The harmonic torsional oscillations of a thin disk submerged in a fluid with a surfactant surface layer

A formulation in terms of a Fredholm integral equation of the first kind is given for the axisymmetric problem of a disk oscillating harmonically in a viscous fluid whose surface is contaminated with a surfactant film. The equation of the first kind is converted to a pair of coupled integral equations of the second kind, which are solved numerically. The resistive torque on the disk is evaluated and surface velocity profiles are computed for varying values of the ratio of the coefficient of surface shear viscosity to the coefficient of viscosity of the substrate fluid, and the depth of the disk below the surface.

Experimental Demonstration of H{infty} Control based Active Vibration Suppression in Composite Fin-tip of Aircraft using Optimally Placed Piezoelectric Patch Actuators

The goal of this study is the multi-mode structural vibration control in the composite fin-tip of an aircraft. Structural model of the composite fin-tip with surface bonded piezoelectric actuators is developed using the finite element method. The finite element model is updated experimentally to reflect the natural frequencies and mode shapes accurately. A model order reduction technique is employed for reducing the finite element structural matrices before developing the controller. Particle swarm based evolutionary optimization technique is used for optimal placement of piezoelectric patch actuators and accelerometer sensors to suppress vibration. H{infty} based active vibration controllers are designed directly in the discrete domain and implemented using dSpace® (DS-1005) electronic signal processing boards. Significant vibration suppression in the multiple bending modes of interest is experimentally demonstrated for sinusoidal and band limited white noise forcing functions.

Reliability Analysis of Torsional MEMS Varactor

This paper discusses reliability issues in torsional MEMS varactor. Self-actuation due to high ac signals is analyzed, and solutions are proposed. The mode of failure at high actuation voltages is analyzed and established through experiments. Issues like stiction due to high voltages and effect of high residual stress are studied experimentally.

Reliability analysis of torsional varactor

A torsional MEMS varactor with wide dynamic range, lower actuation voltage and isolation between actuation voltage and signal voltage has been proposed in C. Venkatesh et al. (2005). In this paper we address the effects of pull-in, residual stress and continuous cycling on the performance of torsional MEMS varactor.

Active vibration suppression of beams with discrete actuators using optimal dynamic inversion

Most of the structural elements like beams, cables etc. are flexible and should be modeled as distributed parameter systems (DPS) to represent the reality better. For large structures, the usual approach of 'modal representation' is not an accurate representation. Moreover, for excessive vibrations (possibly due to strong wind, earthquake etc.), external power source (controller) is needed to suppress it, as the natural damping of these structures is usually small. In this paper, we propose to use a recently developed optinial dynamic inversion technique to design a set of discrete controllers for this purpose. We assume that the control force to the structure is applied through finite number of actuators, which are located at predefined locations in the spatial domain. The method used in this paper determines control forces directly from the partial differential equation (PDE) model of the system. The formulation has better practical significance, both because it leads to a closed form solution of the controller (hence avoids computational issues) as well as because a set of discrete actuators along the spatial domain can be implemented with relative ease (as compared to a continuous actuator).

Inelastic Torsional Response of a Single-Story Framed Structure

In this paper, a single-story, bilinear-hysteretic structure, square in plan and supported on four columns, subjected to two horizontal ground motions is studied. The model is assumed to possess three degrees of freedom, viz., translational displacements along the two horizontal orthogonal directions and a rotation about the vertical axis. Interaction of the bending moments in the two perpendicular directions has been considered.

Analysis Of The Hvdc Turbine Generator Torsional Interactions

In the recent past it has been found that HVDC transmission systems and turbine-generator shaft torsional dynamics can interact in an unfavourable manner. This paper presents a detailed linearised state space model of AC/DC system to study this torsional interaction. The model developed is used to study the effect of various system parameters, such as, dc line loading, converter firing angle, the firing scheme employed. The results obtained are compared with those given in[3].

Chlorine-35 nuclear quadrupole resonance study of molecular torsional motion in some chloropyridine-N-oxides and chloroquinoline-N-oxides

Chlorine has been substituted at the 2- and 4-positions in the pyridine and quinoline rings of the corresponding N-oxides and 35Cl n.q.r. spectra have been studied in the temperature range 77–300 K. The change in the n.q.r. frequencies in N-oxides as compared to their parent compounds are interpreted in terms of the conjugative effect and the inductive effect of the N+—O– group. The negative temperature coefficients of the resonance frequencies in chloropyridine-N-oxides have been analysed using the Bayer, Kushida and Brown equations. The calculated torsional frequencies, which are in the range 52–78 cm–1, are found to be only slightly temperature dependent.

