Global Dynamic Response of a Medium-Sized Floating Offshore Wind Turbine with Stall Regulation

In this paper, a two-bladed medium-sized floating wind turbine with variable speed and power regulation by stall is studied. For floating offshore wind turbines, the major challenges are related to the dynamical behavior of the system in response to combined wind and wave loading. Especially for smaller systems, the coupling of aerodynamic and wave forces may lead to large amplitude motions. Coupled aero-hydro-servo-elastic simulations are carried out in OpenFAST. The goal of the study is to investigate the global dynamic response of the hypothetical wind turbine with stall regulation. Stall regulation concept is proposed and the structural loads are computed and results are presented and discussed.

UNSTEADY CHARACTERISTICS OF LIFT GENERATED BY SMALL UNDERWATER CONTROL FIN

Speed reduction or slamming must be restricted for a high-speed oceangoing vessel because of the requirement for punctuality and the high value of the cargo. Speed reduction and slamming are caused by large amplitude motions in waves. A promising ship form for such vessels is so-called “Resonance-Free SWATH (RFS)”, which has negative pitch and roll restoring moments due to the extraordinary small water plane area. As a consequence, the resonance peak is removed from the motion response. The attitude of the RFS with negative restoring moments is adjusted by four pairs of control fins attached to the fore and aft ends of the lower hulls. In previous studies, the steady value of the lift-curve slope is usually used in the motion equation of the frequency domain. However, when working in waves, the controlling fins are not working in a steady state and the lift coefficient is no longer a constant. In addition, there exists a phase lag between the change in the attack angle and the fin-generated lift. In the present study, theoretical predictions using a frequency-domain 3D-Rankine Panel Method, as well as experimental measurement, have been made to analyze the phenomena of the lift generation including the phase lag and the interference between fins, the lower hulls and the struts. The theoretical results agree well with the experimental results in spite of the potential theory being without viscosity. Next, the unsteady characteristics of fin-generated lift are expressed as the function of the encountering wave frequency. Then the effects of the fore fins, the lower hulls and struts on the lift curve-slope of the aft fins are discussed.

A simplistic computational procedure for tunneling splittings caused by proton transfer

In this manuscript, we present an approach for computing tunneling splittings for large amplitude motions. The core of the approach is a solution of an effective one-dimensional Schrödinger equation with an effective mass and an effective potential energy surface composed of electronic and harmonic zero-point vibrational energies of small amplitude motions in the molecule. The method has been shown to work in cases of three model motions: nitrogen inversion in ammonia, single proton transfer in malonaldehyde, and double proton transfer in the formic acid dimer. In the current work, we also investigate the performance of different DFT and post-Hartree–Fock methods for prediction of the proton transfer tunneling splittings, quality of the effective Schrödinger equation parameters upon the isotopic substitution, and possibility of a complete basis set (CBS) extrapolation for the resulting tunneling splittings.

Dynamics of a DC Motor-Driving Arm with a Circular Periodic Potential and DC/AC Voltage Input

In this paper, we investigate the dynamics of an electromechanical system consisting of a DC motor-driving arm within a circular periodic potential created by three permanent magnets. Two configurations of the circular potential appear when one varies the positions of the magnets and the length of the DC motor, respectively. Two different forms of input signal are used: DC and AC voltage sources. For each case, conditions under which the mechanical arm can perform a complete rotation are obtained. Under the DC voltage excitation, the arm oscillates and then is stabilized at an equilibrium position for a DC voltage lower than a critical value [Formula: see text]. When the DC voltage is higher than the critical value [Formula: see text], the arm performs large amplitude motions (complete rotation). Submitted to an AC voltage with amplitude lower than a critical value, the mechanical arm exhibits sinusoidal oscillations around the equilibrium position [Formula: see text] with amplitudes less than one turn. Angular oscillations with amplitudes greater than one turn are observed when the voltage amplitude is higher than the critical value. Bifurcation diagrams show that the simple system can enter chaotic regime with the amplitudes of angular oscillations varying erratically from small to high values.

Ab Initio Study of the Large Amplitude Motions of Various Monosubstituted Isotopologues of Methylamine (CH3-NH2)

CCSD(T)-F12 theory is applied to determine electronic ground state spectroscopic parameters of various isotopologues of methylamine (CH3-NH2) containing cosmological abundant elements, such as D, 13C and 15N. Special attention is given to the far infrared region. The studied isotopologues can be classified in the G12, G6 and G4 molecular symmetry groups. The rotational and centrifugal distortion constants and the anharmonic fundamentals are determined using second order perturbation theory. Fermi displacements of the vibrational bands are predicted. The low vibrational energy levels corresponding to the large amplitude motions are determine variationally using a flexible three-dimensional model depending on the NH2 bending and wagging and the CH3 torsional coordinates. The model has been defined assuming that, in the amine group, the bending and the wagging modes interact strongly. The vibrational levels split into six components corresponding to the six minima of the potential energy surface. The accuracy of the kinetic energy parameters has an important effect on the energies. Strong interactions among the large amplitude motions are observed. Isotopic effects are relevant for the deuterated species.

Innovative elastomeric shear leg mount concepts for quasi-zero stiffness isolation

Passive vibration isolation may be a cost-effective solution to isolate a supported system containing a source and/or receiver from the supporting structure. The standard linear theory suggests a low-stiffness joint to create a mobility mismatch in the transmission path, but this solution may lead to large amplitude motions in the supported system. To achieve both motion control and isolation with the same mount and without compromising either objective, an innovative, nonlinear mount concept is proposed. Taking advantage of geometric nonlinearity for large displacements, a quasi-zero stiffness is generated by exploiting the interaction between the nonlinear mechanisms that govern the motion of a number of inclined shear legs. For example, a three-regime stiffness profile is created, including a medium-stiffness preload regime, a quasi-zero stiffness isolation regime, and a high-stiffness motion control regime. This concept offers significant benefits compared with a more conventional compromise approach in that low-amplitude vibrations are exceptionally isolated while large amplitude transient motions are controlled. Illustrative computational examples will be presented to support the underlying linear and nonlinear design principles. Limiting cases will be discussed as well.

Large Amplitude Motions of Pyruvic Acid (CH3-CO-COOH)

Torsional and rotational spectroscopic properties of pyruvic acid are determined using highly correlated ab initio methods and combining two different theoretical approaches: Second order perturbation theory and a variational procedure in three-dimensions. Four equilibrium geometries of pyruvic acid, Tc, Tt, Ct, and CC, outcome from a search with CCSD(T)-F12. All of them can be classified in the Cs point group. The variational calculations are performed considering the three internal rotation modes responsible for the non-rigidity as independent coordinates. More than 50 torsional energy levels (including torsional subcomponents) are localized in the 406–986 cm−1 region and represent excitations of the ν24 (skeletal torsion) and the ν23 (methyl torsion) modes. The third independent variable, the OH torsion, interacts strongly with ν23. The A1/E splitting of the ground vibrational state has been evaluated to be 0.024 cm−1 as it was expected given the high of the methyl torsional barrier (338 cm−1). A very good agreement with respect to previous experimental data concerning fundamental frequencies (νCAL − νEXP ~ 1 cm−1), and rotational parameters (B0CAL − B0EXP < 5 MHz), is obtained.