Strut Position Research Articles

A comparison of suprarenal and infrarenal fixation and renal volumetric analysis after endovascular aneurysm repair

ObjectiveClinical and experimental studies of the stent-graft fixation impact on the renal volume after endovascular abdominal aortic aneurysm repair have focused on glomerular filtration rate, and the results were controversial. The aim of this study was to analyze and compare the impact of the suprarenal (SRF group) and infrarenal (IRF group) stent-graft fixation on the renal volume. MethodsBetween December 2016 and December 2019, all patients treated with endovascular aneurysm repair were retrospectively analyzed. Patients with atrophic or multicystic kidney, renal transplantation, ultrasound examination, or incomplete follow-up were excluded. The renal volume in both groups was extracted with a semiautomatic segmentation from contrast-enhanced computed tomography scan performed before the procedure, at 1 month, and at 12 months of follow-up. A subgroup analysis of the SRF group was performed in order to study the impact of the stent strut position relative to the renal arteries. ResultsA total of 63 patients were analyzed (SRF: 32 and IRF: 31). Demographic and anatomic characteristics were similar between the groups. The procedure contrast volume was higher in the IRF group (P = .01). At 12 months, we observed a decrease in the renal volume of 1.4% in the SRF group and 2.3% in the IRF group (P = .86). The SRF subgroup analysis showed only two patients with no stent struts crossing the renal arteries. In the remaining cases, struts crossed one renal artery in 60% of cases (19 patients) and two renal arteries in 34% of cases (11 patients). The renal volume decrease was not correlated with the presence of stent wire struts, crossing a renal artery. ConclusionsStent graft with suprarenal fixation seems not to be correlated with renal volume deterioration. A randomized clinical trial with a higher effective and longer follow-up is needed to assess the impact of SRF on renal function.

Mechanical Properties of AISI 316L Lattice Structures via Laser Powder Bed Fusion as a Function of Unit Cell Features.

The growth of additive manufacturing processes has enabled the production of complex and smart structures. These fabrication techniques have led research efforts to focus on the application of cellular materials, which are known for their thermal and mechanical benefits. Herein, we studied the mechanical behavior of stainless-steel (AISI 316L) lattice structures both experimentally and computationally. The lattice architectures were body-centered cubic, hexagonal vertex centroid, and tetrahedron in two cell sizes and at two different rotation angles. A preliminary computational study assessed the deformation behavior of porous cylindrical samples under compression. After the simulation results, selected samples were manufactured via laser powder bed fusion. The results showed the effects of the pore architecture, unit cell size, and orientation on the reduction in the mechanical properties. The relative densities between 23% and 69% showed a decrease in the bulk material stiffness up to 93%. Furthermore, the different rotation angles resulted in a similar porosity level but different stiffnesses. The simulation analysis and experimental results indicate that the variation in the strut position with respect to the force affected the deformation mechanism. The tetrahedron unit cell showed the smallest variation in the elastic modulus and off-axis displacements due to the cell orientation. This study collected computational and experimental data for tuning the mechanical properties of lattice structures by changing the geometry, size, and orientation of the unit cell.

Influence of Position of Intake Struts on Unsteady Load and Vibration of First-Stage Rotor

To investigate the influence law and mechanism of the relative circumferential position of intake struts on the unsteady load and vibration of the first stage rotor, the first 1.5-stage of a heavy-duty gas turbine compressor with intake struts was numerically simulated. The analysis of the flow field and vibration of the rotor blade reveals that the circumferential position of intake struts has little effect on aerodynamic performance but obviously changes the unsteady load and vibration level of the rotor blade. When strut and inlet guide vane wakes coincide, they are strengthened, resulting in the overall enhancement of the unsteady load and vibration on the rotor blade. The circumferential position of struts changes the combined effect of strut wakes and the first stage stator potential flow on the rotor blade, which has an obvious influence on the unsteady load and vibration in the middle chord length but has little influence on the unsteady load near the leading and trailing edges. Research results provide reference and guidance for the installation of struts.

