Theoretical and experimental studies on critical time delay of multi-DOF real-time hybrid simulation

This paper aims to investigate the critical stability of a multi-degree-of-freedom(multi-DOF)real-time hybrid simulation(RTHS).First,the critical time-delay analysis models are developed using the continuous-and discrete-time root locus(RL)techniques,respectively.A bilinear transform is introduced into the first-order Padéapproximation while conducting the discrete RL analysis.Based on this technique,the time delay can be explicitly used as the gain factor and thus the instability mechanism of the multi-DOF RTHS system can be analyzed.Subsequently,the critical time delays calculated by the continuous-and discrete-time RL techniques,respectively,are compared for a 2-DOF RTHS system.It is shown that assuming the RTHS system to be a continuous-time system will result in overestimating the critical time delay.Finally,theoretically calculated critical delays are demonstrated and validated by numerical simulation and a set of RTHS experiments.Parametric analysis provides a glimpse of the effects of time step,frequency and damping ratio in a performing partitioning scheme.The constructed analysis model proves to be useful for evaluating the critical time delay to predict stability and performance,therefore facilitating successful RTHS.     

Phosphorus speciation,transformation and benthic processes with implications for environmental impacts in the aquaculture area of Rushan Bay

Phosphorus(P) is an essential nutrient for many organisms in the ocean, which plays a central role in the stability of ecosystems and the evolution of the environment. The distribution, occurrence and source-sink process of P in offshore waters are highly influenced by mariculture activities. P transformation in water-sediment system is the key process in P cycling, however, the mechanism is poorly documented in the coastal sea which is influenced by human activities. Based on the comprehensive ...     

Spatiotemporal changes of biogenic elements in the Changjiang River Estuary and adjacent waters in summer over the last decade

The long-term spatiotemporal changes of surface biogenic elements in the Changjiang River Estuary and adjacent waters during the summer of 2008-2016 were analyzed in this study.The concentrations of dissolved inorganic nitrogen(DIN),soluble reactive phosphate(PO₄^3-) and silicate(SiO₃^2-) were generally stable,with a slight decrease of DIN and PO₄^3-,and a slight increase of SiO₃^2-,which mainly occurred in the e...     

Microbiota of a seepage face at the mouth of a subterranean estuary:diversity,distribution and substrate dependence

Subterranean estuaries, i.e., the mixing zone between terrestrial groundwater and recirculated seawater, host a wide range of microbiota. Here, field campaigns were conducted at the mouth of the subterranean estuary at the Sanggou Bay(Shandong Province, China) over four consecutive seasons at a seepage face(0-20 cm depth). The diversity of benthic microbiome was characterized via 16S rRNA gene sequencing and metagenomics, combined with physic-chemical parameters, e.g., organic carbon, total nitr...     

Epipelagic mesozooplankton communities in the northeastern Indian Ocean off Myanmar during the winter monsoon

The northern Andaman Sea off Myanmar is one of the relatively high productive regions in the Indian Ocean. The abundance, biomass and species composition of mesozooplankton and their relationships with environmental variables in the epipelagic zone(～200 m) were studied for the first time during the Sino-Myanmar joint cruise(February 2020). The mean abundance and biomass of mesozooplankton were(1 916.7±1 192.9) ind./m³ and(17.8±7.9) mg/m³, respectively. A total of 213 specie...     

In-situ detection equipment for radon-in-water:unattended operation and monthly investigations

Radon is recognized as a powerful tracer of certain geophysical processes in marine and aquatic environments. In the past few decades, the instruments and methods for measuring radon concentration in water have been developed to some extent but still lack underwater in-situ measurements. Here we present an in-situ detection equipment for radon-in-water(pulsed ionization chamber(PIC)-radon) to measure dissolved radon in ocean and groundwater settings. The equipment has been successfully deployed ...