Reconciling plate convergence and orogeny: The influence of India-Asia convergence rate on the formation of the Himalayas

<p>The collision of India and Eurasia since ~50 Ma has resulted in a broad range of deformation along the Himalaya-Tibetan orogeny, accommodating >2700 km of convergence. The region is characterised by the Tibetan Plateau, the Himalayan internal units and fold-and-thrust belt from North to South. These formed as a consequence of a convergence history characterised by a progressive decrease in velocity, from ~10 cm/yr 50 Ma, to ~8 cm/yr 42.5 Ma and to present-day values of ~4 cm/yr around 20 Ma. Here, we test the controls of such a convergence velocity history on the orogeny of a viscoplastic wedge during collision, above a subducting continental lithosphere. We compare numerical models simulating India-Asia plate convergence and collision, comparing the structures observed throughout the evolution with those observed in the Himalayan-Tibetan region. The models display distinct phases of growth and structural style evolution in the Himalayan-Tibetan region that are a result of the change in convergence velocity and long-term collision. After an initial stacking, the high convergence velocity forces deformation migration towards the upper plate, where a plateau forms, while late stage slowdown of collision favours the formation of the Himalayan fold-and-thrust belt. While the latter is in agreement with the structuring of the southermost domains and the South Tibetan Detachment (STD) fault, the former provide constraints to the initial uplift of the Tibetan Plateau.</p>

Meander migration: the observation method

River meanders migrate over time and the consequences of this migration can create a problem for bridges and embankments near the river. This is why it is important to predict the lateral extent of future migration over the life of neighboring infrastructure. In the observation method for meander migration (OMM), the past movement and velocity history of the meander are used to back-calculate site specific erosion parameters. Those parameters serve as input to predict the meander migration for a chosen future velocity hydrograph. In this article and after a review of existing knowledge, the analytical steps leading to the development of the OMM are described, then the field and laboratory work at four full-scale meander migration case histories are presented, and then the four full-scale meander migration case histories are used to evaluate the OMM. The OMM has been automated in an Excel spreadsheet.

The Ablation Mechanism of Magnetic Driven Flyer Plate

It is found that the samples usually melt and even gasify in the magnetic driven high-speed flying plate experiments, which phenomenon goes against the investigation on materials’ equation of state (EOS). To understand this phenomenon, the whole process of magnetic driven flying plate experiment is simulated by the magnetohydrodynamic code MDSC. The ablation mechanism of magnetic driven flying plate is analyzed through the control of thermal conduction coefficient, and resistivity coefficient which is related to the magnetic diffusion velocity, in the energy conversing equation. Inside the flying plate the velocity of stress wave is much higher than that of magnetic diffusion, and hence the current goes into the inside of sample no early than the stress wave, so the magnetic diffusion doesn’t play an important role in the first stage of flyer free surface velocity history. The thermal conduction doesn’t influence the whole free surface velocity history of the flying plate much, while the Ohmic heating has a big effect on it, without which more than 20% error will be produced. The energy transportation in the flying plate medium is mainly caused by the Ohmic heating from magnetic diffusion. Besides, the relationship between the magnetic diffusion and temperature of flying plate is also analyzed.

Experimental Investigation into Spall of Carbon Phenolic Composites

The velocity history of free-surface particle for carbon phenolic composites (density is 1.4g/cm3) is obtained based on the loading technology of the light gas gun, the relationship between the striking velocity of flyer and the spall thickness as well as time is investigated. Besides, spall strength and thickness are obtained by analyzing the samples data and curves. The high pressure physical characteristics, such as type Hugoniot curve and Murnagham state equation for this material, are acquired by analyzing the velocity history of free-surface and spall characteristics. This study provides a methodology to quantify spall and physical characteristics for carbon phenolic composites under tensile wave loading.

A Wiener-Laguerre Model of VIV Forces Given Recent Cylinder Velocities

Slender structures immersed in a cross flow can experience vibrations induced by vortex shedding (VIV), which cause fatigue damage and other problems. VIV models that are used in structural design today tend to assume harmonic oscillations in some way or other. A time domain model would allow to capture the chaotic nature of VIV and to model interactions with other loads and nonlinearities. Such a model was developed in the present work: for each cross section, recent velocity history is compressed using Laguerre polynomials. The compressed information is used to enter an interpolation function to predict the instantaneous force, allowing to step the dynamic analysis. An offshore riser was modeled in this way: some analyses provided an unusually fine level of realism, while in other analyses, the riser fell into an unphysical pattern of vibration. It is concluded that the concept is promising, yet that more work is needed to understand orbit stability and related issues, in order to produce an engineering tool.

Experimental and Numerical Investigation into Dynamic Spall Damage of Porous Phenolic Composites

A damage evolution law for porous phenolic composites is developed by using phenomenological point, which along with the improved Johnson-Cook model is then implemented into a finite difference code for one-dimensional strain wave problem. The velocity history of free-face particle is recorded and correlated with the simulated result to evaluate the damage parameters. Good agreement shows that the proposed damage evolution law and spall rule are feasible. Besides, the relationships between the striking velocity of flyer and the spall thickness as well as spall time are investigated. This study provides a methodology to quantify the damage evolution of phenolic composites under impact loading.