A rectangular strut on the expansion ramp of a scramjet thruster for thrust vector control

Cold flow experiments were conducted on a laboratory model of a scramjet thruster consisting of a rectangular strut spanning the width of the expansion ramp of the model. The cross section of the strut was square. The strut was placed at halfway of the ramp length. The experiments were conducted at six different thruster pressure ratios (TPR) i.e., the ratio of inlet total pressure to ambient pressureranging from 5 to 10 at each of six strut heights. The internal wall pressure distributions of the thruster and schlieren images of the flow obtained from experiments were examined. The possibility of using the strut as a supplementary device in the thruster for the control of a hypersonic vehicle which normally employs aerodynamic control was studied. The inlet Mach number of the combustor was 1.8. The thruster model consisted of an isolator, a diverging area combustor and a single expansion ramp. The inlet flow to the thruster was provided by a supersonic nozzle with a rectangular exit of matching dimensions to the rectangular isolator. The diverging combustor was of rectangular cross section, the bottom wall being flat and the upper wall making an inclination of 2.44oto the bottom wall. From the top and bottom wall pressure distributions, two-dimensional internal force coefficients and pitching moment coefficients were calculated and variation of these coefficients with strut height were studied. Larger strut heights caused an increase in side force coefficient at all expansion levels of the ramp nozzle i.e., for all the TPRs employed in the present work (5–10). The variation of pitching moment coefficient with strut height exhibited the similar behavior as that of the side force coefficient. Shifting of strut position from expansion ramp tail end to the ramp mid position did not affect the nature of these variations. These variations were in general nonlinear in nature but the degree of non-linearity varied based on the value of TPR. Larger non linearity in side force coefficient variation was observed at TPRs 5,9 and 10. Larger moment coefficients resulted at lower TPR for the mid ramp position of the strut when compared to ramp tail end position. Large strut heights caused noticeable downward deflection of ramp surface flow. Calculations using the experimental data on wall pressure in the range of strut height variation employed in the present experiments indicate that increments up to 12% in moment coefficient, 20% in side force coefficient and 4% in axial force coefficients were achieved when the strut height was increased to its maximum value (12% of combustor entry section hydraulic diameter). Schlieren images show that the exhaust flow over the expansion ramp suffered a downward deflection and the strut position & height affected the magnitude of the deflection.

Early experience managing complex deformities using Autostrut™ robotic-controlled hexapod external fixators

Context: Hexapod circular external fixators allow bone manipulation in all planes to correct complex deformities. However, the patient must perform the strut adjustments consistently and correctly, often multiple times daily for weeks or months, to achieve intended corrections. This presents a potential source of variability, error, and anxiety to the patient. A computer-programmed, robotic automated motorized strut adjustment technology (Maxframe Autostrut™ Multi-Axial Correction System, Orthospin Ltd., Yoqneam, Israel) has been developed which automatically adjusts the struts without patient or clinician involvement. Aims: The aims of this study were as follows: first, to determine whether the motors performed the programmed initial and residual schedules and, second, to identify technology-specific problems and their management. Settings and Design: This was a retrospective observational study of a consecutive series of the first 16 patients who had the motorized hexapod frame applied. Subjects and Methods: A chart review was performed to record demographic information, indications and goals for hexapod frame care, whether the care goals were achieved, and whether unexpected and/or adverse events occurred (such as technical difficulties and medical complications) and the management of those issues. Statistical Analysis Used: Not applicable. Results: All patients achieved the index and residual adjustments as programmed. Conclusions: The Autostrut™ system appears reliable and safe. It executes programmed index and residual adjustments as well as strut change scenarios as directed. The system recognizes unexpected mechanical or programming issues and ensures patient safety by halting progress and alerting the patient. Future versions of the technology may benefit from added features such as remote reprogramming or current strut position monitoring.

