Torsional Dynamics Research Articles

TICT, and Deep-Blue Electroluminescence from Acceptor-Donor-Acceptor Molecules.

Donor-acceptor (D-A) materials based on butterfly-shaped molecules could inhibit exciton-migration-induced quenching due to molecular twist. To explore this attribute towards beneficial photophysical properties, three novel bipolar acceptor-donor-acceptor (A-D-A) molecules with triphenyl triazine end capping along with substitution ortho to the Tröger's base (TB) scaffold varying from H, Me, and F were explored. The installation of H/Me/F imparted an electron push-pull effect with concomitant maneuvering of photophysical properties. On increasing solvent polarity, a remarkable bathochromic shift with a significant decrease in emission efficiency was observed due to the twisted intramolecular charge transfer state (TICT). Emission enhancement in the ethylene glycol-water mixture and diminution in the THF-water mixture further confirmed the existence of TICT states in these TBs. The torsional dynamics in the excited state were also evidenced by the time-dependent density-functional theory (TD-DFT) calculations. Owing to the butterfly architecture of the TB that suppressed TICT, TB-Trzs exhibited a significant blue shift, accompanied by a favorable quantum yield in the solid state. Among the three compounds, Me-TB-Trz exhibited deep-blue photoluminescence and was explored as a dopant in organic light-emitting diodes (OLEDs) to obtain deep-blue electroluminescence of brightness 4128 cdm-2 and CIE coordinates of (0.16, 0.09).

Control of a Directional Downhole Drilling System Using a State Barrier Avoidance Based Method

Abstract Vibrations such as bit-bouncing, stick–slip, and whirl motion can significantly reduce downhole drilling's performance and efficiency. These phenomena are likely to arise once the dynamical states of drilling fall into undesired operating regimes, as verified by both theoretical analyses and experimental studies. To effectively avoid such undesired operating conditions of a downhole drilling process, this paper introduces an advanced nonlinear state-constrained control method to formulate a setpoint tracking problem of high-order directional drilling dynamics under state constraints. These constraints are carefully defined using the field test results, and their shapes are in complex state-space regions, causing additional complexity to the control design. Moreover, unlike vertical drilling, the directional drilling system requires modeling of coupled axial and torsional dynamics with a higher degree-of-freedom (DOF). In this study, the proposed method will tackle these challenges by converting the original high-order constrained control problem into a standard nonlinear control problem. Leveraging on the linear parameter varying (LPV) method that is applied to the converted system, we can actively prevent drilling from falling into the undesired regimes, to achieve the constrained control objective.

Torsional Mechanics of Circular DNA.

Circular DNA found in the cell is actively regulated to an underwound state, with their superhelical density close to σ ∼ - 0.06. While this underwound state is essential to life, how it impacts the torsional mechanical properties of DNA is not fully understood. In this work, we performed simulations to understand the torsional mechanics of circular DNA and validated our results with single-molecule measurements and analytical theory. We found that the torque generated at σ ∼ - 0.06 is near but slightly below that required to melt DNA, significantly decreasing the energy barrier for proteins that interact with melted DNA. Furthermore, supercoiled circular DNA experiences force (tension) and torque that are equally distributed through the DNA contour. We have also extended a previous analytical framework to show how the plectonemic twist persistence length depends on the intrinsic bending persistence length and twist persistence length. Our work establishes a framework for understanding DNA supercoiling and torsional dynamics of circular DNA.

Frequency domain solution method for electromagnetic influence analysis on torsional vibrations

In electric motor-driven machines, mechanical torsional dynamics are nonlinearly coupled with the electrical system through the electromagnetic torque and the counter-electromotive force. In this paper, an approach based on small-signal linearization is proposed for modeling the steady-state torsional dynamics of the coupled system. Using the linearized model, resonance interference diagrams, torsional response, and stability can be evaluated rapidly across numerous operating points, while accurately accounting for the electromagnetic effects. The model is validated with conventional time-stepping simulations of two induction machines. An example analysis of a 3 MW motor-driven compressor train displays the modification of torsional properties due to the electromagnetic coupling effect and explains the mechanism of torsional destabilization. Finally, previously published measurements of a 37 kW motor test bench are considered to validate the instability of the elastic torsional mode predicted by the model.

