Influence of Bending Stiffness on Snap Loads in Marine Cables: A Study Using a High-Order Discontinuous Galerkin Method

Marine cables are primarily designed to support axial loads. The effect of bending stiffness on the cable response is therefore often neglected in numerical analysis. However, in low-tension applications such as umbilical modelling of ROVs or during slack events, the bending forces may affect the slack regime dynamics of the cable. In this paper, we present the implementation of bending stiffness as a rotation-free, nested local Discontinuous Galerkin (DG) method into an existing Lax–Friedrichs-type solver for cable dynamics based on an hp-adaptive DG method. Numerical verification shows exponential convergence of order P and P+1 for odd and even polynomial orders, respectively. Validation of a swinging cable shows good comparison with experimental data, and the importance of bending stiffness is demonstrated. Snap load events in a deep water tether are compared with field-test data. The bending forces affect the low-tension response for shorter lengths of tether (200–500 m), which results in an increasing snap load magnitude for increasing bending stiffness. It is shown that the nested LDG method works well for computing bending effects in marine cables.

A Preisach Model for Monotonic Tension Response of Structural Mild Steel with Damage

This paper presents the new type of Preisach model that describes the elastoplastic behavior of structural mild steel under axial monotonic tension load with damage. Newly developed model takes into account elastic region, horizontal yield plateau, plastic hardening region, and softening region due to material damage under tension. In order to study the monotonic behavior of structural mild steel and find suitable material properties for the model, monotonic axial tensile tests up to the failure are carried out. Tests are conducted on specimens of the three most common types of European structural steel S235, S275, and S355. The basis of the model represents a mathematical description of material single crystal monotonic axial behavior. In the multilinear mechanical model, a drop in stress, after achieving ultimate stress under tension is achieved by a negative stiffness element. The good agreement with experimental results is accomplished by parallel connection of infinitely many single crystal elements, forming the polycrystalline model. The model represents a good solution for common engineering practice due to its geometrical representation in form of Preisach triangle.

Membrane stiffness is a key determinant of E coli MscS channel mechanosensitivity

Prokaryotic mechanosensitive (MS) channels have an intimate relationship with membrane lipids. Membrane lipids may influence channel activity by directly interacting with bacterial MS channels or by influencing the global properties of the membrane such as area stretch and bending moduli. Previous work has implicated membrane stiffness as a key determinant of the mechanosensitivity of E. coli (Ec)MscS. Here we systematically tested this hypothesis using patch fluorometry of azolectin liposomes doped with lipids of increasing area stretch moduli. Increasing DOPE content of azolectin liposomes causes a rightward shift in the tension response curve of EcMscS. These rightward shifts are further magnified by the addition of stiffer forms of PE such as the branched chain lipid DPhPE and the fully saturated lipid DSPE. Furthermore, a comparison of the branched chain lipid DPhPC to the stiffer DPhPE showed a rightward shift in the tension response curve in the presence of the stiffer DPhPE. We show that these changes are not due to changes in membrane bending rigidity as the tension threshold of EcMscS in membranes doped with PC18:1 and PC18:3 are the same, despite a two-fold difference in their bending rigidity. We also show that after prolonged pressure application sudden removal of force in softer membranes causes a rebound reactivation of EcMscS and we discuss the relevance of this phenomenon to bacterial osmoregulation. Collectively, our data demonstrate that membrane stiffness is a key determinant of the mechanosensitivity of EcMscS.

Effects of Damaged Fiber Ropes on the Performance of a Hybrid Taut-Wire Mooring System

In this study, effects of damage levels of fiber ropes on the performance of a hybrid taut-wire mooring system are investigated. The analysis is performed using a numerical floating production storage and offloading (FPSO) model with a hybrid mooring system installed in 3000 m of water depth. An in-depth study was conducted using the numerical model, the dynamic stiffness equation of damaged fiber ropes, the time-domain dynamic theory, the rainflow cycle counting method, and the linear damage accumulation rule of Palmgren-Miner. Results indicate that, in a mooring line with an increasing damage level, the maximum tension decreases, while the offset of the FPSO increases. Particularly, when a windward mooring line failure occurs, in addition to the significant increase in the offset of the FPSO, the maximum tension, tension range, and annual fatigue damage levels of the remaining lines adjacent to the failed also increase significantly. The present work can be of great benefit to the evaluation of the offset of the floating platform, the tension response, and the service life of the hybrid mooring systems.

Propagating actomyosin-generated force to intercellular junction

Actomyosin II contractility in epithelial cells plays an essential role in tension-dependent adhesion strengthening. One key unsettling question is how cellular contraction transmits force to nascent cell-cell adhesion when there is no stable attachment between the nascent adhesion complex and actin filament. Here, we showed that application of intercellular tension induces myosin 1c accumulation at the lateral membrane between epithelial cells. We hypothesized that the accumulation of myosin 1c at the cell-cell interface allows coupling of actomyosin contractility to the generation of intercellular tension, thus is essential for tension-induced junction maturation. We showed that myosin 1c KD compromises a-actinin-4 recruitment to cell-cell adhesion during normal junction maturation driven by endogenous actomyosin contractility. However, application of cyclic tension to intercellular junction from outside of the cells rescued tension-dependent a-actinin-4 accumulation, suggesting that myosin-1c KD did not compromise the tension response or disrupt the overall integrity of the junctional complex. Our study identifies myosin-1c as a novel tension-sensitive protein on the lateral membrane and underscores a non-junctional contribution to adhesion strengthening at the epithelial cell-cell adhesion interface.

Long Term Analysis of TLP Extreme Tendon Tensions Using a Coupled Model and Comparison With the Contour Line Approach

This paper presents a full long term analysis of a TLP extreme tendon tensions using the all seas approach, and its comparison to the results estimated by the contour line approach. The analysis of the TLP tendon tension response is performed in the time domain using a coupled model where the floater is modelled in the software SIMO, while the tendon system is represented by a Finite Element Model in RIFLEX, including therefore the effects of non-linear restoring from the tendon system and bending and deformations of the tendons. The characteristic tendon tensions with q-annual probability of exceedance are estimated from a full long term analysis where both the short and long term variability are considered. These results are then compared to those obtained through the long term estimate from the contour line approach when assuming the 90th percentile for the worst sea state with q-annual probability of exceedance. The results from the full long term analysis will allow us to verify the adequate percentile level to be used with a contour line approach when estimating extreme TLP tendon tensions.