Outer Load Research Articles

STEADY-STATE THERMOELASTIC ANALYSIS OF A FUNCTIONALLY GRADED ROTATING ANNULAR DISK

This paper is concerned with the thermoelastic analysis of a functionally graded rotating annular disk subjected to a nonuniform steady-state thermal load. Material properties are assumed to be temperature independent and continuously varying in the radial direction of the annular disk. The variations of Young's modulus, material density, thermal expansion and conductivity coefficients are represented by a novel exponential-law distribution through the radial direction of the disk, but Poission's ratio is kept constant. The governing differential equations are exactly satisfied at every point of the disk. Exact solutions for the temperature and stress fields are derived in terms of an exponential integral and Whittaker's functions. Presented are some results for stress, strain and displacement components due to thermal bending of the rotating disk. The effects of angular velocity, inner and outer temperature loads and material properties on the stress, strain and displacement components are discussed.

Spanwise Lift Distribution for Blended Wing Body Aircraft.

A study is presented of the effects of spanwise lift distribution on aerodynamic efficiency for a blended wing body (BWB) configuration of a given baseline planform. The baseline geometry is initially assessed by a high-fidelity aerodynamic model based on a multiblock structured grid Reynolds-averaged Navier-Stokes (RANS) solution. The accuracy of the simulation is investigated by a grid sensitivity study regarding total drag and its pressure drag and skin-friction drag components. Excessive outer wing loading with associated shock wave, hence, wave drag, has been revealed to be the major factor degrading the aerodynamic performance of the baseline BWB model. To relieve the outer wing, an efficient low-fidelity panel method aerodynamic model is used for the inverse design to achieve the target lift distributions through the variation of twist distribution along the span, shifting the load inboard. For the given BWB geometry, the baseline model is retwisted to achieve an elliptic, a triangular, and an averaged elliptic/triangular spanwise loading distribution. The designs are then analyzed using the high-fidelity RANS aerodynamic model. The wave drag component of the total drag for different span loadings is extracted from the flowfield solution to gain insight into the drag reduction provided by the new twist designs

Contemporary type of analysis on contact problems with friction using the finite element approach

This paper elaborates theoretic methods which give solutions for nonlinear problems of contact with friction that arise from stick-slip phenomenon. The aim of the study is anticipation of tension and deformations on the contact surface as well as inside of components that come in contact, because contact surface is changing progressively owing to outer load induction. In this paper it is presumed that materials are linearly elastic, while motions and deformations are minor, and contact surface is continuous and plane. It is also presumed that it does not come to mutual perforation of the objects surfaces in contact. The paper is based on finite elements method, modified for contact problems, on iterative-incremental method and with contemporary mathematical theoretical assumption for contact problem solving.

Hydro turbine speed control using robust cascade governor controllers

AbstractThis paper presents a cascade control approach to the design of governors for speed control of hydro turbines in power generation units. The key issues include the problems of model uncertainty, inner and outer loop disturbances, load rejections and attenuation of measurement noise. Gate position deviation signal is used as a supplementary inner loop manipulated variable in the proposed cascade control. The effect of water hammer, travelling waves and inelastic water penstocks is included in the hydro turbine model. The polynomial H∞ design method is used to design cascade governor controllers. Dynamic weighting functions of the H∞ design method provide the required control actions. A cascade robust governor ensures that the overall system remains asymptotically stable for all permissible norm‐bounded uncertainties and system oscillations. The results presented in the time and frequency domains are compared with conventional PID and PID cascade designs. The results show that the performance of the system is significantly improved by the proposed cascade governor design. Copyright © 2004 John Wiley & Sons, Ltd.

Analysis of Flexure Tests for Transverse Tensile Strength Characterization of Unidirectional Composites

