scholarly journals Cyclic overlay model of p-y curves for laterally loaded monopiles in cohesionless soil

2021 ◽  
Author(s):  
Junnan Song ◽  
Martin Achmus
Keyword(s):  
Cyclic Loading ◽  
Large Diameter ◽  
Three Dimensional ◽  
Element Model ◽  
Offshore Wind ◽  
Cohesionless Soil ◽  
Triaxial Tests ◽  
Cyclic Loads ◽  
Ongoing Research ◽  
Overlay Model

Abstract. The bearing behaviour of large-diameter monopile foundations for offshore wind turbines under lateral cyclic loads in cohesionless soil is an issue of ongoing research. In practice, mostly the p-y approach is applied in the design of monopiles. Recently, modifications of the original p-y approach for monotonic loading stated in the API regulations (API 2014) have been proposed to account for the special bearing behaviour of large-diameter piles with small length-to-diameter ratios (e.g. Thieken et al. 2015, Byrne et al. 2015). However, cyclic loading for horizontally loaded piles predominates the serviceability of the offshore wind converters, and the actual number of load cycles cannot be considered by the cyclic p-y approach of the API regulations. This research is therefore focusing on the effects of cyclic loading on the p-y curves along the pile shaft and aiming to develop a cyclic overlay model to determine the cyclic p-y curves valid for a lateral load with a given number of load cycles. The “Stiffness Degradation Method (SDM)” (Achmus et al. 2009) is applied in a three-dimensional finite element model to determine the effect of the cyclic loading by degrading the secant soil stiffness according to the magnitude of cyclic loading and number of load cycles based on the results of cyclic triaxial tests. Thereby, the numerical simulation results are used to develop a “cyclic overlay model”, i.e. an analytical approach to adapt the monotonic (or static) p-y curve to the number of load cycles. The new model is applied to a reference system and compared to the API approach for cyclic loads.

Axial performance of micropile groups in cohesionless soil from full-scale tests

2020 ◽  
Vol 57 (7) ◽  
pp. 1006-1024
Author(s):  
Maged A. Abdlrahem ◽  
M. Hesham El Naggar
Keyword(s):  
Group Performance ◽  
Large Diameter ◽  
Small Diameter ◽  
Element Model ◽  
Cohesionless Soil ◽  
Drill Bit ◽  
Load Testing ◽  
Dense Sand ◽  
Full Scale Tests ◽  
Square Configuration

Hollow bar micropile (HBMP) groups are used for supporting large loads as an alternative foundation option to large diameter drilled shafts. In such cases, it may be necessary to increase the micropile’s diameter by increasing the drill bit diameter (Db). This paper investigates experimentally and numerically the effect of increasing Db and micropile spacing on the group performance. A field load testing program was conducted on four groups of HBMPs installed in sand; each group comprised four micropiles arranged in a square configuration. All micropiles were constructed with the same size hollow bar, Dh = 51 mm; two groups comprised micropiles constructed with drill bit, Db = 115 mm, and two groups comprised micropiles constructed with drill bit, Db = 152 mm. One group of each set was installed with spacing to micropile diameter ratio, S/Db = 3 and the other group with S/Db = 5. In addition, full 3D finite element model (FEM) was developed and calibrated to simulate the behaviour of micropile groups and to evaluate the failure load for groups that were not loaded to failure. The results demonstrated that micropile groups constructed with the large diameter drill bits displayed higher stiffness and load carrying capacity than the groups constructed with small diameter bits, which confirms the effectiveness of using a larger drill bit. In addition, the group efficiency ratio values at both working load and ultimate capacity were found to be close to unity for all groups. The ultimate skin friction values of grouted micropiles obtained from this study were higher than the values suggested by the US Federal Highway Administration for medium to very dense sand. It was also found that the settlement of the 4-HBMP group increased by 25% to 33% over that of a single HBMP due to group effect.