Transcribing RNA polymerases: Dynamics of twin supercoiled domains

Gene transcription by an RNA polymerase (RNAP) enzyme requires that double-stranded DNA be locally and transiently opened, which results in an increase of DNA supercoiling downstream of the RNAP and a decrease of supercoiling upstream of it. When the DNA is initially torsionally relaxed and the RNAP experiences sufficiently large rotational drag, these variations lead to positively supercoiled plectonemes ahead of the RNAPs and negatively supercoiled ones behind it, a feature known as “twin supercoiled domain” (TSD). This work aims at deciphering into some more detail the torsional dynamics of circular DNA molecules being transcribed by RNAP enzymes. To this end, we performed Brownian dynamics simulations with a specially designed coarse-grained model. Depending on the superhelical density of the DNA molecule and the ratio of RNAP’s twist injection rate and rotational relaxation speed, simulations reveal a rich panel of behaviors, which sometimes differ markedly from the crude TSD picture. In particular, for sufficiently slow rotational relaxation speed, positively supercoiled plectonemes never form ahead of an RNAP that transcribes a DNA molecule with physiological negative supercoiling. Rather, negatively supercoiled plectonemes form almost periodically at the upstream side of the RNAP and grow up to a certain length before detaching from the RNAP and destabilizing rapidly. The extent to which topological barriers hinder the dynamics of TSDs is also discussed.

Modeling and analysis of a flexible spinning Euler-Bernoulli beam with centrifugal stiffening and softening: A linear fractional representation approach with application to spinning spacecraft

The derivation of a linear fractional representation (LFR) model for a flexible, spinning and uniform Euler-Bernoulli beam is accomplished using the Lagrange technique, fully capturing the centrifugal force generated by the spinning motion and accounting for its dependence on the angular velocity. This six degrees of freedom (DOF) model accounts for the behavior of deflection in the moving body frame, encompassing the bending, traction and torsion dynamics. The model is also designed to be compliant with the Two-Input-Two-Output Port (TITOP) approach, which offers the possibility to model complex multibody mechanical systems, while keeping the uncertain nature of the plant and condensing all the possible mechanical configurations in a single LFR. To evaluate the effectiveness of the model, various scenarios are considered and their results are tabulated. These scenarios include uniform beams with fixed root boundary conditions for different values of tip mass, root offset and angular velocity. The results from the analysis of the uniform cantilever beam are compared with solutions found in the literature and obtained from a commercial finite element software. Ultimately, this paper presents a multibody model for a spinning spacecraft mission scenario. A comprehensive analysis of the system dynamics is conducted, providing insights into the behavior of the spacecraft under spinning conditions.

A Simplified 4-DOF Dynamic Model of a Series-Parallel Hybrid Electric Vehicle

To research the dynamic response of a new type of dedicated transmission for a hybrid electric vehicle, a detailed dynamics model should be built. However, a model with too many degrees of freedom has a negative effect on controller design, which means the detailed model should be simplified. In this paper, two dynamic models are established. One is an original and detailed powertrain dynamics model (ODPDM), which can capture the transient response, and it is validated that the ODPDM can be used to accurately describe the real vehicle in some specific operating conditions. The other is a simplified torsional vibration dynamics model to study the torsional vibration characteristics of the hybrid electric vehicle. Compared with the full-order model, which is based on the ODPDM, the simplified model has a very similar vibration in low frequency. This study provides a basis for further vibration control of the hybrid powertrain during the process of a driving-mode switch.

Nick Induced Dynamics in Supercoiled DNA Facilitates the Protein Target Search Process.

A DNA nick, defined as a discontinuity in a double-stranded DNA molecule where the phosphodiester bond between adjacent nucleotides of one strand is absent due to enzyme action, serves as an effective mechanism to alleviate stress in supercoiled DNA. This stress release is essential for the smooth operation of transcriptional machinery. However, the underlying mechanisms and their impact on protein search dynamics, which are crucial for initiating transcription, remain unclear. Through extensive computer simulations, we unravel the molecular picture, demonstrating that intramolecular stress release due to a DNA nick is driven by a combination of writhing and twisting motions, depending on the nick's position. This stress release is quantitatively manifested as a step-like increase in the linking number. Furthermore, we elucidate that the nicked supercoiled minicircles exhibit enhanced torsional dynamics, promoting rapid conformational changes and frequent shifts in the identities of juxtaposed DNA sites on the plectoneme. The dynamics of the juxtaposition sites facilitates communication between protein and DNA, resulting in faster protein diffusion compared with native DNA with the same topology. Our findings highlight the mechanistic intricacies and underscore the importance of DNA nicks in facilitating transcription elongation by actively managing torsional stress during DNA unwinding by the RNA polymerase.

