Constant Cross-sectional Area Research Articles

Intelligent device for measuring water level in irrigation channels of constant section

The article discusses the problems of online monitoring of water metering in the irrigation systems of Central Asia, in particular the Republic of Uzbekistan, and identifies existing problems. The development of intelligent level measurement devices is aimed at solving these problems. A technique has been created for developing an intelligent level measurement device capable of operating stably even under various disturbing influences, considering abrupt climate changes. Based on this method, an intelligent device has been developed that allows online measurement of the water flow and its amount flowing in the channel based on measuring the water level in channels with a constant cross-sectional area. The device has the function of automatic selection of alternative networks for the exchange of information, such as GSM or Lora, depending on the conditions of information transmission over long distances. The device also includes the function of autonomous charging using solar energy in places with no power supply. The industrial sample of the device was tested and certified in laboratory and field conditions and at the National Certification Center of the Republic of Uzbekistan, and permission was obtained for its mass production. Because local manufacturers produce this device, it has advantages over its imported counterpart in terms of low cost, the availability of customization options, and easy adaptation to difficult conditions. In exchange for applying a smart filtering algorithm, the stabilization of received signals is improved by 74.2% due to intelligent filtering algorithms in a smart device. The reliability of information decreased by 8.2% in total. This result is less than the 9.5% target for information reliability.

ЗІСТАВЛЕННЯ ДЕФОРМАЦІЙНИХ ВЛАСТИВОСТЕЙ ОХОРОННИХ СПОРУД ПІДГОТОВЧИХ ГІРНИЧИХ ВИРОБОК

Purpose. Investigate and compare the deformation properties of protective structures in the form of coal pillars and structures made of crushed rock for a justified choice of the protection method, which can make it possible to ensure the stability of side rocks in the coal massif and preparatory works in the mining areas in the coal mine. Methodology. To achieve the goal, laboratory studies were performed on experimental samples subjected to uniaxial compression. For pillars, their thickness was changed, whereas for structures made of crushed rock the thickness of the rock layer was changed at a constant cross-sectional area. Results. As a result of the conducted research, the deformation properties of protective structures that were subjected to uniaxial compression have been determined. A 15% reduction in their stiffness was recorded for pillars, when their thickness h0 was two times changed, and for the external static load, which varied according to a linear dependence. Within the limits of the safe deformation resource, when the relative deformation is in the range of values 0.18≤λ≤0.23, the stability of the pillars and their bearing capacity is ensured. At the same time, the relative change in their volume should not exceed 7-9%. It has been established that exceeding the limit level of the specific potential energy of deformation by an average of 12-14% causes the destruction of coal pillars. For protective structures made of crushed rock with a relative volume change of 0.35≤δV≤0.28, the value of the compaction coefficient of the original material decreases from kcons = 1.5 to kcons = 1.42 with a simultaneous increase in the work of compression and an increase of more than 20% in the specific potential energy of deformation, thanks to which the rigidity of the embedded material and the bearing capacity of protective structures made of crushed rock are ensured. Scientific novelty. The regularities of formation of deformation properties of protective structures under conditions of uniaxial compression, taking into account the change in the specific potential energy of deformation and the relative change in their volume, have been established. Practical significance. In order to ensure the stability of side rocks in the coal massif and preparatory workings at excavation sites in the coal mine, the feasibility of using partial or complete paving of the produced space from crushed rock, which limits the movement of side rocks in the produced space, has been substantiated.

One Case of Shock-free Deceleration of a Supersonic Flow in a Constant Cross Section Area Channel

Air flows with supersonic speeds are used in many cases, for example, as aircraft air intakes, wind tunnels, and energy separation devices. In many cases it is necessary to decelerate the flow to sonic speeds. Traditionally the deceleration realized through the shocks system, which leads to total pressure losses. The article considers the method of deceleration of supersonic flows using permeable surfaces. In this case, the deceleration process occurs without shocks and, therefore, with lower total pressure losses. We have considered the flow in a tube with permeable wall located behind a supersonic nozzle. One-dimensional and axisymmetric mathematical models of such a device are developed. The calculation results are compared with experimental data. It is shown that, depending on the ratio of pressure inside the tube and the ambient pressure, different flow regimes inside the tube are possible: pure subsonic, transitional from supersonic to subsonic, and pure supersonic. The transition from supersonic to subsonic flow occurs without shocks due to the suction and friction combined effects.

