Semicircular Grooves Research Articles

Study of subcritical crack growth in andesite using the Double Torsion test

Abstract Subcritical crack growth is one of the main causes of time-dependent behavior in rocks. Double torsion (DT) tests have often been used to study subcritical crack growth in rocks. There are three methods used for the DT test, each with different loading conditions: the constant load (CL) method, the constant displacement (CDR) method, and the load relaxation (RLX) method. The RLX method is convenient, because the wide range of data of subcritical crack growth can be obtained with a single experimental run. In this study, subcritical crack growth in andesite was investigated using RLX method of the DT test. To determine the appropriate shape for the guide groove in DT specimens, tests were performed using rectangular, semi-circular, and triangular section grooves. The level of reproducibility of the test results was highest for specimens with a rectangular groove. Hence, this is an appropriate guide groove shape for DT specimens. DT tests were also performed for different water vapor pressures to investigate the effects on subcritical crack growth. The results showed that crack growth was facilitated at higher water vapor pressures. Additionally, the activation energy for subcritical crack growth in andesite was determined from the experimental results, and the crack velocity values for various temperature, humidity, and stress conditions were calculated theoretically. The crack velocity can be predicted from theory for various environmental and stress conditions.

An implementation of harmonic-suppression microstrip filters with periodic grooves

In this paper, a new parallel-coupled-line microstrip band pass filter (BPF) improving the harmonic suppression performance of the second harmonic signal (2f/sub o/, twice the passband frequency) is described. It is found that the desired passband performance is improved and the harmonic passband signal is diminished by enforcing the consecutive patterns in coupled-line and increasing the number of grooves to the optimum values. The recalculation of design parameters such as space-gap between lines, line widths and lengths is not required due to the simple modification of the conventional filter by inserting periodic patterns. To evaluate the validity of this novel technique, order-3 Butterworth BPF centered at 2.5 GHz with a 10% fractional bandwidth (FBW) and order-5 Chebyshev BPF centered at 10 GHz with a 15% FBW were used. When five and three square grooves are used, over 30-dB suppression at second harmonic signal is achieved in simulation and experiment. Finally, the comparison between the characteristics of filters with square and semicircular periodic grooves has been carried out by using the simulated results.

Acoustic Characteristics of Supersonic Jets from Grooved Nozzles

The effect of internal grooves cut along the inner surface of the diverging portion of a Mach 1.8 convergingdiverging nozzle on the characteristics of an axisymmetric jet was investigated experimentally. Decay, growth, and noise suppression characteristics of supersonic jets from plain nozzle, nozzle with two semicircular grooves, and nozzle with two square grooves are presented. The grooves act as effective passive controls, resulting in significant enhancement of jet mixing. The shock cell structure from grooved nozzle is weaker than that of plain nozzle. Acoustic measurement was taken in the nozzle exit plane and in the far field. In the grooved plane grooves show a definite advantage in terms of jet noise attenuation. However, in the plane normal to the grooved plane they are not effective in screech suppression. Further, the present results authenticate that nozzle pressure ratio plays an important role in the case where an adverse pressure gradient exists near the nozzle exit. Nomenclature M = nozzle-exit Mach number Pa = ambient pressure Pc = jet centerline pitot pressure P0 = stagnation pressure in the settling chamber X = coordinate perpendicular to the nozzle-exit plane Y = coordinate parallel to the grooved plane Z = coordinate normal to the grooved plane I. Introduction T HE passive control scheme investigated in this study is based on the modification of the boundary layer, growing along the nozzle inner walls achieved through partial notches. Streamwise vortices generated by the notches cut at the nozzle exit have been demonstrated to be effective in jet noise reduction. 1 These vortices provide the necessary secondary instabilities that aid the faster amplification of the primary instabilities and hence the growth of the coherent structures. In effect, the streamwise vortices bring in threedimensionality to the otherwise, basically, two-dimensional spanwise organized vortical structures (coherent structures). Thus the evolution of the large-scale structures gets altered by the notches, which, in turn, alter the mixing and acoustic characteristics of the jet. In view of the effectiveness and simplicity of the notched axisymmetric nozzles, they were investigated in the present study. Similar studies have been conducted by many researchers. 1−3 Pannu and Johannesen 1 investigated underexpanded jets issuing from notched nozzles. The centerline pitot-pressure data indicated that the shock cell structure was modified and the jet decayed faster than the unnotched nozzle flow beyond the core region. They demonstrated that the dominant feature of the flow which determined the structure far downstream was the trailing vortices shed from the swept edges of the notches. They concluded that the notches were effective silencers, mainly because they caused the noise sources to be surrounded by a broad region of low-speed turbulent flow. Smith and Hughes 2 presented experimental results obtained for jets from notched nozzles in a coflowing freestream. The results showed