Propagation of Buckles in Sandwich Pipes Under External Pressure

2005 ◽  
Author(s):  
I. P. Pasqualino ◽  
M. I. Lourenc¸o ◽  
T. A. Netto
Keyword(s):  
Three Dimensional ◽  
Nonlinear Behavior ◽  
Element Model ◽  
External Pressure ◽  
Core Material ◽  
Small Scale ◽  
Ongoing Research ◽  
Scale Models ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

Sandwich pipes have been considered feasible conceptions for ultra deepwater pipelines, since they are capable to work at low temperatures and withstand high hydrostatic pressures. Sandwich pipelines are composed by inner and outer metallic pipes and a suitable core material which must provide high compression strength and good thermal insulation. The aim of this ongoing research is to study the quasi-static propagation of buckles in sandwich pipes. In this paper, a three-dimensional finite element model considering material and geometric nonlinear behavior is presented. The mesh discretization is determined through a detailed mesh sensitivity analysis. Some experiments with small scale models combining aluminum pipes and polypropylene as core material were carried out to calibrate the numerical model. The propagation pressure is evaluated under different bonding conditions between pipe layers.

scholarly journals Reliability analysis of offshore wind turbine foundations under lateral cyclic loading

2020 ◽  
Vol 5 (4) ◽  
pp. 1521-1535
Author(s):  
Gianluca Zorzi ◽  
Amol Mankar ◽  
Joey Velarde ◽  
John D. Sørensen ◽  
Patrick Arnold ◽  
...  
Keyword(s):  
Cyclic Loading ◽  
Wind Turbine ◽  
Limit State ◽  
Large Diameter ◽  
Probabilistic Approach ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Fe Model ◽  
Foundation Design

Abstract. The design of foundations for offshore wind turbines (OWTs) requires the assessment of long-term performance of the soil–structure interaction (SSI), which is subjected to many cyclic loadings. In terms of serviceability limit state (SLS), it has to be ensured that the load on the foundation does not exceed the operational tolerance prescribed by the wind turbine manufacturer throughout its lifetime. This work aims at developing a probabilistic approach along with a reliability framework with emphasis on verifying the SLS criterion in terms of maximum allowable rotation during an extreme cyclic loading event. This reliability framework allows the quantification of uncertainties in soil properties and the constitutive soil model for cyclic loadings and extreme environmental conditions and verifies that the foundation design meets a specific target reliability level. A 3D finite-element (FE) model is used to predict the long-term response of the SSI, accounting for the accumulation of permanent cyclic strain experienced by the soil. The proposed framework was employed for the design of a large-diameter monopile supporting a 10 MW offshore wind turbine.

Dynamic Response of a Large-Diameter Monopile Considering 35-Hour Storm Conditions

2019 ◽  
Author(s):  
Erin E. Bachynski ◽  
Ana Page ◽  
George Katsikogiannis
Keyword(s):  
Soil Structure ◽  
Temporal Evolution ◽  
Large Diameter ◽  
Element Model ◽  
Offshore Wind ◽  
Intermediate Water ◽  
Peak Period ◽  
The North ◽  
The North Sea ◽  
Standard Models

Abstract As a part of the assessment of foundation resistance for monopiles, several offshore wind standards prescribe symmetric 35-hour (or 42-hour) storm sequences in terms of wind speed and significant wave height. The temporal evolution of the peak period is not specified explicitly in the standards, despite the fact that large monopile wind turbines are sensitive to the wave period. In the present work, the storm sequences according to the standards are first compared to hindcast data for intermediate water depth locations in the North Sea. An alternative storm sequence is proposed based on the hindcast data, and possible values of the peak period evolution are proposed for the standard models. The responses of a 10 MW monopile wind turbine are then computed for both the standard and proposed sequences using a time domain aero-hydro-servo-elastic code coupled to a macro element model for the soil-structure interaction. The resulting mudline load cycles are then compared for the different storm sequences.

