Effects Of Changes In Geometry Research Articles

Effect of angular variation and in vitro degradation on mechanical properties of PBAT 3D scaffolds

AbstractThe customization of polymeric prototypes is available to meet the specific needs of individual patients, considering tissue location and patient‐specific characteristics. Poly (butylene adipate‐co‐terephthalate) (PBAT) has shown great promise among various polymers in this scenario due to its biodegradability and processability properties. However, the effect of geometry changes on the mechanical properties of PBAT 3D scaffolds and their mechanical stability after in vitro degradation are crucial to determining the final application. This study focuses on the structural, morphological, and mechanical characterization of PBAT prototypes with different architectures and evaluating their mechanical properties before and after in vitro degradation. Three‐dimensional structures were 3D printed with rectilinear deposition angles of 15°, 30°, 45°, 60°, 75°, and 90°. Mechanical tests revealed that the prototype architecture influenced the stiffness, elongation, and maximum tension, where a greater resistance was observed for filaments containing the lowest angles. The thermal stability of PBAT remained unaffected either by reprocessing or hydrolytic degradation; however, in vitro degradation affected the mechanical behavior by increasing the stiffness and decreasing the elongation of the scaffold. Biological assays have demonstrated the nontoxic nature of PBAT and its potential to promote cell viability at a rate of 95%. These findings underscore the possibility of optimizing the PBAT design and structure to tune the mechanical properties and contribute to advancing tissue engineering strategies.

Investigating the Effect of Abrupt Change in Geometry on Structural Failure of Artillery Projectile 155 mm

Investigating the Effect of Abrupt Change in Geometry on Structural Failure of Artillery Projectile 155 mm

High temperature effects in hypersonic double-wedge flow simulations

Numerical simulations of inviscid hypersonic flow over a double-wedge geometry are conducted. High temperature effects are studied using a local thermodynamic equilibrium based model for air. A finite volume based flow solver is developed by combining a weighted essentially non-oscillatory scheme with an approximate Riemann solver. An iterative method to compute shock polars under local thermodynamic equilibrium conditions is suggested. Numerical simulations are conducted to study the effects of changes in geometry, upstream temperature, and upstream velocity. A range for the second wedge angle is identified for which the solution becomes oscillatory. An explanation for this oscillatory nature of the solution is suggested. Existence of a hysteresis phenomenon is also identified. A change in the nature of interaction is observed with changes in upstream temperature and upstream velocity. Local thermodynamic equilibrium based results are compared to those obtained using a calorically perfect gas model for air. Significant differences are observed. Effects of viscosity on the flow field are also studied.

The deposition kinetics of barium sulphate scale: model development

The deposition kinetics of barium sulphate scale: model development

Assessing the effects of road geometry and fidelity on driver behaviour in driving simulator experiments

The paper presents a set of programs created specifically to investigate the driver’s behaviour along a road circuit when the driving simulation scenario changes in the quantity and quality of the displayed Level of Details (LOD) (fidelity), as well as when the road curvature ratio (geometry) varies. In the experiments, carried out on a sample of 29 drivers who drove on the same circuit twice, data on vehicle features (speed, trajectory, and gas pedal usage), physiological factors of the drivers (SC, skin conductance), and information from an eye-tracking equipment (gaze) were collected. The programs used in this study are designed to study the complex and position-based information present in the data that cannot be analysed by classical statistical methods. The results are twofold. On one side, they show the applicability and usefulness of the proposed functions, which are capable of extracting information and referring it to a specific point in the circuit. On the other side, they give effective insights on driving behaviour. When driving is more demanding (i.e., along curvilinear stretches), variations between different scenarios are nearly non-existent, and the effect of geometry changes greatly depending on the signal being investigated (speed, trajectory, gas pedal, gaze, skin conductance). The effects of vehicle speed are essentially the same for all drivers and are closely tied to the geometry of the road. Trajectory and gas-pedal usage signals exhibit diverse effects on drivers, indicating that their choice of trajectory and frequency of gas-pedal usage is undoubtedly influenced by their driving style as well as by geometry. Skin conductance appears to be significantly altered where driving is more challenging, but it varies greatly from driver to driver. The results of gaze analysis also demonstrate that the driver’s behaviour strongly depends on geometry and much less on LOD and loop sequence.

