Practical method of calculating the stability of the planar bending mode of metal beams in the elastoplastic region under the influence of a system of concentrated forces

1987 ◽  
Vol 19 (3) ◽  
pp. 397-403
Author(s):  
M. Kh. Mullagulov
Keyword(s):  
Practical Method ◽  
Bending Mode ◽  
Elastoplastic Region ◽  
Concentrated Forces ◽  
The Stability

Seismic stability analyses of reinforced tapered landfill cover systems considering seepage forces

2018 ◽  
Vol 36 (4) ◽  
pp. 361-372 ◽  
Author(s):  
Afshin Khoshand ◽  
Ali Fathi ◽  
Milad Zoghi ◽  
Hamidreza Kamalan
Keyword(s):  
Parametric Study ◽  
Limit Equilibrium ◽  
Practical Method ◽  
Seismic Stability ◽  
Design Parameters ◽  
Cover System ◽  
Landfill Cover ◽  
Cover Systems ◽  
Landfill Cover System ◽  
The Stability

One of the most common and economical methods for waste disposal is landfilling. The landfill cover system is one of the main components of landfills which prevents waste exposure to the environment by creating a barrier between the waste and the surrounding environment. The stability and integrity of the landfill cover system is a fundamental part of the design, construction, and maintenance of landfills. A reinforced tapered landfill cover system can be considered as a practical method for improving its stability; however, the simultaneous effects of seismic and seepage forces in the reinforced tapered landfill cover system have not been studied. The current paper provides a solution based on the limit equilibrium method in order to evaluate the stability of a reinforced tapered landfill cover system under seismic and seepage (both horizontal and parallel seepage force patterns) loading conditions. The proposed analytical approach is applied to different design cases through parametric study and the obtained results are compared to those derived from literature. Parametric study is performed to illustrate the sensitivity of the safety factor (FS) to the different design parameters. The obtained results reveal that parameters which describe the geometry have limited effects on the stability of the landfill cover system in comparison to the rest of the studied design parameters. Moreover, the comparisons between the derived results and available methods demonstrate good agreement between obtained findings with those reported in the literature.

Analysis of Tensile Stresses in Transfer Zone of Prestressed Concrete U-Beams

2005 ◽  
Vol 1928 (1) ◽  
pp. 134-141 ◽  
Author(s):  
Dongzhou Huang ◽  
Mohsen Shahawy
Keyword(s):  
Prestressed Concrete ◽  
Practical Method ◽  
Tensile Stresses ◽  
Prestressed Girders ◽  
Plate Elements ◽  
Mechanical Models ◽  
Concentrated Forces ◽  
Shell Plate ◽  
Finite Shell ◽  
Transfer Zone

Prestressed U-beam bridges compare favorably in cost and appearance to traditional concrete I-beam bridges. Consequently, U-beam bridges are gaining in popularity and usage, especially when aesthetic issues are deemed important. U-beam bridges first appeared in Florida in 2000; however, during construction, cracks developed in the webs of the U-beams. This paper presents results of an analysis of representative cracking of U-beams and proposes a practical method for the transfer zone stirrup design. For the purpose of the analysis, the U-beam is divided into a series of finite shell-plate elements, and the prestressing tendons are simulated as a number of concentrated forces. Two different mechanical models of the U-beams are developed on the basis of the stages of construction. Analytical results show that high tensile stresses occur in the end zone of the U-beam because of the prestressing tendons and that these tensile stress must be properly considered in bridge design. The research results are applicable to the design of prestressed U-beams and similar types of prestressed girders.

scholarly journals Buckling Analysis and Stability of Compressed Low-Carbon Steel Rods in the Elastoplastic Region of Materials

2019 ◽  
Vol 2019 ◽  
pp. 1-9
Author(s):  
Gaioz Partskhaladze ◽  
Ingusha Mshvenieradze ◽  
Elguja Medzmariashvili ◽  
Gocha Chavleshvili ◽  
Victor Yepes ◽  
...  
Keyword(s):  
Structural Reliability ◽  
Significant Risk ◽  
Stability Loss ◽  
Low Carbon ◽  
New Approaches ◽  
Critical Curves ◽  
Critical Stresses ◽  
Elastoplastic Region ◽  
The Stability

