Effect Of Geometrical Characteristics Research Articles

Penetration resistance of corrugated hybrid structures with ceramic insertions against steel projectile impact

Ceramic-metal corrugated structures have attracted extensive attention because of their strong penetration resistance. In this study, the effects of geometric features and boundary constraints on corrugated structures consisting of a TC4 frame and five SiC ceramic prisms were explored by performing a series of ballistic tests. Deformation results were obtained using a three-dimensional scanner, and the dynamic response was observed using a high-speed imaging system. Numerical models of these tests were established and validated using experimental results. The results suggest that increasing the support and confining strength of ceramics delay their failure and increase their degree of breakage, thereby increasing the internal energy conversion ratio of the projectile and the energy absorption ratio of ceramics by 14% and 10%, respectively. Notably, a reasonable reduction in the strength of the frame partition expands the plastic deformation range of the frame and increases its energy absorption ratio by 10%. The conclusions of this study provide a reference for designing corrugated composite structures.

Mechanical Performance and Failure Analysis of a 3D-Printed "Continuous Layer-Lattice Layer-Continuous Layer" Sandwich Structure.

Sandwich structures are engineered with continuous layers surrounding the inner lattices, which combines the advantages of the high strength of the continuous layer and the light weight of the lattice layer. They are widely employed in weight-critical energy-absorbing engineering fields such as aerospace, automobile, and robotics. However, the application of sandwich structures made of polymer matrix composites is still limited due to lack of essential performance investigation and adequate reference data. The following innovative works are accomplished in this paper: (i) Continuous long glass fiber (CGF) is employed within the continuous layer of the sandwich structure, with composite short carbon fiber/polyamide (SCF/N) applied within the lattice layer. (ii) Sandwich structures with different cell types and orientations of the lattice infills are designed and prepared by additive manufacturing. (iii) The basic mechanical properties of the sandwich structures, i.e., the bi-directional tension/compression compound performance, failure modes and mechanisms in characteristic directions, are analyzed systematically. (iv) The effects of geometric features on the three-point bending properties of L-shaped sandwich structures are investigated and compared with those of pure SCF/N structures. The results show that the bending resistance per unit weight was up to 54.3% larger than that of pure SCF/N, while the weight could be decreased by 49%, and the bending flexibility before fracture could be increased by 44%. These studies contribute fundamental research data to the application of sandwich structures prepared by fiber reinforced polymer matrix composites.

Effect of geometrical features on the capping behavior of biconvex tablets

Capping is a common industrial issue during the manufacturing of pharmaceutical tablets. It is influenced by both process and formulation parameters. In this work, a systematic study of the influence of the geometrical features of biconvex tablets on capping occurrence was performed on a model formulation, using a design of experiment. Capping was characterized by the pressure at which half of the produced tablets were capped. The influence of the tablet geometry was assessed by varying three parameters: the diameter (D), the band thickness (W) and the ratio between the radius of curvature (R) and the diameter, i.e. R/D. Results showed that having a large diameter, a low band thickness and a high curvature (i.e. a low R/D) favored capping occurrence. Moreover, the effects are not independent as cross-effect were detected. Finally, even for homothetic tablets (i.e. same R/D and W/D) it is shown that a large diameter increases capping occurrence. These results could be used in the future as a guideline for punch selection during tablet development.

