Burial and scour around short cylinder under progressive shoaling waves

The results of a laboratory experimental program aimed at better understanding the scour around and burial of heavy cylindrical objects under oscillating flow on a sandy bed are described. This study was motivated by its application to the dynamics of isolated cobbles/mines on a sandy floor under nonlinear progressive waves, such as that occur in shallow coastal waters beyond the wave-breaking region. In the experiments, nonlinear progressive waves were generated in a long wave tank of rectangular cross-section with a bottom slope. Model mines (short cylinders) were placed on the sandy bottom and the temporal evolution of the bed profile and the velocity field in the near field of the object were observed. Experiments were conducted at relatively high Reynolds numbers for a range of flow conditions, which can be characterized by the Keulegan–Carpenter number and Shields parameter. Depending on the values of these parameters, four different scour regimes around the cylinder including periodical burial of cylinder under migrating sand ripples were observed; they were classified as: (i) no scour/burial, (ii) initial scour, (iii) expanded scour, and (iv) periodic burial cases. A scour regime diagram was developed and the demarcation criteria between different regimes were deduced. Semi-empirical formulae that permit estimation of the scour depth with time, the equilibrium maximum scour depth and length, and conditions necessary for the burial of the cylinder as a function of main external parameters are also proposed.     

A note on estimation of the Jacobian elliptic parameter in cnoidal wave theory

A new and simple calculating technique for the Jacobian elliptic parameter is presented in this study. The technique is very useful in generating a train of cnoidal waves in both laboratory and numerical wave tanks. Upon specification of water depth, the wave height and either the wave period or the wavelength, the proposed technique uses the Newton–Raphson method to estimate the Jacobian elliptic parameter directly, without trial and error procedures or look-up in tables. It is shown that the technique provides equally accurate results as the ad hoc methods previously used.     

Experimental Studies of Aerosols in the Atmosphere of Semiarid Landscapes of Kalmykia: 1. Microphysical Parameters and Mass Concentration of Aerosol Particles

Izvestiya, Atmospheric and Oceanic Physics - This paper summarizes the results of long-term (2004–2016) comprehensive experimental studies of microphysical parameters and the mass...     

Distribution of suspended particulate matter in the northern Bohai Bay in summer and its relation with thermocline

Field observations of suspended particulate matter (SPM) in the Bohai Bay, China have not been widely reported. The aim of this paper is to describe the horizontal and vertical distribution of mass and volume concentrations of SPM, respectively, based on observed data at 312 stations in the northern Bohai Bay during summer of 2006. A numerical model ECOMSED coupled with a sediment transport module was also established to further discuss the mechanism of the thermocline effect on the vertical distribution of SPM. The mass concentrations of SPM exhibited high inshore values and low offshore values in the horizontal distribution; while in the vertical direction, characteristics of the volume concentration of SPM can be divided into two types: one with a sharp peak at depth of 10–15 m and another without. The peak value at the depth of the thermocline was resulted from concentrated phytoplankton. A numerical experiment further displayed that the thermocline can also prevent particles from being resuspended upward.     

An Experi mental Study on Wave-Induced Dynamic Stresses in Seabed

1 .IntroductionEvery year ,Taiwanis subjectedtotwo or three typhoonintrusions in average which always causedisasters . Most of the disasters which occur around the coastal zone are due to seabed instability andcoastal structure destruction caused bytyphoo…     

Reduction of hydroelastic responses of a very-long floating structure by a floating oscillating-water-column breakwater system

The hydroelastic responses of a very-long floating structure (VLFS) placed behind a reverse T-shape freely floating breakwater with a built-in oscillating water column (OWC) chamber are analyzed in two dimensions. The Bernoulli–Euler beam equation is coupled with the equations of rigid and elastic motions of the breakwater and the VLFS. The interaction of waves between the floating rigid breakwater and the elastic VLFS is formulated in a consistent manner. It has been shown numerically that the structural deflections of the VLFS can be reduced significantly by a suitably designed reverse T-shape floating breakwater.     