This paper presents new approaches for solving a problem of the stability of compressed rods in the elastoplastic working region of materials. It is known that the columns of buildings, supports of engineering devices, drill rods of oil, and gas extraction industry may be subjected to significant risk of stability loss. Nowadays, there are design methods based on test results defining the relations (e.g., critical stresses-slenderness) to avoid this risk due to stability loss, but the precision and limits of definition are not always known. The main objectives of the study were to develop new approaches that would allow specifying the values of critical stresses of compressed elements beyond the proportional limit. The problem of stability of the compressed elements in the elastoplastic region was studied according to the stability theory. The authors suggested an original approach to the issue; in particular, the determination of values of the critical stresses and the finding of the points of the bifurcation were carried out by the tangent established by experimental results and by the approximation of the so-called double modulus. Comparative analysis showed the advantage of the proposed approach, particularly that the new critical curves were located below the curves of Engesser-Karman and Shanley and above the critical curves established by building codes. A new approach for the determination of critical stresses in the elastoplastic region was developed through which the structural reliability and economic efficiency was increased by almost 12% compared to the existing approaches.

A Practical Method for Estimating Percent Body Fat of Adult Mentally Retarded Males

1987 ◽  
Vol 4 (2) ◽  
pp. 117-125 ◽  
Author(s):  
Luke E. Kelly ◽  
James H. Rimmer
Keyword(s):  
Body Fat ◽  
Standard Error ◽  
Mentally Retarded ◽  
Practical Method ◽  
Prediction Equation ◽  
Stepwise Multiple Regression ◽  
Percent Body Fat ◽  
Criterion Measure ◽  
The Stability ◽  
New Equation

The subjects were 170 moderately and severely mentally retarded men who were divided into two groups. The first group was used to formulate a new prediction equation and the second group was used to cross-validate and ascertain the stability of the derived equation. The prediction equation, employing waist and forearm circumferences, height and weight as predictors, and estimated percent body fat calculated by the generalized regression equation of Jackson and Pollock (1978) as the criterion measure, was formulated using a stepwise multiple regression analysis. A multiple R value of .86 was obtained for the derived equation with a standard error of estimate value of 3.35. The equation was cross-validated on the second sample to ascertain its stability. An r of .81 and a standard error of estimate of 4.41 was obtained between the subjects’ estimated percent body fat, using the new equation, and the criterion measure. This simplified equation provides practitioners with an accurate, reliable, and inexpensive method of estimating percent body fat for adult mentally retarded males.

The observation of the simultaneous development of a long- and a short-wave instability mode on a vortex pair

1994 ◽  
Vol 265 ◽  
pp. 289-302 ◽  
Author(s):  
P. J. Thomas ◽  
D. Auerbach
Keyword(s):  
Vortex Pair ◽  
Short Wave ◽  
Wave Mode ◽  
Core Diameter ◽  
Vortex Pairs ◽  
Long Wave ◽  
Instability Modes ◽  
Bending Mode ◽  
Theoretical Predictions ◽  
The Stability

Experiments on the stability of vortex pairs are described. The vortices (ratio of length to core diameter L/c of up to 300) were generated at the edge of a flat plate rotating about a horizontal axis in water. The vortex pairs were found to be unstable, displaying two distinct modes of instability. For the first time, as far as it is known to the authors, a long-wave as well as a short-wave mode of instability were observed to develop simultaneously on such a vortex pair. Experiments involving single vortices show that these do not develop any instability whatsoever. The wavelengths of the developing instability modes on the investigated vortex pairs are compared to theoretical predictions. Observed long wavelengths are in good agreement with the classic symmetric long-wave bending mode identified by Crow (1970). The developing short waves, on the other hand, appear to be less accurately described by the theoretical results predicted, for example, by Windnall, Bliss & Tsai (1974).

The Effect of Dynamical Parameters on Precession in Rotary Drilling

2001 ◽  
Vol 123 (3) ◽  
pp. 181-186 ◽  
Author(s):  
A. The´ron ◽  
E. de Langre ◽  
C. Putot
Keyword(s):  
Closed Form ◽  
Circular Hole ◽  
Rotating Disk ◽  
Rolling Motion ◽  
Rotary Drilling ◽  
Bending Mode ◽  
Dynamical Parameters ◽  
The Stability ◽  
Stiffness And Damping ◽  
Opposing Effect

Precession, which is the rolling motion of the drillstring on the walls of the borehole, is investigated by considering the various possible motions of a rotating disk in a circular hole. Due to the simplicity of the model, closed-form results are derived on the stability of precession and on the evolution of impacting motions towards precession. It is found that increasing coefficients of friction and contact damping have a favoring effect on precession, while the stiffness and damping of the drillstring bending mode have an opposing effect.

