Two-dimensional Test Research Articles

Fingering Flow in Homogeneous Sandy Soils Under Continuous Rainfall Infiltration

In order to establish a physical model leading to stable (uniform) and unstable (non-uniform fingering) flows in unsaturated soils, two-dimensional tests on continuous rainfall infiltration were carried out by changing not only the initial water content (air dry, 0.5%, 1.0%) but also the rainfall intensity (15, 30, 180 mm/h). The physical mechanism of fingering flow was discussed on the basis of precise suction measurements inside and outside the fingers. The results show that wetting fronts developed in unsaturated sandy soils can be classified into three types; 1) fingering flow, 2) wavy front, and 3) plane front. Two types of fingering flow can be further distinguished by the difference of the swelling velocity; i.e., low-swell finger and high-swell finger flows. In each of the low-swell and high-swell fingers, a core and a swelling zone are developed while a finger is growing. Based on suction measurements inside them, it is found that the water condition in the finger core changes from wetting to drying processes while the water condition in the swelling zone remains in the wetting process. This hysteretic behavior in the core can be explained by the moisture distribution changing along a finger from tip to tail. Fingers swell when water moves from a finger core to surrounding dry sand. Such a swelling process is mainly controlled by the hydraulic conductivity for the wetting process at a finger tail.

Bestimmung des Makroreinheitsgrades von Wälzlagerstählen mittels Ultraschall

Determining macro-cleanliness of bearing steels by means of ultrasonic immersion technique has gained increased importance in comparison with conventional two-dimensional testing methods. In order to get reliable and comparable test results, standardization of testing and evaluation is indispensable and therefore the influencing parameters should be well known. The present paper deals with a number of parameters influencing the test results by means of practical investigations and points out the problems concerning an uniform valuation.

Model Tests and Numerical Simulation of Braced Excavation in Sandy Ground: Influences of Construction History, Wall Friction, Wall Stiffness, Strut Position and Strut Stiffness

ABSTRACT Two-dimensional model tests and elastoplastic finite element analyses for excavation problems with a braced wall are performed to investigate the influence of construction history, wall friction, wall stiffness and the struts on the ground movements and the earth pressures on the wall. Test results show that the surface settlements of the backfill and earth pressure on the wall depend on the deflection process of the wall, even if the final wall deflections are the same. The wall friction, wall stiffness and the position and stiffness of strut significantly affect the earth pressure on the wall and the ground movement including the surface settlements. The computed results, in which mechanical behavior of soil and structure, behavior of interface between soil and wall and the process of excavation were properly taken into consideration, describe well the results obtained in the model tests. Such influence on the deflection of the wall, the earth pressure on the wall and the ground movements has not been evaluated properly in the present design practice.

A Domain Decomposition Approach for Incompressible Flows Past Multiple Objects

A domain decomposition approach has been developed to solve for flow around multiple objects. The method combines features of mask and multigrid algorithm implemented within the general framework of a primitive variable, pseudospectral elements formulation of fluid flow problems. The computational domain consists of a global rectangular domain, which covers the entire flow domain, and local subdomains associated with each object, which are fully overlapped with the rectangular domain. There are two key steps involved in calculating flow past multiple objects. The first step approximately solves the flow field by the mask method on the Cartesian grid alone, including on those grid points falling inside an object (a fuzzy boundary between the fluid-object interface), but with the restriction that the velocity on grid points within and on the surface of an object should be small or zero. The second step corrects the approximate flow field predicted from the first step by taking account of the object surface, i.e., solving the flow field on the local body-fitted (curvilinear) grid surrounding each object. A smooth data communication between the global and local grids can be implemented by the multigrid method when the Schwarz Alternating Procedure (SAP) is used for the iterative solution between the two overlapping grids. Numerical results for two-dimensional test problems for flow past elliptic cylinders are presented in the paper. An interesting phenomenon is found that when the second elliptic cylinder is placed in the wake of the first elliptic cylinder a traction force (a negative drag coefficient) acting on the second one may occur during the vortex formation in the wake area of the first one.

