Taper Geometry Research Articles

Improved Load Carrying Capacity of Crosshead Bearings (Measurement of Oil Film Thickness using LIF Method)

The crosshead bearing in large two-stroke diesel engines operates under severe lubrication conditions, because hydrodynamic action is limited by low amplitude, low velocity oscillation under high unidirectional load. The recent trend towards more compact engines with increased output raises the bearing specific load, thereby causing the lubrication severity to increase significantly. Thus it is very important to improve the load carrying capacity of the crosshead bearing. In the present study, experiments using a dynamically loaded bearing test apparatus were carried out to clarify how the oil film characteristics could be improved. The oil film thickness was accurately measured using a laser induced fluorescence (LIF) method. The major results are : (1) A decrease in the clearance ratio is generally effective in enhancing squeeze action on the entirety of the bearing pads. When the clearance ratio becomes too low, however, the ability to form an adequate wedge film is degraded, thereby causing the oil film thickness to decrease ; (2) Even when the bearing has a very low clearance ratio, because incorporating the taper geometry on both sides of the oil-groove promotes wedge action, a significant improvement in the oil film characteristics can be expected ; and (3) The minimum oil film thickness becomes a maximum when using the taper geometry with a subtended length of 5 degrees and a taper angle of 0.1 degree.

Locking of southward extrusion in favour of rapid crustal-scale buckling of the Greater Himalayan sequence, Nar valley, central Nepal

Abstract The South Tibetan detachment system (STDS) bounds the upper limit of the Greater Himalayan sequence (GHS), which consists of the exhumed middle crust of the Himalaya. In the Annapurna range of central Nepal, the GHS comprises a sequence of amphibolite-grade augen gneisses with a 3.5 km thick leucogranite at the higher structural levels (Manaslu granite). Two major low-angle normal-sense shear zones have been mapped. The Chame detachment has similar grade metamorphic rocks above and below and is interpreted as a ductile shear zone wholly within the GHS. The Phu detachment is a ductile-brittle normal fault which wraps around the top of the Manaslu leucogranite and defines the uppermost, youngest strand of the STDS, placing folded unmetamorphosed Palaeozoic rocks of the Tethyan sedimentary sequence above the GHS. Our data indicate that ductile flow and southward extrusion of the GHS terminated with cessation of movement on the brittle upper strand of the Phu detachment at c. 19 Ma, which was followed almost immediately by crustal-scale buckling. Argon thermochronology reveals that the bulk of the metamorphic rocks and lower portions of the Tethyan sedimentary sequence in the Nar valley cooled through the hornblende, biotite and muscovite closure temperatures at c. 16 Ma, suggesting very rapid cooling rates. The thermochronology results indicate that this cooling occurred 2–3 million years earlier than in the frontal part of the extruded GHS. Although the extrusion in the frontal part of the GHS must have locked at the same time as in the Nar valley, the exhumation there was slower, and most probably only assisted by erosion, rather than by rapid folding as is the case in the Nar valley. This buckling indicates a step northward in deformation within the Himalayan belt, which may be a response to a lower deforming taper geometry in the foreland.

High-efficiency defect-based photonic-crystal tapers designed by a genetic algorithm

A method based on a genetic algorithm (GA) is used to design the optimum configuration of defects that when put within a photonic-crystal (PhC) taper improve the coupling efficiency between dielectric and PhC waveguides (WGs). This approach optimizes the whole configuration of defects simultaneously and, therefore, takes into account the correlation among the defects. Transmission efficiencies up to 94% have been predicted for a 3-/spl mu/m-wide dielectric WG into a single-line-defect PhC-WG. This result significantly improves the transmission efficiency of the same PhC taper without defects. The influence on the coupling efficiency of the PhC taper length and geometry are also discussed.

Modelling and numerical investigation of the residual stress state in a green metal powder body

Die pressing of metal powder results in a green body. After release from the die, the green body must have enough strength to be handled, to endure transport to a sintering furnace and heating to the sintering temperature. Drilling, turning and milling, which are common operations in the green state, require a green body of high strength, with no defects and excellent mechanical properties. A plane strain finite element model is used to analyse pressing of metal powder into a rectangular bar. The powder behavior is described by a “cap” model, which is implemented as a user material subroutine in the non-linear finite element program LS-DYNA. To improve modelling of strength in the green state a new non-linear density dependent failure envelope has been used. The model is adjusted to the properties of a water atomised metal powder from Höganäs AB. To resolve the severe stress gradient at the side surface of the green body, the smallest element size was chosen to be 65 μm. The aim of this work is to numerically capture and understand the development of the residual axial stress in particular at the side surface. The influence of kinematics, friction, compacting pressure and die taper are studied. Results from the numerical study show that the thickness of the compressive stress region close to the side surface of the green body varies between 50 μm and 600 μm along the surface. Compacting pressure, “upper punch hold down” and die taper geometry all have a significant influence on the residual stress state while die wall friction has only a small influence. The numerical results are in agreement with results from X-ray and neutron diffraction measurements.

