On One Imperfection Estimation Method for Thin Shell Buckling in the Design Code RCC-MR

2019 ◽  
Vol 5 (4) ◽  
Author(s):  
Ashok Kumar ◽  
Anindya Chatterjee
Keyword(s):  
Thin Shell ◽  
Estimation Method ◽  
External Pressure ◽  
Alternative Methods ◽  
Design Code ◽  
Linear Elastic ◽  
The Third ◽  
Quantification Method ◽  
Shell Buckling ◽  
Shell Design

The thin shell design code RCC-MR is used for sodium-cooled fast breeder reactor components operating at high temperatures. Thin shells from such applications can be designed using linear elastic buckling analysis, following procedures given in RCC-MR. For human safety, such procedures can and should be examined by the broader scientific community. Among such procedures, RCC-MR provides three alternative methods to quantify an imperfection value; and that value is used in subsequent calculations to determine safe loads. Of these methods, the third seems potentially nonconservative for some situations. Here, we examine that third method using detailed numerical examples. These examples, found by trial and error, are the main contribution of this paper. The first example is a nonuniform cylindrical shell closed with a spherical endcap under external pressure. The second is a cylinder with an ellipsoidal head under internal pressure. The third is an L-shaped pipe with an end load. In all three cases, the new computed imperfection quantity is found to be surprisingly small compared to the actual value used for computations (e.g., 25 times smaller), and in two cases, the result is insensitive to the actual imperfection. We explain how the three examples “trick” the imperfection quantification method in three different ways. We suggest that this imperfection quantification method in RCC-MR should be re-examined. The primary value of our paper lies not in new mechanics, but in identifying unexpected ways in which a particular step in shell design using RCC-MR could be potentially nonconservative.

scholarly journals The thickness functions of the shells of revolution subjected to axisymmetrical loads

2005 ◽  
Vol 27 (2) ◽  
pp. 66-73
Author(s):  
Ngo Huong Nhu ◽  
Pham Hong Nga
Keyword(s):  
Differential Equations ◽  
Thin Shell ◽  
Numerical Solutions ◽  
External Pressure ◽  
Shells Of Revolution ◽  
Varying Thickness ◽  
Shell Design ◽  
Mathematical Difficulties ◽  
Thickness Function

The inverse problems for determining the meridian shape or varying thickness function of momentless shells of revolution under given loads were concerned in many works [2, 3, 4]. However, for the complexity of loads or configuration of a shell these problems haven' t bee.n solved perfectly because of its mathematical difficulties. In this paper, the problem for determining the thickness function of shells of revolution such as a parabola, sphere arc! under axisymmetrical loads is considered. The general integro-differential equations for determination of the meridian form and shell thickness are obtained. A solution of differential equations by semi-analytical and numerical methods for the thickness is presented. The numerical solutions are given for the parabola under external pressure, the sphere immerged in the fluid and the sphere arc. Obtained results may be used in the thin shell design.

A Nondestructive Differential-Pressure Test for Thin Shells

1953 ◽  
Vol 20 (1) ◽  
pp. 48-52
Author(s):  
J. C. New
Keyword(s):  
Thin Shell ◽  
Salient Feature ◽  
External Pressure ◽  
Differential Pressure ◽  
Thin Shells ◽  
Pressure Test ◽  
Shell Design ◽  
Mechanical Factors ◽  
The Difference ◽  
Internal Volume

Abstract The differential-pressure test is an original, nondestructive, experimental technique for determining incipient buckling pressures of thin shells subjected to external pressure. Extensions of the basic test permit study of many buckling parameters as well as other mechanical factors in thin-shell design and evaluation. The salient feature of the technique is the filling of the internal volume of the shell with a compressible fluid, such as water, to control the magnitude and rate of shell deformation. The incipient buckling pressure is detected by noting the point at which the difference in internal and external pressure becomes constant. Experimental verification of the technique and its nondestructive aspect is presented. Applications and limitations of the test are discussed.

