Mm In Steps Research Articles

Evaluation of corneal power from an AS-OCT thick lens model and ray tracing: reliability of the keratometer index

Purpose: To investigate and compare different strategies of corneal power calculations using keratometry, paraxial thick lens calculations and ray tracing. Setting: Tertiary care center. Design: Retrospective single-center consecutive case series. Methods: Using a dataset with 9780 eyes of 9780 patients from a cataractous population the corneal front (Ra/Qa) and back (Rp/Qp) surface radius/asphericity, central corneal thickness (CCT), and entrance pupil size (PUP) were recorded using the Casia 2 tomographer. Beside keratometry with the Zeiss (PKZ) and Javal (PKJ) keratometer index, a thick lens paraxial formula (PG) and ray tracing (PR) was implemented to extract corneal power for pupil sizes from 2 mm to 5 mm in steps of 1 mm and PUP. Results: With PUP PKZ/PKJ overestimates the paraxial corneal power PG in around 97%/99% of cases and PR in around 80% to 85%/99%. PR is around 1/6 or 5/6 diopters (D) lower compared with PKZ or PKJ. For a 2 mm pupil PR is around 0.20/0.91 D lower compared with PKZ/PKJ and for a 5 mm pupil PR is comparable with PKZ (around 0.03 D lower) but around 0.70 to 0.75 D lower than PKJ. Conclusions: “True” values of corneal power are mostly required in lens power calculations before cataract surgery, and overestimation of corneal power could induce trend errors in refractive outcome with axial length and lens power if compensated with the effective lens position.

Influence of wall thickness on mechanical properties and porosity of additive manufactured polymer-based porous structures for fibula bone regeneration

In the recent past, Bone tissue engineering (BTE) has become a potentially effective solution for repairing bone defects. In the meantime, various fields, such as material science, additive manufacturing, and clinical medicine, are interlinked in the fast-emerging field of bone tissue engineering. Additive Manufacturing (AM) is a unique technology that accumulates content rather than waste materials in the form of chips. AM techniques like selective laser sintering (SLS), commonly used to create complex polymer structures, allow for the direct fabrication of complex structural implant components for use in BTE. However, the wall thickness of the product limits the SLS systems. In detail, research into the influence of wall thickness on mechanical properties and scaffold porosity is required to develop such lightweight and complex structures. In this study, Polyamide12-based bone Scaffolds were fabricated using the SLS technique by varying the wall thickness ranging from 0.9 mm to 1.10 mm in steps of 0.05 mm. Compression tests, porosity, scanning electron microscopy, and differential scanning calorimetry were conducted on the fabricated specimens. The studies demonstrated that the higher wall thickness benefits in reduction of porosity. The sample fabricated with a wall thickness of 1.1 mm has about 76% less porosity than the sample fabricated with a wall thickness of 0.9 mm. In addition, the study also found that compression strength decreases as porosity increases. The compressive strength of the scaffolds has been measured to be between 45.62 and 90.67 MPa for a wall thickness between 0.90 and 1.10 mm. The maximum compressive strength of a porous polyamide specimen is 90.67 MPa at a wall thickness of 1.10 mm. The fabricated samples with wall thicknesses of 0.9 and 0.95 mm were not mechanically stable, as their compressive strength values were lower than the compressive strength of human fibula bone (68 N/mm2).

Aerodynamic Drag Improvements on a Simplified Heavy Vehicle using Three-sided Plain and Notched Base Flaps

An experimental investigation has been undertaken to determine the effects of plain and notched base flaps on the drag performance of simplified tractor-trailer combination without any intermediate gap, Generalized European Transport System (GETS). Both plain and notched base flaps are rigid, made up of three identical flaps whose length is equal to the width of the GETS model, and not angled inward or outward. The experiments examined three-sided flap configurations corresponding to various combinations of seven heights of the plain part (from 10 to 40 mm in steps of 5 mm), four notch amplitudes (from 2.5 to 10 mm in steps of 2.5 mm), and five notch wavelengths (from 10 to 50 mm in steps of 10 mm). It is shown that the drag performance of the plain flap at zero yaw highly depends on the height of the plain flap. The maximum drag reduction occurs for e/w=0.1 yielding a drag reduction of 1.9% when compared to the GETS model without flap (baseline GETS). It was shown that the time-averaged drag coefficient increased slightly until a maximum was reached at e/w=0.3 but then decreased slightly with increasing e/w. Under zero yaw angle conditions, GETS model with a notched base flap, e10-a05.0-λ20, gives the lowest drag. The addition of this base flap to the GETS model resulted in a 2.8% drag reduction. This notched base flap was shown to be more effective not only at reducing <CD> under yawed flow conditions tested but also at reducing time-averaged side coefficient under yawed flow conditions tested, compared to the e10-a00.0-λ00 flap.

