Field calibration and validation of remote-sensing surveys

The Optical Collection Suite (OCS) is a ground-truth sampling system designed to perform in situ measurements that help calibrate and validate optical remote-sensing and swath-sonar surveys for mapping and monitoring coastal ecosystems and ocean planning. The OCS system enables researchers to collect underwater imagery with real-time feedback, measure the spectral response, and quantify the water clarity with simple and relatively inexpensive instruments that can be hand-deployed from a small vessel. This article reviews the design and performance of the system, based on operational and logistical considerations, as well as the data requirements to support a number of coastal science and management projects. The OCS system has been operational since 2009 and has been used in several ground-truth missions that overlapped with airborne lidar bathymetry (ALB), hyperspectral imagery (HSI), and swath-sonar bathymetric surveys in the Gulf of Maine, southwest Alaska, and the US Virgin Islands (USVI). Research projects that have used the system include a comparison of backscatter intensity derived from acoustic (multibeam/interferometric sonars) versus active optical (ALB) sensors, ALB bottom detection, and seafloor characterization using HSI and ALB.     

Consolidation analysis of elasto-plastic soil

Non-linear consolidation analysis using a finite element formulation based on Biot's consolidation theory has been used to study the behaviour of strip and circular footings resting on an elastic-perfectly plastic soil satisfying the Mohr-Coulomb yield criterion. The initial stress method with a modified Newton-Raphson iterative scheme has been used for this study. Displacement of the footing and pore pressure dissipation in the soil are compared with those of linear analysis. Incorporation of the plastic behaviour of soil increases the consolidation rate and settlement. Effects of flow rule and p₀/c ratio on consolidation behaviour have also been reported.     

An efficient DIPIE algorithm for CAD of electrostatically actuated MEMS devices

Pull-in parameters are important properties of electrostatic actuators. Efficient and accurate analysis tools that can capture these parameters for different design geometries, are therefore essential. Current simulation tools approach the pull-in state by iteratively adjusting the voltage applied across the actuator electrodes. The convergence rate of this scheme gradually deteriorates as the pull-in state is approached. Moreover, the convergence is inconsistent and requires many mesh and accuracy refinements to assure reliable predictions. As a result, the design procedure of electrostatically actuated MEMS devices can be time-consuming. In this paper a novel Displacement Iteration Pull-In Extraction (DIPIE) scheme is presented. The DIPIE scheme is shown to converge consistently and far more rapidly than the Voltage Iterations (VI) scheme (>100 times faster!). The DIPIE scheme requires separate mechanical and electrostatic field solvers. Therefore, it can be easily implemented in existing MOEMS CAD packages. Moreover, using the DIPIE scheme, the pull-in parameters extraction can be performed in a fully automated mode, and no user input for search bounds is required.     

Sensitivity analysis,calibration and validation of EPIC for modelling soil phosphorus dynamics in Swiss agro-ecosystems

Proper management of soil phosphorus (P) is essential to ensure sustainability in agriculture. To avoid excessive P accumulation in soil, a methodology for predicting long-term variations in soil P content is required. Using the Swiss Soil Monitoring Network (NABO) database, we tested the efficiency of the model EPIC to predict soil P temporal changes for typical Swiss arable and grassland sites. After performing a sensitivity analysis to identify the most influential model parameters for which calibration was needed, we calibrated the influential parameters on the available topsoil P data of 4 selected NABO sites and then we tested the calibrated model by comparison of predictions with data from a second set of 14 sites. We found that the model performance for grassland sites improved significantly when site-specific estimates of bioturbation depth were used. These site-specific estimates showed a close relationship to independently assessed subsoil hydromorphy.     

A review of current calibration and validation practices in land-change modeling

Land-change models are increasingly used to explore land-change dynamics, as well as for policy analyses and scenario studies. In this paper we review calibration and validation approaches adopted for recently published applications of land-change models. We found that statistical analyses and automated procedures are the two most common calibration approaches, while expert knowledge, manual calibration, and transfer of parameters from other applications are less frequently used. Validation of model results is predominantly based on locational accuracy assessment, while a small fraction of the applications assessed the accuracy of the generated land-use or land-cover patterns. Of the reviewed model applications, thirty-one percent did not report any validation. We argue that to mature as a scientific tool, and to gain credibility for scenario studies and policy assessments, the validation of land-change models requires consideration of challenges posed by uncertainty, complexity, and non-stationarity of land-change processes, and equifinality and multifinality of land-change models.     

