Abrupt Change In Cross-section Research Articles

Influence of non-uniform inflow on performance of reactor coolant pump and improved design

In Chinese Advanced Passive (CAP) series reactors, the two canned Reactor Coolant Pumps (RCP) are directly connected to the bottom of the steam generator (SG) rather than a longer pipe for the full development of inflow, which leads to a decrease in head and efficiency of RCP. However, the head of the RCP determines whether the reactor coolant system can circulate normally. The efficiency determines the power of cannedmotorstator. Overload power under limited size conditions will bring failure risk to the canned motor stator. With such a large impact, we first employed numerical simulation to investigate the influence mechanism of the non-uniform inflow and improve the RCP design, and then verified by experiment. It is found that the flow separation due to the SG asymmetrical structure and the abrupt change of cross section when linking to the inlet pipe is the main cause of non-uniform inflow. Accordingly, we proposed an improved RCP design which can effectively improve the head and efficiency of RCP by more than 1% under non-uniform inflow condition. This research reveals the formation mechanism of the non-uniform inflow of RCP and proposes the improved design scheme to improve the performance of RCP under the non-uniform inflow conditions for the first time, which provides guidance for the design of the RCP.

Gas and Aerosol Resonance Oscillations in an Open Pipe with an Abrupt Change in Cross Section

Gas and Aerosol Resonance Oscillations in an Open Pipe with an Abrupt Change in Cross Section

Closed-Form Solution of Fundamental Frequency of Steel-Concrete Hybrid Wind Turbine Tower

With the development of wind power energy, the steel-concrete hybrid tower has been gradually popularized as the onshore tall wind turbine tower. To avoid the resonant response that brings violent damage to the wind turbine tower, the fundamental frequency of the hybrid tower must be carefully analyzed. This study develops a closed-form solution of the fundamental frequency of the hybrid tower, where the abrupt changes of cross-section and material properties, the effect of prestressing, and the mass and rotary inertia of the wind turbine are taken into account. It provides an effective way to obtain the fundamental frequency in the preliminary design of the hybrid tower. The effectiveness of the proposed solution is validated by comparing it with the results of finite element analysis, showing good agreement. By using the proposed solution, a parametric analysis is conducted to investigate the variation rules of the fundamental frequency to the design parameters. It indicates that with the variation of the proportion of the concrete/steel segments, the correlations between the fundamental frequency and the design parameters also change significantly. The parametric analysis conducted herein may provide instructive guidelines to adjust the parameters in the preliminary design of the hybrid tower.

Seismic Retrofitting Method Using CFRP Sheets for H-Section Steel Beam with Variable Cross Section

Severe damage to steel bridge piers and steel rigid-frame piers starting from regions of abrupt change in cross section has been widely reported. Therefore, finding a simple and effective seismic retrofitting method for steel structural members with variable cross sections to improve their plastic deformation performance is currently an urgent concern. The objective of this study was to establish an effective seismic retrofitting method for H-section steel beams with abruptly variable cross sections using a carbon fiber–reinforced plastic (CFRP) sheet because of its outstanding properties such as light weight, high strength, and superior durability. Bending and bending-shear cyclic loading tests were conducted with two parameters, including the type of CFRP sheets, and whether or not polyurea putty was inserted between the CFRP sheet and steel beam. The test results indicate that the proposed retrofitting method using intermediate-modulus CFRP and polyurea putty increases the load-carrying capacity, ductility, energy dissipation capacity, and bending stiffness of H-section steel beams significantly without any failure. Further, by implementing finite-element (FE) analyses considering the actual cyclic plasticity properties of steel, anisotropic performance of the CFRP sheets, and nonlinear bond-slip properties of the polyurea putty layer, the cyclic loading test results were reproduced accurately. Moreover, in the cases in which the polyurea putty was applied, parametric FE analysis of the CFRP bonding method with and without creating a stepped length at the top of each CFRP sheet showed that the retrofitting method without the stepped length was similar in effectiveness to the method with the stepped length.