Film Cooling Holes Performance on A Flat Plate

The present study aims to evaluate numerically the influence of film cooling holes configuration. Five models of holes configuration were studied to examine the effectiveness of a single film cooling hole (8 mm diameter). A cylindrical hole, square hole, rotated square, triangle hole and rotated triangle hole was employed to eject the coolant air with constant cross sectional area at 350 angle of injection. A 3-D finite-volume method was utilized to describe the turbulent flow over flat plate surface (as a model of a turbine blade surface). The mainstream domain (40d x10d x4d) had been represented in ANSYS FLUENT 16 with a standard turbulence model. So far, in term of effective cooling, the numerical results elucidate noticeable enhancement realized at BR=0.5 due to a reduction in plate surface temperature compared with BR =0.25 and 1 for cylindrical hole model. Moreover, the holes configuration performance demonstrate a better surface effectiveness about 1.6 % and 1.2 % for rotated triangle and square models respectively compared with the cylindrical holes model at BR=1. It was found that the numerical results had an excellent matching with related published results which show the solidity of ANSYS FLUENT code to predict the cooling efficiency with varying blowing ratio.

Prediction of mechanical properties for three-dimensional woven composites considering interference between tows

The mechanical performance of three-dimensional woven composites is usually modeled by an ideal model with straight tow paths and constant cross-sectional areas. This ideal model predicts inaccurate properties due to oversimplification of tow shapes. In this paper, we present a more accurate method to predict properties of the 3D woven composite considering waviness and contraction of tows due to interference between them. The tow waviness is defined by elliptic and trigonometric functions. The shrinkage of the tow cross-sectional area is modeled using a cubic polynomial. The elastic moduli are predicted using the modeled tows and the weighted average model. The predicted properties are compared with test results to verify the accuracy. In addition, the usefulness of the present method is verified by comparing the calculated moduli using the ideal model. We conclude that the present method is useful for the design of structures to which 3D woven composites are applied.

Pneumatic system for pressure probe measurements in transient flows of non-ideal vapors subject to line condensation

This paper presents the design, construction and commissioning of a pneumatic system for pressure probe measurements in flows of organic vapors in non-ideal conditions, namely in the thermodynamic region close to the liquid–vapor saturation curve and the critical point where the ideal gas law is not applicable.Experiments were carried out with fluid siloxane MM (hexamethyldisiloxane, C6H18OSi2), commonly employed in medium/high temperature Organic Rankine Cycles (ORCs), in the Test Rig for Organic VApors (TROVA), a blow-down wind tunnel at the Laboratory of Compressible fluid dynamics for Renewable Energy Applications (CREA lab) of Politecnico di Milano. TROVA operation is intrinsically transient due to its batch nature, with a low frequency content (∼1Hz) related to the emptying of the high-pressure reservoir feeding the test section.The challenges linked to possible condensation in pneumatic lines, such as vapor–liquid menisci, hydrostatic head and mass-sink effects, were evaluated by means of theoretical calculation and experiments. To avoid these issues, a nitrogen-flushed pneumatic system for absolute and differential pressure measurements was designed and successfully tested with superheated MM vapor expanding in planar choked converging nozzles characterized by a portion with constant cross-sectional area yielding design Mach numbers of 0.2, 0.5 and 0.7. Commissioning of the complete system including a probe was performed with the first ever testing of an L-shaped Pitot tube in non-ideal subsonic flows of siloxane MM vapor at Mach numbers M=0.2 and 0.5. Measurement delay issues were identified and assessed through a dynamic testing procedure, and were solved by reducing the overall pneumatic lines volume including the one hidden within pressure transducers. The correct performance of the complete system was therefore verified for probe measurements of total, static and dynamic pressure in non-ideal flows of organic vapors. This sets the foundation for future directional pressure probes calibration and use in the characterization of such flows, as in direct measurement of total pressure losses across shocks and in testing of ORC turbine blade cascades.

