bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Design of Large Elevator Platforms
Authors: Hymans F. 
Published: April 2021

Abstract
Large elevator platforms are, in effect, complex systems of a comparatively few main framing members, coupled by a large number of stringers which support the flooring. As set forth in the paper, and as is qualitatively well known, a load placed on one of the main members is not carried by that member alone. Deflections, impressed by the loaded member on the stringers, induce forces which cause neighboring members to share in the support of the load. However, means to evaluate the distribution of the load with reasonable accuracy, important as it is for a rational design of the platform with the lightest structural shapes, hitherto have not been available. To furnish these is the purpose of the paper. With the aid of two assumptions, and the introduction of certain auxiliary forces, the problem is quickly reduced to the case of a beam, subject to a force at an arbitrary point, supported at its ends, and resting on a flexible foundation.
Polygonal Approximation Method in the Hodograph Plane
Authors: Poritsky H. 
Published: April 2021

Abstract
This paper extends the discussion of the approximate method of integrating the equations of compressible fluid flow in the hodograph plane first presented by the author before the Sixth International Congress of Applied Mechanics, Paris, France, September, 1948. As an introduction to the discussion of the polygonal approximation method, fundamental fluid-flow equations are reviewed briefly. Determination of the flow function ψ by the “Method of Reflections” is described and an application of the method illustrated. How flow in the physical plane can be determined by superposition of solutions discussed is shown for the simpler incompressible case.
A Strain-Energy Expression for Thin Elastic Shells
Authors: Langhaar H. L. 
Published: April 2021

Abstract
A derivation is given for the strain energy of an isotropic elastic shell whose radii of curvature are sufficiently large that strains may be assumed to vary linearly throughout the thickness. The work of Love (1) has been the only previous general investigation which expresses the strain energy in terms of the displacements of the middle surface. The effects of the tangential displacements upon the energy due to bending are found to differ appreciably from Love’s results in the first-order terms. As in the classical large-deflection theory of flat plates, quadratic terms in the derivatives of the normal deflection are retained in the strain tensor, but quadratic terms which involve the tangential displacements are neglected. Special forms of the general energy expression derived in this paper are given for shells in the shapes of flat plates, circular cylinders, elliptical cylinders, ellipsoids of revolution, and spheres. These applications, as well as certain intuitive observations, provide checks on the theory.
Stresses and Displacements in a Semi-Infinite Elastic Body With Parabolic Cross Section Acted on by Its Own Weight Only
Authors: Hank R. J. , Scrivner F. H. 
Published: April 2021

Abstract
The earlier solution for the stress distribution in a semi-infinite elastic wedge is compared with the solution for a cross section of parabolic shape. Displacement diagrams for two extreme values of Poisson’s ratio are given for the parabolic section.
Analysis of a Single Stiffener on an Infinite Sheet
Authors: Benscoter S. U. 
Published: April 2021

Abstract
The use of stiffened-sheet construction in aircraft design has brought about the study of many problems in mechanics in which concentrated loads are introduced into stiffeners and transferred to the sheet. In the present paper a basic problem of this type is considered. A single stiffener of finite length is assumed to be attached to a sheet of infinite extent. A concentrated force is applied to the stiffener at each end. Any given problem may be divided into symmetrical and antisymmetrical parts. The physical condition that governs the problem is that the axial strain in the stiffener must be equal to the normal strain in the sheet at all points along the stiffener. In order to formulate the solution, it is necessary to employ an influence function for the strain in the sheet. This function is known from the classical theory of elasticity. The solution is found to be governed by an integral equation which has the same form as the equation which governs spanwise air-load distribution on an airplane wing. Hence a number of mathematical methods are known for solving the equation. A numerical example is presented.
Energy Method for Determining Dynamic Characteristics of Mechanisms
Authors: Quinn B. E. 
Published: April 2021