Interpretation of non-conventional miniaturized creep test: derivation of equivalent gauge length

The objective of this paper is to clarify the nature of the equivalent gauge length of miniaturized creep test methods. A mechanics-based approach was employed to allow conventional uniaxial creep data to be obtained from non-conventional miniaturized creep tests, under steady-state creep. The data interpretation is based on the reference stress method. On this basis, the theoretical derivation of the equivalent gauge lengths for a range of miniature specimen types is presented, including sub-size uniaxial, small punch, impression, small rings, miniature 2 bars, and miniature bending beams and plate. Then the effect of geometry change due to the creep test on the conversion parameters is evaluated. Finally, several theoretical and practical aspects, related to specimen deformation modes, the basis of the correlation methods, the sensitivity of “strain measurements”, the effective volumes, the choice of test methods, etc, are addressed.

Development of an improved limit pressure equation for structurally distorted thin-walled pressurized 90 degree pipe bends

PurposeThis paper aims to present the approximate limit pressure solutions for thin-walled shape-imperfect 90° pipe bends. Limit pressure was determined by finite element (FE) limit analysis with the consideration of small geometry change effects.Design/methodology/approachThe limit pressure of 90° pipe bends with ovality and thinning has been evaluated by geometric linear FE approach. Internal pressure was applied to the inner surface of the FE pipe bend models. When von-Mises stress equals or just exceeds the yield strength of the material, the corresponding pressure was considered as the limit pressure for all models. The current FE methodology was evaluated by the theoretical solution which has been published in the literature.FindingsOvality and thinning produced a significant effect on thin-walled pipe bends. The ovality weakened pipe bend performance at any constant thinning, while thinning improved the performance of the bend portion at any constant ovality. The limit pressure of pipe bends under internal pressure increased with an increase in the bend ratio and decreased with an increase in the pipe ratio. With a simultaneous increment in bend radius and reduction in wall thickness, there was a reduction in limit pressure. A new closed-form empirical solution was proposed to evaluate limit pressure, which was validated with published experimental data.Originality/valueThe influences of structural deformation (ovality and thinning) in the limit pressure analysis of 90° pipe bends have not been investigated and reported.

Analytical Framework for Space Debris Collision Avoidance Maneuver Design

An analytical formulation for collision avoidance maneuvers involving a spacecraft and a space debris is presented, including solutions for the maximum deviation and minimum collision probability cases. Gauss’s planetary equations and relative motion equations are used to map maneuvers at a given time to displacements at the predicted close approach. The model is then extended to map changes in state between two times, allowing one to propagate covariance matrices. The analytical formulation reduces the optimization problem to an eigenproblem, for both maximum deviation and minimum collision probability. Two maximum deviation cases, total deviation and impact parameter, are compared for a large set of spacecraft–debris conjunction geometries derived from European Space Agency’s Meteoroid and Space Debris Terrestrial Environment Reference (MASTER-2009) model. Moreover, the maximum impact parameter and minimum collision probability maneuvers are compared assuming covariances known at the maneuver time, to evaluate the net effect of lead time in collision probability. In all cases, solutions are analyzed in the b-plane to leverage its natural separation of phasing and geometry change effects. Both uncertainties and maximum deviation grow along the time axis for long lead times, limiting the reduction in collision probability.

Necessary Height of the Vertical Stiffeners in Steel Silos on Discrete Supports with Accounting of Imperfections

To ensure unloading of the whole amount of stored product by gravity, the steel silos are often placed on supporting frame structure. The values of stresses in the joints between the thin shell and supporting frame elements are extremely high. It can cause local loss of stability in the shell. To prevent it, many designers place stiffening elements above the supports. Here the question is how high should be the stiffening elements? The appropriate solution is that they should rise to that level till which the values of meridional normal stresses above the supports and in the middle between them are equalized. But where is this level? Many researchers worked on values and ways of distribution of normal meridional stresses above the supports of the cylindrical shells. As a result of their efforts are determined critical height Hcr of the shell and the ideal position HI of intermediate stiffening ring. But these heights are considerably different between each other. To which of them our vertical stiffening elements should achieve? Considering the nonlinear behaviour of the steel, the effects of changes in geometry during loading and imperfections caused by welding works, the author tried to obtain an answer to this question.

