Variable Cross-sectional Area Research Articles

Visualization Study of Methane Deflagration Characteristics in Variable Diameter Pipelines Based on Schlieren Technique

ABSTRACT The phenomenon of pipe diameter change often exists in urban natural gas pipelines. To study the impact of pipe diameter variation on the propagation characteristics of combustible gas deflagration and provide theoretical basis for the prevention and emergency treatment of gas pipeline explosion accidents, this work uses a self-developed circular explosion pipe test bench with a length of 12 m and an inner diameter of 90 mm to study the methane deflagration characteristics in variable diameter pipelines. Under four experimental conditions of variable cross-sectional area ratio (VR) of 1.0, 0.6, 0.4, and 0.2, the schlieren images of the deflagration process of methane/air premixed gas with a methane concentration of 9.5% were captured by a high-speed camera. Combined with the traditional pressure and flame signal point source information, the research results show that the existence of variable diameter pipelines can change the flame structure and shape, causing the flame front to transform into a tulip flame in advance. The flame propagation speed under different experimental conditions is: VR = 0.4 > VR = 0.2 > VR = 0.6. The influence of the variable diameter pipeline on flame velocity depends on the suppression effect of the reflected wave generated by the cross-section area of the variable diameter pipe and the coupling effect of the reduced aperture area of the variable diameter section on the flame acceleration effect. When the reflected wave acts on the flame front, the flame propagation speed decreases, and in severe cases, it will cause flame stagnation and backfire.

Characterization and comparative appraisal of two novel annular channel designs with variable flow areas for supercritical heat transfer

Deterioration of heat transfer is a common concern for any supercritical heat transport system, regardless of the geometric orientation. Present study proposes two novel designs of annular channel with variable cross-sectional area and numerically assesses their respective performances, with the primary objective being the enhancement of overall heat transport characteristics in comparison with an equivalent traditional plain annular channel. Both the configurations exhibit substantial gain in terms of overall heat transfer coefficient and prevailing temperature level, while also eliminating deterioration over the entire parametric ranges explored here, with the diverging one demonstrating relatively superior characteristics. The converging channel generally maintains a flatter temperature profile and comparatively lower maximum temperature, and hence can be employed at larger power-to-mass-flux ratios. Taper angle is earmarked as the most influencing design variable, illustrating enhanced performance with greater tapering, albeit at the cost of nominal increase in pressure drop. Both the designs are found to be insensitive to flow acceleration, which is a primary reason of not encountering deterioration. Strong buoyancy effect can be present within the entrance region of the converging design, affecting its overall performance. Local thermalhydraulics have been noted to be contingent to the effective level of turbulence and distribution of specific heat in the radial direction, which also contribute to the favorable response from the diverging design.

Free vibration of flexible two links manipulator with variable cross-sectional areas

This paper demonstrated the free vibration of a planar two-link flexible manipulator with harmonic drivers and non-uniformity in the cross-section of links. A dynamic model has been developed that incorporates flexibilities in both link and joint experiencing harmonic vibration, with joint flexibility modeled as torsional spring-inertia components combination. Two links were modeled based on Von Karman’s nonlinear strain relations and theory of the Euler-Bernoulli beam. The nonlinear governing equations were derived using the extended Hamilton’s principle for planar two-link flexible manipulators with variable cross-sections for each link. The coefficients of the obtained partial differential equations were as a function of spatial coordinates and were reduced to the ordinary differential equations for a family of cross-section geometries with exponentially varying widths of rectangular sections of each link. The frequency equation was obtained and analytical solutions of the vibration were achieved for different exponential shapes of each link (widening and narrowing beam for each link). Natural frequencies and mode shapes were presented for varying cross-section areas of the links. The effects of the end masses, payload, beam mass density, flexural rigidity ratio, and joint frequency were investigated on the mode shapes and natural frequencies when the power of the exponential function of the cross-sectional areas of two links was varied. The numerical results were verified with experimental results.