Abstract
Two types of problems are dealt with in the paper which are involved in the design of mechanisms required to have specified dynamic characteristics: (1) Determination of applied forces required to produce specified dynamic characteristics. (2) Determination of the dynamic characteristics which will result from the application of known forces. While graphical methods may be used in the solution of type (1) problems involving more or less complex mechanical systems, they do not afford a direct approach to type (2) problems. The energy method which will be outlined can be applied in either case, although this paper will be primarily concerned with the determination of the dynamic characteristics which result when a known force is applied to a given mechanism.
A Force Applied in the Median Plane at the Center of a Circular Insert in a Plate
Authors: Dokos S. J. 
Published: April 2021

Abstract
The problem to be considered in this paper is the determination of the state of stress in a plate containing a right, circular, cylindrical hole filled with a material of different elastic properties, subjected to a central concentrated force in the median plane of the plate. A special solution is also presented in which the modulus of rigidity of the insert is allowed to approach infinity such that no deformation occurs.
The Behavior of Long Beams Under Impact Loading
Authors: Duwez P. E. , Clark D. S. , Bohnenblust H. F. 
Published: April 2021

Abstract
This paper presents the results of a theoretical and experimental investigation of the plastic deformation of long beams which are subjected to a concentrated transverse impact of constant velocity. In the theoretical analysis, the beam is supposed to be of infinite length, and plane cross sections are assumed to remain plane. The bending moment is assumed to depend on the curvature according to a function that is obtained from the stress-strain curve of the material. The theory neglects both the lateral displacement of the cross sections against each other due to the shearing force and the rotary kinetic energy of the motion of the beam. The theory shows that a strain is not propagated along a beam at constant velocity, as in the case of longitudinal impact. The strain depends on the ratio between the square of the distance from the point of impact and the time. This is correct regardless of the shape of the moment - curvature curve. If certain approximations are applied to the bending moment - curvature curve, the theory provides a method of computing the deflection curve of a beam at any instant during impact. An experimental study has been made in which the deflection curves of long simply supported beams have been obtained during impact. The deflection characteristics of a cold-rolled steel and an annealed-copper beam have been computed by approximating the bending moment - curvature curves. It is shown that for materials such as cold-rolled low-carbon steel, for which plastic deflection is localized at the point of impact, the observed deflection curve is closely approximated by computing a curve based on the assumption that the beam remains elastic. For a soft material like annealed copper, plastic deformation extends over a relatively large distance from the point of impact and, taking plastic deformation into account, a satisfactory agreement is obtained between theory and experimental results.
Effect of Imperfections on Buckling of Thin Cylinders and Columns Under Axial Compression
Authors: Donnell L. H. , Wan C. C. 
Published: April 2021

Abstract
Von Kármán and Tsien have shown that under elastic conditions the resistance of perfect thin cylinders subjected to axial compression drops precipitously after buckling. It is considered that this indicates that this type of buckling is very sensitive to imperfections or disturbances. In this paper the effects of certain imperfections of shape (assumed to be equivalent to all the actual defects or disturbances combined) are studied by the large-deflection shell theory developed in a previous paper (2).
It is found that two types of buckling failure may occur. One is of a purely elastic type which occurs when the peak of the average stress versus average strain curve is reached, while the other type is precipitated by yielding, which for thicker cylinders or lower-yield material may occur before such a peak is reached. Curves are derived giving the dependence of each type of failure upon the dimensions and elastic and yield properties of the specimen and also upon an “unevenness factor” U which determines the magnitude of the initial imperfections and is assumed to depend on the method of fabrication. The relations derived are in line with test results, and similar studies of the buckling of struts indicate that the magnitude of the initial imperfections which have to be assumed to explain test strengths are reasonable.
A Quantitative Comparison of Flow and Deformation Theories of Plasticity
Authors: Hodge P. G. , White G. N. 
Published: April 2021