Influences of Taper Geometry Modified Oil-Grooves on Load Carrying Capacity of Crosshead Bearings

The crosshead bearing in large two-stroke diesel engines operates under severe lubrication conditions, because the bearing oscillates within a small angle at a low speed and is always subject to a high downward load. The recent trend towards more compact engines with increased output raises the bearing specific load, thereby causing the lubrication severity to increase significantly. Thus it is very important to improve the load carrying capacity of the crosshead bearing. In the present study, experiments using a dynamically loaded bearing seizure test apparatus were carried out to clarify the influences of the clearance ratio and the oil-groove geometry on the load carrying capacity. The electrical resistance of the oil film was also measured to evaluate the extent of the oil film formation. The major results are : (1) A decrease in the clearance ratio is effective in enhancing squeeze action on the entirety of the bearing pads, thereby improving the load carrying capacity. When the clearance ratio becomes too low, however, the ability to form an adequate wedge film is degraded, causing the load carrying capacity to decrease, (2) Because incorporating the taper geometry on both sides of the oil-groove promotes a thicker oil film, a significant improvement in the load carrying capacity can be expected ; and (3) The maximum load carrying capacity is achieved by the taper geometry of a subtended length of 5 degrees and a taper angle of 0.1 degree.

Elastic stiffness model for the critical temperature Tc of Nb 3Sn including strain dependence

A calculation is established for the critical temperature T c of the superconductor Nb 3Sn that includes the dependence on applied mechanical strain. The calculation employs the formalism of strong coupling phonon superconductivity, as usually given in frequency space. The directional nature of strain is included by expressing the equations of strong coupling in wave vector space. The relation between wave number and frequency is provided by the dispersion relations incorporating the effective elastic constants for the symmetry directions of the cubic crystal. An analytical formalism is established in which the elastic constants are derived in a unified way from an assumed strain energy potential function. The form of the strain energy potential is governed by the cubic symmetry. The scalar invariants of the strain tensor under the cubic symmetry group are determined as a set of basis functions for the strain energy potential. In the harmonic approximation, the relation between the strain energy function and the elastic constants determines the harmonic amplitudes of the strain potential from the measured dispersion relations. The electron–phonon coupling characteristic is approximated in a simple analytic form determined by inspection of the experimentally determined tunneling and phonon density of states. The critical temperature is calculated, through the equations of strong coupling, as a sum over the crystal symmetry directions. The anharmonic terms of the strain energy potential are introduced as the source of the strain dependence of the critical temperature. The allowed form of the anharmonic terms is again governed by cubic symmetry. The amplitudes of the anharmonic terms are determined from the strain dependence characteristics of single crystals and composite superconductors. The calculations are found to represent the observed strain dependence well with a strain energy function that contains three scalar invariants of the strain tensor, including the spherical (hydrostatic) strain invariant, and the principle parts of the second and third invariants of the deviatoric strain tensor. The formalism is applied to the analysis of composite conductors. The characteristics of the strain dependence of wire and tape geometries under longitudinal and transverse loads are related to the symmetry of the conductor and direction of applied load. Implications of conductor symmetry and constraint on the measurement of the strain dependent properties are identified.

Effect of taper geometries and launch angle on evanescent wave penetration depth in optical fibers

A large penetration depth of an evanescent wave is the key to success for developing an ultra high-resolution fiber-based evanescent wave biosensor. Tapering the fiber and launching light at an angle has the potential of increasing the penetration depth of evanescent wave manifolds. The effects of tapering, launch angle and taper length of the fiber have been explored in detail using a ray-tracing model to calculate the highest possible penetration depth of the evanescent field. Evanescent wave penetration depths of the order of the size of living cells have been achieved by optimizing the parameters relating geometry of tapered fibers.

