249 research outputs found
Fatigue tests of axially loaded butt welds up to very high cycles
Fatigue strength curves that are established from fatigue tests provide a basis for the fatigue assessment applying nominal stress approach. In the codes valid for steel structures, like the EC 3, the fatigue strength curves for constant amplitude loading have a knee point in the transition region. The fatigue strength curve beyond this knee point is commonly assumed to be a horizontal asymptote. However, the behaviour of the fatigue strength curve in the area of very high cycles and more importantly the existence of an endurance limit are much discussed. In the case of welded joints the experimental data beyond 107 load cycles is limited due to the possibilities in testing. Testing techniques with high frequencies are necessary to obtain experimental data with very high cycles in a reasonable period of time. In this scope a testing device with approximately 390 Hz operates by alternating current magnets and using resonance amplification, which was developed by a third party. This testing device was investigated and advanced for the application of long term tests reaching 5·108 load cycles. Fatigue tests on axially loaded butt welds with constant amplitude loading are conducted in three test series until very high cycles. The fatigue tests include the area of high and very high cycles. The influence of test frequency and stress ratio is investigated
One-loop corrections to gaugino (co-)annihilation into quarks in the MSSM
We present the full supersymmetric QCD corrections
for gaugino annihilation and co-annihilation into light and heavy quarks in the
Minimal Supersymmetric Standard Model (MSSM). We demonstrate that these
channels are phenomenologically relevant within the so-called phenomenological
MSSM. We discuss selected technical details such as the dipole subtraction
method in the case of light quarks and the treatment of the bottom quark mass
and Yukawa coupling. Numerical results for the (co-)annihilation cross sections
and the predicted neutralino relic density are presented. We show that the
impact of including the radiative corrections on the cosmologically preferred
region of the parameter space is larger than the current experimental
uncertainty from Planck data.Comment: 19 pages, 9 figures. Matches version published in Phys.Rev.
Interplay of gaugino (co)annihilation processes in the context of a precise relic density calculation
The latest Planck data allow one to determine the dark matter relic density
with previously unparalleled precision. In order to achieve a comparable
precision on the theory side, we have calculated the full
corrections to the most relevant annihilation and
coannihilation processes for relic density calculations within the Minimal
Supersymmetric Standard Model (MSSM). The interplay of these processes is
discussed. The impact of the radiative corrections on the resulting relic
density is found to be larger than the experimental uncertainty of the Planck
data.Comment: 7 pages, 2 figures, 18th International Conference From the Planck
Scale to the Electroweak Scale, 25-29 May 2015. Ioannina, Greec
Precision predictions for supersymmetric dark matter
The dark matter relic density has been measured by Planck and its
predecessors with an accuracy of about 2%. We present theoretical calculations
with the numerical program DM@NLO in next-to-leading order SUSY QCD and beyond,
which allow to reach this precision for gaugino and squark (co-)annihilations,
and use them to scan the phenomenological MSSM for viable regions, applying
also low-energy, electroweak and hadron collider constraints.Comment: 6 pages, 1 table, 8 figures, proceedings of ICHEP 201
3D cut-cell modelling for high-resolution atmospheric simulations
Owing to the recent, rapid development of computer technology, the resolution
of atmospheric numerical models has increased substantially. With the use of
next-generation supercomputers, atmospheric simulations using horizontal grid
intervals of O(100) m or less will gain popularity. At such high resolution
more of the steep gradients in mountainous terrain will be resolved, which may
result in large truncation errors in those models using terrain-following
coordinates. In this study, a new 3D Cartesian coordinate non-hydrostatic
atmospheric model is developed. A cut-cell representation of topography based
on finite-volume discretization is combined with a cell-merging approach, in
which small cut-cells are merged with neighboring cells either vertically or
horizontally. In addition, a block-structured mesh-refinement technique is
introduced to achieve a variable resolution on the model grid with the finest
resolution occurring close to the terrain surface. The model successfully
reproduces a flow over a 3D bell-shaped hill that shows a good agreement with
the flow predicted by the linear theory. The ability of the model to simulate
flows over steep terrain is demonstrated using a hemisphere-shaped hill where
the maximum slope angle is resolved at 71 degrees. The advantage of a locally
