A Calculation Method for Damping of Soil-Foundation Interactions in Marine Engineering

Abstract

This invention relates to a calculation method for soil-soil interaction damping in marine engineering foundation structures, comprising the following steps: obtaining the soil element damping ratio-cyclic shear strain curve; establishing a finite element analysis model; constructing a static implicit analysis step; defining the interaction between models and boundary conditions; performing mesh generation and calculation; post-processing to extract stress, strain, and other data; calculating elastic strain energy and dissipated energy; and finally obtaining the damping ratio. Compared with existing technologies, this invention, through a finite element analysis model combined with actual soil layer characteristics, uses fine meshes and contact models to realistically simulate the interaction between soil and structure. Considering the different soil material properties and employing appropriate constitutive models, it improves calculation accuracy and provides engineers with an effective tool for optimizing structural design and enhancing safety and economy.

Description

Technical Field

[0001] This invention relates to the field of soil-foundation interaction technology for marine engineering foundations such as offshore wind power and oil and gas, and in particular to a calculation method for damping of soil-foundation interaction in marine engineering. Background Technology

[0002] The load response of the superstructure of offshore wind turbines and oil and gas platforms depends on the pile-soil interaction stiffness and damping. The pile-soil interaction stiffness has a significant impact on the natural frequency of the superstructure and is crucial for accurately predicting fatigue damage. In most cases, it dominates the dimensional design of offshore wind turbine and oil and gas platform foundations, and even influences the type of offshore wind turbine foundation. Foundation-soil interaction damping plays a positive role in reducing the load on the superstructure and the fatigue damage of the foundation structure; however, compared with foundation-soil interaction stiffness, research on foundation-soil interaction damping is still lacking, and there is no consensus within the industry.

[0003] Currently, research on pile-soil interaction stiffness is relatively mature, while research on pile-soil interaction damping lags behind. Due to the complexity of the marine engineering environment, including dynamic effects such as waves, wind, and ocean currents, pile-soil interaction damping has a significant impact on the safety and economy of structures. However, the lack of unified calculation methods and standards makes it difficult to accurately assess the impact of pile-soil interaction damping in practical engineering applications, which has become a technical bottleneck for the industry's development.

[0004] Given the challenges mentioned above, it is particularly important to develop an accurate calculation method to assess the damping of marine engineering foundation-soil interactions. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies by providing a calculation method for soil-pile interaction damping in marine engineering foundation structures. This proposed method aims to fill this research gap. Through a finite element analysis model combined with the soil characteristics of actual sites, it provides engineers with a reliable tool to predict and evaluate pile-soil interaction damping, thereby optimizing structural design and improving structural safety and economy. By combining the soil element damping ratio-cyclic shear strain curve with the finite element analysis model, and through fine mesh generation and contact model definition, the interaction between soil and foundation structure can be simulated more realistically. Furthermore, this invention considers the stress-strain relationships of different soil materials and adopts a suitable constitutive model, further improving the accuracy and applicability of the calculation.

[0006] In the conceptualization process, the applicant believed that the connotation of viscous damping of the foundation structure-soil interaction is the energy loss dissipated by the soil within the range of foundation structure movement under cyclic shear action. Based on this understanding, a calculation method for viscous damping of the foundation structure-soil interaction based on finite element numerical calculation was proposed. This method can accurately assess the damping of the foundation structure-soil interaction of offshore wind turbines and oil and gas platforms.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] This invention provides a calculation method for damping of soil-foundation interaction in marine engineering, comprising the following steps:

[0009] S1: Obtain the soil element damping ratio-cyclic shear strain curve of the target site soil layer;

[0010] S2: Based on the soil element damping ratio-cyclic shear strain curve, a finite element analysis model of the interaction between the foundation structure and the soil is established;

[0011] S3: Based on the aforementioned finite element analysis model, establish a static implicit analysis step;

[0012] S4: Define the interaction between the foundation structure model and the soil model, where the tangential direction of the foundation structure-soil interface adopts Rough contact and the normal direction adopts Hard contact.