Study of the unsteady aerodynamic performance of an inter-city train passing through a station in a tunnel

Based on sliding mesh technology, this paper numerically investigates the aerodynamic performance of an 8-car inter-city train passing through a underground station at full speed. The effects of the gap between the car and the platform screen doors on the aerodynamic performance of the train passing through underground stations are analyzed. The curve of pressure variations at survey points on the train and the tunnel surface obtained from numerical simulation agree with those obtained from the moving model test. The asymmetrical internal structure of the station and the abrupt change in cross-section are the main factors contributing to the poor running stability of the inter-city train, with car 1 and car 8 showing the worst running stability. When the gap between the car and the platform screen doors increases from 130 mm to 425 mm, the maximum side force drops by 52.72% when car 1 passes the platform screen doors, and a linear relationship between the maximum side force and the gap between the car and the platform screen doors is observed.

General solution for shear strength estimate of RC elements based on panel response

The capacity of structural systems subjected to shear loads commonly distinguished by discontinuities such as point loads or supports, or abrupt changes of cross section, where complex fields of stresses and strains are generated, is vital information for design. Four structural systems that present stress concentration due to applied shear loads are commonly short walls, deep beams, corbels and beam-column joints. In the present work a model is developed to predict the shear capacity of these elements based on a panel model that considers average strain and stresses in a reinforced concrete orthotropic material, which covers the section of the structural element subjected to stress concentration. In addition, the panel element complies with the longitudinal equilibrium, by equalizing the applied axial load with the internal stresses of the structural element, requiring constitutive material laws for both concrete and steel reinforcement. The original model that has shown good shear strength prediction requires solving the non-linear equation of vertical equilibrium. Thus, this work eliminates the need to solve the iterative problem for the capacity estimation of four possible limit states (failure of concrete in tension and compression, and yielding of longitudinal web and boundary reinforcement). For that, an expression is calibrated for the strain of the model with respect to relevant parameters, for each limit state, that allow the generation of a non-iterative model. The model results in an average predicted capacity over experimental capacity ratio, Vmodel/Vtest, of 1.0 and a COV of 0.25, with similar performance for all four structural systems. When comparing these results with the general model that requires an iterative method, a similar performance is observed, with an average strength ratio and COV of 0.98 and 0.23, respectively. Likewise, in comparison with the ACI 318, the latter shows worse predictions (on average 24% lower) and with greater scatter (on average 28% higher). The expression in AASHTO code presents better correlation than ACI with predictions closer the proposed model.

Experimental Acoustic Flow Analysis Inside a Section of an Acoustic Waveguide

Abstract Noise propagation within ducts is of practical concern in many areas of industrial processes where a fluid has to be transported in piping systems. The paper presents experimental data and visualization of flow in the vicinity of an abrupt change in cross-section of a circular duct and on obstacles inside where the acoustic wave generates nonlinear separated flow and vortex fields. For noise produced by flow wave of low Mach number, laminar and turbulent flows are studied us- ing experimental sound intensity (SI) and laser particle image velocimetry (PIV) technique adopted to acoustics (A-PIV). The emphasis is put on the development and application of these methods for better understanding of noise generation inside the acoustic ducts with different cross-sections. The intensity distribution inside duct is produced by the action of the sum of modal pressures on the sum of modal particle velocities. However, acoustic field is extremely complicated because pressures in non-propagating (cut-off) modes cooperate with particle velocities in propagating modes, and vice versa. The discrete frequency sound is strongly influenced by the transmission of higher order modes in the duct. By under- standing the mechanism of energy in the sound channels and pipes we can find the best solution to noise abatement technology. In the paper, numerous methods of visualization illustrate the vortex flow as an acoustic velocity or sound intensity stream which can be presented graphically. Diffraction and scattering phenomena occurring inside and around the open-end of the acoustic duct are shown.