Study Of The Hvdc-Torsional Interactions Through Digital Dynamic Simulation

This paper presents the detailed dynamic digital simulation for the study of phenomenon of torsional interaction between HVDC-Turbine generator shaft, dynamics using the novel converter model presented in [ 1 ] The system model includes detailed representation of the synchronous generator and the shaft dynamics, the ac and dc network transients. The results of a case study indicate the various factors that influence the torsional interaction.

Empirical torsional potential functions from protein structure data. Phi- and psi-potentials for non-glycyl amino acid residues.

The torsional potential functions Vt(phi) and Vt(psi) around single bonds N--C alpha and C alpha--C, which can be used in conformational studies of oligopeptides, polypeptides and proteins, have been derived, using crystal structure data of 22 globular proteins, fitting the observed distribution in the (phi, psi)-plane with the value of Vtot(phi, psi), using the Boltzmann distribution. The averaged torsional potential functions, obtained from various amino acid residues in L-configuration, are Vt(phi) = 1.0 cos (phi + 60 degrees); Vt(psi) = 0.5 cos (psi + 60 degrees) - 1.0 cos (2 psi + 30 degrees) - 0.5 cos (3 psi + 30 degrees). The dipeptide energy maps Vtot(phi, psi) obtained using these functions, instead of the normally accepted torsional functions, were found to explain various observations, such as the absence of the left-handed alpha helix and the C7 conformation, and the relatively high density of points near the line psi = 0 degrees. These functions derived from observational data on protein structures, will, it is hoped, explain various previously unexplained facts in polypeptide conformation.

Empirical torsional potential functions from protiesn structure DATA Phi- and Psi-Potentials for Non-glycyl Amino Acid Residues

The torsional potential functions Vt(φ) and Vt(ψ) around single bonds N–Cα and Cα-C, which can be used in conformational studies of oligopeptides, polypeptides and proteins, have been derived, using crystal structure data of 22 globular proteins, fitting the observed distribution in the (φ, ψ)-plane with the value of Vtot(φ, ψ), using the Boltzmann distribution. The averaged torsional potential functions, obtained from various amino acid residues in l-configuration, are Vt(φ) = – 1.0 cos (φ + 60°); Vt(ψ) = – 0.5 cos (ψ + 60°) – 1.0 cos (2ψ + 30°) – 0.5 cos (3ψ + 30°). The dipeptide energy maps Vtot(φ, ψ) obtained using these functions, instead of the normally accepted torsional functions, were found to explain various observations, such as the absence of the left-handed alpha helix and the C7 conformation, and the relatively high density of points near the line ψ = 0°. These functions, derived from observational data on protein structures, will, it is hoped, explain various previously unexplained facts in polypeptide conformation.

Analysis of Torsional Interactions with Power System Stabilizer

Torsional interactions can occur due to the speed input Power System Stabilizer (PSS) that are primarily used to damp low frequency oscillations. The solution to this problem can be either in the form of providing a torsional filter or developing an alternate signal for the PSS. This paper deals with the formulation of a linearized state space model of the system and study of the interactions using eigenvalue analysis. The effects of the parameters of PSS and control signals on the damping of torsional modes are investigated.

Active vibration suppression of beams with discrete actuators using optimal dynamic inversion

Most of the structural elements like beams, cables etc. are flexible and should be modeled as distributed parameter systems (DPS) to represent the reality better. For large structures, the usual approach of 'modal representation' is not an accurate representation. Moreover, for excessive vibrations (possibly due to strong wind, earthquake etc.), external power source (controller) is needed to suppress it, as the natural damping of these structures is usually small. In this paper, we propose to use a recently developed optimal dynamic inversion technique to design a set of discrete controllers for this purpose. We assume that the control force to the structure is applied through finite number of actuators, which are located at predefined locations in the spatial domain. The method used in this paper determines control forces directly from the partial differential equation (PDE) model of the system. The formulation has better practical significance, both because it leads to a closed form solution of the controller (hence avoids computational issues) as well as because a set of discrete actuators along the spatial domain can be implemented with relative ease (as compared to a continuous actuator)

Study of Layering Procedures in Finite-Element Analysis of RC Flexural and Torsional Elements

A new postcracking formulation for concrete, along with both implicit and explicit layering procedures, is used in the analysis of reinforced-concrete (RC) flexural and torsional elements. The postcracking formulation accounts for tension stiffening in concrete along the rebar directions, compression softening in cracked concrete based on either stresses or strains, and aggregate interlock based on crack-confining normal stresses. Transverse shear stresses computed using the layering procedures are included in material model considerations that permit the development of inclined cracks through the RC cross section. Examples of a beam analyzed by both the layering techniques, a torsional element, and a column-slab connection region analyzed by the implicit layering procedure are presented here. The study highlights the primary advantages and disadvantages of each layering approach, identifying the class of problems where the application of either procedure is more suitable.