A difference scheme for a triangular system of conservation laws with discontinuous flux modeling three-phase flows

<abstract><p>A triangular system of conservation laws with discontinuous flux that models the one-dimensional flow of two disperse phases through a continuous one is formulated. The triangularity arises from the distinction between a primary and a secondary disperse phase, where the movement of the primary disperse phase does not depend on the local volume fraction of the secondary one. A particular application is the movement of aggregate bubbles and solid particles in flotation columns under feed and discharge operations. This model is formulated under the assumption of a variable cross-sectional area. A monotone numerical scheme to approximate solutions to this model is presented. The scheme is supported by three partial theoretical arguments. Firstly, it is proved that it satisfies an invariant-region property, i.e., the approximate volume fractions of the three phases, and their sum, stay between zero and one. Secondly, under the assumption of flow in a column with constant cross-sectional area it is shown that the scheme for the primary disperse phase converges to a suitably defined entropy solution. Thirdly, under the additional assumption of absence of flux discontinuities it is further demonstrated, by invoking arguments of compensated compactness, that the scheme for the secondary disperse phase converges to a weak solution of the corresponding conservation law. Numerical examples along with estimations of numerical error and convergence rates are presented for counter-current and co-current flows of the two disperse phases.</p></abstract>

Concept of mathematical modeling of lumbar and thoracic spine based on elastic beam theory

Modeling of the human spine is important for establishing quantitative assessment methods of low back pain (LBP) caused by manual material handling (MMH). This study developed mathematical models of the lumbar and thoracic spine based on the elastic beam theory. Two types of models, uniform and non-uniform, were derived. First, to simplify the Bernoulli-Euler beam theory, three assumptions were introduced for the uniform beam model: (i) the vertebrae and intervertebral disc were considered as a composite material, (ii) constant cross-sectional area, and (iii) conversion of muscular strength to bending moment. However, on fitting to the actual spine position data from the literature, the uniform beam model was found to be unable to reproduce the spine shape, particularly in the lumbar region. Therefore, the non-uniform beam model was derived by removing assumption (ii), which does not agree with the actual human spine profile. Consequently, the spine was modeled as a trapezoid from around S1 to C7 in the sagittal plane, by adjusting the proportionality factor of trapezoid via tapering or widening, and the non-uniform beam model was found to better reproduce the spine shape, including the lumbar region. The model has practicability, such as estimation of spine shape; however, the proportionality factor that was used to reproduce the spine shape did not agree with the actual human spine profile; further theoretical development has been left as future work.

A novel method for the evaluation of ejector based on a virtual nozzle and two indexes

This paper presents a novel method for ejector evaluation by developing a virtual nozzle, which provides the ejector’s maximum ability to overcome its back pressure and the minimum constant cross-section area based on two newly-derived evaluation indexes. The method was developed based on the assumption that the total energy and the ratio of dynamic enthalpy to total energy before normal shock of the virtual nozzle are the same as those of the real ejector. Under the condition that the initial state of the virtual nozzle is the same as that of the primary fluid of the ejector, two evaluation indexes, which include the relative pressure ratio and the relative area ratio, were derived to indicate the extent to which the ability to overcome back pressure and area demand deviate from the benchmark obtained from the virtual nozzle. Using the new method, the case studies of ejector evaluation were carried out involving with theoretical data of 13 refrigerants selected as working fluid of ejector and experimental data of four refrigerants. And the relationship between the two indexes was expressed by a high-accuracy fitting correlation equation that was validated by both theoretical calculation and experimental data and was found meaningful.

Numerical and Theoretical Study of Performance and Mechanical Behavior of PEM-FC Using Innovative Channel Geometrical Configurations