Unidirectional Flow Through Time-Dependent Cross-Sectional Areas of a Compliant Tube and a Valve: A Nonlinear Model

This work investigates the conditions for net flow generation by a straight tube with a cross-sectional area harmonically varying in time that connects two tanks—a problem that is mainly found in the design of impedance pumps. By assuming a quasi-one-dimensional flow and applying continuity and momentum equations, a first-order differential equation with respect to the flow rate is derived and presented for the first time, including a nonlinear term that is responsible for net flow rate generation. Namely, the net flow rate is found to be nonzero (as is the nonlinear term) if the cross-sectional areas of the two tanks are unequal and one of them is smaller than that of the straight tube. In this case, the flow is directed from the smaller to the larger tank and the net flow rate increases with the frequency of the tube’s cross-sectional area variation. In contrast, when the tanks’ cross-sections are equal, the net flow is generated only if a valve is installed, e.g., at one end of the tube, due to the large asymmetries imposed in the hydraulic losses with respect to the tube mid-length. Compared with constant valve opening, the net flow rate is augmented significantly if the valve opening is time-dependent. By employing the same equation, the flow rate of an intra-aortic counter-pulsating balloon pump is also examined, in which the valve (representing the aortic valve) opens during the shrinkage of the tube, and it is shown that the net flow rate increases with the frequency and amplitude of the tube’s cross-sectional area. Conclusively, the harmonic oscillation in time of a tube’s wall can cause unidirectional flow only if asymmetric losses are present with respect to its mid-length.

Vibroscope method for determination of cross-sectional area of glass and carbon fibres – Experiments and analyses

Determination of cross-sectional area of glass and carbon fibres is a critical part of mechanical testing of the fibres. The present study focuses on the vibroscope method which is based on frequency measurements of a fibre under tension. Three data analysis procedures, named simple, direct and iterative, are presented, providing estimates of the fibre cross-sectional area with increasing accuracy. The simple procedure underestimates the cross-sectional area with about 0.4 – 2.0 % and 0.4 – 3.7 % for the tested glass fibres and carbon fibres, respectively. The cross-sectional area determined by the direct procedure deviates only marginally from the most accurate cross-sectional area as determined by the iterative procedure. Histograms of cross-sectional areas of glass and carbon fibres are presented to show the large variation of cross-sectional areas between individual fibres. Stress–strain curves of the tensile tested fibres are presented, and the small variation of stress–strain curves between individual fibres contributes to the validation of the vibroscope method.

Stress Wave Propagation in a Rayleigh-Love Rod with Sudden Cross-Sectional Area Variations Impacted by a Striker Rod.

This paper presents an in-depth study of the stress wave behavior propagating in a Rayleigh-Love rod with sudden cross-sectional area variations. The analytical solutions of stress waves are derived for the reflection and transmission propagation behavior at the interface of the cross-sectional area change in the rod, considering inertia and Poisson's effects on the rod material. Examples solved using the finite element method are provided to verify the correctness of the analytical results. Based on the forward analysis of Rayleigh-Love wave propagation in a rod impacted by a striker rod, an impact-echo-type nondestructive testing (NDT) method is proposed to conduct defect assessment in rod-type structural components with sudden cross-sectional area changes within a cover medium. This proposed NDT method can identify the location, extension, and cross-sectional area drop ratios of an irregular zone in the rod to be inspected.

The Gradient Variation of Location Distribution, Cross-Section Area, and Mechanical Properties of Moso Bamboo Vascular Bundles along the Radial Direction

The Gradient Variation of Location Distribution, Cross-Section Area, and Mechanical Properties of Moso Bamboo Vascular Bundles along the Radial Direction

Socialization of the Use of Cross-sectional Area Variations Container for the Amount of Weight Reduction in Organic Waste by Using BSF Maggots (Black Soldier Fly)

Organic waste processing is a major challenge in environmental management that requires an effective solution. One promising method is using Black Soldier Fly (BSF) larvae to convert organic waste into high-value biomass. Therefore it is necessary to do itsocialization of the use of variations in the cross-sectional area of ​​containers in cultivating BSF larvae for processing organic waste.The method done ieSocialization to the community includes BSF larvae, life cycle, cultivation procedures and benefits. Results: SSocialization shows an increase in public understanding about cultivating BSF larvae and the influence of variations in the cross-sectional area of ​​containers on waste processing efficiency. Discussion:What happens in the socialization is optimizing the growth conditions for BSF larvae and the obstacles that may occur in cultivating BSF larvae. So thatregulate the water content of BSF Larva feed and maintain the condition of the container. The conclusion of this outreach is increased understanding among the community about the importance of processing organic waste and the role of BSF larvae in reducing waste. So this results in efforts to manage organic waste and create new jobs for the community.

