588 research outputs found
Idealised steady-state and transient simulations of Miocene Antarctic ice-sheet variability using 3D thermodynamical ice-sheet model IMAU-ICE
No full textWe present results from simulations of the Miocene Antarctic ice sheet, that were performed using the 3D thermodynamical ice-sheet model IMAU-ICE (v1.1.1-MIO). Five steady-state present-day simulations were conducted for reference (PI_ref), and 12 experiments using Miocene settings. Each Miocene experiment comprises 11 steady-state and 4 transient simulations. In the README file, the experiments and simulations are listed.
IMAU-ICE was run using a 40x40km grid covering the Antarctic continent. Initial conditions were obtained from reconstructions of the Antarctic bathymetry and bedrock topography pertaining to 23 to 24 million years (Myr) ago (dataset doi:10.1594/PANGAEA.923109). The simulations were forced by climate input data obtained from GENESIS simulations with varying CO2 levels (280 to 840 ppm) and Antarctic ice sheet cover (no ice to a large East-Antarctic ice sheet), and with present-day insolation. We utilized a matrix interpolation method to construct the time-varying climate forcing, based on the prescribed CO2 levels and ice cover simulated by IMAU-ICE.
For each simulation, we provide the run script, 1D output variables including CO2 level and the sea level contribution of the Antarctic ice sheet, and 3D output variables including ice thickness, bedrock and surface height, surface mass balance, basal mass balance, ice velocities, and ice temperatures. For more information, please contact L.B. Stap at [email protected]
Author Correction:Vitamin D status and severity of COVID-19 (Scientific Reports, (2022), 12, 1, (19823), 10.1038/s41598-022-21513-9)
No full textSanne Grundvald Boelt was omitted from the author list in the original version of this Article. The Author Contributions section now reads: “A.A. contributed to the conception and idea of the work. N.M.N., A.S.C., L.B. and A.A. contributed to the design of the study. N.M.N., A.S.C., L.B. S.G.B contributed to the acquisition of data. N.M.N., A.H., L.B., S.G.B and T.G.J. contributed to the analyses of the data. All authors contributed to the interpretation of the data and the results in the manuscript. N.M.N. drafted the manuscript, made Fig. 1, T.G.J. made Fig. 2. All the authors revised the manuscript critically and has approved the final version.” The original Article has been corrected.</p
Simulation of northern hemispheric, southern hemispheric and global temperature over the past 5 million years
No full textModel output of the intermediate complexity climate model CLIMBER-2 over the past 5 million years. The simulations were forced with insolation data (O), insolation and land ice data (OI), insolation and carbon dioxide data (OC) and with insolation, land ice and carbon dioxide data (OIC). Sheet 1 contains the main results: northern hemispheric (30-90 deg N), southern hemispheric (30-90 deg S) and global temperatures. Sheet 2 contains the land ice and carbon dioxide forcing in terms of globally averaged radiative forcing. Details are given in the publication. More information or data can be obtained by contacting L.B. Stap ([email protected])
De Marke naar minimale broeikasgasemissie
No full textDe Marke gaat in twee stappen naar minimale emissie van lachgas en methaan. De eerste stap is efficiënt nutriëntengebruik. Deze stap is door De Marke in de afgelopen jaren maximaal uitgevoerd en wordt ook door praktijkbedrijven al in verschillende mate toegepast. De tweede stap is het verhogen van voerefficiëntie in de veestapel. Deze stap krijgt op De Marke in 2012 volop de aandacht en moet leiden tot de gewenste minimale emissie van lachgas en methaan. Hierna kan nog een stap gezet worden
Simulation of benthic δ¹⁸O, CO2, ice-volume-equivalent sea level and temperature over the past 38 million years
No full textModel output of a coupled ice sheet-climate model, inversely forced by benthic d18O over the past 38 million years. Sheet 1 contains the main results from the reference simulation: benthic d18O, CO2, ice-volume-equivalent sea level and global temperature. Sheet 2 contains global, Northern Hemisphere (40-80 deg N), and Antarctic (60-90 deg S) temperatures, from the reference run and the run with ice uncoupled, only albedo coupled, and only surface height coupled. Sheet 3 contains global temperature, from the reference run, and the runs with fixed PD ice, fixed LGM ice, and no ice. Details are given in the publication. More information or data can be obtained by contacting L.B. Stap ([email protected])
Simulations of the response of the Miocene Antarctic ice sheet to CO2-driven climate variability
