement finite element analysis, encompassing: i) undamaged thin-walled piles installed through embedded layers of different sized boulders; and ii) initially 'pre-dented' piles driven through homogeneous sand triggering progressive distortion. Numerical analysis was used to develop predictive guidelines for conditions that might cause significant pile tip damage. The guidelines were validated by comparison with results from model tests and also through well documented field cases where extrusion buckling occurred. The paper provides guidance for choosing the critical parameters involved in the calculation processes to enable direct application in design, allowing assessment of whether more detailed investigation and analysis should be undertaken. [ABSTRACT FROM AUTHOR]

Most of the present knowledge on submarine landslides relies upon back-analysis of post-failure deposits identified using geophysical techniques. In this paper, the runout of slides on rigid bases is explored using the material point method with focus on the geotechnical aspects of the morphologies. In MPM, the sliding material and bases are discretised into a number of Lagrangian particles, and a background Eulerian mesh is employed to update the state of the particles. The morphologies of the slide can be reproduced by tracking the Lagrangian particles in the dynamic processes. A real case history of a submarine slide is back-analyzed with the MPM and also a depth-averaged method. Runout of the slides from steep slopes to moderate bases are reproduced. Then different combinations of soil and basal parameters are assumed to trigger runout mechanisms of elongation, block sliding and spreading. The runout distances predicted by the MPM match well with those from large deformation finite element analysis for the elongation and block sliding patterns. Horst and grabens are shaped in a spreading pattern. However, the current MPM simulations for materials with high sensitivities are relatively mesh sensitive. [ABSTRACT FROM AUTHOR]

The typical depth–frequency distribution of earthquake hypocentres (DFDE) demonstrates that, below an upper cutoff, the earthquake frequency increases with depth up to a maximum value and then decreases and ceases at a lower cutoff. Such regular behaviour of earthquakes implies the existence of some fundamental mechanisms responsible for the distribution. Conventional models of lithospheric strength based upon the assumption that the frictional strength along pre-existing faults represents a lower limit on the rock shear strength do not provide any intrinsic logic for the observed DFDE. The paper shows that these models ignore the specific properties of intact hard rocks which can exhibit extremely low transient strength (significantly lower than the frictional strength) during failure under the high confining stresses corresponding to seismogenic depths. The low transient strength is provided by a recently identified fan-head shear rupture mechanism which can be initiated in intact rocks in the proximity of pre-existing faults. The low transient shear strength of intact rock determines the correspondingly low transient strength of the lithosphere, which favours generation of new earthquake faults in the intact rock mass adjoining pre-existing faults in preference to frictional stick-slip instability along these faults. The efficiency of the fan-mechanism within the seismogenic layer is variable, with maximum efficiency at the middle range between the upper and lower cutoffs, thus providing minimum transient strength of the lithosphere and maximum earthquake frequency at that depth. We believe that this intrinsic property of hard rocks is responsible for the observed DFDE. Importantly, the formation of new faults in intact rock generated by the fan-mechanism can be accompanied by very small stress-drops (similar to, or lower than, stress-drops for frictional stick-slip instability) combined with abnormally high energy release. The paper proposes an improved concept of lithospheric strength and earthquake activity at seismogenic depths. [ABSTRACT FROM AUTHOR]

Background Carved autologous costal cartilage and porous polyethylene implants (Medpor) are the most common approaches for total ear reconstruction, but these approaches may have inconsistent cosmetic outcomes, a high risk of extrusion, or other surgical complications. Engineering ear cartilage to emulate native auricular tissue is an appealing approach, but often the cell-seeded scaffolds are susceptible to shrinkage and architectural changes when placed in vivo . The aim of this study was to assess the most favorable conditions for in vitro pre-culture of cell-seeded type I collagen scaffolds prior to in vivo implantation. Methods Sheep auricular chondrocytes were seeded into this type I collagen scaffold. The cell-seeded constructs were cultured in either static or dynamic conditions for two days or two weeks and then implanted into nude mice for another six weeks. The harvested constructs were evaluated histologically, immunohistochemically, and biochemically. Results Robust neo-cartilage formation was found in these collagen scaffolds seeded with auricular chondrocytes, which was comparable to native cartilage morphologically, histologically, and biochemically. Culture under dynamic conditions prior to implantation improved the neo-cartilage formation histologically and biochemically. Conclusion Dynamic culture of this cell-seeded fibrous collagen material could permit predictable engineered auricular cartilage and a promising approach for external ear reconstruction. [ABSTRACT FROM AUTHOR]