Spatial and temporal variations of mesozooplankton in the Pearl River estuary, China

This paper examines spatial and temporal variations of mesozooplankton abundance, biomass and community structure during three cruises of July 2002 (summer), January 2003 (winter), and April 2003 (spring) in the Pearl River estuary, China. Zooplankton abundance and biomass fluctuated widely and showed distinct heterogeneity in the Pearl River estuary. A total of 154 species were identified during three surveys. The number of zooplankton species richness was strongly linked to salinity. Hierarchical cluster analysis identified three zooplankton groups during this study. Estuarine, neritic and pelagic groups corresponded to the upper, middle and lower reaches in the Pearl River estuary. The difference among groups could be mainly ascribed to changes in the relative contributions of the dominant species. The fluctuations in the zooplankton abundance, biomass and community structure were determined by the interactive effects of freshwater inflow, tidal and coastal currents, chlorophyll a, salinity and temperature. Significant spatial variability in the distribution of zooplankton species, abundance and biomass can be ascribed to the virtual presence of a horizontal gradient in salinity.     

Large-Scale Structures in Comet Hale–Bopp

The plasma tails of comets clearly show the demarcation of the solar wind into distinct equatorial and polar regions (Brandt and Snow (2000), Icarus 148, 52–64).The boundary is determined by the maximum extent in latitude of the heliospheric current sheet (HCS). The observational record contains many well-observed equatorial comets, but observations of comets in the polar region are relatively rare. In addition to its size and brightness, comet Hale–Bopp had an orbital inclination of 89.4° and was well observed for months in the polar region. We document the comet's large-scale appearance throughout the apparition, including the polar region and its transition into the equatorial region. The bright dust tail hampered observations of the plasma tail, particularly near the head, but images taken with a CO⁺ filter show a very large disconnection event (DE) on May 7 and May 8, 1997. The time of disconnection is estimated at approximately May 4.0. This DE is associated with a crossing of the HCS. The model calculations of the HCS indicate that other crossings might have occurred in late April, but given the uncertainty in the calculation, the comet might have missed the HCS. Sparse observational coverage and the bright dust tail prevent further investigation of the potential earlier HCS crossings. The plasma tail shows anomalous orientations at the highest latitudes and possible explanations are discussed.     

Multiple magnetic clouds in interplanetary space

An interplanetary magnetic cloud (MC) is usually considered the byproduct of a coronal mass ejection (CME). Due to the frequent occurrence of CMEs, multiple magnetic clouds (multi-MCs), in which one MC catches up with another, should be a relatively common phenomenon. A simple flux rope model is used to get the primary magnetic field features of multi-MCs. Results indicate that the magnetic field configuration of multi-MCs mainly depends on the magnetic field characteristics of each member of multi-MCs. It may be entirely different in another situation. Moreover, we fit the data from the Wind spacecraft by using this model. Comparing the model with the observations, we verify the existence of multi-MCs, and propose some suggestions for further work.     

Hydrous and anhydrous alterations of chondrules in Kaba and Mokoia CV chondrites

Abstract— Chondrules in the Bali-like CV chondrite Kaba and the Allende-like portion of the Mokoia breccia have been studied to explore the relationship between hydrous alteration to form phyllosilicates and anhydrous alteration resulting in secondary olivine zonation, replacement of enstatite by ferroan olivine and formation of feldspathoids (nepheline and sodalite). All Kaba chondrules experienced extensive hydrous alteration; whereas, anhydrous alteration was minor and resulted only in the olivine zonation. On the other hand, all of the Mokoia chondrules experienced both extensive anhydrous and hydrous alteration. Bronzite rims formed between relic enstatite grains and phyllosilicates in both Kaba and Mokoia during the hydrous alteration. Petrographic observations indicate that phyllosilicates in Mokoia postdate formation of the secondary ferroan olivine and feldspathoids. We conclude that anhydrous alteration in Kaba and Mokoia predated hydrous alteration and took place before accretion of chondrules into the CV parent asteroid.