Strut Profile Research Articles

In-Situ visual reconstruction of strut profiles in pulsed wire arc additive manufacturing of lattice structures

In-Situ visual reconstruction of strut profiles in pulsed wire arc additive manufacturing of lattice structures

Numerical Optimisation of Excavation Pit Design Using Finite Element Analyses

The present study focusses on optimising a single supported excavation pit to achieve a more economical design using finite element analyses. Two methods for automating the derivation of the excavation pit’s necessary embedment depth are presented, which involve either embedment depth reduction using additional calculation phases or adapting the entire model with renewed discretisation. The bending moments as well as the earth pressure distribution along the wall show good agreement, indicating that both methods are suitable for application. Subsequently, the feasibility of using optimisation algorithms (Particle Swarm Optimisation and Differential Evolution) for dimensioning the single supported excavation pit regarding stress analysis of the wall is investigated. Therefore, the embedment depth and the position of the strut are varied for five different sheet pile walls and three different strut profiles. The results demonstrate that both algorithms perform well, particularly with a higher number of calculation steps. After varying iteration steps and population size, the Differential Evolution approach shows better performance compared to Particle Swarm Optimisation by means of finding the optimal solution after a lower number of computational steps.

Effect of different strut design on the mixing performance of H2 fueled two-strut based scramjet combustor

Strut fuel injection approach significantly influences the combustion mechanism inside the scramjet engines. To address this issue, researchers are nowadays mainly focused on a scramjet model with two struts. As the performance of the two-strut model is improved as compared to the original single-strut model as per the latest research findings, therefore the current research is focused on the impact of the different shapes of the two-strut on the combustion flow-field study of scramjet engines. Initially, experimental data from the already-published literature for a single strut is used to validate the implemented simulation techniques. Then, to investigate the combustion performance, different shapes of the two-strut are included in the already-existing DLR scramjet combustor. The SST k-ω turbulence model and steady RANS equations are used to carry out the numerical simulation. The semi-circular trailing edge half-wedge strut, with a combustion efficiency of roughly 92%, is the most effective strut configuration obtained in the current study. The findings also revealed that the semi-circular trailing edge half-wedge strut profile attains a stronger as well as a wider wake region, ensuring better combustion performance, and indicating that the two-strut model can be used as an efficient flame holder in subsequent works. Next, an analysis of how various inward fuel injection angles affect the performance of the optimum strut shape in terms of mixing efficiency and total pressure loss is provided. According to the study, an increase in the inward fuel injection angle significantly improves the mixing performance of the two-strut scramjet combustor. Additionally, the mixing and total pressure loss profiles reveal that the geometry with a 60° strut injection angle achieves early complete mixing within 0.145 m at the cost of only a slight increase in total pressure loss, and this outcome may lead to the development of a short-length supersonic combustor to minimize the drag forces and heat generation. Last but not the least, the optimal inward fuel injection angle (60°) of the two-strut and its effects on mixing performance under different freestream conditions are investigated, illustrating that mixing efficiency decreases with increasing Mach number in the same manner as single strut geometry.

Recommendation for strut designs of vertical axis wind turbines: Effects of strut profiles and connecting configurations on the aerodynamic performance

The strut is a necessary support structure that connects the vertical axis wind turbine blade to the rotating shaft and transfers the torque, and is one of the key factors affecting the aerodynamic performance of the wind turbine. However, research on struts is limited and the appropriate strut design remain uncertain. Therefore, in this paper, the struts of a straight-bladed vertical axis wind turbine are investigated by a three-dimensional computational fluid dynamics approach, to find the appropriate strut design parameters that minimize the impact on the aerodynamic performance. Thirty strut profiles with different chord lengths, thicknesses, areas, and streamlined shapes were parametrically created and analyzed, including a novel strut-specific profile proposed in this paper. Furthermore, all strut connecting parameters, such as spanwise and chordwise positions, connecting angle and fairing were investigated. The results show that the power loss of a vertical axis wind turbine has a relatively linear relationship with the dimensionless absolute thickness of the strut within a certain range. The strut chord length is another important influencing factor. Equal chord lengths of the strut and the blade should be avoided as much as possible. The proposed novel olivary strut profile has lower drag characteristics and more favorable geometrical structural properties compared to the most used NACA airfoil. The influence of the spanwise connecting position (within the range around the blade quarter span) is minor. But the chordwise position has a significant effect, and special attention should be paid to avoid the strut maximum thickness position connecting with the blade aerodynamic center, which will result in the greatest performance degradation. Analysis of the connecting angles shows that inclined struts are suitable for small wind turbines. The fairing is effective when the strut chord length is equal to or longer than the blade chord length. With these results, a set of recommended design parameters for vertical axis wind turbine struts is presented.

