Rod Configuration Research Articles

A computational framework to obtain nonlinearly elastic constitutive relations of special Cosserat rods with surface energy

We present a computational framework to obtain nonlinearly elastic constitutive relations of special Cosserat rods with surface energy. The framework allows the rod’s cross-section to have arbitrary shape and the rod material to obey arbitrary three-dimensional material model for its bulk volume and arbitrary surface energy model for its lateral surface. The kinematics of the Helical Cauchy–Born rule is used to first construct a family of six-parameter (corresponding to the six strain measures of rod theory) helical rod configurations in which the generated three-dimensional strain field is uniform in the rod’s arc-length coordinate. This uniformity allows the three-dimensional nonlinear equations of elasticity to reduce to just the rod’s cross-sectional plane wherein the cross-section’s boundary also experiences traction due to the inherent surface energy in the rod’s lateral surface. The solution of this cross-sectional problem yields the induced in-plane displacement and out-of-plane warping in the cross-section for arbitrarily prescribed strain measures of the rod. We then derive expressions for the induced internal contact force, moment and stiffnesses of the rod in terms of the solution of the deformed cross-section and the prescribed strains of the rod. A finite element formulation is presented to solve the nonlinear cross-sectional deformation problem and further obtain the induced internal contact force, moment and stiffnesses. The presented framework will be useful for modeling of nanorods where surface energy plays a dominant role. Several numerical examples are presented using the presented framework to illustrate the effect of surface energy parameters on the deformation of the nanorod’s cross-section and the nanorod’s bending, torsional, extensional and shearing stiffnesses. We also derive improved analytical formulas for the extensional and bending stiffnesses of isotropic rectangular nanorods in their reference state. These formulas reduce to the existing widely used formulas for a special choice of material parameters, i.e., when the surface Poisson’s ratio and the bulk Poisson’s ratio match thus highlighting the limitation of the existing formulas.

Validation of deterministic code OpenNTP for the analysis of the C5G7-1D benchmark with different configurations

This study was conducted with the aim of verifying that the OpenNTP (Open Neutron Transport Package) code is capable of reproducing high-performance and exact calculation results. Therefore, a thorough analysis of the One-dimensional C5G7 benchmark with different configuration of control rods was performed. This benchmark was chosen because of its strong heterogeneity. For the modelling of the pin cell geometry, different sets of spatial meshes are used to study the sensitivity of the multiplication factors on the spatial and angular discretization. In addition, the influence of the control rods has been studied by analysing the scalar fluxes, the power in each pin cell and the power of the assemblies. It was found that assembly power distribution errors were significant for the Unrodded case of the C5G7 benchmark. The calculation results in the present paper have a good agreement with the reference values, which demonstrates that the OpenNTP code can solve neutronics problems accurately.

Influence of double rods and interbody cages on range of motion and rod stress after spinopelvic instrumentation: a finite element study.

To compare instrumentation configurations consisting of bilateral single or double rods and additional interbody cages (IBCs) at different levels in terms of Range of Motion (ROM) and distribution of von Mises stress in rods. A previously validated L1-pelvis finite element model was used and instrumented with configurations consisting of single or double bilateral rods and IBCs at multiple levels. Pure moments of 7.5N.m were applied to L1 in main directions in addition to a follower load of 280N. Global, segmental ROM and distribution of von Mises stress in rods were studied. All configurations reduced segmental and global ROM from 50 to 100% compared to the intact spine. Addition of IBCs slightly increased ROM at levels adjacent to the IBC placement. The simple rod configuration presented the highest von Mises stress (457MPa) in principal rods at L5-S1 in flexion. Doubling rods and IBC placement reduced this value and shifted the location of maximum von Mises stress to other regions. Among studied configurations, double rods with IBCs at all levels (L2-S1) showed the lowest ROM. Maximal von Mises stresses in secondary rods were lower in comparison to main rods. Double rods and IBCs reduced global and segmental ROM as well as von Mises stress in rods. The results suggest a possible benefit in using both strategies to minimize pseudarthrosis and instrumentation failure. However, increased ROM in adjacent levels and the shift of maximal von Mises stress to adjacent areas might cause complications elsewhere.