Stent graft performance in the treatment of abdominal aortic aneurysms: The influence of compliance and geometry

The long-term success of the endovascular procedure for the treatment of Abdominal Aortic Aneurysms (AAAs ) depends on the secure fixation of the proximal end and the geometry of the stent–graft (SG) device. Variations in SG types can affect proximal fixation and SG hemodynamics. Such hemodynamic variations can have a catastrophic effect on the vascular system and may result from a SG/arterial wall compliance mismatch and the sudden decrease in cross-sectional area at the bifurcation, which may result in decreased distal perfusion, increased pressure wave reflection and increased stress at the interface between the stented and non-stented portion of the vessel. To examine this compliance mismatch, a commercial SG device was tested experimentally under a physiological pressure condition in a silicone AAA model based on computed tomography scans. There was a considerable reduction in compliance of 54% and an increase in the pulse wave velocity of 21%, with a significant amount of the forward pressure wave being reflected. To examine the SG geometrical effects, a commercial bifurcated geometry was compared computationally and experimentally with a geometrical taper in the form of a blended section, which provided a smooth transition from the proximal end to both iliac legs. The sudden contraction of commercial SG at the bifurcation region causes flow separation within the iliac legs, which is known to cause SG occlusion and increased proximal pressure. The blended section along the bifurcation region promotes a greater uniformity of the fluid flow field within the distal legs, especially, during the deceleration phase with reduced boundary layer reversal. In order to reduce the foregoing losses, abrupt changes of cross-section should be avoided. Geometrical tapers could lead to improved clinical outcomes for AAA SGs.

Analysis of shear wall structures of variable cross section

AbstractA method has been proposed for the analysis of three‐dimensional shear wall and shear core assemblies having stepwise changes in the cross section. The analysis is based on a variant of the continuous connection method. In the continuous approach, the connecting beams are replaced by equivalent continuous connections. The differential equation systems for shear wall structure segments of constant cross section are uncoupled by orthogonal eigenvectors. The solution matches the boundary conditions of the upper and lower parts of the wall at the plane of contiguity, at which an abrupt change in cross section occurs. This yields a system of linear equations, which enable the determination of the integration constants. The correctness and efficiency of the proposed method are illustrated by its application to the analysis of plane and three‐dimensional shear wall systems of variable cross section. Copyright © 2010 John Wiley & Sons, Ltd.

An improved closed-form solution to interfacial stresses in plated beams using a two-stage approach

Shear stress and normal stress in the thickness direction at interfaces (referred to as interfacial shear and transverse normal stresses, respectively, hereafter) have played a significant role in understanding the premature debonding failure of beams strengthened by bonding steel/composite plates at their tension surfaces. Due to the occurrence of dissimilar materials and the abrupt change of cross-section, the stress distribution at plate ends becomes singular and is hence considerably complicated. Extensive experimental and analytical analyses have been undertaken to investigate this problem. Large discrepancies have been found from various studies, particularly from experimental results due to the well-acknowledged difficulty in measuring interfacial stresses. Numerical analyses, e.g. 2-D or 3-D finite-element analysis (FEA), may predict accurate results, but they demand laborious work on meshing and sensitivity analysis. Analytical solutions, in particular those in a closed form, are more desirable by engineering practitioners, as they can be readily incorporated into design equations. This paper reports an improved closed-form solution to interfacial stresses in plated beams using a two-stage approach. In this solution, beams and bonded plates can be further divided into a number of sub-layers to facilitate the inclusion of steel bars or multiple laminae. Thermal effects may also be considered by using equivalent mechanical loads, i.e. equivalent axial loads and end moments. Numerical examples are presented to show interfacial stresses in concrete or cast iron beams bonded with steel or FRP plates under mechanical and/or thermal loads. The effect of including steel reinforcements with various ratios in the RC beam on interfacial stresses is also investigated. Compared with previously published analytical results, this one improves the accuracy of predicting the transverse normal stresses in both adhesive–beam and plate–adhesive interfaces and the solution is in a closed form.