Patient-specific simulation of stent-graft deployment in type B aortic dissection: model development and validation

Thoracic endovascular aortic repair (TEVAR) has been accepted as the mainstream treatment for type B aortic dissection, but post-TEVAR biomechanical-related complications are still a major drawback. Unfortunately, the stent-graft (SG) configuration after implantation and biomechanical interactions between the SG and local aorta are usually unknown prior to a TEVAR procedure. The ability to obtain such information via personalised computational simulation would greatly assist clinicians in pre-surgical planning. In this study, a virtual SG deployment simulation framework was developed for the treatment for a complicated aortic dissection case. It incorporates patient-specific anatomical information based on pre-TEVAR CT angiographic images, details of the SG design and the mechanical properties of the stent wire, graft and dissected aorta. Hyperelastic material parameters for the aortic wall were determined based on uniaxial tensile testing performed on aortic tissue samples taken from type B aortic dissection patients. Pre-stress conditions of the aortic wall and the action of blood pressure were also accounted for. The simulated post-TEVAR configuration was compared with follow-up CT scans, demonstrating good agreement with mean deviations of 5.8% in local open area and 4.6 mm in stent strut position. Deployment of the SG increased the maximum principal stress by 24.30 kPa in the narrowed true lumen but reduced the stress by 31.38 kPa in the entry tear region where there was an aneurysmal expansion. Comparisons of simulation results with different levels of model complexity suggested that pre-stress of the aortic wall and blood pressure inside the SG should be included in order to accurately predict the deformation of the deployed SG.

Vascularized Bone Grafts for Spinal Fusion-Part 2: The Rib.

Pseudoarthrosis, or failure to achieve bony union, is a well-known complication of spinal fusion operations. Rates range from 5% to 40% and are influenced by both patient and technical factors. Patients who do not achieve complete fusion may experience a return or worsening of their preoperative pain. For patients with complicated pathologies, vascularized bone grafts (VBGs) have been shown to provide better outcomes than nonvascularized bone grafts (N-VBGs). To enhance an instrumented spinal fusion by the innovative technique presented herein that utilizes a rotated, pedicled VBG from the left eighth rib under the paraspinous musculature into the midlumbar posterolateral gutter. For posterior approaches, the rib can be easily accessed and rotated into the appropriate strut position. The rib is dissected out, identifying and preserving the neurovascular bundle medially. The rib is then tunneled medially and appropriately positioned as the spinal graft, with the curve providing anatomic kyphosis or lordosis, depending on the surgical location. It is then successfully fixated with plates and spinal screws. In our limited experience to date, vascularized rib grafting procedures augment fusion and reduce operating room time and bleeding compared to free flap procedures. No patients have experienced complications related to these grafts. Pedicled vascularized rib grafts can be utilized to provide the advantages of a vascularized bone flap in complicated pathologies requiring spinal fusion as far as the L2-L3 level, without the morbidity associated with free tissue transfer.

A Methodology for Computed Tomography-Based Non-Destructive Geometrical Evaluations of Lattice Structures by Holistic Strut Measurement Approach

Abstract The presence of lattice structures is increasing in the manufacturing domain especially in the air/spacecraft and biomedical applications due to their advantages of high strength-to-weight ratios, energy absorption, acoustic and vibrational damping, etc. Dimensional accuracy of a lattice structure is one of the most important requirements to meet the desired functionality as there could be significant deviations in the as-produced part from the designed one. Evidently, an approach (non-destructive) to evaluate the dimensional accuracy of all the elements and eventually the lattice quality is of great significance. X-ray computed tomography (CT) has emerged as a promising solution in the field of industrial quality control over the last few years due to its non-destructive approach. In this work, we propose a methodology for geometrical evaluations of a lattice structure by measuring the deviation in the shape and size of its strut elements holistically. The acquired CT data of the complete lattice are extracted in the form of a point cloud and then segmented and stored as a single strut element with unique identification so that measurements can be performed on the strut individually. As demonstrated with a metallic BCCz-type lattice structure, the methodology helps in critical evaluation of its quality and the correlation with spatial position of the individual struts; e.g., the lattice exhibits large variations of shape among the inclined struts while the vertical struts possess consistency in their shape.