Optimization of impeller contour and diversion blade of a moist air turbo expander with spontaneous condensation

The turbo-expander is the crucial equipment for obtaining refrigeration capacity and power in the system, and the aerodynamic performance is vital for the system. Spontaneous condensation of moist air in a high-speed turbo expander has a significant effect on the efficiency and output power. Based on the model of non-equilibrium spontaneous condensation, the flow of moist air in a high-speed turbo expander was studied, which is verified by the experiments. The meridional surface shape affects the variation of the flow passage cross-sectional area. The impeller with a uniform variation in cross-sectional area has the highest efficiency. Based on the optimal meridional surface shape, the condensation flow of moist air with different impeller blade diversion curvature was compared. The optimal curvature can increase the efficiency of the moist air turbo-expander by 2.83 %, and the optimized impeller has 3.53 % higher output power. The largest curvature of the blade leads to an efficiency reduction by 3.06 %, but it has little droplet condensation in the impeller, which can help to avoid damage of high-speed blades.

Analysis on unconfined groundwater availability during dry and rainy season using dynamic approach in Ngemplak, Sleman, Yogyakarta, Indonesia

Groundwater is a natural resource with disparity across the different regions throughout time. In comparison to surface water, the groundwater in unconfined aquifers is easily accessible and generally of good quality. Groundwater macro zoning is classified into three, namely water catchment areas, transition areas, and groundwater discharge areas. Based on the macro zoning, previous research has mostly been carried out in catchment areas and discharge areas with a focus on groundwater potential and temporary groundwater conditions. The dynamics of groundwater availability, especially in the water transition zone, has not been studied much, even though the dynamics of groundwater availability in the transition zone plays a vital role for areas in the discharge zone. This study identified the availability of groundwater during rainy and dry seasons in groundwater transition zone. Groundwater availability was assessed through a dynamic discharge approach. The study variables included the hydraulic conductivity of the aquifer, the hydraulic gradient, and the cross-sectional area of the aquifer. Dynamic discharges were analysed during the rainy and dry seasons. The results showed that the availability of groundwater during the rainy season was 4,333,906.1 liters/day and 3,898,850.4 liters/day during the dry season. Based on the calculation of the dynamic discharge (Q), the decrease in the quantity of groundwater is affected by the variable hydraulic gradient (I) and cross-sectional area of the aquifer (A). The numbers of these two variables are smaller during the dry season than the rainy season. The decrease in the quantity of groundwater during the dry season is of course closely related to reduced rainfall which is a source of infiltration and percolation. Reduced rainfall causes the groundwater level to decrease, then technically reduces the groundwater hydraulic gradient (I) and aquifer cross-sectional area variable (A). There was no indication of groundwater scarcity in the study area. This study can serve as a reference related to the application of dynamic discharge theory to assess groundwater availability. Periodic monitoring of groundwater quantity, rainwater harvesting, and intensification of water infiltration wells can be carried out as a recommendation to anticipate problems related to groundwater availability in the study area. This study can serve as a reference related to the application of dynamic discharge theory to assess groundwater availability.

On designing a wavy sinusoidal micromixer for efficient mixing of viscoelastic fluids harnessing elastic instability and elastic turbulence phenomena

Effective mixing in microscale systems encounters difficulties due to the inherently low Reynolds numbers. This investigation delves into harnessing elastic instability and elastic turbulence phenomena to improve the mixing performance of viscoelastic fluids within a wavy sinusoidal micromixer with variable cross-sectional areas. Previous experiments demonstrated enhanced mixing efficiency, while our numerical simulations indicate that this enhancement is true up to a certain Weissenberg number. Beyond this threshold, a further increase in the Weissenberg number results in diminished mixing efficiency. Moreover, we observe that mixing efficiency increases with the Deborah number, albeit with an exponential increase in pressure drop. Conversely, mixing efficiency also increases with the number of turns in the micromixer, albeit with a linear increase in pressure drop. Hence, selecting a wavy micromixer with more turns and a relatively lower Deborah number is advisable for achieving comparable efficiency with reduced pressure drop. Additionally, the shear-thinning properties of viscoelastic fluids impede mixing efficiency by suppressing elastic instability and elastic turbulence phenomena. In conclusion, this study provides valuable insights for designing optimal wavy micromixers that effectively mix viscoelastic fluids by utilizing elastic instability and elastic turbulence phenomena.

Influence of Narrow Titanium Dental Implant Diameter on Fatigue Behavior: A Comparison between Unitary and Splinted Implants.

