A 4-node assumed-stress hybrid shell element with rotational degrees of freedom

An assumed-stress hybrid/mixed 4-node quadrilateral shell element is introduced that alleviates most of the deficiencies associated with such elements. The formulation of the element is based on the assumed-stress hybrid/mixed method using the Hellinger-Reissner variational principle. The membrane part of the element has 12 degrees of freedom including rotational or drilling degrees of freedom at the nodes. The bending part of the element also has 12 degrees of freedom. The bending part of the element uses the Reissner-Mindlin plate theory which takes into account the transverse shear contributions. The element formulation is derived from an 8-node isoparametric element. This process is accomplished by assuming quadratic variations for both in-plane and out-of-plane displacement fields and linear variations for both in-plane and out-of-plane rotation fields along the edges of the element. In addition, the degrees of freedom at midside nodes are approximated in terms of the degrees of freedom at corner nodes. During this process the rotational degrees of freedom at the corner nodes enter into the formulation of the element. The stress field are expressed in the element natural-coordinate system such that the element remains invariant with respect to node numbering

Direct formulation of a 4-node hybrid shell element with rotational degrees of freedom

A simple 4-node assumed-stress hybrid quadrilateral shell element with rotational or drilling degrees of freedom is formulated. The element formulation is based directly on a 4-node element. This direct formulation requires fewer computations than a similar element that is derived from an internal 8-node isoparametric element in which the midside degrees of freedom are eliminated in favor of rotational degree of freedom at the corner nodes. The formulation is based on the principle of minimum complementary energy. The membrane part of the element has 12 degrees of freedom including rotational degrees of freedom. The bending part of the element also has 12 degrees of freedom. The bending part of the quadratic variations for both in-plane and out-of-plane displacement fields and linear variations for both in-plane and out-of-plane rotation fields are assumed along the edges of the element. The element Cartesian-coordinate system is chosen such as to make the stress field invariant with respect to node numbering. The membrane part of the stress field is based on a 9-parameter equilibrating stress field, while the bending part is based on a 13-parameter equilibrating stress field. The element passes the patch test, is nearly insensitive to mesh distortion, does not lock, possesses the desirable invariance properties, has no spurious modes, and produces accurate and reliable results

Multiple methods integration for structural mechanics analysis and design

A new research area of multiple methods integration is proposed for joining diverse methods of structural mechanics analysis which interact with one another. Three categories of multiple methods are defined: those in which a physical interface are well defined; those in which a physical interface is not well-defined, but selected; and those in which the interface is a mathematical transformation. Two fundamental integration procedures are presented that can be extended to integrate various methods (e.g., finite elements, Rayleigh Ritz, Galerkin, and integral methods) with one another. Since the finite element method will likely be the major method to be integrated, its enhanced robustness under element distortion is also examined and a new robust shell element is demonstrated

Friedel oscillations responsible for stacking fault of adatoms: The case of Mg(0001) and Be(0001)

We perform a first-principles study of Mg adatom and adislands on the Mg(0001) surface, and Be adatom on Be(0001), to obtain further insights into the previously reported energetic preference of the fcc faulty stacking of Mg monomers on Mg(0001). We first provide a viewpoint on how Friedel oscillations influence ionic relaxation on these surfaces. Our three-dimensional charge-density analysis demonstrates that Friedel oscillations have maxima which are more spatially localized than what one-dimensional average density or two-dimensional cross sectional plots could possibly inform: The well-known charge-density enhancement around the topmost surface layer of Mg(0001) is strongly localized at its fcc hollow sites. The charge accumulation at this site explains the energetically preferred stacking fault of the Mg monomer, dimer and trimer. Yet, larger islands prefer the normal hcp stacking. Surprisingly, the mechanism by which the fcc site becomes energetically more favorable is not that of enhancing the surface-adatom bonds but rather those between surface atoms. To confirm our conclusions, we analyze the stacking of Be adatom on Be(0001) - a surface also largely influenced by Friedel oscillations. We find, in fact, a much stronger effect: The charge enhancement at the fcc site is even larger and, consequently, the stacking-fault energy favoring the fcc site is quite large, 44 meV.Comment: Submitted to Physical Review

Convergence of strain energy release rate components for edge-delaminated composite laminates

Strain energy release rates for edge delaminated composite laminates were obtained using quasi 3 dimensional finite element analysis. The problem of edge delamination at the -35/90 interfaces of an 8-ply composite laminate subjected to uniform axial strain was studied. The individual components of the strain energy release rates did not show convergence as the delamination tip elements were made smaller. In contrast, the total strain energy release rate converged and remained unchanged as the delamination tip elements were made smaller and agreed with that calculated using a classical laminated plate theory. The studies of the near field solutions for a delamination at an interface between two dissimilar isotropic or orthotropic plates showed that the imaginary part of the singularity is the cause of the nonconvergent behavior of the individual components. To evaluate the accuracy of the results, an 8-ply laminate with the delamination modeled in a thin resin layer, that exists between the -35 and 90 plies, was analyzed. Because the delamination exists in a homogeneous isotropic material, the oscillatory component of the singularity vanishes

Large-scale structural analysis: The structural analyst, the CSM Testbed and the NAS System