Effect of added struts and intake velocity on flame stabilization in supersonic combustors

In the present computational study, the impact of strut positions and the effect of inlet Mach numbers on the combustion efficiency are investigated in a strut-based supersonic combustor. An experimentally investigated model combustor developed at the German Aerospace Center (DLR) is simulated and validated. Then, a model combustor with three struts placed at different positions is investigated. Two-dimensional, compressible, reacting-flow governing equations are solved along with single-step chemistry reaction and k-ω SST turbulence model using a commercial CFD code FLUENT. The oblique shock from the struts has a profound influence on the mixing and combustion process. The H2O mole fraction, H2 mole fraction contours, and combustion efficiency of various configurations are compared for finding better mixing and flame stabilization. The combustion efficiency reduces when the two struts are located in farther downstream or placed at the same downstream location. At higher Mach numbers, the combustion is delayed, and the mixing of fuel with the supersonic mainstream is incomplete.

Experimental study of internal forces and moments generated by strut injection in a supersonic cross-flow in a C-D nozzle

An experimental investigation was conducted to obtain wall pressure distribution in a convergent divergent nozzle with a strut inserted through the diverging wall and to find out the possible generation of side force. The strut inserted through the nozzle wall represented an active control method for thrust vector control. Laboratory tests were carried out to examine whether this type of strut injection would be effective and serve as an alternative thrust vector control method for the other widely used such as secondary injection thrust vector control. The nozzle model used in the experiments had a design Mach number of 1.84 with a corresponding area ratio of 1.48. The solid strut which was inserted through the diverging wall of the nozzle had a square cross section. Experiments were conducted for identifying three different strut positions from the nozzle throat, i.e. at Ld/3, Ld/2, and 2Ld/3, where Ld was the length of the diverging section of the nozzle. At each strut position, the strut height was varied and the maximum strut height corresponded to the radius of the local cross section where the strut was inserted. The nozzle was operated at overexpansion conditions such as nozzle pressure ratios of 3.4 and 5. The strut side and the opposite side of the nozzle wall had eight wall pressure tappings each and the wall pressure data were obtained using a pressure scanner. The asymmetrical pressure distributions of the strut side and the non-strut side (opposite side) of nozzle wall were used for the calculation of side force and pitching moment in the nominal plane through the wall pressure ports of both sides. The calculated two-dimensional side force, axial force, and pitching moment coefficients were plotted against strut height at each strut position from the nozzle throat. From the experimental data and calculations, it was found that the axial force varied more or less linearly with strut height irrespective of the strut position. However, the side force and pitching moments varied nonlinearly with strut height and the nature of variation of the two was similar. Both the side force and pitching moment exhibited maximum and minimum values at two specific values of the strut height. The change in the strut position did not alter the nature of the above variations and the strut height values for maximum and minimum. The magnitude of the side force was found to be 1–10% of the axial force generated as a fluid dynamic pressure drag. Both positive and negative side force and pitching moments were produced with increase in the strut height.

Effectiveness of servo struts in controlling excavation-induced wall deflection and ground settlement

Deformations in deep excavations can be controlled by providing adjustable support using servo struts; however, the design of strut positions and applied forces remains to be optimized. In this study, the influences of varied forces applied by servo struts on excavation-induced wall deflection and ground settlement were analyzed through numerical simulations and a field investigation. A reference numerical model and input parameters were validated using a well-documented excavation case study. Using the validated model, three servo struts were installed on a diaphragm wall at the top, middle, and bottom levels of an excavation model, and a constant force was applied on the beam elements. Comprehensive numerical simulations were carried out with various forces applied at the upper-, middle-, and lower-level struts. Both wall deflection and ground settlement were analyzed in relation to the applied force. Additionally, a field investigation was carried out at an excavation site in Hangzhou, China, where comparative analyses of applied forces and servo strut locations were performed. Both the numerical and field results confirm the effectiveness of servo struts in controlling excavation-induced wall deflection and ground surface settlement. Their effectiveness is closely related to their applied force and installation position. Wall deformation and ground settlement decrease with increases in applied force. Middle-level servo struts showed the greatest efficiency in controlling maximum wall displacement and maximum ground surface settlement.

Visibility of Bioresorbable Vascular Scaffold in Intravascular Ultrasound Imaging.

