Elastic Tube Research Articles

Influence of Forced Field on Blood Flow in an Overlapping Stenosed Arterial Section

This article presents the theoretical analysis of the nonlinear behavior of the blood flow through an angled arterial segment with overlapping stenosis. A mathematically created time-variant stenosis emerges from the formation of arterial narrowing brought on by atheroma. An elastic cylindrical tube with a moving wall is used to represent the artery, and the Casson liquid is used to simulate blood that flows through it. The nonlinear elements that arise in the equations, govern blood flow are taken into account. The impact of the pulsatile pressure gradient that caused by the regular heartbeat on the flow process in the stenosed artery is demonstrated mathematically. By employing the boundary conditions, the present analytical technique can easily compute the velocity profiles, wall shear stress, and flow resistivity. To carry out a systematic quantitative study, the desired quantities are numerically computed. The results are graphically presented in the discussion section. They provide an overview of how the degree of stenosis and the malleability of the artery wall influence blood flow abnormalities. The application of the current model is adequately justified by many significant conclusions.

Elasto-inertial rectification of oscillatory flow in an elastic tube

Elasto-inertial rectification of oscillatory flow in an elastic tube

Numerical investigation of the effect of the structure and number of spiral baffles on the vibration and heat transfer coefficient of spiral tubes within spiral tube heat exchangers

In response to the advantages of compactness and high efficiency of spiral elastic tube heat exchanger and its easy-to-vibrate characteristics, this study aims to further improve its heat transfer efficiency by utilizing fluid-induced vibration-enhanced heat transfer technology, so a design scheme of reverse baffle spiral tube heat exchanger (RB-STHE) is proposed to enhance the turbulence characteristics of the shell-side fluid by installing spiral baffles, thus promoting the vibration of the spiral tube. In this study, four new types of the RB-STHE (Model A, B, C, and D) were used as research objects, and the two-way fluid–structure coupling calculation method (using CFX and Transient Structure software) was adopted to systematically investigate the effect of fluid-induced spiral tube vibration on the comprehensive heat transfer coefficient (HTC) of the RB-STHE under different flow velocities and structure schemes, and based on the research data, the objective of no reduction in the comprehensive HTC and savings in the use of materials is taken as the goal, so as to put forward the improved Model C-1. The results show that: although the fluid-induced spiral tube vibration can effectively improve the HTC of the spiral tube, it also increases the pressure drop in the RB-STHE, and the larger the amplitude, the higher the degree of influence; among them, Model C is most affected by the spiral tube vibration, and its HTC and pressure drop are maximally enhanced by 6.33% and 5.85%, respectively. The change in the number of baffles has a significant effect on the comprehensive HTC of the RB-STHE. Compared to the Model D without a spiral baffle, the maximum improvement in the comprehensive HTC of Model C with one spiral baffle installed in the RB-STHE is 14%, while the Model A with four spiral baffles and the Model B with two spiral baffles have a maximum reduction in the comprehensive HTC of 20% and 3%, respectively. In addition, compared to Model C, the structure improved Model C-1 significantly reduces the size of the spiral baffle while effectively maintaining the comprehensive HTC of the RB-STHE, making the structure more reasonable, which provides a reference for heat exchanger design.

Numerical investigation of three-dimensional incompressible fluid flow in curved elastic tube

Numerical investigation of three-dimensional incompressible fluid flow in curved elastic tube

A semi-analytical time-domain model with explicit fluid force expressions for streamwise fluidelastic instability of a single and multiple flexible tube array

Fluidelastic instability (FEI) within steam generator tube arrays poses a significant safety concern for nuclear power plants. Traditionally assumed to manifest in the transverse direction, recent failures at the San Onofre Nuclear Generating Station have underscored the importance of understanding streamwise FEI (SFEI). These incidents have spurred analytical investigations into SFEI, but progress has been hindered by the lack of explicit fluid force formulations, particularly in semi-analytical SFEI models. This paper presents a novel semi-analytical time-domain SFEI model featuring an ideal geometry-based decay function and meticulously derived explicit fluid elastic force expressions. The proposed model supports both frequency-domain stability analysis and true time-domain response analysis, and it is applicable to configurations featuring either a single elastic tube in a rigid array or multiple flexible tubes in an array. Additionally, the tube motion phases are obtained by comparing time-domain responses and employing modified multi-tube frequency-domain SFEI analyses. The stability thresholds predicted for a parallel triangular array using our theoretical model closely align with reported experimental data, thereby validating its accuracy. Our work supplements and advances semi-analytical modeling, alleviating implementation challenges for analyzing SFEI phenomena.