Finite element based model for predicting induced residual stresses and cutting forces in AISI 1020 steel alloy

AbstractThe application of finite element models is a promising method for ensuring part quality during machining to accurately predict induced residual stresses and cutting forces. The present study applied Analysis System software to formulate a 3D model to predict induced residual stress and forces for AISI 1020 alloy. Taguchi method was applied in the design of the experiment with three levels and three factors selected: Cutting speed, feed rate and depth of cut. For validation, stresses are measured using an x‐ray diffractometer from the surface to a depth of 0.6 mm in steps of 0.2 mm. The cutting forces are determined using a force dynamometer. Simulation results showed that cutting speed, feed rate and depth of cut contributed 94.76 %, 0.048 %, and 0.11 % respectively. The predictive model equations were statistically significant with a p‐value of <0.005. The average induced residual stress on the superficial layer from the experiment and simulation were −367.7 MPa and −365.6 MPa respectively. The average residual stresses obtained at depths of 0.2 mm, 0.4 mm, and 0.6 mm were −260 MPa, −233 MPa, and −211 MPa, respectively. The proposed model offers a potential solution to reducing the costs of experimental methods.

An Investigation of the Effects of Thermal Interference between Adjacent Nitinol Spring Actuators in a Tactile Display

Over the years, there has been increased research interest in the application of Nitinol as an actuator, due to its shape memory behaviour, simplicity, high power-to-weight ratio, compactness, and extreme high fatigue resistance to cyclic motion, and noiseless operation. Nitinol has found application in tactile displays which reproduce tactile parameters such as texture and shape, depending on the application. This paper presents the effects of thermal interference between adjacent Nitinol spring actuators in a tactile display. The tactile display is made of a 3 by 3 pin array whose spatial resolution was varied from 4 mm to 6 mm in steps of 1 mm while a current of 1.5 A was used to actuate 8 of the springs, and the centre spring was left unactivated to observe the thermal effects on it due to the heat gradient formed. A Finite Element (FE) model was developed using COMSOL Multiphysics and the results were further verified through experimentation. In both cases, there was visible thermal interference between actuators. The increase in spatial resolution saw a decrease in thermal interference by 12.7%. Using a fan to introduce forced convection, reduced the thermal interference in the simulation by 20% and during experimentation by 11%. The results of this research indicate a spatial resolution of 6 mm reduced the thermal inference to a negligible rate. However, thermal interference could not be eliminated with these two methods.

Influence of Wall-lumen Ratio of Umbilical Arteries on the Stress Distribution in Wharton's Jelly.

The umbilical cord is the link between fetus and the placenta. It consists of one vein and two arteries, encased inside Wharton's jelly. In this study, the influence of morphological parameters of umbilical arteries, namely the wall-lumen ratio and lumen diameter, on the stress distribution in Wharton's jelly is analyzed using a 3D finite element model. The lumen diameter of the arteries is varied from 0.4 mm to 2.0 mm in steps of 0.4 mm. The variation of average and maximum effective stresses in the Wharton's jelly with wall-lumen ratio is analyzed. Further, differences in stresses between the placental and fetal ends of umbilical cord are analyzed. Results show that, the average and maximum effective stresses at both ends of the umbilical cord vary nonlinearly with the wall-lumen ratio. For all the considered lumen diameters, the average effective stress is found to decrease with an increase in wall-lumen ratio at both the ends. An increase in the lumen diameter is found to be associated with a nonlinear decrease in average stress ratios. Clinical Relevance- The results of this study could be useful for the early diagnosis of fetal abnormalities and might be helpful to develop better treatment strategies.