PCM-based ceiling panels for passive cooling in buildings: A CFD modelling

To relieve the upsurge of the energy demand associated to building indoor cooling, passive cooling employing phase change materials (PCMs) has been proposed as a promising technique to stabilise indoor air temperature fluctuation and reduce building energy demand. PCMs can exchange a large amount of latent heat during the melting and solidification processes, which can be utilised in line with the discharging and charging processes of a cooling system. The use of encapsulated PCM ceiling panels in buildings has immense application potential for passive cooling, which has attracted investigations in recent years. The geometry selection of the PCM ceiling panel is vital as it determines the exposed surface area to the surrounding air and the natural convection, and therefore the heat transfer rate to/from the PCM, which generally suffers from low thermal conductivity. This paper builds on the geometric optimisation of enclosed PCM capsules driven by natural convection, aiming to investigate the phase change behaviour and thermal performance of encapsulated PCM ceiling panels of different geometries. Here, the presented study focuses on the conjugate heat transfer phenomena through the surrounding air, panel shell, and PCM. A mixture of lauric, capric, and oleic acids was selected as PCM encapsulated in a thin-shell enclosure made of acrylonitrile butadiene styrene plastic, which forms the aesthetic panels attached to the ceiling. A computational fluid dynamics model was validated using full-scale experimental data and further employed to analyse the discharging process and design considerations of the PCM ceiling panels. The effects of various influencing factors were explored, such as panel volume, the initial temperature difference between PCMs and surrounding air, shell thickness, and geometrical features. The results indicate that the panel comprised of a pyramid array is more advantageous than the tetrahedral-based panel in terms of thermal performance, where the average melting rate is 20.8 % higher when the panel volume is 250 mL. In addition, tweaking the geometric features of the panel will largely impact its thermal performance as the effective heat transfer area and natural convection conditions are varied. Finally, it was found that hanging the panel to the ceiling will effectively enhance the heat transfer compared to directly attaching it to the ceiling. The results complement the knowledge body of macro-encapsulated PCM ceiling panels in terms of thermal performance and geometric optimisation. The effects of geometric features on the thermal performance of the PCM ceiling panels are studied in a more holistic manner.

Metallic Microneedles for Transdermal Drug Delivery: Applications, Fabrication Techniques and the Effect of Geometrical Characteristics.

Current procedures for transdermal drug delivery (TDD) have associated limitations including poor administration of nucleic acid, small or large drug molecules, pain and stress for needle phobic people. A painless micro-sized device capable of delivering drugs easily and efficiently, eliminating the disadvantages of traditional systems, has yet to be developed. While polymeric-based microneedle (MN) arrays have been used successfully and clinically as TDD systems, these devices lack mechanical integrity, piercing capacity and the ability to achieve tailored drug release into the systemic circulation. Recent advances in micro/nano fabrication techniques using Additive Manufacturing (AM), also known as 3D printing, have enabled the fabrication of metallic MN arrays, which offer the potential to overcome the limitations of existing systems. This review summarizes the different types of MNs used in TDD and their mode of drug delivery. The application of MNs in the treatment of a range of diseases including diabetes and cancer is discussed. The potential role of solid metallic MNs in TDD, the various techniques used for their fabrication, and the influence of their geometrical characteristics (e.g., shape, size, base diameter, thickness, and tip sharpness) on effective TDD are explored. Finally, the potential and the future directions relating to the optimization of metallic MN arrays for TDD are highlighted.

Numerical analysis on heat transfer enhancement of sCO2 in the tube with twisted tape

Supercritical carbon dioxide (sCO2) has the advantages of easy to reach critical conditions, inactive chemical properties and good safety, which can be used as reactor coolant. However, the thermophysical properties of sCO2 change drastically near the pseudo-critical point. The resulting buoyancy and flow acceleration effects may cause local heat transfer deterioration in the coolant channel. Twisted tape is a good structure for heat transfer enhancement in tube. It can enhance turbulence, generate secondary flow, and disturb fluid flow boundary layer and thermal boundary layer, which can effectively mitigate the heat transfer deterioration of sCO2. The numerical analysis of sCO2 heat transfer deterioration and the heat transfer enhancement of twisted tape is presented in the article using ANSYS Fluent. The default turbulent Prandtl number model was modified to improve the calculation of turbulence generation and diffusion. The heat transfer enhancement characteristic of sCO2 with twisted tape under different working conditions was considered, and the effects of geometric characteristics were also discussed. The results indicate that when the flow rate is low and the heat flux is high, adding twisted tape can effectively suppress the heat transfer deterioration by reducing the viscous sublayer thickness and enhancing the turbulence intensity near the wall. The smaller the twist ratio, the more obvious the enhancement of heat transfer.

