Variation Of Tension Research Articles

Parametric resonance of fractional viscoelastic webs under time-dependent tension

The focus of this paper is on the parametric resonance of fractional viscoelastic webs under time-dependent tension. The novelty of this work lies in the introduction of a fractional order model for viscoelastic webs and the time-dependent tension in roll-to-roll manufacturing. The time-dependent tension is induced by the web treatment processes in roll-to-roll mass production. The rheological properties of viscoelastic webs are represented by the fractional Kelvin-Voigt relation. Considering the geometric nonlinearity, the governing equation is derived based on the Hamilton principle, and then the resulting equation is reduced to a fractional ordinary differential equation by using the Bubnov-Galerkin method. The multiple-scale method is applied to analyze the occurrence condition and dynamic responses of parametric resonance, and the solution stability is demarcated by the Routh-Hurwitz criterion. The effects of the tension variation coefficient, viscoelastic parameter and initial tension on the resonance responses are discussed. The results reveal that the increase in tension variation coefficient and initial tension not only widen the unstable zone of the response curve, but also enhance the resonance amplitude. Moreover, the resonance amplitude decreases with a larger fractional order. This investigation aims to explore the cause of the instability phenomena and thus avoid the unexpected failure of flexible fabrication.

Dynamic analysis of a dual-spar floating offshore wind farm with shared moorings in extreme environmental conditions

The concept of a shared mooring system was proposed to reduce mooring and anchoring costs. Shared moorings also add complexity to the floating offshore wind farm system and pose design challenges. To understand the system dynamics, this paper presents a dynamic analysis for a dual-spar floating offshore wind farm with a shared mooring system in extreme environmental conditions. First, a numerical model of the floating offshore wind farm was established in a commercial simulation tool. Then, time-domain simulations were performed for the parked wind farm under extreme wind and wave conditions. A sensitivity study was carried out to investigate the influence of loading directions and shared line mooring properties. To highlight the influence of the shared line, the results were compared to those of a single spar floating wind turbine, and larger platform motions and higher tension loads in single lines are observed for the wind farm with shared moorings. The loading direction affects the platform motions and mooring response of the floating offshore wind farm. Comparing the investigated loading directions to the 0-deg loading direction, the variation of mean mooring tension at the fairlead is up to 84% for single lines and 16% for the shared line. The influence of the shared line properties in the platform motions and the structural responses is limited. These findings improve understanding of the dynamic characteristics of floating offshore wind farms with a shared mooring system.

A new organisational design in skeletal muscle fibres.

In vertebrate skeletal muscles, the architecture of myofibrils is particularly well conserved throughout the taxa. It is composed of suites of repeating functional units called sarcomeres which give the muscle its striated structure. Here, we show that the skeletal sound producing muscles of the cusk eel Parophidion vassali have a different organisation, distinct from the classical type found in textbooks. Within sarcomeres, filaments are not straight lines but have a Y-shaped structure. This looks like chicken wire, with one branch connecting to a branch from the myofibril above and the other connecting to a branch from the myofibril below. This organisation seems to be an adaptation to counteract a trade-off between the speed and force. The low ratio of myofibrils within cell muscles and the high volume of sarcoplasmic reticulum strongly suggest that these muscles are capable of fast contractions. In parallel, the Z-bands are quite wide about 30% of the sarcomere length. This extraordinary long Z-band could smooth out the tension variations found in high-speed muscle contraction, helping to produce sounds with low variabilities in the sound features. Simultaneously, the Y-shaped structure allows having more cross-bridges, increasing the force in this high-speed muscle.

