Noncircular Section Research Articles

Brazilian savannah tree as bio-inspiration for hydraulic transient control in a penstock of a small hydropower plant

This study proposes an innovation, which is to use a non-circular and bio-inspired forced conduit (a new penstock with a cross section inspired by a tree trunk), to control the effects of hydraulic transients in Brazilian small hydropower plants (SHPs). The aim is to demonstrate that natural structures, adapted to periodic environmental disturbances, are better at hydraulic transient control than traditional conduits. The proposed methodology includes the following steps: (1) problem identification; (2) potential biological model identification; (3) development of alternatives; (4) implementation and testing; and (5) solution selection. This research was conducted at the São Tadeu I SHP, in the city of Santo Antônio de Leverger/MT, Brazil. The following tree biological models from the Brazilian savannah (Cerrado) were used: Handroanthus capitatus and Strychnos pseudoquina. The proposed innovation improves the conduit of the traditional circular section and the relief valve solution of the criteria studied. The reason for this improvement was the reduction of wave speed in the non-circular section (from 1126 to 583 m s−1).

Torsional vibration behavior of a restrained non-circular nanowire in an elastic matrix

This study introduces an approach to analyze torsional vibration in non-circular nanowires within magnetic fields, considering various boundary conditions on an elastic foundation. Analytical formulas for natural angular frequencies are obtained using nonlocal strain gradient theory. The analysis covers three non-circular cross-sections, incorporating the warping effect. Elastic springs at the wire ends simulate support conditions, restricting rotation around the wire’s axis. The torsion function around the axis is represented by a Fourier series, discretized at the spring points and linked using the Stokes’ transform alongside the boundary values. This leads to an eigenvalue problem that includes higher-order material size parameters (strain gradient, nonlocal), spring parameters, and the warping function. The study’s novelty lies in effectively solving torsional vibration for non-circular sections, addressing warping function, elastic medium, and size effects under both deformable and non-deformable boundary conditions. The presented solution is capable of determining vibration frequencies for both rigid and deformable boundary conditions. This is accomplished by specifying the torsional spring stiffness values, thereby obviating the necessity for additional recalculations. In order to verify the obtained results and compare them with the existing literature, nanowires with free and clamped boundary conditions are solved numerically by changing the spring parameters in the eigenvalue problem. In the formulation of natural angular frequency; length scale parameters, warping, magnetic field, elastic medium effects are included. In addition, since the support conditions are modeled with elastic springs, the resulting formulas are quite general and can be used to solve different types of torsional vibration problems.

Design and Flow Analysis of Special-Shaped Cross-Section Flow Channel Based on Selective Laser Melting

Selective laser melting has the potential to be applied into hydraulic pipelines manufacturing because it can realize the forming of flow channels with arbitrary direction and curvature. Due to the stacking of layers, selective laser melting still has many limitations while processing complex flow channels. In particular, the manufacturing of overhanging structures with circular cross sections needs to use internal supports to prevent surface collapse, which is challenging to be removed. Therefore, it is necessary to optimize the flow channel with a self-supporting ability, then systematically discussing its forming quality with the influence on fluid dynamics to compromise. In this paper, a simplified multi-channel structure with 1 inlet and 4 outlets is extracted from a hydraulic valve block of an aero-engine system, and the cross-section of its branch channel is re-designed to guarantee its self-supporting ability based on additive manufacturing optimization strategy. Numerical simulation was used to analyze the influence of different shape sections on the pressure loss and mass flow rate of multi-channel structure. The results show that the pressure loss and outlet flow of the 45° rhombus + ellipse section are the closest to the circular area. According to the maximum internal deformation of the three outlets, the 65° rhombus section has the better forming quality and the non-circular section is not the worst.

Morphological Changes of Anomalous Coronary Arteries From the Aorta During the Cardiac Cycle Assessed by IVUS in Resting Conditions.

