Elastic Tube Research Articles

Cross-sectional flattening-induced nonlinear damped vibration of elastic tubes subjected to transverse loads

This paper presents an analytical solution of the cross-sectional flattening-induced nonlinear vibration of elastic tubes when subjected to transverse harmonic excitation. It is shown that the equation of motion describing the beam-type transverse vibration of elastic tubes can be characterized by the Duffing equation with cubic nonlinearity, in which the nonlinear term reflects the influence of the cross-sectional flattening on the beam-type transverse vibration of the tubes. The degree of nonlinearity of the transverse vibration is found to be governed directly by the dimensionless amplitude of the harmonic force. The nonlinear feature and corresponding stability of the beam-type response of the tubes under the action of harmonic excitation are discussed. Numerical examples are provided to demonstrate the rationality of the present analytical model.

Supervised home-based resistance training for managing idiopathic peripheral polyneuropathy – A case report

PurposeThis case report aimed to investigate the effects of supervised home-based resistance training (RT) on functional capacity and mental health on a man with idiopathic peripheral polyneuropathy (PP). MethodA 50-year-old man diagnosed with PP with no previous experience in RT performed 24 session of home-based RT for 12 weeks. Resistance training consisted of 3 exercises performed with 3 sets and lasted approximately 30 min per session. Exercises were performed with minimal implements (e.g., elastic tubes and light dumbbells). The Patient was evaluated for muscle performance, functionality, anxiety levels, and depressive symptoms before and after intervention period. Muscle performance was evaluated though 30-s push up test (PU30), functional capacity was evaluated through functional tests [sit to stand test (SST), arm curl (AC), and 2-min step test (2-MST)] and anxiety levels and depressive symptoms were evaluated through the State-Trait Anxiety Inventory (STAI) and Beck's depression inventory (BDI), respectively. ResultsAfter 12 weeks, the performance on PU30 increased 40% (from 8 to 11 repetitions), while the performance on SST, AC and 2-MST increased 100% (from 4 to 8 repetitions), 44% (from 16 to 23 repetitions) and 157% (from 47 to 121 repetitions), respectively. Anxiety state and trait levels have been reduced 24% (from 42 to 32 scores) and 4% (from 47 to 45 scores), respectively. There was no change for BDI. ConclusionSupervised home-based RT using low cost and affordable equipment was a feasible strategy to provide functional capacity and mental health benefits in a patient with PP.

Mechanics of Biohybrid Valveless Pump-Bot

Abstract Engineering living systems is a rapidly emerging discipline where the functional biohybrid robotics (or “Bio-bots”) are built by integrating of living cells with engineered scaffolds. Inspired by embryonic heart, we presented earlier the first example of a biohybrid valveless pump-bot, an impedance pump, capable of transporting fluids powered by engineered living muscle tissues. The pump consists of a soft tube attached to rigid boundaries at the ends, and a muscle ring that squeezes the tube cyclically at an off-center location. Cyclic contraction results in a net flow through the tube. We observed that muscle force occasionally buckles the tube in a random fashion, i.e., similar muscles do not buckle the tube consistently. In order to explain this anomaly, here we develop an analytical model to predict the deformation and stability of circular elastic tubes subjected to a uniform squeezing force due to a muscle ring (like a taught rubber band). The prediction from the model is validated by comparing with experiments and finite element analysis. The nonlinear model reveals that the circular elastic tube cannot buckle irrespective of muscle force. Buckling state can be reached and sustained by bending and folding the tube before applying the muscle ring. This imperfection may appear during assembly of the pump or from nonuniform thickness of the muscle ring. This study provides design guides for developing advanced biohybrid impedance pumps for diverse applications.

Fully elastic multilayered triboelectric energy harvester made of polymer thin films and elastic tubes

This paper presents a triboelectric energy harvester that can be stacked in multiple layers and fabricated using an elastic hollow tube, polymer film, and conductive tape. Using the compression deformation characteristic of the elastic tube, the proposed device can stably generate high average powers at large displacements and generate energy even at small vibrations, where the two materials are not entirely separated. The proposed device was fabricated by attaching a conductive tape to the film and a self-assembled monolayer coating. Peak-to-peak values of 33.5 V and 11.5 μA were measured when a force of 50 N at 4 Hz was applied to a single-layer device. When the device was pressed by 1 mm in advance, the outputs decreased to 19.2 V and 6.6 μA. A three-layer device exhibited the same open-circuit voltage, whereas the maximum short-circuit current was measured to be 33 μA, approximately three times higher. When the device was operated in the full contact–separation mode, the maximum power was measured to be 837 µW, whereas when a 1 mm preload state was maintained, the measured power was 419 µW.