Effects of the variation of viscosity on the stability of thin liquid film flows along a uniformly heated substrate under heat flux boundary condition

The effects of variable viscosity on the stability of gravity-driven, Newtonian, thin liquid film flowing down a uniformly heated substrate under heat flux (HF) boundary condition is investigated. HF boundary condition allow us to consider the heat loss from the system at the solid–air interface as well as the heat flux by the rigid wall to the surrounding liquid, both of which effects the temperature gradient on the solid–liquid interface. This model is more realistic in comparison with specified temperature (ST) boundary condition/Dirichlet condition. The underlying assumption of ST boundary condition is that the heat flux at the solid–liquid interface is equal to the heat loss at the solid–air interface. It results in vanishing temperature gradient on the top surface of the rigid wall. Consequently, both the heat flux at solid–liquid and solid–air interfaces have no influence on the thin liquid film flow over the rigid substrate. Considering exponential variation of viscosity, together with the linear variation of surface tension, an evolution equation is constructed, using long-wave expansion technique. This evolution equation captures the effect of the variation of viscosity, thermocapillarity, and heat flux at the solid–air interface, through the parameters, Kμ (coefficient of dynamical viscosity), MBs (products of film Marangoni and free surface Biot number), and Bw (wall film Biot number), respectively. Using normal mode approach, the linear stability analysis reveals the destabilizing behavior of Kμ, MBs, and stabilizing effect of Bw. Using multiple-scale analysis, the weakly nonlinear study demarcates the supercritical (subcritical) stable (unstable) zones and their dependence on Kμ and Bw. Finally, the numerical simulation of the evolution equation, by the spectral method over a periodic domain, confirms the results obtained by the linear and weakly nonlinear study.

Multifunctional Debye temperature acoustical and surface tension studies in combination of Ortho-xylene and Amyl acetate at four temperatures T (=303.15, 308.15, 313.15 to 318.15) K

In the material mixture of Ortho-xylene and Amyl acetate over the complete mole fraction range of Ortho-xylene,basic acoustical parameters have been measured at different temperatures T = (303.15, 308.15, 313.15 and 318.15) K. From these basic measurements, Debye temperature and surface tension variation trends are studied. The variation trends of these parameters are observed to be increasing with mole fraction and decreasing with temperature which implies that there exist molecular interactions between the mixture. The molecular contribution with thermal energy fluctuations in binary liquid mixtures have been estimated. Debye temperature analogy, together with the differences in viscosity are carefully examined to explain molecular interactions between the constituent molecules of liquid mixtures.

Oscillatory Marangoni flow in a deep layer of a Carreau fluid

We study the spreading dynamics of an insoluble and non-diffusive surfactant on the free surface of a deep layer of a Carreau fluid. When a non-uniform distribution of surfactant is imposed on the free surface of an initially motionless fluid, variations in surface tension are induced, causing the fluid motion from regions of lower surface tension to those of higher tension. Such movement redistributes the surfactant concentration until a uniform condition is reached. The two-dimensional momentum and convection–diffusion equations are employed to determine the hydrodynamics in the deep fluid layer and the evolution of the surfactant on the fluid surface. The modified vorticity-stream function formulation is used to solve numerically the hydrodynamic field, where the non-Newtonian dependent variables of the problem are decomposed into a Newtonian part and a non-Newtonian contribution. One of the most critical variables in practical applications regarding this phenomenon concerns the time required for the surfactant to reach a uniform distribution over the interface. The results show that the dimensionless parameters that control the decay of the variations in surfactant concentration in time are the Reynolds number Re, the fluid behavior index n, and ε, reflecting the influence of the inertia of the fluid. The results show that the temporal decay of the surfactant concentration on the fluid surface increases significantly for high values of the Reynolds number, it is more attenuated in pseudoplastic fluids than in Newtonian fluids, and the surfactant concentration decay exhibits asymmetric oscillations when inertial effects increase.

Modeling of tow tension fluctuations and parameter optimization during the stable transfer phase for automated fiber placement

The fluctuation in tow tension is critical for Automated Fiber Placement (AFP). However, it has not been widely studied. In this paper, a tension variation equation was developed to represent the tension fluctuation during AFP, and experiments were used to demonstrate the validity of the equation. According to the equation, the degree of bending rigidity, power-law friction, and extensibility influence on the tension change was obtained. Additionally, the effects of bending rigidity and extensibility can be disregarded during AFP. Moreover, automatic wire feeding and laying trials were carried out separately, and proper tensions (T = 3 N) for wire feeding and layup under experimental conditions were obtained. Therefore, the equation provides theoretical support for the structural and parameter optimization of the AFP.