Influence of pedicle screw thread width and recovery time after surgery on fixation strength

Abstract Introduction: Pedicle screw fixation systems are widely used for treatment of various spinal pathologies, including spinal stenosis, scoliosis, spinal deformities and fractures. Stress shielding is considered to be a major factor contributing to insufficient fixation strength, leading to screw loosening. In this study, the influence of pedicle screw thread width on the displacement of pedicle screw and stress transfer is analyzed using 2-Dimensional axisymmetric finite element (FE) model. Methods: FE model consisting of cancellous and cortical bone, along with pedicle screw is developed for this study. The pedicle screw thread width is varied between 0.1 mm and 0.6 mm in steps of 0.1 mm, while the other geometric parameters, including screw half-angle, pitch, diameter, and length are kept constant. Three different contact conditions between screw and bone, such as frictionless, frictional, and bonded are considered to simulate hours, days, and months after surgery, respectively. The material properties and boundary conditions are applied based on previous studies. An axial force of 80 N is applied on the screw head to simulate axial pull-out test. Results: Similar patterns of stress distribution are observed for all screw models, with high stress concentration above the first thread. The highest displacement in screw is observed shortly after surgery, while the highest displacement in cancellous and cortical bone is observed few days and months after the surgery, respectively. The average von Mises stress in screw decreases with increase in thread width for all contact conditions. In few hours/days after the surgery, stress transfer parameter increases with increase in thread width, up to a thread width of 0.5 mm and then decreases. The changes in stress transfer parameter are negligible few months after the surgery. Conclusion: This study highlights the influence of thread width on displacement and stress transferred to the bone, at different durations after the surgery. It is observed that a thread width of 0.5 mm exhibits the highest stress transfer, leading to reduced stress shielding and improved bone remodeling. It appears that this study might aid in developing better pedicle screws for the treatment of various spinal pathologies.

Technical light-field setup for 3D imaging of the human nerve head validated with an eye model

Abstract With the new technology of 3D light field (LF) imaging, fundus photography can be expanded to provide depth information. This increases the diagnostic possibilities and additionally improves image quality by digitally refocusing. To provide depth information in the human optic nerve head such as in glaucoma diagnostics, a mydriatic fundus camera was upgraded with an LF imager. The aim of the study presented here was the validation of the technical setup and resulting depth estimations with an appropriate eye model. The technical setup consisted of a mydriatic fundus camera (FF450, Carl Zeiss Meditec AG, Jena, Germany) and an LF imager (R12, Raytrix GmbH, Kiel, Germany). The field of view was set to 30°. The eye model (24.65 mm total length) consisted of a two-lens optical system and interchangeable fundus models with papilla excavations from 0.2 to 1 mm in steps of 0.2 mm. They were coated with red acrylic lacquer and vessels were drawn with a thin brush. 15 images were taken for each papilla depth illuminated with green light (wavelength 520 nm ± 20 nm). Papilla depth was measured from the papilla ground to the surrounding flat region. All 15 measurements for each papilla depth were averaged and compared to the printed depth. It was possible to perform 3D fundus imaging in an eye model by means of a novel LF-based optical setup. All LF images could be digitally refocused subsequently. Depth estimation in the eye model was successfully performed over a 30° field of view. The measured virtual depth and the printed model papilla depth is linear correlated. The presented LF setup allowed high-quality 3D one-shot imaging and depth estimation of the optic nerve head in an eye model.

Delineation of cutter force and cutter wear in different edge configurations of disc cutters – An analysis using discrete element method

Disc cutters are used to cut the rocks in variable load conditions which results in cutter wear and failure. The wear of the cutter plays a vital role in the overall time cycle, efficiency and economics of tunneling projects. It changes the shape of the cutter, influences the cutting efficiency and has a detrimental effect on the annual cost of maintenance, availability, and utilization. In tunneling using TBMs, assessment of wear behavior of the cutters is the most crucial problem to investigate. In this study, interactions between cutter and rock were presented. Cutters with various configurations such as 0, 10, and 20-degree tip angles with different tip widths 7.3 mm and 4.5 mm were used. Cutter penetration varied from 2 to 8 mm in steps of 2 mm. The diameter of cutters are fixed at 6.5 in. and simulation runs against the rock were done for 1.2 m in length. In this simulation, normal force, tangential force, and wear were computed with the help of EDEM software for each configuration. Simulation results show that the tip angle of the cutter and depth of penetration directly affected the cutter wear. A tip angle of 100 with 7.3 mm tip width and 6 mm depth of penetration in the rock is the best configuration for obtaining the minimum wear of the cutter. The simulation results are also verified with the previous mathematical models suggested by different researchers. The suggested approach for simulation can help analyze the cutter wear behavior close to real life with given input parameters.

