Variable Tension Research Articles

On variable length induced vibrations of a vertical string

Abstract The purpose of this paper is to study the free lateral responses of vertically translating media with variable length, velocity and tension, subject to general initial conditions. The translating media are modeled as taut strings with fixed boundaries. The problem can be used as a simple model to describe the lateral vibrations of an elevator cable, for which the length changes linearly in time, or for which the length changes harmonically about a constant mean length. In this paper an initial-boundary value problem for a linear, axially moving string equation is formulated. In the given model a rigid body is attached to the lower end of the string, and the suspension of this rigid body against the guide rails is assumed to be rigid. For linearly length variations it is assumed that the axial velocity of the string is small compared to nominal wave velocity and the string mass is small compared to car mass, and for the harmonically length variations small oscillation amplitudes are assumed and it is also assumed that the string mass is small compared to the total mass of the string and the car. A multiple-timescales perturbation method is used to construct formal asymptotic approximations of the solutions to show the complicated dynamical behavior of the string. For the linearly varying length analytic approximations of the exact solution are compared with numerical solution. For the harmonically varying length it will be shown that Galerkin׳s truncation method cannot be applied in all cases to obtain approximations valid on long timescales.

Black strings from minimal geometric deformation in a variable tension brane-world

We study brane-world models with variable brane tension and compute corrections to the horizon of a black string along the extra dimension. The four-dimensional geometry of the black string on the brane is obtained by means of the minimal geometric deformation approach, and the bulk corrections are then encoded in additional terms involving the covariant derivatives of the variable brane tension. Our investigation shows that the variable brane tension strongly affects the shape and evolution of the black string horizon along the extra dimension, at least in a near-brane expansion. In particular, we apply our general analysis to a model motivated by the Eötvös branes, where the variable brane tension is related to the Friedmann–Robertson–Walker brane-world cosmology. We show that for some stages in the evolution of the universe, the black string warped horizon collapses to a point and the black string has correspondingly finite extent along the extra dimension. Furthermore, we show that in the minimal geometric deformation of a black hole on the variable tension brane, the black string has a throat along the extra dimension, whose area tends to zero as time goes to infinity.

Fuzzy Control with Adjustable Factors in Tension Control System

The variable tension control system of strip winding is a nonlinear, strong coupling and time-varying system. Traditional fuzzy controller with fixed control rules cannot obtain the desired control performance of the strip winding system. So the fuzzy control algorithm with adjustable factorαis proposed, and the introduction of adjustable factors can change the fuzzy control rules. The tension fuzzy controller with adjustable factorαis designed, and simulation model of the system is established using Matlab software. The result of simulation shows that tension fluctuation of the tension fuzzy control system with adjustable factor get small, comparing the tension fuzzy control system with adjustable factors with the ordinary tension fuzzy control system. The tension fuzzy control system with adjustable factors has fast system response and strong anti-interference ability.

Growth of a Vapour Bubble in a Superheated Liquid of Variable Surface Tension and Viscosity Between Two-phase Flow

The growth of a vapour bubble in a superheated liquid of variable surface tension and viscosity between two finite boundaries is introduced. The problem is solved analytically using the modified method of Plesset and Zwick method. The pressure difference is described in terms of temperature difference and initial pressure diffe rence. The surface tension, viscosity, and initial and final time of bubble growth are derived in terms of some physical parameters. The growth of bubble radius is proportional to the thermal diffusivity, the initial pressure difference and its coefficient. On contrary the growth is inversely proportional to the initial void fraction and the density ratio. Moreover, better agreements with some experimental data are achieved rather than some of previous theoretical efforts.

Gradient-enhanced damage model for large deformations of elastic-plastic materials

This paper deals with the development of a family of gradient-enhanced elasticitydamage-plasticity models for the simulation of failure in metallic and composite materials. The model incorporates finite deformations and is developed with the assumption of isotropy and isothermal conditions. The gradient enhancement applied to the damage part of the model aims at removing pathological sensitivity to the finite element discretization which can occur due to material softening. The attention is focused on the algorithmic aspects and on the implementation of the model using AceGen tool. The numerical verification tests of the described model are performed using the Mathematica-based package AceFEM. Particularly, uniaxial tension test for a bar with a variable cross-section and tension of a perforated plate are examined.

Control of centrifugal fingering via a variable interfacial tension approach

We study the centrifugal fingering instabilities that occur in rotating Hele-Shaw cells containing two different fluids. A weakly nonlinear analysis of the problem is performed, considering that the surface tension between the rotating fluids changes with the local curvature of the interface. It is shown that the coupling between the contact angle and the variable interfacial tension permits the control of the interface disturbances. As a result, linear perturbations and nonlinear finger competition phenomena can be properly controlled and suppressed.