refined grid around a 3D hill, with cut-cells at the terrain surface, is also
demonstrated using the hemisphere-shaped hill. The model reproduces smooth
mountain waves propagating over varying grid resolution without introducing
large errors associated with the change of mesh resolution. At the same time,
the model shows a good scalability on a locally refined grid with the use of
OpenMP.Comment: 19 pages, 16 figures. Revised version, accepted for publication in
QJRM
Zum Ermüdungsverhalten von Stumpfnahtverbindungen bei sehr hohen Lastwechselzahlen
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Comparison of terrain following and cut cell grids using a non-hydrostatic model
Terrain following coordinates are widely used in operational models but the cut cell method has been proposed as an alternative that can more accurately represent atmospheric dynamics over steep orography. Because the type of grid is usually chosen during model implementation, it becomes necessary to use different models to compare the accuracy of different grids. In contrast, here a C-grid finite volume model enables a like-for-like comparison of terrain following and cut cell grids. A series of standard two-dimensional tests using idealised terrain are performed: tracer advection in a prescribed horizontal velocity field, a test starting from resting initial conditions, and orographically induced gravity waves described by nonhydrostatic dynamics. In addition, three new tests are formulated: a more challenging resting atmosphere case, and two new advection tests having a velocity field that is everywhere tangential to the terrain following coordinate surfaces. These new tests present a challenge on cut cell grids. The results of the advection tests demonstrate that accuracy depends primarily upon alignment of the flow with the grid rather than grid orthogonality. A resting atmosphere is well-maintained on all grids. In the gravity waves test, results on all grids are in good agreement with existing results from the literature, although terrain following velocity fields lead to errors on cut cell grids. Due to semi-implicit timestepping and an upwind-biased, explicit advection scheme, there are no timestep restrictions associated with small cut cells. We do not find the significant advantages of cut cells or smoothed coordinates that other authors find
Degeneration Effects of Thin-Film Sensors after Critical Load Conditions of Machine Components
In the context of intelligent components in industrial applications in the automotive, energy or construction sector, sensor monitoring is crucial for security issues and to avoid long and costly downtimes. This article discusses component-inherent thin-film sensors for this purpose, which, in contrast to conventional sensor technology, can be applied inseparably onto the component’s surface via sputtering, so that a maximum of information about the component’s condition can be generated, especially regarding deformation. This article examines whether the sensors can continue to generate reliable measurement data even after critical component loads have been applied. This extends their field of use concerning plastic deformation behavior. Therefore, any change in sensor properties is necessary for ongoing elastic strain measurements. These novel fundamentals are established for thin-film constantan strain gauges and platinum temperature sensors on steel substrates. In general, a k-factor decrease and an increase in the temperature coefficient of resistance with increasing plastic deformation could be observed until a sensor failure above 0.5% plastic deformation (constantan) occurred (1.3% for platinum). Knowing these values makes it possible to continue measuring elastic strains after critical load conditions on a machine component in terms of plastic deformation. Additionally, a method of sensor-data fusion for the clear determination of plastic deformation and temperature change is presented
Requirements and problems in parallel model development at
Nearly 30 years after introducing the first computer model for weather forecasting, the Deutscher Wetterdienst (DWD) is developing the 4th generation of its numerical weather prediction (NWP) system. It consists of a global grid point model (GME) based on a triangular grid and a non-hydrostatic Lokal Modell (LM). The operational demand for running this new system is immense and can only be met by parallel computers. From the experience gained in developing earlier NWP models, several new problems had to be taken into account during the design phase of the system. Most important were portability (including efficieny of the programs on several computer architectures) and ease of code maintainability. Also the organization and administration of the work done by developers from different teams and institutions is more complex than it used to be. This paper describes the models and gives some performance results. The modular approach used for the design of the LM is explained and the effects on the development are discussed
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