Impact of dilating forcing amplitudes on a peristaltically driven non-Newtonian fluid in an elastic tube: application to swallowing disorders

Abstract We investigate the flow dynamics within an elastic tube transporting a power-law fluid, where the tube is subject to a specified external forcing in the form of a progressive traveling wave. The oesophagus is cylindrical in shape and exhibits linear elastic properties. The flow is creeping, and the long wavelength and low Reynolds number approximations are employed for a solution. The relationship between the pressure distribution within the oesophagus and the radial variation of the tube characterizes the behavior of the tube. Findings reveal that the elasticity and the variations in the applied dilating forcing amplitude substantially impact pressure resulting from sinusoidal wave forcing. Notably, even a nominal increase in the inward radial force amplitude for dilatant fluid results in significant pressure changes compared with Newtonian fluid. We also observe a notable distinction between time-averaged volume flow rate and velocity in pseudo-plastic and dilatant forms. Our study also identifies that the radial velocity experiences either attenuation or enhancement due to the fluid’s shear thickening and thinning characteristics. Moreover, our research uncovers a novel dimension by highlighting that in shifting from pseudo-plasticity to dilatancy, the fluid requires higher pressure to propel the bolus toward the hiatus. This observation has important implications, suggesting that feeding a more dilatant fluid to patients with pre-diagnosed swallowing disorders, such as sliding hiatus hernia, is not advisable, fearing increased pressure.

Controlled swelling-induced shape change of soft gel filled structures

Gels are polymers that can imbibe large amounts of solvent and generate large volumetric deformations in a process commonly termed swelling. The swelling-induced deformations can be harnessed to produce pressure against surrounding elastic elements, and therefore lead to spatial shape changes without the need for an external energy source. In the present paper, we consider a thin cylindrical elastic tube that encapsulates a gel and deforms in response to the swelling-induced forces. It is expected that by controlling the spatial stiffness distribution of the tube, the deformed swelling-induced shape can be programmed. We exploit this simple idea to obtain controlled shape change driven by the large volumetric expansion of gels. To this end, we train a machine learning algorithm through many FE simulations that enable solving the inverse problem: for any prescribed swelling-induced target shape, the algorithm provides the spatial stiffness distribution of the thin tube. The results confirm that precise controlled shape change is achievable by exploiting the large swelling-induced volumetric deformations in an autonomous manner (i.e. without the need for any external energy source). This work paves the way for new perspectives in the design of shape-change systems based on the simple yet proper elastic distribution of confining structures.

Observation of Deformation Process of Elastic Tubes for Pulsatile Flows by Impinging Jet Flows and Its Application to Novel Measurement Method of Blood Pressure

Observation of Deformation Process of Elastic Tubes for Pulsatile Flows by Impinging Jet Flows and Its Application to Novel Measurement Method of Blood Pressure

Hemodynamic characteristics of blood flow in an inclined overlapped stenosed arterial section

This work presents a theoretical analysis of the non-linear behavior of blood flow along an angled arterial section with overlapping stenosis. An elastic cylindrical tube with a moving wall is used to represent the artery, and a Casson liquid is used to simulate blood flowing through it. The nonlinear equations that govern blood flow are taken into account. The influence of the pulsatile pressure gradient caused by the regular heartbeat on the flow process in the stenosed artery is demonstrated mathematically. The current analytical method can compute the wall shear stress, flow resistivity, and velocity profiles with mild stenosis assumption by applying the boundary conditions. Numerical calculations of the desired quantities are carried out systematically. They provide an overview of how the degree of stenosis and the malleability of the artery wall influence blood flow abnormalities. Concerning the height of stenosis, the surface shear stress and the resistivity to flow increase together with an increase in the proclivity angle.

Vibration-Enhanced Heat Transfer Analysis and Improvement of Spiral Elastic Tube Heat Exchanger

Using the fluid–solid coupling approach in fluid-induced vibration studies, the effect of flow-induced vibration on a heat exchanger is investigated. This paper analyzes the impact of flow parameters for shell fluid on heat transfer characteristics enhanced by the vibration of a spiral elastic tube bundle (SETB). Improvement schemes for heat exchangers are also proposed, and they are studied and compared. The results show that there is a positive correlation between the inlet velocity and the heat transfer coefficient of the SETB heat exchanger. As the inlet velocity rises to 0.9 from 0.3 m/s, the Nusselt number of the hollow SETB heat exchanger under vibration conditions is increased by 153.10, 45.55, and 26.73% sequentially. The vibration generated by impacting the elastic element during fluid flow can improve the Nusselt number effectively. As the flow velocity increases to 0.9 from 0.3 m/s, the flow-induced vibration enhances the Nusselt number of the hollow SETB heat exchanger by 2.13, 1.53, 1.05, and 0.89%. When the inlet flow velocity of fluid is in the range of 0.3–0.9 m/s, under the same flow velocity, same pressure drops, and same pumping power conditions, the performance of the improved heat exchanger is greater than that of the SETB heat exchanger before the structural improvement.