This paper presents a refined analytical solution for pipe-laying on an elasto-plastic seabed. The solution builds on previous work, extending it to include elastic rebound of the pipe. The approach simplifies the pipeline as the combination of four segments: a natural catenary through most of the water column; a boundary-layer segment in the water close to the seabed where the bending stiffness of the pipe modifies the shape of the catenary; a beam under uniform tension through the touch down zone up to the point where maximum pipe–soil load concentration occurs, within which the soil responds plastically; and finally a rebound segment, also modelled as a beam under uniform tension, where the soil rebounds elastically as the pipe–soil contact force reduces back to the submerged pipe weight. Continuity of displacement, gradient, bending moment, shear and deduced tension along the pipeline are preserved. In comparison with previous models, such as a rigid-plastic seabed model, the distribution of seabed resistance is continuous. Results from the solution are presented for the case of seabed resistance to pipe penetration increasingly proportionally with depth, as is approximately the case at very shallow depths within the seabed. The lower the gradient of seabed resistance, the greater is the pipe embedment, but the maximum contact force and curvature of the pipe both reduce. Analyses also show that the rebound stiffness can have a marked effect on pipeline embedment, which increases with increasing rebound stiffness. However, the effect on pipe embedment becomes small beyond a certain ratio of rebound stiffness to shear strength. [ABSTRACT FROM AUTHOR]

Abstract: Assessment of interaction forces between deep water pipelines and potential submarine slides, debris flows and turbidity currents is an important aspect of geohazard studies. Historically, interaction forces have tended to be expressed in terms of drag factors, within a traditional fluid mechanics framework, with the drag factors depending strongly on an equivalent Reynolds number for the non-Newtonian debris material. Here, we have followed a more geotechnical approach, allowing the interaction forces to be expressed in terms of a strain-rate dependent shear strength of the debris material, and with the inclusion of a drag term (with fixed drag coefficient) for high velocity, low strength, combinations. This superposition approach treats separately the interaction forces that arise from the strain-rate dependent strength and the inertia of the debris, rather than combining them into a single drag force. A failure envelope is proposed, allowing axial and normal interaction forces to be estimated for any angle of attack of the debris flow. [Copyright &y& Elsevier]

Abstract: The paper presents an overview of recent developments in geotechnical analysis and design associated with oil and gas developments in deep water. Typically the seabed in deep water comprises soft, lightly overconsolidated, fine grained sediments, which must support a variety of infrastructure placed on the seabed or anchored to it. A particular challenge is often the mobility of the infrastructure either during installation or during operation, and the consequent disturbance and healing of the seabed soil, leading to changes in seabed topography and strength. Novel aspects of geotechnical engineering for offshore facilities in these conditions are reviewed, including: new equipment and techniques to characterise the seabed; yield function approaches to evaluate the capacity of shallow skirted foundations; novel anchoring systems for moored floating facilities; pipeline and steel catenary riser interaction with the seabed; and submarine slides and their impact on infrastructure. Example results from sophisticated physical and numerical modelling are presented. [Copyright &y& Elsevier]

Abstract: Geo-hazard assessment of the potential damage to a pipeline caused by a submarine landslide requires a quantitative model to evaluate the impact forces on the pipeline. In contrast with typical geotechnical problems, the strain rate within the fast moving, flow-like submarine landslide is typically far higher, which will lead to enhancement of the soil strength and therefore result in larger impact forces. Generally, there are two possible predictive frameworks for strain-rate dependence: a fluid dynamics framework and a geotechnical framework. By comparison of common rheological models adopted in these two different approaches, a unified additive power-law model, a normalised form of the Herschel–Bulkley model from fluid mechanics, is explored in this paper. This model has been used in conjunction with a large deformation finite element approach to investigate the undrained limiting loads on a cylinder moving steadily through inertia-less soft rate-dependent material, in order to quantify the strain-rate effects. The flow mechanism and the effects of the shear-thinning index and Oldroyd number on the shear zones are explored. The calculated resistance factors are compared with the drag coefficients obtained from computational fluid dynamics analysis. The average rate of strain experienced by the soil flowing past the cylinder is estimated for a given flow velocity and an expression in the form of a conventional bearing capacity equation, but with shear strength linked directly to the normalised flow velocity, is proposed to predict the magnitude of the viscous force exerted by the debris flow. [Copyright &y& Elsevier]

Abstract: This paper presents an analytical solution for the response of a poroelastic medium around a laterally loaded rigid cylinder using Biot’s consolidation theory. A plane-strain section of the cylinder-porous medium system is considered and the problem is formulated in polar coordinates. Expressions for the pore fluid pressure, stresses and displacements in the Laplace domain are derived analytically. The inverse of the Laplace transform is evaluated numerically using an efficient scheme. Curves showing decay of the pore fluid pressure with time, the corresponding change in mean effective stress and the variation of displacement, are plotted in non-dimensional form. [Copyright &y& Elsevier]