Automated Stability Testing of Elastic Rods With Helical Centerlines Using a Robotic System

Experimental analysis of the mechanics of a deformable object, and particularly its stability, requires repetitive testing and, depending on the complexity of the object’s shape, a testing setup that can manipulate many degrees of freedom at the object’s boundary. Motivated by recent advancements in robotic manipulation of deformable objects, this letter addresses these challenges by constructing a method for automated stability testing of a slender elastic rod — a canonical example of a deformable object — using a robotic system. We focus on rod configurations with helical centerlines since the stability of a helical rod can be described using only three parameters, but experimentally determining the stability requires manipulation of both the position and orientation at one end of the rod, which is not possible using traditional experimental methods that only actuate a limited number of degrees of freedom. Using a recent geometric characterization of stability for helical rods, we construct and implement a manipulation scheme to explore the space of stable helices, and we use a vision system to detect the onset of instabilities within this space. The experimental results obtained by our automated testing system show good agreement with numerical simulations of elastic rods in helical configurations. The methods described in this letter lay the groundwork for automation to grow within the field of experimental mechanics.

Pedicle Subtraction Osteotomy Construct Optimization: A Cadaveric Study of Various Multirod and Interbody Configurations.

Fourteen cadaveric specimens were separated into two groups: (1) L3 pedicle subtraction osteotomy (PSO) with transforaminal lumbar interbody fusion (TLIF) or (2) lateral lumbar interbody fusion (LLIF). A 2-rod configuration (2R) was compared with two supplemental rod configurations: 4-rod (4R) with accessory rods (ARs) using connectors or 4R with satellite rods (SRs) without connectors. Compare PSO constructs with different rod configurations and adjacent-level interbody support. Supplemental rods and anterior column support enhance biomechanical performance. Pure moments were applied in (1) intact, (2) pedicle screws and rods, (3) PSO + 2R, (4) 4R AR, and (5) 4R SR conditions. Primary and supplemental rods had strain gauges across the index level. Sacral screw bending moments and range of motion (ROM) were recorded. For TLIF, AR decreased ROM during flexion (P = 0.02) and extension (P < 0.001) versus 2R. For LLIF, AR and SR decreased motion versus 2R during left (AR: P = 0.03; SR: P = 0.04) and right (AR: P = 0.002; SR: P = 0.01) axial rotation. For LLIF, sacral screw strain increased with SR compared with AR in compression and right lateral bending (P ≤ 0.03). During lateral bending, rod strain increased with PSO+TLIF+SR versus PSO+LLIF+2R and PSO+LLIF+AR (P ≤ 0.02). For LLIF, SR configuration increased rod strain versus AR during flexion, extension, and lateral bending (P≤ 0.01); for TLIF, rod strain increased with SR versus AR during extension (P = 0.03). For LLIF, AR configuration increased posterior supplemental rod strain versus SR during flexion (P = 0.02) and lateral bending (P < 0.001). Both supplemental rod configurations reduced motion in both groups. Constructs with the SR configuration increased the primary rod strain and the sacral screw bending moment compared with AR constructs, which can share strain. Deep-seated SRs, which have become increasingly popular, may be more vulnerable to failure than ARs. LLIF provided more stability in sagittal plane. Protective effect of supplemental rods on rod strain was more effective with TLIF.Level of Evidence: NA.

Fuel Performance Design Basis for the Versatile Test Reactor

The Fuel Performance Design Basis for the Versatile Test Reactor begins with requirements to maintain safe and efficient reactor operation. For the metal-fueled Versatile Test Reactor, this means a limited number of fuel rod breaches, no fuel melting under steady-state operation and anticipated transients, and continuity of the fuel rod and assembly configuration to avoid impacts to operations of safety systems, maintain expected coolant flow, and allow for efficient fuel handling. Using a large database gathered from previous testing, data were examined to identify and establish preliminary limits on fuel operating conditions. Fuel performance aspects important to fuel operating limits have been identified, including cladding creep, which is addressed with a cladding deformation limit to ensure a limited cladding breach. In addition, fuel-cladding chemical interaction is addressed through limits on cladding temperature and time-at-temperature for steady-state operation, transients, and accidents to mitigate effects leading to cladding breach or fuel melting. Through the implementation of these limits, cladding breach, fuel melting, and deleterious fuel rod and assembly dimensional changes will be prevented.