Abstract
The stresses and displacements in a partly plastic, infinitely long, hollow cylinder are obtained according to the flow type of stress-strain law of Prandtl-Reuss and to the deformation law of Hencky. In both cases the Mises yield condition is used and the compressibility of the material is taken into account. It is shown that under these assumptions the two theories yield substantially the same results for this particular problem, but that one theory or the other may be preferable for computing purposes in certain cases. The results are compared with those of other investigations in which different combinations of stress-strain law, yield condition, compressibility, and end loading were assumed.
An Investigation of Ejector Design by Analysis and Experiment
Authors: Keenan J. H. , Neumann E. P. , Lustwerk F. 
Published: April 2021

Abstract
A one-dimensional method of analysis of jet pumps or ejectors is presented. The analysis considers mixing of the primary and secondary streams at constant pressure, and mixing of the streams at constant area. For the analytical conditions considered, better performance can be obtained when constant-pressure mixing is employed. A comparison between experimental and analytical results shows good agreement over a broad range of variables. Some experimental data on the length of tube required for mixing of the two streams are presented. A method for jet-pump design is given.
Stability of Flow in a Rocket Motor
Authors: Gunder D. F. , Friant D. R. 
Published: April 2021

Abstract
This paper presents an analytical treatment leading to a criterion for the proper design of liquid rocket motors to insure freedom from the phenomenon of “chugging” without unnecessary increase in fuel-tank or fuel-pump pressures. The most successful of the several methods suggested here is that of Nyquist, which involves a simple conformal transformation. The analytical treatment presented in this paper has been applied successfully in practice to eliminate this type of instability.
Effect of Stress-Free Edges in Plane Shear of a Flat Body
Authors: Read W. T. 
Published: April 2021

Abstract
This paper determines the tangential stiffness of a flat rectangular body, or shear pad, with a uniform relative tangential displacement on the upper and lower surfaces. The state of stress differs from pure shear in that the edges are stress-free. The correction to the stiffness in pure shear is obtained as a function of Poisson’s ratio and the length-to-thickness ratio. The paper also illustrates the power of energy methods in furnishing accurate approximations with a small amount of numerical work when only over-all quantities, such as stiffness, are investigated. By manipulating energy relations and using the Prager-Synge approximate method a few hours of slide-rule computation was sufficient to determine both upper and lower bounds for the stiffness.
Vibrations of Elastic Systems Having Hereditary Characteristics
Authors: Volterra Enrico 
Published: April 2021

Abstract
Results of experiments carried out on plastics and rubberlike materials at high rate of straining are given. It is shown that the dynamic stress-strain (σ, ϵ) relationship for those materials can be expressed by the formula σ = f ( ϵ ) + ∫ 0 t ϕ ( t - τ ) d ϵ ( τ ) d τ d τ The first term represents the static stress-strain relationship, while the second depends on the rate of straining de dt . As a first approximation it is supposed that the materials follow Hooke’s law when statically stressed. Equation [1] then becomes σ = E ϵ + ∫ 0 t ϕ ( t - τ ) d ϵ ( τ ) d τ d τ Materials which follow the second equation are called materials with “hereditary characteristics.” Vibrations of single-degree-of-freedom systems having hereditary characteristics are considered. Methods of finding the hereditary function ϕ(t) from forced vibrations are given. Free and forced vibrations of simply supported beams having hereditary characteristics are studied.
Torsional Stress Concentration in Angle and Square Tube Fillets
Authors: Huth J. H. 
Published: April 2021

Abstract
This paper points out the wide variation in the results of previous investigations into the stress concentration at the fillets of angle sections subjected to uniform torsion. The relaxation method is applied and new results are given (not in agreement with previous results) for both angle sections and thin-walled square tube sections. These results are believed to be within about 4 per cent of the correct values, and they cover a complete range of fillets of all sizes. Also, the maximum shearing stress and torsional rigidity are given for a prismatical bar whose cross section is formed by a circular quadrant tangent to two sides of a square. It is pointed out that the stress concentration in angle sections with generous fillets may be lowered considerably by rounding off the outside corner in such a way as to keep the thickness of the section everywhere approximately constant.
Momentum and Mass Transfer in Coaxial Gas Jets
Authors: Forstall Walton , Shapiro Ascher H. 
Published: April 2021