Utilisation d'équations constitutives du comportement du sol pour la prédiction d'essais triaxiaux sur des granulats calcaires

1995 ◽  
Vol 32 (1) ◽  
pp. 156-166 ◽  
Author(s):  
M. Jrad ◽  
F. Masrouri ◽  
J. Monnet
Keyword(s):  
Plastic Flow ◽  
Three Dimensional ◽  
Yield Function ◽  
Cohesionless Soil ◽  
Triaxial Tests ◽  
Soil Behavior ◽  
Limestone Aggregate ◽  
Element Computation ◽  
Internal Angle ◽  
The Relationship

This paper analyses the three-dimensional consolidation and shear behavior of cohesionless soil. It is divided in two parts: In the first part, the law of soil behavior is described. So far, the soil was assumed to be elastoplastic with associated plastic flow and stress hardening behavior. In this study, a new version of the Chaffois–Monnet law presents the yield function during consolidation and shearing in a single energy equation which avoids numerical errors due to the iterative process of the finite element computation, and numerical gap between consolidation and shearing. This new model uses only eight parameters with geotechnical significance. In the second part of this study, the results of the model are compared with experimental data from consolidated drained triaxial tests on three types of limestone aggregates. The validity of the model is finally discussed, and the relationship between the internal angle of friction and the mean stress is shown. Key words : behavior law, elastoplastic, associated, plastic flow, limestone aggregate, triaxial test.

Pore-Pressure Accumulation and Soil Softening Around Pile Foundations for Offshore Wind Turbines

2012 ◽  
Author(s):  
Pablo Cuéllar ◽  
Matthias Baeßler ◽  
Werner Rücker
Keyword(s):  
Cyclic Loading ◽  
Pore Water ◽  
Wind Turbines ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Large Diameter ◽  
Constitutive Law ◽  
Offshore Wind ◽  
External Loading ◽  
Offshore Wind Turbines

The foundation of offshore wind turbines usually involves the installation of large-diameter steel piles in the seabed, either in monopile or multi-pile configurations (jacket, tripod, etc…), which have to ensure a proper fixity of the turbine during its whole service life-time. However, such foundations raise several challenges and novel questions, partly due to the special characteristics of the offshore environment (for instance, the large numbers of load cycles from wind and waves and the possible influence of transient changes of pore water pressure around the pile) and aggravated by their large diameter, reduced slenderness and elevated ratio of lateral to vertical loads (see Fig. 1). This paper studies the effects of cyclic lateral loading on the offshore piles focusing on the possibility of a progressive accumulation of residual pore water pressure within the saturated embedding soil. As it will be shown, this can lead to significant changes of their behaviour under external loading, which can potentially compromise the foundation’s stability or serviceability. The paper will also analyse some singular effects of an irregular loading (e.g. cyclic loading with variable amplitude), in particular the so-called “order effects” and the phenomena arising during a realistic storm of moderate magnitude, and discuss their potential for transient damages to the foundation’s stiffness. All these phenomena, which can lead to a loss of serviceability of the structure, have been investigated by the authors by means of a coupled bi-phasic analytical model of the offshore foundation featuring a versatile constitutive law suitable for the soil. The constitutive model, in the frame of the theory of Generalized Plasticity, can reproduce some complex features of cyclic soil behaviour such as the tendency for a progressive densification under cyclic loading, which is responsible for the soil liquefaction phenomena in undrained conditions. Finally, some implications of these issues for the practical design of offshore monopiles will be discussed and some specific recommendations for the design procedures will be outlined.

scholarly journals Numerical and Experimental Study on Modular-Based Timber Structures

2019 ◽  
pp. 471-478
Author(s):  
Sigurdur Ormarsson ◽  
Johan Vessby ◽  
Marie Johansson ◽  
Le Kua
Keyword(s):  
Three Dimensional ◽  
Shear Stiffness ◽  
Element Model ◽  
Structural Safety ◽  
Test Results ◽  
Structural Behaviour ◽  
Ongoing Research ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element ◽  
Connection Design