Tether response of offshore Triceratops under hurricane conditions

The form-dominant approach is increasingly adopted in offshore platform design; triceratops is one of the very recent examples. These platforms are position-restrained by taut-moored tethers, which govern the dynamic response under extreme environmental loads. Due to the partial isolation of the deck from the buoyant legs in the presence of ball joints, sub-structure analysis is more critical. The present study examines the tether response of triceratops in 2400 m water-depth under hurricane conditions caused by 10-yr, 100-yr, and 1000-yr Gulf of Mexico (GoM) storms. The numerical studies show that the Peak-Wave case governs the dynamic tension variation of tethers for the chosen hurricane conditions. For the 100-yr and 1000-yr storms, they are about 15% and 45% higher than 10-yr storms, respectively. However, the maximum axial tensile stresses are about 8% of the yield, ensuring a no-rupture condition of the tethers. The service lives of the tethers for 10-yr storms are about one-third that of 100-yr and 1000-yr storms. A positive minimum tension for all load cases confirms no slackening of the tethers.

Impact of Natural-Based Viscosity Modifiers of Inhalation Drugs on the Dynamic Surface Properties of the Pulmonary Surfactant

The effectiveness of inhalation therapy depends on aerosol size distribution, which determines the penetration and regional deposition of drug in the lungs. As the size of droplets inhaled from medical nebulizers varies depending on the physicochemical properties of the nebulized liquid, it can be adjusted by adding some compounds as viscosity modifiers (VMs) of a liquid drug. Natural polysaccharides have been recently proposed for this purpose and while they are biocompatible and generally recognized as safe (GRAS), their direct influence of the pulmonary structures is unknown. This work studied the direct influence of three natural VMs (sodium hyaluronate, xanthan gum, and agar) on the surface activity of the pulmonary surfactant (PS) measured in vitro using the oscillating drop method. The results allowed for comparing the variations of the dynamic surface tension during breathing-like oscillations of the gas/liquid interface with the PS, and the viscoelastic response of this system, as reflected by the hysteresis of the surface tension. The analysis was done using quantitative parameters, i.e., stability index (SI), normalized hysteresis area (HAn), and loss angle (φ), depending on the oscillation frequency (f). It was also found that, typically, SI is in the range of 0.15-0.3 and increases nonlinearly with f, while φ slightly decreases. The effect of NaCl ions on the interfacial properties of PS was noted, which was usually positive for the size of hysteresis with an HAn value up to 2.5 mN/m. All VMs in general were shown to have only a minor effect on the dynamic interfacial properties of PS, suggesting the potential safety of the tested compounds as functional additives in medical nebulization. The results also demonstrated relationships between the parameters typically used in the analysis of PS dynamics (i.e., HAn and SI) and dilatational rheological properties of the interface, allowing for easier interpretation of such data.

Mechanically-tunable bandgap closing in 2D graphene phononic crystals

We present a tunable phononic crystal which can be switched from a mechanically insulating to a mechanically conductive (transmissive) state. Specifically, in our simulations for a phononic lattice under biaxial tension (σxx = σyy = 0.01 N m−1), we find a bandgap for out-of-plane phonons in the range of 48.8–56.4 MHz, which we can close by increasing the degree of tension uniaxiality (σxx/σyy) to 1.7. To manipulate the tension distribution, we design a realistic device of finite size, where σxx/σyy is tuned by applying a gate voltage to a phononic crystal made from suspended graphene. We show that the bandgap closing can be probed via acoustic transmission measurements and that the phononic bandgap persists even after the inclusion of surface contaminants and random tension variations present in realistic devices. The proposed system acts as a transistor for MHz-phonons with an on/off ratio of 105 (100 dB suppression) and is thus a valuable extension for phonon logic applications. In addition, the transition from conductive to isolating can be seen as a mechanical analogue to a metal-insulator transition and allows tunable coupling between mechanical entities (e.g. mechanical qubits).