[0013] S5: Define boundary conditions, including constraints on the bottom, sides and back of the soil, as well as symmetric boundary conditions on the symmetric plane;

[0014] S6: Mesh the model and submit the calculation;

[0015] S7: Post-process the model to extract the stress, strain components and volume for each incremental step, as well as the horizontal displacement at the top of the structure;

[0016] S8: Calculate the elastic strain energy of soil elements and structural elements in each incremental step;

[0017] S9: Calculate the dissipated energy of the soil element in each incremental step;

[0018] S10: Calculate the damping ratio of the foundation-soil interaction system for each incremental step to complete the calculation of foundation-soil interaction damping.

[0019] Furthermore, the calculation method for damping of the interaction between marine engineering foundation structure and soil is implemented using finite element numerical analysis software (ABAQUS, Plaxis3D, etc.).

[0020] Furthermore, the marine engineering foundation includes one or more of the following: monopile foundation, suction pile foundation, suction anchor foundation, suction bucket foundation, and pile-anchor foundation.

[0021] Furthermore, in S1, the soil element damping ratio-cyclic shear strain curve of the target site soil layer is obtained from data acquired in one of the following ways:

[0022] 1) Data obtained by experimental methods, i.e., data obtained by combined testing with resonant column and cyclic single shear or cyclic triaxial methods;

[0023] 2) Data obtained through empirical methods, including data calculated using the damping ratio model by Derendeli (2001).

[0024] Furthermore, in S2, the finite element analysis model includes the basic structure and the soil, and is assigned corresponding material properties;

[0025] In S2, the material properties include one or more of the following: mass density, Young's modulus, Poisson's ratio, friction angle, expansion angle, yield strength, and K0 coefficient.

[0026] Furthermore, in S2, an ideal elastoplastic constitutive model satisfying the Mohr-Coulomb yield condition is used to describe the stress-strain relationship of the sand.

[0027] In S2, the stress-strain relationship of clay is described using the ideal elastoplastic Tresca constitutive model.

[0028] Furthermore, in S6, during the meshing process of the model, the mesh is refined in the pre-selected key areas of interest in order to improve computational efficiency and accuracy.

[0029] Furthermore, in S8, the elastic strain energy of each soil element and each structural element in each incremental step is calculated using the following formula:

[0030]

[0031] in, E S0,i Elastic energy of soil elements V el,i : Volume of the soil element, σ kk ε kk τ ki ε kj Stress and strain components of a soil element;

[0032]

[0033] in, E Str,i Elastic energy of structural units Vel,i ′: Volume of the structural unit, σ kk ′、ε kk ′、τ ki ′、ε kj Stress and strain components of structural elements;

[0034] Furthermore, in S9, the energy dissipated by each soil element in each incremental step is calculated using the following formula:

[0035]

[0036] in, E D,i Energy dissipation of the soil element E S0,i Elastic energy of soil elements d i The damping ratio of the soil element is obtained by interpolation of the damping ratio-cyclic shear strain curve of the soil element in S1 based on the generalized shear strain.

[0037] Furthermore, in S10, the damping ratio of the foundation-soil interaction system for each incremental step is calculated using the following formula:

[0038]

[0039] in, d str-soil Damping ratio of the foundation structure-soil system.

[0040] Compared with the prior art, the present invention has the following technical advantages:

[0041] 1. The calculation method for damping of soil-basin interaction in marine engineering as described in this invention is simple, easy to operate, and has high application value.

[0042] 2. The calculation method for damping of soil-foundation interaction in marine engineering described in this invention can take into account the actual soil layer distribution and the damping-strain characteristics of each soil layer, resulting in more accurate calculation results.

[0043] 3. The calculation method of this invention, by obtaining the soil element damping ratio-cyclic shear strain curve of the target site soil layer, can more accurately simulate the interaction between the marine engineering foundation structure and the soil. Furthermore, this method is applicable to various marine engineering foundation structures, such as monopile foundations and suction pile foundations, demonstrating excellent versatility.