Studies on high speed jets from nozzles with internal grooves

Experiments were carried out on jets issuing from circular nozzles with grooved exits and the results compared with those of the plain nozzle. The plain nozzle had an exit diameter of 10mm. Because of the introduction of semi-circular grooves at the exit, the effective or equivalent diameter of the grooved nozzles was 10·44mm. The groove lengths were varied as 3, 5 and 8mm. The nozzles were operated at fully expanded sonic and underexpanded exit conditions. The corresponding fully expanded Mach numbers were 1·0 and 1·41. The shock cell structure of the underexpanded jets from grooved nozzles appeared to be weaker than that of the plain nozzle, as indicated by lesser amplitudes of the cyclic variation of the Pitot pressure. The iso-Mach contours indicate that the jet spread along the grooved plane is significantly higher than that along the ungrooved plane. Off-centre peaks were observed in the mean pressure profile of underexpanded jets from grooved nozzles. They were probably due to the streamwise vortices shed from the grooves.

A microfabricated hybrid device for DNA sequencing.

We have created a hybrid device of a microfabricated round-channel twin-T injector incorporated with a separation capillary in order to extend the straight separation distance for high speed and long readlength DNA sequencing. Semicircular grooves on glass wafers are obtained using a photomask with a narrow line-width and a standard isotropic photolithographic etching process. Round channels are made when two etched wafers are face-to-face aligned and bonded. A two-mask fabrication process has been developed to make channels of two different diameters. The twin-T injector is formed by the smaller channels whose diameter matches the bore of the separation capillary, and the "usual" separation channel, now called the connection channel, is formed by the larger ones whose diameter matches the outer diameter of the separation capillary. The separation capillary is inserted through the connection channel all the way to the twin-T injector to allow the capillary bore flush with the twin-T injector channels. The total dead-volume of the connection is estimated to be approximately 5 pL. To demonstrate the efficiency of this hybrid device, we have performed four-color DNA sequencing on it. Using a 200 microm twin-T injector coupled with a separation capillary of 20 cm effective separation distance, we have obtained readlengths of 800 plus bases at an accuracy of 98.5% in 56 min, compared to about 650 bases in 100 min on a conventional 40 cm long capillary sequencing machine under similar conditions. At an increased separation field strength and using a diluted sieving matrix, the separation time has been reduced to 20 min with a readlength of 700 bases at 98.5% base-calling accuracy.

The response of a turbulent boundary layer to different shaped transverse grooves

The response of a turbulent boundary layer to three different shaped transverse grooves was investigated at two values of momentum thickness Reynolds numbers ( R θ =1000 and 3000). A 20-mm wide square, semicircular and triangular groove with depth to width ( d / w) ratio of unity was used. In general, the effects of the grooves are more significant at the higher R θ , with the most pronounced effects caused by the square groove. An increase in wall shear stress τ w was observed just downstream of the groove for all three shapes. The increase in τ w is followed by a small decrease in τ w below the smooth-wall value before it relaxes back to the corresponding smooth-wall value at x / δ 0≈3. At the higher R θ , the maximum increase in τ w for the square groove is about 50% higher than for the semicircular groove and almost twice that for the triangular groove. The effect of the square groove on U / U 0, u ′/ U 0 and v ′/ U 0 is much more significant than the effect of the semicircular and triangular grooves. There is an increase in the bursting frequency ( f B +) on the grooved-wall compared to the smooth-wall case. The distribution of f B + downstream of the different shaped grooves is similar to the τ w distribution.

Design of the labial cuticle in Cenocorixa bifida Hung. (Hemiptera: Corixidae) with reference to ionic transport.

The surface topography and ultrastructure of the labial cuticle of Cenocorixa bifida were examined by scanning and transmission electron microscopy. The dorsal wall of the labium consists of seven sclerotized transverse bars each displaying two rows of semicircular grooves and pores. The cuticle is about 20 microm thick and is composed of epicuticle and lamellate exocuticle and endocuticle, the latter separated from the underlying epidermis by subcuticle containing amorphous material. The epicuticle is subdivided into an electron-dense very thin outer epicuticle and a homogenous thick inner epicuticle, which is penetrated by grooves. The exocuticle is filled with electron-dense blocks of material, which may provide mechanical support to the labial wall. The elongate epidermal cells display extensive infoldings of the apical plasma membrane (facing the cuticle) and contain abundant mitochondria in the cytoplasm. The presence of deep epicuticular grooves and pores in the thin labial cuticle and extensive apical membrane infolding and abundant mitochondria in the epidermal cells suggest that the labium in C. bifida is the site of osmoregulatory ionic uptake.