Nonlinear vortex-induced vibrations of fluid-conveying tensioned pipes in super-critical regimes

Nonlinear vortex-induced vibration (VIV) properties of the fluid-conveying pipes in super-critical regimes subjected to the combined action of external fluid and axial tension are investigated. A new nonlinear dynamic model taking into account the variation of axial tension and the action of external flow is proposed. According to the van der Pol equation, the interaction between the pipe and external flow is evaluated. More specifically, the nonlinear governing equations are established based on Hamilton's principle, and they are then discretized via the Galerkin method and solved by the fourth-order Runge-Kutta method. The VIV amplitudes obtained from the present theoretical model are compared with the published experimental results, which validates the effectiveness and accuracy of the proposed nonlinear dynamic model. It is found that keeping the external fluid velocity constant, with the increase of internal fluid velocity, the growth rates of the maximum response amplitudes in different directions of the buckled pipe are the same under different tensions. When the internal fluid velocity is kept constant, for the pipe in post-buckling state, increasing the tension will be accompanied by decreasing the dynamic stiffness of the pipe, which leads to the increase of the dynamic displacement response. When the pipe in super-critical regime is subjected to variable tension, the increase of the time-varying tension amplitude can either enhance the maximum response amplitude in the cross-flow (CF) direction of the pipe or suppress it.

Yarn modeling and winding process simulation based on 3D beam elements

In order to study the tension variation of cotton yarn in the winding process, a finite element model of yarn based on three-dimensional beam elements is proposed. As the size of yarn in the length direction is much larger than the cross-sectional size, this paper assumes that the yarn cross-section is circular and ignores the change of the cross-sectional area in the winding process. The winding process of yarn is simulated using Abaqus dynamic explicit, and the influence of the yarn fineness on the yarn tension during winding is analyzed. The results show that the average relative error between the simulation results and the experimental data is 14.09%, and the maximum relative error is 17.06%; therefore the model is reasonable. Compared with the solid element model of yarn, the yarn simulated by this model can save a lot of computing resources while taking into account the yarn stacking effect. The winding length that can be simulated in the same time is tens of times that of the solid element model, thus the winding simulation of nine-layer yarn on the bobbin is realized. The conclusion is that the inner yarn loop presents weak tension while the outer yarn loop has large tension.

Numerical simulation of vortex flow evolution during droplet formation in T-inlet microchannel

The formation of microdroplets in T-inlet microchannel device was numerically simulated based on the conservation level set method. The strength of the swirling flow is evaluated by defining the average rotational angular velocity of the fluid inside the microdroplet under the condition of no shear. The differences in the evolution of swirling flow caused by the alteration of viscosity ratio at low capillary number (Ca≤0.01) were analyzed, and the influence of two-phase interfacial tension on the vortex evolution is also discussed. Numerical simulation results show that the evolution process of swirling flow in the squeezing droplets can be divided into five phases. The increase of capillary number will lead to an improvement of internal swirling intensity during the development of microdroplet. However, raising the viscosity ratio will inhibit the swirling strength. The variation of the interfacial tension between the two-phase fluids has a significant effect on the swirling intensity, the swirling intensity inside the droplet increases with increasing interfacial tension.

Body Forces Drive the Apparent Line Tension of Sessile Droplets.

The line tension of a three-phase contact line is implicated in a wide variety of interfacial phenomena, but there is ongoing controversy, with existing measurements spanning six orders of magnitude in both signs. Here, we show that computationally obtained magnitudes, sign changes, and nontrivial variations of apparent line tension can be faithfully reproduced in a parsimonious model that incorporates only liquid-substrate interactions. Our results suggest that the origin for the remarkable variation lies in the failure of a widely used estimation method to eliminate body forces, leading measured line tensions to behave like an extensive quantity.