Proton exchange membrane fuel cell (PEM-FC) aggregation pressure causes extensive strains in cell segments. The compression of each segment takes place through the cell modeling method. In addition, a very heterogeneous compressive load is produced because of the recurrent channel rib design of the dipole plates, so that while high strains are provided below the rib, the domain continues in its initial uncompressed case under the ducts approximate to it. This leads to significant spatial variations in thermal and electrical connections and contact resistances (both in rib–GDL and membrane–GDL interfaces). Variations in heat, charge, and mass transfer rates within the GDL can affect the performance of the fuel cell (FC) and its lifetime. In this paper, two scenarios are considered to verify the performance and lifetime of the PEM-FC using different innovative channel geometries. The first scenario is conducted by adopting a constant channel height (H = 1 mm) for all the differently shaped channels studied. In contrast, the second scenario is conducted by taking a constant channel cross-sectional area (A = 1 mm2) for all the studied channels. Therefore, a computational fluid dynamics model (CFD) for a PEM fuel cell is formed through the assembly of FC to simulate the pressure variations inside it. The simulation results showed that a triangular cross-section channel provided the uniformity of the pressure distribution, with lower deformations and lower mechanical stresses. The analysis helped gain insights into the physical mechanisms that lead to the FC’s durability and identify important parameters under different conditions. The model shows that it can assume the intracellular pressure configuration toward durability and appearance containing limited experimental data. The results also proved that the better cell voltage occurs in the case of the rectangular channel cross-section, and therefore, higher power from the FC, although its durability is much lower compared to the durability of the triangular channel. The results also showed that the rectangular channel cross-section gave higher cell voltages, and therefore, higher power (0.63 W) from the fuel cell, although its durability is much lower compared to the durability of the triangular channel. Therefore, the triangular channel gives better performance compared to other innovative channels.

Experimental Investigation to Evaluate the Behavior of Concrete-Filled Steel Tubular Columns under the Effect of the Distribution of the ‎Total Steel Area between the Internal Concrete Core and the External Steel Tube

Composite columns are generally installed in high-rise buildings and bridges. As well as being smaller and lighter than conventional reinforced concrete columns, composite columns offer high efficiency and ductility. In this research, experimental and analytical studies were carried out to investigate the optimal distribution of the ‎total steel area of the Concrete-Filled Hollow Steel Tube (CFHST) columns; the experimental program included 20 CFHST columns. ‎The main variables of the experimental study were the distribution of the total steel cross-sectional area over the internal concrete core (steel reinforcement) and the external steel tube, the cross-sectional shape, the width-to-breadth ratio t/b, and the presence or absence of shear connectors. In addition, using equations of different codes, comparison was conducted between the experimental and analytical results. For a constant steel cross-sectional area, the use of internal steel bars and external steel tubes, together with the use of shear connectors, was found to exhibit a better ultimate load capacity, stiffness, and ductility for the CFHST columns.

Optimal shape of the rotating nano rod

By using a Pontryagin’s principle, we study the optimal shape of a rotating nano rod and determine the optimal cross-section that is stable against buckling due to centrifugal forces. We generalize the results of the earlier studies focused on the constant cross-sectional area of nano rods. The problem of the optimal shape of a Bernoulli–Euler rotating rod is analyzed first. The optimal nano rod with fixed volume was found to have larger critical rotation speed than the optimally shaped Bernoulli–Euler rod with the same volume. Similarly, for fixed rotational speed, the optimally shaped nano rod was found to have smaller volume than the optimally shaped Bernoulli–Euler rod.

ЛОКАЛИЗАЦИЯ ПЛАСТИЧЕСКОЙ ДЕФОРМАЦИИ ТЕХНИЧЕСКИ ЧИСТОГО ТИТАНА В СЛОЖНОМ НАПРЯЖЕННОМ СОСТОЯНИИ ПРИ ВЫСОКОСКОРОСТНОМ РАСТЯЖЕНИИ

In this work, the effect of a triaxiality stress state on the mechanical behavior and fracture of commercially pure titanium VT1-0 (Grade 2) in the range of strain rates from 0.1 to 1000 s−1 is studied. Tensile tests are carried out using a servo-hydraulic testing machine Instron VHS 40 / 50-20 on flat specimens with a constant cross-sectional area and on flat specimens with a notch. To study the effect of the complex stress state on the ultimate deformation before fracture, the samples with the notch of various radii (10, 5, 2.5 mm) are used in the experiments. Phantom V711 is employed for high-speed video registration of specimen’s deformation. Deformation fields in a working part of the sample are investigated by the digital image correlation method. It is shown that the effect of the strain rate on the ultimate deformations before fracture has a nonmonotonic behavior. An analysis of strain fields in the working part of the samples shows that the degree of uniform deformation of the working part decreases with an increase in the strain rate. At strain rates above 1000 s−1, the shear bands occur at the onset of a plastic flow. Commercially pure titanium undergoes fracture due to the nucleation, growth, and coalescence of damages in the bands of localized plastic deformation oriented along the maximum shear stresses. The results confirm that the fracture of commercially pure titanium exhibits ductile behavior at strain rates varying from 0.1 to 1000 s−1, at a triaxiality stress parameter in the range of 0.333 ≤ η <0.467, and at a temperature close to 295 K.

