Marine oil spills can be remediated by mechanical skimmers in calm waters,but performance degrades with increased wave height.We have developed and demonstrated a system that quantifies local wave characteristics with...Marine oil spills can be remediated by mechanical skimmers in calm waters,but performance degrades with increased wave height.We have developed and demonstrated a system that quantifies local wave characteristics with an uncertainty of four inches of heave.Our system is intended for the measurement of wave characteristics during oil spill recovery.It conveys this information to coordinators and responders in real time via WiFi and remote reporting through a satellite network.This information will allow for enhanced situational awareness during an oil spill response,assisting stakeholders and optimizing mechanical skimming operations.Our wave characterization module(WCM)uses accelerometer outputs from a very small inertial measurement unit(IMU)to generate wave statistics and calculate wave characteristics.It is configured such that a WCM can either be attached to a skimmer float or incorporated into a microbuoy.Wave height and period are transmitted via WiFi and/or a satellite-enabled mesh-grid network to a cloud-hosted geographic information system(GIS).Here,we discuss the bare-bones sensors-plus-algorithm approach we developed by using spring-mass systems to approximate the wave height and period regime of interest.We then describe open water tests carried out using that development system both mounted to a weir skimmer mockup and packaged in a microbuoy.Finally,we present controlled tests in the wave tank at Ohmsett,the National Oil Spill Response Test Facility in New Jersey,with the WCMs communicating the wave characteristics via WiFi to tankside laptops and via satellite to the cloud-based GIS.Snapshot determinations of wave height calculated using the scalar magnitude of the three-axis accelerometer in the IMU were within four inches of the benchmark wave measurement system at Ohmsett.展开更多
The reflection and transmission characteristics of an anisotropic half-space medium normally illuminated by a plane wave are analyzed by kDB coordination. The general formula of reflection coefficient at the air-mediu...The reflection and transmission characteristics of an anisotropic half-space medium normally illuminated by a plane wave are analyzed by kDB coordination. The general formula of reflection coefficient at the air-medium interface is given, and its validity is also discussed. The possible propagating modes in different mediums and the effect of medium parameters on these modes are emphatically studied. This work provides the theoretical preparations for the parameter reconstruction of an anisotropic material.展开更多
Carbon dioxide(CO2) capture and geological storage(CCS) is one of promising technologies for greenhouse gas effect mitigation. Many geotechnical challenges remain during carbon dioxide storage field practices, among w...Carbon dioxide(CO2) capture and geological storage(CCS) is one of promising technologies for greenhouse gas effect mitigation. Many geotechnical challenges remain during carbon dioxide storage field practices, among which effectively detecting CO2 from deep underground is one of engineering problems. This paper reviews monitoring techniques currently used during CO2 injection and storage.A method developed based on measuring seismic microtremors is of main interest. This method was first successfully used to characterize a site in this paper. To explore its feasibility in CO2 storage monitoring,numerical simulations were conducted to investigate detectable changes in elastic wave signatures due to injection and geological storage of CO2. It is found that, although it is effective for shallow earth profile estimation, the surface wave velocity is not sensitive to the CO2 layer physical parameter variations,especially for a thin CO2 geological storage layer in a deep underground reservoir.展开更多
The reliable estimation of the wavenumber space(k-space)of the plates remains a longterm concern for acoustic modeling and structural dynamic behavior characterization.Most current analyses of wavenumber identificatio...The reliable estimation of the wavenumber space(k-space)of the plates remains a longterm concern for acoustic modeling and structural dynamic behavior characterization.Most current analyses of wavenumber identification methods are based on the deterministic hypothesis.To this end,an inverse method is proposed for identifying wave propagation characteristics of twodimensional structures under stochastic conditions,such as wavenumber space,dispersion curves,and band gaps.The proposed method is developed based on an algebraic identification scheme in the polar coordinate system framework,thus named Algebraic K-Space Identification(AKSI)technique.Additionally,a model order estimation strategy and a wavenumber filter are proposed to ensure that AKSI is successfully applied.The main benefit of AKSI is that it is a reliable and fast method under four stochastic conditions:(A)High level of signal noise;(B)Small perturbation caused by uncertainties in measurement points’coordinates;(C)Non-periodic sampling;(D)Unknown structural periodicity.To validate the proposed method,we numerically benchmark AKSI and three other inverse methods to extract dispersion curves on three plates under stochastic conditions.One experiment is then performed on an isotropic steel plate.These investigations demonstrate that AKSI is a good in-situ k-space estimator under stochastic conditions.展开更多
