Hemispherical Bottom Research Articles

Multi-objective optimization of loading path for sheet hydroforming of tank bottom

As a critical component of the propellant tank, the tank bottom is subjected to complex loads such as internal pressure and vibration and has high requirements for structural load-bearing capacity. Hydroforming deep drawing is one of the techniques for the integral forming of the tank bottom. As the tank bottom is a large-size thin-walled structure, defects such as cracks and wrinkles are prone to occur during the hydroforming deep drawing process. Aiming at reducing these defects, the hydraulic pressure loading path and blank holder force loading path of the hydroforming deep drawing process are studied, and a multi-objective optimization method is proposed to improve the surface accuracy and thickness distribution uniformity of the tank bottom. The complex loading path curve optimization problem is transformed into a functional relationship between hydraulic pressure and blank holder force with time. The hydraulic pressure and blank holder force at each time node are used as design variables, and the maximum wall thickness reduction rate, rupture trend factor, wrinkle height, and wrinkle trend factor are used as optimization targets. The radial basis function (RBF) neural network is used to establish the approximate model between the loading path and the optimization target, and the multi-objective particle swarm optimization (MOPSO) algorithm is used to optimize the solution. Taking the hemispherical tank bottom as an example, the optimal hydraulic pressure loading path and blank holder force loading path are obtained, and the quality of the formed part is improved.

Viscous effects on the added mass and damping forces during free heave decay of a floating cylinder with a hemispherical bottom

This paper presents an analysis of viscous effects on the added mass and damping forces during free heave decay of a cylinder with a hemispherical bottom. Results from unsteady Reynolds-averaged Navier–Stokes (URANS) simulations and linear potential-flow solutions are compared. Expressions for the cycle-averaged viscous added mass and damping coefficients are derived based on first-order Fourier analysis of the URANS results. Viscous effects are extracted by comparing the URANS results and linear potential-flow solutions, as nonlinear potential-flow effects in this case are demonstrated to be negligible. It is observed that viscous effects on the added mass coefficient are minor during heave decay, such that the linear potential-flow model can predict the value of the added mass coefficient to within 5% deviations. In contrast, the viscous damping coefficient exhibits strong cycle-dependent variations. A parametric study of the effects of initial displacement, cylinder diameter and draft shows that viscous damping forces can play an important role when the cylinder has a relatively small diameter and large draft. Further, the damping coefficient is transformed to the nondimensional drag force coefficient, and its dependence on the Reynolds number Re is investigated, for Keulegan–Carpenter numbers in the range KC= 1.5–2.5. It is found that the drag force coefficient is likely to be unrelated to Re and KC during the first cycle. From the second cycle to the fourth cycle, the drag force coefficient rapidly decreases with increasing Re, up to Re≈3×105.

Viscous Effects on the Added Mass and Damping Forces During Free Heave Decay of a Floating Cylinder with a Hemispherical Bottom

Viscous Effects on the Added Mass and Damping Forces During Free Heave Decay of a Floating Cylinder with a Hemispherical Bottom

Nonlinear modelling of a point-absorber wave energy converter based on the weak-scatterer approximation

In this study, a nonlinear time-domain model based on the weak-scatterer approximation is developed to investigate the hydrodynamic performance of a point-absorber wave energy converter (WEC). The simplified WEC consists of a floating cylindrical buoy with a hemispherical bottom, a single tether and a power take-off (PTO) system. The efficiency and survivability of the WEC are analysed by the proposed numerical model in moderately steep regular waves and focused wave groups, respectively. The effects of wave steepness on the power absorption of the WEC and the PTO force are highlighted in the study of regular wave tests by comparison with a linear frequency-domain model, and the influence of the PTO damping coefficient on the performance is discussed. Then the survivability of the WEC in focused wave groups is analysed and validated against the published experimental data. It appears that in terms of the motion responses of the buoy and the mooring force, the present results have a satisfactory agreement with the experimental data. The time–frequency characteristics of the motion responses of the buoy are further analysed based on wavelet transforms.