Sensitivity to termination morphology of light coupling in photonic-crystal waveguides

We use a transfer-matrix method to investigate light coupling problem in single-end photonic-crystal (PC) waveguides. We find that the coupling efficiency is sensitive to the surface termination morphology of the waveguide. A slightly tapering geometry can lead to an order of magnitude difference in the coupling efficiency of an external extended wave into the waveguide. However, this tapering geometry does not necessarily lead to enhanced coupling of a guided wave out of the PC waveguide. We have attributed this strong asymmetric coupling characteristic to the significant difference in the scattering behavior of an extended wave and a localized wave by the complex surface microstructure of a PC waveguide.

クロスヘツド軸受の負荷能力に及ぼす油溝形状の影響(エンジンのトライボロジー・潤滑油,エンジンのトライボロジー・潤滑油)

The crosshead bearing in large two-stroke diesel engines operates under severe lubrication conditions, because the bearing oscillates within a small angle at a low speed and is always subject to a high downward load. The recent trend towards more compact engines with increased output raises the bearing specific load, thereby causing the lubrication severity to increase significantly. Thus it is very important to improve the load carrying capacity of the crosshead bearing. In the present study, experiments using a dynamically loaded bearing seizure test apparatus were carried out to clarify the influences of the clearance ratio and the oil-groove geometry on the load carrying capacity. The electrical resistance of the oil film was also measured to evaluate the extent of the oil film formation. The major results are: (1) A decrease in the clearance ratio is effective in enhancing squeeze action on the entirety of the bearing pads, thereby improving the load carrying capacity. When the clearance ratio becomes too low, however, the ability to form an adequate wedge film is degraded, causing the load carrying capacity to decrease; (2) A significant improvement in the load carrying capacity can be expected, because incorporating the taper geometry on both sides of the oil-groove promotes a thicker oil film; and (3) A taper geometry with a subtended length of 5 degrees and a taper angle of 0.1 degree produces the maximum load carrying capacity.

High brightness, index-guided parabolic bow-tie laser diodes

The category of devices of interest in the paper is that of high power semiconductor lasers that also have high brightness. However, to achieve simultaneously high output optical power and a 'good' quality (narrow single-lobed) output beam from semiconductor lasers that can be fabricated relatively simply and cheaply, it is necessary to carefully design the cavity to control the output beam characteristics. The authors present the outcome of a systematic study on compact, index-guided semiconductor lasers of different geometry to show that with suitable design of the laser cavity it is possible to achieve the desired operational characteristics. In particular, the parabolic taper geometry has been found to be well-suited to achieve high brightness. Details of the specially designed high power semiconductor material used to fabricate the devices are also presented. The main advantage of the proposed compact devices is that the narrow output beam is achieved without the use of external lenses, thereby reducing the device cost for applications involving free-space propagation. Output powers in excess of 600 mW per facet have been measured from parabolic lasers (45% wall-plug efficiency) without catastrophic optical damage, at I = 1 A = 20I/sub th/, with a full width at half maximum far field intensity profile of /spl sim/2.5/spl deg/.

Tape edge study in a linear tape drive with single-flanged guides

Improved tape guiding and tape dimensional stability are essential for magnetic tape linear recoding formats to take advantage of vastly increased track density and thereby achieve higher storage capacities. Tape guiding is dependent on numerous parameters, such as type of the guides and tape path geometry, quality of virgin tape edge, drive operating parameters (e.g., tape speed and tape tension), mechanical properties of the tape, and tape geometry (e.g., cupping and curvature). The objective of the present study is to evaluate guiding and tribological performance of single-flanged guides with porous air bearings in a linear tape drive. A comparison of guiding performance of the dual flanged stationary guides and single-flanged guides with porous air bearings is performed. The effect of tape path geometry, drive operating conditions (speed and tension) and tape edge quality of factory-slit tapes on tape guiding are evaluated during short-term tests. A lateral force measurement technique is used to measure the force exerted by the tape edge on the guide flange. A technique for the lateral tape motion measurement is used to study the effect of continuous sliding on tape guiding. Wear tests up to 5000 cycles are conducted and coefficient of friction and lateral tape motion are monitored to study the effect of drive operating conditions (speed and tension), edge quality of factory-slit tapes and tape thickness on tape guiding. Optical microscopy, atomic force microscopy and scanning electron microscopy are employed to study and quantify the quality of tape edge.