Disturbances produced by an electric potential probe on MHD flows in rectangular ducts

Experimental data for local velocity in liquid metal duct flows exposed to an external magnetic field can be obtained from measurements of electric potential differences recorded by probes that are moved along the channel width. These instruments, known as conduction anernometers or Liquid-metal Electromagnetic Velocity Instruments (LEVI), have been used in the past preferentially for investigating almost fully developed magnetohydrodynamic (MHD) flows in poorly conducting ducts and flows with smooth variations along the channel axis. For such applications, where electric current density is negligible, the probe was assumed to give reliable results and the potential gradient signal was directly interpreted as a velocity measure. If the flow varies along its path on very short length scales, like in ducts with abrupt change of cross section or in manifolds, non-negligible 3D electric currents occur so that the LEVI readings may become inaccurate. Moreover, the presence of the probe itself may perturb significantly the flow field due to the formation of internal layers that develop along magnetic field lines tangential to the shaft and the insulating body of the instrument. Experiments showed an asymmetry in the distribution of the measured transverse potential gradient and its underestimation compared with the one expected from flow rate measurements and from theoretical predictions for fully developed MHD flows. A numerical analysis of MHD flows around a probe inserted in a rectangular duct has been performed to support the physical interpretation of potential measurements and to study and quantify the influence of the instrument itself on the readings. A calibration procedure is suggested, which allows using measurements of potential differences to get reliable data for velocities in the duct.

Interpretation of LEVI velocity signals in 3D MHD flows

For experimental determination of velocities in magnetohydrodynamic (MHD) liquid metal flows, probes that measure electric potential gradient are often used. They are known as Liquid-metal Electromagnetic Velocity Instruments (LEVI) or as Conduction Anemometers (CA) and they have been used in the past preferentially for investigating more or less fully developed flows in poorly conducting ducts and flows with smooth variations along the channel axis. For such applications, where electric current density is negligible, the probe was assumed to give reliable results since the potential gradient signals can be directly interpreted as a velocity measure. If the flow varies along its path on very short length scales, like in ducts with abrupt change of cross-section or in manifolds, 3D electric currents may occur that are not negligible any more so that the LEVI readings may become inaccurate. Moreover the presence of the probe itself may introduce already strong perturbations to the flow field since internal layers, which touch the shaft and body of the probe at both sides develop along magnetic field lines. This effect perturbs the flow not only locally in the vicinity of the probe tips but also along an entire region located between the internal layers. The present paper aims at quantifying these effects in order to obtain reliable velocity data.

Analysis of the Acoustic Flow at an Abrupt Change in Section of an Acoustic Waveguide Using Particle Image Velocimetry and Proper Orthogonal Decomposition

In the vicinity of an abrupt change in cross section, an acoustic wave generates a nonlinear flow. This is investigated experimentally using Particle Image Velocimetry (PIV). The effect of both the acoustic level and the radius of curvature of the abrupt change in section on the flow is studied. At sufficiently high acoustic levels, and past a value of about 0.5 for the Strouhal number, the flow separates and a vortex is formed. Its evolution with the different parameters is studied. Proper Orthogonal Decomposition (POD) is applied to the ensemble of phase-averaged flow fields in the vicinity of the abrupt change. It is used as a means to separate the global acoustic movement from the localized non linear movements induced by it. The quantity of energy flowing from the first (acoustic) mode toward the higher (nonlinear) modes is calculated and is shown to be largely governed by the Strouhal number.

OS1-4-1 Measurement of Stress Distribution around a Circular Hole in a Plate under Bending Moment using Phase-shifting Method with Reflective Photoelastic Arrangement

