Round Pipe Research Articles

The effect of the roller profile on cave-in defect in reshaping process by considering nonlinear combine strain hardening

The reshaping process of pipes is an important method in producing non-circular pipes. Desired profile products are produced by passing round pipe through the rotating rollers. Cave-in defect is one of the common defects in the reshaping process. Roller design issues can decrease this kind of defect. In this paper, a method based on the slab method and the incremental plasticity has been presented to the numerical study of a 2D reshaping process. For investigating the Cave-in defect, the contact model has been developed. The concept of element elongation has been introduced to increase the accuracy of the contact model. Based on the presented method, numerical software has been developed to simulate the 2D reshaping process. Elastic-plastic equations for this subject have been driven based on the incremental method, J yielding criterion, and non-linear combined hardening. The effects of the radius of the roller profile on cave-in defects have been investigated by using the presented software (DARF). A set of experiments has been conducted in a forming station to verify the results. Results show that the presented model has higher accuracy than the Abaqus commercial software in predicting the cave-in defect. Based on the results of the model, the local increase of yielding stress directly affects the cave-in defect. Also, a meaningful relationship between the radius of the roller and the amount of the cave-in has been observed.

Experimental and numerical studies of intensified turbulent heat transfer in round pipes with curved wing vortex generators

Turbulent airflow and heat transfer characteristics in round pipes with curved wing vortex generators (CWVGs) were numerically and experimentally evaluated for Reynolds number (Re) between 5896 and 20,283. The CWVGs were streamlined and placed in the near-wall regions to reduce the flow blockage. Numerical results showed that counter-rotating vortex pairs were induced at the trailing edge of CWVGs, and these vortices presented a more lasting effect on the downstream flow field with the larger width ratio (WR) or smaller pitch ratio (PR), resulting in the thinning thermal boundary layer and improved fluid mixing. With the increasing WR, the friction factor and Nusselt number were intensified by 195%–604% and 50%–110% over the smooth tube, respectively; the thermal enhancement factor (TEF) increased firstly with WR and reached a peak at WR = 0.20 for Re = 6023, while at WR = 0.15 for other Re. With a reduction in PR, the TEF value reached a peak at PR = 1.0, and the maximum TEF of 1.27 was achieved at Re = 5962, WR = 0.20, and PR = 1.0. Also, correlations for Nusselt number and friction factor were derived according to the experimental data for industrial applications.

Experimental-numerical study on the structural failure of concrete sewer pipes

The structural failure of round and egg-shaped sewer pipes is investigated by means of laboratory experiments and finite element method analyses. Two different round pipes are considered, which have an inner diameter of 400 mm and 500 mm, and are respectively referred to as R400 and R500 sewer pipes. The egg-shaped pipe considered in this study has a horizontal inner diameter of 400 mm and a vertical inner diameter of 600 mm, and is labeled as the E400/600 sewer pipe. Sewer pipes with these dimensions are most commonly used in the Netherlands. In full-scale experimental tests the sewer pipe specimens are subjected to biaxial loading, whereby the horizontal pressure loading is set equal to 1/3 times the vertical pressure loading. This loading condition is representative of a sewer pipe embedded in a well-graded sandy gravel and subjected to neutral horizontal earth pressure. Apart from the global load–displacement behaviour, the local strain response is measured at various locations, which indicates how the applied load is distributed across the sewer pipe. The fracture pattern at catastrophic failure is recorded by means of cameras placed at the front side of the pipe specimen. The round pipes fail under the development of 4 distinctive failure cracks, which are located at the top and bottom of the sewer pipe, and halfway the left and right sides. The egg-shaped sewer pipes also fail under the development of 4 failure cracks, which emerge at the top and bottom of the pipe, and at the top-left and top-right sides. The round R500 pipe fails at the lowest ultimate failure load, which is, respectively, a factor of 1.16 and 2.25 smaller than the ultimate failure loads of the round R400 pipe and the egg-shaped E400/600 pipe. The FEM models of the round and egg-shaped pipes accurately predict both the failure response and the fracture pattern measured in the experiments. Accordingly, the FEM model of the round R400 sewer pipe is used to analyse the sensitivity of the overall failure response of the sewer pipe to various parameters, which are the load contact area, the ratio between the applied horizontal and vertical loads, the wall thickness of the sewer pipe, and the tensile strength, mode I toughness and Young’s modulus of the concrete. The variation of these parameters mimics how the load bearing capacity of a sewer pipe decreases under the effects of soil erosion, changes in lateral earth pressure, biochemical degradation, and ageing. The knowledge obtained from the experimental–numerical study may support the decision making process on maintenance and replacement of sewer systems.