Background: Scientific literature lacks strong support for using narrow diameter implants (NDI) in high masticatory force areas, especially in molars. Implant splinting in cases of multiple missing teeth reduces lateral forces, improves force distribution, and minimizes stress on implants. However, no studies have evaluated the fatigue load resistance of unitary or splinted implants. Methods: This in vitro study compares five groups of new metal alloy implants, including unitary and splinted implants with varying diameters. Mechanical characterization was assessed using a BIONIX 370 testing machine (MTS, Minneapolis, MN, USA) according to ISO 14801. For each of the five study sample groups, (n = 5) specimens underwent monotonic uniaxial compression at break testing and (n = 15) cyclic loading to determine the maximum force (Fmax) and the fatigue life (LF) values. Scanning electron microscopy (SEM) was employed for the fractographic analysis of the fractured samples. Results: The Fmax values for unitary samples ranged from 196 N to 246 N, whereas the two-splinted samples displayed significantly higher values, ranging from 2439 N to 3796 N. Similarly, the LF values for unitary samples ranged from 118 N to 230 N, while the two-splinted samples exhibited notably higher values, ranging from 488 N to 759 N. Conclusions: The observed resistance difference between sample groups in terms of Fmax and LF may be due to variations in effective cross-sectional area, determined by implant diameter and number. Additionally, this disparity may indicate a potential stiffening effect resulting from the splinting process. These findings have significant implications for dental clinical practice, suggesting the potential use of splinted sets of small-sized NDI as replacements for posterior dentition (premolars and molars) in cases of alveolar bone ridge deficiencies.

Enhancing Flexural Resistance in Pre-Damaged RC Beams with Near-Surface Mounted GFRP Bar and Bolt Anchoring System

The objective of this research was to explore the mechanical properties and failure mechanisms of reinforced concrete beams (RC beams) strengthened with near-surface mounted (NSM) glass fiber-reinforced polymer (GFRP) bars. This study focused on evaluating the effect of various factors on the load-deflection response and failure patterns of RC beams, including pre-existing damage, end anchorage, bar length, bar number, and the condition of concrete cover. The tested RC beams were divided into three groups. The first group included undamaged and damaged control beams. The second group involved the strengthening of beams after inducing damage, with variations in bar length, number, and cross-sectional area. This group also included beams strengthened by GFRP bars with and without anchors. In the third group, the effects of different cover materials, cover bonding techniques, and anchor bolts on the strengthening bars were examined. The results of the experiment indicated a notable decrease in both cracking and maximum load capacity for beams that were pre-damaged. The inclusion of anchor bolts appeared to have a noticeable effect, enhancing the load-carrying capacity and reducing mid-span deflection. Opting for two bars proved to be more effective than using three bars, leading to a higher maximum load and improved ductility. Moreover, prioritizing the bonding of the concrete cover at the end of the bars was found to be more important than bonding in the area of maximum moment.

Stability of a compressed-tensioned rod of variable cross-section with combined loading

Objective. The purpose of the study is to determine the stability of a straight rod of variable cross-section under combined axial loading. Method. The longitudinal bending of the rod is described by the classical theory using Bernoulli’s hypothesis, and the critical forces are determined from the Euler problem with appropriate assumptions. Result. An algorithm for a numerical method for solving the problem of determining the eigenvalues of the differential equation for longitudinal bending of a rod is proposed. External loads are considered “dead”. The functions of changing the variable cross-sectional area, variable stiffness and distributed load are considered given. The curved axis of the rod after bifurcation is described using a linear ordinary differential equation. Conclusion. The implementation of the numerical method was carried out by the finite difference method using numerical methods and modern computer software.

Performance Enhancement of a Variable Cross-Sectional Area Square Pipe Solar Heater

Performance Enhancement of a Variable Cross-Sectional Area Square Pipe Solar Heater

Altitude controller influence on environmental and economic performance of NGV fuel-powered engines

The relevance of research is conditioned by the need to ensure efficient operation of the internal combustion engine ICE on NGV fuel at different altitudes above sea level, where there is atmospheric air rarefaction up to 20÷25%. This direction is dictated by the fact that when transferring the ICE operation from gasoline to gas-engine fuel, the engine power decreases from 5 to 15%, moreover, the atmospheric air rarefaction leads to an even greater reduction in engine power and ultimately reduces the performance of the vehicle. Due to violation of the process of combustion of gas-air charge in the cylinder is formed a large amount of carbon monoxide (CO). Research objective is to develop and propose a method of providing such a stoichiometric, fractional composition of the gas-air charge, which will ensure the restoration of the lost power of ICE and provide the optimal value of traction-dynamic characteristics of the car, without increasing toxic emissions. Research object: Variable crosssectional area of the intake manifold path (ICE), adjustable lumen for atmospheric air intake, atmospheric air pressure sensors adjustable diaphragm with stepper motor. Research methods: analytical modeling of the relationship of the aperture diameter depending on the altitude of the terrain above sea level, on the number of revolutions of the ICE, on the density and temperature of the ambient air. The process of combustion of the gas-air charge in the combustion chamber will be evaluated by the fractional composition of the exhaust, exhaust gases. Research results: Qualitative and quantitative assessment of the application of altitude corrector on the ICE operation mode, stability of the value of excess air ratio at different altitudes above sea level, formation of toxic gas, carbon monoxide, as well as carbon dioxide, hydrocarbon, oxygen, etc. is given.

