A mobile marine seismometer(MMS)is a vertical underwater vehicle that detects ocean seismic waves.One of the critical operational requirements for an MMS is that it remains suspended at a desired depth.This article ai...A mobile marine seismometer(MMS)is a vertical underwater vehicle that detects ocean seismic waves.One of the critical operational requirements for an MMS is that it remains suspended at a desired depth.This article aimed to propose a fixed-depth suspension control for the MMS with a limited onboard energy supply.The research team established a kinematic model to analyze fluctuations in the vertical motion of the MMS and the delayed response of the system.We ascertained a direct one-to-one correlation between the displacement volume of the mobile ocean seismic instrument and the depth at which it reaches a state of neutral buoyancy(commonly referred to as the hover depth).A fixed-depth control algorithm was introduced,allowing a gradual approach to the necessary displacement volume to reach the desired suspension depth.The study optimized the boundary conditions to reduce unnecessary adjustments and mitigate the time delay caused by the instrument’s inertia,thereby significantly minimizing energy consumption.This method does not require calculating the hydrodynamic parameters or transfer functions of the MMS,thereby considerably reducing the implementation complexity.In the three-month sea trial in the South China Sea,the seismic instrument was set to hover at 800 m,with a permissible fluctuation of±100 m,operating on a seven-day cycle.The experimental results show that the seismic instrument has an average hover error of 34.6 m,with a vertical drift depth of 29.6 m per cycle,and the buoyancy adjustment system made six adjustments,indicating that our proposed control method performs satisfactorily.In addition,this method provides new insights for the fixed-depth control of other ocean observation devices that rely on buoyancy adjustment.展开更多
Throughout the years, many studies have evaluated changes in soil organic carbon (SOC) mass on a fixed-depth (FD) basis without considering changes in soil mass caused by changing bulk density (ρb). This study evalua...Throughout the years, many studies have evaluated changes in soil organic carbon (SOC) mass on a fixed-depth (FD) basis without considering changes in soil mass caused by changing bulk density (ρb). This study evaluates the temporal changes in SOC caused by two factors: 1) changing SOC concentration;and 2) changing equivalent soil mass (ESM) in comparison with FD. In addition, this study evaluates calculating changes in SOC stock over time using a minimum equivalent soil mass (ESMmin) basis from a single sampling event compared with the FD scenario. A tillage [no-tillage (NT) and chisel plow (CP)]-crop rotation (multiple crop and continuous corn), and irrigation (full and delayed)) study was initiated in 2001 on Weld silt loam soil. After seven years, SOC concentration in the 0 - 30 cm depth was 19.7% greater in 2008 compared with 2001. Standardizing the soil mass of 2001 to the ESM of 2008 for each individual treatment showed an average gain in SOC of 5.8 Mg C·ha-1 in 2008 compared with 2001. However, the increase in SOC using ESM was twice the SOC gained with the FD calculation, where some treatments lost SOC after seven years of management. Estimating SOC levels using the ESMmin and, thereby, eliminating the confounding effect of soil ρb indicated that SOC stock was influenced by crop species and their interaction with irrigation, but not by tillage practices. Over all, the ESM calculation appears to be more effective in evaluating SOC stock than the FD calculation.展开更多
基金The National Key Research and Development Program of China under contract Nos.2021YFC3101401 and 2022YFC3003802the Deep Blue Fund under contract No.SL2103+2 种基金the Zhejiang Provincial Key Research and Development Program under contract No.2021C03186the Zhejiang Provincial Natural Science Foundation of China under contract No.LDQ24D060001the Open Fund Project of Key Laboratory of Ocean Observation Technology,MNR under contract No.2024klootA11.
文摘A mobile marine seismometer(MMS)is a vertical underwater vehicle that detects ocean seismic waves.One of the critical operational requirements for an MMS is that it remains suspended at a desired depth.This article aimed to propose a fixed-depth suspension control for the MMS with a limited onboard energy supply.The research team established a kinematic model to analyze fluctuations in the vertical motion of the MMS and the delayed response of the system.We ascertained a direct one-to-one correlation between the displacement volume of the mobile ocean seismic instrument and the depth at which it reaches a state of neutral buoyancy(commonly referred to as the hover depth).A fixed-depth control algorithm was introduced,allowing a gradual approach to the necessary displacement volume to reach the desired suspension depth.The study optimized the boundary conditions to reduce unnecessary adjustments and mitigate the time delay caused by the instrument’s inertia,thereby significantly minimizing energy consumption.This method does not require calculating the hydrodynamic parameters or transfer functions of the MMS,thereby considerably reducing the implementation complexity.In the three-month sea trial in the South China Sea,the seismic instrument was set to hover at 800 m,with a permissible fluctuation of±100 m,operating on a seven-day cycle.The experimental results show that the seismic instrument has an average hover error of 34.6 m,with a vertical drift depth of 29.6 m per cycle,and the buoyancy adjustment system made six adjustments,indicating that our proposed control method performs satisfactorily.In addition,this method provides new insights for the fixed-depth control of other ocean observation devices that rely on buoyancy adjustment.
文摘Throughout the years, many studies have evaluated changes in soil organic carbon (SOC) mass on a fixed-depth (FD) basis without considering changes in soil mass caused by changing bulk density (ρb). This study evaluates the temporal changes in SOC caused by two factors: 1) changing SOC concentration;and 2) changing equivalent soil mass (ESM) in comparison with FD. In addition, this study evaluates calculating changes in SOC stock over time using a minimum equivalent soil mass (ESMmin) basis from a single sampling event compared with the FD scenario. A tillage [no-tillage (NT) and chisel plow (CP)]-crop rotation (multiple crop and continuous corn), and irrigation (full and delayed)) study was initiated in 2001 on Weld silt loam soil. After seven years, SOC concentration in the 0 - 30 cm depth was 19.7% greater in 2008 compared with 2001. Standardizing the soil mass of 2001 to the ESM of 2008 for each individual treatment showed an average gain in SOC of 5.8 Mg C·ha-1 in 2008 compared with 2001. However, the increase in SOC using ESM was twice the SOC gained with the FD calculation, where some treatments lost SOC after seven years of management. Estimating SOC levels using the ESMmin and, thereby, eliminating the confounding effect of soil ρb indicated that SOC stock was influenced by crop species and their interaction with irrigation, but not by tillage practices. Over all, the ESM calculation appears to be more effective in evaluating SOC stock than the FD calculation.