The Computational Structural Mechanics (CSM) activity is developing advanced structural analysis and computational methods that exploit high-performance computers. Methods are developed in the framework of the CSM testbed software system and applied to representative complex structural analysis problems from the aerospace industry. An overview of the CSM testbed methods development environment is presented and some numerical methods developed on a CRAY-2 are described. Selected application studies performed on the NAS CRAY-2 are also summarized

Reexamining the Seventh Amendment Argument Against Issue Certification

Issue certification does not run afoul of the Seventh Amendment because of the constitutional doctrines of standing and ripeness. Part II(A) and II(B) examines FRCP 23 and the history of class actions and issue certifications. Next, Part II(C) analyzes Rhone Poulenc and its Seventh Amendment analysis. Part III(A) argues that ripeness and standing undermine Seventh Amendment arguments concerning reexamination. First, as to ripeness, the reexamination argument relies on a series of speculations: that the class plaintiffs will prevail on the trial of the common issues; and that a second jury would—contrary to legal presumptions — ignore the trial judge’s instructions, and then reexamine some part of the class decision. These multiple suppositions should not preclude issue classes. Second, even if the matter becomes ripe, the defendant will still lack standing: it is only when the issue-class plaintiff prevails on the first round that a second jury could exist. If the second jury spurns the trial court’s instructions by revisiting issues decided in the first trial, that reexamination would likely redound to the defendant’s benefit, diminishing in some manner the common issue finding favoring the class plaintiffs. Thus, the defendants would lack standing to advance a Seventh Amendment claim because the defendants would suffer no harm. Finally, Part III(B) notes that the class plaintiffs—the likely potential victims of any jury reexamination—can avoid a Seventh Amendment complaint by voluntarily and knowingly waiving violations, just as American citizens can for any of their constitutional rights

Changes of the body weight, fat mass and aerobic capacity and energy intake, following the skipped meal in young women

زمینه و هدف: یکی از روش های معمول کنترل وزن بویژه در بین زنان جوان محدودیت دسترسی غذایی است. این مطالعه با هدف بررسی تغییرات وزن بدن و سایر شاخص های فیزیولوژیک از جمله نمایه توده بدن (BMI)، توده چربی (Fat mass) و ظرفیت هوازی (VO2 max) در زنان جوان به دنبال حذف یک وعده اصلی غذایی روزانه انجام شد. روش بررسی: طی یک مطالعه نیمه تجربی 40 دانشجوی دختر داوطلب به صورت در دسترس از دانشکده علوم تغذیه و صنایع غذایی دانشگاه علوم پزشکی شهید بهشتی وارد مطالعه شدند. وزن و قد توده چربی، ظرفیت هوازی (VO2 max) و انرژی دریافتی در شروع (شرایط معمولی) و پس از چهار هفته (محدودیت دریافت باحذف یک وعده غذایی) اندازه گیری شد. از نرم افزار تغذیه ای NutritionIII برای آنالیز یادآمد خوراک استفاده شد. نتایج بدست آمده از طریق آزمون t زوج مقایسه گردید. یافته ها: به ترتیب در شروع وچهار هفته بعد میانگین وزن 5/8±4/57 و 4/8±3/57 کیلوگرم، میانگین نمایه توده بدنی 4/2±9/21 و 3/2±8/21 کیلوگرم بر متر مربع، میانگین ضخامت چربی 6/5±3/20 و 2/5±8/19 میلی لیتر و ظرفیت هوازی (VO2 max) 0/8±6/52 و 7/8±3/52 میلی لیتر به کیلوگرم بر دقیقه بود (05/0P>). همچنین میانگین دریافت انرژی در قبل و یک ماه بعد به ترتیب 319±1973 و 443±1951 کیلوکالری در روز بود (05/0P>). نتیجه گیری: حذف یک وعده غذایی اصلی روزانه با کم نشدن میزان انرژی دریافتی تاثیری بر کنترل وزن نداشته و به نظر می رسد افراد مورد بررسی با ایجاد تعادل بین دریافت و مصرف انرژی در برابر محدودیت دسترسی به غذا، تطابق فیزیولوژیکی برقرار کرده اند. پایش مستمر دریافت غذا و دریافت انرژی برای کنترل و ثبات وزن بدن ضروری به نظر می رسد. 27

Webometric analysis of Iranian universities of medical sciences

There are many researches have been conducted on webometrics, especially the impacts of websites on each other and the web impact factor. However, there are few studies focusing on the websites of Iranian universities. This study analyzed the websites of Iranian universities of medical sciences according to the webometric indicators. In a cross-sectional study, the number of web pages, inlinks, external inlinks and also the overall and absolute web impact factors for Iranian universities of medical sciences with active exclusive websites were calculated and compared using AltaVista search engine. Finally, the websites were ranked based on these webometric indicators. The results showed that the website of Tehran university of medical sciences with 49,300 web pages and 9860 inlinks was ranked first for the size and number of inlinks, while its impact factor was ranked 38th. Rafsanjan UMS with 15 web pages and 211 links had the highest rank for the web impact factor among Iranian universities of medical sciences. The study revealed that Iranian universities of medical sciences did not have much impact on the web and were not well known internationally. The major reason relies on linguistic barriers. Some of them also suffer from technical problems in their web design. © 2009 Akadémiai Kiadó, Budapest, Hungary