Albert A. Groenwold and Nielen Stander
A 4‐node flat shell quadrilateral finiteelement with 6 degrees of freedom per node, denoted QC5D‐SA, ispresented. The element is an assembly of a modification of thedrilling…
Abstract
A 4‐node flat shell quadrilateral finite element with 6 degrees of freedom per node, denoted QC5D‐SA, is presented. The element is an assembly of a modification of the drilling degree of freedom membrane presented by Ibrahimbegovic et al., and the assumed strain plate element presented by Bathe and Dvorkin. The part of the stiffness matrix associated with in—plane displacements and rotations is integrated over the element domain by a modified 5‐point reduced integration scheme, resulting in greater efficiency without the sacrifice of rank sufficiency. The scheme produces a soft higher order deformation mode which increases numerical accuracy. A large number of standard benchmark problems are analyzed. Some examples show that the effectiveness of a previously proposed “membrane locking correction” technique is significantly reduced when employing distorted elements. However, the element is shown to be generally accurate and in many cases superior to existing elements.
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Fiona Yu, Alana Cavadino, Lisa Mackay, Kim Ward, Anna King and Melody Smith
Limited evidence exists regarding a group of nurses' physical activity patterns and association with resilience. Less is known about the physical activity health paradox in nurses…
Abstract
Purpose
Limited evidence exists regarding a group of nurses' physical activity patterns and association with resilience. Less is known about the physical activity health paradox in nurses (the positive health effects of leisure time physical activity vs the negative health effects of occupational physical activity). This study aimed to explore the profiles of intensive care nurses' physical activity behaviours and associations with resilience, following a developed study-specific job demands–recovery framework.
Design/methodology/approach
A cross-sectional study was conducted with intensive care unit (ICU) nurses to explore their physical activity profiles and associations with resilience. The Connor-Davidson Resilience Scale 25 (CD-RISC 25) was used to assess resilience, and accelerometry was utilised to record participants' four-day activity (two workdays, two non-workdays). Hierarchical cluster analysis was employed to define groups of nurses by activity behaviours.
Findings
Participants (N = 93) were classified as low actives (n = 19), standers (n = 36), sitters (n = 31) and movers (n = 7). During two 12-h shifts, movers had the highest mean level of dynamic standing and the lowest mean level of sitting. During two non-workdays, movers had the highest mean level of walking as well as the lowest mean level of sitting and sleep time.
Originality/value
The uniqueness of this study was that it analysed ICU nurses' physical activity profiles and associations with resilience using identified clusters. However, the small number of participants limited this study's ability to determine significant relationships between resilience and the grouped physical activity profiles.
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Nielen Stander and Edward L. Wilson
An assessment is made of a 4‐node quadrilateral membrane element with one rotational and two translational degrees of freedom per node, as formulated by Taylor and Simo. The…
Abstract
An assessment is made of a 4‐node quadrilateral membrane element with one rotational and two translational degrees of freedom per node, as formulated by Taylor and Simo. The element, QC9, is formed by degeneration of the 9‐node Lagrange element and condensation of the centre degrees of freedom. An 8‐point, modified reduced integration scheme is implemented in this element, QC9(8), to improve on the 3 × 3 quadrature performance, yet avoid the additional rank deficiency due to reduced integration (2 × 2). QC9(8) performs as good or better than all elements surveyed. It is shown that a similar degeneration of the 16‐node Lagrangian element can be carried out, but that the resulting element fails the patch test.
W.J. Roux, R.J. du Preez and N. Stander
A general approach for the construction of global approximations to structural behaviour using response surface methodology is presented. The computation and use of these…
Abstract
A general approach for the construction of global approximations to structural behaviour using response surface methodology is presented. The computation and use of these approximations are demonstrated using a semi‐solid tyre example. The use of these global approximations to the responses made it viable to utilise the capabilities of non‐linear analysis software in design optimisation. The insight gained from a preliminary low fidelity model was utilized in a two‐stage approach to achieve the maximum benefit from a more expensive high fidelity model. The resulting high‐accuracy approximations greatly reduced the cost of subsequent design calculations such as multidisciplinary and discrete optimisation.
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Nielen Stander, Anton Matzenmiller and Ekkehard Ramm
A critical assessment of the 4‐node assumed strain element as proposed by Dvorkin and Bathe is made. The element performed excellently in all investigated shell problems which…
Abstract
A critical assessment of the 4‐node assumed strain element as proposed by Dvorkin and Bathe is made. The element performed excellently in all investigated shell problems which sometimes caused difficulties for other assumed strain techniques. For efficient computation in the non‐linear range, linearization of the virtual work equation is done to yield the consistent tangent stiffness. The shell formulation is done for stress and strain tensors based on local element coordinates. To demonstrate the effectiveness and rapid convergence of the non‐linear formulation, three examples are tested for large displacements.