No full textWe present ice thickness and bedrock height from simulations of the Miocene Antarctic ice sheet (AIS), using the 3D thermodynamical Parallel Ice Sheet Model (PISM) version 0.7.3. The applied climate forcing consists of temperature and precipitation anomalies with respect to a preindustrial reference simulation, obtained from simulations using the atmosphere-ocean general circulation model COSMOS. These anomalies are added to an ERA-40/WOD-09 base climate. COSMOS was run using preindustrial settings, and Miocene settings with CO2 levels of 278 ppm (low), 450 ppm (medium), and 600 ppm (high). The steady state simulations using PISM are started with present-day bedrock conditions, with a present-day AIS (Bedmap2), and isostatically rebounded after removal of the ice. Additional simulations are started with the Wilson et al. (2012) late-Eocene bedrock topography reconstruction. The steady state simulations are conducted by applying the same climate forcing over 200 kyr. The transient simulations are performed by using an index method to interpolate between different forcing climate states. In these runs, the forcing climate state is gradually varied over quasi-orbital timescales of 400 kyr, 40 kyr, 1600 kyr, or 200 kyr.
Details are given in the accompanying publication. For more information or data, please contact L.B. Stap mailto:[email protected].
Dataset 2019_Stap_steadystate_startfrom_presentdayAIS.nc contains the data to plot Fig. 1.
Dataset 2019_Stap_PISM_transient.xlsx contains the data to plot Fig. 2 and 3.
Datasets 2019_Stap_steadystate_startfrom_noice.nc and 2019_Stap_steadystate_startfrom_Wilson_noice.nc contain additional data plotted in Fig. 2 and 3
Towards a New Durable and Environmentally Compliant Adhesive Bonding Process for Aluminium Alloys
No full textAerospace Engineerin
Stress analysis of fatigue cracks in mechanically fastened joints: An analytical and experimental investigation
No full textThe two historical fuselage failures, Comet in 1954 and Aloha in 1988, illustrate that similar accidents must be avoided which requires a profound understanding of the fatigue mechanisms involved, including analytical models to predict the fatigue behavior of riveted joints of a fuselage structure. The scope of the research project covers a variety of joint types and joining techniques for both monolithic and laminated sheet materials. The fuselage structure is a rather complicated system of parts consisting of skin sheets, tear straps, stringers, frames and doublers. These parts are interconnected by mechanically fastened and bonded joints, or a combination of both. The complex fuselage structure in the present research is reduced to specimen level size for laboratory testing and theoretical analysis.\par The major topics of the thesis are: Calculations of the combined tension and bending stress distribution in joints, which implies an extension of the so-called secondary bending model (Chapter 3). Find a direct and simple relation between the formed rivet head and squeeze force. (Chapter 4). Development of stress intensity factors for fatigue cracks in joints loaded under combined tension and application to fatigue crack growth results (Chapter 5). Fractographic observations with the scanning electron microscope of crack front shapes occurring in riveted joints under combined tension and bending (Chapter 5). Analysis of the residual strength of joints with fatigue cracks (Chapter 6). Neutral line model For mechanically fastened lap splice and butt joints in a fuselage structure, a dominant load is introduced by the Ground Air Ground (GAG) pressurization cycle. The hoop load is transferred from one skin panel to the next via the fasteners in the joint. The hoop load is offset by eccentricities in the load path, which causes secondary bending. The bending stress is a non-linear function of the applied tension load. The stress system in the joint then encompasses the membrane stress, the secondary bending stress and the bearing stress associated with the fastener loads on the holes. The secondary bending is highly depending on the magnitude of the eccentricity and the flexural rigidity of the joint between the fastener rows. The theory used to derive the bending stresses is based on the advanced beam theory. A further development of the neutral line model incorporates the internal moment, which is a useful representation of the load transfer occurring in multiple row joints. The calculation of the load transfer can be made for complicated lap splice and butt joints. With the developments of the present research, the neutral line model is still a very powerful tool to use in the early stages of joint design. It gives a good picture of the stresses in a joint. Riveting Solid rivets and more advanced fasteners are still widely used in aircraft fuselage design efforts. The fasteners are characterized by various parameters associated with the fastener material and geometry, sheet material and