Model Uncertainties for Soil-Structure Interaction in Offshore Wind Turbine Monopile Foundations

Monopiles are the most common type of foundation used for bottom-fixed offshore wind turbines. This investigation concerns the influence of uncertainty related to soil–structure interaction models used to represent monopile–soil systems. The system response is studied for a severe sea state. Three wave-load cases are considered: (i) irregular waves assuming linearity; (ii) highly nonlinear waves that are merged into the irregular wave train; (iii) slamming loads that are included for the nonlinear waves. The extreme response and Fourier amplitude spectra for external moments and mudline bending moments are compared for these load cases where a simpler static pile-cap stiffness and a lumped-parameter model (LPM) are both considered. The fundamental frequency response of the system is well represented by the static pile-cap stiffness model; however, the influence of higher modes (i.e., the second and third modes with frequencies of about 1 Hz and 2 Hz, respectively) is significantly overestimated with the static model compared to the LPM. In the analyzed case, the differences in the higher modes are especially pronounced when slamming loads are not present

Comparison Between Dynamic Responses of Hollow and Solid Piles for Offshore Wind Turbine Foundations

The offshore wind energy industry is turning out ever larger numbers of offshore wind turbines every year. One way to achieve a cost-effective design is to have a better understanding of the dynamic response of offshore structures. That is why it is getting more and more important to understand the dynamic behavior of soil and interaction between soil and piles. To avert damage to offshore foundation, it becomes necessary to identify and quantify the soil-structure interaction and the related damping effects on the system. In this study, a single pile is investigated by means of boundary integral equations. The pile is modeled as a solid or hollow cylinder and the dynamic excitation is applied vertically. The surface along the entire interface is considered rough and with full contact between the soil and the structure. Somigliana’s identity, Betti’s reciprocal theorem and Green’s function are employed to derive the dynamic stiffness of pile, assuming that the soil is a linear viscoelastic medium. The dynamic stiffness is compared for solid and hollow cylinders by considering different values of material properties including the material damping. Modes of resonance and anti-resonance are identified and presented. It is observed that the absolute value of normalized dynamic stiffness is independent of Young’s modulus and Poisson’s ratio, whereas it is dependent on the soil’s damping

Comparison Between Dynamic Responses of Hollow and Solid Piles for Offshore Wind Turbine Foundations

The offshore wind energy industry is turning out ever larger numbers of offshore wind turbines every year. One way to achieve a cost-effective design is to have a better understanding of the dynamic response of offshore structures. That is why it is getting more and more important to understand the dynamic behavior of soil and interaction between soil and piles. To avert damage to offshore foundation, it becomes necessary to identify and quantify the soil-structure interaction and the related damping effects on the system. In this study, a single pile is investigated by means of boundary integral equations. The pile is modeled as a solid or hollow cylinder and the dynamic excitation is applied vertically. The surface along the entire interface is considered rough and with full contact between the soil and the structure. Somigliana’s identity, Betti’s reciprocal theorem and Green’s function are employed to derive the dynamic stiffness of pile, assuming that the soil is a linear viscoelastic medium. The dynamic stiffness is compared for solid and hollow cylinders by considering different values of material properties including the material damping. Modes of resonance and anti-resonance are identified and presented. It is observed that the absolute value of normalized dynamic stiffness is independent of Young’s modulus and Poisson’s ratio, whereas it is dependent on the soil’s damping

Flooring-systems and their interaction with furniture and humans

Flooring-system designs may be sensitive in terms of their vibrational performance due the risk that serviceability-limit-state problems may be encountered. For evaluating the vibrational performance of a flooring system at the design stage, decisions must be made by the engineer in charge of computations. Passive humans and/or furniture are often present on a floor. Typically, these masses and their way of interacting with the floor mass are ignored in predictions of vibrational behaviour of the flooring system. Utilizing a shell finite-element model, the paper explores and quantifies how non-structural mass can influence central parameters describing the dynamic behaviour of the flooring system with focus on elevated non-structural mass

Geotechnical Site Assessment by Seismic Piezocone Test in North of Denmark

These days cone penetration tests (CPT) have gained more popularity as an alternative to the conventional laboratory tests for subsurface investigation and estimation of soil parameters. Due to increasing interest in soil dynamics in the last decades, there is a development of CPT as a seismic piezocone penetration test (SCPTU) which provides shear wave velocity measurements simultaneously with measurements of tip resistance (qc), sleeve friction (fs) and pore pressure (u). The results can be used for determination of deformation parameters of soil. In this regard there have been proposed different empirical correlations between cone data and shear wave velocity measurements to estimate geotechnical parameters but their validity still needs to be verified in a case study and uncertainty remains about the choice of empirical correlations. In this study a site at the East Harbor of Aalborg (sandy site) and another at the Harbor of Frederikshavn (clayey site) in Denmark, where several SCPTU tests have been conducted, are considered. The data were used and analyzed based on different correlations presented in the literature. The results are further compared and verified with the measurements of shear wave velocity achieved from SCPTU tests

Geotechnical Site Assessment by Seismic Piezocone Test in North of Denmark

These days cone penetration tests (CPT) have gained more popularity as an alternative to the conventional laboratory tests for subsurface investigation and estimation of soil parameters. Due to increasing interest in soil dynamics in the last decades, there is a development of CPT as a seismic piezocone penetration test (SCPTU) which provides shear wave velocity measurements simultaneously with measurements of tip resistance (qc), sleeve friction (fs) and pore pressure (u). The results can be used for determination of deformation parameters of soil. In this regard there have been proposed different empirical correlations between cone data and shear wave velocity measurements to estimate geotechnical parameters but their validity still needs to be verified in a case study and uncertainty remains about the choice of empirical correlations. In this study a site at the East Harbor of Aalborg (sandy site) and another at the Harbor of Frederikshavn (clayey site) in Denmark, where several SCPTU tests have been conducted, are considered. The data were used and analyzed based on different correlations presented in the literature. The results are further compared and verified with the measurements of shear wave velocity achieved from SCPTU tests