Summary: The problem of allogeneic skin rejection is a major limitation to more widespread application of clinical composite tissue allotransplantation (CTA). Previous research examining skin rejection has mainly studied rejection of conventional skin grafts (CSG) using standard histological techniques. The aim of this study was to objectively assess if there were differences in the immune response to CSG and primarily vascularized skin in composite tissue allotransplants (SCTT) using in vivo techniques in order to gain new insights in to the immune response to skin allotransplants. CSG and SCTT were transplanted from standard Lewis (LEW) ad Wistar Furth (WF) to recipient transgenic green fluorescent Lewis rats (LEW–GFP). In vivo confocal microscopy was used to observe cell trafficking within skin of the transplants. In addition, immunohistochemical staining was performed on skin biopsies to reveal possible expression of class II major histocompatibility antigens. A difference was observed in the immune response to SCTT compared to CSG. SCTT had a greater density cellular infiltrate than CSG (p <0.03) that was focused more at the center of the transplant (p <0.05) than at the edges, likely due to the immediate vascularization of the skin. Recipient dendritic cells were only observed in rejecting SCTT, not CSG. Furthermore, dermal endothelial class II MHC expression was only observed in allogeneic SCTT. The immune response in both SCTT and CSG was focused on targets in the dermis, with infiltrating cells clustering around hair follicles (CSG and SCTT; p <0.01) and blood vessels (SCTT; p <0.01) in allogeneic transplants. This study suggests that there are significant differences between rejection of SCTT and CSG that may limit the relevance of much of the historical data on skin graft rejection when applied to composite tissue allotransplantation. Furthermore, the use of novel in vivo techniques identified characteristics of the immune response to allograft skin not previously described, which may be useful in directing future approaches to overcoming allograft skin rejection. [Copyright &y& Elsevier]

Background: The surgical approach used today in the repair of peripheral nerve injuries rarely achieves full functional recovery. This study determines whether isolation of the nerve repair site using photochemical tissue bonding (PTB) in combination with human amniotic membrane can improve both functional and histologic recovery. Methods: New Zealand white rabbits (n = 24) underwent transection of the right common peroneal nerve. Epineural nerve repair was performed using 10-0 nylon sutures. The repair site was then wrapped in a cuff of human amniotic membrane, which either was secured with sutures or sealed using PTB. Standard neurorrhaphy alone was assessed as a control group. Functional recovery was recorded at 30-day intervals postoperatively by electrophysiologic assessment. At 120 days, animals were killed humanely and nerves harvested for histomorphometry. Results: Nerves treated with amnion wraps and sealed with PTB demonstrated a statistically significant improvement across both functional and histologic parameters. Functional recovery, as measured by repeated electrophysiologic studies over time, revealed a 26.2% improvement over standard neurorrhaphy alone (P < .05). Nerves treated with PTB-sealed amnion wraps had significantly greater (P < .001) axon (5.08 ± 1.06 μm) and fiber diameters (7.46 ± 1.37 μm), as well as myelin thickness (2.39 ± 0.7 μm) and the g ratio (axon diameter/fiber diameter ratio; 0.68 ± 0.07) distal to the repair site compared to standard neurorrhaphy alone (4.98 ± 1.81 μm, 6.77 ± 1.94 μm, 1.79 ± 0.42 μm, and 0.71 ± 0.09, respectively). Conclusion: Isolation of the repair site using a photochemically sealed amnion wrap improves electrophysiologic and histologic recovery compared to standard suture neurorrhaphy. [Copyright &y& Elsevier]

Background: Ischemia-reperfusion injury of skeletal muscle is a common clinical and experimental problem. To date, there has been no uniform and reproducible method to assess the extent of histologic injury. In this study, we developed a novel statistical methodology for evaluating injury in individual myocytes and 3 distinct methods for the interpretation of this data. Methods: C57/BL6 mice underwent 2 h of hindlimb ischemia followed by reperfusion for 3 (n = 11), 24 (n = 12), or 48 (n = 10) h. The gastrocnemius muscles were harvested, stained, and evaluated under microscopy. Standardized criteria were applied to score individual myocytes as healthy or injured, and injury score was expressed as injured fibers/total fibers %. Three methods of analyzing myocyte data were developed and evaluated with statistical Block-Random Sampling to determine the number of counted fibers required to represent accurately the total injury. The Full-Frame Counting, Fourfold Divided Counting, and Stratified Individual Counting methods differ in the random order in which fibers or microscopic fields are scored. Results: The 3 methods were found to be statistically sound at all experimental time points. Using the Full-Frame, Fourfold, and Stratified methods, the maximum number of required fibers at all time points was 600, 300, and 100, respectively, to obtain an estimation of injury with a 95% confidence interval. Conclusions: These criteria and statistical methods for histologic evaluation of ischemia-reperfusion injury in skeletal muscle are accurate and reproducible. The Fourfold method is the most practical and technically efficient method of assessing injury. Such a quantitative, direct assessment of injury is important and will be useful for future studies. [Copyright &y& Elsevier]