Reflection and transmission due to inhomogeneity from an incident wave in a fluid-filled elastic tube

The present paper studies the reflection and transmission of nonlinear waves in an inhomogeneous fluid-filled elastic tube due to an incident wave using the reductive perturbation method. It is found that the numbers and amplitudes of both reflected and transmitted envelope solitary waves due to inhomogeneity depend on the inhomogeneity of the radius, Young’s modulus, thickness, and density of the vessel wall, among other factors. The dependence of the reflection and transmission due to the incident wave on these system parameters is given in the present paper. The results show that the number of the reflected envelope solitary waves is only one or zero, while the number of the transmitted envelope solitary waves may be more than one. The reflection and transmission of an incident nonlinear wave due to inhomogeneity in a fluid-filled elastic tube have potential applications for blood waves in an arteries for both humans and animals.

#1192 Impact of intradialytic exercise on all-cause mortality in frail patients undergoing hemodialysis: a three-year multicenter cohort study

Abstract Background and Aims Frailty prevalence is notably high among older hemodialysis patients, correlating with poorer prognoses. Prior smaller-scale studies have underscored the benefits of various exercise interventions in individuals with Chronic Kidney Disease and those receiving dialysis treatments. Addressing frailty in older hemodialysis patients by exercise therapy is crucial for healthcare professionals aiming to enhance patient outcomes. Despite this, a standardized exercise therapy protocol for this demographic has not been broadly implemented in clinical practice. Our study sought to evaluate the impact of intradialytic resistance exercise programs on the prognosis of frail individuals undergoing hemodialysis. Method This retrospective, multicenter, non-randomized clinical trial encompassed 2006 participants (mean age 70.1±11.7 years) from 17 outpatient clinics within the Kaikoukai Medical Group. Enrollment spanned from April to December 2018, with patients stratified according to baseline frailty levels, determined by the Japanese Frailty Criteria for the Diagnosis of Frailty in the Elderly. In this study, patients meeting the criteria for frailty or pre-frailty, as defined by the Japanese Criteria for Health and Social Services (J-CHS), were collectively classified as 'frail’. Participants were invited to join a voluntary exercise program during dialysis, which included stretching and four types of resistance exercises using elastic tubes. The cohort was divided into four groups based on their frailty status and participation in the exercise program. Patient outcomes were monitored until either death or the study's conclusion in December 2021. Kaplan-Meier and log-rank analyses were utilized to assess prognostic differences among the groups, with significance levels adjusted using the Bonferroni correction. Ethical approval was granted by the Nagoya Kyoritsu Hospital's ethical committee. Results The study comprised 112 non-frail exercising, 398 frail exercising, 205 non-frail non-exercising, and 1287 frail non-exercising patients. Over the study period (median 25 months), mortality was recorded in 338 (16.9%) patients, including 8 (7.1%) non-frail exercising, 50 (12.6%) frail exercising, 16 (7.8%) non-frail non-exercising, and 264 (20.5%) frail non-exercising participants. Prognostic analysis revealed that the frail non-exercising group had a significantly poorer prognosis than both the non-frail exercising and non-frail non-exercising groups, as well as the frail exercising group (p<0.05). Conclusion This investigation is pioneering in establishing a link between intradialytic resistance exercise interventions and prognosis in frail patients. The findings indicate that, although frail patients inherently face a more challenging prognosis, participation in intradialytic exercise can yield substantial improvements. Therefore, clinicians are encouraged to advocate for exercise therapy as a means to enhance prognosis in frail patients undergoing hemodialysis.