Effect of strut profile, angled injection, and blunting of leading edge on mixing of supersonic hydrogen-air streams

Mixing fuel and air in a scramjet combustor is one of the key challenges in its development due to the short residence time available. Strut based injection is considered a viable alternative and is widely investigated. In the present work, the effect of the strut profile, angled injection of fuel, and the blunting of the leading edge of the strut on the mixing of fuel and air is studied using the Finite Volume Method (FVM). The base case chosen is an experiment with Hydrogen fuel injection from a strut at Mach 2.3 in a supersonic air stream of Mach 2. The popular strut profiles of diamond and wedge shapes are considered. The mixing due to wedge strut with dual injection from the trailing face and the effect of the inclination angle of the two fuels is studied. It is observed that the wedge strut with single fuel injection results in the highest mixing efficiency. Compared to the diamond strut, the distance to reach the complete mixing of fuel and air is reduced by 100 mm for the wedge strut with single injection. The high thermal load on the leading edge of the strut requires blunting (and rounding) for heat removal, and its effect is also investigated. The blunting of the leading edge of the strut leads to a decrease in mixing efficiency and an increase in total pressure loss as well as rise in entropy compared to a strut with pointed leading edge. Blunted wedge strut with single injection requires 40 mm more length for complete mixing than wedge strut with pointed leading edge. Also, after blunting, its rounding increases the mixing efficiency slightly but reduces the total pressure loss and entropy rise noticeably.

The impact of strut profile geometry and malapposition on the haemodynamics and drug-transport behaviour of arteries treated with drug-eluting stents

Purpose Stent malapposition is one of the most significant precursors of stent thrombosis and restenosis. Adverse haemodynamics may play a key role in establishing these diseases, although numerical studies have used idealised drug transport models to show that drug transport from malapposed drug-eluting stent struts can be significant. This paper aims to study whether drug transport from malapposed struts is truly significant. Another aim is to see whether a streamlined strut profile geometry – with a 61% smaller coating but a 32% greater coating-tissue contact area – can mitigate the adverse haemodynamics associated with stent malapposition while enhancing drug uptake. Design/methodology/approach Two- and three-dimensional computational fluid dynamics simulations were used in this study. Unlike past simulations of malapposed drug-eluting stent struts, a qualitatively validated drug-transport model which simulates the non-uniform depletion of drug within the drug coating was implemented. Findings It was shown that even a 10-µm gap between the strut and tissue dramatically reduces drug uptake after 24 h of simulated drug transport. Furthermore, the streamlined strut profile was shown to minimise the adverse haemodynamics of malapposed and well-apposed stent struts alike and enhance drug uptake. Originality/value Unlike prior numerical studies of malapposed stent struts, which did not model the depletion of drug in the drug coating, it was found that stent malapposition yields negligible drug uptake. The proposed semicircular-profiled strut was also shown to be advantageous from a haemodynamic and drug transport perspective.

Non-Invasive Treatment for Coronary In-Stent Restenosis via Wireless Revascularization With Nitinol Active Stent.