Anomalous aortic origin of coronary artery (AAOCA) with intramural segment is associated with risk of sudden cardiac death, probably related to a compressive mechanism exerted by the aorta. However, the intramural compression occurrence and magnitude during the cardiac cycle remain unknown. We hypothesized that (1) in end diastole, the intramural segment is narrower, more elliptic, and has greater resistance than extramural segment; (2) the intramural segment experiences a further compression in systole; and (3) morphometry and its systolic changes vary within different lumen cross-sections of the intramural segment. Phasic changes of lumen cross-sectional coronary area, roundness (minimum/maximum lumen diameter), and hemodynamic resistance (Poiseuille law for noncircular sections) were derived from intravascular ultrasound pullbacks at rest for the ostial, distal intramural, and extramural segments. Data were obtained for 35 AAOCA (n=23 with intramural tract) after retrospective image-based gating and manual lumen segmentation. Differences between systolic and end-diastolic phases in each section, between sections of the same coronary, and between AAOCA with and without intramural tract were assessed by nonparametric statistical tests. In end diastole, both the ostial and distal intramural sections were more elliptical (P<0.001) than the reference extramural section and the correspondent sections in AAOCA without intramural segment. In systole, AAOCA with intramural segment showed a flattening at the ostium (-6.76% [10.82%]; P=0.024) and a flattening (-5.36% [16.56%]; P=0.011), a narrowing (-4.62% [11.38%]; P=0.020), and a resistance increase (15.61% [30.07%]; P=0.012) at the distal intramural section. No-intramural sections did not show morphological changes during the entire cardiac cycle. AAOCA with intramural segment has pathological segment-specific dynamic compression mainly in the systole under resting conditions. Studying AAOCA behavior with intravascular ultrasound during the cardiac cycle may help to evaluate and quantify the severity of the narrowing.

Torsional vibration of Timoshenko-Gere non-circular nano-bars

The displacement field and governing equation completely depend on the cross-section shape in the torsion of nano-bars. Due to the torsion of structure and warping of its cross-section, axial strain is created. A review of the literature demonstrates that the effect of the normal strain in the torsional analysis of nanostructures with non-circular cross-sections is ignored for the sake of simplicity and causes a computational error. While in the torsion of short nano-bars due to the great warping of the cross-section the normal strain appears and it shouldn’t be ignored. Therefore, for the first time, the effect of normal strain based on the torsion of Timoshenko-Gere theory is considered in this research. In this theory, the twist rate of non-circular sections in the axial direction is not considered constant, unlike studies in the literature. The governing equation of torsional vibration is extracted using the Hamilton principle, and the nonlocal strain gradient theory is used to show the size-dependent effects. The fundamental frequency is calculated for the arbitrary cross-section shape by using Galerkin’s method. The effect of parameters such as size effects, the thickness of nano-bar, mode number, and dimensions changes of cross-section versus natural frequency of nano-bar for both the Timoshenko-Gere and typical theories are investigated. Results indicate that neglecting normal strain due to warping the cross-section causes a significant error in the short nano-bars, especially at higher mode numbers. Also, a comparison is made between the obtained natural frequencies and those of the results reported in the literature.

Investigation of spontaneous capillary flow and heat transfer characteristics in parallel microchannels based on phase-field model

• The mechanism of liquid surface oscillation in capillary flow is revealed. • Effect of channel structure on capillary flow and heat transfer is discussed. • A novel heat sink based on parallel capillary microchannels is constructed. • Non-circular heat sink obtains better capillary flow and heat transfer performance. Passive heat dissipation based on capillary flow has excellent applications in the thermal management of electronic devices and spacecraft due to its advantages of spontaneity and high stability. However, the conflicting relationship between capillary pressure and permeability in conventional sintered capillary wick severely limits its heat dissipation limit, and the complex and tortuous flow path is the key limiting factor. In this study, a novel close-packed capillary microchannel is constructed to provide an unobstructed flow path, and based on the phase-field model, the capillary flow and heat transfer characteristics of capillary microchannels with different structures are investigated. First, for the single channel, the oscillatory mechanism of phase interface in the initial stage of capillary flow, which has received little attention before, is revealed, which is mainly caused by the reconstruction of the advancing meniscus. This provides more nuanced insights into the initiating mechanism of capillary flow. In the noncircular channel, due to the change in curvature of the liquid surface at the acute angle and the expansion of the adsorption layer on the wall surface, the capillary velocity and heat transfer capacity improve compared to circular channels of equal hydraulic diameter. In addition, the effects of channel diameter and wettability on capillary flow and heat transfer are discussed. Capillary microchannels with better wettability and larger diameter achieve better capillary flow and heat transfer capabilities. On this basis, the parallel capillary microchannels inside the block are analyzed, and the non-circular channels achieve a higher capillary velocity while ensuring capillary pressure. Furthermore, the design of the noncircular section obtains a smaller thermal resistance and greater heat transfer efficiency, where the triangular microchannels show the best results. For the same hydraulic diameter and total block area, the performance decreases continuously as the inner angle of the channel increases. These results provide new ideas and a theoretical basis for designing high-performance passive heat sinks based on capillary flow.

