Impacts of Coastal Terrain on Warm-Sector Heavy-Rain-Producing MCSs in Southern China

Warm-sector heavy rainfall in southern China refers to the heavy rainfall that occurs within a weakly-forced synoptic environment under the influence of monsoonal airflows. It is usually located near the southern coast, and is characterized by poor predictability and a close relationship with coastal terrain. This study investigates the impacts of coastal terrain on the initiation, organization and heavy-rainfall potential of MCSs in warm-sector heavy rainfall over southern China using quasi-idealized WRF simulations and terrain-modification experiments. Typical warm-sector heavy rainfall events were selected to produce composite environments that forced the simulations. MCSs in these events all initiated in the early morning and developed into quasi-linear convective systems along the coast with a prominent backbuilding process. When the small coastal terrain is removed, the maximum 12-h rainfall accumulation decreases by ~46%. The convection initiation is advanced ~2 h with the help of orographic lifting associated with flow interaction with the coastal hills in the control experiment. Moreover, the coastal terrain weakens near-surface winds and thus decreases the deep-layer vertical wind shear component perpendicular to the coast and increases the component parallel to the coast; the coastal terrain also concentrates the moisture and instability over the coastal region by weakening the boundary layer jet. These modifications lead to faster upscale growth of convection and eventually a well-organized MCS. The coastal terrain is beneficial for backbuilding convection and thus persistent rainfall by providing orographic lifting for new cells on the western end of the MCS, and by facilitating a stronger and more stagnant cold pool, which stimulates new cells near its rear edge.

The Matata Earthquake Sequence of 1977, Bay of Plenty, New Zealand

<p>An ML. 5.4 earthquake and an associated sequence of smaller earthquakes, including foreshocks, were well recorded in 1977 by a network of 10 seismographs set for a microearthquake survey in the Bay of Plenty region, which is transitional between back-are spreading regions of the Havre Trough and the continental North Island. Upper crustal aftershock origins clustered and migrated within an area 7 km by 15 km elongated east-west. The aftershocks were relatively swarm-like, producing a b- value of 1.29 [plus or minus] 0.13, and were apparently of long sequence duration, with decay coefficient p = 0.67 [plus or minus] 0.03. A northeast-trending rupture fitted for the mainshock, originating close to where foreshocks were centred, and passing between tight concentrations of later aftershock activity to either side. Teleseismic waveforms, in addition to providing a 10.5 km estimate of focal depth, helped to constrain the solution of focal mechanism for the mainshock. The preferred solution is for mainly right-lateral slip on a northeast striking plane but with a normal component. The slip trend parallels the front of recent volcanism. Mechanisms for related events range from normal to strike slip, on parallel and intersecting planes, and are indicative of the complexity of geological structure where north-trending faults of the North Island shear belt meet with the front of recent volcanism. as well as of a prevailing traction across the volcanic front. The volcanic region is characterised by a low Poisson's ratio, suggested by the Wadati method to be v= 0.19 [plus or minus] 0.01 in contrast to v =0.27 [plus or minus] 0.01 for the greywacke region to the southeast; this difference is attributed to contrasting rock types and other conditions either side of the volcanic front. The multiplicity of earthquake sequences in the volcanic region indicates a high degree of heterogeneous structure. A low stress drop of 2.8 MPa inferred for the Matata mainshock suggests that the faulting occurs on pre-existing planes. Off-fault aftershocks occurred where the failure stress increased as a result of the mainshock rupture. A concurrent sequence of earthquakes originating near 50km depth indicated thrusting on the lithospheric plate interface underlying the North Island; thrusting on the interface apparently extends to about 70km depth, where the plates become decoupled. Oblique plate convergence and stick-slip motion on the weakly coupled interface provides the regional dextral shear component observed in the volcanic region for the Matata mainshock. An extensional component is therefore a necessary addition for the observed normal component of faulting, which predominated for the 1987 Edgecumbe mainshock. Wave mode conversions inferred for subcrustal earthquakes and the Matata sequence mainshock indicate that the Moho shallows from 28.5 km to 22 km northwestwards across the volcanic front, suggesting that new crust in the Bay of Plenty region is being created over a wide region rather than by active rifting along a sharp margin.</p>