Quantification of boiling flows in single and multiple heater rods assembly by recurrence plots and recurrence quantification analysis

Tracer particle position time series obtained by RPT experiments were used to quantify the changes in hydrodynamics induced by boiling flows in single and multiple rods assembly. The test section under consideration is a “scaled-down” version of a typical boiling water nuclear reactor (Advanced Heavy Water Reactor (AHWR) of the Department of Atomic Energy, India). The analysis of the above-mentioned time series was done by Recurrence Plots (RP) and Recurrence Quantification Analysis (RQA). Visual differences in the RPs were detected with changes in the inlet condition and heater rods configuration. The constructing feature of the recurrence plot can be categorized in two forms: local white areas (LWA) and local bold areas (LBA). However, the change cannot be quantified by visual observation, and for this quantification RQA parameters such as Recurrence Rate (RR), Determinism (DET), and Entropy (ENT) were used. Experimental results show that the increase in liquid flow rate, decrease in inlet liquid temperature, and increase in the number of the heater rods caused increased RR, increased DET, and increased ENT.

Active depletion torque between two passive rods.

The active depletion torque experienced by two anisotropic objects in an active bath is a conceptional generalization of the equilibrium entropic torque. Using Brownian dynamics simulations, we compute the active depletion torque suffered by two passive rods immersed in an ensemble of active Brownian particles. Our results demonstrate that the active depletion torque is qualitatively different from its passive counterpart. Interestingly, we find that the active depletion torque can be greatly affected by the external constraint applied on the rotational degree of freedom of the rods, and even the direction may be changed with the orientational constraint, which is in contrast to the equilibrium depletion torque. The main reason for the remarkable features of the active depletion torque is that the active particles can significantly accumulate in the vicinity of the rods due to persistent self-propulsion, which is sensitively dependent on the constraint strength and the rod configurations. Our findings could be relevant for understanding the self-assembly and dynamics of anisotropic macromolecules in living environments.

Photocatalytic degradation of contaminants of emerging concern using a low-cost and efficient black bismuth titanate-based water treatment reactor

Photocatalysis is recognized as a sustainable technology for wastewater treatment, but it is limited by its scalability and efficiency. Here, we report the fabrication of a bespoke photocatalytic reactor, made from readily available consumer market components. The reactor was loaded with glass rods coated with a bismuth titanate photocatalyst deposited by reactive pulsed DC magnetron sputtering. Bismuth titanate is a remarkable material, which has shown the property of increasing its photocatalytic capabilities over repeated usage due to photoinduced oxygen vacancies, forming oxygen-vacancy rich “black” bismuth titanate. The reactor was tested with different rod configurations and photocatalytic material was cycled over 25 times, equivalent to 125 h of consecutive use, against methylene blue dye under UV light. Orange II dye degradation tests carried out in the presence of scavengers revealed that photocatalytic reactions were driven by superoxide (O2∙−) and holes (h+), when using pristine bismuth titanate and by superoxide (O2∙−), electrons (e−) and holes (h+), when using “black” bismuth titanate. Finally, the reactor was used to successfully degrade levofloxacin, a typical antibiotic, which was verified by UV–Vis (ultraviolet-visible) spectroscopy and inhibition zone tests in the presence of three different pathogens (E. coli, S. aureus and A. baumannii).