Research on online monitoring and early warning system of transmission line galloping based on multi-source data

When the conductor is covered with ice on a non-circular section, and there is low-frequency, large-amplitude motion under wind excitation, it is usually called the transmission line galloping phenomenon. Due to the large amplitude, the galloping of the transmission line will lead to line fatigue, increase in tension, damage to hardware, or toppling of towers. In addition, it will also lead to flashover, tripping, and other transmission accidents caused by the short phase distance, which is not conducive to the safe operation of power grids. In order to improve the safety of power grid operation, this paper designed an online monitoring and early warning system for transmission line galloping on the basis of multi-source data and verified the system through implementation. It was found that the safety factor was 1.568, which determines its early warning level and affirms the feasibility of this study. This research has a positive role in improving the safe operation of the power grid.

Role of size on the compression behaviour of hybrid FRP strengthened square RC columns – Experimental and finite element studies

Confinement of reinforced concrete (RC) columns through external bonding (EB) of fibre-reinforced polymer (FRP) composite becomes less effective in non-circular sections. The effectiveness of FRP confinement reduces with an increase in the size of the cross-section. Hence, it is essential to develop an effective FRP strengthening technique for large-sized square columns. Hybrid FRP strengthening combines the advantage of both near-surface mounting (NSM) and EB strengthening procedures for enhancing the overall performance of RC members under different load combinations. Sixteen square RC columns of various size ratios 1.0 and 1.5 were cast, strengthened and tested to understand the efficacy of the hybrid FRP technique. In addition to the tests, detailed nonlinear finite element (FE) models were developed and validated with the test results and data from the literature. Results show that the efficiency of EB and Hybrid FRP strengthening decreased with the increase in sectional ratio of square columns. Hybrid FRP strengthening improved strength and ductility for all size ratios compared to EB or NSM FRP strengthening alone. Using validated FE models, a parametric study was also conducted to understand the effect of EB and NSM reinforcement ratio and column size on the efficiency of Hybrid FRP strengthening.

Galloping analysis of the main cable in construction: An advanced nonlinear scheme

The main cables of suspension bridges in construction are non-circular sections and thus prone to galloping vibrations. The traditional galloping analysis is a linear scheme and cannot address the nonlinearities and coupling effects among the multidirectional vibrations. To provide an approach for the nonlinear galloping, this paper proposes an advanced continuum model based on Hamilton's principle and variational calculus, which can systemically consider the translational and rotational vibrations and the nonlinearities from the geometric, damping and wind effects. On this basis, the computational approach for the continuum model in COMSOL Multiphysics is investigated, and the result comparisons between the proposed approach and finite element method indicate that the continuum model together with the computational approach can accurately determine the dynamic responses of the main cable. When the quasi-steady based wind forces are included, the nonlinear model can be easily used for galloping analysis, and the limit cycle oscillations (LCOs) in the post-instability of the adopted example are obtained, which are the typical nonlinear aeroelastic phenomena for bluff bodies. Also, the obtained frequency evolution of the LCOs is discussed.