Building with prefabricated light-frame volume modules is a prevalent and innovative construction method for low and mid-rise timber buildings. Compared to traditionally site-built constructions this method is very advantageous due to its high prefabrication level and the fast on-site assembly of the modules. The focus of this project is to study and optimise the global shear stiffness of the volume modules and to secure a large enough shear and uplift stiffness of the mechanical (or friction based) connections between the modules. Some companies assume that the friction between the modules is sufficient to transfer the wind stabilization forces down through the entire building. Regarding structural safety, connection design is an important task that needs to be numerically studied and experimentally verified. The paper presents numerical and experimental results obtained from two ongoing research projects concerning modular-based timber buildings in Sweden. The final aim of this work is to develop an efficient three dimensional finite-element model to analyse both the global and detailed structural behaviour of these types of buildings. To study the overall shear stiffness of the volume modules, eight different test-modules are to be tested. The test results will be used to calibrate the numerical model.

The Analysis and Application on the Typhoon-Induced Vibration Control of the Wind Turbine with a Pendulum Damper

2013 ◽  
Vol 773 ◽  
pp. 193-198 ◽  
Author(s):  
Jing Li ◽  
Jian Yun Chen ◽  
Xiao Bo Chen
Keyword(s):  
Wind Turbine ◽  
Three Dimensional ◽  
Element Model ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Superposition Method ◽  
Strong Wind ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

As a kind of high-rise structure, the offshore wind turbine is sensitive to wind load; it can generate strong dynamic responses to the excitation of typhoon. In this paper, a three-dimensional finite element model of offshore wind turbine is established with ADINA, responses under strong wind excitation are numerically simulated and performed subsequently. The fluctuating wind velocity time series are simulated by the method of HSM (harmony superposition method). Based on the modal and tine-history analyses of the structures together with self-vibration character, the pendulum damper is employed to control the resulting undesirable vibrations that are induced by wind. With the damper installed, the displacement and acceleration of the tower are reduced by as much as 40% using 1% of the total effective mass.

Experimental Study of the Stationkeeping of a Floater Using Passive Flapping Flat Plates in Waves

2019 ◽  
Author(s):  
Woo-Lim Sim ◽  
Hyunkyoung Shin ◽  
Rupesh Kumar
Keyword(s):  
Experimental Study ◽  
Three Dimensional ◽  
Offshore Wind ◽  
Flat Plates ◽  
Mooring Lines ◽  
Ongoing Research ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines ◽  
Flapping Foils ◽  
The University

Abstract To effectively use the resources of marine environments, it is necessary to consider the deep and remote parts of the ocean. Stationkeeping of floating offshore wind turbines (FOWTs) mainly relies on mooring lines[1][2]. However, current mooring lines have structural and economical limitations for applications in extreme sea environments. The University of Ulsan is conducting ongoing research to develop a new economical stationkeeping system that can maintain the position of a FOWT in the deep sea using passive flapping foils. This paper describes an experimental study of the stationkeeping of actual structures based on the above-mentioned investigations and suggested directions to supplement the deficiencies in stationkeeping systems using passive flapping foils. This experiment was carried out in the three-dimensional “Widetank” and in actual sea conditions, focusing on the drift of a floater in the surge direction.

Buckling Analysis of Pile during Hammer Placement

2012 ◽  
Vol 256-259 ◽  
pp. 467-470
Author(s):  
Shao Zeng Guo ◽  
Run Liu
Keyword(s):  
Finite Element ◽  
Geometric Nonlinearity ◽  
Large Diameter ◽  
Three Dimensional ◽  
Element Model ◽  
Offshore Engineering ◽  
Dimensional Finite Element ◽  
The Stability ◽  
Three Dimensional Finite Element

Large diameter and thin thickness are the main characteristics of the steel pipe piles in offshore engineering. Before piling a pile, heavy hammer will be placed on the top of it, which may emerge a serious risk in pile buckling. A three dimensional finite element model of pile and soil was established for a case study. The modified Riks method which can automatically search a suitable increment factor of loads is adopted to assess the stability of the pile, and the geometric nonlinearity and pile-soil interaction were both considered. The practical example shows that the critical load considering pile-soil interaction is much smaller than that in a fixed constraint.

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