Abstract
The mixing at constant pressure of a circular jet with an annular coaxial stream has been studied for conditions of nearly common density and temperature, but differing initial velocities. By using 10 per cent by volume of helium as a tracer in the inner stream, the mixing region was mapped with respect to both material and momentum transfer. It is concluded that material diffuses more rapidly than momentum; that the principal independent variable determining the shape of the mixing region is the velocity ratio of the streams; and that the integral method of Squire and Trouncer, using experimentally determined constants, is adequate for predicting approximate values of concentration and velocity in the mixing region of a jet flowing into a moving medium of the same density. Data for widely different experiments of various investigators show that the turbulent Prandtl and the Schmidt numbers are both within ±10 per cent of 0.70, independent of the nature of the experiment and the magnitudes of the laminar Prandtl and Schmidt numbers.
The Design of Resonant Quartz-Crystal Ultrasonic Transducers for Research Purposes
Authors: Swanson G. W. , Thomson W. T. 
Published: April 2021

Abstract
Ultrasonic waves have become an important research technique in many fields, including chemistry, mechanics, and others. Piezoelectric crystals excited by a source of alternating voltage are commonly used as a method of producing ultrasonic mechanical vibrations for such purposes. Hence it is often necessary that crystal transducers be designed, and to those unfamiliar with the theory of piezoelectricity, such a design problem may entail time-consuming research. The present paper is intended to co-ordinate the several approaches to the design problem and to present a practical method for designing quartz-crystal transducers for ultrasonic frequencies.
Optimization of the Nodalization of Nuclear System Thermal-Hydraulic Code Applied on Primary Loop Benchmark
Authors: Xu Hong , Badea Aurelian Florin , Cheng Xu 
Published: April 2021

Abstract
In best estimate plus uncertainty approach for thermal-hydraulic simulation in nuclear engineering, a crucial step for the qualification of the scenario simulation is the discretization, i.e., the nodalization of nuclear power plants and related integral test facilities (ITFs). Since intermediate break loss-of-coolant accident (IBLOCA) simulation is getting more and more attention in this decade, we focused on the nodalization of an IBLOCA scenario—a primary loop (PKL) I2.2 benchmark delivered by the organization for economic cooperation and development PKL4-project—using the analyses of thermal-hydraulics for leaks and transients (ATHLET) code. This work followed mainly the nodalization methodology of Petruzzi and D'Auria, including both qualitative and quantitative criteria, being divided into three phases for component volume, steady-state, and transient, respectively. The authors used also some specific approaches: (1) for component volume qualification, a volume fractional parameter was introduced, considering not only the relative error of each component but also the volume fraction in the whole system (an 0.2% acceptability level was chosen for this parameter); (2) the experimental data were not used directly as a reference within the nodalization procedure but the calculated results delivered by the most refined nodalization. Based on the estimator of average amplitude in the fast Fourier transform-based method (FFTBM), the convergence, rationality, and an optimized result of nodalization in the simulation of an actual IBLOCA transient benchmark have been judged. After three phases of nodalization qualification, it has been proved that the final nodalization has the necessary degree of convergence for a good reproduction of the benchmark geometry, allowing the proper simulation of involved phenomena. Finally, a middle-refined nodalization was found as being optimal, fulfilling the convergence criteria with a reasonable central processing unit time consumption. The nodalization scheme in this work was not seen as being the single factor influencing the simulated results, but just as a prerequisite to allow further reliable improvements on the models used by ATHLET (aspects not referred to in this particular study). Therefore, the simulated results presented here will match the experimental ones only as general trends; improvements may be further achieved by using new and more precise models (e.g., for critical mass flow, heat transfer, countercurrent flow, etc.) in the system thermal-hydraulic code.
Prediction of Structural Reliability Through an Alternative Variability-Based Methodology
Authors: Haas Kyle 
Published: April 2021