This paper evaluates a Successive Response Surface Method (SRSM) specifically developed for simulation‐based design optimization, e.g. that of explicit nonlinear dynamics in…
Abstract
This paper evaluates a Successive Response Surface Method (SRSM) specifically developed for simulation‐based design optimization, e.g. that of explicit nonlinear dynamics in crashworthiness design. Linear response surfaces are constructed in a subregion of the design space using a design of experiments approach with a D‐optimal experimental design. To converge to an optimum, a domain reduction scheme is utilized. The scheme requires only one user‐defined parameter, namely the size of the initial subregion. During optimization, the size of this region is adapted using a move reversal criterion to counter oscillation and a move distance criterion to gauge accuracy. To test its robustness, the results using the method are compared to SQP results of a selection of the well‐known Hock and Schittkowski problems. Although convergence to a small tolerance is slow when compared to SQP, the SRSM method does remarkably well for these sometimes pathological analytical problems. The second test concerns three engineering problems sampled from the nonlinear structural dynamics field to investigate the method's handling of numerical noise and non‐linearity. It is shown that, despite its simplicity, the SRSM method converges stably and is relatively insensitive to its only user‐required input parameter.
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K.J. Craig, Nielen Stander, D.A. Dooge and S. Varadappa
The purpose of this paper is to provide a methodology with which to perform variable screening and optimization in automotive crashworthiness design.
Abstract
Purpose
The purpose of this paper is to provide a methodology with which to perform variable screening and optimization in automotive crashworthiness design.
Design/methodology/approach
The screening method is based on response surface methodology in which linear response surfaces are used to create approximations to the design response. The response surfaces are used to estimate the sensitivities of the responses with respect to the design variables while the variance is used to estimate the confidence interval of the regression coefficients. The sampling is based on the D‐optimality criterion with over‐sampling to improve noise filtering and find the best estimate of the regression coefficients. The coefficients and their confidence intervals as determined using analysis of variance (ANOVA), are used to construct bar charts for the purpose of selecting the important variables.
Findings
A known analytical function is first used to illustrate the effectiveness of screening. Using the finite element method (FEM), a complex vehicle occupant impact problem and a full vehicle multidisciplinary problem featuring frontal impact and torsional modal analysis of the vehicle body are modeled and parameterized. Two optimizations are conducted for each FEM example, one with the full variable set and one with a screened subset. An iterative, successive linear approximation method is used to achieve convergence. It is shown that, although significantly different final designs may be obtained, an appropriately selected subset of variables is effective while significantly reducing computational cost.
Practical implications
The method illustrated provides a practical approach to the screening of variables in simulation‐based design optimization, especially in automotive crashworthiness applications with costly simulations. It is shown that the reduction of variables used in the optimization process significantly reduces the total cost of the optimization.
Originality/value
Although variable screening has been used in other disciplines, the use of response surfaces to determine the variable screening information is novel in the crashworthiness field.
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Albert A. Groenwold and Nielen Stander
The constitutive relationship of a four‐node flat shell finite element with six degrees of freedom per node and a modified five‐point quadrature, previously presented by the…
Abstract
The constitutive relationship of a four‐node flat shell finite element with six degrees of freedom per node and a modified five‐point quadrature, previously presented by the authors, is extended to include symmetric and unsymmetric orthotropy. Through manipulation of the kinematic assumptions, provision is made for out‐of‐plane warp. A wide range of membrane and thin to moderately thick plate and shell examples are used to demonstrate the accuracy and robustness of the resulting element.
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THOMAS A. FRANKO, STEPHEN L. RATNER and CAROLINE K. HALL
Rule 382 of the New York Stock Exchange for many years has governed the relationship between clearing and introducing brokers with a focus on responsibility to the client. This…
Abstract
Rule 382 of the New York Stock Exchange for many years has governed the relationship between clearing and introducing brokers with a focus on responsibility to the client. This article surveys the subtle and not so subtle changes impacting these relationships, with a view toward future trends.
Presents a range of numerical results obtained from the geometrically nonlinear analysis of a cantilevered cylindrical shell. Shows that, while the fine‐mesh solution involves no…
Abstract
Presents a range of numerical results obtained from the geometrically nonlinear analysis of a cantilevered cylindrical shell. Shows that, while the fine‐mesh solution involves no limit points, as the mesh is coarsened, an increasing series of “false limit points” is encountered.