Theoretical Analysis of Thin Curved Rod Displacements V. P. Lugovoi1)

The paper presents a comparative theoretical analysis of the movements of the curved rods of various curvature forms, which can be applied as tools for ultrasonic treatment of holes in fragile materials. It has been shown that the traditional processing of holes by an ultrasonic method is based on the use of straight rods, in which the amplitudes of displacements on the working – free end corresponds to the value of displacements at the point of its attachment to the ultrasonic oscillation concentrator. Supplementing the configuration of a straight rod with a curvilinear shape in the form of a circular arc or a spiral twisted by one turn will allow obtaining additional displacements caused by the elastic properties of a section with a curved shape. The paper considers several calculated schemes of a curvilinear rod bounded by angles j equal to p/2, p and 2p, fferent direction of the external force action. The obtained results have shown that an increase in the circular arc angle leads to a corresponding increase in the elastic displacement index of the rod free end. In this case, the total displacements of the rod free end will be made from displacements caused by vibrations of the acoustic system and the displacements of a curved thin rod from an external force. Calculations have established that the magnitude of the elastic displacements of curved rods is influenced by the shape and magnitude of the angle, the direction of the external force, the radius of curvature, the rigidity of the cross section. The considered schemes of thin rods with curvilinear sections can find practical application in ultrasonic oscillatory systems for processing small-diameter holes in fragile materials. This increases the intensity of tool oscillations and improves the process performance.

A Comparative Biomechanical Analysis of Various Rod Configurations Following Anterior Column Realignment and Pedicle Subtraction Osteotomy.

ObjectiveThe objective of this study was to compare the biomechanical differences of different rod configurations following anterior column realignment (ACR) and pedicle subtraction osteotomy (PSO) for an optimal correction technique and rod configuration that would minimize the risk of rod failure. MethodsA validated spinopelvic (L1-pelvis) finite element model was used to simulate ACR at the L3–4 level. The ACR procedure was followed by dual-rod fixation, and for 4-rod constructs, either medial/lateral accessory rods (connected to primary rods) or satellite rods (directly connected to ACR level screws). The range of motion (ROM), maximum von Mises stress on the rods, and factor of safety (FOS) were calculated for the ACR models and compared to the existing literature of different PSO rod configurations. ResultsAll of the 4-rod ACR constructs showed a reduction in ROM and maximum von Mises stress compared to the dual-rod ACR construct. Additionally, all of the 4-rod ACR constructs showed greater percentage reduction in ROM and maximum von Mises stress compared to the PSO 4-rod configurations. The ACR satellite rod construct had the maximum stress reduction i.e., 47.3% compared to dual-rod construct and showed the highest FOS (4.76). These findings are consistent with existing literature that supports the use of satellite rods to reduce the occurrence of rod fracture. ConclusionOur findings suggest that the ACR satellite rod construct may be the most beneficial in reducing the risk of rod failure compared to all other PSO and ACR constructs.

Additional Stylized 3-D Benchmark Problem Set Based on the Pin-Fueled SmAHTR

Previous work presented a set of stylized three-dimensional benchmark problems based on the Oak Ridge National Laboratory (ORNL) preconceptual design of a fluoride-salt-cooled small modular advanced high-temperature reactor, or SmAHTR, with prismatic assemblies fueled by tri-isotropic (TRISO) particles. That previous work created a detailed description of the benchmark problems by closing several outstanding design gaps from the ORNL preconceptual design report, notably by addressing the lack of active control mechanisms, for which control rod “bundles” were implemented. In this paper, the creation of two additional stylized benchmark problem sets based on that past work is detailed, offering two new control rod configurations. The fluoride salt, small size, and highly heterogeneous TRISO-fueled pins make these additional benchmark problem sets useful numerical validation references in benchmarking neutronics tools against continuous-energy stochastic Monte Carlo results. Detailed reference results, including the eigenvalue (keff) and 1/11th assembly-averaged relative fission density distributions, are provided for both control rod configurations in full-core cases with all control rods withdrawn and all control rods fully inserted. A near-critical core benchmark problem and results are provided for one configuration. The provided results are calculated using the continuous-energy Monte Carlo code MCNP.