This paper reports a novel shape memory alloy (SMA) nitinol type active stent for non-invasive restenosis treatment, which operates using a radiofrequency (RF) electro-thermo-mechanical actuation technique for wireless revascularization. The developed stent is equipped with a capacitive pressure sensor for in-artery blood pressure measurement and can provide multiple expansion to restore the blood pressure flow. The device design, working principle, fabrication, and characterization of the nitinol active stent are reported in this work. The wireless monitoring feature is achieved via peak shifting in the reflection coefficient of the S11 parameter. The active stent with initial diameter and resonant frequency of 2 mm and 315 MHz, respectively, is expanded uniformly in stages up to 4.2 mm in diameter when excited with an RF power of ∼30 W for 320 s. The active stent is delivered and deployed ex vivo inside the left coronary artery of a cervine heart. The stented cervine heart before and after wireless actuation is inspected via penetration of X-rays. Endoscopic images reveal the expansion of the stent strut profile within the lumen of the stented artery. The active stent expands in stages up to 3.7 mm in diameter to scaffold the cervine coronary artery after excited with an RF power of 46.7 W. The achievable wireless revascularization capability eradicates the necessity of reintervention and repeat stenting procedure, whereas real-time wireless monitoring provides rapid indication of in-artery re-narrowing occurrence.

Effects of struts profiles and skewed angles on the aerodynamic performance of gas turbine exhaust diffuser

The strut structure directly affects the flow field characteristics and aerodynamic performance of the gas turbine exhaust diffuser. The effects of the strut profiles and strut skewed angles on the aerodynamic performance of the exhaust diffuser at different inlet pre-swirls were numerically investigated using three-dimensional Reynolds-Averaged Navier-Stokes(RANS) and Realizable k-ε turbulence model. The numerical static pressure recovery coefficient of the exhaust diffuser is in agreement with the experimental data well. The reliability of the numerical method for the exhaust diffuser performance analysis was demonstrated. Exhaust diffusers with four kinds of vertical strut profiles obtain the highest static pressure recovery coefficient at the inlet pre-swirl of 0.35. The similar static pressure recovery coefficient of exhaust diffusers with four kinds of vertical strut airfoils are observed when the inlet pre-swirl is less than 0.48. The static pressure recovery coefficient of exhaust diffusers with vertical b1 and b2 struts are higher than that with the a1 and a2 struts when the inlet pre-swirl is greater than 0.48. At the inlet pre-swirl of 0.35, The static pressure recovery coefficient of the exhaust diffuser with the a1 strut decreases with the increasing of the strut skewed angles. The static pressure recovery coefficient of the exhaust diffuser with the b1 strut increases with the increasing of the strut skewed angles, and the static pressure recovery coefficient increases by 3.6% compared with the vertical design when the skewed angle of b1 strut is 40[Formula: see text]. At the inlet pre-swirl of 0.64. The static pressure recovery coefficient of the exhaust diffuser with the a1 strut increases by 8.7% compared with the vertical design when the skewed angle of a1 strut is greater than 20°. In addition, the static pressure recovery coefficient of the exhaust diffuser with the b1 strut decreases by 3.8% compared with the vertical design when the skewed angle of b1 strut is 40°. The method to improve the aerodynamic performance of the exhaust diffuser by appropriate increase the strut maximum thickness and design the strut skewed angle is proposed in this work.

Chiral constrained stent: Effect of structural design on the mechanical and intravascular stent deployment performances

The high mortality of atherosclerosis-caused cardiovascular disease has promoted the requirement of designing novel intravascular stents with comprehensive robust mechanical performances, which is critical for re-constructing the blocked artery and recovering the biomechanical functions of artery vessels during vascular interventional therapy procedures. In this study, a chiral constrained structure with zero/negative Poisson's ratio and robust expansion transformation ability is proposed through combining the axial constraint effect of tetrachiral element and the good stretchability of oscillating wave element along circumferential direction. Afterwards, through applying the theoretical prediction, experimental tests and finite element analysis, the mechanical properties and stenting performances of the chiral constrained structure are explored. The modified tetrachiral topology shows strong orthotropic after integration of oscillating wave strut profile, indicating its capability of handling radial loads without great longitudinal recoil (foreshortening). Finally, stent deployment performances have been evaluated through a highly nonlinear coupling analysis of the stenosed vessels system, in terms of transformation characteristics, dogboning, radial recoil, foreshortening, and plaque prolapse ratio, etc. Especially, remarkable non-conventional performances of anti-dogboning and anti-foreshortening are identified in chiral constrained stent. Synthetically index is generated to compensate the competing behaviors among the above terms, and to improve the comprehensive mechanical performances of chiral constrained stent. These results show the potential in generating a new family of the intravascular stent with chiral mechanical metamaterials and provide a promising clinical application in curing atherosclerosis.