A distributed lumped parameter model of blood flow with fluid-structure interaction.

A distributed lumped parameter (DLP) model of blood flow was recently developed that can be simulated in minutes while still incorporating complex sources of energy dissipation in blood vessels. The aim of this work was to extend the previous DLP modeling framework to include fluid-structure interactions (DLP-FSI). This was done by using a simple compliance term to calculate pressure that does not increase the simulation complexity of the original DLP models. Verification and validation studies found DLP-FSI simulations had good agreement compared to analytical solutions of the wave equations, experimental measurements of pulsatile flow in elastic tubes, and in vivo MRI measurements of thoracic aortic flow. This new development of DLP-FSI allows for significantly improved computational efficiency of FSI simulations compared to FSI approaches that solve the full 3D conservation of mass and momentum equations while also including the complex sources of energy dissipation occurring in cardiovascular flows that other simplified models neglect.

Small superimposed radial oscillations for a class of damaged limited elastic tubes

Small superimposed radial oscillations for a class of damaged limited elastic, incompressible, isotropic and homogeneous thick-walled circular cylindrical tube are examined. Both the damage function and the considered limited elastic class depend only on the first invariant $$ I_{1} $$ of the left Cauchy–Green deformation tensor. The present work puts some light in the context of the surgical procedure of angioplasty, used especially to treat cardiovascular diseases. Our simplified isotropic assumption allows for a much faster and analytical computation of comparably accurate results. The examples of three limited elastic material models are presented, namely the Arruda–Boyce, Gent, and Demiray. The radial oscillations are further investigated for a damaged limited elastic thin membrane, and the examples above are explored. Universal relations are found for the three material membranes. The obtained results are matched with the clinical data of the existing literature. It appears that the pressure ratio for the virgin and damaged arterial tissue is higher before angioplasty and vice versa. A similar trend for the frequency ratio also follows.

Bifurcation analysis of elastic residually-stressed circular cylindrical tubes

The theory of superimposed incremental elastic deformations is applied to a deformed configuration of a residually-stressed circular cylindrical tube. The tube is subject to internal or external pressure and an axial load that maintain its circular cylindrical shape, and then bifurcations from this shape are analysed. Detailed governing equations and boundary conditions are provided for axisymmetric, prismatic and asymmetric bifurcations for a general form of strain–energy function that incorporates radial and circumferential residual stress components. The theory is applied to a simple model strain–energy function with two material parameters and a parameter that reflects the magnitude of the residual stress. Numerical computations are used to illustrate the dependence of the results of the bifurcation analysis on these parameters and the axial and radial underlying deformation. It is shown that in general the presence of residual stress has a significant effect compared with the corresponding results without residual stress.

Numerical Research on Vibration-Enhanced Heat Transfer of Elastic Scroll Tube Bundle

Based on a new type of elastic scroll tube bundle (ESTB) heat exchanger, the influence of shell-side fluid inlet velocity and tube bundle constraint condition on the enhanced heat transfer performances are researched by a two-way fluid–solid coupling calculation method. Numerical results show that the average heat transfer coefficient (HTC) increases with the shell-side fluid inlet velocity increases when the single group of scroll copper tubes is unconstrained. Within the range of calculated parameters in this paper, the maximum increase of average HTC is 140% under vibration conditions, and the maximum increase of average HTC is 216% under nonvibration conditions. The average HTC decreases as the number of constraints increases under vibration conditions, and the maximum decrease is 42.69%. The average performance evaluation criteria values are greater than 1.00, so the overall heat transfer performance of the ESTB heat exchanger is better.

Effects of Resistance Training With Machines and Elastic Tubes on Functional Capacity and Muscle Strength in Community-Living Older Women: A Randomized Clinical Trial.

The aim of the present study is to compare the effects of 12weeks of resistance training with machines and elastic tubes on functional capacity and muscular strength in older women aged 60 years or over. The participants were randomized into two groups: a machine group (n = 23) and an elastic group (n = 20). They performed 12weeks of progressive resistance training, twice a week, with similar exercises. Outcomes were assessed at three time points: baseline, postintervention, and 8weeks after the end of the training. A significant intragroup effect was demonstrated for both groups at postintervention on functional tests and muscle strength. For the functional reach test and elbow flexion strength (180°/s), only the machine group demonstrated significant intragroup differences. No differences were observed between groups for any outcome. At the 8-week follow-up, functional capacity outcome values were maintained. The muscle strength outcome values decreased to baseline scores, without differences between groups.