Void fraction distribution for convective boiling flows in single and multiple heater rods assembly

Void fraction distribution is an essential parameter for the design and development of nuclear reactors. In this work, void fraction measurements have been performed on an experimental setup mimicking the flow behavior in a calandria of Boiling Water Reactor (BWR). Experimental measurements for void fraction distribution were performed on three heater rods configurations at fixed electrical power using non-invasive gamma-ray densitometry at varying inlet liquid flow rates and temperatures. The main focus of this contribution was to measure void fraction distribution of boiling flows in a test section having the arrangement to accommodate different heater rods configurations by keeping the mechanical aspects of the gamma-ray densitometry technique simple. Measurements were done at four axial locations. and at each axial location, void fraction measurement was performed at eight radial locations. Experimental results show that void fraction profiles are not only influenced by the configuration of heater rods but also by the operating conditions. The void fraction profiles of configuration A were flat as compared to all other heater rod configurations. The data reported here help develop CFD models and understand the dependence of void fraction distribution on heater rods configuration.

Influence of conduction shape factor in subterranean cooling for a thermoelectric energy harvesting system at asphalt pavement: An experimental investigation

ABSTRACT This research study’s primary motivation is to study the practicality and feasibility of energy harvesting or energy scavenging using ambient energy such as heat absorbed by asphalt pavement to provide electrical power for small electronic circuits or devices, making them self-sufficient. Therefore, this project investigates the thermal distribution evaluation of multiple diameters of the aluminum rod as a cooling element and examines the optimum designs for the surface heat absorption method using the aluminum plate in the road thermoelectric energy harvesting system (RTEHs). The RTEHs experimental setup consisted of an asphalt-filled wooden base box, “sandwiched” thermoelectric module, top aluminum plate, and bottom aluminum rod, which is partially submerged in the asphalt and soil. Using constructed RTEHs setup and several thermocouples, a series of experiments on multiple diameters of an aluminum rod as a cooling element and few aluminum plate designs were conducted to obtain the best configurations that yield maximum temperature difference between cooling and heating sides in asphalt based RTEHs. Based on the testing results, RTEHs with a mounted triple of Rod C, which has the biggest diameter of 31.75 mm (1.25 inch) and combined with 100 mm × 200 mm of a top plate, proved to be the best performing configuration by producing the highest temperature difference (DT) of 15.19°C. Since the triple rod configuration has a higher value of shape factor, this indicates a better heat transfer performance by conduction. These proved the theory of conduction shape factor for multiple geometries. Based on the results, having a bigger top plate as a heating element promotes a higher heat transfer rate and takes in more heat energy, thus producing the largest DT for the system, which confirmed Stephen-Boltzmann’s law on radiation heat transfer.

Assessment of the burnup characteristics of UO2 and MOX fuel in the mixed solid and annular rod configuration

Modeling and burnup analysis of Uranium dioxide (UO2) and Mixed Oxide (MOX) fuel in square assemblies comprising both solid and annular rods was carried out. The lattice pitch of the models was optimized first in terms of infinite multiplication factor (k∞) using OpenMC. The burnup analysis was performed at the optimized pitch by lattice physics code Dragon for 1620 EFPD. The burnup dependent fission rate density was studied, and the thermal fission rate was found higher for the models as compared to reference designs. The values of k∞ and reactivity were determined and higher values were found for the models at low fuel burnup period. However, models showed a higher criticality period than the reference design consisting of only the annular rod. The fuel and moderator temperature sensitivity of reactivity was investigated for different fuel burnup periods. The burnup-dependent atomic concentrations of fissionable materials, minor actinides, and neutron poisons were also studied. The production of neutron poison, namely Xe-135 and Sm-149 and minor actinides viz. Np-237, Am-241, Cm-242 and Cm-244 were found lower in models as compared to the reference designs.