According to the theories of material strength, where there is a hole in the structure part, an abrupt change in cross section occurs and the stress distribution around the hole will vary correspondingly. Even the size of hole may be small, it should be concerned in design because the stresses in the vicinity of the hole is always much higher than those faraway from the hole and the structure failure often take place in those positions. Due to the complexity of the engineering problems, it is difficult to obtain the stress field around the hole directly by theoretical derivation. Reflective photoelasticity is a widely used experimental full-field technique for accurately measuring surface strains to determine the stresses in a part or structure during static or dynamic testing. Photoelastic phase-shifting method can be used for the determination of the phase values of isochromatics and isoclinics. Conventional Babinet-soleil compensation method and photoelastic phase-shifting technique were utilized to analyze a specimen with a triangle hole and a circular hole under bending. Three groups of results were obtained by conventional compensation method, 8-step phase-shifting method with reflective-type photoelastic arrangement and FEM (ABAQUS) simulation, respectively. They agree with each other relatively well considering experiment error. The reliability of this combined method can both improve and extend the two conventional methods to be applied to more new fields of stress analysis.

An upper bound solution to extrusion of circular billet to circular shape through cosine dies

Metal forming by extrusion is one of the widely used metal forming processes. Conventionally the extrusion is carried out using the shear faced dies. In these dies the metal is forced to go through abrupt change in cross-section. Hence, they suffer from the practical problems such as formation of dead metal zone, non-uniform flow of metal, more redundant work and designed based on empirical methods. Modifications have been done in the extrusion dies to incorporate gradual reduction in the area of cross-section in order to ensure smooth flow of metal and to dispense with the problems faced by the conventional dies. Such modified dies are known as streamlined extrusion dies. The profile of the streamlined extrusion dies is the crucial parameter to optimize the extrusion process. Many profiles such as third order polynomial equation, fifth order polynomial equation, Bezier curve, etc., have been suggested for the design of streamlined extrusion dies with the view to reduce the extrusion load for the given reduction ratio. In this work the extrusion die is assumed to have the cosine profile to extrude circular billet to circular shape. The plastic deformation work required to extrude circular billet to circular cross-section through cosine profile based is determined using upper bound solution. It has been proved that the die designed based on cosine profile is superior to the conventional shear dies and the straightly converging dies. It is also proposed to validate the results by the experiments.

Symplectic analysis for periodical electro-magnetic waveguides

Symplectic analysis is introduced into electro-magnetic waveguide theory, by using Hamiltonian system theory in which the transverse electric and magnetic field vectors are the dual vectors. The method can accommodate arbitrary anisotropic material and includes the interface conditions between adjacent segments of the waveguide. An electro-magnetic stiffness matrix is introduced which relates to the two ends of each segment of the waveguide. Both the pass- and stop-band stiffness matrices for plane waveguides with constant cross-section are given analytically and also a transformation matrix is given to permit abrupt changes of cross-section to occur. The variational principle is applied to obtain the segment combination algorithm needed to generate the electro-magnetic stiffness matrix related to the two ends of the fundamental periodical segment. Then the Wittrick–Williams algorithm is used to extract the eigenvalues. Thereafter, an energy band analysis is performed for a periodical waveguide, e.g., a grating, by using the symplectic eigensolutions.

Einfluss und Bedeutung chemischer Entmischungen auf mechanische Eigenschaften thixogeformter Bauteile

