Improved Dynamic Structural Modelling for Subsea Power Cables With Bitumen Coated Armour Wires

2017 ◽  
Author(s):  
Hugh Martindale ◽  
Steven Rossiter ◽  
Terence Sheldrake ◽  
Richard Langdon
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Dynamic Modelling ◽  
Bending Stiffness ◽  
Offshore Wind ◽  
Power Cables ◽  
Cable Structure ◽  
Non Linear ◽  
Low Tension

This paper presents improved dynamic modelling of subsea power cables using new models for the determination of non-linear cable mechanical properties. The modelling has been developed for cables typically used in offshore wind and for interconnectors, as well as dynamic power umbilicals. The results provide a better simulation of the dynamic response and allow better integration of local and global modelling for determination of stress and fatigue in offshore power cables. Cable response due to bending is modelled by including non-linear adhesion induced stresses due to a yielding bond between armour wire and neighbouring layers, which captures the effects of temperature and strain rate and provides better representation than purely friction-based modelling especially at low tension. Local armour bending stiffness is included by using average wire strain energy after slip along the strained helical path to determine the armour layer bending stiffness contribution. Mathematical modelling for mechanical properties is verified by sample testing and FEA, to provide a robust method for predicting cable response. Although dynamic subsea power cables are essentially non-bonded structures there is a certain amount of adhesion within the structure. Previous work has focused on friction-tension based modelling of armour wire-core interaction, that is not appropriate as critical slip curvatures at low tension are understated and full-slip stress distributions do not account for work done against friction during further bending. The principal result of this new approach is the improved determination of lifetime stresses for critical components within the cable structure. Non-linear bend stiffness modelling produces characteristic moment-curvature relations including hysteresis on reversal of bending. These curves provide an improved representation of the onset of slip in the armour wires and allow for the influence of temperature and strain rate on the cable bending stiffness to be included. The bend-stiffness model has been validated against test data both of complete bundles and individual components. The overall result is a methodology that typically results in increased fatigue life and can reduce the requirement for ancillary products such as ballast/buoyancy and bend stiffeners/restrictors. Additionally, the non-linear, hysteretic response of a cable significantly reduces certain phenomena that are often associated with numerical modelling of cables using a linear bend stiffness. Specifically, a cable catenary attached to a vessel and modelled with a linear bend stiffness will often experience ‘compression waves’ when the vessel is moving in response to wave loading. Use of a non-linear, hysteretic bend stiffness minimises the compression wave phenomenon, giving a much more realistic response and often greatly improving operability windows for offshore operations.

scholarly journals Performance validation and dynamic response analysis of a deepwater cable bending restrictor

2020 ◽  
Vol 37 (3) ◽  
pp. 95-101
Author(s):  
Kang Yongtian ◽  
Xiao Wensheng ◽  
Zhang Dagang ◽  
Zhang Liang ◽  
Zhou Chouyao ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Numerical Analysis ◽  
Dynamic Response ◽  
Bending Stiffness ◽  
Offshore Wind ◽  
Response Analysis ◽  
Analysis Model ◽  
Element Analysis ◽  
Cable Structure ◽  
Pipe Model

The deepwater cable bending restrictor is an important protective device for risers, umbilicals and cables in offshore engineering, protecting cable structure by controlling minimum bending radius. Its mechanical properties are analysed based on the numerical analysis model and finite element analysis (FEM) of ø175. The sensitivity analysis of using quantity of bending restrictors is also performed to show the effect of the quantity on bending stiffness. A testing scheme of bending stiffness of the bending restrictor is then formulated based on its structure. From numerical analysis results through test simulation, the tolerance is less than 3 %, which verifies the reliability of the numerical analysis model. Performance of the bending restrictor and dynamic response are analysed according to environmental parameters that occur once per 100 years from offshore wind power farms and pipein-pipe models, respectively. The results show the bending restrictor can effectively protect cable structure, and the pipein-pipe model is suitable for calculating mechanical properties of interaction between the bending restrictor and cable.

Stiffness and strength properties of five paperboards and their moisture dependency

TAPPI Journal ◽  
2020 ◽  
Vol 19 (2) ◽  
pp. 71-85
Author(s):  
GUSTAV MARIN ◽  
MIKAEL NYGARDS ◽  
SOREN OSTLUND
Keyword(s):  
Mechanical Properties ◽  
Mechanical Property ◽  
Shear Strength ◽  
Three Dimensional ◽  
Strength Properties ◽  
Bending Stiffness ◽  
Moisture Ratio ◽  
Machine Direction ◽  
Product Series