Identifying complications and failure modes of innovative growing rod configurations using the (hybrid) magnetically controlled growing rod (MCGR) and the spring distraction system (SDS)

BackgroundMagnetically controlled growing rods (MCGRs) offer non-invasive distractions in Early-Onset Scoliosis (EOS). However, implant-related complications are common, reducing its cost-effectiveness. To improve MCGRs functionality and cost-effectiveness, we often combine a single MCGR with a contralateral sliding rod (hybrid MCGR). Recently, we developed the spring distraction system (SDS) as an alternative, which provides continuous distraction forces through a helical spring. This study aims to identify complication rates and failure modes of EOS patients treated with either of these innovative systems.MethodsThis single-centre retrospective study included EOS patients treated with a (hybrid) MCGR or SDS between 2013 and 2018. Baseline demographics, and data regarding complications and implant growth were measured. Complication rate, complication profile, complication-free survival and implant growth were compared between groups.ResultsEleven hybrid- and three bilateral MCGR patients (4.1-year follow-up) and one unilateral, eleven hybrid and six bilateral SDS patients (3.0-year follow-up) were included. Groups had similar age, sex, aetiology distribution, and pre-operative Cobb angle. Complication rate was 0.35 complications/patient/year for MCGR patients and 0.33 complications/patient/year for SDS patients. The most common complications were failure to distract (MCGR-group; 8/20 complications) and implant prominence (SDS-group; 5/18 complications). Median complication-free survival was 2.6 years, with no differences between groups (p = 0.673). Implant growth was significantly higher in the SDS-group (10.1 mm/year), compared to the MCGR-group (6.3 mm/year).Conclusion(Hybrid) MCGR and SDS patients have similar complication rates and complication-free survival. Complication profile differs between the groups, with frequent failure to distract leading to significantly reduced implant growth in (hybrid) MCGR patients, whereas SDS patients frequently exhibit implant prominence and implant kyphosis.Level of evidenceIII.

A statistical mechanics-based investigation of a solute atmosphere interacting with a crack: Solute redistribution and image effects

Although continuum frameworks have been developed in the past for studying how material defects behave in solid solutions, recent studies have demonstrated that the self-stress field of the solutes which enter the chemical potential in the prevalent continuum models must be excluded, and instead the image stresses included, in a correct treatment. Here, working within the framework of Gibbs canonical ensemble of statistical mechanics, and accounting for the image stresses of the solutes arising due to the presence of the boundaries, we examine the interaction between a solute atmosphere and a crack in the presence of an external loading. Relying on a plane strain model, the solute atmosphere is treated as a distribution of misfitting solute rods, infinitely long in the direction normal to the plane of analysis. Since solutes interact through their image stress fields and can move around in the solid, Monte Carlo simulations, fully accounting for both the energy of interaction between the solute rods and their interaction with the external loading, are performed to explore various configurations of the solute rods in the host, and to compute the temperature-dependent ensemble averages of the enthalpy, equilibrium solute distribution, and the energy release rate (ERR) of crack growth. It is shown that solute redistribution induced by a tensile loading of the solid results in an increase in the ERR. Our simulations further interestingly reveal that even in the limit of large temperatures where a nearly uniform solute distribution prevails, the interaction between the collective image stress field of the solutes and the stress field of the loading results in an added contribution to the ERR which, at a fixed average concentration and a fixed loading-induced stress intensity factor, does not fade away with increasing solid dimensions, and further strengthens both with the solute concentration and with the external loading.

Use of the dual construct lowers rod strains in flexion-extension and lateral bending compared to two-rod and two-rod satellite constructs in a cadaveric spine corpectomy model

