Techniques for modeling large diameter monopiles
Inventors
Mozaffari, Navid • Jhita, Parvinder
Assignees
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Publication Number
US-12197823-B1
Publication Date
2025-01-14
Expiration Date
Abstract
In example embodiments, a new model for modeling monopiles in is provided that, in addition to distributed lateral load along the monopile, considers distributed moment along the length of the pile, base moment at the pile tip, and base shear force at the pile tip. The new model may avoid the overly conservative designs for large diameter piles (e.g., 10 m+) with small length-to-diameter ratios (e.g., <6), while using standardized reaction curves (i.e., p-y curves and t-z curves) and considering axial and combined loading.
Core Innovation
The invention provides an improved monopile modeling model in structural analysis and design software. It extends the Winkler approach by incorporating distributed lateral load and distributed moment along a monopile, together with base moment, base shear force, and corresponding base stiffnesses at the pile tip. The model is used to model a monopile description output by the structural analysis and design software.
The method accesses standardized nonlinear soil reaction curves, including p-y curves and t-z curves, for a type of soil for a monopile at each of one or more layers. Each p-y curve is a nonlinear function relating lateral soil reaction force (p) to lateral displacement (y), and each t-z curve is a nonlinear function relating skin friction (t) to vertical displacement (z). Rotational stiffness at a given node is determined as a function of both force per unit area from a respective t-z curve for the layer of the given node and slope of the respective t-z curve for the layer of the given node.
Base rotational stiffness and base shear stiffness are determined from curve-derived quantities at the pile tip. Base rotational stiffness is calculated as a function of both force per unit area from a respective p-y curve for the layer of the pile tip and slope of the respective p-y curve for the layer of the pile tip. Base shear stiffness is calculated as a function of slope of a respective t-z curve for the layer of the pile tip and pile tip area, and the model iteratively solves a system of non-linear equations using a structural stiffness matrix that includes rotational stiffness, base rotational stiffness, and base shear stiffness in addition to pile material structural stiffness to model the monopile.
Claims Coverage
The document includes three independent claims (method, computing device, and non-transitory computing device readable medium). Across these independent claims, the main inventive features are the curve-based determination of rotational stiffness, base rotational stiffness, and base shear stiffness, and the iterative solution of a non-linear equation system using a structural stiffness matrix that includes those stiffness terms in addition to pile material structural stiffness.
Accessing and using nonlinear p-y and t-z curves for layered soil
Access a p-y curve and a t-z curve for a type of soil for a monopile at each of one or more layers, where each p-y curve is a nonlinear function relating lateral soil reaction force (p) to lateral displacement (y), and each t-z curve is a nonlinear function relating skin friction (t) to vertical displacement (z), the monopile including a plurality of nodes in the one or more layers.
Rotational stiffness from t-z curve force per unit area and slope
Determine a distributed moment along the monopile and based thereon a rotational stiffness of a given node, where the rotational stiffness is calculated as a function of both force per unit area from a respective t-z curve for the layer of the given node and slope of the respective t-z curve for the layer of the given node.
Base rotational stiffness from p-y curve force per unit area and slope
Determine a base moment at a pile tip of the monopile and based thereon a base rotational stiffness, where the base rotational stiffness is calculated as a function of both force per unit area from a respective p-y curve for the layer of the pile tip and slope of the respective p-y curve for the layer of the pile tip.
Base shear stiffness from t-z curve slope and pile tip area
Determine a base shear force at the pile tip and based thereon base shear stiffness, where the base shear stiffness is calculated as a function of slope of a respective t-z curve for the layer of the pile tip and pile tip area.
Iterative non-linear equation system with structural stiffness matrix including rotational and base stiffnesses
Iteratively solve a system of non-linear equations that uses a structural stiffness matrix that includes the rotational stiffness, the base rotational stiffness and the base shear stiffness in addition to pile material structural stiffness to model the monopile.
Outputting description of the modeled monopile
Outputting a description of the modeled monopile.
Collectively, the independent claims cover modeling a monopile by accessing nonlinear p-y and t-z curves for layered soil, computing rotational stiffness at nodes from t-z curve force per unit area and slope, computing base rotational stiffness from p-y curve force per unit area and slope, computing base shear stiffness from t-z curve slope and pile tip area, and iteratively solving a non-linear equation system with a structural stiffness matrix that includes these stiffness terms plus pile material structural stiffness to produce a modeled monopile description.
Stated Advantages
Avoiding overly conservative designs.
Enabling modeling for large-diameter ( 10 m+) monopiles with small length-to-diameter ratios ().
Reducing need for new, non-standard soil reaction curve field testing.
Enabling axial/combined loading.
Documented Applications
Modeling a monopile used in offshore wind.
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