Comparison of the Effect of Resistance and Balance Training on Isokinetic Eversion Strength, Dynamic Balance, Hop Test, and Ankle Score in Ankle Sprain.

Ankle sprain is a commonly recurring sports injury. This study aimed to compare the rehabilitation effects of resistance and balance training programs in patients with recurrent ankle sprain. Patients with recurrent lateral ankle sprain completed a home-based rehabilitation program comprising resistance training (RT; n = 27) or balance training (BT; n = 27). RT consisted of exercises using elastic tube bands, and BT consisted mainly of exercises performed using a variety of balance tools. Exercises were performed for 6 weeks, twice a day for 20 min, 5 days per week. Isokinetic eversion strength, Y-Balance test and hop tests, and foot and ankle outcome score (FAOS) were evaluated. Both RT and BT significantly improved strength and dynamic balance (p < 0.05). Compared to RT, BT also significantly improved the outcome of the crossover hop test (p = 0.008). The changes reflected group and time in pain (p = 0.022), sports (p = 0.027), and quality of life (p = 0.033) of FAOS were significantly greater in BT than RT.

A Magnetic Continuum Robot With Multi-Mode Control Using Opposite-Magnetized Magnets

Magnetic field-controlled continuum robots can be steered dexterously within a small dimension. However, their dexterity, generally being restricted to C-shape, is not sufficient for most practical applications, e.g., avoiding obstacles to reach the target region, fixing the tip orientation, or passing through sharp access with the lowest damage to the human body. In this letter, a novel magnetic continuum robot (MCR) with multi-mode control using opposite-magnetized magnets is proposed and studied. A prototype robot containing a pair of opposite-magnetized magnets and a hollow elastic tube was designed and constructed. This simple structure does not hinder the miniaturization of robots. The robot is steered by an external mobile magnet, which can generate an inhomogeneous field to offer a varying magnetic torque and force on opposite-magnetized magnets to help achieve multi-mode deformation. A practical mathematical model, coupling point-dipole field model and energy-based kinematics, is developed to describe its multi-mode deformation with a mean error of 0.72 ± 0.52 mm along the arc length, and a mean tip position error of 1.44 ± 0.74 mm. Experimental results show that the opposite-magnetized magnetic continuum robot has a larger tip reachable workspace and improved dexterity compared to other uniform-magnetized MCRs.

A Dual-Mode Actuator for Soft Robotic Hand

Fluidic and tendon driven actuators are widely applied in soft robotic hand design. Fluidic actuated soft robotic hands are highly compliant and can adapt to various objects. Tendon driven soft robotic hands are easier to control and have high dexterity and large force output, however, they are less compliant than fluidic actuated ones. Most robotic hands are designed with only one actuation method. Combining both actuation methods can tap the advantages and make up each other's limitations but at the expense of more complicated design and control. In this research, we propose a simple dual-mode actuator that provides both fluidic and tendon actuation. The two actuation modes are achieved simultaneously by twisting an elastic tube filled with gas, liquid, or even a combination. The soft robotic finger, designed as a fluidic elastomer actuator (FEA), is actuated by the fluid displaced from tube twisting, as well as by the tendon due to tube contraction in twisting. The tendon drives a compliant metacarpophalangeal (MCP) joint of the finger in order to provide a large bending angle and bending force to finger. Compared to an FEA soft finger, the proposed design can effectively increase the bending angle up to 150% (from 170 degrees to 260 degrees), and the blocking force up to 134% (from 3.2N to 4.3N). A soft robotic hand prototype with dual-mode actuators design is made for various grasping demonstrations.

Pumping Patterns and Work Done During Peristalsis in Finite-Length Elastic Tubes.

Balloon dilation catheters are often used to quantify the physiological state of peristaltic activity in tubular organs and comment on their ability to propel fluid which is important for healthy human function. To fully understand this system's behavior, we analyzed the effect of a solitary peristaltic wave on a fluid-filled elastic tube with closed ends. A reduced order model that predicts the resulting tube wall deformations, flow velocities, and pressure variations is presented. This simplified model is compared with detailed fluid-structure three-dimensional (3D) immersed boundary (IB) simulations of peristaltic pumping in tube walls made of hyperelastic material. The major dynamics observed in the 3D simulations were also displayed by our one-dimensional (1D) model under laminar flow conditions. Using the 1D model, several pumping regimes were investigated and presented in the form of a regime map that summarizes the system's response for a range of physiological conditions. Finally, the amount of work done during a peristaltic event in this configuration was defined and quantified. The variation of elastic energy and work done during pumping was found to have a unique signature for each regime. An extension of the 1D model is applied to enhance patient data collected by the device and find the work done for a typical esophageal peristaltic wave. This detailed characterization of the system's behavior aids in better interpreting the clinical data obtained from dilation catheters. Additionally, the pumping capacity of the esophagus can be quantified for comparative studies between disease groups.

