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Abstract Compared with jack-up crane vessels that are now widely used in offshore wind turbine installation, floating crane vessels are more flexible with respect to working water depth and are much faster in relocation. They are thus a promising alternative to install offshore wind turbine components, especially in intermediate and deep water. However, the wave-induced motions of the floating vessels make the operations challenging. This study deals with a preliminary feasibility study on offshore single blade installation using floating crane vessels. Two typical floating crane vessels are considered, i.e., a mono-hull vessel and a semi-submersible vessel. They are assumed to be equipped with dynamic positioning systems that can well mitigate the slowly varying horizontal motions. Their overall performance during the blade installation is numerically evaluated by comparing their performance against a typical jack-up crane vessel. The crane dynamics plays a less important role for blade installation by floating vessels, compared to the jack-up crane vessel. The floating vessels' wave-induced motion greatly affects the blade motion. The semi-submersible vessel causes a much smaller blade motion than the mono-hull vessel. The results indicate that it is feasible to install offshore wind turbine blades by using floating crane vessels provided that the vessel type is properly selected. From the operability point of view, semi-submersible vessels are more feasible than mono-hull vessels for offshore single blade installations. [ABSTRACT FROM AUTHOR]

Jack-up crane vessels are commonly used to install offshore wind turbine blades and other components. A jack-up crane vessel is subjected to wind and wave loads, which cause motion at crane tip. Excessive motion at crane tip can lead to failure of lifting operations. Therefore, the crane tip motion should be properly assessed for jack-up crane vessels. In this study, a fully coupled model is developed for a typical elevated jack-up crane vessel, considering the hydrodynamic and aerodynamic loads on the vessel, the soil-structure interaction, and the structural flexibility of the jack-up legs and crane. The vessel model developed is further coupled with the SIMO-Aero code to achieve a fully coupled aero-hydro-soil-elastic-mechanical code SIMO-RIFLEX-Aero for numerical modeling and dynamic analysis of offshore single blade installation using jack-up crane vessels. The SIMO-RIFLEX-Aero code is then applied to study the dynamic response of the DTU 10 MW wind turbine blade installed by a typical jack-up crane vessel under various wind and wave conditions. The results show that significant motion is induced at crane tip, mainly due to wave loads. It is important to consider the structural flexibility of the jack-up legs and crane when modeling the installation of offshore wind turbine blades. [ABSTRACT FROM AUTHOR]

Installation of blades for wind turbines is challenging due to large lifting height and high precision. Assessment of blade dynamic responses during installation needs advanced simulation tools which are limited at present. This paper aims at developing an integrated simulation tool SIMO-Aero for single blade installation for both onshore and offshore wind turbines. Based on the cross-flow principle, the aerodynamic model is established by accounting for the effect of wind turbulence and dynamic stall. Then it is coupled with SIMO to achieve the integrated simulation tool SIMO-Aero which can account for blade aerodynamics, vessel hydrodynamics and system mechanical couplings. The aerodynamic code is verified by code-to-code comparisons with HAWC2. Furthermore, SIMO-Aero is applied in case studies on the wind-induced dynamic responses of a DTU 10 MW blade during installation using a jack-up crane vessel which is assumed to be rigid, including the crane, and rigidly fixed to the seabed. The characteristics of system dynamic responses prior to mating the blade onto the hub are studied. It is shown that the blade motions are dominated by the pendulum motion. Critical parameters of the installation process are identified. The extreme responses of critical parameters are further studied under turbulent winds and wind gusts. [ABSTRACT FROM AUTHOR]

Abstract: We have investigated the structure, dynamical properties and thermodynamic properties of α-Li3N from ab initio density functional theory within local-density approximation (LDA). The results for the lattice constant agree well with available experimental values. A liner response approach to the density functional theory is used to derive the Born effective charge tensors, the dielectric permittivity tensors, the phonon frequencies at the center of the Brillouin zone, the phonon dispersion curves and the corresponding density of states of Li3N. The Born effective charge and the dielectric permittivity tensors are diagonal, which are analyzed in detail. The calculated phonon frequencies at the point of the Brillouin zone show good agreement with the experimental values for most vibrational modes. The thermodynamic properties are investigated within the harmonic approximation based on the calculated phonon dispersion relations. The extensive and successful comparisons with experiments demonstrate once more that the method can provide reliable predictions for the temperature dependence of these quantities, such as the Helmholtz free energy , the entropy , Gibbs free energy , and the enthalpy changes of , and the heat capacity in detail. [Copyright &y& Elsevier]