Climacturia after Definitive Treatment of Prostate Cancer

Prostate cancer treatment results in several sexually related side effects beyond the well studied erectile dysfunction. Climacturia (leakage of urine during orgasm) has been reported after prostatectomy but studies have been limited by multiple factors. In this study we examine the prevalence, causes and impact on orgasm function of climacturia after definitive treatment of prostate cancer with surgery or radiation. A total of 906 anonymous surveys were sent to patients with prostate cancer treated with surgery and/or radiation. Respondents were asked about the presence of urinary leakage, climacturia and various elements related to sexual and orgasmic function. We estimated the prevalence of climacturia, evaluated the differences between those with and without climacturia, and assessed the impact of climacturia on orgasmic function. Overall 412 surveys were returned and available for analysis, and of these respondents 75.2% were sexually active or experiencing orgasms. Climacturia was reported by 22.6% of these respondents, and by 28.3%, 5.2% and 28.6% of those treated with surgery, radiation, or both, respectively (p <0.001). The use of aides to obtain an erection (OR 2.24, 95% CI 1.08-4.93, p = 0.035) and the presence of urinary incontinence (OR 3.09, 95% CI 1.66-5.88, p <0.001) were also associated with climacturia in a multivariate logistic regression model. Climacturia had no significant impact on orgasmic function and satisfaction. Climacturia is experienced by a substantial proportion of men after undergoing definitive treatment of prostate cancer. We found a complex relationship between stress urinary incontinence and climacturia, and noted that the presence of climacturia does not necessarily negatively impact sexual satisfaction.

Verifying the Hanging Chain Model

The wave equation with variable tension is a classic partial differential equation that can be used to describe the horizontal displacements of a vertical hanging chain with one end fixed and the other end free to move. Using a web camera and Tracker software to record displacement data from a vibrating hanging chain, we verify a modified version of the wave equation with variable tension that accounts for damping. Supplemental materials are available for this article. Go to the publisher's online edition of PRIMUS to view the supplemental file.

Self-similar vortex-induced vibrations of a hanging string

AbstractAn experimental analysis of the vortex-induced vibrations of a hanging string with variable tension along its length is presented in this paper. It is shown that standing waves develop along the hanging string. First, the evolution of the Strouhal number $\mathit{St}$ with the Reynolds number $\mathit{Re}$ follows a trend similar to what is observed for a circular cylinder in a flow for relatively low Reynolds numbers ($32\lt \mathit{Re}\lt 700$). Second, the extracted mode shapes are self-similar: a rescaling of the spanwise coordinate by a self-similarity coefficient allows all of them to collapse onto a unique function. The self-similar behaviour of the spatial distribution of the vibrations along the hanging string is then explained theoretically by performing a linear stability analysis of an adapted wake-oscillator model. This linear stability analysis finally provides an accurate description of the mode shapes and of the evolution of the self-similarity coefficient with the flow speed.

Hybridizable discontinuous Galerkin method (HDG) for Stokes interface flow

In this paper, we present a hybridizable discontinuous Galerkin (HDG) method for solving the Stokes interface problems with discontinuous viscosity and variable surface tension. The jump condition of the stress tensor across the interface is naturally incorporated into the HDG formulation through a constraint on the numerical flux. The most important feature of HDG method compared to other DG methods is that it reduces the number of globally coupled unknowns significantly when high order approximate polynomials are used. For problems with polygonal interfaces, it provides optimal convergence rates of order k+1 in L2-norm for the velocity, pressure and as well as the gradient of velocity. Furthermore, a new approximate velocity can be obtained by an element-by-element postprocessing which converges with order k+2 in the L2-norm. For Stokes interface problems with curved interfaces, we use general curvilinear element to ensure the optimal convergence rates. An error estimate is given for the approximation of the interface. It indicates that curvilinear elements of degree 2k+1 should be used for optimal convergence rate of order k+1.

Shape of Water–Air Interface beneath a Drop on a Superhydrophobic Surface Revealed: Constant Curvature That Approaches Zero

The 3D interface between a sessile water drop that is found on a superhydrophobic microtextured surface has been directly imaged using a confocal microscope with an immersion lens. The local mean curvature of the water–air interface was derived and was shown to be constant and close to zero not only for the case of pure water, but also for cases of variable drop density and surface tension. Although the mean curvature is constant and close to zero, the standard deviation on the mean curvature increases with increasing drop density and lower surface tension. The resulting 3D image of the water–air interface at the bottom of a water drop demonstrates the possibility of investigating practical interfaces of water on given textures and confirms that no matter what the superhydrophobic surface characteristics are, the interface remains with a constant curvature of close to zero.