BACKGROUND CONTEXTComplex spinal reconstructions involving corpectomies, or osteotomies, place spinal implants at extremely high stresses that can lead to pseudoarthrosis and ultimately to rod failure, resulting in revision surgery. Current clinical options to increase the biomechanical strength of a construct include increasing rod diameter, changing rod material, or placing an additional satellite/outrigger rod on a standard two rod construct. Fundamentally, all of these constructs still rely on two longitudinal rods across the reconstruction site and are therefore at risk for rod fracture and loss of alignment. Initially described in 2006, the Dual Construct was developed to address this limitation by utilizing four distinct mechanically independent rods, which allowed for the creation of two separate, and distinct, constructs within each patient. Although there is early clinical evidence to support its efficacy, this is the first biomechanical study to compare the Dual Construct to the two-rod and two-rod with satellite configurations in a cadaveric study. PURPOSETo assess the biomechanical impact of the Dual Construct technique to traditional two-rod and two-rod with satellite rod construct in a cadaveric model. STUDY DESIGN/SETTINGBiomechanical cadaveric study METHODSNine fresh-frozen human cadaveric spines (6 males, 3 females, 56 year +/- 9 years) from T9-pelvis were instrumented and tested utilizing all three configurations including two-rod construct, two-rod with satellite construct, and the Dual Construct technique. Biomechanical testing order of the various constructs was randomized to reduce potential effects of order bias. Strain gauges were placed in both the coronal and sagittal planes of the rods to track the strains during flexion-extension and lateral bending while undergoing range of motion testing. Testing was performed using pure-moment flexibility testing protocols. RESULTSIn flexion-extension, the resultant strain in the two-rod construct was an average 600±228 microstrain, the two-rod with satellite rod strain averaged 603±237 microstrain, and the Dual Construct averaged 403±149 microstrain. In lateral bending, the resultant strain in the two-rod construct was an average of 266±134 microstrain, the satellite rod strain was an average of 310±158 microstrain, and the Dual Construct averaged 118±51 microstrain. In both flexion extension and lateral bending, a significant reduction in strain was observed between the Dual Construct condition compared to both the two-rod and satellite configurations. No significant difference was found between the two-rod and two-rod with satellite rod configurations. CONCLUSIONSThe increase in load sharing significantly decreases the strain experienced across the Dual Construct compared to traditional two-rod and two-rod with satellite constructs. Global rod strains on primary rods cannot be reduced by simply increasing the number of satellite rods, but can only be reduce by increasing the actual number of primary rods.

Optimization of Connecting Rod Design Parameters for External Fixation System: A Biomechanical Study

The role of connecting rod in healing process of a fractured bone has always been of significant importance for surgeons. Adding a connecting rod to the fixator would be a secure option for increasing stability without increasing infection rate. The roles of 4 design parameters of the connecting rod (ie, connecting rod diameter, elevation, material, and configuration) were assessed by using finite element models to calculate axial stiffness and interfragmentary strain at the fracture gap. Taguchi method was used to achieve an optimal design set for maximizing stability with regard to connecting rod variables. Also, analysis of variance (ANOVA) approach was employed to determine contribution percentage of each design parameter on outputs. For optimizing connecting rod design parameters, an optimal set of variables consisting of 11 mm, 40 mm, 200 GPa, and Type 3 external fixator were determined by Taguchi for connecting rod diameter, elevation, modulus of elasticity, and configuration, respectively. However, as Type 3 external fixator stability is a little more than Type 2, it would be better if Type 3 external fixator in Taguchi suggestion be replaced by Type 2 external fixator to be as minimally invasive as possible. Furthermore, ANOVA results revealed that the connecting rod configuration is the most important parameter with 95% and 96% effectiveness on the interfragmentary strain and axial stiffness.

Control of the self-sustained shear layer oscillations over rectangular cavities using high-frequency vortex generators

The excitation of acoustic resonance by flow over a rectangular cavity can generate acute noise, cause damage to equipment, and interrupt operation. In this work, a passive control technique to suppress the excitation of acoustic resonance by the flow over rectangular cavities is experimentally investigated. A span-wise rod that generates high-frequency vortices is mounted upstream of the cavity leading edge to prevent the flapping of the shear layer. The effect of the rod parameters on the mechanism of acoustic resonance suppression is identified by means of acoustic pressure and particle image velocimetry (PIV) measurements. It is found that the effectiveness of this control technique is significantly dependent on the streamwise location of the rod with respect to the cavity leading edge, the gap between the rod and the wind tunnel wall, and the cavity aspect ratio. In addition, PIV measurements revealed that, in effective rod configurations, the vortices generated in the gap between the control rod and the wall alter the development of the shear layer. Moreover, analysis of the Reynolds stresses showed that fluctuations in the wake of the rod prevent the shear layer from impinging on the cavity downstream edge. Consequently, this interaction interrupts the initiation of the feedback mechanism responsible for the onset of acoustic resonance excitation. Finally, a universal criterion is developed to predict an optimum region to implement the control rod upstream of the cavity leading edge to effectively suppress the acoustic resonance excitation.