INVESTIGATION OF THE DYNAMIC LOAD OF THE JOINT-PLATFORM OF THE JOINT TYPE FROM ROUND PIPES LOADED BY TANKER CONTAINERS

The dynamic loading of the load-bearing structure of the articulated platform car made of round pipes loaded with tank containers was determined. The research was conducted by mathematical modeling. The solution of the equations of motion is carried out in the MathCad software package. It is established that under the influence of a longitudinal force of 2.5 MN on the front stops of the autocoupling, the acceleration on the first section of the platform car is 27.7 m/s² from the side of the force application, and on the second - 24.4 m/s2. To reduce the dynamic load of the load-bearing structure of the platform car, the possibility of using the concept of a harness device on it as an alternative to a typical self-coupling device is considered. The quenching of the kinetic energy of the impact is carried out due to the viscous resistance forces arising in the concept. The proposed implementation allows to reduce the dynamic load of the load-bearing structure of the platform car by 10% compared to the use of a standard self-coupling device. The conducted researches will promote creation of innovative designs of cars-platforms and increase of efficiency of use of railway transport.

Theory of Heat Transfer in Straight Round Pipes with Square and Triangular Turbulators Under High Reynolds Criteria

Objectives: To carry out mathematical modeling of the structure of vortex zones between periodic flow turbulators with a surface arrangement of triangular and square transverse profiles on the basis of multi-block computing technologies based on solutions of the Reynolds equations (closed by means of the Menter shear stress transfer model) and energy equations (on multi-scale intersecting structured grids) with high Reynolds criteria Re = 106 with an exhaustive analysis of the corresponding current lines. Method: The calculations were carried out on the basis of a theoretical method based on the solution of the Reynolds equations by the factorized finite-volume method, which are closed using the low-Reynolds model of the Menter shear stress transfer, and the energy equation on multi -scale intersecting structured grids (FCOM). Result: Mathematical simulations of the heat exchange process in straight and round pipes with turbulators with d / D = 0.95 ... 0.90 and t / D = 0.25 ... 1.00 square and triangular cross-sections at large Reynolds numbers (Re = 106) on a foundation with multi-block computing technologies, which are based on solutions of the Reynolds equations and energy equations in a finite-volume and factorized way. It is found that the relative intensification of heat transfer [(Nu / Nusm) | Re = 106] / [(Nu / Nusm) | Re = 105] in round pipes with square air turbulators for large Reynolds numbers (Re = 106), which may well be relevant in the channels used in heat exchangers, may be higher with a large-scale increment of hydraulic resistance than for slightly smaller numbers (Re = 105), for relatively high flow turbulators d / D = 0. 90 for the entire range under consideration for the parameter of the relative step between them t / D = 0.25 ... 1.00 a little more than 3%; for turbulators of triangular cross-section, similar indicators are approximately the same. For lower square turbulators with d / D = 0.95, this increase in relative heat transfer for large Reynolds numbers (Re = 106) compared to smaller numbers (Re = 105) does not exceed 6%; for triangular cross-section turbulators, similar indicators are slightly more than 4%. Conclusion: According to the results of calculations based on the developed model, it is possible to optimize the intensification of double turbulators, as well as to control the process of heat transfer intensification. It is shown that for higher square turbulators and at higher Reynolds numbers, a slight increase in the relative Nusselt number Nu / Nusm is accompanied by a significant increase in the relative hydraulic resistance due to the very significant influence of return currents, which can flow directly on the turbulator itself to the greater extent, the higher the Reynolds number; for triangular turbulators, the above trend persists and even deepens.