Purpose: The current trend is to treat distal radius fractures with open reduction and internal fixation with either titanium or stainless steel plates. Both provide stable fixation; however, there is minimal evidence concerning the soft-tissue response to these materials. Our objective was to evaluate the response of adjacent extensor tendons to titanium and stainless steel in a rabbit in vivo model and to evaluate the influence of time. Methods: Forty rabbits were divided into 5 groups of 8 rabbits each. Groups I and II had unilateral osteotomy of the distal radius followed by dorsal fixation with titanium and stainless steel plates, respectively. Groups III and IV had fixation with titanium and stainless steel, respectively, but without osteotomy. Group V had surgical dissection without osteotomy or plates. Two animals per group were killed at 1, 4, 12, and 24 weeks. The specimens (distal radius, plate, overlying soft tissue, and extensor tendon) were harvested en bloc for histologic analysis. For interface preservation between implant and tissues the specimens were embedded in methylmethacrylate, sectioned, and stained with hematoxylin-eosin. Results: Histologic analysis showed a fibrous tissue layer formed over both implants between the plate and the overlying extensor tendons in the groups treated with plating independently of the material and the presence or absence of osteotomy. This fibrous layer contained the majority of debris. Metallic particles were not observed in the tendon or muscle substance of any animals; however, they were visualized in the tenosynovium. Hematoxylin-eosin–stained sections of groups I through IV showed proliferative fibroblasts and metallic particles; however, this layer was not observed in group V. Statistical analysis did not show differences between the groups regarding the number of cells or metallic particles. Conclusions: Our results indicate that both implants generated adjacent reactive inflammatory tissue and particulate debris. There was no difference in cell or particle number produced by both materials. There is a statistically significant increase in inflammatory cells with increasing time of implantation. [Copyright &y& Elsevier]

Abstract Several models for the simulation of soil-riser interaction have been developed and used in practice. The models range from the extreme of a rigid seabed to springs that are either linear elastic or provide more sophisticated nonlinear response to simulate the seabed behaviour in the touchdown zone. The main goal of this study is to review the positive points and limitations of existing nonlinear models and introduce a new hysteretic model to simulate the seabed response more realistically for practical application. The new model uses a unified mathematical approach for different modes of the soil-riser interaction and incorporates an explicit degradation model for the soil behaviour. Development of a trench is simulated, together with incremental penetration of the riser into intact soil. The model can also incorporate variable parameters (e.g. depending on riser penetration rates and depth). The new model has been calibrated against existing data from model tests and found to provide good agreement for a range of test conditions. Highlights • A versatile hysteretic model that can be coded and utilized for complex riser-soil interaction problems. • Soil-riser interaction simulation using a unified hyperbolic-exponential mathematical model. • Soil degradation captured explicitly in soil-riser interaction model. • Nonlinear model explicitly simulates trench formation around touch down zone. • Mathematical model verified from published test data. [ABSTRACT FROM AUTHOR]

Abstract With the increase in demand and supply gap in the oil and gas industry, new developments of oil and gasinfrastructure are moving into deeper water. This requires design and construction of long high temperature and high pressure pipelines from deep sea to shore. These pipelines are subjected to cyclic expansion during operating cycles. Accumulated axial movement due to repeated thermal cycles may lead to global displacement referred to as 'walking'. Walking rates depend on the restraint associated with seabed friction. In conventional analyses, seabed friction is independent of the rate of thermal loading and expansion but it has been recognised that the sliding resistance between a pipe and the seabed varies with velocity, partly due to drainage effects. In this paper a numerical model is used to explore the effect of velocity-dependent seabed friction. A velocity-dependent friction model is implemented in commercial software ABAQUS and validated via single element and simple (flat seabed) pipeline cases. This model features upper and lower friction limits, with a transition that occurs as an exponential function of velocity. A parametric study is performed using differing rates of heating and cool-down in walking situations driven by seabed slope, SCR end tension and the difference between heat up and cool down rates. The walking behaviour is compared to cases with constant friction and solutions are proposed to express the velocity-dependent response in terms of an equivalent constant friction. These equivalent friction values can then be applied in existing simple solutions or more complex numerical analyses, as a short cut method to account for velocity-dependent friction. [ABSTRACT FROM AUTHOR]

New analytical models have recently been presented for evaluating the peak bearing capacity of circular footings penetrating sand-over-clay and the subsequent capacity once embedded in the underlying clay. However, in lieu of any analytical model, current methods of analysis use an inaccurate linear interpolation for the bearing capacity between the peak and the clay surface. This paper proposes an analytical model for calculating the bearing capacity of circular footings after the peak failure in sand-over-clay soils and before the footing enters the clay. Based on observations from visualisation experiments conducted in a geotechnical centrifuge, and consistent with the silo analysis approach used in predicting the peak capacity, the failure mechanism is a vertical frustum of sand progressively being forced into the underlying clay. Analysis of the capability of the new model to retrospectively simulate a database of 66 geotechnical centrifuge tests is provided. Motivation for improved prediction methods comes from the offshore mobile jack-up industry where concerns remain over the punch-through of large 20 m diameter spudcan footings in sand-over-clay. Accurate prediction of not just the peak bearing capacity but the subsequent load-displacement behaviour is required in order to assess the effectiveness of operational methods used to mitigate punch-through incidents. [ABSTRACT FROM AUTHOR]