Finite element (FE) analyses were performed on 3-point and 4-point bending test configurations of glass-epoxy and carbon-epoxy unidirectional tape beams tested at ninety degrees to the fiber direction to identify deviations from beam theory predictions. Both linear and geometric non-linear analyses were performed using the ABAQUS® finite element code. The 3-point and 4-point bending specimens were first modeled with two-dimensional elements. Three-dimensional finite element models were then performed for selected 4-point bending configurations to study the stress distribution across the width of the specimens. For 3-point bend test configurations, both the linear and geometric non-linear 2D plane-strain and plane-stress analyses yielded similar results. The maximum tensile stresses under the center load nose calculated from the FE analysis were slightly lower than stresses predicted by beam theory. The difference (maximum of 4%) was greatest for the shortest span analyzed. For 4-point bend test configurations, both the plane-stress and plane-strain 2D linear analysis results agreed closely with beam theory except right below the load points. However, 2D geometric non-linear analyses deviated slightly from beam theory throughout the inner span as well as below the load points. Plane-stress results deviated from beam theory more than plane-strain results. The maximum tensile stresses between the inner span load points were slightly greater than the beam theory result. This difference was greatest (maximum of 4%) for configurations with the shortest spans between inner and outer load points. A contact analysis was also performed in order to investigate the influence of modeling the roller versus modeling the support as a simple boundary condition at one nodal point. The discrepancy between the FE and beam theory results became smaller (max. 2–3%) when the rollers were modeled in conjunction with contact analysis. Hence, the beam theory yields a reasonably accurate value for the maximum tensile stress in bending compared to 2D FE analysis. The FE results are primarily for guidance in the choice of beam thickness, width, and configuration. For the 3-point bend configuration, longer spans are preferred to minimize the error in beam theory data reduction. Similarly, for the 4-point bend configurations, a longer span between the inner and outer load noses, at least equal to the span between the inner load noses, results in less error compared to beam theory. In addition, these FE results indicate that the span between the inner load noses should not be too long to avoid obtaining a non-uniform maximum stress between the inner load noses. Finally, the 3D analysis indicates that specimens should be sufficiently wide to achieve a fully constrained state of plane-strain at the center of the specimen width.

Flexural strength analysis of brittle materials

The relation between flaw density and strength of ceramic or brittle materials were derived and applied to a commonly used testing method of four-point bending for determining the strengths of ceramic or brittle materials. Previous analysis failed to include the failures outside or at the inner loading positions for four-point test data. The present approach elevates such a constrain so that the relation applies to failures occurs at any points between the outer loading positions for four-point test data.

Elastic buckling of a thin eccentric circular annulus

The contribution treats the elastic buckling of a thin eccentric circular annulus which is on the inner and on the outer boundaries subjected to uniform and constant pressure or tensile loads. The inner and outer boundary are simply supported. To determine the plane stress state and the critical outer load, all equations are expressed with complex variables in the complex plane (z), and conformally mapped into a new complex plane (ζ). The energy method is used for the determination of a critical outer load at which the buckling process appears.

Effect of specimen thickness on Mode II fracture toughness of rock

Anti-symmetric four-point bending specimens with different thickness, without and with guiding grooves, were used to conduct Mode II fracture test and study the effect of specimen thickness on Mode II fracture toughness of rock. Numerical calculations show that the occurrence of Mode II fracture in the specimens without guiding grooves (when the inner and outer loading points are moved close to the notch plane) and with guiding grooves is attributed to a favorable stress condition created for Mode II fracture, i.e. tensile stress at the notch tip is depressed to be lower than the tensile strength or to be compressive stress, and the ratio of shear stress to tensile stress at notch tip is very high. The measured value of Mode II fracture toughness KII C decreases with the increase of the specimen thickness or the net thickness of specimen. This is because a thick specimen promotes a plane strain state and thus results in a relatively small fracture toughness.

Some Existence Results for Noncoercive Problems in Nonlinear Elasticity with Live Loadings

We consider a noncoercive nonconvex minimization problem with nonlinear perturbing terms that arises from equilibrium problems in nonlinear elasticity, in which the body is subjected to live outer loadings. By using a generalized recession method, we find sufficient and necessary conditions for the existence of minimizers of the energy functionals. An example is provided to illustrate the application of the results in cases not treated by usual recession approaches.

Some Existence Results for Noncoercive Problems in Nonlinear Elasticity with Live Loadings

We consider a noncoercive nonconvex minimization problem with nonlinear perturbing terms that arises from equilibrium problems in nonlinear elasticity, in which the body is subjected to live outer loadings. By using a generalized recession method, we find sufficient and necessary conditions for the existence of minimizers of the energy functionals. An example is provided to illustrate the application of the results in cases not treated by usual recession approaches.