A Numerical Study of Flutter in a Transonic Fan

1997 ◽  
Author(s):  
Kousuke Isomura ◽  
Michael B. Giles
Keyword(s):  
Cfd Simulation ◽  
Numerical Study ◽  
Point Model ◽  
Blade Vibration ◽  
Blade Loading ◽  
Pressure Surface ◽  
Dominant Component ◽  
Bending Mode ◽  
The Stability ◽  
Transonic Fan

The bending mode flutter of a modern transonic fan has been studied using a quasi-3D viscous unsteady CFD code. The type of flutter in this research is that of a highly loaded blade with a tip relative Mach number just above unity, commonly referred to as transonic stall flutter. This type of flutter is often encountered in modern wide chord fans without a part span shroud. The CFD simulation uses an upwinding scheme with Roe’s 3rd-order flux differencing, and Johnson and King’s turbulence model with the later modification due to Johnson and Coakley. A dynamic transition point model is developed using the en method and Schubauer and Klebanoff’s experimental data. The calculations of the flow in this fan reveal that the source of the flutter of IHI transonic fan is an oscillation of the passage shock, rather than a stall. As the blade loading increases, the passage shock moves forward. Just before the passage shock unstarts, the stability of the passage shock decreases, and a small blade vibration causes the shock to oscillate with a large amplitude between unstarted and started positions. The dominant component of the blade excitation force is due to the foot of the oscillating passage shock on the blade pressure surface.

Rotordynamic Evaluation of Centrifugal Compressor Using Electromagnetic Exciter

2011 ◽  
Author(s):  
Naohiko Takahashi ◽  
Yohei Magara ◽  
Mitsuhiro Narita ◽  
Haruo Miura
Keyword(s):  
High Pressure ◽  
Frequency Response ◽  
Damping Ratio ◽  
Practical Method ◽  
Magnetic Bearing ◽  
Response Functions ◽  
Mathematical Operation ◽  
Frequency Response Functions ◽  
Calculation Results ◽  
The Stability

Since heavier gases exert larger effects on rotordynamic stability, stability evaluation is important in developing or designing high-pressure compressors. To evaluate the rotor stability during operation, an excitation test using a magnetic bearing is the most practical method. In stability analysis, labyrinth seals can produce significant cross-coupling forces, which particularly reduce the damping ratio of the first forward mode. Therefore, forward modes should be distinguished from backward modes in the excitation test. One method that excites only the forward modes, not the backward modes (and vice versa), is the use of a rotating excitation. In this method, the force is simultaneously applied to two axes to excite the rotor in circular orbits. Two trigonometric functions, i.e., cosine and sine functions, are used to generate this rotation force. Another method is the use of a unidirectional excitation and a mathematical operation to distinguish the forward whirl from the backward whirl. In this method, a directional frequency response function that separates the two modes in the frequency domain is obtained from four frequency response functions by using a complex number expression for the rotor motion. In this study, the latter method was employed to evaluate the rotor stability of a high-pressure compressor. To obtain the frequencies and damping ratios of the eigenvalues, the curve fitting based on system identification methods, such as the prediction error method, was introduced for the derived frequency response functions. Firstly, these methods were applied to a base evaluation under a low-pressure gas operation, in which the stability mainly depends on the bearing property. Using the obtained results, the bearing coefficients were estimated. Next, the same methods were applied to stability evaluations under high-pressure gas operations. The destabilizing forces were also estimated from the test results and compared with the calculation results.

Vibration Control of a Turbo Molecular Pump Suspended by Active Magnetic Bearings

2011 ◽  
Author(s):  
Kai Zhang ◽  
Jinping Dong ◽  
Xingjian Dai ◽  
Xiaozhang Zhang
Keyword(s):  
Controller Design ◽  
Magnetic Bearings ◽  
Control Algorithms ◽  
Active Magnetic Bearings ◽  
Bending Mode ◽  
High Rotation Speed ◽  
Structure Vibration ◽  
The Stability ◽  
Bending Modes ◽  
Gyroscopic Effects

In a turbo molecular pump suspended by active magnetic bearings (AMBs), vibration caused by the rotor’s bending modes, gyroscopic effects and structure vibration modes influenced the pump performance and even cause instability. Different methods were used to deal with these problems. A Cross Feedback method was effective in restraining the nutation and precession of the rotor. A Phase Shaping method provided sufficient damping for the 1st bending mode of the rotor. The structure vibration instability was avoided by adjusting the joint strength between two parts of the pump housing. The gyroscopic effects also destroyed the stability of unbalance control algorithms for the AMBs at a high rotation speed. It was shown that, to ensure the stability of the controller when the unbalance control algorithms were applied, the 1st bending frequency of the rotor should be increased. Experiment results concerning the problems discussed above were provided. With a suitable controller design and an appropriate consideration of the dynamic problems, the rotor was successfully accelerated to 27 000 rpm.

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