On nonlinear dilatational strain gradient elasticity

We call nonlinear dilatational strain gradient elasticity the theory in which the specific class of dilatational second gradient continua is considered: those whose deformation energy depends, in an objective way, on the gradient of placement and on the gradient of the determinant of the gradient of placement. It is an interesting particular case of complete Toupin–Mindlin nonlinear strain gradient elasticity: indeed, in it, the only second gradient effects are due to the inhomogeneous dilatation state of the considered deformable body. The dilatational second gradient continua are strictly related to other generalized models with scalar (one-dimensional) microstructure as those considered in poroelasticity. They could be also regarded to be the result of a kind of “solidification” of the strain gradient fluids known as Korteweg or Cahn–Hilliard fluids. Using the variational approach we derive, for dilatational second gradient continua the Euler–Lagrange equilibrium conditions in both Lagrangian and Eulerian descriptions. In particular, we show that the considered continua can support contact forces concentrated on edges but also on surface curves in the faces of piecewise orientable contact surfaces. The conditions characterizing the possible externally applicable double forces and curve forces are found and examined in detail. As a result of linearization the case of small deformations is also presented. The peculiarities of the model is illustrated through axial deformations of a thick-walled elastic tube and the propagation of dilatational waves.

Fate of a bulge in an inflated hyperelastic tube: theory and experiment

Mechanical instability in a pre-tensioned finite hyperelastic tube subjected to a slowly increasing internal pressure produces a spatially localized bulge at a critical pressure. This instability is studied in controlled experiments on inflated latex rubber tubes, from the perspective of buckling observed in aneurysms and their rupture risk. The fate of the bulge under continued inflation is governed by the end-conditions and the initial tension in the tube. In a tube with one end fixed and a weight attached to the other freely moving end, the bulge propagates axially at low initial tension, growing in length, and the tube relaxes by extension without buckling. Rupture occurs when the tension is high. By contrast, the bulge formed in an initially stretched tube held fixed at both its ends can buckle or rupture, depending on the amount of initial tension. Experiments are reported for different initial tensions and boundary conditions (BCs). Failure maps in the stretch parameter space and in stretch–tension space are constructed by extending existing theories for bulge formation and buckling analyses to the experimentally relevant BCs. Failure maps deduced from the theory are compared against experiments, and the underlying assumptions are critically assessed. Experiments reveal that buckling provides an alternative route to relieve the stress built up during inflation. Hence, buckling, when it occurs, can be a protective fail-safe mechanism against the rupture of a bulge in an inflated elastic tube.

Research on Heat Transfer Enhancement of Vortex-Induced Vibration of Side-by-Side Double Tubes

The fluid-induced vibration heat transfer enhancement technology has great potential, because it can effectively improve the heat transfer efficiency without consuming additional energy. A reasonable design of the elastic heat exchange tube bundle structure is the key to the engineering application of this technology. In this paper, the effects of flow velocity and the center distance on the characteristics of vortex- induced vibration heat transfer in side-by-side double circular tubes are studied. We demonstrate that, when the center distance is no more than (outer diameter), the interference effect of the flowfield around the two tubes is greater, and the amplitude of the double tube is small. However, with the increase of , the flowfield interference decreases. Within the scope of this paper, two modes of vibration are obtained: in-phase vibration and out-of-phase vibration. When and , the fluid vortex-induced elastic supported side-by-side double circular tubes’ vibration can enhance heat transfer. Especially, when , the heat transfer enhancement effect is the strongest, reaching 14.5%. However, when , the heat transfer enhancement effect is not obvious. The research on the heat transfer characteristics of fluid flowing around the static double tube shows that when the distance is small, the flow velocity around the static tubes is larger, resulting in a higher surface average heat transfer coefficient, and as the distance increases, the heat transfer coefficient decreases.