Simplified dynamical model and experimental verification of an underwater hydraulic soft robotic arm

Inherent compliance equips soft robotic arms with such advantages as incomparable flexibility, good adaptability, and safe interaction with the environment, etc. However, the strong nonlinearity also brings challenges to predict their dynamic behaviors. This work presents a simplified dynamic model of an underwater soft robotic arm which has three fiber-reinforced hydraulic chambers distributed symmetrically in each section. By controlling the pressures in the chambers, the soft robotic arm can perform complex spatial motion with multiple degrees of freedom. The model is based on Lagrangian method and piecewise constant curvature hypothesis, and considers the nonlinear viscoelasticity of soft material. The model accuracy is verified by the experiments of a two-section soft robotic arm with different actuation modes. The effects of geometrical features on dynamic response are also investigated through model-based simulation and test verification, which can provide guidance to parameter optimization. The proposed dynamic model can be extended to multiple sections and contribute to behavior analysis, performance prediction, and motion control of the soft robotic arm.

3D printed NiTi alloy lattice cantilever beam acoustic metamaterial

Abstract In this paper, a novel acoustic metamaterial beam attached with lattice structures and resonators is designed for elastic wave attenuation. The proposed acoustic metamaterial beam is fabricated by 3D printing with NiTi alloy. Theoretical analysis using negative effective mass is performed to derive the band gap of structure. The finite element method and experimental analysis are performed to investigate the dispersion relation and transmission spectrum. Furthermore, the effect of geometric features on the band gap is studied by simulations. Results proved that the metamaterial beam can be utilized for the control of low-frequency vibration.

Dynamic Finite-Element analysis of a soft bending actuator

Compliance is both a blessing and a curse in the soft robotics field. Increased flexibility comes with serious challenges in the dynamic modeling of compliant manipulators. Soft bending actuators, with their widespread application in rehabilitative, locomotive, and manipulative robotics, are no exception. Dynamic modeling of these actuators is specifically important, as it directly affects the design criteria. In other words, the effect of geometrical features on different aspects of dynamic response such as natural frequencies or magnitude and phase responses should be investigated. Since analytical modeling of their dynamic response is extremely challenging due to the high nonlinearity of both their geometrical and material features, the Finite-Element method is regarded as a proper technique to model these actuators and gain more insight into their dynamical behavior. This study presents a Finite-Element model to describe the dynamic behavior of a pneumatically-driven soft bending actuator, including an analysis of its natural frequencies and response shape. Since inflation of the actuator impacts its structural stiffness and geometrical domain, its effect is studied on the first five natural frequencies by modeling it as a prestress. The proposed model has been scripted and analyzed in ABAQUS, regarding its hyperelastic material behavior, and then is verified experimentally by comparing the numerical analysis data with the results obtained from the bending behavior of a fabricated prototype in different frequencies. In addition to a favorable match between model and test data, a design platform is presented regarding the effect of changes in length and different thicknesses on the bending angle and curvature. Moreover, it is discovered that the geometrical features of the actuator do not endanger the assumption that its bending shape has a constant curvature. In fact, this assumption is only valid in low-frequency applications.

The effect of geometric characteristics on mechanical properties of asperities

The deformation and failure behavior of fractured rock mass is closely related to the unevenness of the fracture surface. The deformation behavior of asperities on rough fracture surfaces has not been studied comprehensively. This paper aims to study the effect of geometric parameters on the mechanical properties of asperities under normal load. In this work, the uniaxial compression experiment using the discrete element software PFC3D was used to investigate the strength and stiffness law of asperities. The results show that compressive strength and stiffness are less affected by the height-width ratio of spherical asperities. However, the curvature of the asperities tip has a significant impact on the peak compressive strength and stiffness. As the curvature of asperities decreases, the peak compressive strength and stiffness rise. In addition, the strength and stiffness of the unevenness of the surface are also affected by the size effect. The peak compressive strength and stiffness increase as the size of the unevenness of the surface grows. The results show that the mechanical properties of asperities are significantly affected by the curvature and the size effect.

