The steady Couette flow of a Newtonian fluid between two plates, one of them a plane, the other one provided with riblets aligned perpendicular to the flow direction, is taken as a model for ...lubricant friction with wall roughness. In cases where the amplitude of the riblets is small compared to the riblet spacing, Reynolds lubrication approximation leads to an explicit solution. In contrast to this, a treatment of the full hydrodynamic equations is required for higher amplitudes. Under creeping flow conditions, an analytical treatment of the Stokes equations based on complex function theory allows for a reduction of the problem to the solving of ordinary differential and integral equations for functions of one variable. After this problem reduction, the resulting equations are solved by Fourier analysis and computer algebra.
The resulting streamline patterns of the flow reveal the formation of vortices under certain conditions. Since these vortices act like a kind of fluid roller bearings, their influence on the drag force and material transport of the lubricant is studied.
Metformin is the recommended initial drug therapy for patients with type 2 diabetes mellitus (DM). However, the optimal second-line drug when metformin monotherapy fails is unclear.
To determine the ...comparative efficacy, risk of weight gain, and hypoglycemia associated with noninsulin antidiabetic drugs in patients with type 2 DM not controlled by metformin alone.
A literature search via MEDLINE (beginning in January 1950) and Cochrane CENTRAL through January 2010 and a manual search of references for additional relevant studies.
Randomized controlled trials (RCTs) with at least 3 months' duration, evaluating noninsulin antidiabetic drugs added to metformin in patients experiencing an inadequate response to maximized and stable (> or = 4 weeks at > or = 1500 mg or maximally tolerated dose) metformin therapy.
Inclusion/exclusion criteria; duration of patient follow-up; drug, dose, and schedule used; use of concurrent lifestyle modification; and baseline characteristics (age, sex, anthropometrics, glycated hemoglobin A(1c) HbA(1c), duration of DM, and metformin dose). End points collected included mean change in HbA(1c), proportion of patients achieving HbA(1c) goal of less than 7%, change in weight, and incidence of hypoglycemia. Mixed-treatment comparison meta-analysis was used to calculate the weighted mean difference for changes from baseline in HbA(1c) and body weight and relative risk (RR) of HbA(1c) goal attainment and hypoglycemia, with associated 95% credible intervals.
Overall, 27 RCTs (n = 11 198) were included. Mean (range) trial duration was 32 (12-52) weeks. The different classes of drugs were associated with similar HbA(1c) reductions (range, 0.64%-0.97%) compared with placebo. Although use of thiazolidinediones, sulfonylureas, and glinides were associated with weight gain (range, 1.77-2.08 kg), glucagon-like peptide-1 analogs, alpha-glucosidase inhibitors, and dipeptidyl peptidase-4 inhibitors were associated with weight loss or no weight change. Sulfonylureas and glinides were associated with higher rates of hypoglycemia than with placebo (RR range, 4.57-7.50).
When added to maximal metformin therapy, all noninsulin antidiabetic drugs were associated with similar HbA(1c) reductions but differed in their associations with weight gain and risk of hypoglycemia.
Further increasing requirements to the quality of car body components represent a huge challenge for the process planner. Springback effects are causing dimensional deviations of the car body ...components from their respective target geometry. Both elastic membrane and bending stresses result in global and regional distortions and deflections. In addition to these effects in particular the membrane stresses furthermore result in a contraction of the drawshell with the effect that the drawshell is smaller than the tool after drawing. In order to compensate this contraction the drawing tool has to be increased. This process is known as the so-called scaling. An appropriate scaling should result in a contracted part which has the same surface area and unwound lengths as the target geometry. In case of deviations of the unwound lengths unwanted plastic deformations of the part in subsequent operations have to be expected and the part's assembly dimensions will differ from the target geometry which can cause significant quality issues in the car body. Today the scaling is usually done by increasing the tool with a unique global scaling factor or with different scaling factors for different directions. However, since the contraction varies along the part surface in reality the results are only suboptimal. Here a new scaling approach is being presented which uses the simulation results to scale the tool surfaces locally. By doing so the locally different contractions can be better compensated.
Abstract
The requirements for high-strength and low-weight car body structures prove challenging for the stamping process and cause growing problems with the elastic springback. Compensation ...approaches such as the geometrical adjustment of the stamping dies by the amount of and in opposite direction to the springback can be an effective solution in many cases. However, this approach can only lead to satisfactory results if the scatter of the springback is considered, controlled and in the best case reduced. The reduction of the scatter can be provoked by adaption of the part design. Therefore, different methods such as the topology optimization method, the so-called line-of-force method and shape optimization can be applied. In the present work an advanced topology optimization method is suggested. Based on the decomposition of the springback deformation into membrane and bending components, the most efficient optimization of the part design is found relying on unconventional topology optimization. For the proposed adapted topology optimization approach the excellent results are also confirmed when applied to the industry-relevant case of a truck rear panel.