Effect of pipe flattening on pressure drop in vapor core and thermal characteristic of miniature round and flat-shape heat pipe with sintered fiber wick

The effect of pipe flattening on pressure drop in vapor core and also heat transfer characteristic of the sintered fiber heat pipes has been investigated. The original diameter of heat pipes were 2 mm and 3 mm, respectively, with the effective length of 100 mm. Thermal performance of the flat-shaped heat pipe with the sintered fiber bundle wick was experimentally investigated under a horizontal orientation in this study. The proper fiber bundle wicks were fabricated at porosity of 0.54, and firmly filled within internal heat pipe wall by the sintering process. The heat pipes were pressed into two final thickness by the flattened process which results in vapor core minimizing. The numerical method was established in modified forms to represent the related wick-heat pipe design parameters, for example, wick thickness, wick porosity, wall thickness, flattened width and height, corresponding to thermal performance of fiber wick heat pipes. The numerical analysis for pressure drop was only focused on vapor core region. The vapor flow was assumed to be laminar and incompressible. It is found that when the heat pipe was flattened, the pressure drop increased. The flattening of heat pipe caused the smaller space of vapor core, therefore the working fluid in vapor phase could not easily transfer heat. In this case, the critical final thickness of 0.45 mm (for original diameter of 2 mm) which the vapor core area nearly approaches to zero, has an effect on the high value of thermal resistance considered in vapor core (z5). In addition, the overall thermal resistance estimated from ESDU79012 agrees well with that obtained from the experiment with the standard deviation (STD) of ±15 %, and it shows that the thermal resistance model can provides a reasonable prediction for the thermal resistance of flat-shaped heat pipes with sintered fiber wicks. Moreover, the new normalized parameter h′v/hv is proposed to represent the appearance of vapor core after pipe flattening which can be used to suggest a desirable normal region of flattened heat pipe with the sintered fiber wick. The critical remaining vapor core height after pipe flattening has been further analyzed to be 0.06 (about 74% from original diameter).

Experimental study of two-phase flow structure in churn-turbulent to annular flows

The local phase distribution of adiabatic air-water two-phase flow in churn-turbulent to annular flows was experimentally investigated using the Two-Sensor Droplet-Capable Conductivity Probe (DCCP-2). The experiments were performed in a 2.54 cm inner diameter vertical round pipe at downward flows. Twelve flow conditions in churn-turbulent to annular flows were chosen for the current study. The inlet superficial gas velocity ranged from 5.68 m/s to 17.19 m/s, and the inlet superficial liquid velocity ranged from 1.21 m/s to 2.64 m/s. The DCCP-2 is able to distinguish droplets, liquid ligaments, bubbles, and continuous gas. The radial profiles of volume fraction, frequency, axial interfacial velocity, and chord length of droplets, ligaments and bubbles were measured. The experimental results showed that gas volume fraction had a center-peak distribution, and the maximum gas volume fraction in centerline could exceed 95%. The volume fraction of droplets was very low, only on the order of 0.1%. Droplet concentration also showed a center-peak distribution. Both ligament and bubble volume fraction showed a near-wall peak distribution. The ligament volume fraction in the near wall region could reach 80%, which indicated the existence of a film region near the wall and likely includes surface waves on the film. The volume fraction profile of gas, droplets, ligaments, and bubbles showed the tomography structure in churn-turbulent to annular flows. The effects of flow conditions on phase distribution were also studied. An interesting feature was that both the increase of gas flux and the increase of liquid flux tended to increase the bubble volume fraction. The statistical distribution of droplet size was found to be invariant of radial position. The droplet velocity at centerline was generally larger than the superficial gas velocity, which can be attributed to the gravitational effects at downward flows.

Investigation on the Gas Jet Flow Performance Confined in Round Pipe

In this study, the round jet flow behavior arose by the confinement was investigated experimentally and numerically. The confinement characteristics based on multi-scale characterizations in the atmospheric gas jet flow, which generated from a circular symmetrical subsonic nozzle and flowed into a confined round pipe, was used to studied. The studied region near the nozzle possess really short axial length (within 12d), providing initial conditions and boundaries that affected the flow behaviors in this region. A wide range of inlet velocities (0.98 m/s~84.72 m/s) and confined space sizes (1~20) were involved for simulated and quantitative discussions. The velocity profile evolution was recorded by simulations and characterized by a laser Doppler anemometer (LDA) with a resolution of 0.01 m/s. The confinement characteristics were systematically presented to elucidate the performance under the studied confined conditions with different metrics, such as centerline velocity decay (VR), entrainment rate (MR), pressure coefficient (Cp) and length of recirculation region (LR). The results indicated that the recirculation fluid action mainly contributed to the promoted initial velocity profile evolution with the introduction of the confined space. Theoretically, the confined space could reduce the maximum absolute entrainment mass flux, initiating a peak at the center of the recirculation region, which was controlled by the inlet velocity and the confined space size collectively. The remarkable effect of confined space size further contributes to the confinement characteristics of gas jet flow, representing a shortened flow distance despite similar process as that by reducing the diameter ratio (dR). In some cases, because of the miniaturization of confined space size, the dispersion of initial velocity profile evolution was not significant displayed throughout the variable inlet velocity range, especially when the dR was less than 2. This study gives a new insight in the performance of jet flow confined in round pipe, and such knowledge will be helpful to provide great potential and reference to applied fluid mechanics.