The Matata Earthquake Sequence of 1977, Bay of Plenty, New Zealand

<p>An ML. 5.4 earthquake and an associated sequence of smaller earthquakes, including foreshocks, were well recorded in 1977 by a network of 10 seismographs set for a microearthquake survey in the Bay of Plenty region, which is transitional between back-are spreading regions of the Havre Trough and the continental North Island. Upper crustal aftershock origins clustered and migrated within an area 7 km by 15 km elongated east-west. The aftershocks were relatively swarm-like, producing a b- value of 1.29 [plus or minus] 0.13, and were apparently of long sequence duration, with decay coefficient p = 0.67 [plus or minus] 0.03. A northeast-trending rupture fitted for the mainshock, originating close to where foreshocks were centred, and passing between tight concentrations of later aftershock activity to either side. Teleseismic waveforms, in addition to providing a 10.5 km estimate of focal depth, helped to constrain the solution of focal mechanism for the mainshock. The preferred solution is for mainly right-lateral slip on a northeast striking plane but with a normal component. The slip trend parallels the front of recent volcanism. Mechanisms for related events range from normal to strike slip, on parallel and intersecting planes, and are indicative of the complexity of geological structure where north-trending faults of the North Island shear belt meet with the front of recent volcanism. as well as of a prevailing traction across the volcanic front. The volcanic region is characterised by a low Poisson's ratio, suggested by the Wadati method to be v= 0.19 [plus or minus] 0.01 in contrast to v =0.27 [plus or minus] 0.01 for the greywacke region to the southeast; this difference is attributed to contrasting rock types and other conditions either side of the volcanic front. The multiplicity of earthquake sequences in the volcanic region indicates a high degree of heterogeneous structure. A low stress drop of 2.8 MPa inferred for the Matata mainshock suggests that the faulting occurs on pre-existing planes. Off-fault aftershocks occurred where the failure stress increased as a result of the mainshock rupture. A concurrent sequence of earthquakes originating near 50km depth indicated thrusting on the lithospheric plate interface underlying the North Island; thrusting on the interface apparently extends to about 70km depth, where the plates become decoupled. Oblique plate convergence and stick-slip motion on the weakly coupled interface provides the regional dextral shear component observed in the volcanic region for the Matata mainshock. An extensional component is therefore a necessary addition for the observed normal component of faulting, which predominated for the 1987 Edgecumbe mainshock. Wave mode conversions inferred for subcrustal earthquakes and the Matata sequence mainshock indicate that the Moho shallows from 28.5 km to 22 km northwestwards across the volcanic front, suggesting that new crust in the Bay of Plenty region is being created over a wide region rather than by active rifting along a sharp margin.</p>

Flexoelectric and Piezoelectric Coupling in a Bended MoS2 Monolayer

Low-dimensional (LD) transition metal dichalcogenides (TMDs) in the form of nanoflakes, which consist of one or several layers, are the subject of intensive fundamental and applied research. The tuning of the electronic properties of the LD-TMDs are commonly related with applied strains and strain gradients, which can strongly affect their polar properties via piezoelectric and flexoelectric couplings. Using the density functional theory and phenomenological Landau approach, we studied the bended 2H-MoS2 monolayer and analyzed its flexoelectric and piezoelectric properties. The dependences of the dipole moment, strain, and strain gradient on the coordinate along the layer were calculated. From these dependences, the components of the flexoelectric and piezoelectric tensors have been determined and analyzed. Our results revealed that the contribution of the flexoelectric effect dominates over the piezoelectric effect in both in-plane and out-of-plane directions of the monolayer. In accordance with our calculations, a realistic strain gradient of about 1 nm−1 can induce an order of magnitude higher than the flexoelectric response in comparison with the piezoelectric reaction. The value of the dilatational flexoelectric coefficient is almost two times smaller than the shear component. It appeared that the components of effective flexoelectric and piezoelectric couplings can be described by parabolic dependences of the corrugation. Obtained results are useful for applications of LD-TMDs in strain engineering and flexible electronics.