Numerical Prediction and Reduction of Pressure Loss of Air Flow Inside a Sharp 90˚ Elbow Using Turning Vanes

The aim of this study is to calculate the pressure loss and the effect of turning vanes on the pressure loss incurred by the flow in a duct with a 90˚ sharp elbow using numerical fluid mechanics. The main focus this study was to calculate the effects of the number of turning vanes and the length of the turning vanes on the pressure loss. Computational Fluid Dynamics calculations have been carried out using ANSYS Workbench software. Two turbulence models have been used in these calculations. They are the standard k- and the k- turbulence models. The number and length of the vanes were changed in the study to calculate their effects on pressure loss. The length of the vanes was varied from 0mm to 400mm in steps of 100mm on both sides of the bend and the number of vanes was changed from 0 to 3. It was found that a single curved turning vane can reduce the pressure loss significantly. The pressure loss does not reduce further when the length of the vanes was extended. As the number of turning vanes increased beyond one, the predicted pressure loss starts increasing. The turning vanes in duct systems can be used in industries and factories to reduce the pressure loss.

Marker placement sensitivity of the Oxford and Rizzoli foot models in adults and children

Understanding the effect of individual marker misplacements is important to improve the repeatability and aid to the interpretation of multi-segment foot models like the Oxford and Rizzoli Foot Models (OFM, RFM). Therefore, this study aimed to quantify the effect of controlled anatomical marker misplacement on multi-segment foot kinematics (i.e. marker placement sensitivity) as calculated by OFM and RFM in a range of foot sizes. Ten healthy adults and nine children were included. A combined OFM and RFM marker set was placed on their right foot and a static standing trial was collected. Each marker was replaced ± 10 mm in steps of 1 mm over the three axes of a foot coordinate system. For each replacement the change in segment orientation (tibia, hindfoot, midfoot, forefoot) was calculated with respect to the reference pose in which no markers were replaced. A linear fit was made to calculate the sensitivity of segment orientation to marker misplacement in °/mm. Additionally, the effect of foot size on the sensitivity was determined using linear regressions. For every foot segment of both models, at least one marker had a sensitivity ≥ 1.0°/mm. Highest values were found for the markers at the posterior aspect of the calcaneus in OFM (1.5°/mm) and the basis of the second metatarsal in RFM (1.4°/mm). Foot size had a small effect on 40% of the sensitivity values. This study identified markers of which consistent placement is critical to prevent clinically relevant errors (>5°). For more repeatable multi-segment models, the role of these markers within the models’ definitions needs to be reconsidered.

Impact of artificial roughness variation on heat transfer and friction characteristics of solar air heating system

The present study describes the optimization of the spacer length parameter of perforated delta-shaped winglets (PDWs) imposed on the absorber plate of the solar air heater (SAH). An experimental set up is designed to analyze the influence of artificial roughness (AR) variation on the thermo-hydraulic performance of SAH. The variable parameter of the PDWs is the spacer length (Spdw) which varies from0 mm to 300 mm in steps of 100 mm. The impact of variation of Spdw on Nusselt number (Nupdw), friction factor (frpdw) and thermo-hydraulic performance (ηpdw) is investigated. The fixed parameters of the PDWs are relative roughness height of perforated delta-shaped winglets = 0.8, relative longitudinal length of the perforated delta-shaped winglet = 2, relative transversal length of the perforated delta-shaped winglet = 0.66 and angle of incidence = 90°. The Nupdw and frpdwof SAH provided with artificial roughened in the form of PDWs were improved by 5.17 and 4.52 times in comparison to SAH having smooth absorber plate. At the optimum value of spacer lengthSpdw = 0 mm and Re of 12000, ηpdw attains a maximum value of 3.14 (>1). The study reveals the effectiveness of perforated delta winglets in the heat transfer augmentation of SAH.