The Surface Tension of Pure Aluminum and Aluminum Alloys

The surface tension of high purity and commercial purity aluminum in vacuo was determined using the sessile drop method and the results were found to compare favorably with published data. The effects of holding atmosphere, substrate, and “surface fracture” of the sessile drop on the measured surface tension values were investigated together with the effects of different solute elements commonly present in commercial aluminum alloys. The results obtained suggest that the nature of the surface oxide film formed on the droplets (affected by alloy composition and atmosphere) and the rupture of this film are the dominant factors influencing the surface tension values obtained. Changes in surface tension values of up to 60 pct were observed. The possible effect of this variable surface tension on practical casting processes, such as direct chill casting, is suggested.

A linear model of stationary elevator traveling and compensation cables

Based on a recent asymptotic analysis of a nonlinear model of a slack cable, a computationally efficient, linear model is developed for calculating the natural frequencies, mode shapes, and dynamic responses of stationary elevator traveling and compensation cables. The linear cable model consists of two vertical cable segments connected by a half-circular lower loop. The two vertical cable segments are modeled as a string with a variable tension due to the weight of the cable. The horizontal displacements of the cable segments consist of boundary-induced displacements and relative elastic displacements, where the boundary-induced displacements are interpolated from the displacements of the two lower ends of the cable segments, and the relative elastic displacements satisfy the corresponding homogeneous boundary conditions of the cable segments. The horizontal displacement of the lower loop is interpolated from those of the two lower ends of the two cable segments, and the bending stiffness of the lower loop is modeled by a spring with a constant stiffness, which can be calculated from the nonlinear model. Given a car position, the natural frequencies and mode shapes of an elevator traveling or compensation cable are calculated using the linear model and compared with those from the nonlinear model. The calculated natural frequencies are also compared with those from a full-scale experiment. In addition, the dynamic responses of a cable under a boundary excitation are calculated and compared with those from the nonlinear model. There is a good agreement between the predictions from the linear and nonlinear models and between the measured natural frequencies from the full-scale experiment and the corresponding calculated ones.

Manipulation of the Saffman-Taylor instability: A curvature-dependent surface tension approach

A variant of the classic Saffman-Taylor instability problem is reported, in which the surface tension at the fluid-fluid interface depends on the interfacial curvature. We show that the interplay between the variable surface tension and three-dimensional effects connected to the contact angle significantly modifies the scenario of instability formation. This allows the manipulation of the Saffman-Taylor instability, leading to the stabilization (destabilization) of conventionally unstable (stable) situations. This is done analytically through a perturbative mode-coupling approach, providing relevant information about both linear and weakly nonlinear regimes of interface evolution.

Research of the Strategy on the Flatness and Gauge Control Based on Coiling Variable Tension Control Process

Based on the analysis and simulation of the variable tension coiling process, integrated control strategy for strip flatness, thickness and tension has been proposed when the last stand adopts the control means of both position closed loop and pressure closed loop. The strategy pre-controls strip flatness and thickness according to the changing tension to decrease accommodation amplitude and enhance product quality. Practical application shows the strategy improves the control precision on the basis of ensuring the stable operation of unit.

Design of an adaptive–passive dynamic vibration absorber composed of a string–mass system equipped with negative stiffness tension adjusting mechanism

In this study, a new adaptive–passive dynamic vibration absorber design is discussed. The proposed design is composed of a string under variable tension with a central mass attachment as an undamped dynamic vibration absorber (DVA), a negative stiffness mechanism as a string tension adjustment aid and a tuning controller to make it adaptive. The dependency of the natural frequencies of this system on the string tension is determined analytically and verified using the finite element method. It is analytically shown that with the help of a negative stiffness element, the tuning force requirement is almost zero throughout the whole operation range. A string tension adjustment algorithm is proposed, which tunes the DVA system depending on the magnitude and frequency of the most dominant component of the vibration signal. Finally, a prototype of the system is built and a series of experiments are conducted on the prototype that validate the analytical and numerical calculations.