Unequivocally Nonconservative Results From One Method of Imperfection Quantification in RCC-MR

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Ashok Kumar ◽  
Anindya Chatterjee
Keyword(s):  
External Pressure ◽  
Thin Shells ◽  
Geometrically Nonlinear ◽  
Nonlinear Simulation ◽  
The Third ◽  
Quantification Method ◽  
Post Buckling ◽  
Specific Shape ◽  
Large Material ◽  
Safe Load

Abstract Design against buckling of thin shells at high temperatures often follows the code RCC-MR. RCC-MR allows three methods to quantify shell imperfections for use in safe load calculations, where lower imperfection values raise the safe load estimates. In recent work, we showed that the third of these methods can sometimes yield remarkably low imperfection values, leading to potentially nonconservative designs, but nonconservatism of the method was not proved. Here, we prove nonconservatism in two designs based on the third method. Proving such nonconservatism is difficult using experiments or with large material nonlinearity in simulations. We first discuss these difficulties to motivate our approach. We then present two examples: a spherical shell and a torispherical shell, both under external pressure. The shell walls are thin enough so that plasticity is not encountered before structural collapse. For specific shape imperfections, we show with geometrically nonlinear, purely elastic, highly refined, post-buckling analysis using abaqus that the physical loads at which the imperfect shells collapse are overpredicted via RCC-MR's third method by factors of about 8/7 and 11/10, respectively. We emphasize that code-based design using nonlinear simulation prescribes a further safety factor of 2.5, which we have denied ourselves here in order to give the third method the benefit of doubt. We conclude that the third imperfection quantification method in RCC-MR should be reexamined.

scholarly journals Estimating Time: Comparing the Accuracy of Estimation Methods for Interval Timing

2019 ◽  
Author(s):  
Atser Damsma ◽  
Nadine Schlichting ◽  
Hedderik van Rijn ◽  
Warrick Roseboom
Keyword(s):  
Estimation Method ◽  
Interval Estimation ◽  
Reaction Times ◽  
Interval Timing ◽  
Alternative Methods ◽  
Estimation Methods ◽  
Complex Task ◽  
Target Onset ◽  
Spatial Estimation ◽  
Verbal Estimation

In interval timing experiments, motor reproduction is the predominant method used when participants are asked to estimate an interval. However, it is unknown how its accuracy, precision and efficiency compare to alternative methods, such as indicating the duration by spatial estimation on a timeline. In two experiments, we compared different interval estimation methods. In the first experiment, participants were asked to reproduce an interval by means of motor reproduction, timeline estimation, or verbal estimation. We found that, on average, verbal estimates were more accurate and precise than line estimates and motor reproductions. However, we found a bias towards familiar whole second units when giving verbal estimates. Motor reproductions were more precise, but not more accurate than timeline estimates. In the second experiment, we used a more complex task: Participants were presented a stream of digits and one target letters and were subsequently asked to reproduce both the interval to target onset and the duration of the total stream by means of motor reproduction and timeline estimation. We found that motor reproductions were more accurate, but not more precise than timeline estimates. In both experiments, timeline estimates had the lowest reaction times. Overall, our results suggest that the transformation of time into space has only a relatively minor cost. In addition, they show that each estimation method comes with its own advantages, and that the choice of estimation method depends on choices in the experimental design: for example, when using durations with integer durations verbal estimates are superior, yet when testing long durations, motor reproductions are time intensive making timeline estimates a more sensible choice.

Clamped torispherical shells under external pressure — some new results

1988 ◽  
Vol 23 (1) ◽  
pp. 9-24 ◽  
Author(s):  
J Blachut ◽  
G D Galletly
Keyword(s):  
Failure Mode ◽  
External Pressure ◽  
Spherical Cap ◽  
Geometric Imperfections ◽  
Collapse Pressure ◽  
Modes Of Failure ◽  
Shell Buckling ◽  
Bifurcation Buckling ◽  
Initial Geometric Imperfections ◽  
The One

Perfect clamped torispherical shells subjected to external pressure are analysed in the paper using the BOSOR 5 shell buckling program. Various values of the knuckle radius-to-diameter ratio ( r/D) and the spherical cap radius-to-thickness ratio ( Rs/ t) were studied, as well as four values of σyp, the yield point of the material. Buckling/collapse pressures, modes of failure and the development of plastic zones in the shell wall were determined. A simple diagram is presented which enables the failure mode in these shells to be predicted. The collapse pressures, pc, were also plotted against the parameter Λs (√( pyp/ pcr)). When the controlling failure mode was axisymmetric yielding in the knuckle, the collapse pressure curves depended on the value of σyp, which is unusual. However, when the controlling failure mode was bifurcation buckling (at the crown/knuckle junction), the collapse pressure curves for the various values of σyp all merged, i.e., they were independent of σyp. This latter situation is the one which normally occurs with the buckling of cylindrical and hemispherical shells. A limited investigation was also made into the effects of axisymmetric initial geometric imperfections on the strength of externally-pressurised torispherical shells. When the failure mode was axisymmetric yielding in the knuckle, initial imperfections of moderate size did not affect the collapse pressures. In the cases where bifurcation buckling at the crown/knuckle junction occurred, small initial geometric imperfections at the apex did not affect the buckling pressure, but axisymmetric imperfections at the buckle location did influence it. With the other failure mode (i.e., axisymmetric yielding collapse at the crown of the shell), initial geometric imperfections caused a reduction in the torisphere's strength.