Analysis of transverse free vibrations of rotating beams with variable cross-section using the point collocation method

In this article, a study of transverse free vibrations of rotating cantilever beams with variable cross-sectional area is carried out using the point collocation method. The study considers four thickness variation functions, including linear, parabolic, sinusoidal, and exponential types, for the beam’s cross-sectional area changes. The point collocation method uses Gauss-Legendre points to solve the equation of motion and determine the natural frequencies. To enhance the convergence rate, the initial guess function is based on the precise mode shapes of the stationary uniform beam. The effect of section functions and various rotational speeds on the structure’s natural frequencies is investigated. The outcomes of the investigation are compared with 3D finite element simulations and related published results. Through the analysis, the results show that the point collocation method is highly accurate, with a maximum error of 0.0025% compared to 3D finite element simulations. Moreover, the natural frequencies of the rotating cantilever beams decrease as the section functions become steeper. Finally, the increase in rotational speed causes the natural frequencies to increase in a non-linear manner, with the maximum increase rate occurring at a specific rotational speed.

Vocal tract shape variation contributes to individual vocal identity in African penguins.

Variation in formant frequencies has been shown to affect social interactions and sexual competition in a range of avian species. Yet, the anatomical bases of this variation are poorly understood. Here, we investigated the morphological correlates of formants production in the vocal apparatus of African penguins. We modelled the geometry of the supra-syringeal vocal tract of 20 specimens to generate a population of virtual vocal tracts with varying dimensions. We then estimated the acoustic response of these virtual vocal tracts and extracted the centre frequency of the first four predicted formants. We demonstrate that: (i) variation in length and cross-sectional area of vocal tracts strongly affects the formant pattern, (ii) the tracheal region determines most of this variation, and (iii) the skeletal size of penguins does not correlate with the trachea length and consequently has relatively little effect on formants. We conclude that in African penguins, while the variation in vocal tract geometry generates variation in resonant frequencies supporting the discrimination of conspecifics, such variation does not provide information on the emitter's body size. Overall, our findings advance our understanding of the role of formant frequencies in bird vocal communication.

Quasi-one-dimensional treatment of heat transfer in beams of non-uniform cross-section

We test performance of a quasi-one-dimensional approach to steady state heat transfer in broadening beams, characterized by variable cross-sectional area. The results obtained analytically and by solving the governing equation numerically in Python, for three different instances, are compared to FEM simulations. We demonstrate that the quasi-one-dimensional model gives accurate predictions for beam suitably averaged temperatures but the range of Biot numbers for which it can be accurately applied to is currently limited by a crucial parameter.

A Size-Dependent Viscoelastic Model for Microbars with Variable Cross-Section

This paper presents a model for microbars with variable cross-sections using the Kelvin–Voigt model for viscoelastic material, accounting for size-dependent effects based on strain gradient theory. The size-dependent dynamic equations for the rod, which consider the variable cross-sectional area, are obtained through the extended Hamilton’s principle. These equations are then reduced in order using the Galerkin method and solved in the steady state using the harmonic response form and the algebra of complex numbers. To solve the equations from the transient state to the steady state, a combined method is implemented using the Grünwald–Letnikov derivative technique and the Newmark method. Furthermore, a model and analysis based on the finite element method are presented to validate the results. In the results section, various factors such as size-dependent effects, the order of the fractional derivative, the amount of the viscoelastic coefficient, and the shape of the section area are examined through the time history graph, frequency response, and maximum displacement in terms of force. The results demonstrate that the transient response converges to the stable response after a certain period of time. Moreover, it is observed that decreasing the order of the fractional derivative in the pre-resonance range leads to a decrease in response sensitivity, while in the resonance frequency range, the sensitivity increases with the increase in order.