#1067 The impact of hemodialysis (HD) versus hemodiafiltration (HDF) on the effect of intradialytic exercise: a multicentre cohort study

Abstract Background and Aims Diminished physical function in HD patients is a critical issue, necessitating strategic approaches to enhance the efficacy of exercise therapy. The differential impacts of HD and HDF on solute clearance, albumin loss, uremic conditions, and malnutrition could influence the success of exercise interventions. Presently, empirical evidence for this is lacking. This investigation explores how HD and HDF modalities influence the efficacy of exercise therapy administered during dialysis sessions. Method This study encompassed intradialytic resistance exercises, involving 414 patients with end-stage renal disease across 10 centers. Participants were voluntarily enlisted in an exercise regimen during their dialysis sessions. The intradialytic regimen comprised stretching and four types of resistance exercises utilizing elastic tubes, conducted thrice weekly over six months. Parameters such as 10-meter walking speed, knee extensor muscle strength, serum albumin levels (Alb), normalized protein catabolic rate (nPCR), and Creatinine Generation Rate (%CGR) were assessed pre-and post-intervention. Statistical analysis included propensity score matching to adjust for baseline characteristics, segregating patients into HD and HDF cohorts. Changes in the aforementioned indicators before and after intervention (Δ) were calculated. Analytical methods included paired t-tests for within-group comparisons and independent t-tests for between-group comparisons of Δ values. A 5% risk threshold was established for statistical significance. Ethical clearance was obtained from the Seirei Christopher University Ethics Committee. Results A propensity score matching yielded 70 matched pairs. There were no significant differences in baseline subject characteristics after propensity score matching. Within-group analyses in the HD group revealed significant improvements in 10-meter walking speed (1.42 ± 0.41→1.60 ± 0.46 m/s, p = 0.000), knee extensor strength (44.3 ± 14.7→49.6 ± 13.8%, p = 0.000), and a reduction in Kt/V (1.69 ± 0.32→1.64 ± 0.32, p = 0.006) after six months. The HDF group significantly enhanced 10-meter walking speed (1.54 ± 0.40→1.72 ± 0.40, p = 0.000), knee extensor muscle strength (51.7 ± 17.1→57.4 ± 17.7%, p = 0.000), nPCR (0.88 ± 0.15→0.94 ± 0.18, p = 0.009), and %CGR (106.3 ± 23.2→112.9 ± 25.2, p = 0.002) (pre to post value, respectively). There are no significant differences in other variables between pre- and post-values in each group. Comparative analysis between groups demonstrated a significantly lower ΔAlb (HD 0.04 ± 0.24 HDF −0.05 ± 0.27, p = 0.045)and a higher 7, p =0(HD 1.47 ± 18.2 HDF 6.65 ± 17.2, p = 0.004)in the HDF group compared to the HD group. Conclusion The study demonstrated a notable HDF group improvement in %CGR, an indicator of muscle mass, despite a decrease in albumin levels. This suggests that albumin loss due to HDF minimally affects the augmentation of physical function. The findings suggest integrating exercise therapy with HDF may positively influence protein consumption and muscle mass enhancement.

#1062 Effect of intradialytic resistance exercise on patient survival: a multicenter non-randomized cohort study

Abstract Background and Aims Intradialytic exercise significantly benefits the physical function of patients undergoing hemodialysis. Prior research into its impact on patient longevity has been constrained by small participant numbers and the lack of a control group. This study investigates the influence of exercise therapy during hemodialysis on patient lifespan in a broad multicenter cohort. Method This forward-looking, multicenter, non-randomized clinical investigation included 17 outpatient clinics from the Kaikoukai Medical Group, recruited between April and December 2018. Participants were voluntarily enlisted in an exercise regimen during their dialysis sessions and segregated into exercising and non-exercising cohorts. The trial was not blinded. The intradialytic regimen comprised stretching and four types of resistance exercises utilizing elastic tubes, conducted thrice weekly. Baseline data encompassing age, gender, stature, baseline weight, duration of hemodialysis treatment, and concurrent diabetic conditions were collected. Additional data regarding hemodialysis, including Kt/V ratio, hemodialysis blood flow rate (QB), dialysate volume (QD), and duration of dialysis, were recorded. Laboratory parameters such as albumin (Alb), calcium (Ca), potassium (K), hemoglobin (Hb), C-reactive protein (CRP), and creatinine (Cr) levels were extracted from medical records. Patient outcomes were monitored until either the occurrence of death or the study's culmination in December 2021. In statistical analyses, missing values were addressed using multiple imputation techniques, and baseline characteristics between groups were compared using an unpaired t-test. Cox proportional hazards regression analysis was employed to examine the relationship between the exercise intervention and survival, adjusting for multiple confounding variables. Three models were constructed for analysis: Model 1 incorporated basic patient data, Model 2 included hemodialysis parameters, and Model 3 involved laboratory data. The study was approved by the Ethical Committee of Nagoya Kyoritsu Hospital. Results The study encompassed 2006 subjects (average age 70.1±0.3 years), with 512 (25.5%) in the exercise group and 1494 (74.5%) in the control group. Initial comparisons indicated that the exercise group had significantly lower average height (160.9±0.3 vs. 159.7±0.4 cm, p=0.03), baseline weight (57.2±0.3 vs. 55.9±0.5 kg, p=0.04), Kt/V ratio (1.59±0 vs. 1.64±0, p=0.01), and QD (494±0.9 vs. 486.8±1.9 ml, p<0.01). Over the median observation period of 25 months, 338 (16.9%) patients, comprising 58 (11.3%) from the exercise group and 280 (18.7%) from the control group, succumbed. Survival analysis revealed a significant association between exercise intervention and mortality reduction, adjusted for confounders in Model 1 (HR 0.6, 95%CI 0.4-0.9, p=0.01), Model 2 (HR 0.55, 95%CI 0.37-0.8, p=0.02), and Model 3 (HR 0.57, 95%CI 0.38-0.87, p=0.01). Conclusion This research is the first to demonstrate a significant association between intradialytic resistance training and improved survival in hemodialysis patients within a multicenter, non-randomized cohort. This relationship remained significant after adjusting for multiple confounding factors, suggesting that incorporating resistance training into standard hemodialysis care could markedly enhance patient survival outcomes.