A novel super-cooling enhancement method for a two-stage thermoelectric cooler using integrated triangular-square current pulses

In this work, a novel concept of continuous cooling has been proposed to enhance the super-cooling performance of a two-stage thermoelectric cooler, in which integrated triangular-square pulses are used with their modes separately controlled in the upper and lower stages. The 3-dimensionl modeling of the thermoelectric cooler is developed to simulate the super-cooling performance. The non-dominated Sorting Genetic Algorithm II (NSGA-II) is adopted to perform the multi-parameters optimization of pulses forms, in which twelve influencing parameters including pulse amplitude and width, several time constants such as the interval time and input time of pulses are selected as the searching variables, and maximum effective cooling zone with minimum overshoot temperature is set as the multi-objective function. The optimal designs are proved to be better in super-cooling performance for both constant and variable leg cross-sectional area, owing to their well mutual cooperation of the upper and lower stage pulses. Compared to the conventional design with completely identical imposed current form, the effective cooling zone can be improved up to 72.41% by the optimal design when the cooling load is fixed at 0 kW m-2, and the corresponding temperature overshoot can be decreased by 56.48% from 20.29 K to 8.83 K.

Research on the operating boundary of the dual mode scramjet with a constant area combustor through thermodynamic cycle analysis

The maximum pressure ratio of the isolator is important for studying the operating boundary of the dual mode scramjet. In this paper, the pressure rise mechanism of the dual mode scramjet engine and the characteristic of the isolator maximum pressure rise are analyzed. The operating range and performance of scramjet under the pressure rise limit are investigated using the constant cross-sectional area combustor. The maximum pressure ratio of the isolator confines the back pressure from the combustor so that the scramjet engine has a minimum freestream Mach number of each equivalence ratio. When the freestream Mach number is smaller than the minimum freestream Mach number, an expansion section may be arranged between the combustor and the isolator to balance the pressure of the combustor and that of the isolator. The expression of the minimum freestream Mach number is derived and it is found that the minimum freestream Mach number of the dual mode scramjet in both modes increases with the increase of equivalence ratio and compression ratio of the inlet. A variable divergent section is suggested to balance the pressure under different freestream Mach numbers and equivalence ratios.

An experimental study on axial behavior of CFRP-strengthened RC rectangular columns with variable slenderness ratio

In the construction industry, carbon fiber-reinforced polymer (CFRP) composites are widely used for retrofitting and rehabilitation of reinforced concrete (RC) rectangular columns to enrich the service life of structures. The CFRP-confined RC rectangular column with a variable slenderness ratio has limited design provisions in available design codes. The aim of the current experimental work is to explore the efficacy of slenderness ratio on the axial performance of CFRP composite-confined rectangular columns having a constant cross-sectional area and steel reinforcement ratio. The experimental results clearly demonstrated that the yield strength, ultimate strength, and ductility of the RC column after CFRP confinement are significantly influenced by the variation in the slenderness ratio. The response of CFRP wrap, transverse and longitudinal reinforcements in the strengthening process of the RC rectangular column also remarkably varied for different slenderness ratios.

A simplified mechanical model for explaining fast-rising jökulhlaups

The paper describes a simplified mathematical model aimed at fitting available hydrographs of floods from subglacial lakes reaching their peak almost linearly in time, the so-called fast-risingjökulhlaups. The simplifying idea is that the glacier can be treated as a block with fixed width, length and thickness, confining a subglacial lake with a constant cross-sectional area and variable level. We do not consider the role of heat transfer as suggested by many authors for fast-rising events. The model consists of two ordinary differential equations: conservation equation for the lake water and motion equation for the glacier. The glacier vertical movement is supposed to be governed by its own weight, the water pressure generated by the lake and by the forces acting on the lateral sides due to interaction between the glacier and the surroundings. The model has three free parameters and reproduces satisfactorily eight historical hydrographs observed originated by eight jökulhlaups in the Skaftá river (Iceland). These floods, of fast-rising type, are sourced from two ice cauldrons, the Eastern one being responsible of the largest floods (up to 3500 m3s−1). On average, the cauldrons drain almost every two years due to persistent geothermal activity beneath Vatnajökull glacier. This periodicity has a simple mathematical interpretation and is used to obtain another validation of the model.