Stress Concentrations of a Hollow Circular Cylinder with a Semicircular Notch under Internal Pressure.

This paper deals with the stress concentration problem of a hollow circular thick walled elastic cylinder with a semicircular groove under internal pressure. A method of solution is presented for the problem by applying Green's functions for axisymmetric body force problems of a thick plate. The Green's functions are defined as solutions for a thick plate subjected to axisymmetric body forces acting along a circle in the interior of the plate. A principle of the method of solution is to imagine a hollow cylinder with a notch and to distribute axisymmetric body forces in the thick plate so as to satisfy the boundary conditions of the hollow cylinder. The problem is formulated by an intergral equation with unknown functions of body forces. Stress concentrations at the notch are investigated by numerical calculations and stress distributions near the notch and form factors are shown. The maximum stress appears at the bottom of notch or the inner boundary of smallest cross section depending on the inner radius of cylinder and the notch radius.

Analyzing Semicircular Groove Guide with the Conformal Mapping Technique

Semicircular groove guide is a kind of waveguide for millimeter waves. In this paper, a conformal mapping technique is used to analyze it. Several semicircular groove guides are calculated with the method. It is shown that their cutoff wavelength calculated by the method are very close to those calculated by the transverse resonance method.

Flow field analysis of a turbulent boundary layer over a riblet surface

The near-wall flow structures of a turbulent boundary layer over a riblet surface with semi-circular grooves were investigated experimentally for the cases of drag decreasing (s +=25.2) and drag increasing (s +=40.6). One thousand instantaneous velocity fields over riblets were measured using the velocity field measurement technique and compared with those above a smooth flat plate. The field of view was 6.75 × 6.75 mm2 in physical dimension, containing two grooves. Those instantaneous velocity fields were ensemble averaged to get turbulent statistics including turbulent intensities and turbulent kinetic energy. To see the global flow structure qualitatively, flow visualization was also carried out using the synchronized smoke-wire technique under the same experimental conditions. For the case of drag decreasing (s +=25.2), most of the streamwise vortices stay above the riblets, interacting with the riblet tips frequently. The riblet tips impede the spanwise movement of the streamwise vortices and induce secondary vortices. The normalized rms velocity fluctuations and turbulent kinetic energy are small near the riblet surface, compared with those over a smooth flat plate. Inside the riblet valleys, these are sufficiently small that the increased wetted surface area of the riblets can be compensated. In addition, in the outer region (y + > 30), these values are almost equal to or slightly smaller than those for the smooth plate. For the case of drag increasing (s +=40.6), however, most of the streamwise vortices stay inside the riblet valleys and contact directly with the riblet surface. The high-speed down-wash flow penetrating into the riblet valley interacts actively with the wetted riblet surface and increases the skin friction. The rms velocity fluctuations and turbulent kinetic energy have larger values compared with those over a smooth flat plate.

123 半円切欠きみぞをもつ厚肉円筒の内圧による応力集中(GS-1 構造解析・応力解析(1))

This paper deals with the stress concentration problem of a hollow circular thick walled elastic cylinder with a semicircular groove under internal pressure. A method of solution is presented for the problem by applying Green's functions for axisymmetric body force problems of a thick plate. The Green's functions are defined as solutions for a thick plate subjected to axisymmetric body forces acting along a circle in the interior of the plate. A principle of the method of solution is to imagine a hollow cylinder with a notch and to distribute axisymmetric body forces in the thick plate so as to satisfy the boundary conditions of the hollow cylinder. The problem is formulated by an intergral equation with unknown functions of body forces. Stress concentrations at the notch are investigated by numerical calculations and stress distributions near the notch and form factors are shown. The maximum stress appears at the bottom of notch or the inner boundary of smallest cross section depending on the inner radius of cylinder and the notch radius.

A New Method for Producing Amorphous Alloy Wires

A rotating disk casting has been developed as a new method of producing an amorphous alloy wire. The rotating disk, which is made of copper, has a semicircular groove on its upside surface. The amorphous alloy wires with large diameters from 0.5 to 1.5 mm in the Zr-Al-Ni-Cu alloy system with high glass-forming ability have been prepared by the new method. The cross-section of the wires is nearly circular. because the melt is quenched to an amorphous state at the contact with an inner surface in the groove of the rotating disk. The cast amorphous alloy wires exhibit the same thermal stability and mechanical properties as those for the melt-spun amorphous alloy ribbon with the same composition. The formation of the amorphous alloy wires with large diameters is attributed to the high glass-forming ability of the alloy. In any event, the success of forming amorphous alloy wires by the present casting method is important for the future extension of application fields ol amorphous alloys.