SIMULATION OF AIR HEAT TRANSFER IN CIRCULAR PIPES WITH TRIANGULAR AND SQUARE TURBULENCE STIMULATORS FOR HIGH REYNOLDS CRITERIA UP TO ONE MILLION

Objective . Conduct mathematical modeling of tornado zone structure systems between cyclic flow turbulence stimulators with the surface arrangement of triangular and square cross-sections based on multiblock computational techniques, based on solutions of the factorialized finite- volume procedure of the Reynolds equations (closed through the Menter shear stress transport model) and energy equations (on a multiscale intersecting structured grid) at high Reynolds criteria Re=10 6 with an exhaustive analysis of the relevant current lines. Methods. The calculations were carried out on a mathematical foundation based on the solution of the factorized finite-volume procedure of the Reynolds equations, which are closed using the low-Reynolds Menter shear stress transport model, and the energy equations on a multiscale intersecting structured grid (factorized finite-volume procedure). Results . Mathematical simulations of the heat exchange process in straight and round horizontal pipes with turbulence stimulators with d/D=0.95...0.90 and t/D=0.25...1.00 of triangular and square transverse profiles with large Reynolds numbers (Re=10 6 ) on a foundation with multiblock computing technologies, which are based on solutions of factorized and finite-volume Reynolds equations and energy equations, were conducted. It was found that the relative intensification of heat transfer [(Nu/Nu GL )| Re=106 ]/[(Nu/Nu GL )| Re=105 ] in round pipes with square air turbulence stimulators for large Reynolds numbers (Re=10 6 ), which may be relevant in the channels used in heat exchangers, could be higher with a large-scale increment of hydraulic resistance than for slightly smaller numbers (Re=10 5 ), for relatively high flow turbulence stimulators d/D=0.90 for the entire range under consideration for the parameter of the relative step between them t/D=0.25...1.00 a little more than 3%; for triangular turbulence stimulators, the crosssection profiles have similar values. For lower square turbulence stimulators with d/D=0.95, this increase in relative heat transfer for large Reynolds numbers (Re=10 6 ) compared to smaller numbers (Re=10 5 ) does not exceed 6%; for triangular cross-section turbulence stimulators, similar indicators are slightly more than 4%. Conclusion. The calculated results based on the developed model can optimize the intensification by turbulence stimulators and control the processes of heat transfer intensification. It is shown that for higher square turbulence stimulators and higher Reynolds numbers, a limited increase in the relative Nusselt criterion Nu/Nu GL is accompanied by a significant increase in the relative hydro resistance due to the very significant influence of return currents, which can flow directly on the turbulence stimulator to the greater extent, the higher the Reynolds number; for triangular turbulence stimulators, the above trend persists and even deepens.

3D numerical simulation of laminar forced-convection flow subjected to asymmetric thermal conditions. An application to solar thermal collectors

This paper looks at the problem of fluid flow within pipes subjected to thermal asymmetrical boundary conditions, a problem faced in many real industrial situations, such as those related with solar thermal devices. But despite the asymmetry, much simpler bidimensional models based on radial symmetry are currently used for pipe design purposes, ignoring the important consequences of the asymmetry that exists.For this purpose, a 3D steady-state analysis is made of the laminar forced-convection heat transfer process for a fluid flowing through a round pipe when radially asymmetrical external conditions are applied to the tube external surface (a known uniform temperature to the upper surface and adiabatic condition to the lower), taking into consideration axial heat conduction in the fluid. The differential equations are solved numerically. Also, experimental measurements of temperatures are made in thermal solar devices.The results are depicted by reference to the temperature profile, which depends on the radial-spatial coordinate. The isotherms form parallel-like shapes in the top half of the tube, but become distorted in the lower half, where loops appear due to the conduction effects of the pipe wall, illustrating the non-uniformity of the temperatures within the fluid. When the characteristic length of the problem was considered, the 2D approach was found to be no longer valid when asymmetrical boundary conditions existed in the pipe. Our theoretical/mathematical results closely agreed with the experimental measurements made in solar devices. The knowledge gained in this study of the real non-uniform flux inside pipes has many potential implications for the design of solar thermal devices, both flat plate and CPC plants, as well as a wide range of industrial equipment and facilities.