Nonlinear elasto-plastic analysis of slack and taut cable structures

This paper presents the geometrically nonlinear analysis of the slack and taut cable structures considering the material inelasticity subjected to self-weight, pretension, and external loads. The finite element procedure is briefly summarized using the Lagrangian formulation associated with isoparametric interpolation polynomials and the Newton–Raphson iterative scheme with incremental load. The simple and efficient method to determine the initial equilibrium state of the slack cable systems under self-weight as well as support motions is presented using the penalty method. The numerical algorithm to evaluate the tangent modulus of elasticity of cable is presented based on the iterative scheme. The accuracy and reliability of the present study are verified by comparing the predictions with those generated by well-reported slack and taut cable structure problems. The effect of the yielding of cable segments on displacements and stresses of cable structures is investigated.     

基于多传感器系统的统计建模与标定方法

在融合惯性、视觉、磁场信息以及嵌入式技术的多传感器定位系统中,标定模型的准确性会影响传感器测量精度。以非线性最小二乘法为基础,提出了一种低成本高精度的标定方法。首先,分析系统各项参数,以加速度计为例建立模型,并利用重力加速度作中间量对传感器确定性项进行标定。通过仿真实验分析,结果表明提出的方法实用可行,能降低误差,提高系统传感器精度。     

Numerical analysis of local instabilities in elastic and elasto-plastic prismatic plate assemblies

The finite element approach is used in this paper to analyze local instabilities in certain prismatic plate assemblies. Eigenvalue analysis is used to find the critical load factors and the corresponding buckling mode shapes. The stiffness matrices are written out in terms of the unknown buckling half-wavelength L and the critical stresses computed are minimized with respect to this parameter. In the case of inelastic material both the flow and deformation theories of plasticity are thoroughly reviewed when applied to the problem considered. A number of numerical illustrations is discussed.     

一种用于位移测量装置校准的LVDT模拟器

为了实现位移测量装置的自动化校准,根据线性可调差动变压器(LVDT)的工作原理,提出了一种基于D/A转换器的LVDT模拟器的设计思想。该模拟器以LVDT主线圈交流激励信号作为参考电压,利用参考电压和数字给定值的乘积关系,通过改变D/A的数字量得到幅值可变的LVDT副线圈输出电压,从而模拟铁心位置改变时LVDT副边信号的变化关系。试验表明:该模拟器具有0.024%的稳态精度和200Hz的动态带宽,可以高度逼真地模拟LVDT电气行为,完全满足LVDT类位移测量装置的维护和校准需要。相对于采用实际LVDT,利用该模拟器进行校准可省去高精度的运动机构,可以提供更大的灵活性,并可以实现校准过程自动化。     

Geometric analysis of antagonistic stiffness in redundantly actuated parallel mechanisms

Parallel closed-chain mechanical architectures allow for redundant actuation in the force domain. Antagonistic actuation, afforded by this input force redundancy, in conjunction with nonlinear linkage geometry creates an effective stiffness directly analogous to that of a wound metal spring. A general stiffness model for such systems is derived and it is shown that the constitutive relationship between actuation effort and active stiffness is the second-order kinematic constraint set relating the actuation sites. The extent of stiffness modulation possible is then evaluated and necessary conditions for full stiffness modulation are obtained. Configuration-dependent, second-order, geometric singularities affecting stiffness generation are illustrated in terms of a three-degree-of-freedom parallel spherical mechanism example and discussed in relation to their more commonly investigated first-order counterparts that affect force and velocity transmission. Finally, a load distribution methodology for simultaneous motion and stiffness generation is introduced, and it is shown that with hyperredundant actuation the internal load state of the mechanism can be controlled independent of its motion and effective stiffness. © 1993 John Wiley & Sons, Inc.     

Mathematical analysis and test of an electrostatically actuated micro-power relay

This paper reports a mathematical and experimental study on a micro-relay for power applications. The relay is microfabricated using UV-LIGA and electrostatically actuated. The relay was uniquely designed with all major components made of metals except two polymer strips which serve as both mechanical connectors and electrical insulators. The utilization of UV-LIGA fabrication technologies helps to achieve high aspect ratio metal structures in the relay, which helps to achieve high power capacity. Both the static and dynamic characteristics of the prototype relay have been studied. The performances of the prototype relay agreed very with those predicted using mathematical models. The prototype relay was found to be able to operate in a control voltage lower than 18 V and carry a current of 5 A. The prototype relay operated over 10⁶ cycles without any degradation. In addition, the response time of a relay was 3.2–3.5 ms in the “on” operation and 7.9–14.3 ms during the “off” operation.     

