► We develop a shock spectrum analysis (SSA) for barge collisions design of bridge structures. ► We establish the equation of shock spectrum analytically. ► The proposed shock spectrum agrees with ...the numerical result. ► Most combinational rules in earthquake engineering are not always adequate for barge impacts. ► We find that the results from the (SSA) are in good agreement with the expected results.
An equivalent static analysis procedure is employed in most of design specifications for barge collisions, but it fails to account for dynamic effects and potentially underestimates the demand of bridge structures. Alternatively, a shock spectrum analysis (SSA) approach is presented to efficiently determine the dynamic demand of bridge structures under barge collisions. The shock spectrum is developed analytically based on the interaction analysis of barge-bridge collisions, which agrees with the numerical result. The combinational rules are then discussed for the developed SSA. In the case study, results obtained from the SSA are in agreement with the expected results.
•The relative location of a temperature strip and the syn. point affect Mode S.•The location of the syn. point is changed due to the phase speed change of Mode F.•Put a narrow cooling strip upstream ...of the syn. point could stabilize the BL.•Put a narrow heating strip downstream of the syn. point could stabilize the BL.
In this study, a numerical investigation of the perturbation evolution in a Mach 6 flat-plate boundary layer with a local heating or cooling strip is presented. The position of the temperature strip is varied while the strip length is constant and approximated to the boundary-layer thickness. Simulations are based on a time-accurate integration of the compressible Navier-Stokes equations, with a small disturbance of fixed frequency triggered via periodic suction-blowing at the plate leading edge. The stability characteristics of the hypersonic boundary layer are interpreted by spatial linear stability theory (LST). The results indicate that the relative location of a local heating/cooling strip and the synchronization point significantly affect Mode S. With respect to the heating-strip cases, the unstable mode is amplified when a heating strip is located upstream of the synchronization point, and the effect is reversed if the heating strip is placed downstream. In a manner opposite to the local heating effect, placing a narrow cooling strip upstream of the synchronization point stabilizes mode S, while the effect is reversed if the cooling strip is put downstream of the synchronization point. Different from previous stability studies on roughness and porous wall, the location of the synchronization point is not fixed, and this is mainly caused by the change to the phase speed of Mode F. The results suggest that an efficient way to stabilize the boundary layer is to put a narrow cooling strip further upstream of the synchronization point, or put a narrow heating strip downstream of the synchronization point.
Abstract
Soft X-ray emissions induced by solar wind ions that collide with neutral material in the solar system have been detected around planets, and were proposed as a remote probe for solar wind ...interaction with the Martian exosphere. A multi-fluid three-dimensional magnetohydrodynamic model is adopted to derive the global distributions of solar wind particles. Spherically symmetric exospheric H, H
2
, He, O, and CO
2
density profiles and a sophisticated hybrid model that includes charge-exchange and proton–neutral excitation processes are used to study the low triplet line ratio
G
=
i
+
f
r
(0.77 ± 0.58) of O
vii
and the total X-ray luminosity around Mars. We further calculate the emission factor
α
-value with different neutrals over wide ion-abundance and velocity ranges. Our results are in good agreement with those of previous reports. The evolution of the charge stage of solar wind ions shows that sequential recombination due to charge-exchange can be negligible in the interaction region. This only appears below an altitude of 400 km. The anonymous low disk
G-
ratio can be easily explained by the collisional quenching effect at neutral densities higher than 10
11
cm
−3
. However, the quenching contribution is small in Mars’ exosphere and only appears below 400 km. Charge-exchange with H
2
and N
2
is still the most likely reason for this low
G
-ratio. X-ray emissivity maps in collisions with different neutrals differ from each other. A clear bow shock arising from the collision with all the neutrals is in accordance with previous reports. The resulting total X-ray luminosity of 6.55 MW shows better agreement with the XMM-Newton observation of 12.8 ± 1.4 MW than that of previous predictions.
Friction stir processing (FSP) improves the mechanical properties of metals by refining grains to submicron scale. It also introduces significant basal texture in ultrafine grained magnesium alloy by ...tilting the basal poles by various degrees with respect to the depth in the nugget. This texture results in much higher tensile stress and ductility, but lower uniform strain in the transverse direction, than in the processing direction. This paper discusses the effect of FSP-induced texture on anisotropy in mechanical behavior.
► Evaluating model results provides assessment of understanding of the terrestrial carbon cycle. ► The models differ substantially in their estimates of net ecosystem productivity. ► Much of the ...variability in modeled respiration is likely driven by variability in GPP. ► Models can predict plausible values for net ecosystem productivity, but for the wrong reasons. ► Details studies are needed to understand how model formulation and choices impact model performance.
Understanding of carbon exchange between terrestrial ecosystems and the atmosphere can be improved through direct observations and experiments, as well as through modeling activities. Terrestrial biosphere models (TBMs) have become an integral tool for extrapolating local observations and understanding to much larger terrestrial regions. Although models vary in their specific goals and approaches, their central role within carbon cycle science is to provide a better understanding of the mechanisms currently controlling carbon exchange. Recently, the North American Carbon Program (NACP) organized several interim-synthesis activities to evaluate and inter-compare models and observations at local to continental scales for the years 2000–2005. Here, we compare the results from the TBMs collected as part of the regional and continental interim-synthesis (RCIS) activities. The primary objective of this work is to synthesize and compare the 19 participating TBMs to assess current understanding of the terrestrial carbon cycle in North America. Thus, the RCIS focuses on model simulations available from analyses that have been completed by ongoing NACP projects and other recently published studies. The TBM flux estimates are compared and evaluated over different spatial (1°×1° and spatially aggregated to different regions) and temporal (monthly and annually) scales. The range in model estimates of net ecosystem productivity (NEP) for North America is much narrower than estimates of productivity or respiration, with estimates of NEP varying between −0.7 and 2.2PgCyr−1, while gross primary productivity and heterotrophic respiration vary between 12.2 and 32.9PgCyr−1 and 5.6 and 13.2PgCyr−1, respectively. The range in estimates from the models appears to be driven by a combination of factors, including the representation of photosynthesis, the source and of environmental driver data and the temporal variability of those data, as well as whether nutrient limitation is considered in soil carbon decomposition. The disagreement in current estimates of carbon flux across North America, including whether North America is a net biospheric carbon source or sink, highlights the need for further analysis through the use of model runs following a common simulation protocol, in order to isolate the influences of model formulation, structure, and assumptions on flux estimates.