Method of manufacturing reinforced concrete floor slabs using non-removable void formers

The article provides a critical analysis of the work on the manufacture of monolithic reinforced concrete, relying on the contour, hollow floor slabs using box-shaped, spherical and tubular hollow-formers. The paper proposes a method of manufacturing monolithic reinforced concrete hollow floor slabs based on the contour using circular tubular polyethylene cardboard holders of rectangular or square shape in plan. The subject of the research is a method of continuous production of reinforced concrete floor slabs with round voids based on the contour using non-removable void formers, their technical and economic efficiency of solutions to reduce the weight of monolithic floor slabs by reducing the resources for their production. The technical and economic feasibility of manufacturing monolithic reinforced concrete floor slabs based on the contour with the use of non-retrievable void formers from round pipes of square and rectangular shape in plan has been substantiated. Materials for the manufacture of void former are proposed. The technical result has been determined - the maximum weight reduction of the proposed hollow core slabs compared to solid slabs.

The effect of Dean, Reynolds and Womersley numbers on the flow in a spherical cavity on a curved round pipe. Part 2. The haemodynamics of intracranial aneurysms treated with flow-diverting stents.

The flow in a spherical cavity on a curved round pipe is a canonical flow that describes well the flow inside a sidewall aneurysm on an intracranial artery. Intracranial aneurysms are often treated with a flow-diverting stent (FDS), a low-porosity metal mesh that covers the entrance to the cavity, to reduce blood flow into the aneurysm sac and exclude it from mechanical stresses imposed by the blood flow. Successful treatment is highly dependent on the degree of reduction of flow inside the cavity, and the resulting altered fluid mechanics inside the aneurysm following treatment. Using stereoscopic particle image velocimetry, we characterize the fluid mechanics in a canonical configuration representative of an intracranial aneurysm treated with a FDS: a spherical cavity on the side of a curved round pipe covered with a metal mesh formed by an actual medical FDS. This porous mesh coverage is the focus of Part 2 of the paper, characterizing the effects of parent vessel Re, De and pulsatility, Wo, on the fluid dynamics, compared with the canonical configuration with no impediments to flow into the cavity that is described in Part 1 (Chassagne et al., J. Fluid Mech., vol. 915, 2021, A123). Coverage with a FDS markedly reduces the flow Re in the aneurysmal cavity, creating a viscous-dominated flow environment despite the parent vessel Re > 100. Under steady flow conditions, the topology that forms inside the cavity is shown to be a function of the parent vessel De. At low values of De, flow enters the cavity at the leading edge and remains attached to the wall before exiting at the trailing edge, a novel behaviour that was not found under any conditions of the high-Re, unimpeded cavity flow described in Part 1. Under these conditions, flow in the cavity co-rotates with the direction of the free-stream flow, similar to Stokes flow in a cavity. As De increases, the flow along the leading edge begins to separate, and the recirculation zone grows with increasing De, until, above De ≈ 180, the flow inside the cavity is fully recirculating, counter-rotating with respect to the free-stream flow. Under pulsatile flow conditions, the vortex inside the cavity progresses through the same cycle - switching from attached and co-rotating with the free-stream flow at the beginning of the cycle (low velocity and positive acceleration) to separated and counter-rotating as De reaches a critical value. The location of separation within the harmonic cycle is shown to be a function of both De and Wo. The values of aneurysmal cavity Re based on both the average velocity and the circulation inside the cavity are shown to increase with increasing values of De, while Wo is shown to have little influence on the time-averaged metrics. As De increases, the strength of the secondary flow in the parent vessel grows, due to the inertial instability in the curved pipe, and the flow rate entering the cavity increases. Thus, the effectiveness of FDS treatment to exclude the aneurysmal cavity from the haemodynamic stresses is compromised for aneurysms located on high-curvature arteries, i.e. vessels with high De, and this can be a fluid mechanics criterion to guide treatment selection.