Assessment of turbine stages and blade numbers on modified 3D Savonius hydrokinetic turbine performance using CFD analysis

PurposeIn Southeast Asia, the renewable energy produced from hydropower systems has significant potential. Therefore, adequate development is needed to prevent future energy-related crises. This study, therefore, aims to determine the variations effects in geometry and the geometrical factors on turbine performance.Design/methodology/approachThe developed aspects are selected to determine the blade shape, its number and multistage requirements. The study was conducted in 3D simulation, with Ansys software used to calculate a series of computational fluid dynamic problems. The aspect ratio applied in this study utilized the ratio of the overall diameter of the rotor height (D / H), which is 1.FindingsThe results showed that the highest Cp-max value, number of blades and stages were 0.2, two and three, respectively. Furthermore, these attributes combined to improve the performance of hydroturbines.Research limitations/implicationsThe research was fully conducted using numerical simulation, which requires sustainable research in the form of laboratory experiments. Also, pioneer experiments were conducted using benchmarking to ensure the results obtained are reliable.Practical implicationsHydropower is one of the best renewable energy sources in Indonesia with a large potential in the archipelago and tropical countries due to rivers and various water sources. The current generated is a useful reference for Savonius design.Originality/valueThe originality of this study is to examine the three aspects of the geometry of the rotor, such as the number and shape of blades, as well as the stages in the same boundary conditions. Therefore, the comparison of the effects of changes in geometry on turbine performance is more acceptable and complete compared to the pioneer works, which focused on a parameter. This research combines several aspects to determine the effect of rivers and various water sources on the hydroturbine.

Modeling of One-ply and Two-ply Twisted and Coiled Polymer (TCP) Artificial Muscles

Twisted and coiled polymer (TCP) muscles are recently introduced thermal actuators that offer unprecedented performance. Merits such as low cost, high load capacity, and light weight make them suitable for robotics and biomechanics. Using these actuators for practical applications requires an understanding of their behavior in response to the electrical input. In this article, a physics-based model is proposed to predict the displacement of TCP muscles with respect to the input electrical energy and the applied load. We quantified effects of temperature on coefficients of thermal expansion and elastic modulus. It is found that the change of properties above the polymer glass transition temperature has a crucial effect on the actuator performance. A stiffness model is proposed, which include the effect of change in geometry and elastic modulus of TCP muscles. Finally, a set of equations for simulating the TCP muscles are formulated in discrete time representation. The model is generalized for the two-ply case by considering the difference in geometry. The accuracy of the model is tested in comparison with experimental data, acquired at several actuation levels and applied loads, for both one-ply and two-ply configurations. The model showed a good accuracy in predicting the behavior of the actuators both in temperature and displacement. Our model was also compared with other representative models and revealed improvement in the prediction accuracy.

Examining the Effect of Geometry Changes in Industrial Fuel Injection Systems on Hydrodynamic Structures With BiGlobal Linear Stability Analysis

Abstract Shape optimization with respect to the suppression or enhancement of dynamical flow structures is an important topic in combustion research and beyond. In this paper, we investigate the flow in an industrial fuel injection system by experimental means, as well as large eddy simulation (LES) and linear stability analysis (LSA) for two configurations of the swirler. In the first configuration, the reference geometry, a precessing vortex core (PVC) occurs. In the second configuration, a center body is mounted in the interior of the injector. It is shown by both experiments and LES that the PVC is suppressed by the presence of the center body, while the mean flow remains nearly unaffected. The method of LSA is applied in order to explain the effect of the geometry change. The work shows that LSA is capable of explaining the occurrence or disappearance of coherent structures evolving on the turbulent flows if the geometry is changed. This is an important step in using LSA in the context of shape optimization of industrial fuel injectors.