Influence of basket mesh size on the hydrodynamics in the USP rotating basket dissolution testing Apparatus 1

The USP Apparatus 1 (rotating basket), typically used to assess drug product reproducibility and evaluate oral solid dosage forms performance, consists of a cylindrical glass vessel with a hemispherical bottom and a wire basket rotating at constant speed. Baskets with different wire openings can be used in alternative to the standard mesh opening (40-mesh) in order to discriminate between drug formulations during early stage of drug product development. Any changes introduced by different basket geometries can potentially and significantly impact the system hydrodynamics and cause variability of results, thus affecting product quality. In this work, Particle Image Velocimetry (PIV) was used to experimentally quantify the velocity distribution in the USP rotating basket Apparatus 1 using baskets of different mesh sizes (10-, 20-, and 40-mesh size) under the typical operating conditions described in dissolution testing procedures. Similar flow patterns were observed in all cases. However, the radial and axial velocities in the USP Apparatus 1 generally increased with increasingly larger openings of the basket mesh. Increasing the basket agitation speed also resulted in an overall increase in the velocities, especially below in the innermost core region below the basket, where drug fragments typically reside. More importantly, the flow entering and leaving the baskets was quantified from the velocity profiles in the immediate vicinity of the baskets. It was found that the flow increased significantly with increasingly larger mesh openings, which can, in turn, promote faster dissolution of the oral solid dosage forms, thus affecting drug dissolution profiles. Hence, the selection of the basket mesh size must be carefully considered during drug product development.

Simple stationary filtering flows of incompressible non-newtonian oil in a homogeneous formation according to a general nonlinear law

Three stationary hydrodynamic theoretical problems are solved, in which filtrations obey only the General nonlinear law. Simple flows occur in tasks: plane-parallel, plane-radial, and hemispherical-radial. All derived formulas – oil flow rate, filtration rate, pressure gradient, etc. – should be used to solve various practical problems of the development of these deposits and even when drawing up a project for the development of such deposits. It should be noted that a plane-parallel simple filtration flow of oil originates from a strip-like reservoir to a straight gallery. In addition, such a simple filtration fluid flow also occurs when the oil field under development has several parallel rectilinear rows of production production wells and, in some cases, there may be rows of injection water wells in the reservoir. In oil-bearing areas between parallel adjacent rows, oil filtration is also plane-parallel. Hence, the practical significance of solving the first problem of a plane-parallel oil flow in this scientific article becomes clear. Planar-radial simple filtration flow of oil originates from a circular horizontal formation to a central production well. In addition, such a simple filtration fluid flow also occurs when a strip-like oil field being developed has several (usually three or four) parallel straight rows of production production wells. In the drainage zones of these wells, a simple flat-radial filtration flow also occurs. From the foregoing, the practical significance of a radial plane oil flow becomes clear. Hemispherical – a radial simple filtration flow of oil originates from a hemispherical reservoir to a central well, barely penetrated by the reservoir by its hemispherical concave bottom. By analyzing these calculation formulas, you can identify the specific features of the development of deposits, develop and implement measures to eliminate undesirable phenomena.

Experimental study and mathematical modelling of the interaction between the hemispherical bottom of a container with cohesive soil

The object of this study was a product (container) for air defence systems. Experimental and computational studies of the processes of force interaction of a solid body, modelling the bottom of a container, with silt-loam soils of different moisture were carried out in order to assess the parameters of the interaction between the container and the soil. It is shown that the developed empirical model of soil penetration, which assumes constant stress on the indenter-soil contact surface, is suitable for describing the obtained experimental data.

Motion Response and Energy Conversion Performance of a Heaving Point Absorber Wave Energy Converter

The heaving wave energy converter (WEC) is one typical type of point absorber WECs with high energy conversion efficiency but significantly affected by the viscous effect. It is widely known that the bottom shape of such WECs plays an important role in influencing the viscosity, so a detailed qualitative investigation is essential. Here a numerical study is performed for the influence of bottom shape on motion response and energy conversion performance of a heaving WEC. The numerical model is developed based on the potential flow theory with a viscous correction in the frequency domain. Cylindrical WECs with flat, cone, and hemispherical bottoms and the same displacement are considered. WECs with larger diameter-to-draft ratios (DDRs) are found to experience a relatively smaller viscous effect and achieve effective energy conversion in a broader frequency range. With the same DDR, the flat bottom has the most considerable viscous effect, following by the cone bottom with conical angles 90° and the hemispherical bottom. When the DDR is relatively small, the hemispherical bottom had the best energy conversion performance. Similarly, when the DDR is relatively large, the energy conversion performance of the floater with a hemispherical bottom and a cone bottom with 90° is better, while that with the flat bottom is the worst.