A Variational Synthesis Nodal Discrete Ordinates Method

A self-consistent nodal approximation method for computing discrete ordinates neutron flux distributions has been developed from a variational functional for neutron transport theory. The advantage of the new nodal method formulation is that it is self-consistent in its definition of the homogenized nodal parameters, the construction of the global nodal equations, and the reconstruction of the detailed flux distribution. The efficacy of the method is demonstrated by two-dimensional test problems.

Advantages of cylindrical keys for torque transmission

Elastic stresses due to torque transmission through cylindrical keys have been determined from 16 two-dimensional photoelastic tests. Two key diameters were tested with dry and lubricated shafts, using keys which were push or sliding fit, dry or lubricated. The greatest stresses occur in the keyway surface of the shaft at the loaded edge of the keyway and about one-third of the way around the keyway. The total torque is transmitted partly by friction and partly through the key. The latter has been used to calculate the mean shear stresses across the key. The peak stresses are independent of the key diameter, shaft lubrication and key surface condition; unlike rectangular keys, they vary little with torque. Peak stresses are lower than in rectangular keys.

A Sequential Gradient Method for the Inverse Heat Conduction Problem (IHCP)

A sequential-in-time implementation is proposed for a conjugate gradient method using an adjoint equation approach to solve the inverse heat conduction problem (IHCP). Because the IHCP is generally ill-posed, Tikhonov regularization is included to stabilize the solution and allow for the inclusion of prior information. Aspects of the sequential gradient method are discussed and examined. Simulated one and two-dimensional test cases are evaluated to study the sequential implementation. Numerical solutions are obtained using a finite difference procedure. Results indicate the sequential implementation has accuracy comparable to the standard whole-domain solution, but in certain cases requires significantly more computational time. Benefits of the on-line nature of a sequential method may outweigh the additional computational requirements. Methods to improve the computational requirements, which make the method competitive with a whole domain solution, are given.

Piezoelectric polymer actuators for active vibration isolation in space applications

A lightweight actuator for active vibration isolation in space applications is being developed to replace the heavy electromagnetic systems now in use. The actuator has a low effective spring constant that provides for passive vibration damping down to sub-Hertz frequencies while allowing the isolated experiment to follow the near-dc bias motion of the spacecraft. The actuator is currently optimized for the vibration level of the Space Shuttle and assembled from a pair of bimorphs in a leaf-spring configuration. Changing the size and number of sheets used in construction can vary electromechanical properties. Passive damping has been demonstrated in one and two-dimensional tests. For large (greater than a few kilograms) suspended masses, the system is underdamped and relative velocity feedback must be used to remove the resonance. Real-time control of the resonance frequency is achieved by controlling the voltage applied to the actuator with feedback from a displacement sensor. A folded pendulum seismic monitoring device was adapted for use as a one-dimensional low frequency test platform and has obtained accurate measurements of the effective spring constant and damping coefficient. Single-degree-of-freedom active feedback testing is also being conducted using this device. Two-dimensional (three-degree-of-freedom) passive damping tests were conducted on NASA's KC-135 Reduced Gravity Platform in March 1998.

Overtopping Formulas for Caisson Breakwaters with Nonbreaking 3D Waves

From the analysis of an extensive series of two-dimensional and three-dimensional hydraulic model tests on the overtopping response of various types of caisson breakwaters, general design formulas and graphs have been derived. Exponential relationships relate the mean discharge and the percentage of overtopping waves with the relative freeboard. The parametric influence of geometrical changes and of wave obliquity and multidirectionality is described by reduction factors referred to the case of simple vertical structure under long-crested head-on wave attack. Comparisons are made with the three-dimensional overtopping response of sloping structures. Overtopping volumes per wave have also been measured and their distribution fitted with a universal probability function. Even the effects of overtopping waves on pedestrians behind the crownwall were statistically evaluated to allow an upgrading of the existing criteria for the admissible rates over breakwaters.