The need for car body structures of higher strength and at the same time lower weight results in serious challenges for the stamping process. To produce accurate parts at the end the stamping dies ...must be adjusted more or less by the amount of the springback in the opposite direction. Which stamping dies out of a multistage die set need to be adjusted, and how great the respective adjustment needs to be, is still quite often defined by practical experience and trial-and-error. Normally a certain number of compensation iterations based on the same compensation strategy must be realized and in addition to that, even the compensation strategy itself must be modified in some iterations in order to achieve accurate parts within tolerance. In contrast to the today still convenient trial-and-error optimization approach, a compensation guideline has been developed. Key content is the influence of the relevant compensation parameters, such as the measuring reference system (measurement system) including clamping of the parts (orientation of the springback part relative to the target part) and the amount of the compensation in the different stages (compensation factor and compensation strategy).
Abstract
In sheet metal forming, both the dimensional accuracy of the manufactured parts and the robustness of the forming process are significantly compromised by elastic springback effects. In ...contrast to traditional compensation methods mostly relying on modifications of the tool geometry, a part geometry-based approach reduces the amount of springback by appropriately manipulating the part stiffness through slight modifications of the part geometry. To date, part-geometric measures are mostly based on practical experience and trial-and-error processes resulting in a need for simple and effective simulation-based approaches. In the present work three novel simulation-based approaches for a suitable modification of structural component design are suggested relying on unconventional
topology optimization
, the so-called
line-of-force
method and
shape optimization
. First tests with a classical hat profile reveal that the optimized geometries, compared to the nominal one, lead to significant reductions of the springback after stamping and simultaneously to a notable decrease of the process variation when parameters of the forming process are varied slightly. For the adapted
topology optimization
approach the excellent results are also confirmed when applied to the industry-relevant case of a truck rear panel.
The need for car body structures of higher strength and at the same time lower weight results in serious challenges for the stamping process. In order to produce design conform parts the stamping ...dies must be adjusted by the amount of the springback in the opposite direction. This approach can only be successful, if the springback only ranges in a certain bandwidth in series production. To do so, it must be fulfilled that for a common spread of input process parameters first of all the draw-in of the flange edge of the drawshell may not reach the drawbeads, secondly material failure by locally increasing strain may not occur at any possible parameter set and last but not least the location of the part in the respective follow-up operation may not vary in such a way that the springback is being affected considerably. After the three basic requirements have been fulfilled the effect of the integral of the elastic strain energy in bending areas has to be minimized by increasing the tensile stress to a maximum. As a result of that the scatter of the bending springback is being reduced.
Induction of extrinsic stresses states may lead to significant increases of the denting stiffness of skin panels. For this purpose, the component needs to be produced in a dedicatedly malaligned ...shape. Forcing the part into its target geometry in the joining operation evokes said stress states and preserves them in the sheet. The approach discussed herein shall contribute to the reduction of sheet thickness and subsequent weight of skin panels without impairing the haptic quality of the car body.
Construction of Lagrangians in continuum theories Scholle, M.
Proceedings of the Royal Society. A, Mathematical, physical, and engineering sciences,
11/2004, Letnik:
460, Številka:
2051
Journal Article
Recenzirano
For physical systems the dynamics of which is formulated within the framework of Lagrange formalism, the dynamics is completely defined by only one function, namely the Lagrangian. For instance, the ...whole conservative Newtonian mechanics has been successfully embedded into this methodical concept. In continuum theories, however, the situation is different: no generally valid construction rule for the Lagrangian has been established in the past. In this paper general properties of Lagrangians in non-relativistic field theories are derived by considering universal symmetries, namely space- and time-translations, rigid rotations and Galilei boosts. These investigations discover the dual structure, i.e. the coexistence of two complementary representations of the Lagrangian. From the dual structure, relevant restrictions for the analytical form of the Lagrangian are derived which eventually result in a general scheme for Lagrangians. For two examples, namely Schrödinger's theory and the flow of an ideal fluid, the compatibility of the Lagrangian with the general scheme is demonstrated. The dual structure also has consequences for the balances which result from the respective symmetries by Noether's theorem: universally valid constitutive relations between the densities and the flux densities of energy, momentum, mass and centre of mass are derived. By an inverse treatment of these constitutive relations a Lagrangian for a given physical system can be constructed. This procedure is demonstrated for an elastically deforming body.
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