Efekat dužine grla na obrasce protoka u konusnim mlaznicama van dizajna

In the present work, a flow field study was performed for off-design conical nozzles with non-circular cylindrical throat sections such as those found in experimental sounding rocket motor applications. The flow field was simulated with the RANS model in ANSYS-Fluent R16.2 code for 2D domains. The governing equations used are conservation of mass, momentum, energy, and state. Sutherland's equation for viscosity as a function of temperature and the Spalart-Allmaras turbulence model was used to simulate overexpanded flow turbulence. The results showed pressure and Mach number fluctuations as the throat length increased. In the throat section, it is concluded that for the length range of 5 to 15% of the throat diameter, the flow accelerates without the presence of internal shock.

The performance of mechanical characteristics and failure mode for tunnel concrete lining structure in water-rich layer

It's a challenging technical problem at home and abroad that it is inevitable to build tunnels in aquifer with the improvement and development of railway network, particularly under the current stringent environmentally-friendly prerequisite. Therefore, the conventional principle “drainage is dominant and combination of drainage and blockage” should be updated with “blockage is dominant and drainage is limited”. Under this background, the mechanical characteristics for tunnel lining structure in aquifer needs to be studied urgently. A series of model experiments were performed to investigate the load-bearing mechanism of the underwater tunnel lining under water pressure. To investigate the load-bearing characteristics of different types of linings, a fully closed water pressure exerting device for a non-circular section tunnel was invented. A large-scale model experiment (1:30) under combined water and soil pressures was conducted to investigate the mechanical characteristics, deformation, stress distribution, crack development process, and failure mode of the mined-tunnel lining in aquifer. The experiment results indicated that for mined-tunnel lining with large section the key sections for controlling instability of both the drainage lining and the waterproof lining were the bottom of the wall and the inverted arch under the two experiment conditions. One had only water pressure, and the other had a variable water pressure and constant soil pressure. For both types of lining structures, the bottom of the wall and the inverted arch appeared cracks and damaged in turn. Furthermore, based on unified strength theory, it was found that compression-shear failure on the inclined section will occur at the bottom of the wall under the action of water pressure, which was different from the compression bending failure at other parts. In this research, the reasonable ultimate water head of the waterproof lining (thick invert, or large invert) and the drainage lining for the high-speed railway tunnel of Class V surrounding rock with a design speed of 350 km/h was proposed which could provide reference for similar tunnel engineering.

Experimental Investigation of Load-Bearing Mechanism of Underwater Mined-Tunnel Lining

A series of model tests were performed to investigate the load-bearing mechanism of a mined railway tunnel lining under water pressure. To investigate the load-bearing characteristics of different types of linings, a fully closed water pressure exerting device for a noncircular section tunnel was invented. A large-scale model test (1:30) under combined water and soil pressures was conducted to investigate the mechanical characteristics, deformation, stress distribution, crack development process, and failure mode of the underwater mined-tunnel lining. The test results indicated that for the high-speed railway tunnel of Class IV surrounding rock with a design speed of 350 km/h, both the drainage lining and the waterproof lining were controlled by a small eccentric compression under the two test conditions. One had only water pressure, and the other had a variable water pressure and constant soil pressure. The key sections for controlling instability were the bottom of the wall and the inverted arch. The ultimate water head of the drainage lining was 49 m, and the ultimate water head of the waterproof lining was 78 m. In comparison with the drainage lining, the waterproof lining could significantly improve the water-pressure resistance. Thus, design loads of 30 and 60 m are recommended for the drainage and waterproof lining structures, respectively.

Comparative Study on the Influence of Pile Length and Diameter on Bearing Capacity and Efficiency of Root Piles, Straight-Shaft Piles and Pedestal Piles