Oscillation analysis of doubly-fed unit considering wind speed variation

Tower shadow effect and wind shear may cause power oscillation of the unit. In order to study the influence of tower shadow effect and wind shear on the output power of wind turbine, a doubly-fed turbine was taken as an example. Firstly, the influence of tower shadow effect and wind shear was considered to study the periodic power fluctuation characteristics of wind turbines. Then, according to the dynamic model of mechanical transmission mechanism, the influences of the inertia constants of generator, fan and the stiffness coefficient of the shaft system on the transient performance of the wind power generation system were considered respectively. Finally, a single machine infinite bus system model including wind speed model is built on PSCAD/EMTDC platform for simulation. The results show that the tower shadow effect and wind shear component can cause the power fluctuation of the turbine. When the power fluctuation frequency of the turbine is equal to the natural oscillation frequency of the wind turbine shafting, the resonance of the turbine occurs, and the amplitude of oscillation is the largest. Changing the transmission parameters will affect the power fluctuation amplitude and speed response speed of the unit.

An Extension Strain Type Mohr–Coulomb Criterion

Extension fractures are typical for the deformation under low or no confining pressure. They can be explained by a phenomenological extension strain failure criterion. In the past, a simple empirical criterion for fracture initiation in brittle rock has been developed. In this article, it is shown that the simple extension strain criterion makes unrealistic strength predictions in biaxial compression and tension. To overcome this major limitation, a new extension strain criterion is proposed by adding a weighted principal shear component to the simple criterion. The shear weight is chosen, such that the enriched extension strain criterion represents the same failure surface as the Mohr–Coulomb (MC) criterion. Thus, the MC criterion has been derived as an extension strain criterion predicting extension failure modes, which are unexpected in the classical understanding of the failure of cohesive-frictional materials. In progressive damage of rock, the most likely fracture direction is orthogonal to the maximum extension strain leading to dilatancy. The enriched extension strain criterion is proposed as a threshold surface for crack initiation CI and crack damage CD and as a failure surface at peak stress CP. Different from compressive loading, tensile loading requires only a limited number of critical cracks to cause failure. Therefore, for tensile stresses, the failure criteria must be modified somehow, possibly by a cut-off corresponding to the CI stress. Examples show that the enriched extension strain criterion predicts much lower volumes of damaged rock mass compared to the simple extension strain criterion.

Laboratory Investigation of Hydraulic Fracture Behavior of Unconventional Reservoir Rocks

The heterogeneity of the rock fabric is a significant factor influencing the initiation and propagation of a hydraulic fracture (HF). This paper presents a laboratory study of HF created in six shale-like core samples provided by RITEK LLC collected from the same well, but at different depths. For each tested sample, we determined the breakdown pressure, the HF growth rate, and the expansion of the sample at the moment when the HF reaches the sample surface. Correlations were established between the HF parameters and the geomechanical characteristics of the studied samples, and deviations from the general relationships were explained by the influence of the rock matrix. The analysis of the moment tensor inversion of radiated acoustic emission (AE) signals allows us to separate AE signals with a dominant shear component from the signals with a significant tensile component. The direction of microcrack opening was determined, which is in good agreement with the results of the post-test X-ray CT analysis of the created HF. Thus, it has been shown that a combination of several independent laboratory techniques allows one to reliably determine the parameters that can be used for verification of hydraulic fracturing models.