Quantitative assessment of impact forces by submarine landslide is significant for the safe operation of pipelines that must cross potential runout paths. In this paper, the transient process of a submarine landslide impacting a pipeline is modelled using the material point method (MPM) with an enhanced contact algorithm. For simplicity, the partially-embedded pipeline is assumed to be fixed in space. The Herschel-Bulkley rheological model is incorporated to reflect the dependence of the undrained shear strength of the sliding mass on the shear strain rate. The behaviour of the mass flowing over the pipe was reproduced by allowing separation between the pipe and the sliding mass. The horizontal impact forces predicted by the MPM are verified by comparison with those estimated using a computational fluid dynamics approach. The impact forces are interpreted with a hybrid model considering the combined effects due to the soil's inertia, its shear strength, and also the asymmetric static pressure of the sliding material. The coefficients for the three terms are retrieved by a best-fit to the results of an extensive parametric study. The effect of the projected height of the pipe above the seabed is also investigated. [ABSTRACT FROM AUTHOR]

In this paper a novel modelling procedure is proposed to estimate whole-life settlements of tolerably mobile sliding foundations. A new kinematic hardening-critical state-state parameter constitutive model, the Memory Surface Hardening model, is implemented in a one-dimensional analysis to predict accumulated vertical settlements under drained lateral cyclic loading. The Memory Surface Hardening model performance is compared with the Modified Cam Clay and Severn-Trent Sand models. The Memory Surface Hardening model is adopted to simulate available experimental data from centrifuge tests to predict the settlement of a sliding foundation at the final stable state (i.e. no further volume changes occur). [ABSTRACT FROM AUTHOR]

Adequate assessment of fatigue damage in steel catenary risers (SCRs) is essential, and usually evaluated with time consuming numerical analyses. Simplified design strategies would improve the efficiency of the screening tasks in the early design stages. As part of on-going research aiming to define a simplified fatigue design procedure for SCRs in the touchdown zone (TDZ), the sensitivity of fatigue damage to various parameters is explored using a large database (>40,000 cases). An approximation of the maximum stress range in the TDZ is established using several artificial neural networks and predicts well the fatigue life of selected example SCRs. [ABSTRACT FROM AUTHOR]

The material point method (MPM), which is a combination of the finite element and meshfree methods, suffers from significant computational workload due to the fine mesh that is required in spite of its advantages in simulating large deformations. This paper presents a parallel computing strategy for the MPM on the graphics processing unit (GPU) to boost the method’s computational efficiency. The interaction between a structural element and soil is investigated to validate the applicability of the parallelisation strategy. Two techniques are developed to parallelise the interpolation from soil particles to nodes to avoid a data race; the technique that is based on workload parallelisation across threads over the nodes has a higher computational efficiency. Benchmark problems of surface footing penetration and a submarine landslide are analysed to quantify the speedup of GPU parallel computing over sequential simulations on the central processing unit. The maximum speedup with the GPU used is ∼30 for single-precision calculations and decreases to ∼20 for double-precision calculations. [ABSTRACT FROM AUTHOR]

Steel catenary risers (SCRs) are widely used in deep water. Several sources of nonlinearities make SCR fatigue design challenging. Limited understanding of the influence of the various input parameters on the structural response of SCRs leads to unnecessarily high conservatism in design. Also, time consuming numerical simulations are usually performed to assess SCR fatigue damage which is inefficient, especially for early design stages. A simplified framework for fatigue analysis of SCRs in the touchdown zone (TDZ) has been developed previously, using artificial neural networks. The approach may be used to efficiently estimate maximum static and dynamic stress ranges in the TDZ, from which the fatigue damage can be deduced. Comparison of the maximum static and dynamic stress changes for a given input motion allows quantification of the dynamic amplification factor (DAF). This paper explores the sensitivity of the maximum dynamic stress ranges and DAF to the key dimensionless groups of input parameters and also certain individual input parameters. The study illustrates the usefulness of the proposed framework in understanding SCR behaviour in the TDZ, providing guidance on optimisation of SCR design from a fatigue perspective. The paper also reflects on the potential benefits of using DAFs for SCR fatigue design. [ABSTRACT FROM AUTHOR]

Fatigue design of steel catenary risers (SCRs) is an important challenge especially in the touchdown zone (TDZ). Numerous parameters affect the fatigue damage in the TDZ, including those pertaining to riser motions, riser characteristics and soil properties. So far, only a few sensitivity studies have been published with limited applications, considering small ranges, investigating only a selection of input parameters or failing to examine the interactions between input parameters. This paper aims to test the robustness of previous research and extend the ranges of the input parameters for SCR systems under static loading, by means of numerical simulations. An approximation of the critical stress range in the TDZ defined by the authors previously was refined to assist the sensitivity studies. A large database was created using an automation subroutine coded in Python programming language that links the marine analysis software OrcaFlex and the optimisation software modeFRONTIER. Design of experiment techniques were used for post-processing and quantify the relative effects of the various dimensionless groups and their interactions. An approximation using a series of artificial neural networks is presented; it successfully approximates over 99% of the cases of the database with an accuracy of ±5%. [ABSTRACT FROM AUTHOR]