Numerical investigation on implication of strut profile on combustion characteristics in a cavity based scramjet combustor

The present study deals with the implication of a strut profile on the combustion characteristics of a cavity-based scramjet combustor. Three different strut profiles namely, triangular, wedge and diamond-shaped are considered. Moreover, the investigations are carried out to know the interplay of inlet temperature and strut profile on combustion efficiency. Our study reveals that the strut profiles largely affect the flow of physics as indicated by the size of the recirculation region. Further, the strong and multiple reflections of a shock are observed in the case of a diamond-shaped strut. Also, the size of recirculation zone and the penetration height are found to be the largest when the diamond strut is used. Overall, the combustion performance is found to be optimal for diamond-shaped strut among all the configurations of the strut considered. The study on the combined influence of strut profile in conjunction with inlet temperature shows that the combustion efficiency is a strong function of the geometrical configuration of a strut. It is observed that the combustion efficiency is found to increase with the increase in inlet temperature in the case of a diamond strut.

Numerical investigation on influence of diamond shaped strut on the performance of a scramjet combustor

The present work discusses the influence of diamond shaped strut profile on combustion characteristics of a supersonic combustor. The 2D DLR scramjet model was used to investigate the effects of parametric variables which include Mach number, wall pressure ratio and inlet temperatures respectively. Further, interaction between shock-shock, shock-shear layer, and shock-near wall boundary layer is also discussed. It has been observed that the fluid flow behind the strut is oscillating while the primary and secondary recirculation region is present along the centre line of the strut. The study reveals that the optimal size of recirculation region is found at Mach number 2.5 which results into stable combustion. It is observed that the combustion efficiency starts to increase at the trailing edge of the strut due to the strong interaction of shock and the performance of a scramjet combustor is found to deteriorate at very high temperatures and very low Mach number. An optimal combustion efficiency equal to 80% has been obtained at Mach = 2.5, T = 696 K and Pj/P∞ = 0.8 corresponding to minimum pressure loss.

Hemodynamic analysis of a novel bioresorbable scaffold in porcine coronary artery model.

The shear stress distribution assessment can provide useful insights for the hemodynamic performance of the implanted stent/scaffold. Our aim was to investigate the effect of a novel bioresorbable scaffold, Mirage on local hemodynamics in animal models. The main epicardial coronary arteries of 7 healthy mini-pigs were implanted with 11 Mirage Microfiber sirolimus-eluting Bioresorbable Scaffolds (MMSES). Optical coherence tomography (OCT) was performed post scaffold implantation and the obtained images were fused with angiographic data to reconstruct the coronary artery anatomy. Blood flow simulation was performed and Endothelial Shear Stress(ESS) distribution was estimated for each of the 11 scaffolds. ESS data were extracted in each circumferential 5-degree subunit of each cross-section in the scaffolded segment. The generalized linear mixed-effect analysis was implemented for the comparison of ESS in two scaffold groups; 150-µm strut thickness MMSES and 125-µm strut thickness MMSES. ESS was significantly higher in MMSES (150 µm) [0.85(0.49-1.40) Pa], compared to MMSES (125 µm) [0.68(0.35-1.18) Pa]. Both MMSES (150 µm) and MMSES (125 µm) revealed low recirculation zone percentages per luminal surface area [3.17% ± 1.97% in MMSES (150 µm), 2.71% ± 1.32% in MMSES (125 µm)]. Thinner strut Mirage scaffolds induced lower shear stress due to the small size vessels treated as compared to the thick strut version of the Mirage which was implanted in relatively bigger size vessels. Vessel size should be taken into account in planning BRS implantation. Small vessels may not get benefit from BRS implantation even with a streamlined strut profile. This pilot study warrants comparative assessment with commercially available bioresorbable scaffolds.

Mechanical behavior of polymer-based vs. metallic-based bioresorbable stents.