The effect of Dean, Reynolds, and Womersley number on the flow in a spherical cavity on a curved round pipe. Part 1. Fluid mechanics in the cavity as a canonical flow representing intracranial aneurysms.

Flow in side-wall cerebral aneurysms can be ideally modelled as the combination of flow over a spherical cavity and flow in a curved circular pipe, two canonical flows. Flow in a curved pipe is known to depend on the Dean number De, combining the effects of Reynolds number, Re, and of the curvature along the pipe centreline, κ. Pulsatility in the flow introduces a dependency on the Womersley number Wo. Using stereo PIV measurements, this study investigated the effect of these three key non-dimensional parameters, by modifying pipe curvature (De), flow-rate (Re), and pulsatility frequency (Wo), on the flow patterns in a spherical cavity. A single counter-rotating vortex was observed in the cavity for all values of pipe curvature κ and Re, for both steady and pulsatile inflow conditions. Increasing the pipe curvature impacted both the flow patterns in the pipe and the cavity, by shifting the velocity profile towards the cavity opening and increasing the flow rate into the cavity. The circulation in the cavity was found to collapse well with only the Dean number, for both steady and pulsatile inflows. For pulsatile inflow, the counter-rotating vortex was unstable and the location of its centre over time was impacted by the curvature of the pipe, as well as the Re and the Wo in the freestream. The circulation in the cavity was higher for steady inflow than for the equivalent average Reynolds and Dean number pulsatile inflow, with very limited impact of the Womersley in the range studied.

Research of the Vertical Dynamics of the Supporting Structures of Freight Cars Made of Round Pipes

Purpose. This study is aimed at determining the vertical dynamics of supporting structures of freight cars made of round pipes. Methodology. Mathematical modeling of the dynamic loading of the supporting structures of the main types of freight cars made of round pipes (gondola car, covered car, flat car, hopper car) was carried out. The studies were carried out in a plane coordinate system – the XZ plane. At the same time, it was taken into account that the car is moving in an elastic-viscous track so that the reactions of the track are proportional to both its deformation and the rate of this deformation. The studies were carried out for the case of empty cars. The joint inequality is described by a periodic function. The calculation was performed at a speed of 80 km/h. Differential equations of motion were solved in the MathCad software package using the Runge-Kutta method. Findings. Based on the mathematical modeling of the dynamic loading of the supporting structures of cars made of round pipes, the main indicators of their dynamics were obtained: accelerations acting on the supporting structures in the mass center, forces acting in the spring suspension of bogies, dynamics coefficients. For gondola car, covered car, and hopper car, the acceleration at the mass center of the supporting structure is within 0.4 g, and for a flat car – 0.5 g. It was found that the obtained indicators of the dynamics of cars made of round pipes are within the permissible limits. The accelerations acting on the supporting structures of cars made of round pipes are almost the same as those obtained for prototype cars. At the same time, the motion of cars is assessed as "excellent" for gondola car, covered car, and hopper car and "good" for flat car. Originality. Mathematical modeling of the dynamic loading of the supporting structures of cars from round pipes was carried out and the main indicators of their dynamics were obtained. Practical value. The research carried out will contribute to the creation of recommendations for the design of supporting structures of freight cars of round pipes, and can also be useful developments in the creation of innovative car designs.

Creating mathematical model of the bearing structure dynamic load of the flat wagon from round pipes in the main operational modes

At the present stage of development of the railway industry it is necessary to introduce new innovative solutions during the design of the flat wagons of articulated type for their structural design. To reduce the material consumption of flat wagons, in article was proposed to produce bearing elements of their structures from pipes of a circular cross section. Flat wagon of articulated type was designed on the basis of the developed construction in order to improve the operational efficiency of the wagon. The innovation design of a flat wagon of articulated type from round pipes are presented. The mathematical model of the bearing structure dynamic load of the flat wagon from round pipes in the main operational modes are made. Accelerations which act on the bearing structure of articulated flat wagon under I rated conditions (tension – jump) are presented.