Abstract
The often-competing goals of optimization and reliability design amplify the importance of verification, validation, and uncertainty quantification (VVUQ) to achieve sufficient reliability. Evaluation of a system's reliability presents practical challenges given the large number of permutations of conditions that may exist over the system's operational lifecycle. Uncertainty and variability sources are not always well defined and are sometimes not possible to predict, yielding traditional uncertainty quantification (UQ) techniques insufficient. A variability-based method is proposed to bridge this gap in state-of-the-art UQ practice where sources of uncertainty and variability cannot be readily quantified. At the point of incipient structural failure, the structural response becomes highly variable and sensitive to minor perturbations in conditions. This characteristic provides a powerful opportunity to determine the critical failure conditions and to assess the resulting structural reliability through an alternative variability-based method. Nonhierarchical clustering, proximity analysis, and the use of stability indicators are combined to identify the loci of conditions that lead to a rapid evolution of the response toward a failure condition. The method's utility is demonstrated through its application to a simple nonlinear dynamic single-degree-of-freedom structural model. In addition to the L2 norm, a new stability indicator is proposed called the “instability index,” which is a function of both the L2 norm and the calculated proximity to adjacent loci of conditions with differing structural response. The instability index provides a rapidly achieved quantitative measure of the relative stability of the system for all possible loci of conditions.
Validity of Two Wheelchair-Mounted Devices for Estimating Wheelchair Speed and Distance Traveled
Authors: Karinharju Kati S. , Gomersall Sjaan R. , Clanchy Kelly M. , Trost Stewart G. , Yeo Li T. , Tweedy Sean M. 
Published: April 2021

This study evaluated the validity of two wheelchair-mounted devices—the Cateye® and Wheeler—for monitoring wheelchair speed and distance traveled. Speed estimates were validated against a calibrated treadmill at speeds from 1.5 to 10 km/hr. Twenty-five wheelchair users completed a course of known distance comprising a sequence of everyday wheelchair activities. Speed estimate validity was very good (mean absolute percentage error ≤ 5%) for the Wheeleri at all speeds and for the Cateye at speeds >3 km/hr but not speeds <3 km/hr (mean absolute percentage error > 20%). Wheeleri distance estimates were good (mean absolute percentage error < 10%) for linear pushing activities and general maneuvering but poor for confined-space maneuvering. Cateye estimates were good for continuous linear propulsion but poor for discontinuous pushing and maneuvering (both general and confined space). Both devices provided valid estimates of speed and distance for typical wheelchair-based exercise activities. However, the Wheeleri provided more accurate estimates of speed and distance during typical everyday wheelchair activities.
Postvolcanic Aerosols: Measurements of Altitude and Particle Sizes with Twilight-Sky Polarimetry
Authors: Ugolnikov O. S. , Maslov I. A. 
Published: April 2021

Abstract
The intensity and polarization of the twilight-sky background were measured during the epoch of “purple lights” after the Raikoke volcanic eruption in the summer of 2019. The increase in brightness paired with the decrease in polarization was registered, and the changes were especially noticeable in the dusk segment. The altitude distribution of aerosol particles and their mean size were found with previously developed techniques. The median radius of the lognormal distribution (0.11 μm) is typical of the background conditions or weak eruptions; however, the aerosols were mostly concentrated in the upper troposphere and near the tropopause rather than in the stratosphere. From comparison with satellite data obtained almost a decade ago after similar eruptions (like those of the Kasatochi volcano and others), it has been shown that the properties of their aerosols are similar, which confirms that the purple light phenomenon observed in 2019 was of volcanic origin.