Model predictive control for path tracking in cable driven parallel robots with flexible cables: collocated vs. noncollocated control

This paper proposes a novel control scheme for precise path tracking control in cable driven parallel robots (CDPRs) with axially-flexible cables, with particular focus to the challenging case of cable suspended parallel robots (CSPRs). To handle model nonlinearities while ensuring small computational effort, a controller made by two sequential control actions is developed. The first term is a position-dependent, model predictive control (MPC) with embedded integrator to compute the optimal cable tensions ensuring accurate path tracking and fulfilling the feasibility constraints; bounds on the feasible tensions are also included. The second control term transforms the optimal tensions into the commanded motor torques, and hence currents, that are evaluated through the kinetostatic model of the electric motors used for winding and unwinding the cables. Control design is performed through the robot dynamics model, formulated with the assumption of rigid cables. Moreover, the proposed control strategy is presented in two different architectures, collocated control and noncollocated control. Flexibility is handled by penalizing large tension variations in the cost function adopted in the controller design, plus some hard constraints on the maximum tension derivatives. These features, together with the embedding of the integrator within the MPC formulation, ensure smooth control tensions that allow handling the axial flexibility of the cables, although it is not explicitly considered in the controller design.To assess the performances of the proposed control algorithm, a kinematically-determined robot with a suspended, lumped end-effector is simulated by also adopting very flexible cables. Additionally, a simplified dynamic model of the electrical dynamics and the sensor quantization are included to provide a realistic representation of the real environments. The results, together with the fair comparison with a benchmark, corroborate the effectiveness of the proposed approach, its robustness, and its feasibility in real-time controllers due to the wise reduction of the computational effort.

Dynamic In Situ Monitoring of the Salt Counter-ion Effect on Surfactant Effectiveness Using Reconfigurable Janus Emulsions

A straightforward method for visualization and quantification of surfactant effectiveness within different electrolyte environments based on using reconfigurable Janus emulsions as novel optical probes is reported. More specifically, we investigated the effect of different types and concentrations of salt counter-ions on the surfactant surface excess of commercial ionic and non-ionic surfactants, namely sodium dodecyl sulfate (SDS) and Tween 80 via in situ monitoring the morphological reconfigurations of biphasic Janus emulsions comprising hydrocarbon and fluorocarbon oils. We find that significant variations in interfacial tensions of SDS-stabilized interfaces (up to 15 mN·m-1) can be evoked by titrating mono-, di-, and trivalent cationic counter-ions, which is coherent with the lyotropic (Hofmeister) series. In contrast, the salt counter-ion effect on the surfactant effectiveness was less pronounced for the non-ionic surfactant Tween 80 (∼3 mN·m-1). Our results reveal a facile in situ method for monitoring the central role of electrolyte type and concentration on surfactant effectiveness and, more broadly, illustrate that Janus emulsions serve as powerful optical probes to dynamically study the properties of surfactants at liquid interfaces. We demonstrate the utility of our findings for an electro-induced morphological reconfiguration of Janus droplet morphologies by dynamically tuning Cu2+ concentration in solution using an electrode setup. The latter provides a unique platform for liquid-phase, real-time, and continuous tuning of Janus droplet morphologies, e.g., for their application in sensing and dynamic optical device platforms.

Experimental investigation of the sedimentation behavior of metal droplets in liquid–liquid systems

The accurate sedimentation of metal droplets is of great importance in metal droplet-based three-dimensional printing. Detailed investigations of the process of metal droplet collision in a liquid–liquid system are still lacking, relative to studies on the atmospheric environment. In this study, the dynamics of the sedimentation behavior of metal droplets in a liquid–liquid system are experimentally investigated using a high-speed imaging system. The experimental results showed that with an increased impact velocity, metal droplets successively appear after the collision as coalescence, coalescence accompanied by rebound, and rebound. There is a critical impact velocity between the rebound and coalescence, which is related to the surface tension and droplet size of the metal droplets. Analysis of the mechanism of coalescence showed that mechanical oscillations occur during coalescence, which leads to a variation in the inherent surface tension. The greater the impact velocity, the greater the variation. In addition, a semi-empirical prediction formula for the Weber number and maximum spreading factor in the coalescence of metal droplets is developed. This work provides an improved theoretical understanding and superior practical printing efficiency and quality.