Household LPG cylinder fracture and a boiling liquid expanding vapor explosion

Liquefied petroleum gas (LPG) cylinders are designed as thin-wall pressure vessels consisting of a cylindrical body and two almost hemispherical bottoms made of low carbon steel and welded together. LPG cylinders design, manufacturing, inspection and testing follow specific rules, Norms and Regulations. Pressure vessel design theory along with National Regulations and Product Specifications in force provide the initial design parameters and safety margin assumptions. A serious accident occurred on April 2, 2015 at Loutron village, close to the city of Amfilochia, in western Greece, explosion of an LPG bottle at a local restaurant. Five fatalities were reported at the time of the accident and three more injured were pronounced dead some months later. The accident gained extended publicity from the media arising concerns about safety in LPG distribution and operation. The local police requested an expert’s appraisement from the Mechanical Engineering and Aeronautics Department of the University of Patras, for the evaluation of the accident’s contributing factors. The accident investigated was a «boiling liquid expanding vapour explosion», and revealed potential threats from the operation of aged LPG bottles, and marginal inspection and testing procedures followed. A detailed analysis of the LPG cylinder operational characteristics along with a systematic design approach, fatigue, and failure analysis is presented here. The legislation in force, Regulations and Norms are also reviewed.

Wear Mechanism of Abrasive Gas Jet Erosion on a Rock and the Effect of Abrasive Hardness on It

The existing erosion models of abrasive gas jet tend to neglect the effects of the rebounding abrasive. To address this shortcoming, abrasive wear tests were conducted on limestone by using an abrasive gas jet containing different types of particles and with different standoff distances. The results indicate that erosion pits have the shape of an inverted cone and a hemispherical bottom. An annular platform above the hemispherical bottom connects the bottom with the side of the pit. The primary cause of the peculiar pit shape is the flow field geometry of the gas jet with its entrained particles. There is an annular region between the axis and boundary of the abrasive gas jet, and it contains no abrasive. Particles swirling around the axis form a hemispherical bottom. After rebounding, the abrasive with the highest velocity enlarges the diameters of both the hemispherical bottom and erosion pit and induces the formation of an annular platform. The surface features of different areas of the erosion pit are characterized using a scanning electron microscope (SEM). It can be concluded that the failure modes for different locations are different. The failure is caused by an impact stress wave of the incident abrasive at the bottom. Plastic deformation is the primary failure mode induced by rebounding particles at the sides of the hemispherical bottom. The plastic deformation induced by the incident abrasive and fatigue failure induced by the rebounding abrasive are the primary failure modes on the annular platform. Fatigue failure induced by rebounding particles is the primary mode at the sides of the erosion pits. The rock failure mechanism that occurs for particles with different hardness is the same, but the rock damaged by the hard abrasive has a rougher surface.

Finite element simulation and Experimental verification of Incremental Sheet metal Forming

Incremental sheet metal forming is now a proven manufacturing technique that can be employed to obtain application specific, customized, symmetric or asymmetric shapes that are required by automobile or biomedical industries for specific purposes like car body parts, dental implants or knee implants. Finite element simulation of metal forming process is being performed successfully using explicit dynamics analysis of commercial FE software. The simulation is mainly useful in optimization of the process as well design of the final product.This paper focuses on simulating the incremental sheet metal forming process in ABAQUS, and validating the results using experimental methods. The shapes generated for testing are of trapezoid, dome and elliptical shapes whose G codes are written and fed into the CNC milling machine with an attached forming tool with a hemispherical bottom. The same pre-generated coordinates are used to simulate a similar machining conditions in ABAQUS and the tool forces, stresses and strains in the workpiece while machining are obtained as the output data. The forces experimentally were recorded using a dynamometer. The experimental and simulated results were then compared and thus conclusions were drawn.

Studies of oxide growth location on anodization of Al and Ti provide evidence against the field-assisted dissolution and field-assisted ejection theories

Electrochemical anodization, a method of obtaining highly-ordered porous oxides of various metal and alloys, has been studied for decades to elucidate the complicated formation mechanism. Both the widely supported field-assisted dissolution theory and the subsequently proposed field-assisted ejection theory suggest that porous oxide forms at the metal/oxide interface and is dissolved at the oxide/electrolyte interface. Here, in order to test this assertion, three-layered oxide films were fabricated on both Al and Ti foils. Both the inner and outer hemispherical bottoms vanish after the second anodization as they are covered by a new growth of oxide. The disappearance of both inner and outer hemispherical bottoms is evidence against the field-assisted dissolution and field-assisted ejection view that oxide grows only at the metal/oxide interface.