Bioresorbable scaffolds (BRS) were developed to overcome the drawbacks of current metallic drug-eluting stents (DES), such as late in-stent restenosis and caging of the vessel permanently. The concept of the BRS is to provide transient support to the vessel during healing before being degraded and resorbed by the body, freeing the vessel and restoring vasomotion. The mechanical properties of the BRS are influenced by the choice of the material and processing methods. Due to insufficient radial strength of the bioresorbable material, BRS often required large strut profile as compared to conventional metallic DES. Having thick struts will in turn affect the deliverability of the device and may cause flow disturbance, thereby increasing the incidence of acute thrombotic events. Currently, the bioresorbable poly-l-lactic acid (PLLA) polymer and magnesium (Mg) alloys are being investigated as materials in BRS technologies. The bioresorption process, mechanical properties, in vitro observations and clinical outcomes of PLLA-based and Mg-based BRS will be examined in this review.

Multi-objective optimization of nitinol stent design

Nitinol stents continuously experience loadings due to pulsatile pressure, thus a given stent design should possess an adequate fatigue strength and, at the same time, it should guarantee a sufficient vessel scaffolding. The present study proposes an optimization framework aiming at increasing the fatigue life reducing the maximum strut strain along the structure through a local modification of the strut profile.The adopted computational framework relies on nonlinear structural finite element analysis combined with a Multi Objective Genetic Algorithm, based on Kriging response surfaces. In particular, such an approach is used to investigate the design optimization of planar stent cell.The results of the strut profile optimization confirm the key role of a tapered strut design to enhance the stent fatigue strength, suggesting that it is possible to achieve a marked improvement of both the fatigue safety factor and the scaffolding capability simultaneously. The present study underlines the value of advanced engineering tools to optimize the design of medical devices.

Comparison of Radial and Femoral Access for Coronary Angiography Within South Australian Public Cardiac Catheterisation Facilities

analysed using the Ilumein offline review station (St Jude Medical) at 1mm intervals throughout the OCT pullback. Struts were classified as embedded, protruding or malapposed by measuring the distance from the endoluminal strut surface to the intimal wall using standard definitions. Results: A total of 12,853 struts were analysed in 60 patients. No significant difference in baseline charcterstics betweengroups. Therewere 83.3%males (n= 50)with a mean age of 61.86± 10.88, 25% of patients were diabetic. The Promus (n= 13) and Xience (n= 15) stents (each 90 m) contained similar rates of embedded struts, 45% and 57.8%, respectively. The thicker Cypher stent 160 m (n= 15) and BioMatrix 130 m (n= 17) stents had a total of 37.5% and 30.94% embeddedstruts, respectively.Cypher stentshad themost malapposition 10.7% compared with the thinner stents. Conclusion: Stent protrusion is more frequent in stents with thicker strut profiles compared with the thinner stents which are more embedded. How this translates to clinical outcomes remains to be seen. http://dx.doi.org/10.1016/j.hlc.2013.05.313

3D image analysis and stochastic modelling of open foams

AbstractWe present methods for the geometric characterisation and stochastic modelling of open foams based on tomographic 3D image data. In the first step, geometric characteristics of the foam microstructure are estimated from the image. Using these characteristics, a random tessellation model is fitted to the cell system of the foam. The edges of this tessellation then serve as a skeleton for the foam's strut system. The focus of the paper is on the correct simulation of the foam's locally varying strut thickness in the model. For this purpose, the local strut thickness and the strut profiles are estimated from the image and reproduced in the model using locally adaptable morphology.

Evaluation of the effect of stent strut profile on shear stress distribution using statistical moments

BackgroundIn-stent restenosis rates have been closely linked to the wall shear stress distribution within a stented arterial segment, which in turn is a function of stent design. Unfortunately, evaluation of hemodynamic performance can only be evaluated with long term clinical trials. In this work we introduce a set of metrics, based on statistical moments, that can be used to evaluate the hemodynamic performance of a stent in a standardized way. They are presented in the context of a 2D flow study, which analyzes the impact of different strut profiles on the wall shear stress distribution for stented coronary arteries.ResultsIt was shown that the proposed metrics have the ability to evaluate hemodynamic performance quantitatively and compare it to a common standard. In the context of the simulations presented here, they show that stent's strut profile significantly affect the shear stress distribution along the arterial wall. They also demonstrates that more streamlined profiles exhibit better hemodynamic performance than the standard square and circular profiles. The proposed metrics can be used to compare results from different research groups, and provide an improved method of quantifying hemodynamic performance in comparison to traditional techniques.ConclusionThe strut shape found in the latest generations of stents are commonly dictated by manufacturing limitations. This research shows, however, that strut design can play a fundamental role in the improvement of the hemodynamic performance of stents. Present results show that up to 96% of the area between struts is exposed to wall shear stress levels above the critical value for the onset of restenosis when a tear-drop strut profile is used, while the analogous value for a square profile is 19.4%. The conclusions drawn from the non-dimensional metrics introduced in this work show good agreement with an ordinary analysis of the wall shear stress distribution based on the overall area exposed to critically low wall shear stress levels. The proposed metrics are able to predict, as expected, that more streamlined profiles perform better hemodynamically. These metrics integrate the entire morphology of the shear stress distribution and as a result are more robust than the traditional approach, which only compares the relative value of the local wall shear stress with a critical value of 0.5 Pa. In the future, these metrics could be employed to compare, in a standardized way, the hemodynamic performance of different stent designs.