Performance of a Twin-Intake Diesel Engine With Guide Vanes During an Intake Stroke Revealed Through Simulations and Experiments

To improve the flow characteristics of diesel engines with twin intake ports, this study evaluates the installation of guide vanes of varying lengths, heights and angles in front of the intake runner of a CA4DD diesel engine. Considering the interference among various parameters of the guide vane, the parameters were studied with uniform design. To study the effect of guide vanes on the twin-intake diesel engine during the intake stroke, 9 guide vane models, where the vane lengths were 30–70 mm, the vane heights were 1.5-13.5 mm, and the vane angles were 4-36°, were compared with a base model without a guide vane. CATIA was used to build a simulation model, and XFLOW was used to run a three-dimensional (3D) computational fluid dynamics (CFD) simulation. Simulation of different valve lifts of 2–10 mm in steps of 2 mm showed that the guide vane slightly affected the flow coefficient and obviously affected the swirl ratio. Furthermore, designs 4, 5 and 6 had different performance improvements under different valve lifts. The velocity and vorticity of the in-cylinder were evaluated. Moreover, 9 guide vane models were fabricated and tested on a steady-flow test bench. The experimental results show that the swirl ratio average increase of the guide vane models compared to the base model is 21%. The maximum increase is 39% when the guide vane height is 6 mm, the length is 65 mm, and the angle is 24°; when the guide vane height is 7.5 mm, the length is 50 mm, and the angle is 20°, the average increase is 27%. The flow coefficient is less affected and fluctuates at approximately 2%. Hence, the experiments and simulations in this work yield consistent results, and the application of guide vane models compared to a base model can improve the performance of diesel engines.

Behavior of linear compliant mechanism using numerical and experimental method

In today's fast-moving and competitive world, the engineering applications are evaluated based on the precise and accurate results. The intense need for precision motion is achieved with the help of deflection of beams in compliant mechanism. A special class of mechanism is referred to as compliant mechanisms that are based on the rigidity and mobility of a component, which lead to greater precision without affecting its accuracy. Major failures of compliant mechanism are due to in plane and out of plane movement of compliant beams for the repetitive use. Life of compliant mechanism needs to improve for large deflection values. Motion is created by molecular deformation with bending of beams in elastic zone. Compliant mechanism are used in modern techniques such as micro-nano processing microscopy, biomedical scanner are existing mechanisms for precision scanning. Available biomedical scanner is using ball screw mechanism to achieve X directional and Y Directional scanning range. Ball screw mechanism provides 0.5 mm displacement in single stroke which takes so much times to stabilize the image. Compliant mechanism provides displacement of 0.1 mm in step. Biomedical scanner required X and Y Direction scanning range of 6 mm which we can achieve by using compliant mechanism. In present paper Experimental and Numerical analysis of compliant mechanism is done for linear motion which is used in biomedical scanner. Static structural analysis on Compliant mechanism is performed to get linear displacement values with steel, Titanium alloy and Aluminium alloy. Modal analysis of Compliant mechanism is performed to get natural frequency of system with steel, Titanium alloy and Aluminium alloy for better stability of mechanism we can operate Compliant system below that resonance frequency. By using Compliant mechanism we will get smooth range of motion over ball screw mechanism.

Microwave spectrometry for the evaluation of coronary stents

Abstract Background Coronary artery disease (CAD) is the leading cause of death worldwide, and percutaneous coronary intervention with stenting the most widely performed procedure to treat CAD. However, current stent monitoring techniques are invasive and/or ionizing. Microwave spectrometry (MWS) may provide a non-invasive, non-ionizing and cost-effective alternative capable of detecting stent-related pathologies before fatal heart failure. Purpose To develop a new MWS-based technology to detect coronary stents in an in vivo swine model. Methodology First, using two new MWS devices, an in vitro experiment was carried out to demonstrate their ability of detecting the presence of: (1) a stent and (2) stent fractures (SF). To that end, an intact stent was distanced 3, 7, 11 and 15 mm from a MWS near-field probe in open-air conditions. Afterwards, three identical stents were piecemeal cut to emulate type I, II and III SF at different fractions of the stent's length (l): l/5, l/3 or l/2. Additionally, the stent was measured in a phantom substance, to simulate in vivo conditions: it was distanced from 0 to 40 mm in steps of 5 mm. Likewise, using a pair of MWS far-field antennas, the stent in phantom was measured at 10, 20, 30 and 40 mm. Finally, the MWS technology was assessed in vivo. To that end, six Landrace X Large White pigs were submitted to a stent implantation into the circumflex coronary artery (CX). The antennas measured the stent non-invasively, over the rib cage of the animals. MWS analysis were performed baseline (before stent implantation), and at 0, 3, 7, 14, 21 and 35 days of follow up. Measurements were performed only before ventricular systole to avoid differences in the stent position and deformation. Results In vitro, maxima and minima extrema in the microwave frequency response (see figure) were used to detect the stent. Type I and II SF produced 5 and 10% downshifts in the extrema frequencies with respect to the baseline values (unbroken stent), while type III produced 20% upshifts and a maxima splitting. Embedding the stent in phantom produced 25% downshift in the extrema frequencies. In vivo, the MWS antennas were useful to detect the stent presence into the CX artery during all time points of study, in all animals. Conclusions We have developed a new non-invasive and non-ionizing MWS technology capable of detecting the presence of a stent in a porcine model. Furthermore, we have proven how our technology can monitor structural damages in the stent (SF) and changes in its environment. This study proves the MWS potential to become a simple and yet effective method to arise stent-related pathologies in a pre-clinical stage; it could also provide physical insight about additional biological processes. Further improvements on the MWS device as well as in vivo measurements will ensure its consistency when monitoring human stents. Stent detection using MWS technique Funding Acknowledgement Type of funding source: Foundation. Main funding source(s): Fundaciό La MARATÓ de TV3, Generalitat de Catalunya, Red de Terapia Celular – TerCel, CIBER Cardiovascular, Spanish Agencia Estatal de Investigaciόn Unidad de Excelencia Maria de Maeztu, Sociedad Española de Cardilogía