Installation of offshore wind turbines, particularly blades, is challenging and should be executed within the allowable limit of sea states to ensure the safety and the efficiency of installation. During the execution phase where weather forecast will be used in the decision-making process, uncertainty in weather forecast is an important issue required to be dealt with. The purpose of this paper is to assess allowable sea states for offshore blade installation, with emphasis on both considering weather forecast uncertainty and using time-domain numerical models for installation response analysis. The general procedure is presented, which includes generation of the response-based alpha-factor α R (that is a reduction indicator reflecting weather forecast uncertainty) in the planning phase based on time-domain modelling and analysis of blade installation, and assessment of corresponding allowable sea states in the execution phase. Single blade installation by a semi-submersible crane vessel at the North Sea center is studied in this paper, and two typical limiting response parameters, namely the blade root radial motion and velocity, are considered. The α R factors correspond to these two limiting parameters are first generated respectively, based on the forecast uncertainty quantification of sea states, the quantitative assessment of system dynamic responses and the estimation of their characteristic values through probabilistic analysis. The characteristic values of the responses that correspond to a certain exceedance probability (10−2 or 10−4) could be generated with and without the consideration of the weather forecast uncertainty. Finally, the allowable sea states with and without the weather forecast uncertainty are obtained when the characteristic value reaches the allowable response limit. These could be further used to identify overall workable weather windows for the offshore blade installation and support operation decision-making. Results indicate that there is a significant difference between the allowable sea states with and without considering weather forecast uncertainty. As the forecast lead time increases, the allowable sea states gradually decrease. Hence, it is necessary to apply α R to involve and quantify the effect of weather forecast uncertainties on operations. Moreover, since time-domain simulations are used for dynamic response analysis of the installation system, the effect of statistical uncertainty related to the use of a limited number of simulations to derive the characteristic response values is also investigated and is found small. • A procedure for assessing allowable sea states of marine operations including weather forecast uncertainty is presented. • One-day-ahead sea state forecasts generated by the PBML method is utilized in the uncertainty quantification analysis. • A coupled simulation method, SIMO-RIFLEX-Aero, is utilized for time-domain modelling of blade installation. • The response-based alpha factor is estimated to investigate the effect of weather forecast uncertainty on blade installation. • The allowable sea states for blade installation are assessed in terms of forecast lead times. [ABSTRACT FROM AUTHOR]

Abstract: We investigate dynamical and thermodynamic properties of LaNi5 within density-functional theory. The lattice parameters are found to differ by less than 0.6% from the experimental data. Using density-functional perturbation theory, we calculate the phonon dispersion curves and the phonon density of states. The calculated phonon frequencies at the center zone ( point) for the Raman-active and infrared-active modes are assigned. The thermodynamic functions are calculated by using the phonon density of states. The calculated values are in reasonable agreement with experimental data and other calculations. [Copyright &y& Elsevier]

Floater structural flexibility plays a significant role in accurate predictions of global dynamic responses of floating wind turbines (FWTs), especially for ultra-large wind turbines with increasing size and cost-effective floater design. The conventional analysis of FWTs often considers the floater as one rigid body, which cannot capture the correct resonant responses of the floater (especially the column that supports the tower). In this paper, a new approach where the floater is divided into multiple rigid bodies connected by flexible beams is developed for advanced modelling of flexible floaters in combination with coupled time-domain simulations. The hydrostatic and hydrodynmaic loads on each body from a one-body hydrodynamic analysis, together with gravitational loads and inertial loads, are implemented in the beam-based finite element model of the floater to carry out a time-domain analysis. The proposed approach is used to compare the responses of a 15-MW semi-submersible FWT considering a rigid and a flexible floater. The inclusion of floater flexibility reduces the tower natural frequency. It leads to larger bending moment amplitudes at the tower base close to the tower bending natural frequency, particularly in only-wind, irregular wave and wind-wave conditions, but smaller dynamic responses in regular wave conditions. • A new approach to model the floater flexibility of floating wind turbine. • Global dynamic responses are compared under the rigid and flexible floater. • The tower bending natural frequency is decreased for the flexible floater. • The floater flexibility significantly affects the responses around the tower bending natural frequency. [ABSTRACT FROM AUTHOR]