Study of fluid-elastic instability of the spatially bent tube structure in fast reactor intermediate heat exchanger

This study conducts a numerical simulation investigation on the flow field characteristics and fluid-elastic instability of the spatially bent tube structure in the intermediate heat exchanger (IHX) of a fast reactor. The inherent frequencies of the unique structure of the IHX spatially bent tube are calculated by using the wet modal method. They are employing Computational Fluid Dynamics (CFD) in conjunction with a fluid-structure coupling model, establishing an elastic tube model. Considering the bundle concentric circles arrangement, the “transition” arrangement is selected as the model to simulate the fluid-elastic instability. By the analysis of critical flow velocity, displacement, and the main vibration direction, the results indicate that the fluid-elastic instability of the tube bundle with a transition arrangement is mainly manifested by more severe vibrations in the bent tube segment. The instability flow velocity in the straight tube segment, ranging from 4.64 to 4.84 m/s, is greater than the instability flow velocity of 2.85 m/s in the bent tube segment. This study provides theoretical support for the design and operation of the intermediate heat exchanger in fast reactors, offering references for considering tube bundle arrangement and fluid-elastic instability in engineering practice.

Directed Instability as a Mechanism for Fabricating Multistable Twisting Microstructure

Herein, The study of multistable structures, particularly those that can twist, has attracted significant attention in recent years. This ability to transition between multiple stable geometries of these structures paves the way for advances in diverse applications, such as morphing structures and robot actuation mechanisms. Conventional methods of designing and fabricating these structures often involve complex and resource‐intensive fabrication processes, which restrict their widespread adoption and limit their miniaturization. Here, we present a novel inflatable multistable twisting structure, based on helical folds of an elastic tube. Our fabrication approach utilizes directed mechanical instability as a method for a rapid fabrication, which is readily implemented at various length scales. We developed a theoretical model for the deformation of the bistable helical elements comprising the twisting structure, and compared the theoretical results to the experimental data. Furthermore, we demonstrate our fabrication methodology using a variety of polymers, including medical grade polymers, as well as various inner radii ranging from 5 mm to 44 μm and thicknesses of the tubes’ walls ranging from 250 μm to 19 μm.

Numerical analysis on heat transfer performance of spiral elastic copper tube heat exchanger with helical defectors