Kombination aus Dezentrierung und Verkippung der Linse im phaken und pseudophaken Auge – optische Simulation von Defokus, Astigmatismus und Coma

Hintergrund und ZielsetzungDer Einfluss von Dezentrierung und Verkippung von Kunstlinsen auf die Abbildungsqualität ist in den vergangenen Jahren ausgiebig in Simulationen wie auch klinischen Studien untersucht worden. Ziel dieser Arbeit ist es, den Einfluss der Dezentrierung und Verkippung auf die Induktion von Defokus, Astigmatismus und Coma im phaken und pseudophaken Auge zu untersuchen.MethodenAuf der Basis des Liou-Brennan-Modellauges wurde eine Simulation mit Zemax durchgeführt. Ausgehend von der im Augenmodell beschriebenen Position der Gradientenlinse, wurde nach der Bestimmung der Fokusebene die Linse von −1,0 bis 1,0 mm in Schritten von 0,2 mm horizontal dezentriert und von −10° bis 10° in Schritten von 2° um die vertikale Achse verkippt. Zu jeder der 121 Kombinationen wurde bei einer Pupille von 4 mm der Defokus, der reguläre Astigmatismus in 0/180° sowie die horizontale Coma aus der Wellenfront extrahiert. Analog zum phaken Auge wurde die Gradientenlinse durch ein aberrationskorrigierendes Kunstlinsenmodell ersetzt und die Simulation für das pseudophake Auge wiederholt.ErgebnisseIst die Linse im phaken/pseudophaken Auge entsprechend den Vorgaben des Liou-Brennan-Modellauges positioniert, ergibt die Simulation einen Defokus von 0,026/−0,001 dpt, einen Astigmatismus von −0,045/−0,018 dpt sowie eine Coma von −0,015/0,047 µm. Maximale Werte treten bei einer Dezentrierung von 1,0 mm und einer Verkippung von 10° auf: 1,547/2,982 dpt für den Defokus, 0,971/1,871 dpt für den Astigmatismus sowie 0,441/1,209 µm für die Coma. Maximal negative Werte treten im phaken/pseudophaken Auge auf bei: −0,293/−1,224 dpt für den Defokus, −0,625/−0,663 dpt für den Astigmatismus sowie −0,491/−0,559 µm für die Coma.DiskussionIn dieser Studie wurde erstmals der Effekt einer Kombination aus horizontaler Dezentrierung der Linse und Verkippung um die Vertikale auf den induzierten Defokus, Astigmatismus sowie die horizontale Coma in einem Simulationsmodell untersucht. Die Ergebnisse können bei der Ursachenforschung helfen, wenn bei dezentrierter oder verkippter Kunstlinse die Zielrefraktion nicht mit der erreichten Refraktion übereinstimmt oder der resultierende Astigmatismus durch den Hornhautastigmatismus alleine nicht erklärbar ist.