Voice disorders after total thyroidectomy: Prospective patient self-assessment in comparison with traditional and alternative methods of examining the vocal folds

2020 ◽  
Author(s):  
Alexander Shulutko ◽  
Vasiliy Semikov ◽  
Andrey Moiseev ◽  
Elkhan Osmanov ◽  
Yulia Boblak ◽  
...  
Keyword(s):  
Total Thyroidectomy ◽  
Vocal Folds ◽  
Indirect Laryngoscopy ◽  
Alternative Methods ◽  
Original Form ◽  
Self Assessment ◽  
The Third ◽  
The Mean ◽  
The Voice ◽  
Patient Self Assessment

Abstract Background Voice alterations after thyroidectomy with mobile vocal folds are common. Ultrasonography has been used to assess the mobility of the vocal folds after thyroidectomy. Methods 54 patients underwent thyroidectomy. Indirect laryngoscopy, ultrasonography and GRBAS scoring were performed preoperatively,3 days, 2 and 6 months postoperatively. Results On the third postoperative day, the mobility of the vocal folds was preserved in 52 patients and paresis were recorded in 2 patients. All patients after total thyroidectomy noted the presence of voice alteration in the absence of the postoperative paresis of the vocal folds. On the third postoperative day, the voice was impaired by all criteria of the GRBAS scale, but mainly due to roughness (85%). Sixth month postoperatively 62% of the subjects considered the voice to be altered. Asthenia was observed in 39%. On the third postoperative day indirect laryngoscopy revealed the unchanged vocal folds, the symmetrical edema and the shortening of one of the vocal folds in 56%,42% and 1.9%. Six months postoperatively, the vocal folds returned to their original form. Ultrasonography was well correlated to the results of indirect laryngoscopy. Patients with edema of the vocal folds had a significantly higher mean GRBAS grade than patients without edema. The mean GRBAS score decreased from 3.36 to 0.90, 3 days and 6 months postoperatively. Conclusion Voice alteration after total thyroidectomy is always present. Postoperative edema represents a likely main cause of voice alteration and resolves within 6 months. Ultrasonography is recommended as alternative to indirect laryngoscopy in assessing of the vocal folds in thyroid surgery patients.

scholarly journals Isotropic Gravastar Model in Rastall Gravity

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
G. Abbas ◽  
K. Majeed
Keyword(s):  
Black Hole ◽  
Event Horizon ◽  
Analytical Solutions ◽  
Thin Shell ◽  
Graphical Analysis ◽  
Stiff Fluid ◽  
Matter Distribution ◽  
The Third ◽  
Schwarzschild Geometry ◽  
Third Phase

In the present paper, we have introduced a new model of gravastar with an isotropic matter distribution in Rastall gravity by the Mazur–Mottola (2004) mechanism. Mazur–Mottola approach is about the construction of gravastar which is predicted as an alternative to black hole. By following this convention, we define gravastar in the form of three phases. The first one is an interior phase which has negative density; the second part consists of thin shell comprising ultrarelativistic stiff fluid for which we have discussed the length, energy, and entropy. By the graphical analysis of entropy, we have shown that our proposed thin shell gravastar model is potentially stable. The third phase of gravastar is defined by the exterior Schwarzschild geometry. For the interior of gravastar, we have found the analytical solutions free from any singularity and the event horizon in the framework of Rastall gravity.

The linear elastic in-plane bending of curved hollow profiles having a thin-walled rectangular section

1992 ◽  
Vol 27 (3) ◽  
pp. 145-149 ◽  
Author(s):  
F J M Q De Melo ◽  
M A P Vaz
Keyword(s):  
Cross Section ◽  
Thin Shell ◽  
Transverse Section ◽  
Accurate Solution ◽  
Rectangular Section ◽  
Element Analysis ◽  
Linear Elastic ◽  
Graphical Result ◽  
Thin Walled ◽  
Shell Finite Element

This paper presents a simple solution for the flexibility calculation of curved profiles having a rectangular thin-walled cross-section. Some assumptions related to geometric details about the shape of the deformed structure are included in the present analysis, aiming at an economic and accurate solution. Results concerning the distortion of the transverse section are compared with the corresponding data from the solution with a thin shell finite element analysis. A flexibility factor for the structure analysed here is presented as a graphical result.

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