Five commercial multiply folding boxboards made on the same paperboard machine have been analyzed. The paperboards were from the same product series but had different grammage (235, 255, 270, 315, 340 g/m2) and different bending stiffness. The paperboards are normally used to make packages, and because the bending stiffness and grammage varies, the performance of the packages will differ. Finite element simulations can be used to predict these differences, but for this to occur, the stiffness and strength properties need to be deter-mined. For efficient determination of the three-dimensional properties in the machine direction (MD), cross direction (CD), and Z direction (ZD), it is proposed that the paperboard should be characterized using in-plane tension, ZD-tension, shear strength profiles, and two-point bending. The proposed setups have been used to determine stiff-ness and strength properties at different relative humidity (20,% 50%, 70%, and 90% RH), and the mechanical proper-ties have been evaluated as a function of moisture ratio. There was a linear relation between mechanical properties and moisture ratio for each paperboard. When the data was normalized with respect to the standard climate (50% RH) and plotted as a function of moisture ratio, it was shown that the normalized mechanical properties for all paperboards coincided along one single line and could therefore be expressed as a linear function of moisture ratio and two constants. Consequently, it is possible to obtain the mechanical properties of a paperboard by knowing the structural prop-erties for the preferred level of RH and the mechanical property for the standard climate (50% RH and 23°C).

Determination of the Heat Release Distribution in Turbulent Flames by a Model Based Correction of OH* Chemiluminescence

2011 ◽  
Author(s):  
Martin Lauer ◽  
Mathieu Zellhuber ◽  
Thomas Sattelmayer ◽  
Christopher J. Aul
Keyword(s):  
Strain Rate ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Correction Method ◽  
Turbulent Flames ◽  
Lookup Table ◽  
Rate Model ◽  
Non Linear

Imaging of OH* or CH* chemiluminescence with intensified cameras is often employed for the determination of heat release in premixed flames. Proportionality is commonly assumed, but in the turbulent case this assumption is not justified. Substantial deviations from proportionality are observed, which are due to turbulence-chemistry interactions. In this study a model based correction method is presented to obtain a better approximation of the spatially resolved heat release rate of lean turbulent flames from OH* measurements. The correction method uses a statistical strain rate model to account for the turbulence influence. The strain rate model is evaluated with time-resolved velocity measurements of the turbulent flow. Additionally, one-dimensional simulations of strained counterflow flames are performed to consider the non-linear effect of turbulence on chemi-luminescence intensities. A detailed reaction mechanism, which includes all relevant chemiluminescence reactions and deactivation processes, is used. The result of the simulations is a lookup table of the ratio between heat release rate and OH* intensity with strain rate as parameter. This lookup table is linked with the statistical strain rate model to obtain a correction factor which accounts for the non-linear relationships between OH* intensity, heat release rate, and strain rate. The factor is then used to correct measured OH* intensities to obtain the local heat release rate. The corrected intensities are compared to heat release distributions which are measured with an alternative method. For all investigated flames in the lean, partially premixed regime the corrected OH* intensities are in very good agreement with the heat release rate distributions of the flames.

Flexural Properties of Polyamides: Influence of Strain Rate, Friction and Moulding-Induced Anisotropy

2014 ◽  
Vol 601 ◽  
pp. 29-32
Author(s):  
Dan Andrei Serban ◽  
Tudor Voiconi ◽  
Liviu Marsavina ◽  
Vadim V. Silberschmidt
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Tensile Tests ◽  
Flexural Properties ◽  
Induced Anisotropy ◽  
Flexural Behaviour ◽  
Bending Tests ◽  
Three Point Bending ◽  
Cooling Conditions

In recent years, advances in material testing equipment caused the determination of mechanical properties by means of three-point bending tests to lose ground in detriment to more accurate tensile tests. However, if components undergo bending deformation in service, the identification of the materials flexural behaviour is essential. The investigated material is a thermoplastic polymer, test specimens being cut in prismatic shapes from injected sheets, which present a variation in properties due to cooling conditions. This paper presents results of three-point bending tests with emphasis on the influence of strain rate and anisotropy on flexural strength and chord modulus. Results show an increase in flexural properties with strain rate and a considerable influence of anisotropy on mechanical properties.

The Determination of Stresses and Temperatures in Cooling Bodies by Finite Elements

1976 ◽  
Vol 98 (3) ◽  
pp. 478-484 ◽  
Author(s):  
R. W. Lewis ◽  
B. R. Bass
Keyword(s):  
Mechanical Properties ◽  
Finite Element Method ◽  
Finite Element ◽  
Heat Conduction ◽  
Thermal Stress ◽  
Physical And Mechanical Properties ◽  
Complex Geometries ◽  
Linear Boundary ◽  
Non Linear

This paper presents a finite element method for solving non-linear heat conduction and thermal stress problems. The nonlinearity is caused by the variation of thermo-physical and mechanical properties of the material with respect to temperature. The distribution of temperature and stress in a cooling body can be followed from the onset of solidification. The method is capable of handling complex geometries and initial non-linear boundary conditions.

Sign in / Sign up

Export Citation Format

Share Document