In order to popularize the application of root pile (RP), which is a miniaturized application after the simplified construction procedure of root foundation and a promising new type of noncircular section pile, and to verify the bearing capacity and efficiency advantages of RP over traditional straight-shaft pile and pedestal pile (SP and PP, respectively), on the basis of validation of the numerical model, numerical simulation of the three pile types with different lengths and diameters and root sizes was carried out under vertical (including uplift and compressive) and lateral static loading. The results show that both the vertical and lateral bearing capacities and efficiency of RP are higher than those of SP and PP, and the larger the pile length and diameter are, the greater the advantages are. Specifically, compared with the bearing capacity of SP, vertical capacity could be improved greatly only by RP instead of PP when the pile length is no less than 15 m, and not the enlarged base of PP but the roots arranged on the upside of RP could improve lateral capacity. Besides, increasing pile length could not improve lateral capacity when the pile length is no less than 10 m, and both the vertical and lateral bearing capacities could be improved by increasing pile diameter. Two efficiency comparison methods were put forward, and their application condition, advantage and disadvantage were analysed to compare the efficiency of pile length and diameter in improving capacity, according to which the economic way to improve vertical and lateral capacities is to increase pile length and diameter, respectively. Enlarged base of PP and roots of RP could be played more fully when the displacement is large enough; therefore, the difference of capacity and efficiency of the three pile types with failure criterion of small displacement (10 mm lateral and 30 mm vertical displacement) is smaller than that with large displacement (30 mm lateral and 60 mm vertical displacement). Furthermore, in order to facilitate the application of RP, it is suggested that roots length should not exceed 0.5 times of pile diameter, and the height and width should not greater than the spacing between stirrup bars or main steel bar, respectively. In addition, roots annulus spacing of 0.4 ~ 0.5 m is appropriate, and the spacing of root layers should not be less than 2.4 m. On the whole, it is of great significance to popularize root piles in practice.

Study of Adiabatic Flame Temperature of a Jet Combustor using a Non-Circular Inlet

An experimental investigation on heat transfer at various zones of the combustion chamber has been carried out using a non-circular inlet at the flame tube. With an aim to improve the turbulent level in flow, the non-circular section used here is an elliptical one. In addition to this, two rectangular tabs are placed at major axis of the ellipse to achieve an efficient mixing of fuel and air. Fuel used for combustion is kerosene while LPG gas is used for pre ignition. Fuel is fed to the chamber by gravity system and it has been atomized by two fish tank pumps. Ignition of the fuel is done by spark plug with a separate setup. The setup comprises of growler and CDI coil which are powered electrically. During the experiment, combustion has been initiated by allowing the air from blower to the chamber. The fuel is sprayed into the flame tube through fuel injector placed at a specified distance. After the proper mixing of fuel and air, the mixture is ignited by spark plug setup. Initially LPG gas was used for preheating followed by kerosene for combustion. Fuel tank has been calibrated for mass flow rate. The experiment has been carried out for different intervals of time and the heat transferred from the flame tube wall and chamber wall is been measured using an infrared gun (ray gun) by pointing laser on the wall. The temperatures at different zones have been measured. It is seen that the overall heat transfer at secondary zone is minimum when compared with other zones for the same period of time. This indicates that if the fuel injector is placed before the secondary zone, then a maximum flame temperature can be obtained. This leads to an improvement in efficiency of the combustion chamber.

Processing ultrafine grained non-circular cross-section profiles via severe plastic deformation

In this study, a new technique is presented for processing ultrafine-grained noncircular thin section profiles via severe plastic deformation. For the first time, a noncircular thin section profiles can be severe plastic deformation processed by this method entitled the noncircular thin section cyclic extrusion–compression (NCTS-CEC). In this technique, the whole length of the profile is passed through a neck zone while it is fully enclosed by the tools set. Therefore, the whole length of the specimen experiences a cyclic extrusion and compression, which accumulates a high level of strain in the material. The feasibility of the NCTS-CEC was successfully examined on aluminum profiles with L, U, and hollow square cross-sections. The microstructure evolution of the processed specimens was investigated by metallographic observations and X-ray diffraction analysis, which demonstrate the formation of a ultrafine-grained microstructure after processing by two cycles of the NCTS-CEC. Moreover, evaluations of the mechanical properties of the processed profiles show remarkable improvements in the yield and ultimate strengths. The microhardness of the processed specimens was also increased after the second cycle to ∼55 Hv from the initial value of 30 Hv. The deformation behavior of the material during processing by the NCTS-CEC method was also numerically simulated by the commercial finite element software DEFORM TM-3D V11.