Changes in Pipe Geometry in the Course of Sequential Creation of Stresses on the Inner Surface under External Thermomechanical Impacts

In modern high-technology industry, pipe bending technology is widely used. Pipe bends are an integral part of pipeline systems. The most widely used methods are techniques of cold pipe bending accompanied by a number of negative phenomena such as reduction in the wall thickness on the outer side of the bend, ovalization of the cross section, and formation of crimps. The article presents a study of the influence of deforming pipe billets by rolling under high tension on the structure and properties of the billet’s material. The pipe deformation by rolling under tension allows obtaining radially bent billets without destroying them and without causing obvious defects on the surface and microstructure. The tests were conducted using samples manufactured of 3sp (ASTM 284 grade D) and 12Cr18Ni10Ti (UNS S32100) grade steels. The microstructure was examined in accordance with GOST 5639–82 state standard, the mechanical properties were investigated in accordance with GOST 1397–84, and the microhardness—in accordance with GOST 9450–76. The effect of geometry changes of the pipe billets on their structure and properties was studied. It is shown that the pipe deformation by rolling leads to changes in the mechanical properties of the tested materials. The microhardness and strength values increase, while the grain points decrease. In the course of deformation, the microstructure of the material may change as a result of structural transformations (quenching). The plastic flow of the metal during the thermomechanical deformation suggests possible change in the pipe wall structure as a result of recrystallization and heat treatment of the material in the bend area, which requires further study and in-depth analysis of the technology in question.

A Numerical Study of fluid flow and Pressure Drop analysis of Catalytic Converter using Commercial CFD code

In recent years catalytic converter is a necessary device to achieve low emissions in all the vehicles. This study of the after treatment device is to understand the fluid flow and to optimize the design. It is important to know the pressure drop taking place inside the catalytic converter in order to design the catalytic converter. In this paper, a numerical study has been conducted to study the effect of fluid flow inside the catalytic converter and effect of change in geometry using commercial CFD tool. The working fluid considered in this study is air. A 3D simulation is carried out having straight inlet pipe and with change in inlet pipe angle of the catalytic converter. The monolith substrate region is modeled as a porous medium. The governing equations namely conservation of mass, momentum are used for solving the analysis. The analysis involved determining pressure variation across the geometry of the converter system for different mass flow rates and change inlet pipe angle. The numerical results were used determine the pressure drop across the substrate and the flow characteristics inside the catalytic converter. The numerical study shows good conformance with the experimental results with maximum deviation of error 2.54% for straight inlet pipe configuration. The effect of change in inlet pipe angle, effect of inlet cone angle and effect of splitting the substrate into sections are also presented.

The effect of angle of attack on the aeroacoustic environment within the weapons bay of a generic UCAV

Cavity flow studies are generally concerned with observing the effect of geometry changes whilst maintaining a fixed zero angle of attack. Cavities employed as weapons bays will, however, experience a range of angles of attack. This paper presents the first known results showing the effect of flight angle of attack on the aeroacoustic characteristics of an internal weapons bay installed in an uninhabited combat air vehicle (UCAV). The UCAV geometry consisted of a Boeing M219-type cavity in a Boeing UCAV1303 airframe. Numerical simulation was conducted using a full-scale detached eddy simulation model and representative transonic flight conditions. As well as the reference case of zero degrees, data for angles of attack of 3.0, 4.5 and 6.0 degrees were analysed. Experimental data was used to validate the reference computational model, which agreed with the overall fluctuating sound pressure level (OAFPL) to within the experimental uncertainty of 4 dB. Data from the computational model was post-processed with frequency-domain and time-frequency-domain techniques showing that the flow structure within the weapons bay was altered significantly by the angle of attack changes, affecting the mean pressure distribution, frequency spectra and resonant modes. Overall, increasing the angle of attack from 0.0 to 3.0 degrees produced an increment in the acoustic load whilst a further increase tended to affect the resonance mechanism and thereby reduce the coherence and the temporal footprints of the resonant modes.

A finite strain electro-chemo-mechanical theory for ion transport with application to binary solid electrolytes

An electro-chemo-mechanical formulation of ion transport in solid electrolytes, in particular for binary systems, is presented. Starting with conservation laws and the second law of thermodynamic, we state a consistent Helmholtz-energy-based framework taking electrostatics, component transport and nonlinear elastic mechanical interaction into account. With the help of finite strain continuum mechanics, we include the effect of geometry changes on ion transport. Changes of local concentration cause swelling and shrinkage and hence stress assisted diffusion. Further coupling originates via an osmotic pressure. Since binary systems are of special interest in battery applications, we formulate both, a fully resolved and an electroneutral model for ion transport. The latter turns out to be an extended version of Newman’s concentrated solution theory taking mechanical effects into account. We demonstrate the importance of these mechanical effects by means of double layers adjacent to blocking electrodes and concentration profiles during galvanostatic charging. Further, we investigate the effect of external deformation as, e.g. found in dendrite growth.