Elaboration of the Equipment and Technology for Cutting Rolled Round Bars and Pipes with the Cyclic Circular Bending Method

A brief overview of methods for cutting round bars and pipes is presented, their main advantages, disadvantages and field of application are considered. It is proposed to use the effect of fatigue fracture for round bars and pipes breaking. The task is to study this process under the action of cyclic loads. The possibility of applying the known provisions of calculating theory of strength analysis for low-cycle fatigue for this process is tested. A comparative assessment of theoretical and experimental data is given and their significant difference is established. New calculated dependences are proposed, which are in good agreement with the experimental data. A theoretical assessment of the productivity of the process of round bars and pipes breaking by the method of cyclic circular bending was carried out using new results and various options for the design of a device for breaking were considered with an analysis of the features of their operation. Based on the results of the analysis, a variant of the device for the implementation of a continuous process of breaking the pointed ends of thick-walled fuel pipes during drawing in coils and a diagram of the mechanism for breaking the ends of the pipe with its supply from the coil were selected. Samples of pipes obtained by brittle cyclic bending are presented.

Dependence of the throughput of drain pipes of different cross-section

Flat drain pipes are a modern drainage solution. The flat profile increases the strength and rigidity of the pipe. The paper considers the experience of using flat pipes for drainage of territories in the whole world. A study of the dependence of the throughput of flat drain pipes on the slope was carried out, and a comparison was made with the throughput of round pipes. With the help of roughness, calculations of the throughput of flat and round pipes were made, and the low throughput of the section of a flat corrugated pipe compared to a round one was proved. A comparison of the efficiency of using pipes of different cross-sections is made using the example of wall drainage. The inexpediency of using flat drain pipes as wall drainage has been substantiated.

Determining the strength indexes of the bearing structure of the flat wagon of articulated type made from round pipes

In the article the parameters of the structural strength of the flat wagon of articulated type made from round pipes has been determined. The model of the strength of the bearing structure of a flat wagon of an articulated type from round pipes is present. The calculation is based on the finite element method implemented in the CosmosWorks programming environment. Isoparametric tetrahedra were used when constructed the finite-element model of the bearing structure. The strength parameters of the bearing structure of a flat wagon of an articulated type from round pipes were determined.

Transition Problem and Localized Turbulent Structures in Pipes

In the classical experiments of O. Reynolds made in 1883 the critical value of a dimensionless parameter, named now the Reynolds number, $${\text{R}}{{{\text{e}}}_{c}} \approx 2000$$ , was determined. As this value is exceeded in a pipe of circular cross-section, a turbulent flow regime can occur. The attempts to define this value more exactly undertaken during the twentieth century have not met with success. In this study, we present a review of theoretical, experimental, and numerical investigations of flows in a round pipe at the stage of transition to turbulence performed in recent years, which make it possible to formulate a new view on the nature of laminar-turbulent transition in these flows.

Substantiation of the influence of the channel shape and the roughness of machine canals on the pressure loss of irrigation pumping stations

To take into account the influence (on the value of head losses) of the channel cross-sectional shape and the presence of a flow with a free surface in it, additional correction factors are introduced (when using the concept of hydraulic radius), as well as new dependencies and formulas for determining the coefficient of hydraulic friction are presented, taking into account the influence of the morphometric elements of the channel on the hydraulic resistance of the machine channels of pumping stations. The article presents the results of hydraulic studies in free-flow and pressure water pipelines, the results of which showed that the dependencies obtained for calculating hydraulic resistance in round pressure pipes cannot be extended without appropriate adjustments to the pressure-free channels (provided that the pipe diameter is replaced in the corresponding calculations D-value 4R, where R-hydraulic radius). This position is justified by the presence of a number of factors that distinguish the pressure movement of liquid in pipes from its free-flow movement in the channels, where there is a free flow surface, a wider range of roughness of the channel bottom and walls, a different (than in pipes) distribution of tangential stresses along the wetted perimeter, the possibility of two different flow states (depending on the slope of the channel bottom). The work also considers the general equation of fluid motion in free-flow channels and the functional dependences of the hydraulic friction coefficient on the Reynolds number, relative roughness and on the shape of the free section of the channel; resistance formulas, first for the simplest channels with respect to the cross-sectional shape (round and infinitely wide rectangular), and then for channels with a more complex cross-sectional shape.