Steel catenary risers (SCRs) are dynamically sensitive structures and their fatigue design in the touchdown zone is challenging. The dynamic response of SCRs is traditionally assessed by performing a series of long time history analyses but a simplifying approach has recently been proposed. The simple method is based on the use of dynamic amplification factors that quantify the dynamic response for a given perturbation at the hang-off point relative to the static response. The determination of the static response of SCRs is therefore a prerequisite to this approach. In this paper, an existing analytical model is extended to accommodate the displacement at the hang-off point of the SCR and predict the static stress range. The results of this analytical model are validated against numerical simulations. Then, using this simple and efficient analytical model, various sensitivity analyses are performed to explore the impact of key dimensionless groups on the static stress range in the touchdown zone. [ABSTRACT FROM AUTHOR]

Abstract: Large deformation finite element (LDFE) analysis is being applied increasingly in geomechanics as it allows numerical interpretation of problems in which the structural element moves a relatively long distance through the soil. The ‘remeshing and interpolation technique with small strain’ (RITSS) method for LDFE analysis, in which the soil domain is periodically remeshed with the stress and material properties interpolated from the old to the new within the standard Lagrangian finite element framework, has been successfully applied to a number of practical applications. It allows any standard finite element theory to be used in the Lagrangian analysis, and because the mesh topography and connectivity are not influenced by the previous deforming increment, large deformations are possible. The major barrier of the RITSS method is that the remeshing and interpolation requires specialised and user-dependent computer code. This has limited its application to specialists and hindered its routine application in engineering practice. This paper proposes a simpler, more practical method to implement RITSS for geotechnical applications. By utilising the ABAQUS in-built procedures for interpolation and remeshing, it avoids any need for user-defined code (although a piece of Python script can be used to automate the iteration instead of operating the ABAQUS user interface). A series of four example problems benchmarking this new approach show it to be robust and numerically accurate. [Copyright &y& Elsevier]

Abstract: This study reports the results of small strain finite element analyses undertaken to determine the rate of displacement of skirted foundations subjected to uplift loading, due to combined swelling and seepage. Compatibility of foundation movement with cumulative seepage of water into the skirt compartment is modelled using a layer of soft poroelastic material immediately below the foundation top plate. Performance of the model is first assessed for a range of stiffness values for the soft layer. The model is then used to investigate the rate of displacement for skirt depths ranging from 0.1 to 1 times the foundation diameter. The results are compared with available theoretical solutions and experimental results, and expressions are provided for calculating the equivalent seepage lengths and resulting uplift velocities. The effect on the seepage behaviour of the presence of a gap down the external skirt–soil interface is also discussed. [Copyright &y& Elsevier]

Abstract: Steel catenary risers (SCRs) are one of the most cost effective types of risers in deep water, but their design, particularly in the touchdown zone (TDZ), is challenging. Design uncertainties arise due to limited understanding of the influence of various parameters on the SCR response, pertaining to the SCR geometry and structural properties, environmental loading and the seabed characteristics. An improved framework that provides quantitative guidance on how each parameter affects the overall structural response, and in particular fatigue damage in the touchdown zone, would facilitate design and increase confidence in the use of SCRs. This paper details the application of dimensional analysis to SCR behaviour. Suitable dimensionless groups are proposed and validated through a series of numerical tests, comparing the response of similar SCR systems defined by appropriate scaling of parameters. Due to the fundamental effect of the seabed response on fatigue damage, two types of soil models are considered in the study: a linear and a nonlinear model. The study provides a framework for design of SCRs, facilitating sensitivity analyses, enabling better control on parameters and reducing the number of simulations required. [Copyright &y& Elsevier]

Using recent advances in data analytics techniques and tools, this paper proposes a novel data-centric paradigm for riser fatigue analysis in which practitioners can efficiently make use of large hindcast and measured metocean datasets directly in the design process. In the conventional fatigue design method for offshore risers systems, in order to reduce the computational cost practitioners tend to condense large hindcast metocean datasets into small wave datasets, so-called wave scatter diagrams, to represent the long-term variation in significant wave height, H s , and peak period, T p, at a site of interest. These methods tend to predict rather conservative riser loading conditions and hence fatigue lives due to the information lost in the condensing method, which can limit the application of steel catenary and lazy wave risers (SCRs and SLWRs) with larger diameters (outside diameter, OD > 18") whose design is governed by fatigue. This paper proposes enhanced frameworks for more accurate prediction of the fatigue life of SCRs and SLWRs located in swell dominant regions by enabling the direct use of large measured and hindcast metocean datasets in the fatigue design process of risers. Firstly, we introduce a novel detailed framework that uses an "ANN-based technique" with a "representative (P50) year" concept to enable large metocean datasets to be directly used for accurate estimation of riser fatigue life that is suitable for detailed design stages. Secondly, we propose an alternative innovative framework based on the use of Monte Carlo methods for more efficient long-term fatigue assessment of risers. Finally, we demonstrate the usefulness of the proposed frameworks by calculating the riser fatigue lives and comparing them against those obtained via conventional wave-condensing strategies. For the case studied here, the results show that using the proposed framework can significantly increase the estimated riser fatigue life over the values estimated using conventional wave condensing methods. [ABSTRACT FROM AUTHOR]