Torsional behaviors of motor rotor of permanent magnet semi-direct drive system for aerial passenger device

Considering the influence of motor shaft torsional damping, the torsional dynamics equations of a permanent magnet semi-direct drive rotor system in an aerial passenger device are derived. The derivation relies on the coupling between the mathematical model and the gear dynamics model of the permanent magnet motor, and the Lagrange–Maxwell equations are used for streamlined analysis. To protect the motor under extreme working conditions, the influence of supercritical Hopf bifurcation caused by different torsional dampings of the motor shaft on the torsional vibration of the motor rotor is investigated. Based on the Hurwitz criterion, the influence of the linear control gain and nonlinear gain of the washout filter on the system bifurcation point and the limit cycle amplitude of the system is analyzed. Then, from the perspective of the system instability and oscillation caused by friction damping change of the drive motor and the complex electromechanical coupling behavior in the permanent magnet semi-direct drive cutting drive system of the aerial passenger device, the system stability domain is defined. The results can be applied to effectively suppress the torsional vibration of the shaft system in the permanent magnet semi-direct drive system of the aerial passenger device, providing a theoretical guidance for stable operation of the system.

Temporal dynamics of ocular torsion and vertical vergence during visual, vestibular, and visuovestibular rotations.

Ocular torsion and vertical divergence reflect the brain's sensorimotor integration of motion through the vestibulo-ocular reflex (VOR) and the optokinetic reflex (OKR) to roll rotations. Torsion and vergence however express different response patterns depending on several motion variables, but research on their temporal dynamics remains limited. This study investigated the onset times of ocular torsion (OT) and vertical vergence (VV) during visual, vestibular, and visuovestibular motion, as well as their relative decay rates following prolonged optokinetic stimulations. Temporal characteristics were retrieved from three separate investigations where the level of visual clutter and acceleration were controlled. Video eye-tracking was used to retrieve the eye-movement parameters from a total of 41 healthy participants across all trials. Ocular torsion consistently initiated earlier than vertical vergence, particularly evident under intensified visual information density, and higher clutter levels were associated with more balanced decay rates. Additionally, stimulation modality and accelerations affected the onsets of both eye movements, with visuovestibular motion triggering earlier responses compared to vestibular motion, and increased accelerations leading to earlier onsets for both movements. The present study showed that joint visuovestibular responses produced more rapid onsets, indicating a synergetic sensorimotor process. It also showed that visual content acted as a fusional force during the decay period, and imposed greater influence over the torsional onset compared to vergence. Acceleration, by contrast, did not affect the temporal relationship between the two eye movements. Altogether, these findings provide insights into the sensorimotor integration of the vestibulo-ocular and optokinetic reflex arcs.

Beam modeling in a floating frame of reference for torsion dynamics of helicopter rotor blades

AbstractIn the ongoing development of DLR’s Versatile Aeromechanics Simulation Tool, an elastic-beam model is integrated into the multibody system based on the floating frame-of-reference formulation. Although the application of this formulation for one-dimensional beam models has already been addressed in the literature, the challenge remains to properly model the torsion dynamics of rotor blades – especially under high centrifugal loads. To this aim, this work suggests the consideration of rotational shape functions in the inertia shape integrals and in the application of gravitational, inertial, and external loads. This modified approach is validated based on the structural analysis of a rotor blade with complex geometrical properties.

Vyladenie mechanickej sústavy pohonu piestového kompresora z hľadiska veľkosti torzného kmitania

One of possible ways to change the amount of compressed air delivered by a piston compressor is to change its operating speed. However, it can cause an improper tuning of the mechanical system of piston compressor drive in terms of torsional dynamics. In order to avoid excessive torsional vibration, a suitable pneumatic flexible shaft coupling can be used in the system. An optimum air pressure value in a pneumatic coupling was determined experimentally for three various operating modes of an experimental mechanical system of piston compressor drive.

Control of Axial–Torsional Dynamics of a Distributed Drilling System

Control of Axial–Torsional Dynamics of a Distributed Drilling System

Protein stability in a natural deep eutectic solvent: Preferential hydration or solvent slaving?