Comprehensive Study of the Deformation Behavior during Diffusion Bonding of 1.4301 (AISI 304) as a Function of Material Width and Aspect Ratio

In this paper, the impact of material width as well as aspect ratio on deformation during diffusion bonding of layered samples were investigated. For this, six annular samples with a constant cross-sectional area but an increasing diameter and thus decreasing material width were designed. In a first set of experiments, specimens of a constant height of h = 20 mm were examined. Each sample consisted of 10 sheets, 2 mm in thickness each. Diffusion bonding was performed at T = 1075 °C, t = 4 h and p = 15 MPa. Subsequently, additional samples with a constant aspect ratio of about three but different material width were diffusion bonded. For this, additional layers were added. It was expected that the deformation should be nearly constant for a constant aspect ratio. However, comparing the deformation to a sample possessing an aspect ratio of about three from the first batch, a much higher deformation was obtained now. Bonding a third sample, a deformation in the same range as for the other two samples of the second batch was obtained. It was found that due to the evaporation of metals, the thermocouples were subjected to aging, which was proven indirectly by the evaluation of heating power. Since the diffusion coefficient of the metals follows an exponential law, deformation changes considerably with temperature. This emphasizes that exact temperature measurement is very important, especially for bonding microprocessor devices at constant contact pressure. The experiments showed that the deformation depends strongly on geometry. Bonding parameters cannot be generalized. For layered setups, the contribution that thickness tolerances from manufacturing and leveling of surface roughnesses of sheets add to the overall deformation cannot be reliably separated. After diffusion bonding, thickness tolerances increase with a lateral dimension. Obviously, the stiffness of the pressure dies is crucial.

Influence of water injection on performance of scramjet engine

In order to investigate the influence of water injection on performance of scramjet engine, a thermodynamic model with the constant cross sectional area heating process was developed to analyze the effects of water content and energy on performance of scramjet engine. The influence of water injection on the maximum fuel equivalence ratio of scramjet engine was also studied. The maximum specific thrust was obtained by optimizing the compression ratio of the inlet, the fuel equivalence ratio and the water content. Results show that the specific thrust of scramjet engine can be augmented by water injection at the cost of the decrease of fuel impulse. The maximum fuel equivalence ratio of scramjet engine can be increased by water injection at high flight Mach numbers, while slightly decreased at low flight Mach numbers. So thrust augmentation by water injection is more suitable for scramjet engines operated at high flight Mach numbers, which is further confirmed by optimization results of the maximum specific thrust of scramjet engine. Optimization results of the maximum specific thrust also show that improving the isentropic efficiency of the inlet and the maximum combustion temperature is beneficial to the augmentation of the maximum specific thrust of scramjet engine.

THEORETICAL INVESTIGATION OF CONCRETE FILLED STEEL HOLLOW SECTION COLUMNS

Steel concrete composite columns are widely used in high rise buildings and bridges. Composite columns provide not only great reduction for the column size and weight, but also high columns efficiency and ductility. In Concrete Filled Steel Tube (CFST) columns, the steel tube provides formwork for the concrete; the concrete prevents local buckling of the steel tube. This paper illustrates a theoretical study of the behavior of CFST columns subjected to centric load by using ANSYS (18.1). The study divided into two parts. In the first part, the verification of the program was done using an experimental work of previous research, this verification showed that the capability of ANSYS program for analysis of the CFST columns with very good accuracy. In the second part: a parametric study was carried out to study the behavior of CFST braced, constant cross section area, centric loaded columns. The main variables were the shape of cross section (three shapes: square, rectangular and circular) and slenderness ratio (λ). The analysis shows that the increase of the slenderness ratio led to decrease the ultimate load capacity, stiffness and ductility of the CFST columns. The current ECP of concrete code underestimates the values of ultimate load capacity while, ECP of steel predicts the reasonable values for an ultimate load capacity of CFST columns.