Planetary and figure-figure effects on the moon's rotational motion

An accurate theory of the rotation of the Moon has been constructed by numerical integration. All direct perturbations on the Moon's rotational motion have been analysed. The requirements of the current observational accuracy are such that some improvements had to be added to the theoretical models. First, the gravitational figure of the Moon has been developed up to the fifth degree harmonics. Second, mutual potential effects between the figure of the Moon and the figure of the Earth have been expanded farther up. The direct action of planets must be taken into account, its effects being very small but not always negligible. The physical librations resulting of planetary effects and Earth-Moon figure-figure interactions are presented in this paper.     

Dynamic Responses of A Semi-Type Offshore Floating Wind Turbine During Normal State and Emergency Shutdown

This paper addresses joint wind-wave induced dynamic responses of a semi-type offshore floating wind turbine (OFWT) under normal states and fault event conditions. The analysis in this paper is conducted in time domain, using an aero-hydro-servo-elastic simulation code-FAST. Owing to the unique viscous features of the reference system, the original viscous damping model implemented in FAST is replaced with a quadratic one to gain an accurate capture of viscous effects. Simulation cases involve free-decay motion in still water, steady motions in the presence of regular waves and wind as well as dynamic response in operational sea states with and without wind. Simulations also include the cases for transient responses induced by fast blade pitching after emergency shutdown. The features of platform motions, local structural loads and a typical mooring line tension force under a variety of excitations are obtained and investigated.     

Investigation of terrain illumination effects on vegetation indices and VI-derived phenological metrics in subtropical deciduous forests

We used RapidEye and Moderate Resolution Imaging Spectroradiometer (MODIS)/Terra data to study terrain illumination effects on 3 vegetation indices (VIs) and 11 phenological metrics over seasonal deciduous forests in southern Brazil. We applied TIMESAT for the analysis of the Enhanced Vegetation Index (EVI) and the Normalized Difference Vegetation Index (NDVI) derived from the MOD13Q1 product to calculate phenological metrics. We related the VIs with the cosine of the incidence angle i (Cos i) and inspected percentage changes in VIs before and after topographic C-correction. The results showed that the EVI was more sensitive to seasonal changes in canopy biophysical attributes than the NDVI and Red-Edge NDVI, as indicated by analysis of non-topographically corrected RapidEye images from the summer and winter. On the other hand, the EVI was more sensitive to terrain illumination, presenting higher correlation coefficients with Cos i that decreased with reduction in the canopy background L factor. After C-correction, the RapidEye Red-Edge NDVI, NDVI, and EVI decreased 2%, 1%, and 13% over sunlit surfaces and increased up to 5%, 14%, and 89% over shaded surfaces, respectively. The EVI-related phenological metrics were also much more affected by topographic effects than the NDVI-derived metrics. From the set of 11 metrics, the 2 that described the period of lower photosynthetic activity and seasonal VI amplitude presented the largest correlation coefficients with Cos i. The results showed that terrain illumination is a factor of spectral variability in the seasonal analysis of phenological metrics, especially for VIs that are not spectrally normalized.     

On the understanding of cyclic interaction mechanisms in an energy pile group

Integrating ground heat exchanger elements into concrete piles is now considered as an efficient energy solution for heating/cooling of buildings. In addition to the static load of buildings, the concrete piles also undergo a cycle of thermal deformation. In the case of single energy pile, calculation methods already exist and permit to perform a proper geotechnical design. In the case of energy pile group, the thermo‐mechanical interactions within the group are more complex. Very few experimental results on the energy pile group are available so that numerical analysis can be an interesting way to provide complementary results about their behavior. This paper deals with a numerical analysis including a comparison between a single energy pile and an energy pile group with different boundary conditions at the pile head. In order to take into account the stress reversal induced by the thermal expansions and contractions, a cyclic elastoplastic constitutive model is introduced at the soil–pile interface. The analysis aims to give some insights about the long‐term cyclic interaction mechanisms in the energy pile group. Based on this qualitative study, some guidance can be brought for the design of energy piles in the case where group effects should be considered. Copyright © 2015 John Wiley & Sons, Ltd.     

Influences of vegetation disturbance on hydrogeomorphic response following wildfire

Quantifying the linkages between vegetation disturbance by fire and the changes in hydrologic processes leading to post‐fire erosional response remains a challenge. We measured the influence of fire severity, defined as vegetation disturbance (using a satellite‐derived vegetation disturbance index, VDI), landscape features that organize hydrologic flow pathways (relief and elongation ratios), and pre‐fire vegetation type on the probability of the occurrence of post‐fire gully rejuvenation (GR). We combined field surveys across 270 burned low‐order catchments (112 occurrences of GR) and geospatial analysis to generate a probabilistic model through logistic regression. VDI alone discriminated well between catchments where GR did and did not occur (area under the curve = 0.78, model accuracy = 0.72). The strong effect of vegetation disturbance on GR suggests that vegetation exerts a primary influence on the occurrence of infiltration excess run‐off and post‐fire erosion and that major gully erosion will not occur until fire consumes aboveground biomass. Other topographic and local factors also influenced GR response, including catchment elongation, per cent pre‐fire shrub, mid‐slope riparian vegetation, armoured headwaters, firehose effects, and concentration of severe burn in source areas. These factors highlight the need to consider vegetation effects in concert with local topography and site conditions to understand the propensity for flow accumulation leading to GR. We present a process‐based conceptual hydrologic model where vegetation loss from fire decreases rainfall attenuation and surface roughness, leading to accelerated flow accumulation and erosion; these effects are also influenced by interactions between fire severity and landscape structure. The VDI metric provides a continuous measure of vegetation disturbance and, when placed in a hydrologic context, may improve quantitative analysis of burned‐area susceptibility to erosive rainfall, hazard prediction, ecological effects of fire, landform evolution, and sensitivity to climate change. Copyright © 2015 John Wiley & Sons, Ltd.     