[0044] 4. This invention employs Rough and Hard contact when defining the interaction between the foundation structure model and the soil model, which more realistically reflects the contact state between the foundation structure and the soil in actual engineering. By defining reasonable boundary conditions, including constraints on the bottom, sides, and back of the soil, as well as symmetrical boundary conditions on symmetrical planes, boundary effects in actual engineering can be simulated more accurately. During mesh generation, refining the mesh in key areas of interest improves computational efficiency and accuracy, which helps to obtain more reliable results with limited computational resources. By calculating the elastic strain energy and dissipated energy of soil and structural elements in each incremental step, the energy behavior of the system can be analyzed in depth, providing richer information for structural design. Attached Figure Description

[0045] Figure 1 This is a complete flowchart of the present invention;

[0046] Figure 2 This is the cyclic shear strain-damping ratio curve of the clay of this invention;

[0047] Figure 3 This is the cyclic shear strain-damping ratio curve of the sand in this invention;

[0048] Figure 4 This is a schematic diagram of the finite element model of the basic structure-soil of this invention;

[0049] Figure 5 This is a schematic diagram of the local mesh refinement of the finite element model of the basic structure-soil of the present invention;

[0050] Figure 6 The curve results of the normalized pile head displacement versus pile-soil interaction system damping are presented in this invention.

[0051] Figure 7 This is a schematic diagram of the core process of the present invention. Detailed Implementation

[0052] Overall, the calculation method for soil-foundation interaction damping in marine engineering projects presented in this invention belongs to the technical field of soil-foundation interaction in marine engineering projects such as offshore wind power and oil and gas. The method uses finite element numerical analysis software such as ABAQUS and includes the following steps: S1, obtaining the soil element damping ratio-cyclic shear strain curve of the target site soil layer; S2, establishing a finite element analysis model of the soil-foundation interaction, including the foundation structure and soil, assigning corresponding material properties to each established model, and assembling the numerical calculation analysis model; S3, establishing a static implicit analysis step; S4, establishing the foundation structure... S5. Define boundary conditions; S6. Mesh the established numerical analysis model and submit the calculation; S7. Post-processing: extract the 6 stress components and 6 strain components of all soil elements and the foundation structure below the mud surface in each increment step, as well as the volume of each soil element, and extract the horizontal displacement of the top of the structure in each increment step; S8. Calculate the elastic strain energy of each soil element and each structural element in each increment step; S9. Calculate the energy dissipated by each soil element in each increment step; S10. Calculate the damping ratio of the foundation structure-soil interaction system in each increment step.

[0053] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Component models, material names, connection structures, control methods, algorithms, and other features not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0054] Example 1

[0055] like Figure 1 and 7 As shown, this invention provides a calculation method for damping of soil-foundation interaction in marine engineering. The method uses the finite element numerical analysis software ABAQUS and includes the following steps:

[0056] S1. Obtain the soil element damping ratio-cyclic shear strain curve of the target site soil layer. There are two options for this step: 1) Indoor test method, using a combination of resonant column (≤0.01% strain level) and cyclic single shear or cyclic triaxial (≥0.1% strain level); 2) Empirical method, if there is a lack of test data of soil element damping ratio-cyclic shear strain curve, an empirical method can be used, such as the damping ratio calculation by Derendel (2001).

[0057] Derendeli (2001) proposed the following damping ratio model:

[0058]

[0059]

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066]

[0067] in: γ For cyclic shear strain γ r Reference shear strain (%) d min The small strain damping ratio (%) of the material. a The curve shape parameter φ5 is equal to, b This is the scaling factor. d Adiusted The damping ratio (%) of the adjusted material. σ′ 0 represents the average effective confining pressure (atm). PI Plasticity index (%) OCR It is an over-consolidation ratio. frq For loading frequency, N φ is the number of iterations. i For calculating parameters, G / G max This is the normalized shear modulus.

[0068] There are two different sets of calculation parameters for sandy soil and clay soil.

[0069] Mixed sand:

[0070] φ1=0.0334, φ2=-0.0001, φ3=0.2490, φ4=0.4820, φ5=0.8450, φ6=0.8890, φ7=0.0202, φ8=-0.1000, φ9=-0.3720,φ 10 =0.2330, φ 11 =0.7760, φ 12 =-0.0294.

[0071] Clay:

[0072] =0.0258, =0.0020, =0.0992, =0.2260, =0.9750, =0.9580, =0.0057, =-0.1000, =-0.1960, =0.3680, =0.4660, =0.0223.

[0073] like Figure 2 and Figure 3 As shown, the cyclic shear strain-damping ratio curves of clay and sand at a certain target site were obtained through a combination of indoor resonant column test and dynamic single shear test.