Mixing Characteristics and Enhancement of Sonic Elliptic Jets from a Twin Elliptic Orifice

The knowledge of jet mixing and its enhancement of elliptic jet are important in a propulsion system of aircraft, rocket, and missile’s system design for advancement of combustion via fuel-air mixture increment, lowering the jet noise and reduction of the plume infrared (IR) signature. The jet issuing from a twin elliptic orifice is non-uniform in shape that promotes the faster mixing and it influences by orifice exit conditions, so knowledge of absence of boundary layer and jet mixing characteristics is important. Hence, an experimental work helps to study the jet mixing for a twin elliptic orifice of aspect ratio two at nozzle pressure ratios of one, two, and three. The proximity between the orifices kept as one to 3mm in steps of one. The experimental readings were taken using pitot probe. The results revealed that jet mixing is faster and effective when the proximity between the orifices is closer to each other than the faraway distances at measured nozzle pressure ratios. Difference in orifice jet core exerted a noticeable influence at high proximity levels of nozzle pressure ratio of three and four for elliptic orifice.

Influence of stepped cylindrical turbulence generators on the thermal enhancement factor of a flat plate solar air heater

This study presents the numerical analysis on the enhancement of thermal performance of a flat plate solar air heater provided with stepped cylindrical turbulators attached below the absorber plate for assessing performance parameters such as Thermal Enhancement Factor and Thermohydraulic Performance Parameter for Reynolds numbers ranging from 3000 to 24,000. The study reveals that the cylindrical stepped turbulators led to the flow becoming highly turbulent. This flow behavior with the flow separation around the stepped generators has a beneficial aspect with regards to the performance. An attempt has been made in this paper to explain the complex flow behavior as observed from the analysis. For core diameter varying from 3 mm to 7 mm in steps of 1 mm and the relative roughness pitch ratio is varied as 11.11, 16.67, 22.22, and 27.78. The number of steps on the turbulator is varied from 1 to 3 and the number of rows of turbulators is varied from 1 to 3. The maximum Nusselt number of 76.41 is obtained for a core diameter of 7 mm corresponding to a three-row configuration at a flow Reynolds number of 24,000. It is found from the study that the thermal enhancement factor increases with the increment in number of rows and also increases with decrease in core diameter for Reynolds number range beyond 12,000. With the increasing roughness pitch the thermal enhancement factor decreases for a given configuration, while for the increase in number of steps there is a remarkable improvement in the thermal enhancement factor. A maximum thermal enhancement factor of 1.14 is achieved corresponding to a Reynolds number of 15,000. A maximum thermohydraulic performance parameter of 1.49 is achieved corresponding to a Reynolds number of 18,000 from the analysis.

Torque Ripple Reduction of Switched Reluctance Motor by Changing the Rotor Pole Tip Radius

Switched Reluctance Motor has the main limitation of high torque ripple because of its doubly salient structure. This paper presents the Finite Element (FE) analysis of 5 hp, 655 V, 8/6 Switched Reluctance Motor with rotor pole shaping to reduce torque ripple. It is observed that rotor pole tip radius variation significantly affects torque ripple. Tapered rotor pole having high tip radius results into reduced torque ripple. Rotor pole tip radius is changed from 0 to 5 mm in step of 1 mm and FE analysis is carried out to obtain average torque and torque ripple. It is examined that torque ripple is reduced from 69.1 % to 39.3 % with this technique.

Numerical Analysis on Cone Length and its Effect on Performance of an Automotive Catalytic Converter

Internal combustion engines are one of the major contributors of air pollution. Exhaust gas from these engines contains HC, CO, NOx, PM and smoke which are the harmful pollutants to humans as well as to the environment. The stringent norms enforced by governments has necessitated in improving the after-treatment processes of these exhaust gas. A three-way catalytic converter is one of the most effective devices in treating the HC, CO and NOx pollutants into non-toxic gases. In this paper, numerical investigation is carried out by using commercial CFD code, ANSYS Fluent to analyse the effect of cone length on the conversion efficiency of the Catalytic Converter (CC). Pressure drop, back pressure and temperature are the parameters which are monitored in this study. The cone length of the CC is varied from 70mm to 90mm in steps of 10mm. All the CCs are analysed for identical test conditions. It is observed that temperature and pressure showed an appreciable decrease with increase in cone length to 90mm. On the other hand, velocity increases with increase in cone length to 90mm. A lower pressure drop and temperature is observed for the CC with cone length of 90mm. As conversion efficiency of the CC is dependent on the lower pressure drop, lesser back pressure and lower temperature, the CC with cone length of 90mm is found to be the apt choice.