提出了用低频多模式超声兰姆波定征方法来估计超薄弹性层的纵波声速、横波声速、厚度和密度等参数。这里“超薄”是指材料厚度 h 远小于材料中的声波波长λ,由此导致在时域上材料前后界面的各次回波信号相互混迭。文中采用水浸耦合方式...提出了用低频多模式超声兰姆波定征方法来估计超薄弹性层的纵波声速、横波声速、厚度和密度等参数。这里“超薄”是指材料厚度 h 远小于材料中的声波波长λ,由此导致在时域上材料前后界面的各次回波信号相互混迭。文中采用水浸耦合方式,结合空间波场设计和泄漏兰姆波频域分析方法获取了材料零阶对称与反对称模式兰姆波色散曲线,并以色散特性为基础的零阶对称模式兰姆波定征方法、简化方法、零阶反对称模式兰姆波定征方法和最小二乘意义下以材料色散曲线为基础的反向算法对材料进行了参数估计。文中分析了影响估计准确性的各种因素,研究了低频多模式超声兰姆波定征方法对各材料参数的灵敏度及其在误差传递中的意义。实验结果表明,该方法能够准确估计厚度小到26μm展开更多
文摘Marine oil spills can be remediated by mechanical skimmers in calm waters,but performance degrades with increased wave height.We have developed and demonstrated a system that quantifies local wave characteristics with an uncertainty of four inches of heave.Our system is intended for the measurement of wave characteristics during oil spill recovery.It conveys this information to coordinators and responders in real time via WiFi and remote reporting through a satellite network.This information will allow for enhanced situational awareness during an oil spill response,assisting stakeholders and optimizing mechanical skimming operations.Our wave characterization module(WCM)uses accelerometer outputs from a very small inertial measurement unit(IMU)to generate wave statistics and calculate wave characteristics.It is configured such that a WCM can either be attached to a skimmer float or incorporated into a microbuoy.Wave height and period are transmitted via WiFi and/or a satellite-enabled mesh-grid network to a cloud-hosted geographic information system(GIS).Here,we discuss the bare-bones sensors-plus-algorithm approach we developed by using spring-mass systems to approximate the wave height and period regime of interest.We then describe open water tests carried out using that development system both mounted to a weir skimmer mockup and packaged in a microbuoy.Finally,we present controlled tests in the wave tank at Ohmsett,the National Oil Spill Response Test Facility in New Jersey,with the WCMs communicating the wave characteristics via WiFi to tankside laptops and via satellite to the cloud-based GIS.Snapshot determinations of wave height calculated using the scalar magnitude of the three-axis accelerometer in the IMU were within four inches of the benchmark wave measurement system at Ohmsett.
文摘The reflection and transmission characteristics of an anisotropic half-space medium normally illuminated by a plane wave are analyzed by kDB coordination. The general formula of reflection coefficient at the air-medium interface is given, and its validity is also discussed. The possible propagating modes in different mediums and the effect of medium parameters on these modes are emphatically studied. This work provides the theoretical preparations for the parameter reconstruction of an anisotropic material.
基金the financial supports from the State Key Laboratory for Geomechanics & Deep Underground Engineering, China University of Mining and Technology (No. SKLGDUEK1002)the Fundamental Research Funds for the Central Government Supported Universities of Tongji University, China (No. 0270219037)
文摘Carbon dioxide(CO2) capture and geological storage(CCS) is one of promising technologies for greenhouse gas effect mitigation. Many geotechnical challenges remain during carbon dioxide storage field practices, among which effectively detecting CO2 from deep underground is one of engineering problems. This paper reviews monitoring techniques currently used during CO2 injection and storage.A method developed based on measuring seismic microtremors is of main interest. This method was first successfully used to characterize a site in this paper. To explore its feasibility in CO2 storage monitoring,numerical simulations were conducted to investigate detectable changes in elastic wave signatures due to injection and geological storage of CO2. It is found that, although it is effective for shallow earth profile estimation, the surface wave velocity is not sensitive to the CO2 layer physical parameter variations,especially for a thin CO2 geological storage layer in a deep underground reservoir.
基金supported by the Lyon Acoustics Center of Lyon University,Francefunded by the China Scholarship Council(CSC)。
文摘The reliable estimation of the wavenumber space(k-space)of the plates remains a longterm concern for acoustic modeling and structural dynamic behavior characterization.Most current analyses of wavenumber identification methods are based on the deterministic hypothesis.To this end,an inverse method is proposed for identifying wave propagation characteristics of twodimensional structures under stochastic conditions,such as wavenumber space,dispersion curves,and band gaps.The proposed method is developed based on an algebraic identification scheme in the polar coordinate system framework,thus named Algebraic K-Space Identification(AKSI)technique.Additionally,a model order estimation strategy and a wavenumber filter are proposed to ensure that AKSI is successfully applied.The main benefit of AKSI is that it is a reliable and fast method under four stochastic conditions:(A)High level of signal noise;(B)Small perturbation caused by uncertainties in measurement points’coordinates;(C)Non-periodic sampling;(D)Unknown structural periodicity.To validate the proposed method,we numerically benchmark AKSI and three other inverse methods to extract dispersion curves on three plates under stochastic conditions.One experiment is then performed on an isotropic steel plate.These investigations demonstrate that AKSI is a good in-situ k-space estimator under stochastic conditions.
文摘提出了用低频多模式超声兰姆波定征方法来估计超薄弹性层的纵波声速、横波声速、厚度和密度等参数。这里“超薄”是指材料厚度 h 远小于材料中的声波波长λ,由此导致在时域上材料前后界面的各次回波信号相互混迭。文中采用水浸耦合方式,结合空间波场设计和泄漏兰姆波频域分析方法获取了材料零阶对称与反对称模式兰姆波色散曲线,并以色散特性为基础的零阶对称模式兰姆波定征方法、简化方法、零阶反对称模式兰姆波定征方法和最小二乘意义下以材料色散曲线为基础的反向算法对材料进行了参数估计。文中分析了影响估计准确性的各种因素,研究了低频多模式超声兰姆波定征方法对各材料参数的灵敏度及其在误差传递中的意义。实验结果表明,该方法能够准确估计厚度小到26μm