Testing a motor performance series and a kinematic motion analysis as measures of performance in high-functioning stroke patients: Reliability, validity, and responsiveness to therapeutic intervention

Objective: To assess measurement properties of motor performance tests when used with high-functioning stroke patients. Design: Test-retest reliability study with an interval of 2 days; responsiveness study with assessment before and after training; validity study assessing the tests' ability to discriminate between the high-functioning stroke patients and healthy subjects. Setting: Referral center for neurorehabilitation. Participants: Twenty-nine high motor-functioning stroke patients and 20 healthy control subjects. Intervention: Two special training sessions per day on 5 consecutive days, plus regular therapy. Outcome Measures: Scores on the motor performance series, a two-dimensional tracking test, and a kinematic task analysis. Results: All tests (except the bimanual test) were able to document performance deficits with these patients and showed a moderately high to high test-retest reliability without systematic trend from test to retest (intraclass correlation coefficients for main variables, .61 to .89). The kinematic task especially demonstrated changes after training (standardized response means for timing variables, .53 to .66). A subset of variables indicated a modifying effect of limb side, age, and gender. Conclusion: All tests (except the bimanual test) can be used for both cross-sectional and follow-up group studies with high-functioning stroke patients. Measurement properties and the lack of comprehensive normative data limit their use with individual patients.

Large-Scale Experiments on Ex-Vessel Core Melt Behavior

In the framework of European research activities on nuclear safety, experimental work on ex-vessel core melt behavior under prototypical conditions is being performed. Spreading on various material surfaces and verification of relevant computer codes are the main tasks of the COMAS project, leading to an improvement of the design basis for corium retention systems. In particular, the large-scale two-dimensional spreading test [1:6 with respect to the European pressurized water reactor (EPR) spreading area] shows a quick and uniform melt distribution even for thin melt layers supporting the EPR corium stabilization concept.

Calculating Flux Perturbations with a Davidson Algorithm

In perturbation calculations, obtaining an accurate flux shape of a perturbed core is more difficult than the multiplication factor. Generalized Davidson algorithms using a symmetric successive overrelaxation preconditioner are developed to solve the unperturbed eigenvalue problem and the related perturbed eigenvalue problem of large sparse matrices. The bases of the subspace obtained from the sequence of solving the unperturbed problem through the algorithm can be used in the perturbed problem to save computational time. One- and two-dimensional test problems indicate that by incorporating symmetric successive overrelaxation iteration, the optimized relaxation factor, and the newly developed shifted form-function vector method for a large perturbation, a considerable amount of computational time can be saved in the perturbed calculations with accuracy comparable to the existing CITATION code. This method also provides an efficient means for survey calculations where the requirement of accuracy is not stringent.

A structural analysis of visual spatial ability in academically talented students

The structure of spatial ability in a population of academically talented youth was explored. Methods of Facet Theory and Multidimensional Similarity Structure Analysis (SSA) were used to analyze the correlational structure of performance on 14 types of figural spatial tests in 2 samples of subjects. As in previous research, a cylindrical wedge model was found to describe the underlying structure well. The facet of dimensionality was represented in a polar way with the three-dimensional tasks in the core of a radex-like configuration and the two-dimensional tests in the periphery. The facet of mental rotation was identified to play a modular role as two different subregions in the SSA solutions, one representing two-dimensional rotation and one representing three-dimensional rotation. Memory load was represented in a similar fashion in one of the projections. Speededness emerged as a separate dimension in one of the plots. Indications for the existence of one more facet were found. The results agreed quite well with findings of previous research in this area.