Modeling dynamic deformation and failure of thin-walled structures under explosive loading

In the framework of mechanics of damaged media, behavior of thin-walled structures under pulsed loading is described. Account is taken of the interaction of the processes of dynamic deformation and damage accumulation, as well as of the main characteristic features of the dynamic failure process: the multi-staged character, nonlinear summation of damage, stressed state history and accumulated damage level. The chosen system of equations of thermo-plasticity describes the main effects of dynamic deformation of the material for random deformation trajectories. The equations of state are based on the notions of yield surface and the principle of gradientality of the plastic strain rate vector. Evolutionary equations of damage accumulation are written for a scalar parameter of damage level and are based on energy principles. The effect of the stressed state type and the accumulated damage level on the processes of nucleation, growth and merging of microdefects is accounted for. Results of numerically modelling processes of dynamic deformation and failure of spherical and closed cylindrical shells with plane and hemispherical bottoms under single pulsed explosive loading are presented. The computational results are compared with experimental data.

Pore Embryos in Porous/Compact/Porous Anodic Alumina by Three-Step Anodization

In order to study the formation process of the pore embryos in porous anodic alumina (PAA) and compact aluminum oxide (CAO), a new three-tier structure (PAA-CAO-PAA) was designed and fabricated in 3 wt% H2C2O4 and 8 wt% ammonium sebacate aqueous solutions. By exactly controlling the time of the third anodization in 3 wt% H2C2O4 solution, the formation process of the pore embryos is explicitly seen for the first time. The hemispherical pore bottom and hemispherical barrier-oxide base generated in the first anodization. After the second anodization, two hemispherical structures disappear and two interfaces become flat. When the third anodization finished under given voltage and anodizing time, the hemispherical structures reappear. A bigger hemispherical barrier-oxide base and spiny oxide formed in the third anodization. Besides, the newly formed pore embryos are not connected with the above pores and the channels cannot be observed in the compact oxide layer. All these facts cannot be explained by the traditional field-assisted dissolution model. Based on the oxide flow model and the electronic current theory, the formation process of pore embryos under the compact layer can be elucidated by the oxygen bubble mould effect.

Heat transfer and critical phenomena during evaporation and boiling in a thin horizontal liquid layer at low pressures

The results of an experimental study of heat transfer and high-speed video recording of evaporation and boiling processes in horizontal liquid films of n-dodecane are presented for the wide ranges of layer height and pressure. Evaporation regimes at low reduced pressures were characterized by formation of dry spots and structures with the shape of “funnels” (depressions with a hemispherical bottom on the layer surface) and “craters” in the layers. In contrast to dry spots, the surface of “craters” is covered with a residual layer of liquid. The paper presents regime maps indicating the regions of dry spots, “funnels”, “craters”, and nucleate boiling observed for each layer height depending on the reduced pressure and heat flux density. It is shown that in the region of low reduced pressures, the Kutateladze formula describes change in hydrodynamics in the layers, whose height is equal to the Laplace constant or higher, by the regime where only “craters” remain in the layer. In the region of reduced pressures less than 7.4 · 10−5 (133 Pa) the critical heat fluxes (CHF) decrease with decreasing pressure. In the range of reduced pressures from 7.4 · 10−5 (133 Pa) to 5.5 · 10−3 (104 Pa), the CHF depends weakly on the pressure. With an increase in the layer height, CHFs increase sharply, and when achieving a constant value, are described by the Yagov dependence obtained for pool boiling of liquids. For the reduced pressure above 5.5 · 10−3 (104 Pa), in the layers with a height exceeding the Laplace constant, the CHF is the same as that calculated by the Kutateladze and Yagov formulas for nucleate boiling crisis. The slope of the curve of heat flux dependence on the temperature head depends on the layer height at both evaporation and nucleate boiling.

Study of gas dynamics of the intersecting jets in a semi-open channel

The subject of the study is axisymmetric channel with a hemispherical bottom. The compressed air flows into the channel through the holes located on the surface of the hemispherical bottom. The ratio of all holes area to the outlet area of the channel is equal to 0.25. The experimental and numerical study of jets intersecting at a single point is performed. The countermoving jets and the focused jets are investigated. The distribution of pressure over the surface of the channel and the total pressure at the output of the channel are obtained. The main experimental result is as follows: the total pressure recovery coefficient for the focused jets is twice more than that for the countermoving jets.