Stability analysis of a parallel channel-loop system with single-phase natural circulation under asymmetric conditions

Flow instability can cause mechanical oscillations in the equipment as well as periodic changes in the thermal stress, both of which have a great impact on the safety of the reactor. In addition, flow instability can interfere with the control system, making it difficult to capture stable parameters. In this study, to examine the change in the stability of a parallel channel-loop system with natural circulation under asymmetric conditions, the single-loop natural circulation system is taken as the starting point, and the control equations are obtained by using a dimensionless analysis method. The Fourier expansion of displacement term in the control equations is carried out to obtain the Jacobian matrix representing the single-loop natural circulation system. Based on this matrix, the Jacobian matrix model of parallel channel-loop system is constructed. According to the model, the natural circulation stability of parallel channel-loop under different load and resistance difference is analyzed, and the effects of geometric characteristics, coolant and power on the stability boundary under asymmetric condition are examined. The results show that there are two critical Reynolds numbers, and the system becomes unstable when the load difference introduced by the left and right loops is greater than the critical Reynolds numbers. The area of stable region can be increased by increasing the aspect ratio and heating zone length, and reducing the pipe diameter and cooling zone length. Furthermore, the stability boundary of natural circulation is sensitive to the aspect ratio and the length of heating zone. In addition, the stability can be improved within the allowable range of the natural circulation by choosing liquid metal coolant and increasing the pressure drop, and this model cannot accurately describe the changes in the stability boundary at low power. Overall, the above results can serve as useful reference for the design of the parallel channel-loop systems and can be used to improve the stability of natural circulation. The stability boundary can be used to preliminarily judge the stability distribution and the variation trend of the parallel channel-loop system with a certain degree of reliability.

Combination resonance analysis of imperfect functionally graded conical shell resting on nonlinear viscoelastic foundation in thermal environment under multi-excitation

In this work, nonlinear forced vibrations of truncated conical shells are presented using a semi-analytical method. The material properties are varied along the thickness direction as a power law distribution. The functionally graded truncated conical shells are exposed to external harmonic load and placed in the thermal environment and have an initial imperfection. Furthermore, the functionally graded truncated conical shells rests on generalized nonlinear viscoelastic foundations which consisted of a Winkler and Pasternak foundation parameters augmented by a Kelvin–Voigt viscoelastic model and a nonlinear cubic stiffness. The fundamental equations are extracted using first-order shear deformation theory in conjunction with nonlinear von Kármán relationships. The partial differential equations of truncated conical shells are reduced through Galerkin’s method, and the result is extracted using the multiple scales method. To analyze the resonance analyses, a two-term external excitation is considered. In this regard, various secondary resonances are investigated, and finally, the analyses about combination resonances are represented. To investigate the presented approach, a comparison study is performed with those addressed by other researchers. To analyze the nonlinear combination resonance behavior of truncated conical shells, the effect of geometrical characteristics, material properties, power law index, thermal effects, external load amplitude, and initial imperfection are examined. Finally, the steady-state responses of the nonlinear system are analyzed. As one of the most interesting results, the softening behavior of truncated conical shells with inverse quadratic distribution is the most, and for the quadratic distribution is the least.

Response Modification Factor and Seismic Fragility Assessment of Skewed Multi Span Continuous Concrete Girder Bridges

Skewed bridges, being irregular structures with complicated dynamic behavior, are more susceptible to earthquake damage. Reliable seismic-resistant design of skewed bridges can be achieved by accurate determination of nonlinear seismic demands. However, the effect of geometric characteristics on the response modification factor (R-factor) is not accounted for in bridge design practices. This study attempts to investigate the effects of changes in the number of spans, skew angle and bearing stiffness on R-factor values and to assess the seismic fragility of skewed bridges. Results indicated that changes in the skew angle had no significant effect on R-factor values which were in consonance with code-prescribed R values. Also, unlike the increase in the number of spans that resulted in a decrease in the R-factor, the increase in bearing stiffness led to higher R-factor values. Findings of the fragility analysis implied that although the increase in the number of spans, as well as the increase in the skew angle, led to a higher failure probability, greater values of bearing stiffness reduced the collapse probability. For practicing design engineers, it is recommended that maximum demands on substructure elements to be calculated when the excitation angle is applied along the principal axes of skewed bridges.