Variable tension control for discontinuous tape winding of composites based on constant extension ratio

Discontinuous tape winding, which has obvious advantages in large extension ratio winding, is widely used in the molding of composites. Therefore, the research on technological parameters becomes the focus of many scholars. However, how to accomplish the variable tension control is usually not fully considered. Accordingly, the constant extension ratio and the smoothness of winding process cannot be ensured. Aiming at the problem of tension control, this paper first gives a comparatively deep research on the control method and the interaction mechanism of tension, extension ratio, automatic lap and automatic rectification. Then, according to the winding process features, the mechanical device and the mathematical model of tension control system are established respectively. With regard to the characteristics of PID controller and fuzzy controller, the fuzzy self-tuning PID controller is designed. As a result, the variable tension control is realized during the winding and lapping process, and the constant extension ratio is guaranteed. Finally, a sample application is presented for demonstration. By presenting the variable tension control techniques for discontinuous tape winding, the constant extension ratio of tapes is achieved, the consecution and the automation degree of winding process is improved as well. Thus, the quality of wound products is guaranteed.

Efficacy of a penile variable tension loop for improving climacturia after radical prostatectomy

WHAT'S KNOWN ON THE SUBJECT? AND WHAT DOES THE STUDY ADD?: Climacturia is present in ∼20-40% of men after radical prostatectomy, and adversely affects sexual satisfaction. Although several strategies have been proposed for the treatment of climacturia, none have been systematically studied to date. This observational study shows that use of a penile variable tension loop can significantly reduce the degree and frequency of orgasm-associated incontinence, and the associated distress experienced by patients and partners. Climacturia resolves completely in half the patients, and occurs occasionally or rarely in the remainder. To define the impact of the use of a penile variable tension loop on climacturia and on the distress level experienced by patients and their partners as a result of climacturia. All patients presenting for sexual function assessment after radical prostatectomy (RP) were questioned regarding climacturia. The study population consisted of men who had undergone RP < 6 months before initial evaluation, had reported having climacturia on ≥25% attempts where orgasm was achieved, had agreed to use the variable tension loop consistently, and continued to have climacturia when not using the loop at follow-up. Patients were interviewed regarding the frequency and degree of climacturia, and their own and their partner's distress levels secondary to climacturia, both with and without the use of the variable tension loop. The study population comprised 124 men. At baseline, the degree of climacturia was small, moderate, and large in 16%, 72%, 12% of patients, respectively, and 28%, 26% and 0%, respectively, at follow-up (all P < 0.01). Climacturia occurred rarely, occasionally, most of the time, or always in 15%, 48%, 16% and 21% of cases, respectively, at baseline, and 48% of patients experienced no climacturia with use of the variable tension loop. Distress was experienced by 14% and 61% of patients and partners at baseline, and 2% and 11% of patients and partners at follow up (P < 0.01). Severity of distress was significantly lower at follow-up for both partners and patients (P < 0.01). Climacturia is a common complication of radical prostatectomy. Application of the variable tension loop can result in a significant decrease in the frequency and volume of climacturia. Use of the variable tension loop is a simple and non-invasive strategy for relieving the distress associated with climacturia in patients who have undergone RP and their partners.

Physical Foundations of Consciousness: Variable Width Synapses

The many facets of consciousness divide into two distinct categories. First: the organisational state of the neural networks at any one time, which determines whether a person is conscious – awake, or unconscious – asleep. Second; the processes, or traffic of electrical signals across these networks that accounts for the experiences of conscious awareness. This paper addresses the former; namely, how the state of the billions of neural networks and the trillions of additional axons, dendrites and synapses varies over the daily cycle - what physically changes when we go to sleep – what happens in our brain as we wake up? Synapses play a major role in the operation of the brain. We submit that the widths of synaptic clefts are not fixed, but are variable, and that this variable tension across the synapses is the neural correlate of consciousness. Various experiments are suggested to explore this hypothesis. NeuroQuantology | June 2012 | Volume 10 | Issue 2 | Page 268-275

Black string corrections in variable tension braneworld scenarios

Braneworld models with variable tension are investigated, and the corrections on the black string horizon along the extra dimension are provided. Such corrections are encrypted in additional terms involving the covariant derivatives of the variable tension on the brane, providing profound consequences concerning the black string horizon variation along the extra dimension, near the brane. The black string horizon behavior is shown to be drastically modified by the terms corrected by the brane variable tension. In particular, a model motivated by the phenomenological interesting case regarding Eotvos branes is investigated. It forthwith provides further physical features regarding variable tension braneworld scenarios, heretofore concealed in all previous analysis in the literature. All precedent analysis considered uniquely the expansion of the metric up to the second order along the extra dimension, what is able to evince solely the brane variable tension absolute value. Notwithstanding, the expansion terms aftermath, further accomplished in this paper from the third order on, elicits the successive covariant derivatives of the brane variable tension, and their respective coupling with the extrinsic curvature, the Weyl tensor, and the Riemann and Ricci tensors, as well as the scalar curvature. Such additional terms are shown to provide sudden modifications in the black string horizon in a variable tension braneworld scenario