[0074] S2. Establish a finite element analysis model of the foundation structure-soil interaction, including the foundation structure and soil. Assign corresponding material properties to each model and assemble the numerical calculation analysis model; such as... Figure 4 As shown, this example uses a monopile foundation commonly used in offshore wind power and oil and gas fields. Due to the symmetry of the research problem, only half a pile and the soil are modeled. To eliminate boundary effects, the soil area is 192m in the load application direction (20 times the pile diameter), and 96m in the direction perpendicular to the load application direction (10 times the pile diameter). The soil layer thickness below the pile tip is 14.4m, 1.5 times the pile diameter. Soil layer information is shown in Table 1.

[0075] Table 1 Soil layer information in the finite element model of the foundation structure-soil

[0076]

[0077] In the finite element analysis, a solid cross-section continuous element was used for the single pile, with a pile diameter of 9.6m, and a linear elastic material was used to simulate the single pile. By equivalence with the bending stiffness EI of a hollow steel pipe pile with a pile diameter of 9.6m and a wall thickness of 0.08m, the equivalent Young's modulus was calculated to be 13.7GPa.

[0078] The soil was simulated using the Mohr-Coulomb model. In the finite element analysis, the internal friction angle was set to 0, and the Mohr-Coulomb model was simplified to the Tresca model. The Young's modulus was calculated as E=2(1+µ) G=3G (µ=0.5 under undrained conditions), and G was calculated based on Gmax / su and su. In Abaqus, µ was set to 0.48 (to avoid numerical calculation non-convergence when µ=0.5).

[0079] S3. Establish the static implicit analysis step;

[0080] S4. Establish the interaction between the foundation structure model and the soil model. The foundation structure-soil interface adopts Rough contact in the tangential direction, i.e., no slip, and Hard contact in the normal direction. The interface is not allowed to separate.

[0081] S5. Define boundary conditions: the soil is constrained at the bottom (U3), the sides (U1), and the back (U2). Symmetrical boundary conditions are applied to the symmetry plane, i.e., constraints U2, UR1, and UR3. All loads are applied to the top of the single pile. The pile-soil interface uses Rough contact in the tangential direction (no slippage) and Hard contact in the normal direction (no separation of the pile-soil interface is allowed). It should be noted that geometric nonlinearity is disabled in the finite element analysis; therefore, the p-Δ effect is not considered.

[0082] S6. The established numerical calculation and analysis model is meshed and submitted for calculation. Balancing computational efficiency and accuracy, the mesh needs to be refined in key areas of interest. Figure 5 shows the mesh refinement of the soil around the pile. The mesh within a 1.5-fold pile diameter radius outwards from the pile is gradually denser from the outside in. Both the soil and single-pile mesh types use C3D8R.

[0083] S7. Post-processing: Extract the 6 stress components and 6 strain components of all soil elements in each increment step, as well as the volume of each soil element; extract the 6 stress components and 6 strain components of the foundation structure below the mud surface in each increment step, as well as the volume of each structural element; extract the horizontal displacement of the top of the structure in each increment step.

[0084] S8. Calculate the elastic strain energy of each soil element and each structural element in each incremental step:

[0085]

[0086] in, E S0,i Elastic energy of soil elements V el,i : Volume of the soil element, σ kk ε kk τ ki ε kj Stress and strain components of a soil element.

[0087]

[0088] in, E Str,i Elastic energy of structural units V el,i ′: Volume of the structural unit, σ kk ′、ε kk ′、τ ki ′、εkj Stress and strain components of structural elements;

[0089] S9. Calculate the energy dissipated by each soil element in each increment step:

[0090]

[0091] in, E D,i Energy dissipation of the soil element E S0,i Elastic energy of soil elements d i The damping ratio of the soil element is obtained by interpolation of the soil element damping ratio-cyclic shear strain curve in step S1 based on the generalized shear strain.

[0092] S10. Calculate the damping ratio of the foundation-soil interaction system for each incremental step:

[0093]

[0094] in, d str-soil Damping ratio of the foundation structure-soil system.

[0095] Figure 6 Curves of normalized pile head displacement versus pile-soil interaction system damping are presented.