Numerical analysis of the geotechnical behaviour of energy piles

Energy geostructures are rapidly gaining acceptance around the world; they represent a renewable and clean source of energy that can be used for the heating and cooling of buildings and for de‐icing of infrastructures. This technology couples the structural role of geostructures with the energy supply, using the principle of shallow geothermal energy. The geothermal energy exploitation represents an additional thermal loading, seasonally cyclic, which is imposed on the soil and the structure itself. Because the primary role of the piles is the stability of the superstructure, this aspect needs to be ensured even in the presence of the additional thermal load. The goal of this paper is to numerically investigate the behaviour of energy pile foundations during heating–cooling cycles. For this purpose, the finite element method is used to simulate both a single and a group of energy piles. The piles are subjected to a constant mechanical load and a seasonally cyclic thermal load over several years, imposed in terms of injected–extracted thermal power. The soil and the pile–soil interface behaviours are reproduced using a thermoelastic‐thermoplastic constitutive model. The thermal‐induced stresses inside the piles and the additional displacements of the foundations are discussed. The group model is used to investigate the interactions between the piles during thermo‐mechanical loading. The presented results are specific to the studied cases but lead to the conclusion that both the thermal‐induced displacements and stresses, despite being acceptable under normal working conditions, deserve to be taken into account in the geotechnical design of energy piles. Copyright © 2014 John Wiley & Sons, Ltd.     

Predicting river width,depth and velocity at ungauged sites in England and Wales using multilevel models

Using a dataset of gauged river discharges taken from sites in England and Wales, linear multilevel models (also known as mixed effects models) were applied to quantify the variability in discharge and the discharge‐hydraulic geometry relationships across three nested spatial scales. A jackknifing procedure was used to test the ability of the multilevel models to predict hydraulic geometry, and therefore width, mean depth and mean velocity, at ungauged stations. These models provide a framework for making predictions of hydraulic geometry parameters, with associated levels of uncertainty, using different levels of data availability. Results indicate that as one travels downstream along a river there is greater variability in hydraulic geometry than is the case between rivers of similar sizes. This indicates that hydraulic geometry (and therefore hydrology) is driven by catchment area, to a greater extent than by natural geomorphological variations in the streamwise direction at the mesoscale, but these geomorphological variations can still have a major impact on channel structure. Copyright © 2008 John Wiley & Sons, Ltd.     

Simplified numerical modelling of pile penetration – the press‐replace technique

This paper presents a simplified finite element analysis technique, the ‘Press‐Replace’ technique, to model pile penetration problems in geotechnical engineering, particularly, pile jacking. The method is employed in standard finite element analysis software. The method involves a straining and a consequent geometry update phase. First, a cone penetration test in (undrained) clay is modelled and compared with the results of analytical, semi‐analytical and more advanced finite element techniques. The model sensitivity for the step size and mesh is investigated using a hypoplastic constitutive model. An optimum way of modelling based on the numerical performance is shown. Copyright © 2015 John Wiley & Sons, Ltd.     

Empirical evaluation of microtremor H/V spectral ratio

The objective of this work is to perform a purely empirical assessment of the actual capabilities of the horizontal-to-vertical (H/V) spectral ratio technique to provide reliable and relevant information concerning site conditions and/or site amplification. This objective has been tackled through the homogeneous (re)processing of a large volume of earthquakes and ambient noise data recorded by different research teams in more than 200 sites located mainly in Europe, but also in the Caribbean and in Tehran. The original recordings were first gathered in a specific database with information on both the sites and recorded events. Then, for all sites close to an instrumented reference, average site-to-reference spectral ratios (“spectral ratio method” (SSR)) were derived in a homogeneous way (window selection, smoothing, signal-to-noise ratio threshold, averaging), as well as H/V ratios (“HVSRE–RF”) on earthquake recordings. H/V ratios were also obtained from noise recordings at each site (either specific measurements, or extracted from pre- or post-event noise windows). The spectral curves resulting from these three techniques were estimated reliable for a subset of 104 sites, and were thus compared in terms of fundamental frequency, amplitude and amplification bandwidth, exhibiting agreements and disagreements, for which interpretations are looked for in relation with characteristics of site conditions. The first important result consists in the very good agreement between fundamental frequencies obtained with either technique, observed for 81% of the analyzed sites. A significant part of the disagreements correspond to thick, low frequency, continental sites where natural noise level is often very low and H/V noise ratios do not exhibit any clear peak. The second important result is the absence of correlation between H/V peak amplitude and the actual site amplification measured on site-to-reference spectral ratios. There are, however, two statistically significant results about the amplitude of the H/V curve: the peak amplitude may be considered as a lower bound estimate of the actual amplification indicated by SSR (it is smaller for 79% of the 104 investigated sites), and, from another point of view, the difference in amplitude exhibits a questioning correlation with the geometrical characteristics of the sediment/basement interface: large SSR/HV differences might thus help to detect the existence of significant 2D or 3D effects.