Deep eutectic solvents (DESs) emerged as potential alternative solvent media in multiple areas, including biomolecular (cryo)preservation. Herein, we studied the stability of a small protein (ubiquitin) in water and a betaine-glycerol-water (B:G:W) (1:2:ζ; ζ = 0, 1, 2, 5, 10) DES, through molecular dynamics. An AMBER-based model that accurately describes the density and shear viscosity of the DES is proposed. We find that water molecules are largely trapped in the solvent, precluding the formation of a full hydration layer, seemingly opposite to osmolytes’ preferential exclusion/preferential hydration mechanism. Although the protein is stable in the DES, structural fluctuations are largely suppressed and only recovered upon sufficient hydration. This is explained by a solvent-slaving mechanism where β-fluctuations are key, with the non-monotonic hydration of some amino acids with the water content providing an explanation to the non-monotonic folding of some proteins in aqueous DESs. A major thermal stability enhancement in the DES is also observed, caused by a similar slowdown of the backbone torsional dynamics. Our results support a kinetic stabilization of the protein in the DES, whereas a possible thermodynamic stabilization does not follow a preferential hydration or water entrapment mechanism.

Investigation of field scenarios using a 4n degrees of freedom transient torque and drag model

A coupled drill string dynamics model presents an opportunity to understand, replicate and potentially control the vibrations occurring along a drill string in a deep well. This paper describes a 4n degrees of freedom (4nDOF) model of the axial, torsional and lateral dynamics, consisting of coupled wave equations and lumped elements, which include modeling of the contact between the drill string and wellbore with a stiff string assumption. The model accounts for the bit-rock interaction, structural damping, and hydraulic forces acting on the lumped elements. The 4nDOF model is compared with three field scenarios from a drilling operation in the North Sea: a three-stage top drive start-up procedure, a drilling sequence starting from off-bottom conditions, and a backreaming operation at low rotational speed. The selected cases include instances of stick–slip and higher modes of torsional vibrations, which persist despite the use of a surface vibration mitigation system. High-frequency data recorded by a downhole measurement sub placed near the drill bit are used to verify the simulated downhole rotational speed and triaxial accelerations. The model is useful for analyzing torsional stick–slip events, which are replicated with a similar period and amplitude as in the downhole measurements. Furthermore, the model accurately reproduces the transition between first and second mode torsional oscillations upon the activation of a tuned top drive vibration mitigation system. The model can also be used to analyze lateral deformations and whirling of the drill string at various depths. The field case simulations show that the lateral dynamics can undergo significant changes at certain points in the drill string during torsional stick–slip and higher-mode torsional oscillations. The proposed model can be used to run simulations in close to real-time on a standard personal workstation, thus making it a valuable tool for devising and testing new drill string vibration mitigation solutions.

Stick–Slip Vibration Characteristics Study of the Drill String Based on PID Controller

In order to address the issue of drill string stick–slip vibration, which leads to drill bit wear and reduces the drilling velocity, we conducted a study on the characteristics of stick–slip vibration using a proportional-integral-derivative (PID) controller. By applying the principles of rigid body mechanics, we established a two-degree-of-freedom torsional dynamics equation and derived the first-order differential dynamics equation for the drill string. Subsequently, we designed a PID controller and obtained an equation for the control of stick–slip vibration. The research findings indicate that variations in the difference between the static and dynamic friction coefficients directly impact the nature of the limit cycles in the phase plane. As this difference decreases, the limit cycle narrows and the stick–slip vibrations weaken progressively. When the static and dynamic friction coefficients are equalized, no stick–slip vibrations occur within the drill string. The implementation of PID control effectively manages stick–slip vibrations in the drill string, with greater efficiency observed in controlling the turntable velocity compared to the drill bit velocity. This research provides valuable insights for the development of control strategies aimed at mitigating stick–slip vibrations in drilling engineering applications, thereby facilitating the efficient and safe extraction of oil and gas resources.

The measurement of the influence of the adhesion loss on the dynamic load of the drive reaction rod on the roller rig

The dynamic behaviour and dynamic phenomena in traction drives of railway vehicle has been studied for decades. Generally, in these days the motivation for this research is to look for answers related with service problems, which has been risen, e.g. an overloading of mechanical components as wheelsets or an intention to improve control systems of traction drives of railway vehicles. This problematic has also motivated the research at the Faculty of Mechanical Engineering at the Czech Technical University (CTU) in Prague. Nowadays it is also usual, that the main research tool has been a simulation based on a mathematical model of a railway vehicle or its specific components, as testing on real vehicles is very demanding regarding costs. However, there is an alternative – a roller rig. At the CTU in Prague there has been modernized the second roller rig for purposes of measurement regarding the torsion dynamics research, to support PhD students for their theses and possibly to extend the education for students oriented on the railway vehicle’s design. This contribution brings results of measurements just from the problematics of torsion oscillations and dynamics. Specifically, further presented measurements are on the loss of the adhesion in the contact of the wheelset and rollers, as the substitution for the railway, its impact on the reaction rod overloading and study of the axle load influence on the transition phenomena.