Coupled Finite Element Modelling of Geosynthetic Reinforced Embankment Slope on Soft Soils Considering Small and Large Displacement Analyses

The behaviour of a real case of geosynthetic reinforced embankment slope (GRES) over soft cohesive soils with a prefabricated horizontal drains system (PHDs) was studied by two-dimensional finite element method, considering both small and large displacement assumptions. In order to determine the input geotechnical parameters accurately, laboratory tests and finite element back analysis were carried out. Coupled mechanical and hydraulic analysis was conducted to predict time-dependent behaviour of GRES under staged loading applied in the undrained conditions. The main objective of this study is to assess the effects of changes in geometry on deformation and stress behaviour during the consolidation process. Indeed, the developments of the settlement, horizontal displacement, excess pore pressures, normal effective stress and shear stress during and after construction periods were investigated. According to the large displacement computation results, the combined use of geosynthetic reinforcement with PHDs significantly reduces both the settlement and horizontal displacement but increases pore pressures. Therefore, the required number of construction stages can be reduced. The results of small and large displacement analyses show that the shear strength improvement in the upper embankment part is induced by the combination of surface roughness (skin friction) and arching effects within the embankment fill, while in the lower part it is mainly due to the confinement effect.

CFD Analysis of Turbocharger Compressor to Study the Effect of Geometry Change on Surge and Performance of Compressor

CFD Analysis of Turbocharger Compressor to Study the Effect of Geometry Change on Surge and Performance of Compressor

Load-Separation Method, Spb, Used to Estimate Crack Extension for J-R Curves, Modified for Geometric Variations in Blunt-Notched Remaining Ligament

Abstract The Spb method estimates stable crack growth in fracture mechanics precracked specimens test. It compares the load ratio between a precracked specimen that exhibits stable crack growth and a blunt-notched specimen with apparent constant crack length when tested at constant displacement. When it was applied to very tough material, it was found that blunt-notched remaining ligaments varied by as much as 11.83 %, affecting visibly the results. Therefore, to apply the Spb method to very tough material for which non-standard specimens could be used as coiled tubing, the methodology limits are investigated. In this work, particularly the effect of geometry changes through an incipient crack growth produced on the blunt-notched specimens for very tough materials is analyzed. Hence, a modified Spb method is presented that takes into account the change in geometry of the blunt-notched specimens. Results provided in this paper are quite encouraging.

Analysis of the effect of repair welding/grinding on the performance of railway crossings using field measurements and finite element modeling

In this paper, the effects of repair welding and grinding, which are currently the main components used in the maintenance of crossings, on the performance of crossings are analyzed. It has been observed that sometimes the welding and grinding activities that directly affect the geometry of the crossings and/or material properties can have negative effects on the performance and ultimately on the service life of the crossings. In this paper, the effect of the changes of geometry has been studied experimentally, while the effect of the changes in the material properties has been analyzed using a numerical model. When grinding the shape of the crossing nose, the resulting profile can deviate from the original one. To analyze the geometry-related effects of welding and grinding, the geometry of crossings (cross-sectional profiles) as well as the corresponding dynamic accelerations due to passing trains are measured before and after the welding and grinding activities. Based on the comparison of the measured accelerations, the performance of the measured crossings has been assessed. Also, a welding repair that is not properly performed can lead to undesirable changes in the material properties of the rails, resulting in defects in rails. The material-related effects of the welding and grinding are studied using the three-dimensional explicit finite element model wherein a wheelset moves over a railway crossing. To understand the microstructure of the welding defect and provide an input for the numerical model, the results of ultrasonic and microscopic analyses of some welded crossings are presented first. Then, a number of the numerical simulations of the crossing with the welding defect are performed to investigate the failure mechanism of the crossing. Furthermore, assessment using the fatigue model (coupled with the finite element model) that accounts for the ratcheting behavior of material by calculating a number of the load cycles to the crack initiation is performed. Finally, conclusions on the effects of changes in geometry and material of the crossings due to repair welding and grinding are given.