Bioresorbable vascular scaffold (BVS) has recently been spotlighted for its unique characteristics of absorbing into blood vessels and eventually disappearing. Although intravascular ultrasound (IVUS) is the most common guiding tool for stent deployment, the echogenicity of BVS struts has changed as the center of stent lumen and scanning rotation is not concentric, which may cause a critical erroneous measurement in practice. This study investigated the physical conditions for dimming the stent brightness in IVUS images using a finite-difference method (FDM) to numerically solve acoustic wave propagation through nonhomogeneous medium. The dimmed brightness is caused by an angled rectangular cross section of a strut and its similar acoustic impedance with water. Imaging frequency is not a major cause. However, the angle between the acoustic beam and the BVS surface is the major cause of the dimmed brightness. As a solution, an approach using a frequency compounding method with signal polarity comparator was proposed to recover the reduced brightness without sacrificing spatial resolutions. Based on the simulation study, the signal level from BVS can be attenuated down by 17 dB when the angle between the acoustic beamline and the surface of BVS is more than 45°. With the proposed frequency compounding approach, the reduced signal can be recovered by 6 dB. In the experimental BVS IVUS imaging, strut brightness was reduced by 18 dB with an angled strut position and recovered by 5 dB with the proposed frequency compounding method. A pig coronary was imaged to demonstrate the performance of the proposed method.

Valuation Of Implanted-Stent Impact On Coronary Artery Trifurcation Blood Flow By Using CFD.

We investigated the influence of stent implanted in left main coronary artery trifurcation on blood flow by means of CFD. We simulated various stent positions and arrangement patterns considering KBT. The velocity and WSS (wall shear stress) distribution were found to depend on the stent arrangements. In addition, a strut position inhibiting the inflow velocity peaks into the branched (LCX) vessel exhibited a strong impact, which provided suppression of WSS on the high-lateralside surface of the LCX entrance. By KBT, such an impact of stent implantation can be avoided.

Numerical methods for polyline-to-point-cloud registration with applications to patient-specific stent reconstruction.

We present novel numerical methods for polyline-to-point-cloud registration and their application to patient-specific modeling of deployed coronary artery stents from image data. Patient-specific coronary stent reconstruction is an important challenge in computational hemodynamics and relevant to the design and improvement of the prostheses. It is an invaluable tool in large-scale clinical trials that computationally investigate the effect of new generations of stents on hemodynamics and eventually tissue remodeling. Given a point cloud of strut positions, which can be extracted from images, our stent reconstruction method aims at finding a geometrical transformation that aligns a model of the undeployed stent to the point cloud. Mathematically, we describe the undeployed stent as a polyline, which is a piecewise linear object defined by its vertices and edges. We formulate the nonlinear registration as an optimization problem whose objective function consists of a similarity measure, quantifying the distance between the polyline and the point cloud, and a regularization functional, penalizing undesired transformations. Using projections of points onto the polyline structure, we derive novel distance measures. Our formulation supports most commonly used transformation models including very flexible nonlinear deformations. We also propose 2 regularization approaches ensuring the smoothness of the estimated nonlinear transformation. We demonstrate the potential of our methods using an academic 2D example and a real-life 3D bioabsorbable stent reconstruction problem. Our results show that the registration problem can be solved to sufficient accuracy within seconds using only a few number of Gauss-Newton iterations.

Effect of parametric variation of strut layout and position on the performance of a typical two-strut based scramjet combustor

The two equation Shear stress transport k-ω turbulence model and the 2D compressible Reynolds-Averaged Navier–Stokes (RANS) equations along with single-step chemical reaction mechanism have been applied to analyze the effect of strut lip height, staggered strut and the strut position relative to the combustor entrance on the combustion enhancement of a two-strut scramjet combustor. Here all the computational simulations have been carried out using ANSYS 14-FLUENT code. Moreover, validation has been performed for the single strut scramjet engine by comparing its outcome with the open experimental data. The computational results show acceptable similarity with the experimental results available in the open literature. The presence of two struts improves the mixing and combustion efficiency of the combustor appreciably compared to single strut. The current results represent the presence of an optimal lip height of the strut for which the performance of the two-strut combustor notably increases and strong combustion phenomena take place within the combustion region. Again mixing phenomena are not enhanced with the use of staggered strut due to the formation of separation region on both the wall two times during front as well as aft fuel injection. Further combustion phenomena are totally affected by the small relative distance between the entrance of the combustor and strut base. The combustion efficiency is found to be maximum only when overlapping occurs between the intersectional point and the divergence point inside the two-strut combustor.

