Bendstiff

Application

• Offshore engineering
  • riser bend stiffener designers & manufacturers
  • offshore engineering contractors
  • riser manufacturers and installers.
• General
  • electrical cable manufacturers.

Introduction

Bendstiff performs fast analysis or design of flexible pipe bend stiffeners.

Loading is determined from dynamic global analyses performed by Zenriser or other proprietary analysis software.

Extreme and operational loading allowable curvatures are derived according to API 17J from the specified minimum spool storage radius of curvature.

The software employs recognised large displacement analysis methods which cater for non-linear bend stiffener polymer material properties. A power law stress-strain curve is fitted to stress-strain data points. Material properties are stored in separate files for re-use.

Geometric design parameters can be restricted within user defined ranges (e.g. manufacturing restrictions on minimum root diameter to allow for steel reinforcement). By fully "clamping" all design parameters an analysis of an existing design can be performed.

The inclusion of non-linear materials in the formulation obviates the need for finite element analysis within the design loop.

Bendstiff is implemented using a Microsoft Windows GUI. Emphasis has been placed upon ease of use and rapid analysis times. A typical analysis with several load cases is completed within 3 minutes on a Pentium 200 MHz PC.

Technical capabilities

• Analysis types
  • design of bend stiffener dimensions to satisfy all loading conditions; evaluated bend stiffener dimensions are: root diameter and cone length / taper
  • analysis of existing bend stiffener design.

• Geometry input data for design
  • maximum & minimum root diameter
  • constant root section length
  • cone tip external diameter
  • riser outside diameter, EA & EI
  • maximum and minimum cone length
  • length from root of applied riser loading.

• Geometry input data for analysis
  • as for design except root diameter and cone length clamped.

• Material properties
  • bend stiffener stress-strain data points.

• Boundary conditions
  • root clamped
  • riser tension and angle of departure from undeformed bend stiffener axis for each load case
  • type of load (operational or extreme).

• Analysis control
  • number of shooting points (nodes)
  • analysis convergence tolerance.

• Additional design control
  • tolerance for curvature convergence
  • maximum number of design iterations.

Results output & presentation

• Text file and graphical plots give the following quantities along the deformed bend stiffener and riser axis for all load cases:
  • axial and lateral displacement
  • curvature
  • departure angle
  • total bending modulus
  • total bending moment
  • total shear force
  • total tension
  • stress and strain (section maxima).

User friendliness

• menu-driven Microsoft Windows GUI
• all user data entered via GUI with error checking
• full validation of input data
• user-transparent interface to analysis and design module
• view all text and graphical output within GUI
• analysis error checking reports.

Verification

Bendstiff has been verified against Abaqus large displacement finite element analyses using non-linear material properties and solid brick elements for the bend stiffener.

Availability

Bendstiff is currently only available for in-house use by Zentech personnel.

Consultancy

Zentech offers a comprehensive offshore analysis service. Bendstiff is one of several products used to meet the needs of our clients and the demands of the industry.