Deterministic Stress Modeling of Hot Gas Segregation in a Turbine

Simulation of unsteady viscous turbomachinery flowfields is presently impractical as a design tool due to the long run times required. Designers rely predominantly on steady-state simulations, but these simulations do not account for some of the important unsteady flow physics. Unsteady flow effects can be modeled as source terms in the steady flow equations. These source terms, referred to as Lumped Deterministic Stresses (LDS), can be used to drive steady flow solution procedures to reproduce the time-average of an unsteady flow solution. The goal of this work is to investigate the feasibility of using inviscid lumped deterministic stresses to model unsteady combustion hot streak migration effects on the turbine blade tip and outer air seal heat loads. The LDS model is obtained from an unsteady inviscid calculation. The inviscid LDS model is then used with a steady viscous computation to simulate the time-averaged viscous solution. The feasibility of the inviscid LDS model is demonstrated on a single-stage, three-dimensional, vane-blade turbine with a hot streak entering the vane passage at midpitch and midspan. The steady viscous solution with the LDS model is compared to the time-averaged viscous, steady viscous, and time-averaged inviscid computations. The LDS model reproduces the time-averaged viscous temperature distribution on the outer air seal to within 2.3 percent, while the steady viscous has an error of 8.4 percent, and the time-averaged inviscid calculation has an error of 17.2 percent. The solution using the LDS model is obtained at a cost in CPU time that is 26 percent of that required for a time-averaged viscous computation. [S0889-504X(00)00601-2]

STIFFNESS CHARACTERISTICS OF GEOMETRICALLY NON-LINEAR BEAM FINITE ELEMENT/GEOMETRIŠKAI NETIESINIO LENKIAMO STRYPO BAIGTINIO ELEMENTO STANDUMO RODIKLIŲ NUSTATYMAS

STIFFNESS CHARACTERISTICS OF GEOMETRICALLY NON-LINEAR BEAM FINITE ELEMENT/GEOMETRIŠKAI NETIESINIO LENKIAMO STRYPO BAIGTINIO ELEMENTO STANDUMO RODIKLIŲ NUSTATYMAS

Development and Test Results of Magnetically Controlled Persistent Current Switches

We have developed 50A, 50A-high resistance, 200A, and 1kA class fast response magnetically controlled persistent current switches (magnetic PCS), which are thought to be necessary for small-to medium scale superconductive magnetic energy storage(SMES) systems. In this paper, we report test results on the 200A class magnetic PCS. A 6.6m long cable made from 6 strands of 55 core, in-situ processed CuNb composite wire (0.3mm?, B c2 ∼0.6T, J c ∼136A at 4.2K and OT) with high resistivity CuNi alloy matrix was non-inductively wound on a FRP bobbin and set into a control magnet which can be swept up to the maximum 1.2T within 2sec. The magnetic PCS was combined with a small superconducting magnet (-SOmH, 200A, 2.72T) and realized a persistent current mode at 200A. The fast response was checked with a combination of an outer resistance load and by a switching-off of the magnetic PCS in a persistent current mode. The switching lime of the magnetic PCS was shorter than 0.16sec. The recent results of an energy retaining test for 10 hours by a 1kA class magnetic PCS at 1kA will be also reported briefly.

Development of a 50 A-fast response, magnetically controlled persistent current switch

We have developed a 50 A-fast response, magnetically controlled persistent current switch (Magnetic PCS), which is thought to be necessary also for a small to medium scale superconducting magnetic energy storage (SMES) system. A 10 m-long, 55 core, in-situ processed CuNb composite wire (0.3 mm /spl phi/, B/sub c2//spl sim/0.6 T, I/sub c//spl sim/136 A at 4.2 K and 0 T) with high resistivity CuNi alloy matrix was noninductively wound on a FRP bobbin and set into a control magnet which can be swept up to the maximum 1.2 T within 2 sec. The magnetic PCS was combined with a small superconducting magnet (0.5 H, 50 A, 5.5 T) and realized a persistent current mode at 50 A. The fast response was checked with a combination of an outer resistance load and by a switching-off of the magnetic PCS in a persistent current mode. The switching-off time of the magnetic PCS was shorter than 0.3 sec. An energy retaining test for about 50 min. was also performed. >

Decrease of Wheel Load on Transition Curve.

A simulation program of vehicle dynamics for analysis of running safety of a railway vehicle was developed. Curving performance simulations were made. Original waveforms obtained from the measured 10m chord's versed sine of the track inspection car were used as the data of track irregularity for our simulation. Simulation results agreed well with measurement results. By using this simulation program, we found that an outer wheel load decreases running on an exit transition curve. The results show that the stiffness of a primary suspension is related to wheel load decrease.