Stable engraftment of hematopoietic progenitors and multilineage chimerism following in utero bone marrow transplantation could be a promising modality for treatment of prenatally diagnosed blood dyscrasias. For treatment of these diseases, stable chimerism in the myeloid and erythroid lineages is important because it is anticipated that donor-derived cells will compensate for defects in these host lineages. In the present study, a preparation of bone marrow that includes fresh, unmanipulated marrow mixed with T-cell–depleted marrow to achieve 1.5% T-cell content, was injected into the intrahepatic portion of the umbilical vein of porcine fetuses at mid-gestation. Donor hematopoietic progenitor cell engraftment was assessed in fetal liver and recipient bone marrow postnatally by donor-specific polymerase chain reaction of colony-forming units. Chimerism was assessed in lymphoid tissues and peripheral blood by flow cytometry. Graft-versus-host disease (GVHD) was assessed by histological analysis of biopsies of skin, bone marrow, liver, and intestine. In this report, we demonstrate that stable multilineage chimerism across a full major histocompatibility complex disparity can be achieved without GVHD through in utero bone marrow transplantation. [Copyright &y& Elsevier]

Monopiles supporting offshore wind turbines are generally of relatively low slenderness ratio and are subjected to lateral loads that emanate from high above the seabed at an eccentricity that in most cases exceeds the embedded length of the pile. The rotational stiffness is a critical aspect of their design, owing to tight tolerances on the cumulative rotation that is permitted by industry guidelines. From a practical perspective, most design calculations for the lateral response are performed using load transfer analysis. However, the low slenderness ratio and high moment loading relative to the horizontal load have prompted closer scrutiny of the load transfer formulations that have been used historically in the offshore oil and gas industry, since these were calibrated from the response of much longer piles under very different loading conditions. Recent industry-led studies have led to new recommendations, including the addition of lateral and rotational springs at the pile base and rotational load transfer springs distributed down the pile shaft. As a first step to evaluate the initial stiffness of such springs, this paper presents results from three-dimensional finite element analyses of a homogenous elastic soil, with the aim of relating values of spring stiffness to the elastic shear modulus of the soil. Effects of non-uniform soil stiffness are discussed and the gradually increasing benefits of including the additional spring terms are quantified. [ABSTRACT FROM AUTHOR]

Quantifying the risk of system failure is a key input to a risk-based decision-making process for the in-service integrity management of aging steel catenary risers (SCRs), which are prone to fatigue failure within the touchdown zone (TDZ). However, in practice the computational cost of assessing the probability of failure (POF) for SCRs is prohibitive. In this paper, we propose an efficient framework for quantifying the fatigue POF within the SCR TDZ by using the Bayesian machine learning technique adopting Gaussian Processes (GP) for regression. GP-based predictive models perform stochastic response prediction rapidly and are therefore attractive for rapid evaluation of the SCR fatigue POF. In this paper, we introduce innovative techniques for predicting fatigue damage profiles within the SCR TDZ generated by an irregular sea-state applied to the host vessel at its mean offset position, and for dimensionality reduction in the regression analysis. We utilize a realistic case study to demonstrate the framework, which consists of a representative 20″ SCR connected to a semi-submersible host vessel located in 950 m water depth. In addition, we use a site-specific 32-year hindcast wave data and 1-year measured current data, with associated statistical distributions, for the long-term fatigue loading conditions. We also employ numerical simulation and a random sampling technique to create simulation-based input and output datasets for training and testing of the derived probabilistic simulation-based surrogate. The results show that the proposed method is able to predict the fatigue life of the representative riser efficiently and accurately. Finally, we demonstrate the usefulness of the proposed method by rapidly generating the fatigue POF for the 20″ SCR considering the uncertainties associated with input loads, material properties, geometric parameters, and soil stiffness. • A practical machine-learning frameworks is proposed to enable adopting quantified risk-based process for in-service integrity management of SCRs. • A systematic approach is introduced for developing and verifying probabilistic simulation-based surrogates using the Gaussian Process concept for rapidly predicting the damage profile at SCR touchdown zone (TDZ) due to irregular sea-states. • An efficient methodology is proposed for rapid and accurate quantification of the fatigue probability of failure (POF) at SCRs TDZ. • The accuracy and usefulness of the framework is demonstrated using a realistic case study where the probability distribution of the fatigue life of a representative 20″ SCR is quantified via Monte Carlo Simulation. [ABSTRACT FROM AUTHOR]