Based on the flow-induced vibration mechanism, three kinds of spiral elastic copper tube heat exchangers were proposed to improve the comprehensive heat transfer performance, involving the spiral elastic copper tube heat exchanger with no defector, the spiral elastic copper tube heat exchanger with forward helical deflector and the spiral elastic copper tube heat exchanger with reverse helical deflector. A both-way fluid–structure coupling method was utilized to investigate the effects of helical defectors and their arrangements on the vibration-enhanced heat transfer performance of the spiral elastic copper tubes at different inlet velocities by numerical simulation. The results indicate that: when the inlet velocity ranges from 0.1 m/s to 0.7 m/s, the heat exchanger with reverse helical deflector possesses better heat transfer performance than the other two heat exchangers. For the heat exchangers with no defector and forward helical deflector, the flow-induced vibration always promotes the comprehensive heat transfer performance. Compared with the heat exchanger with no defector, the comprehensive heat transfer performance of the heat exchanger with reverse helical deflector is higher 4.02 % averagely, while that of the heat exchanger with forward helical deflector is lower 29.34 % averagely. Furthermore, a structural optimization is presented to improve the existing disadvantages of the heat exchanger with reverse helical deflector, after structural optimization, the average amplitude of the heat exchanger with forward helical deflector is decreased by 3.26 % averagely and the heat transfer performance is raised to a maximum of 26.24 %, which are of great significance to extend the service life and improve the energy efficiency of heat exchanger.

Numerical study on lead–bismuth cross-flow induced vibration in the elastic tube bundle

The physical properties of liquid lead–bismuth eutectic fluid are quite different from that of water or air. It needs to be verified whether the cross-flow vibration mechanism and the empirical prediction model of fluidelastic instability in conventional media are applicable to lead–bismuth. In this work, for an in-line elastic tube bundle with pitch ratio P/D = 1.5, the flow excitation of lead–bismuth at 200 °C is studied and compared with that of water in uncoupled flow field. Then, two cases of lead–bismuth flow-induced vibration with different mass-damping parameters are simulated and studied by fully coupled numerical simulation considering fluid viscous damping. The tube bundle experiences the process from turbulence-induced vibration in low flow velocity to fluidelastic instability in high velocity. The results of flow excitation show that the pressure coefficient distribution of the front row tube in lead–bismuth is basically consistent with that in water, while the inconsistency of the pressure coefficient distribution for the back row tube is caused by the bi-stable deflective flow. The results of lead–bismuth flow-induced vibration show that, in fluidelastic instability, the vibration of tube bundle and the vortex shed from tube bundle are dominated by the frequency close to the first wet modal frequency of tube bundle. The different deflective directions of lead–bismuth and water, caused by bi-stable characters, have less effect on the onset of fluidelastic instability. The instability points of lead–bismuth agree with the experimental results of other media and the Connors prediction model considering fluid viscous damping. The prediction model is suggested to predict the onset of fluidelastic instability induced by lead–bismuth cross-flow in the tube bundle.

The large strain snap-through effect in free torsion of highly elastic soft thin-walled tubes with exact closed-form solutions

It is found for the first time that, as the applied torque attains a critical value, a freely twisted highly elastic tube may jump from one to another state over large strain range. Unlike usual approximate buckling analyses of thin shell structures with Hooke’s law for small strain, such large strain snap-through effect needs to be studied with a large strain model that can accurately simulate nonlinear elastic behaviors of soft materials. As such, nonlinear coupling issues have to be treated both in large strain kinematics and in hyper-elastic constitutive formulation.It appears that exact results would be rare even for buckling analyses with small strain but large deflections. Here, the above coupling issues are treated with a novel and decoupled approach. To this end, explicit and decoupled forms of the dual potentials for hyper-elastic stress–strain and strain–stress relationships are constructed with well-designed invariants of the Hencky strain and the deviatoric Cauchy stress and, hence, multiple data sets from benchmark tests are accurately matched with these forms in a decoupled sense. It is then shown that the nonlinear coupling equations for large torsion of elastic thin tubes can be worked out to produce exact closed-form solutions for the average radius ratio, the axial length ratio and the thickness ratio as well as the applied torque. With these solutions, the large strain snap-through effect is disclosed with an explicit criterion. Furthermore, numerical examples are provided with comparison to test data and, in particular, the large torsion response features with the snap-through effect are discussed with reference to possible correlations to certain symptoms in vascular abnormalities of blood vessels, etc.

Analysis of modulational instability of waves in the fluid-filled elastic tube

In this paper, we investigate the modulational instability of waves within a fluid-filled elastic tube considering the fluid viscosity. Through the reductive perturbation method, we derived a modified Nonlinear Schrödinger Equation (NLSE) with damping term for the system. Based on the modified NLSE, we found that modulational instability exists in this system though the fluid viscosity is considered. Both the instability and the stability region are given. Furthermore, the growth rate of the instability is obtained. The dependence of the growth rate on the system parameters such as perturbation wave length, the background wave length, the viscosity of the fluid and the elasticity of the tube is given in the present paper. It indicates that the fluid viscosity refrain the modulational instability. The results may be used to predict the production of the rogue wave in this system, as well as to the other similar system.