Subcrustal density inhomogeneities of Northern Eurasia as derived from the gravity data and isostatic models of the lithosphere

For the territory of Northern Eurasia (6°E–165°W; 30–75°N) the distribution of anomalous masses in the lithosphere has been estimated in accordance with the lithosphere isostatic model. The method of model construction is based on the admittance technique. The experimental admittance presents a relation between the part of the outer load uncompensated by the Moho undulations and the residual gravity field and is used to select the best model. The 1 × 1° averaged values of topography elevations, basement and Moho depths, sedimentary cover density and gravity anomalies have been used as initial data. According to the correlation equation relating the outer load and Moho depths, the mean density contrast between the lower crust and the subcrustal lithosphere is 0.43 g/cm 3, but the Moho undulation can not provide complete isostatic equilibrium. In some areas, the part of the outer load uncompensated by Moho undulations may be as large as 10 7 kg/m 2 and the residual gravity field is as intensive as + 260 mGal. Assuming that for loads of wavelength > 200 km, local isostatic compensation is valid, in accordance with the admittance analysis, the anomalous masses compensating for the part of the outer load, which is not compensated by Moho undulations, have to be located partly in the lower crust and in the subcrustal layer. The regional trend of anomalous compensating masses is negative under Western Europe, the Mediterranean, Eastern Asia and adjacent marginal seas, and positive under the East European Platform and Western and Central Asia. The local compensating masses correspond to particular tectonic units. The isostatic gravity anomalies of Northern Eurasia have been determined and the long-wave component of the field reflecting anomalous masses under the isostatic compensation level has been evaluated.

A method for measuring the structural properties of the rat mandible

The rat mandible has been used to study fractures, ridge augmentation, bone defects, and the effects of cryosurgery, all of which affect the structural properties of the mandible. The only previously described mechanical test of the rat mandible used three-point bending with a piece of foam placed between the lingual surface of the mandible and the support. The accuracy and reproducibility of this test were not determined. Two different, three-point bending tests for characterizing the structural properties of the rat mandible have now been evaluated. Acrylic specimens representing three different-sized mandibles were tested in three-point bending with either potted ends or foam interposed between the specimen and the outer load points. Flexural stiffness and failure load were compared against data from a conventional three-point bending test. In addition, five paired halves of 90- and 210-day-old rat mandibles were tested either with interposed foam or with potted ends and the mean coefficients of variation of the stiffness and failure loads were determined. Failure loads of the acrylic specimens with the potted and foam methods were significantly higher (50 and 10%, respectively; p < 0.05) than with the conventional method. The stiffness of the acrylic specimens with the potted and foam methods was significantly different (75% higher and 21% lower, respectively; p < 0.05) than with the conventional test. In addition, there was no difference between the coefficient of variation in stiffness (26 + 11%) or failure load (10 + 4%) measured with the foam test and the comparable values (16 + 11%) and (18 + 13%) in the potted test. Thus it appears that the foam test more accurately reflects the stiffness and failure load of the acrylic specimens than the potted test. Although there was no difference in the coefficients of variation in the potted and foam tests, the technical difficulties associated with potting indicate that the foam test is a better method for testing the structural properties of the rat mandible. The objective of this experiment was to establish a method for accurately measuring the structural properties of the rat mandible and for detecting differences in structural properties between different treatment groups.

The impact of comet Shoemaker‐Levy 9 on the Jovian magnetosphere

By the time of the impact of comet P/Shoemaker‐Levy 9 with Jupiter, the freshly‐broken surfaces of the accompanying rubble will have been outgassing for about two years, and will have produced an expanding and co‐moving cloud of gas hundreds of RJ across. Much of this gas, escaping from the cometary fragments at low (≤ 1 km/s) speed, will arrive in the Jovian magnetosphere contemporaneously with the comet and drift through the magnetosphere. This gas, as it is photoionized, will be picked up primarily in the outer magnetosphere and the resulting high‐energy ions should intensify magnetospheric processes, such as Io plasma torus and auroral emissions, that are thought to be powered by outer magnetospheric mass loading. If the composition of the comet is similar to that of P/Halley, the power available from mass loading should be comparable to that driving the aurora (1014W) and at least an order of magnitude larger than that exciting the plasma torus for several weeks or months. Measurement of these emissions during and after the cometary encounter may constrain the mechanisms for energization of magnetospheric charged particle populations and magnetospheric transport processes.