Torsional Dynamics of Axially Graded Viscoelastic Carbon Nanotubes

Torsional vibration analysis of the axially functionally graded carbon nanotubes has been carried out. Nonlocal stress gradient elasticity theory has been used in continuum mechanics model of the carbon nanotube. Variation of the material properties of the axially graded nanostructure has been assumed in exponential form. Differently from the majority of literature works, viscous damping and nonlocal parameters have been assumed in grading form. Energy functional for the carbon nanotube has been achieved with minimum potential energy principle and weak form solution has been obtained with the Ritz Method. Effects of material grading, nonlocality and viscoelasticity to the torsional dynamics of axially graded carbon nanotube have been investigated. Results of the present work could be useful in modeling and production of axially functionally graded nanostructures.

Distributed model for the drill-string system with multiple regenerative effects in the bit-rock interaction

In this paper, an integrated model is presented to study the axial–torsional dynamics of a distributed drill string. The coupled axial and torsional drill string dynamics typically lead to severe phenomena such as bit-bounce and stick–slip, which are the main causes of failure and efficiency reduction. The top-drive dynamics and the Bottom Hole Assembly (BHA) dynamics are interconnected through the drill pipes. In order to preserve the infinite-dimensional feature of the drill pipes in the mathematical modeling, a distributed model in terms of Delay Differential Algebraic Equations (DDAE) is proposed to represent the dynamics of the drill string. The bit-rock interaction, which consists of the cutting and the frictional components, is responsible for the coupling between the axial and torsional dynamics. A rate-independent bit-rock interaction law is employed for both cutting and frictional components. In order to capture the global bit motion, including multiple regenerative effects, the well-bottom depth function is used to determine the depth of cut. The well-bottom pattern evolution is formulated through algebraic equations rather than Partial Differential Equations (PDEs). A new formulation for the linearized drill string system in terms of Neutral-type Delay Differential Integral Equations (NDDIEs) is proposed to investigate the initiation of the oscillations around the nominal operation. By this formulation, the local stability of the distributed system is studied by determining the right-most eigenvalue of the linearized dynamics. A simulation-based case study reflecting real-life scenarios is presented to investigate the dynamical behavior of the system under different operating conditions.

A comprehensive Cosserat rod drill-string model for arbitrary well geometry that includes the dynamics of the cutting and lateral contact

In this paper, a comprehensive continuous Cosserat rod model is developed to study the dynamics of a drill-string. The model presents the following features: (1) it can simulate the 3-D dynamics of the system, including lateral, axial and torsional motion; (2) it includes damping effects by adopting a Kelvin–Voigt material; (3) it uses a velocity-independent bit-rock interaction formulation in which the forces and torques at the bit are obtained by considering the dynamics of the cutting blades and the evolution of the soil profile, which is simulated with the help of an advection equation; (4) lateral contact is also included. In this paper, two application cases are analysed. The first one deals with a vertical borehole. It includes four simulations that are used to further investigate the hypothesis that low-dimensional lumped formulations are not able to capture the dynamics of a drill-string and, while doing so, evaluate the effect of the damping in the system’s response. The predictions are compared with those given by two other models: the first one considers a 2-degrees-of-freedom (DOF) formulation, with 1-axial and 1-torsional DOF; the second one is a semi-discrete approach, with 1 DOF for the axial dynamics and a continuous formulation for the torsional one. Divergences between the predictions are found, associated with the presence of higher frequencies in the signals obtained with the Cosserat model, which reassures the hypothesis that the new continuous approach can capture aspects of the dynamics that cannot be modelled with low-dimensional representations. The efficiency of the drilling is also assessed for the simulations obtained with the new model. The highest performance was observed in those simulations where only axial oscillations occurred, while a performance drop was seen when those vibrations were accompanied by torsional stick–slip, suggesting that an optimum damping value associated with the best drilling performance could be found, were damping controllable. Finally, the second application case is used to illustrate the full potential of the new model to tackle the 3-D lateral, axial, and torsional dynamics in a curved borehole.