Experimental study on combustion modes of a liquid kerosene fueled RBCC combustor

To enable the dual-mode scramjet engine operate in the whole flight trajectory, the urgent development of the Rocket Based Combined Cycle (RBCC) propulsion system has been put forward. The behavior of ram-scram combustion mode transition was examined using direct-connect experiments of a model RBCC combustor along with pressure measurements. At an inflow stagnation condition of P0=1.5MPa and T0=1280K, four combustion modes, namely weak combustion mode, rocket-scram mode, rocket-ram mode and ram mode were classified through wall pressure distributions, combustor inlet Mach number, and flame plume visualization. Both the position of fuel strut injectors and the cavity installation location had a significant effect on RBCC combustion modes. When rocket jets were added, the change of the fuel strut position could cause mode transition. Furthermore, as the rockets were turned off, different locations where the cavities were installed could lead mode transition as well. When the primary heat release zone was stabilized at the downstream in the combustor, the addition of rocket jets would make the burning zone jump to upstream abruptly. The discovery of this phenomenon provided a new method and feasible strategy for mode transition.

The Impact of Housing Features Relative Location on a Turbocharger Compressor Flow

This work presents an investigation on a flow phenomenon marked by in-plane velocity non-uniformity associated with a ported shroud turbocharger compressor observed upstream of the compressor inlet at lower operating speeds. The effect of structural struts in the ported shroud (PS) cavity and the location of the volute tongue on velocity non-uniformity is studied in this paper by numerically modelling the complete compressor stage using a (Un)steady Reynolds Averaged Navier-Stokes (RANS & URANS) approach. The results show that the amplitude of in-plane velocity non-uniformity is reduced by removing the struts from the PS cavity. Furthermore, the change in location of the volute tongue is shown to either substantially diminish or enhance the amplitude of velocity non-uniformity based on the relative position of the volute tongue and the struts. The study concludes that the velocity non-uniformity is dependent on the coupled effect of volute tongue and the strut position in the PS cavity.

Estimation of Design Parameters for Braced Excavation in Clays

In this study, the optimum values of the design parameters (position of struts, embedment depth of the wall, thickness of the wall and the strut stiffness) for braced excavation in clayey soil have been determined by using the numerical tool, FLAC. The design parameters are determined by studying their effects on the factors such as strut force, wall deflection, wall moment and displacement of the ground surface adjacent to the braced excavation which play significant role in the design of braced excavation. The results of the present numerical model are compared with the observed values obtained from a case study on braced excavation in a clayey soil. A close agreement between the result as obtained from the present numerical study and that measured in the field has been observed. On the basis of the parametric studies done on two different clayey soil profiles, it is found that the most effective design of excavation in a clayey soil can be done when the embedment depth of the wall, the thickness of the wall and the strut stiffness are kept within the range of (80–100)% of the depth of excavation (6–7)% of the depth of excavation and (5–25) × 105 kN/m/m, respectively. The top strut can be kept at a height of (2–3) m below the ground level without endangering the safety of the system.

CFD analysis of strut influence on blood flow in stent-implanted left main coronary artery bifurcation.

We numerically studied blood flows in a simulated branching pipe of coronary artery bifurcation, which is affected by stent implantation. We found that stent struts provide effects as guide vanes and blockages on the flow into circumflex branch. The former effect increases the flow rate and shear stress on the arteriosclerosis-prone site. The blockage effect may overwhelm the guide effect depending on a strut position against the inflow.

2F22 動脈瘤ネックの流入領域に対するストラットの相対位置が瘤内流れに与える影響

2F22 動脈瘤ネックの流入領域に対するストラットの相対位置が瘤内流れに与える影響