Theoretical model and numerical simulation of tower-wake-induced vibration of a flexible suspender

For a suspension bridge, suspenders in the wake of bridge tower interfered by the shedding vortices, would experience a large-amplitude vibration, named as tower-wake-induced vibration (TWIV). At specific wind speeds, the vibrating frequency of suspenders during TWIV would be captured by the shedding frequency of the tower wake, which is the lock-in of TWIV. The present research establishes the governing equations of flexible suspenders, considering the tension variations caused by the deformation, also adopts the aerodynamic model of TWIV, to study the lock-in phenomenon and the TWIV characteristics. To explore the variation trend of nonlinear frequency with amplitude of suspenders, the difference of dynamic parameters of suspenders in two vibrating motions are recognized through free vibration motions at first. Then, a formula for the equivalent amplitude-dependent (EAD) frequency of the suspender is raised. The lock-in phenomenon of TWIV is reproduced in these two motions as well. Eventually, TWIVs of four suspenders at various positions in the rear of bridge tower are simulated based on practical engineering, considering the variation of aerodynamic forces along the altitude due to the wind profile. The conclusions indicate that TWIV of suspenders is a low-frequency and low-order-mode vibration at high wind speeds.

Modeling of a detailed bow spring centralizer description in stiff-string torque and drag calculation

Flexible bow spring centralizers are commonly used in the drilling industry to ensure a good centralization of casings inside the borehole. A bow spring centralizer consists of multiple bows evenly spaced around the tubular. They are attached to the casing at multiple locations via connections or rings, and run-in hole such that the bows are sliding against the borehole. To provide a good centralization, the bows must be stiff enough to push the casing away from the borehole. Also, it must be flexible enough to avoid large contact forces and consequently friction forces that can cause excessive drag. This paper aims to present a theoretical model for bow-spring centralizers and its implementation in a stiff-string torque and drag model based on the finite element method.Our modeling approach assumes that the flexible centralizer bows are identical. Each bow acts independently from the others and could be in contact with the borehole or not, depending on the lateral displacement and orientation of the centralizer. The bow force follows a power law based on a constant stiffness and a stiffness power coefficient that are computed based on test measurements provided by the manufacturer.When introduced in a stiff-string torque and drag model, the contact forces are computed on each individual bow. For drag forces, the bows are assumed to be non-rotating inside the borehole, so the axial friction force at a bow spring is related to the algebraic sum of all bow contacts. When the casing is rotating inside the centralizer, a tangential friction force is generated between the casing and bow spring rings. It is related to the resultant contact force i.e., the vector sum of all bow contacts.An example of the calibration for a bow-spring centralizer is studied in this paper. The theoretical bow-spring model showed its capacity to have a good interpretation of the measurements. It also showed the importance of specifying the testing condition with regards to the possible clearance between the casing and centralizer rings. The finite element torque and drag model is firstly validated against another model. When applied to a case study of running in hole a casing string with bow-spring centralizers, the model shows its effectiveness to describe the casing centralization along the wellbore as well as the tension variations at the surface.

Tattooing of Scars and Disfiguring Burn Lesions.

Cutaneous scars are permanent and the result of physiological wound healing with formation of disorganized collagen instead of the normally structured connective tissue network (or "textile") of the dermis. A scar restores the physical and tensile integrity of skin; skin is a vital protective layer on the body. Scars are of many types and with a broad spectrum of individual variations of color, texture, thickness, furrowing, tension, and contraction. Scars can be red and hypertrophic and, moreover, aggressive and manifested as keloids. White scars can be changed in color into a normal tone and look by the application of medical tattooing. This can help many scar victims regain their quality of life. High level of skill is required by the tattoo artist, who shall be experienced. Tattooing may restore skin color, but it cannot restore textural and structural changes, which may need correction using other methods before the tattoo is ready to correction of color by tattooing. The medical tattooist needs to cooperate with other specialists and develop a consistent strategy of the treatments to be applied including the sequence of treatments with tattooing added at the end for final color correction back towards normal. The medical tattooist from start shall take responsibility and select the clients who are likely to benefit from tattooing and exclude clients, who shall not be offered this treatment.