Die RWTH Aachen zeichnet sich durch stark interdisziplinär ausgerichtete Forschung auf dem der Gebiet der Produktionstechnologie und Werkstofftechnik für Metalle aus. Mit der Einrichtung des SFB 289 “Formgebung metallischer Werkstoffe im teilflüssigen Zustand” wurde in Aachen neben den USA und Japan auch in Deutschland ein Forschungsschwerpunkt auf dem Gebiet der Formgebung metallischer Werkstoffe im teilerstarrten Zustand geschaffen. Thixoforming ist ein endabmessungsnahes Formgebungsverfahren, bei dem die Verarbeitung zu Bauteilen im teilflüssigen Zustand erfolgt. Daher können die Vorteile der konventionellen Ur- und Umformprozesse wie Gießen und Schmieden gemeinsam genutzt werden. Gleichzeitig können jedoch für das Thixoforming typische Fehlererscheinungen auftreten. Die chemische Entmischung über ausgedehnte Bauteilbereiche, die als Makroseigerung bezeichnet wird, scheint sich als einer der wichtigsten Fehlererscheinungen beim Thixoforming herauszukristallisieren. Ziel dieser Arbeit ist es, den Einfluss der chemischen Entmischung und der damit verbundenen Gefügeinhomogenität innerhalb eines Bauteils auf die mechanischen Eigenschaften aufzuzeigen und zu bewerten. Die Ergebnisse von Gefügeuntersuchungen und lokalen Elementenverteilungen im Bauteil werden mit Untersuchungen zu den mechanischen Kennwerten aus Zug-, Kerbschlagbiege- und Ermüdungsversuchen korreliert. Abschließend wird die Bedeutung von Makroseigerungen, die unter ungünstigen Umständen beim Thixoforming auftreten können, auf die mechanischen Eigenschaften bewertet. Untersucht werden Prinzip-Bauteile aus den Aluminiumgusslegierungen vom Typ AlSi7Mg0,3 und AlSi6Cu3. Chemical Segregation Effect on Mechanical Properties of Thioxo Formed Components Thixoforming is a near net shape forming process of semi solid billets with a stiffness, which is comparable to “butter”. Advantages of conventional forming and casting processes can be combined due to this modern forming process technology. The objective of this investigation is to identify the effect of local chemical segregation regarding the microstructure and mechanical properties in various parts of a component. Different components and component regions – with diverse cross-sections and flow lengths – have been tested. Tensile, charpy and fatigue tests are completed by metallography and local chemical analysis. The investigation was focused on AlSi7Mg0.3 and AlSi6Cu3 aluminium casting alloys. It can be confirmed, that chemical composition of the raw material and segregation are important effects on mechanical properties of components. Chemical segregation can be caused by abrupt changes in cross-section. The inhomogeneity verified by chemical analysis and metallography are important effects on mechanical properties of Thixoforming components. In future the counteract between metal structure and processing steps regarding mechanical properties of components must be examined more intensively. The aim is to create a fundamental understanding of the relationship between the structure, chemical composition, homogeneity and characteristics of aluminium materials.

On Flow Fields in Tubular Heat Exchangers – Numerical Calculations and Flow Visualization

Tubular heat exchangers belong to heat equipment, which is frequently used in industry. During their design it is usually assumed that nearly the same velocity prevails in all pipes of a bundle. Because of the abrupt changes of cross section in the inlet chamber the fluid cannot follow the chamber contour and flow separation occurs. Vortices are formed in the inlet chamber, which lead to different flow rates into the tube bundle. A method for the hydrodynamic optimization of tubular heat exchangers is represented within the framework of this work, which consists of measurements on a real tubular heat exchanger, visualization of the flow field in a water channel and numerical calculations with CFD programs. It will be shown what velocity profile appears in a bundle of pipes, and which parameters have an influence on it. Using the results obtained on the distribution of the flow medium, it is possible to estimate the effect of the nonhomogeneity on heat transfer, dissipation and fouling.

Vibration and stability of non-uniform beams with abrupt changes of cross-section by using C1 modified beam vibration functions

A unified method is presented for the analysis of vibration and stability of axially loaded non-uniform beams with abrupt changes of cross-section. The beam may also be supported on Winkler elastic foundation, and both the axial force and the foundation stiffness can be varied arbitrarily. The method is based on the Euler–Lagrangian approach using a family of C 1 admissible functions as the assumed modes. The assumed modes comprise essentially the vibration modes of a single span hypothetical prismatic beam with the same end supports but without the intermediate supports, modified by piecewise C 1 cubic polynomials. The chosen admissible functions therefore possess both the advantages of fast convergence of the eigenfunctions and the appropriate order of continuity at the location of abrupt change of cross-section. The method allows extensive use of matrix notations and programming is rather straightforward. Numerical results also show that the method is versatile, efficient and accurate.

Development of a model for calculation of losses in the example of a pipe with an abrupt change of cross section

Development of a model for calculation of losses in the example of a pipe with an abrupt change of cross section