Blind micro-hole array Ti6Al4V templates for carrying biomaterials fabricated by fiber laser drilling

Blind micro-hole array templates were constructed by laser drilling using a 20W fiber laser on a Ti6Al4V substrate to improve carrying capacity of Ti6Al4V substrate to biomaterials in this study. The influence of laser parameters on the morphology of the blind holes was investigated and the blind micro-hole array templates were fabricated by the optimized laser parameters. Three typical morphologies were generated through adjusting laser parameters. The type II micro-hole characterized by column-shaped entrance and a hemispherical dome bottom is believed to have a suitable morphology, which was produced by the optimized laser parameters, i.e., defocusing distance 0mm, laser average power 16W, laser irradiation time 1ms and repetition rate 25kHz. The blind micro-hole templates with different micro-hole density were constructed by the mentioned-above optimized parameters and then the nano-sized hydroxyapatite (HA) powders were uniformly deposited into the blind micro-hole templates by electrophoretic deposition. Finally, the dynamic behavior of laser-drilling process was analyzed.

The nesting biology of the bee, Osmia dimidiata Morawitz, 1870 (Hymenoptera, Megachilidae) in the Crimea

The structure and composition of Osmia dimidiata nests were studied based on the material of 133 nests obtained from trap-nests in five localities of the Crimea. The nests contained from 1 to 9 cells (on average, 2.2), separated with partitions made of masticated leaves. Most of the cells had a massive hemispherical bottom and a thin flat cover. The final plug had a structure similar to the cell bottom. The cells occurred singly in the nest cavity or were arranged in rows of 2 or 3 cells separated by galleries. The diameter of the occupied cavities was positively correlated with the fraction of the females in the progeny and with the mass of the cocoons, but negatively correlated with the cell length. The cells with females were 1.5 times as long as those with males. The cocoons with females were twice as heavy as those with males. The peculiar characters of the nest structure of O. dimidiata may mean that the typical nesting substrates of this species are abandoned cells of other bee and wasp species. The characteristic mechanism of estimating the mass of the pollen loaf stored in the cells and determining the brood sex ratio has evolved in the O. dimidiata due to its tenantry. This mechanism is based on two constants: the sex-linked cell length and the fixed distance between the pollen loaf and the cell cover. When choosing the nesting cavities, the female prefers broader and longer tubes for cells with females and narrower and shorter ones for cells with males. The overall sex ratio of the progeny was male-biased (1 ♀: 2.5 ♂) and depended on the food supply abundance. The adults of O. dimidiata fly in the Crimea from the last decade of May until the end of July. Hibernation occurs at the adult stage in the cocoons. Females collect pollen from flowers of Asteraceae or, rarely, Fabaceae. The nests may be destroyed by Melittobia acasta, Monodontomerus aereus, M. obscurus, Sapyga quinquepunctata, Stelis phaeoptera, and Trichodes apiarius; 21% of the progeny died from these enemies, and 22%, due to other factors. The previously proposed synonymy of Pseudosmia taurica Radoszkowski, 1874 (nec Osmia taurica Radoszkowski, 1887) and O. dimidiata is rejected.

In Situ Electrochemical Thinning of Barrier Oxide Layer of Porous Anodic Alumina Template

We present three different in-situ post anodization electrochemical techniques to thin down the barrier oxide layers. These techniques include exponential voltage decay, exponential voltage decay with steps and exponential current decay. Faster rate of voltage drops in case of exponential voltage decay results in pore bottom without any modification, where as exponential voltage decay with steps modifies the pore bottom with formation of irregular pore branches. However, exponential current with critical decay constant reduces the oxide barrier layer thickness effectively with formation of narrow open channels along the radial directions of hemispherical pore bottom. The samples prepared under exponential current decay was subjected in KCl solution for a very short span of time to widen channels diameter using cathodic polarization and the resulting structure (porous alumina with open pores) remains on the aluminum substrate. The resulting AAO membrane along with aluminum substrate was used to grow silver nano-wires.

Numerical Simulation of Hydro-Forming Cylindrical Cup with a Hemispherical Bottom

In order to improve the hydro-forming accuracy, the process parameter’s effect on the technology was studied by using finite element method. The numerical simulation model of the forming process was established. The deformation and thinning were studied. The FLD was used to determine the safe limit of the sheet metal operation. FLD showed that the cylindrical hydro-drawing process could be successfully done in one stroke.