New Triaxial Connection Safety Factor for Tubular Design

Summary The American Petroleum Institute (API) equation for internal leak of API connections is uniaxial because it ignores axial force and external backup pressure. The ISO 13679 (2002) standard for qualification of premium connections is biaxial at best. It includes tension/compression but ignores backup pressure for both internal and external leak tests. For tubular design, this paper introduces a new fully triaxial safety factor for threaded connections with dependence on thread shear and hydrostatic pressure. Triaxial hydrostatic behavior is modeled with the mean normal stress, and thread shear behavior is modeled with the shear component of the von Mises stress. A leak line for use like the pipe body ellipse is proposed for quick leak assessment. Leak ratings and correlation with finite element analysis (FEA) results are presented for an example case of a 7-in.35-ppf N80 long-thread-casing (LTC) connection. The new triaxial safety factor with two connection constants applies to all types of threaded connections, including tubing, casing, and drillpipe, so long as the two constants are evaluated with appropriate but simple physical tests.

Experimental recommendations for estimating lower extremity loading based on joint and activity

Researchers often estimate joint loading using musculoskeletal models to solve the inverse dynamics problem. This approach is powerful because it can be done non-invasively, however, it relies on assumptions and physical measurements that are prone to measurement error. The purpose of this study was to determine the impact of these errors - specifically, segment mass and shear ground reaction force - have on analyzing joint loads during activities of daily living. We preformed traditional marker-based motion capture analysis on 8 healthy adults while they completed a battery of exercises on 6 degree of freedom force plates. We then scaled the mass of each segment as well as the shear component of the ground reaction force in 5% increments between 0 and 200% and iteratively performed inverse dynamics calculations, resulting in 1,681 mass-shear combinations per activity. We compared the peak joint moments of the ankle, knee, and hip at each mass-shear combination to the 100% mass and 100% shear combination to determine the percent error. We found that the ankle was most resistant to changes in both mass and shear and the knee was resistant to changes in mass while the hip was sensitive to changes in both mass and shear. These results can help guide researchers who are pursuing lower-cost or more convenient data collection setups.

Shear-Related Gold Ores in the Wadi Hodein Shear Belt, South Eastern Desert of Egypt: Analysis of Remote Sensing, Field and Structural Data

Space-borne multispectral and radar data were used to comprehensively map geological contacts, lithologies and structural elements controlling gold-bearing quartz veins in the Wadi Hodein area in Egypt. In this study, enhancement algorithms, band combinations, band math (BM), Principal Component Analysis (PCA), decorrelation stretch and mineralogical indices were applied to Landsat-8 OLI, ASTER and ALOS PALSAR following a pre-designed flow chart. Together with the field observations, the results of the image processing techniques were exported to the GIS environment and subsequently fused to generate a potentiality map. The Wadi Hodein shear belt is a ductile shear corridor developed in response to non-coaxial convergence and northward escape tectonics that accompanied the final stages of terrane accretion and cratonization (~680–600 Ma) in the northern part of the Arabian–Nubian Shield. The evolution of this shear belt encompassed a protracted ~E–W shortening and recurrent sinistral transpression as manifested by east-dipping thrusts and high-angle reverse shear zones. Gold-mineralized shear zones cut heterogeneously deformed ophiolites and metavolcaniclastic rocks and attenuate in and around granodioritic intrusions. The gold mineralization event was evidently epigenetic in the metamorphic rocks and was likely attributed to rejuvenated tectonism and circulation of hot fluids during transpressional deformation. The superposition of the NW–SE folds by NNW-trending, kilometer scale tight and reclined folds shaped the overall framework of the Wadi Hodein belt. Shallow NNW- or SSE-plunging mineral and stretching lineations on steeply dipping shear planes depict a considerable simple shear component. The results of image processing complying with field observations and structural analysis suggest that the coincidence of shear zones, hydrothermal alteration and crosscutting dikes in the study area could be a considered as a model criterion in exploration for new gold targets.