Computational modelling of gradient‐enhanced damage in quasi‐brittle materials

To avoid the well-known drawbacks of the classical continuum damage theory when localization occurs, an isotropic gradient-enchanced damage model is proposed in which the loading function not only depends on the damage value, but also on its Laplacian. The initial boundary value problem obtained adopting this model is considered both in statics and in dynamics. In the dynamic context the finite-step problem is formulated according to a Newmark scheme; the constitutive law is integrated by the backward difference rule. An iterative procedure for the finite-step solution is discussed. Finite elements space discretization is carried out in terms of generalized variables on the basis of two variational principles pertinent to the two phases of the iterative process. One- and two-dimensional numerical tests show the regularizing effect of the gradient term and the effectiveness of the proposed discretization technique. Copyright © 1999 John Wiley & Sons, Ltd.

3-D-Modellanalyse des Oberkiefers von Säuglingen mit LKG-Spalten - Three-dimensional Analysis of Casts of the Maxilla in Infants with Cleft Lip and Palate

For the investigation of three-dimensional morphological changes in the maxilla of children with cleft lip and palate, the use of two-dimensional test analysis is inadequate. Since no standardised three-dimensional method has so far been available, a three-dimensional digital, computer-aided procedure was developed to visualize and metrically analyse the growth of the edentulous maxilla of infants with cleft lip and palate. Chronologically consecutive casts of the maxillas (obtained at the ages of one week, and three, six and twelve months) of five children with complete unilateral CLP were measured optically with the instrument Micromeasure 70. Following digitation, the casts were reconstructed in the computer, aligned and superimposed using the Orthosurf program. The distances between the surfaces were then measured; in addition, the surfaces were segmented perpendicular to the alveolar crest at reference points C1, C1', C2, C2' and I. The volumes of the resulting segments were determined and compare with one another. Specially designed software automated the following steps: 1. identification of reference points; 2. alignment of the cloud of points in a system of coordinates, and 3. identification of the alveolar crest. Our initial results show that (1) the new method enables visualization of the extent and direction of morphological changes of the mucosal surface, and (2) reproducible quantification of these changes via the determination of changes in the volume of defined alveolar segments. The three-dimensional analysis presented here permits a comprehensive three-dimensional measurement of the models of the edentulous maxilla of infants with cleft lip and palate.

Simulation of three-dimensional polymer mould filling processes using a pseudo-concentration method

Mould filling processes, in which a material flow front advances through a mould, are typical examples of moving boundary problems. The moving boundary is accompanied by a moving contact line at the mould walls causing, from a macroscopic modelling viewpoint, a stress singularity. In order to be able to simulate such processes, the moving boundary and moving contact line problem must be overcome. A numerical model for both two- and three-dimensional mould filling simulations has been developed. It employs a pseudo-concentration method in order to avoid elaborate three-dimensional remeshing, and has been implemented in a finite element program. The moving contact line problem has been overcome by employing a Robin boundary condition at the mould walls, which can be turned into a Dirichlet (no-slip) or a Neumann (free-slip) boundary condition depending on the local pseudo-concentration. Simulation results for two-dimensional test cases demonstrate the model's ability to deal with flow phenomena such as fountain flow and flow in bifurcations. The method is by no means limited to two-dimensional flows, as is shown by a pilot simulation for a simple three-dimensional mould. The reverse problem of mould filling is the displacement of a viscous fluid in a tube by a less viscous fluid, which has had considerable attention since the 1960's. Simulation results for this problem are in good agreement with results from the literature. © 1998 John Wiley & Sons, Ltd.

Multidimensional DIF Analyses: The Effects of Matching on Unidimensional Subtest Scores

Popular techniques for assessing differential item functioning (DIF) assume that the test under study is unidimensional. When this assumption is tenable, number-correct score is a reasonable matching criterion. When a test is intentionally multidimensional, matching on a single test score does not ensure comparability and may result in inflated error rates. An alternate approach is to match on all relevant traits simultaneously, using a procedure such as logistic regression. In this study, data were generated to simulate two-dimensional tests. The dimensional structure of the tests, the discrimination levels of the items, and the correlation between the traits measured by the test were varied. Standard DIF analyses were conducted using total test score as the matching variable. High false-positive error rates were found. Items were divided into subtests using nonlinear factor analysis and DIF analyses were repeated with subtest scores as the matching criteria. False-positive error rates were reduced for most datasets. The dimensional structure of the test and the discrimination level of the items influenced false-positive rates for both sets of DIEF analyses. The findings suggest that assessing the dimensional structure of a test can be an important first step in DIF analysis. If a dataset is intentionally multidimensional, conditioning on scores reflecting each dimension can enhance the validity of the analyses.