Threshold stress intensity for oxidative crack healing in sintered silicon nitride

In applying ceramics to stuctural components, the assurance of minimum strength is an important factor in achieving high reliability. The fracture strength of ceramics is generally determined by the worst processing flaw. Flaws induced by machining have taken on greater importance than ever before since ceramic processing technologies have made progress toward the successful elimination of internal flaws such as inclusions, agglomerates, exaggerated particles and voids. This means that the elimination of surface flaws produced during machining is a key to further improvement in strength. When strength is governed by surface flaws, strength recovery can be expected to occur at high temperatures. As indicated by Evans [1], crack healing in ceramics can actually take place at high temperatures below the threshold stress intensity, and negative crack velocity is described as a function of the applied stress intensity. Crack tip blunging, another phenomenon occurring under hightemperature loads, works to counteract subcritical crack growth. It was reported that the strength of sintered silicon nitride, having a Knoop indentation flaw, increased due to crack tip blunting below a stress intensity of 0.1 MPam 1/2 at 1200 °C in a nitrogen atmosphere [2]. These studies seem to indicate that diffusional flow along the crack interface to the crack tip produces crack tip blunting, and that further diffusional flow to the crack interface results in crack healing. Oxidation forming a dense surface layer can heal a crack. The strengthening of silicon carbide as a result of oxidation at 1400 °C was thought to be attributed to the healing of surface cracks [3]. Similar phenomena can be expected to occur in silicon nitride at high temperatures because a dense silicon oxide layer can be formed on the surface. If an oxide layer is formed at the crack interface, blunting the crack, higher threshold stress intensity values may be obtained than those seen for diffusion mechanisms. A novel technique, using a modified stress rupture test, has been proposed as a way of determining the threshold stress intensity at high temperatures, based on the idea that strength can increase under a stress level below the threshold [2, 4]. This technique was used in the present study to explore the threshold stress intensity for oxidative crack healing at high temperatures, resulting in increased strength. The material used in this study was sintered silicon nitride having a density of 3.11 g cm -3. This material was fabricated by compacting and sintering a powder mixture (SN-COA, Ube Co., Ltd) having a composition of 90 wt% Si3N4, 5 wt% Y203 and 5 wt% A1203 in a nitrogen atmosphere under a pressure of 0.1 MPa at 1650 °C for 4 h. Specimens prepared for the tests were ground to the dimensions of 3 mm x 4 mm x 38 mm. At the centre of the surface where tensile stress was applied, a crack was introduced with a Knoop indenter at a load of 198 N. The surface layer with a thickness of 100/xm was ground to eliminate the residual stress induced by the indentation [2, 5]. Fig. 1 shows the apparatus for applying flexural stress at high temperatures. The applied static load was transmitted through the level arm mechanism. In order to detect the time to failure, a microswitch connected to a timer was positioned just below the lever arm. The compact furnace was made of silicon carbide heating elements. The fixtures and the loading rods were machined from dense silicon carbide. The load was applied at the outset at room temperature to avoid healing the crack before reaching the test temperature. It took about 1.5 h to reach the test temperature of 1100 °C, and the temperature was then kept constant for 3 or 20 h. The electric power was switched off to let the furnace cool down after the test in order to remove the specimen. The strength of the specimens after being subjected to high temperature loading was measured in a four-point speed of 0.5 mm min -1. lengths for both high strength measurement at and 30 mm, respectively. flexural test at a crosshead The inner and outer span temperature loading and room temperature were 10

Verapamil decreases cyclic load-induced calcium incorporation in ROS 17/2.8 osteosarcoma cell cultures

Bone is a tissue that responds to mechanical load by changing its internal architecture. However, the mode of transmission of mechanical stimuli into biological signals and the effect of load at the cellular level are still not clear. An in vitro system, a Flexercell® Strain Unit, was used to apply cyclic load to osteoblast-like cells in culture. In the first series of experiments, ROS 17/2.8 rat osteosarcoma cells, cultured on Flex I®, flexible bottomed culture plates, were subjected to a 0.05 Hz, 0.24 STRAIN cyclic load regime for 3 and 7 days, in vitro. One group subjected to load received verapamil, a calcium channel blocker, throughout the experimental period. A second group was exposed to load but received no verapamil. A third group had no drug or load and a fourth group had no load but received verapamil. Cultures were incubated for 24 hours prior to collection with 10 μCi of 45CaCl in the medium, then well bottoms were divided to yield outer (maximum) and inner (minimum) load zones for assay of radioactivity. The effect of verapamil during a 7-day loading period was studied by adding the drug to individual cultures at daily intervals. Results indicated that mechanical loading stimulates calcium incorporation in ROS 17/2.8 cell cultures by day 7 but not by day 3. Only early verapamil addition decreased load-induced calcium incorporation when drug was added prior to day 4. If verapamil was added after 4 days, the channel blocker did not diminish load-induced calcium incorporation.