Production of Zr-based Amorphous Wires by Rotating Disk Casting Method

AbstractContinuous amorphous wires with high strength and good ductility have been produced for the Zr55Al10Ni5Cu30and Zr55Ti5Al10Ni10Cu20alloys by a rotating disk casting technique. The rotating disk, which is made of copper, has a semicircular groove on its upside surface. The amorphous wires have a nearly circular cross-section, smooth peripheral surfaces and diameters in the range from 0.5 to 1.5mm. The amorphous alloy wires have good bending ductility. The maximum tensile strength, μf, is 1600 MPa for Zr55Al10Ni5Cu30 amorphous wire and 1900 MPa for Zr55Ti5Al10Ni10Cu20 amorphous wire, respectively. The success of forming amorphous alloy wires in a continuously long form by the present casting method is important for the further extension of application fields of amorphous alloys.

Footprinting of Yeast DNA Topoisomerase II Lysyl Side Chains Involved in Substrate Binding and Interdomainal Interactions

Footprinting of yeast DNA topoisomerase II and its NH2- and COOH-terminal truncation derivatives was carried out to map the locations of lysyl side chains that are involved in enzyme-DNA interaction, in the binding of ATP, or in interaction between domains of the same enzyme molecule. Several conclusions were drawn based on these measurements and the crystal structures of a 92-kDa fragment of the yeast enzyme and a 43-kDa fragment of Escherichia coli gyrase B-subunit. First, the footprinting results support the model previously inferred from the 92-kDa fragment crystal structure that the main site of DNA binding is comprised of a pair of semicircular grooves. Second, the binding of a nonhydrolyzable ATP analog to the yeast enzyme appears to affect citraconylation at a minimum of six lysines in the ATPase domain of each polypeptide. Two of these lysines are probably involved in contacting the nucleotide directly, and one probably becomes buried when the two ATPase domains of a dimeric enzyme come into contact upon ATP binding; for the others, changes in lysine reactivity appear to reflect allosteric changes following ATP binding. Third, from a comparison of the footprint of the intact enzyme and those of the truncated polypeptides comprised of either the NH2- or the COOH-terminal half of the intact polypeptide, it appears that there are few contacts between the NH2- and COOH-terminal half of yeast DNA topoisomerase II.

A Numerical Study of the Stable Dynamic Behavior of Radial Face Seals With Grooved Faces

This paper presents a simple numerical method for modeling the dynamic tracking modes of a grooved face seal. The stability is verified using a method derived from that developed for smooth face seals. The method, enabling the calculation of the kinematic parameters which describe the steady-state response of the grooved seal, is of interest in designing this type of seal. A parametric study is presented for the case of a rotor face with eight semicircular grooves. The principal effect of the grooves is to increase the hydrostatic component of the load. In turn, this makes the seal less sensitive to fluctuations of the hydrodynamic phenomena. Sinusoidal waviness is used to simulate the periodic distortions induced by the grooves and affects the dynamic behavior only in the presence of cavitation. This occurs for very small values of the film thickness and, consequently, for very small leakage flow. In this case, the dynamic response of the seal is then strongly dependent upon the hydrodynamic effects.

Experiments on drag-reducing surfaces and their optimization with an adjustable geometry