Two-dimensional stress-relaxation behavior of human skin as influenced by non-enzymatic glycation and the inhibitory agent aminoguanidine

In order to simulate the in vivo stress alterations of diabetic skin in an in vitro model, we examined the viscoelastic properties of long-term glycated human skin samples. Since skin is subjected to biaxial tension, we used two-dimensional multiaxial testing which better reflects the in vivo situation than the uniaxial testing mode. For native skin samples from the abdominal region we found a direction-dependent elastic stress–strain behavior. The viscous stress component was separated from the elastic stress component by relaxation tests at consecutive incremental steps of radial strains. We hypothesize that glycation-induced changes in the tissue stiffness are generated in a direction-dependent mode. A marked increase of the direction-dependent stiffness was found upon long-term incubation with glucose-6-phosphate. This increase was statistically significant for the maximum principal elastic stress component which was highly correlated with the degree of non-enzymatic collagen modification. The viscous fractions obtained from twodimensional relaxation tests at consecutive radial strains were inversely correlated with non-enzymatic modification. Only at 30% radial strain a significant decrease of the viscous fraction engendered by glucose-6-phosphate was observed together with a directiondependent significant increase of the expectation value of the time constant. The biomechanical and biochemical effects of long-term glycation could be partially reversed by aminoguanidine, a potential therapeutic agent for patients with diabetes mellitus. Our findings suggest that additional cross-links generated by long-term glycation cause two-dimensional biomechanical alterations in human skin, which can be unequivocally detected by multiaxial testing.

On the numerical integration of multi-dimensional, initial boundary value problems for the Euler equations in quasi-linear form

A matricial formalism to solve multi-dimensional initial boundary values problems for hyperbolic equations written in quasi-linear based on the λ scheme approach is presented. The derivation is carried out for nonorthogonal, moving systems of curvilinear coordinates. A uniform treatment of the integration at the boundaries, when the boundary conditions can be expressed in terms of combinations of time or space derivatives of the primitive variables, is also presented. The methodology is validated against a two-dimensional test case, the supercritical flow through the Hobson cascade n.2, and in three-dimensional test cases such as the supersonic flow about a sphere and the flow through a plug nozzle. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 781–814, 1998

A simple but accurate mass conservative, peak-preserving, mixing ratio bounded advection algorithm with FORTRAN code

A simplified but very accurate method for calculating advection of mixing ratios in a mass conservative and monotonic manner is presented. This scheme replaces the polynomial approximations of other advection algorithms with dual-linear segments, and employs a special treatment near local maxima and minima to preserve extremes very well. Before updating mixing ratios, fluxes at grid-cell faces are bounded to yield conservative, monotonic, maximum-bounded and minimum-bounded solutions to the advection equation with very little numerical diffusion, even in locally deformational flows. “Bounded” here means that updated mixing ratios never exceed local maxima or fall below local minima. If an initial tracer distribution is everywhere positive, the solution is positive-definite, but negative values can be advected. With a “sharpening” option fully enabled, local maxima or minima are usually perfectly preserved, and features as small as 2–3Δ x in width are advected with virtually no numerical diffusion for many Courant numbers and advection distances. Algorithms are presented for advecting mixing ratios through variable-spaced grids in any flow, including strongly deformational flows. One- and two-dimensional tests of the scheme are presented. Relative to other advection algorithms, this scheme yields significantly lower peak, distribution and rms errors, especially when advecting poorly resolved features with sizes 1–3Δ x. Therefore this scheme may be useful in applications where peak and minima preservation of small features is desirable. A 41-line FORTRAN advection subroutine which can be readily applied for general advection problems is provided in the appendix.