Comparison of voltage–current characteristics of high quality Bi-2223 tapes with Hall-sensor measurements and computed current density distributions

Abstract The critical current reduction caused by the self-field of the current is measurable on modern HTS tapes. The current density reduction is strongest near the tape edges due to tape geometry and strong anisotropy. In voltage ( V )–current ( I ) measurement the self-field also increases with rising current. In this paper V ( I ) measurements are simulated with Finite Element Method to study the evolution of the current density distribution in increasing self-field. The computations are based on local magnetic flux density dependent current density-electric field characteristics, which have been derived from V ( I ) characteristics measured at external magnetic fields. Current densities determined with least squares method from measured magnetic flux density profiles are compared to the computed ones. The results show good correlation between the power law model calculations and measurements, but only with current amplitudes bigger than half of the critical current.

Mechanical properties of reinforced MgB/sub 2/ wires

For technical application in windings of coils, transformers or motors, a reinforcement of MgB2 wires and tapes is necessary to withstand applied stresses and strains and to avoid cracks in the filaments. Therefore, the response of the superconducting transport currents on applied axial strain in different magnetic background fields was investigated for differently stainless steel reinforced MgB2 wires, by means of an axial strain rig. Increased amounts of stainless steel in the sheath caused a stronger decrease of the critical currents in fields above 3 T as a consequence of a changed irreversibility field. Heat treated wires have a quite different mechanical behaviour compared to as-cold-worked wires, but an about 10 times higher transport current level. Tape geometries, having generally higher current carrying capabilities than wires, showed much poorer mechanical properties with a less effective filament precompression from the matrix.

A theoretical study of tapered, porous clad optical fibers for detection of gases

In this paper, the detection of gases using attenuated total internal reflection (ATR) technique has been theoretically described in multimode step-index, tapered fiber with porous cladding. Using a modal approach the response time and sensitivity of the sensor have been obtained in cases of parabolic, linear and exponential–linear tapered optical fiber. It has been shown that the sensor response time and the minimum detectable concentration depend on the taper ratio and geometry of the taper profiles for given fiber parameters, the absorptivity of gas and the diffusion coefficient in the porous cladding. For a given taper profile, the higher the taper ratio, the smaller the response time and the minimum detectable concentration. Additionally, the sensor with the exponential–linear taper profile has showed faster response times and lower minimum detectable concentrations than those with the parabolic and linear profile in the case of a particular taper ratio.

Clay smear seals and fault sealing potential of an exhumed growth fault, Rio Grande rift, New Mexico

The Calabacillas fault, New Mexico, is an exhumed growth fault that provides insights on the processes of clay smear formation and the effectiveness of fault seal prediction for faults of this type in the subsurface. Exposed clay smears range from being continuous and having a taper geometry to being semicontinuous and segmented by secondary faults. In some cases, source beds are truncated at the fault and there as no attached clay smear. Detailed mapping of the fault zone shows that there is a veneer of clay gouge on the fault that is interrupted by multiple gaps that would reduce the ability of the fault to be an effective seal over geologic timescales. The presence of releasing dip relays in footwall source beds and the evolution of the dip relay during the growth of the fault zone primarily control the variability in clay smear type and continuity. Source bed plasticity, composition, and thickness play a secondary role. As the fault zone grows, the dip relay is breached, and the clay smear is progressively segmented by normal faults that translate it down the fault and eventually truncate it from its source. Smearing-type algorithms (CSP, for example) overpredict the likelihood of fault seal at the base of the source bed, because the clay smear is commonly detached from its source. A key threshold for fault seal prediction is the stage of fault growth at which the clay smear tapers become separated from their source beds. Below this threshold, smear-type algorithms work best. Above this threshold, abrasion-type algorithms work best.

Maximisation of the crushing performance of a tubular device by shape optimisation

A tapered tubular steel component to be used as an energy-absorbing device has been optimised by taking into account two design variables describing the tapering geometry. The minimisation of a load uniformity parameter evaluated as the ratio between the maximum and the average crushing loads has been considered as objective function. The optimisation process has been carried out by using a multi-point approximation scheme based on the response surface methodology. The optimisation process led to the identification of two promising geometrical configurations characterised by a quite low value of the load uniformity parameter. The two solutions have been analysed with respect to their sensitivity towards two model parameters, the sheet thickness and the Young modulus of the material.