Effects of aerobic training combined with strength training with elastic resistance on functional capacity of older adults: a controlled randomized clinical trial

The combination of aerobic (AT) and strength (ST) training, i.e., Combined Training (CT) is a strategy used to combat the deleterious effects of aging. However, ST requires specialized equipment and environments that hinder the practice of the elderly population; thus, elastic devices can help in the practice of ST because they are easy to apply. To evaluate the effects of CT on the functional capacity (FC) of older adults after 8 weeks of intervention. Participants were randomly allocated to the combined training group (CTG) or control group (CG). The CTG performed, with 3 weekly sessions, a TA (70–85% of the heart rate reserve) followed by ST with elastic tubes (6 exercises; 2 × 15 repetitions) with load progression through the perception of effort scale, color, and elastic extension. Before and after the intervention, six FC tests and a maximum isometric strength test of the knee extensors were evaluated. Two-way ANOVA was applied, with Bonferroni post hoc, adopting a p < 0.05. Twenty-two older people participated in the study (CTG, 62.91 ± 5.88; CG, 62.70 ± 5.29), of both sexes (CTG, 8/4; CG, 6/4). An improvement of 6.60% was observed in the Timed Up and Go test (p = 0.026), 20.56% in the sit and stand test (p = 0.007), 17.71% in the elbow flexion test (p = 0.026), and 15.64% and 26.94% for the right (p = 0.026) and left knee extensors (p = 0.006), respectively, for the CTG compared to the CG. AT associated with ST with elastic tubes was effective in improving FC and knee extensor muscle strength in older adults. RBR-8FDWTH; retrospectively registered. March 10, 2020.

Investigation of Fluid-Induced Vibration and Heat Transfer of Helical Elastic Coiled Tube

The study of fluid-induced vibration of helical elastic coiled tubes to enhance heat transfer is very important for engineering practice and energy saving. Fluid-induced vibration and enhanced heat transfer of a helical elastic coiled tube heat exchanger were analyzed based on its finite element model, by using a two-way fluid–solid coupling method. Vibration response of the helical elastic coiled tubes, heat transfer coefficient per unit volume, and Nusselt number in vibration and nonvibration were studied at different entrance velocities and winding numbers. The results illustrate that there are a lot of vortexes in the heat exchanger and around the helical elastic coiled tubes. In the range of the entrance velocity , the vibration frequency is constant, whereas the vibration amplitude increases, and the tube vibration enhances the heat transfer of the helical elastic coiled tubes by 0.38%, 0.89%, 1.93%, and 13.65%, respectively. As the winding number increases from 5 to 9, it has a greater effect on the vibration amplitude, and the tube vibration enhances the heat transfer of the helical elastic coiled tubes by 1.93%, 3.39%, and 3.59%, respectively.

A new efficient fourth order collocation scheme for solving Burgers’ equation

In present work a new fourth order modified cubic B-spline (mCB) based upon collocation technique (mCBCT4) has been developed to evaluate new numeric results of the nonlinear Burgers’ equation, appear in rigorous real-world physical phenomena like - sound & shock waves in viscous medium, waves in fluid filled viscous elastic tubes, magneto-hydrodynamic-waves in medium with finite electrical-conductivity, in modeling of turbulent fluid, and in continuous stochastic processes. At first, the Burgers’ equation is remodeled into a set of 1st order ordinary differential equations (ODE), in which fourth order accurate approximation of the unknown functions, and its spatial derivatives obtained via mCBCT4. In this way a set of first-order ODE is obtained, which we solve via SSP-RK(ℓ+1,ℓ) scheme (ℓ=3,4). The accuracy, efficiency and effectiveness of the developed technique mCBCT4 is demonstrated in terms of six different test examples of nonlinear Burgers’ equation by computing the error norms: L2 and L∞ errors. The proposed mCBCT4 scheme is also tested for nonlinear Burger’s equation with very small kinematic viscosities. The proposed mCBCT4 is shown unconditionally stable scheme. The numerical findings demonstrate that the developed mCBCT4 performs better than some recently developed good techniques and enables to produces comparably more accurate solutions than some recently developed reliable techniques.

An experimental investigation to model wheezing in lungs.

A quarter of the world's population experience wheezing. These sounds have been used for diagnosis since the time of the Ebers Papyrus (ca 1500 BC). We know that wheezing is a result of the oscillations of the airways that make up the lung. However, the physical mechanisms for the onset of wheezing remain poorly understood, and we do not have a quantitative model to predict when wheezing occurs. We address these issues in this paper. We model the airways of the lungs by a modified Starling resistor in which airflow is driven through thin, stretched elastic tubes. By completing systematic experiments, we find a generalized ‘tube law’ that describes how the cross-sectional area of the tubes change in response to the transmural pressure difference across them. We find the necessary conditions for the onset of oscillations that represent wheezing and propose a flutter-like instability model for it about a heavily deformed state of the tube. Our findings allow for a predictive tool for wheezing in lungs, which could lead to better diagnosis and treatment of lung diseases.