[0096] Those skilled in the art will understand that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0097] The meaning of "and / or" as used in this application includes situations where each exists alone or both exist simultaneously.

[0098] This application example uses a single pile foundation, but the method is still applicable to suction piles, suction buckets, suction anchors, pile anchors, and suction tubes for jacket structures, so they are all within the protection scope of this invention.

[0099] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A calculation method for damping of soil-foundation interaction in marine engineering, characterized in that, Includes the following steps: S1: Obtain the soil element damping ratio-cyclic shear strain curve of the target site soil layer; S2: Based on the soil element damping ratio-cyclic shear strain curve, a finite element analysis model of the interaction between the foundation structure and the soil is established; S3: Based on the aforementioned finite element analysis model, establish a static implicit analysis step; S4: Define the interaction between the foundation structure model and the soil model, where the tangential direction of the foundation structure-soil interface adopts Rough contact and the normal direction adopts Hard contact. S5: Define boundary conditions, including constraints on the bottom, sides and back of the soil, as well as symmetric boundary conditions on the symmetric plane; S6: Mesh the model and submit the calculation; S7: Post-process the model to extract the stress, strain components and volume for each incremental step, as well as the horizontal displacement at the top of the structure; S8: Calculate the elastic strain energy of soil elements and structural elements in each incremental step; S9: Calculate the dissipated energy of the soil element in each incremental step; S10: Calculate the damping ratio of the foundation-soil interaction system for each incremental step to complete the calculation of foundation-soil interaction damping. In S8, the elastic strain energy of each soil element and each structural element in each incremental step is calculated using the following formula: in, E S0,i Elastic energy of soil element V el,i : Volume of the soil element, σ kk ε kk τ ki ε kj Stress and strain components of a soil element; in, E Str,i Elastic energy of structural units V el,i ′: Volume of the structural unit, σ kk ′、ε kk ′、τ ki ′、ε kj Stress and strain components of structural elements; In S9, the energy dissipated by each soil element in each incremental step is calculated using the following formula: in, E D,i Energy dissipation of the soil element E S0,i Elastic energy of soil element d i Damping ratio of the soil element: The damping ratio of the soil element is obtained by interpolation of the damping ratio-cyclic shear strain curve of the soil element in S1 based on the generalized shear strain. In S10, the damping ratio of the foundation-soil interaction system for each incremental step is calculated using the following formula: in, d str-soil Damping ratio of the foundation structure-soil system.

2. The calculation method for damping of soil-foundation interaction in marine engineering according to claim 1, characterized in that, The calculation method for damping of marine engineering foundation-soil interaction is implemented using finite element numerical analysis software.

3. The calculation method for damping of soil-foundation interaction in marine engineering according to claim 1, characterized in that, The marine engineering foundation includes one or more of the following: monopile foundation, suction pile foundation, suction anchor foundation, suction bucket foundation, and pile-anchor foundation.

4. The calculation method for damping of soil-foundation interaction in marine engineering according to claim 1, characterized in that, In S1, the soil element damping ratio-cyclic shear strain curve of the target site soil layer is obtained from data acquired in one of the following ways: 1) Data obtained by experimental methods, i.e., data obtained by combined testing with resonant column and cyclic single shear or cyclic triaxial methods; 2) Data obtained through empirical methods, including data calculated using the damping ratio model of Derendeli version 2001.

5. The calculation method for damping of soil-foundation interaction in marine engineering according to claim 1, characterized in that, In S2, the finite element analysis model includes the basic structure and the soil, and is assigned corresponding material properties; In S2, the material properties include one or more of the following: mass density, Young's modulus, Poisson's ratio, friction angle, expansion angle, yield strength, and K0 coefficient.

6. The calculation method for damping of soil-foundation interaction in marine engineering according to claim 1, characterized in that, In S2, an ideal elastoplastic constitutive model that satisfies the Mohr-Coulomb yield condition is used to describe the stress-strain relationship of the sand. In S2, the stress-strain relationship of clay is described using the ideal elastoplastic Tresca constitutive model.

7. The calculation method for damping of soil-foundation interaction in marine engineering according to claim 1, characterized in that, In S6, during the mesh generation process of the model, the mesh is refined in the pre-selected key areas of interest in order to improve computational efficiency and accuracy.

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