Previous research has established that surfaces with tiny ribs (riblets) aligned in the streamwise direction can reduce the turbulent wall-shear stress below that of a smooth surface. Typical skin-friction reductions have been found to be about 5%. The results of the present investigation, however, demonstrate a considerable improvement over this value. This improvement is achieved by a systematic experimental optimization which has been guided by theoretical concepts.A key feature of our experiments is the utilization of an oil channel. Previous experiments in wind tunnels had to contend with very small riblet dimensions which typically had a lateral rib spacing of about 0.5 mm or less. By contrast, in our oil channel, the ribs can have a lateral spacing of between about 2 and 10 mm. This increased size of the surface structures enables test surfaces to be manufactured with conventional mechanical methods, and it also enables us to build test surfaces with adjustable geometry. In addition, the Berlin oil channel has a novel shear stress balance with an unprecedented accuracy of ±0.3%. This latter feature is a prerequisite for a systematic experimental optimization.In the present investigation, surfaces with longitudinal ribs and additional slits are studied. The experiments cover a fairly large range of parameters so that the drag reduction potential of a surface with ribs and/or slits is worked out conclusively. A large parameter range is made possible because of the adjustability of the surfaces as well as the automatic operation of the oil channel. In particular, the following tests were run:(i) Shear stress measurements with conventional riblet configurations, i.e. with triangular and semi-circular grooves, have been carried out. These measurements were necessary in order to establish the connection between our oil channel data and previous data from wind tunnels. As was previously established, we found a drag reduction of about 5%.(ii) An adjustable surface with longitudinal blade ribs and with slits was built and tested. Both groove depth and slit width could be varied separately and continuously during the experiment. It turned out, that slits in the surface did not contribute to the drag reduction. Nevertheless, these investigations show how perforated surfaces (e.g. for boundary-layer control) can be designed for minimal parasitic drag. On the other hand, with closed slits, an optimal groove depth for the rib surface could be determined, i.e. half of the lateral rib spacing. For this configuration, we found an 8.7% skin-friction reduction. By carefully eliminating deleterious effects (caused by little gaps, etc.), the skin-friction reduction could be improved to a record value of 9.9%.(iii) A quantitative comparison between theory and experiment was carried out. The theory is based on the assumption that riblets impede the fluctuating turbulent crossflow near the wall. In this way, momentum transfer and shear stress are reduced. The simplified theoretical model proposed by Luchini (1992) is supported by the present experiments.(iv) For technological applications of riblets, e.g. on long-range commercial aircraft, the above thin-blade ribs are not practical. Therefore, we have devised a surface that combines a significantly improved performance (8.2 %) with a geometry which exhibits better durability and enables previously developed manufacturing methods for plastic riblet film production to be used. Our riblet geometry exhibits trapezoidal grooves with wedge-like ribs. The flat floor of the trapezoidal grooves permits an undistorted visibility through the transparent riblet film which is essential for crack inspection on aircraft.

Ball Parts Lapping with Semicircular Grooved Lap. 1st Report. Study for Form Error with Three Lobes in Cross Section.

Ball parts assembled in rolling bearings are finished by the lapping process. Usually, the ball parts are lapped while rolling between coaxial circular grooves machined on the two laps. These grooves have a V shape or a semicircular cross section. The difference between radius of the semicircular cross-sectional grooves and the radius of the ball parts is very small. The high conformity, which stands for degree of agreement between the radius of the balls and the grooves, lead to a high sphericity of the ball parts. However, in the case of lapping with a large stock allowance, a form error which has three lobes along the circumference of the cross section increases. In this report, the lapping condition and mechanism of increase in the form error with three lobes are experimentally investigated. A small decrease in conformity between the ball parts and the grooves results in an increase in the form error. In this condition, gap between the ball and groove becomes enough large for a form error of the ball to give rise to displacement of the ball mass center.

Blocking Inhibitors in Cathodic Leveling: II. Experimental Investigation

A model for cathodic leveling based on a diffusion‐adsorption‐reduction mechanism for the leveling agent was tested experimentally by electrodepositing nickel into a semicircular groove in the presence of coumarin. The inhibition of nickel by coumarin was measured on a rotating disk electrode, and kinetics for the reduction of coumarin and Langmuir adsorption coefficient were obtained from polarization data. Satisfactory agreement was found between experimentally measured and simulated leveling for groove depths on the order of the diffusion layer thickness or smaller.

Blocking Inhibitors in Cathodic Leveling: I. Theoretical Analysis

A model for predicting leveling during electrodeposition in the presence of an inhibiting additive is presented. Based on a diffusion‐adsorption mechanism, the model assumes that the additive is consumed at the cathode by electroreduction. Using the approximation of a flat, stagnant diffusion layer, leveling during metal electrodeposition into triangular and semicircular grooves is simulated. The variation of the leveling agent concentration along the groove profile is determined by solving a concentration field problem with a boundary element method, and the advancement of the groove profile is simulated with a flexible moving‐boundary algorithm. Leveling performance depends on three dimensionless groups characterizing leveling‐agent reduction, metal‐ion reduction, and the geometrical ratio of the diffusion layer thickness to the groove depth.

Application of the Indirect Fictitious-Boundary Integral Method to Unsteady Elastodynamic Problem. Three-Dimensional Axisymmetric Problem.

The indirect fictitious-boundary integral method is applied to unsteady elastodynamic problems. At first, the impulsive stresses are analyzed for a spherical cavity in infinite medium subjected to impulsive pressure at the surface boundary, and these results are compared in detail with the analytical solution and the other one. Next, the longitudinal impact problem of a circular bar with a semi circular groove is treated, and the dynamic stress concentration factors and the stress distributions are accurately analyzed. Finaly, the availability of this method to unsteady elastodynamic problems is shown.