Video-based person-dependent and person-independent facial emotion recognition

Facial emotion recognition is a challenging problem that has attracted the attention of researchers in the last decade. In this paper, we present a system for facial emotion recognition in video sequences. Then, we evaluate the system for a person-dependent and person-independent cases. Depending on the purpose of the designed system, the importance of training a personalized model versus a non-personalized one differs. In this paper, first, we compute 60 geometric features for video frames of two datasets, namely RML and SAVEE databases. In the next step, k-means clustering is applied to the geometric features to select k most discriminant frames for each video clip. Then, we employ various classifiers like linear support vector machine (SVM) and Gaussian SVM to find the best representative k. Finally, five pre-trained convolutional neural networks, namely VGG-16, VGG-19, ResNet-50, AlexNet, and GoogleNet, were used evaluating two scenarios: person-dependent and person-independent emotion recognition. Additionally, the effect of geometric features in keyframe selection for a person-dependent and person-independent scenarios is studied based on different regions of the face. Also, the extracted features by CNNs are visualized using the t-distributed stochastic neighbor embedding algorithm to study the discriminative ability in these scenarios. Experiments show that person-dependent systems result in higher accuracy and suitable to be used in personalized systems.

Effect of geometrical features on the contra-rotating propeller hydrodynamic performances

New contra-rotating four-bladed DTMB propeller configurations operating in open water are numerically studied to determine their hydrodynamic performances. The unsteady turbulent flow around propellers is modelled by RANS equations with Kω SST model then solved by a CFD code. The computational domain is divided in two blocks linked with a rotating interface. The obtained results show that thrust and efficiency of the contra-rotating (CRP) increase compared to the single propeller, leading to a significant reduction of the propeller diameter. The variation in axial spacing and angular displacement seems to have little effect on the CRP efficiency. The results also show that the thrust can be further improved by adopting a moderate negative twist angle of the rear propeller.
 Keywords: CRP contra-rotating propeller, axial spacing, angular spacing, twist angle, CFD.

A study of fluid dynamics and human physiology factors driving droplet dispersion from a human sneeze.

Recent studies have indicated that COVID-19 is an airborne disease, which has driven conservative social distancing and widescale usage of face coverings. Airborne virus transmission occurs through droplets formed during respiratory events (breathing, speaking, coughing, and sneezing) associated with the airflow through a network of nasal and buccal passages. The airflow interacts with saliva/mucus films where droplets are formed and dispersed, creating a route to transmit SARS-CoV-2. Here, we present a series of numerical simulations to investigate droplet dispersion from a sneeze while varying a series of human physiological factors that can be associated with illness, anatomy, stress condition, and sex of an individual. The model measures the transmission risk utilizing an approximated upper respiratory tract geometry for the following variations: (1) the effect of saliva properties and (2) the effect of geometric features within the buccal/nasal passages. These effects relate to natural human physiological responses to illness, stress, and sex of the host as well as features relating to poor dental health. The results find that the resulting exposure levels are highly dependent on the fluid dynamics that can vary depending on several human factors. For example, a sneeze without flow in the nasal passage (consistent with congestion) yields a 300% rise in the droplet content at 1.83 m (≈6 ft) and an increase over 60% on the spray distance 5 s after the sneeze. Alternatively, when the viscosity of the saliva is increased (consistent with the human response to illness), the number of droplets is both fewer and larger, which leads to an estimated 47% reduction in the transmission risk. These findings yield novel insight into variability in the exposure distance and indicate how physiological factors affect transmissibility rates. Such factors may partly relate to how the immune system of a human has evolved to prevent transmission or be an underlying factor driving superspreading events in the COVID-19 pandemic.

