排序方式: 共有17条查询结果,搜索用时 46 毫秒
1.
E. Uhlmann S. Henze R. Gerstenberger K. Brömmelhoff W. Reimers T. Fischer N. Schell 《Production Engineering》2013,7(4):401-408
There are numerous cutting models which describe the chip formation process. However, they are based on a number of simplifying assumptions. In order to verify these assumptions and to get a better understanding of the cutting process, the different stress states in the chip formation zone were determined by means of diffraction experiments with monochromatic high-energy synchrotron X-radiation during orthogonal, quasistatic cutting of the material C45E. The results from the experiments are compared with simulated stresses. The experimental data indicate that the assumption of a free chip flow according to the shear angle model of Opitz and Hucks is not valid. The model was therefore extended considering the normal stresses in direction of the chip flow. 相似文献
2.
Optical parametric oscillation tunable over the 940-1220-nm spectral region has been obtained from a monolithic magnesium-oxide-doped lithium niobate ring resonator. The monolithic optical parametric oscillator (OPO) was pumped by the 532-nm second harmonic of a diode-laser-pumped single-frequency Q -switched Nd:YAG laser. The exceptional frequency and amplitude stability of the single-frequency pump source provided stable OPO output pulses 相似文献
3.
Eckart Uhlmann Stefan Herter Robert Gerstenberger Martin Roeder 《Production Engineering》2009,3(3):261-270
As a result of the development of new materials for high temperature applications the potential for mass reduction and increased
process temperatures is constantly being expanded. Intermetallic γ-TiAl alloys can meet these demands to a large extent. The
properties necessary for these applications have an adverse effect on the machinability however and render intermetallic titanium
aluminides as difficult to machine materials. Cutting operations tend to produce damaged surfaces which are unsuitable for
the intended applications. As the basis for a reliable and economic cutting technology, the chip formation of the intermetallic
TiAl alloy TNBV5 has been examined in quasi-static cutting experiments. Observations showed that increased workpiece temperatures
lead to a transition of the chip formation from segmented to continuous chips. By decreasing the undeformed chip thickness
crack-free surfaces could be produced at low workpiece temperatures. In this case other mechanisms than the thermal activation
of slip systems must be the reason for the observed large plastic deformations. The theory that hydrostatic pressure leads
to this behavior is substantiated by the results of finite element simulations. This offers the possibility for damage free
machining at lower cutting speeds, thus enabling the use of conventional tool materials at an acceptable tool life. 相似文献
4.
Carina Gerstenberger 《时间序列分析杂志》2018,39(1):90-104
We introduce a robust estimator of the location parameter for the change‐point in the mean based on Wilcoxon statistic and establish its consistency for L1 near‐epoch dependent processes. It is shown that the consistency rate depends on the magnitude of the change. A simulation study is performed to evaluate the finite sample properties of the Wilcoxon‐type estimator under Gaussianity as well as under heavy‐tailed distributions and disturbances by outliers, and to compare it with a CUSUM‐type estimator. It shows that the Wilcoxon‐type estimator is equivalent to the CUSUM‐type estimator under Gaussianity but outperforms it in the presence of heavy tails or outliers in the data. 相似文献
5.
Timon Rabczuk Goangseup Zi Axel Gerstenberger Wolfgang A. Wall 《International journal for numerical methods in engineering》2008,75(5):577-599
We have developed a new crack tip element for the phantom‐node method. In this method, a crack tip can be placed inside an element. Therefore, cracks can propagate almost independent of the finite element mesh. We developed two different formulations for the three‐node triangular element and four‐node quadrilateral element, respectively. Although this method is well suited for the one‐point quadrature scheme, it can be used with other general quadrature schemes. We provide some numerical examples for some static and dynamic problems. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
6.
7.
3D fluid–structure-contact interaction based on a combined XFEM FSI and dual mortar contact approach
Ursula M. Mayer Alexander Popp Axel Gerstenberger Wolfgang A. Wall 《Computational Mechanics》2010,46(1):53-67
Finite deformation contact of flexible solids embedded in fluid flows occurs in a wide range of engineering scenarios. We
propose a novel three-dimensional finite element approach in order to tackle this problem class. The proposed method consists
of a dual mortar contact formulation, which is algorithmically integrated into an eXtended finite element method (XFEM) fluid–structure
interaction approach. The combined XFEM fluid–structure-contact interaction method (FSCI) allows to compute contact of arbitrarily
moving and deforming structures embedded in an arbitrary flow field. In this paper, the fluid is described by instationary
incompressible Navier–Stokes equations. An exact fluid–structure interface representation permits to capture flow patterns
around contacting structures very accurately as well as to simulate dry contact between structures. No restrictions arise
for the structural and the contact formulation. We derive a linearized monolithic system of equations, which contains the
fluid formulation, the structural formulation, the contact formulation as well as the coupling conditions at the fluid–structure
interface. The linearized system may be solved either by partitioned or by monolithic fluid–structure coupling algorithms.
Two numerical examples are presented to illustrate the capability of the proposed fluid–structure-contact interaction approach. 相似文献
8.
Axel Gerstenberger Raymond S. Tuminaro 《International journal for numerical methods in engineering》2013,94(3):248-272
This article proposes an algebraic multigrid (AMG) approach to solve linear systems arising from applications where strong discontinuities are modeled by the extended finite element method. The application of AMG methods promises optimal scalability for solving large linear systems. However, the straightforward (or ‘black‐box’) use of existing AMG techniques for extended finite element method problems is often problematic. In this paper, we highlight the reasons for this behavior and propose a relatively simple adaptation that allows one to leverage existing AMG software mostly unchanged. Numerical tests demonstrate that optimal iterative convergence rates can be attained that are comparable with AMG convergence rates associated with linear systems for standard finite element approximations without discontinuities. Published 2012. This article is a US Government work and is in the public domain in the USA. 相似文献
9.
Carina Gerstenberger 《时间序列分析杂志》2021,42(1):34-62
In this article we introduce a robust to outliers Wilcoxon change‐point testing procedure, for distinguishing between short‐range dependent time series with a change in mean at unknown time and stationary long‐range dependent time series. We establish the asymptotic distribution of the test statistic under the null hypothesis for L1 near epoch dependent processes and show its consistency under the alternative. The Wilcoxon‐type testing procedure similarly as the CUSUM‐type testing procedure (of Berkes I., Horváth L., Kokoszka P. and Shao Q. 2006. Ann.Statist. 34:1140–1165), requires estimation of the location of a possible change‐point, and then using pre‐ and post‐break subsamples to discriminate between short and long‐range dependence. A simulation study examines the empirical size and power of the Wilcoxon‐type testing procedure in standard cases and with disturbances by outliers. It shows that in standard cases the Wilcoxon‐type testing procedure behaves equally well as the CUSUM‐type testing procedure but outperforms it in presence of outliers. We also apply both testing procedure to hydrologic data. 相似文献
10.
An undesirable side-effect of the anticholinergic drugs used in the premedication is an unpleasent drying of the mouth and pharynx. According to the experience of the authors, this often distressing feeling can be successfully relieved by means of application of synthetic saliva. This is of special importance for patients operated under reginal anaesthesia. 相似文献