A review on start-up characteristics of the pulsating heat pipe

Pulsating heat pipe (PHP) is a two-phase heat transfer device, and the start-up characteristics plays a crucial role in its practical application and stable operating performance. This paper introduced the start-up principle of PHP and reviewed the influences of the cross-sectional shape, the physical property parameters and the external field action (i.e., magnetic field, ultrasonic wave etc.) on the starting characteristics of PHP. Based on the results of present literature, the pressure distributions in PHP with non-circular channel section or irregular channel are uneven, which easily form an oscillation cycle motion and is beneficial to the efficient operation of PHP. Simultaneously, the fluids with high thermal conductivity, low dynamic viscosity and low surface tension (such as nano-fluid, deionised water, etc.) are more conductive to starting characteristics of PHP. In addition, reviewed studies reported that as an active heat transfer enhancement method, external field has great potential in terms of enhancing heat transfer and controlling the heat transfer process.

Physical modeling and geometry configuration simulation for flexible cable in a virtual assembly system

Purpose In this paper, a novel and unified method for geometry configuration simulation of flexible cable under certain boundary conditions is presented. This methodology can be used to realize cable assembly verification in any computer-aided design/manufacturing system. The modeling method, solution algorithm, geometry configuration simulation and experimental results are presented to prove the feasibility of this proposed methodology. The paper aims to discuss these issues. Design/methodology/approach Considering the gravity, bending and torsion, modeling of cable follows the Kirchhoff theory. For this purpose, Euler quaternions are used to describe its spatial geometry configuration by a carefully chosen set of coordinates. Then the cable is discretized by the FEM, and the equilibrium condition per element is computed. In this way, the global static behavior is independent of the discretization. The static evolution of the cable is obtained by numerical integration of the resulting Kirchhoff equations. Then the manner is demonstrated, in which this system of equations can be decoupled and efficiently solved. Geometry configuration simulation examples with different boundary conditions are presented. Finally, experiment validation are given to describe the effectiveness of the models and algorithms. Findings The method presented in this paper can be adapted to computer-aided assembly verification of flexible cable. The experimental results indicate that both of the model and algorithm are efficient and accurate. Research limitations/implications The method should be extended to flexible cables with multiple branches and more complex constraints (holes, curved surfaces and clamps) and non-circular sections. Dynamic assembly process simulation based on the Kirchhoff theory must be considered in the future. Originality/value Unlike in previous approaches, the cable behavior was independent of the underlying discretization, and the finite element approach enables physically plausible cable assembly verification.

Study on flexible two-axis roll-bending process for component with non-circular section

Two-axis roll-bending technology, with the advantages of small curvature radius, short straight section and high efficiency, is widely used in fields of aerospace and automobile. By adjusting indentation depth in two-axis roll-bending process, different curvature radius of circular and elliptic component can be formed. Roll-bending experiments and numerical simulations for component with circular and elliptic section are conducted. The results show that the forming curvature radius of circular component and its deviation both decrease with ascending indentation depth. The relationship between forming curvature radius and indentation depth is polynomial fitted. On this basis, ellipse parameter equation is established and different curvature radius at different position of the ellipse is achieved by adjustment of indentation depth. The relationship between indentation depth and forming time is obtained for elliptic component. Elliptic components with different sizes are formed. The stress distribution is uniform after roll-bending process and it increases with ascending indentation depth.

Prediction Accuracy of Seismic Behavior of RC Noncircular Columns Retrofitted with FRP Sheets and the Impact of Local Concrete Compression Behavior

AbstractMore than 40 models have been established to date to determine the axial compressive behavior of noncircular (square or rectangular) concrete sections confined with fiber-reinforced polymer...

Strengthening of square concrete columns with composite materials. Investigation on the FRP jacket ultimate strain

An accurate estimation of the effective ultimate strain of the FRP jacket is crucial to determine the values of strength and ultimate strain of FRP confined concrete. However, this is one of the main aspects not yet resolved by the theoretical models. Published design recommendations differ on this aspect, particularly in the case of non-circular sections. In this work, an experimental program carried out on 38 square section concrete specimens confined with FRP is presented. The results show a great influence of the radius of rounding of the corners on the behaviour of FRP confined square columns. The experimental values of effective ultimate strain are compared with the recommended values given by design guidelines.