Analytical and finite element investigations of the cross-arranged trapezoidal- and sinusoidal-corrugated-cores panels

This article intends to study the performance of sandwich panels consisting of four isotropic flat plates and three trapezoidal or sinusoidal cores. The sandwich panels, subjected to the uniform loading resting on simply supported edges, are analyzed by an analytical method based on the classical plate theory and commercially available software. The homogenization method is used for the analytical method to replace the core by a flat plate with an equivalent stiffness. Results show that the deflected shape of the equivalent sandwich plate with the flat core is similar to that of the original corrugated plate measured by using shell elements in ABAQUS. The effects of geometric characteristics on the deflection and Von-Mises’s stress are also studied by the finite element method analysis. Results show that the trapezoidal-core panel has better performance as compared to the sinusoidal-core one. Moreover, results show that the corrugation thickness and amplitude have considerable effects on the performance of the panel. A wide validity range is also obtained for the thickness of the sinusoidal-core panel as compared to the trapezoidal-core panel.

Impact of Geometric Features on Color Similarity Perception of Displayed 3D Tablets

Abstract To explore the effects of geometric features on the color similarity perception of displayed three-dimensional (3D) tablets designed by color 3D modeling techniques or printed by color 3D printing techniques, two subjective similarity scaling tasks were conducted for color tablets with four shape features (circular, oval, triangular-columnar, and rounded-cuboid shapes) and four notch features (straight V, straight U, crisscross V, and crisscross U shapes) displayed on a calibrated monitor using the nine-level category judgement method. Invited observers were asked to assort all displayed samples into tablet groups using six surface colors (aqua blue, bright green, pink, orange yellow, bright red, and silvery white), and all perceived similarity values were recorded and compared to original samples successively. The results showed that the similarity perception of tested tablets was inapparently affected by the given shape features and notch features, and it should be judged by a flexible interval rather than by a fixed color difference. This research provides practical insight into the visualization of color similarity perception for displayed personalized tablets to advance precision medicine by 3D printing.

Nonlinear vibration of functionally graded porous variable thickness toroidal shell segments surrounded by elastic medium including the thermal effect

The present study deals with the nonlinear vibration of functionally graded porous (FGP) variable thickness toroidal shell segments surrounded by elastic medium subjected to axial compression and external pressure, including the thermal effects. Three types of uniform, symmetric, and non-symmetric porosity distributions are considered. The improved Donnell shell theory with von-Karman nonlinearity, and Stein and McElman’s assumptions are used to obtain the equations of motion of toroidal shell segments. The dynamic characteristics of shells such as natural frequencies and nonlinear frequency-amplitude relation are determined by using the solution in terms of displacements in conjunction with Galerkin's method. The present approach is validated by comparing with the available results for particular cases. Effects of geometrical characteristics, the porosity distribution types, the porosity coefficient, the thickness distribution parameter, temperature and pre-loaded static axial compression on the nonlinear vibration response of the FGP variable thickness convex and concave toroidal shell segments are studied in detail.

Variables impacting the severity of crashes involving traffic barriers on horizontal curves: actual crash analysis of interstate roads in Wyoming

Despite numerous past studies conducted on traffic barriers, research is still needed to analyze the performance of traffic barriers on superelevated horizontal curves. Based on the literature of traffic barrier studies, the effect of geometric features of traffic barriers (such as height and post-spacing) on crashes involving horizontal curves has not been investigated considering actual crash data analysis. This paper seeks to study the effect of various variables affecting the severity of traffic barrier crashes on horizontal curves. Geometric features of 95 miles of traffic barriers were collected, conducting a field inventory on all interstate roads in Wyoming. All the traffic barriers collected were located on horizontal curves with at least one historical crash report between 2008 and 2017. Random-parameters ordered logit was used to develop two models to investigate the factors impacting the severity of horizontal curve crashes involving side and median traffic barriers, respectively, on interstate roads. Based on the results, median box beam barriers with a post-spacing of 6.1 ft resulted in lower injury severity. Median W-beam barriers with a height taller than 31 inches were involved with a higher probability of severe collisions. Side box beam barriers located on the front side-slope were also more likely to increase the severity of crashes.