首振り型推進器を有する船の針路安定性改善

Using a ship model with azimuthing propellers (PODs) which are arranged in parallel at stern part, captive model tests were carried out to investigate the effect of POD strut profile area and the effect of stern fins on the hydrodynamic force characteristics related to ship maneuvering. The subject ship was unstable for course keeping.With increasing the strut area, ship control forces due to POD steering increase and the course stability of the ship was improved. Thus, the strut area is important for the performances of both ship control force and course stability.Stern fins were also useful for improving the course stability. However, effective control forces were reduced about 15% by attaching the stern fins. This is due to decrease of additional lateral force component acting on the hull induced by POD steering. Improvement of the course stability of the subject ship was insufficient by enlarging the strut profile area and attaching the stern fins. Further investigations are needed.

Analysis of wall shear stress in stented coronary artery using 3D computational fluid dynamics modeling

In this study, an investigation on the effects of stent geometry on blood flow in a stented human coronary artery 2D and 3D computational fluid dynamics (CFD) models with different stent geometries is reported. Blood velocity profiles and shear stress values were computed in three different sites, including stented arterial segment, pre-stent, and post-stent regions. Blood flow was assumed as a fully developed incompressible Newtonian flow. Rigid boundary conditions were assumed for all models. The governing Navier–Stokes equations were solved using commercial software. The arterial wall shear stress distribution was investigated in three major regions and critical sites were located. It is concluded that shear stress is influenced by three stent design parameters, i.e., strut spacing, strut profile, and number of struts. To achieve the most secure shear stress value, the optimum stent geometry can be obtained with respect to the mentioned parameters for a specific arterial segment. Different stents may be used for different arteries and arterial branches due to the dependency of the shear stress value to the geometry of the artery. It is shown that analyses of wall shear stress profile between stent struts, and in pre-stent and post-stent regions are essential in stent design. Additionally, it is shown that by application of a flow divider, the wall shear stress in stented segment increases markedly.

Initial and Mid-Term Results of a 4F Compatible Self-Expanding Low Strut Profile Nitinol Stent in the Superficial Femoral Artery

To evaluate the initial and mid-term results of a new self-expanding low strut profile nitinol stent for treatment of atherosclerotic lesions stenoses and occlusions in the superficial femoral artery (SFA). In 8 patients (4 male, 4 female, mean age 74.8 +/- 8.8 years) with SFA lesions and non-satisfying results after PTA treatment alone, 10 self-expanding nitinol Xpert stents were deployed via a 4 F sheath. Stent characteristics and handling were graded by the interventionalist. Fontaine classification, duplex flow measurements and ankle brachial index (ABI) at rest and stress were taken prior and one day after stent placement. Patients were followed 3, 6 and 12 months after the procedure obtaining the same parameters at each appointment. Initial stent treatment was successful in all patients. Stent handling and positioning were rated very good and safe. All patients improved clinically by at least one Fontaine stage (range before treatment: stage IIb to IV). The mean ABI at rest (stress) improved initially from 0.68 (0.70) to 1.07 (0.99). During a mean follow-up period of 8.3 months no case of clinically relevant in-stent stenosis was observed with stable values of ABI at rest and stress. Treatment of SFA lesions using the 4F-compatible self-expanding nitinol Xpert stent is technically simple, safe and shows good initial and mid-term results.