► We proposed a FEM failure criterion to simulate the elongation of plate samples. ► The FEM simulation result showed good agreement with experiment result. ► We found that the elongation increases ...as the thickness of the specimen increase. ► The size effect was due to the stress distribution at neck region of different size.
Specimens with a rectangular cross-section are commonly used to measure the tensile properties of materials. However, the specimen size may influence the results. In this study, the tensile properties of FH550 and X80 steels were investigated using rectangular cross-section specimens with different thicknesses and the same width. Both an experimental study and a 3D finite element method (FEM) study have been conducted. The results show that the uniform elongation is independent of specimen size, but the post-necking elongation increases dramatically as specimen thickness increases, which was attributed to the stress distribution near neck region. Single factor analysis results show that both the yield and the ultimate tensile strength of the specimens are independent of the thickness when the specimen thickness is larger than 1
mm.
Background
To evaluate the stability of jointed rock masses subjected to dynamic disturbance, laboratory dynamic shear test on rock joint is necessary. Developing dynamic shear test equipment for ...rock joint is currently a pressing issue.
Objective
To address this issue, a new apparatus is developed to reproduce the shear-slip process of rock joint subjected to dynamic disturbance under various initial stress state.
Methods
The disturbance load, which has a dominant frequency close to that of seismic waves, is generated by an electromagnetic-driven disturbance generator, and its amplitude and duration can be accurately controlled in a stable manner. The initial normal and shear stresses can be applied in the shear test under dynamic disturbance using servo-controlled loading unit, which facilitates the simulation of the real stress state of rock joint.
Results
The shear tests under dynamic disturbance show that when an initial shear stress is applied to rock joint, an additional deformation stage of stress recovering can also trigger a slip displacement, which contributes to the destabilization of jointed rock masses. With increasing initial shear stress, the dynamic slip displacement, stress drop and post-disturbing deformation increase. The feasibility of the apparatus to conduct quasi-static direct shear tests with both the constant normal loading (CNL) and constant normal stiffness (CNS) boundaries is also verified.
Conclusions
Test results demonstrate that using the new apparatus, shear-slip properties of rock joint subjected to dynamic disturbance can be tested in various initial stress states.
The level of microRNA-205 (miR-205) is commonly deregulated in a number of cancers. Through the screening of the microRNA expression profile in bladder cancer tissue and cell lines, we found that ...expression of miR-205 was significantly suppressed. In addition, the levels of miR-205 expression had a negative correlation with the degree of bladder cancer malignancy. However, the biological functions of miR-205 remained unclear. In this study, we have demonstrated that miR-205 had a role in the inhibition of proliferation, migration and invasion of bladder cancer cells. Moreover, we have identified cyclin J (CCNJ) gene, which is involved in cell cycle regulation, as a novel target for miR-205. Furthermore, a long non-coding RNA HOTAIR (HOX transcript antisense RNA) was observed to participate in the silencing of miR-205 in bladder cancer cells by breaking the balance of histone modification between H3K4me3 (histone H3 at lysine 4 methylation) and H3K27me3 on miR-205 promoter. This study elucidates an important role that miR-205 had in the regulation of proliferation, migration and invasion of bladder cancer cells, suggesting a potential therapeutic target for combating bladder cancer.
Experimental observations of self-sustained pitch oscillations of a NACA 0012 airfoil at transitional Reynolds numbers were recently reported. The aeroelastic limit cycle oscillations, herein ...labelled as
laminar separation flutter, occur in the range 5.0×10
4≤Re
c
≤1.3×10
5. They are well behaved, have a small amplitude and oscillate about
θ=0°. It has been speculated that laminar separation leading to the formation of a laminar separation bubble, occurring at these Reynolds numbers, plays an essential role in these oscillations. This paper focuses on the Re
c
=7.7×10
4 case, with the elastic axis located at 18.6% chord. Considering that the experimental rig acts as a dynamic balance, the aerodynamic moment is derived and is empirically modelled as a generalized Duffing–van-der-Pol nonlinearity. As expected, it behaves nonlinearly with pitch displacement and rate. It also indicates a dynamically unstable equilibrium point, i.e. negative aerodynamic damping. In addition, large eddy simulations of the flow around the airfoil undergoing prescribed simple harmonic motion, using the same amplitude and frequency as the aeroelastic oscillations, are performed. The comparison between the experiment and simulations is conclusive. Both approaches show that the work done by the airflow on the airfoil is positive and both have the same magnitude. The large eddy simulation (LES) computations indicate that at
θ=0°, the pitching motion induces a lag in the separation point on both surfaces of the airfoil resulting in negative pitching moment when pitching down, and positive moment when pitching up, thus feeding the LCO.
PDF