• We bioengineered rat fibroblasts to secrete a biomarker: Gaussia Luciferase. • Machine perfusion was used to engraft these genetically modified cells in rat limbs. • After transplantation we could track the biomarker secretion for 4 days. • It is the first step toward engraftment of biosensor cells before transplantation. • Vascularized Composite Allotransplantation would benefit from in situ cell therapy. Transplantation of the hand or face, known as vascularized composite allotransplantation (VCA), has revolutionized reconstructive surgery. Notwithstanding, there are still several areas of improvement to mitigate immune rejection while sparing systemic adverse effects. The goal of this study was to evaluate the engraftment and viability of a genetically modified cell population pre-engrafted into a VCA transplant, to potentially act as a local biosensor to report and modify the graft in vivo. A rat fibroblast cell line genetically modified to secrete Gaussia-Luciferase (gLuc), which served as a constitutive biomarker of cells, was incorporated into a VCA to study the viability of biosensor cells in a syngeneic rat heterotopic partial hindlimb transplantation model. Five perfusions were first performed as engineering runs to have a stable limb perfusion protocol, followed by 3 perfusions to analyze the cell engraftment during machine perfusion, and finally 4 perfusions to study in vivo persistence of the cell biosensors. Blood samples were collected to monitor gLuc secretion during perfusion and postoperatively. A time-dependent increase in gLuc secretion in the limb perfusion outflow during machine perfusion indirectly verified the presence of biosensors within the graft. After the ex vivo perfusion, VCA hindlimbs were analyzed for near infrared fluorescence emission that showed a presence of dyed engineered cells in all areas of the limbs. Postoperatively, gLuc was detectable 4 to 5 days after transplantation (W = 16, P =.02857). This study demonstrated that engineered cells could be successfully preimplanted into VCAs—an important step toward development of an in vivo biosensor platform to use in modulating acute VCA outcomes. [Display omitted] [ABSTRACT FROM AUTHOR]

Lateral buckling analysis of on-bottom submarine pipelines is of particular interest in the offshore industry due to the complexities involved in the analysis, and the potential design efficiencies that can be unlocked. Classical buckling theories by previous researchers and recent joint industry projects provide a basis for estimation of the critical buckling load of a straight, or in some cases imperfect, pipe on either a rigid or elastic seabed. However, systematic solutions for the combined effects of nonlinear soil properties and the as-laid geometry – specifically the out-of-straightness – on the buckle initiation behaviour have not been developed previously. This paper reports an investigation of the buckling problem of an imperfect (non-straight) on-bottom pipeline subjected to axial compressive loading. The seabed was modelled with lateral and axial nonlinear, springs to idealise the load-displacement behaviour of the soil and the pipe was modelled with pipe elements. Buckling was performed by a displacement controlled finite element method with the modified Riks algorithm that is available in the commercial software ABAQUS. This numerical tool was used to develop a parametric solution for the present problem in terms of the various pipe material and geometry parameters and the lateral and axial pipe-soil interaction parameters. In particular, the influence of the magnitude and stiffness of the lateral pipe-soil response was investigated, highlighting the sensitivity of the pipeline response to the geotechnical inputs. The results have been synthesised in a generic non-dimensionalised design chart to estimate the buckling load, valid for the range of inputs covered by the parametric study. [ABSTRACT FROM AUTHOR]

The mathematical model of an equilibrium fan-structure in the interface between two elastic blocks, simulating the shear rupture head in a hard rock under high confining pressure, is constructed. The stress–strain state far from the fan-structure is analyzed with the help of a solution of the problem on edge dislocation. The fan length is estimated using this solution. The model of formation of two oppositely directed fans due to the localized action of tangential stress, which pushes two edge dislocations with antiparallel Burgers vectors, is proposed. In complete formulation, the problem on an equilibrium fan-structure in the interface between infinite elastic half-planes is analyzed by means of original method of superposition of dislocations, leading to two nonlinear integral equations in the fan zone. To solve them numerically, the method of successive approximations is applied. Based on this method, fields of stresses and displacements around the equilibrium fan modelling of a deep-seated shear rupture in the seismogenic zone of the Earth’s crust are computed. Such fields can be used, when setting the initial data in the analysis of dynamics of the fan-shaped mechanism. [ABSTRACT FROM AUTHOR]

Full-flow penetrometer testing in fine-grained soils indicates that undrained shear strength decreases due to remoulding induced generation of excess pore pressures and increases due to strain rate effects and dissipation of excess pore pressures. This paper presents a viscoplastic strain-softening–hardening constitutive model that captures this duality of behaviour via non-local regularisation, strain rate dependency, and consolidation induced recovery of sensitivity. The model is based on Structured Modified Cam Clay and Perzyna's overstress framework. Validation of the implementation is first demonstrated through simulation of constant rate of strain triaxial and oedometer compression tests performed on different clays. The model is then applied in large deformation finite element analyses of monotonic and variable rate T-bar penetration to demonstrate successful numerical implementation and its ability to simulate strain rate effects. Finally, the model is applied in the simulation of undrained cycles of penetration of a T-bar penetrometer in kaolin clay and a carbonate silt and compared with data from geotechnical centrifuge experiments. The results show that the model without sensitivity recovery significantly underestimates the consolidated-undrained resistance in both soils, suggesting that recoverable sensitivity is an aspect of behaviour that ought to be considered in the development of constitutive models for soft sensitive soils. [Display omitted] [ABSTRACT FROM AUTHOR]