installation process. The present investigation focuses on solid rivets installed in aluminum and Glare. The expansion of a solid rivet in a rivet hole is important with respect to the fatigue properties of joints. The expanding rivet inside a fastener hole will create a compressive residual stress around the hole and this will delay fatigue crack nucleation. It is important to know the correct squeeze force used to form the driven head of a rivet. Measurements of the formed rivet head (diameter or protruding height) can be used to obtain information about the applied squeezing force. The riveting process is a non linear deformation process characterized by large plastic strains. Simple equations based on constant volume of the rivet and the Holloman model for uniform plastic deformation, were adopted to evaluate the riveting process. Useful results were obtained about the correlation between the rivet head deformation and the applied squeezing force. Stress intensity factors As a result of combined tension and secondary bending in a lap joint, fatigue cracks at the edge of a hole start at one side of the sheet only. Initially these cracks at the edge of a hole are growing as a part through the thickness corner crack, which later become a through the thickness crack, a so called through crack. But also for a through crack, the shape of the crack front is usually curved and the crack length measured at both sides of the sheet will be different. In view of fatigue crack growth predictions it then is necessary to obtain stress intensity factors for such slant and curved crack fronts. In the present investigation this problem has been explored for a simple configuration, which is an open hole in a sheet specimen subjected to combined tension and bending. Fatigue tests were carried out on specimens of AL 2024 T3 clad sheet material with three different thicknesses (1.0, 1.6 and 2.0 mm). In each specimen a single open countersunk hole was present. The development of the crack front is these specimens could be recorded because so-called marker load cycles were applied in these tests. It then was possible to observe the crack fronts in the scanning electron microscope, which still was a rather strenuous work. Reconstruction of the crack growth could be done for the larger part of the fatigue cracks.\par K-values were obtained for a large variety of crack front shapes and crack sizes. Comparison of the new calculated K values with existing solutions showed that the new solutions capture near the surface phenomenon more accurately than the previously published data. The improvement is a result of using an increased mesh density. For through the thickness cracks growing away from the countersunk hole, the normalized stress intensity factors approach the values of the normalized stress intensity factors for cracks emanating from a straight shank hole. Thus, the effect of the countersunk hole decreases with increasing crack length. The solutions for the pin loading b values show a dominant influence of the countersunk shape in the b/t values.\par Residual strength Static failure of a joint occurs when that joint is not able to carry the applied load anymore. The type of static failure in joints depends on the loading condition and the joint configuration. The most common static failure modes in monolithic aluminum joints are fastener shear failure, plate tension failure, bearing failure and plate shear failure. In Glare joints another failure mechanism, fastener pull-through, is often observed. This failure mechanism is related to the lower stiffness of Glare in thickness direction, leading to increased tilting of the fasteners and hence increased tensile stresses in the fastener. \par In the present thesis, a method is proposed to calculate the residual strength of joints of monolithic and fiber metal laminates. The method uses the remaining net section. For the fiber metal laminates the net section includes the remaining intact metal layers in combination with the intact fibers. The method starts with the blunt notch strength of the un cracked joint and the metal volume fraction for the fiber-metal laminates. The Norris failure criterion and the metal volume fraction are used to calculate the blunt notch strength for any possible Glare lay up. Secondary bending has a significant influence on the ultimate strength of both Glare and aluminum. The ultimate tensile strength reduces with increasing bending. Taking this into account, an empirically found reduction of 10% of the blunt notch values results in a more accurate representation of the stress system. Difficulties arise if significant plastic deformation occurs at the most critical fastener row, and further research using a finite element model is recommended.Aerospace Engineerin
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