Modeling the HSK Toolholder-Spindle Interface

The HSK toolholder-spindle connection was developed to overcome shortcomings of the 7/24 steep-taper interface, especially at higher speeds. However, the HSK system was standardized quickly, without detailed evaluation based on operational experience. Several issues concerning the reliability, maintainability, and safety of the interface have been raised within the international engineering community. This study was undertaken to analytically investigate factors which influence the performance and limitations of the HSK toolholder system. Finite Element Models were created to analyze the effects of varying toolholder and spindle taper geometry, axial spindle taper length, drawbar/clamping load, spindle speed, applied bending load, and applied torsional load on HSK toolholders. Outputs considered include taper-to-taper contact pressures, taper-to-taper clearances, minimum drawbar forces, interface stiffnesses, and stresses in the toolholder. Static deflections at the end of the holder predicted by the models agreed well with measured values. The results showed that the interface stiffness and load-carrying capability are significantly affected by taper mismatch and dimensional variations, and that stresses in the toolholder near the drive slots can be quite high, leading to potential fatigue issues for smaller toolholders subjected to frequent clamping-unclamping cycles (e.g., in high volume applications). The results can be used to specify minimum toolholder material properties for critical applications, as well as drawbar design and spindle/toolholder gaging guidelines to increase system reliability and maintainability.

A morphological model of vertebral trabecular bone

In their micro-structures, typical natural cellular materials such as vertebral trabecular bone have a network of doubly tapered struts, thickening near the strut joints. However, past analytical models for vertebral trabecular bone do not take account of the effect of strut taper on the mechanical properties. This paper presents an analytical cell model comprised of doubly tapered struts to predict the global mechanical properties of vertebral trabecular bone. The predicted results for male, female, and both sexes fit the experimental data well. By considering several strut taper geometries, it is shown that the horizontal Young's modulus and the horizontal uniaxial collapse stress are, in some cases, approximately 1.8- and 2.2-fold higher, respectively, than those of the uniform strut model. This finding illustrates the importance of increased trabecular thickening near the strut joints (i) for improving the accuracy of calculating the mechanical properties and (ii) for the effective treatment of aged bone using drug therapy. It also highlights the need to combine trabecular architecture measurements with information about the morphology near the strut joints.

The Swiss Alps and their peripheral foreland basin: Stratigraphic response to deep crustal processes

This paper gives a synoptic view of the Cenozoic evolution of the Swiss Alps and their northern foreland basin. In this orogen, deep crustal processes (subduction, nappe stacking, underplating, and exhumation) are intimately linked with surface processes (surface uplift, erosion, basin formation, and basin‐axis migration). Within the foreland basin the spatial pattern of subsidence and alluvial fan construction suggests that an increase in flexure of the foreland plate and the creation of relief in the orogen migrated from east to west in the course of collision. In the orogen itself, crustal thickening involved lower crust of the Adriatic margin in the east and the European margin in the west. Exhumation of upper crustal units occurred earlier in the east as compared with the west. An Adriatic mantle wedge (the Ivrea body) and its associated wedge of lower crustal material are identified as an extra lithospheric load which contributed to downward flexure of the European plate. As a result of enhanced subsidence of the foreland plate, relief was generated presumably in order to adjust to critical taper geometry. It appears, therefore, that the westward motion of the Adriatic wedge ultimately caused the contemporaneous westward propagation of the location of enhanced rates of alluvial fan construction. Coeval strike‐slip and N‐S convergence juxtaposed the Adriatic wedge sequentially to different European upper crustal units which resulted in different styles of crustal structure and evolution along strike within the orogen.

An investigation into melt flow dynamics during repetitive pulsed laser drilling of transparent media

This paper presents an investigation into the dynamics of repetitive pulsed laser drilling of a visually transparent media using a CO 2 laser source. This enabled the use of a high-speed imaging system for observing, in real time, the behaviour of the drilling process in the laser drilled cavity of 1.5 mm diameter holes of up to 18.5 mm in depth. The work revealed that the instantaneous drilling velocity within each laser pulse can vary considerably from the average drilling velocity as a result of the non-uniform temporal pulse shape and the oscillation of the melt ejection rate. During beam breakthrough, both upward and downward melt ejections were observed to occur inside the drilled hole for a short period of time, after which the material was ejected through the exit end of the holes. It has been shown in this work that the downward melt flow velocity increases with hole depth for a positively tapered hole (from 0.09 to 1.43 m/ s) and decreases with hole depth for a negatively tapered hole geometry (from 0.4 to 0.1 m/ s ), as a result of the change in the assist gas velocity inside the drilled hole with respect to the hole taper geometry. The mechanisms of forming the positively and negatively tapered holes in the transparent media have been correlated with the hole geometry and melt flow velocity. The work has demonstrated a new method of studying the melt dynamics in laser drilling.