A semi-analytical approach to elasto-plastic analysis of hollow spheres

The integral form of the analytical solution for the problem of an elasto-plastic hollow sphere subjected to uniform loads is presented. This integral equation is solved through a numerical integration scheme involving an iteration technique. The numerical model developed on this basis is shown to satisfy the theoretical solution under fully-plastic conditions. The generality of the model is demonstrated by analysing the full elasto-plastic response of a hollow sphere and discussing the implications of the computational results.     

危急遮断转速装置的校验研究

危急遮断器可防止汽轮机超速,准确、快速追忆汽轮机撞击子的机械飞出的瞬间实际转速,保证机组安全运行.对危急遮断转速装置的校验,应该模拟现场实际情况.为撞击子传感器安装提供可靠的理论依据,是我们迫切需要解决的问题.     

Fabrication and dynamic analysis of the electrostatically actuated MEMS variable capacitor

Future microwave networks require miniature high-performance tunable elements such as switches, inductors, and capacitors. In this paper, high performance variable capacitor was fabricated by simple microelectromechanical systems (MEMS) technology. The capacitance and quality (Q) factor at 1 GHz are 0.792 pF and 51.6. The pull-in voltage is 13.5 V and the tuning ratio of the capacitor is more than 1.31:1. A reduced-order model for the dynamic characteristics of the capacitor is established based on the equilibrium among the plate flexibility.     

Analysis and classification of data sets for calibration and validation of agro-ecosystem models

Experimental field data are used at different levels of complexity to calibrate, validate and improve agro-ecosystem models to enhance their reliability for regional impact assessment. A methodological framework and software are presented to evaluate and classify data sets into four classes regarding their suitability for different modelling purposes. Weighting of inputs and variables for testing was set from the aspect of crop modelling. The software allows users to adjust weights according to their specific requirements. Background information is given for the variables with respect to their relevance for modelling and possible uncertainties. Examples are given for data sets of the different classes. The framework helps to assemble high quality data bases, to select data from data bases according to modellers requirements and gives guidelines to experimentalists for experimental design and decide on the most effective measurements to improve the usefulness of their data for modelling, statistical analysis and data assimilation.     

Equivalent area nonlinear static and dynamic analysis of electrostatically actuated microstructures

Nonlinear dynamic investigation of electrostatically actuated micro-electro-mechanical-system (MEMS) microcantilever structures is presented. The nonlinear analysis aims to better quantify, than the linear model, the instability threshold associated with electrostatically actuated MEMS structures, where the pull-in voltage of the microcantilever is determined using a phase portrait analysis of the microsystem. The microcantilever is modeled as a lumped mass-spring system. The nonlinear electrostatic force is incorporated into the lumped microsystem through an equivalent area of the microcantilever for a given electrostatic potential. Electro-mechanical force balance plots are obtained for various electrostatic potentials from which the static equilibrium positions of the microcantilever are obtained and the respective conservative energy values are determined. Subsequently, phase portrait plots are obtained for the corresponding energy values from which the pull-in voltage is estimated for the microsystem. This pull-in voltage value is in good agreement with the previously published results for the same geometric and material parameters. The results obtained for linear electrostatic models are also presented for comparison.     

Numerical simulation and analysis of electrically actuated microbeam-based MEMS capacitive switch

The MEMS capacitive switch based on fixed-fixed microbeam has garnered significant attention due to their geometric simplicity and broad applicability. The accurate model which describes the multiphysical coupled-field of MEMS capacitive switch should be developed to predict their electromechanical behaviors. The improved macromodel of the fixed-fixed microbeam-based MEMS capacitive switch is presented to investigate the behavior of electrically actuated MEMS capacitive switch in this paper, the macromodel provides an effective and accurate design tool for this class of MEMS devices because of taking account into some effects simultaneously including fringing field effect, midplane stretching effect, residual stress and multiphysical coupled-field effect. The numerical analysis of mechanical characterizations of electrically actuated microbeam-based MEMS capacitive switch are performed by the finite element Newmark method, and the performances of static and dynamic of MEMS capacitive switch are obtained. The numerical results show that, with only a few nodes used in the computation, the FEM-Newmark gives the identical results to other numerical methods, such as the shooting method and experiments. Moreover, the proposed model can offer proper and convenient approach for numerical calculations, and promote design of MEMS devices.     

Experimental validation of compact damping models of perforated MEMS devices

Measured damping coefficients of six different perforated micromechanical test structures are compared with damping coefficients given by published compact models. The motion of the perforated plates is almost translational, the surface shape is rectangular, and the perforation is uniform validating the assumptions made for compact models. In the structures, the perforation ratio varies from 24 to 59%. The study of the structure shows that the compressibility and inertia do not contribute to the damping at the frequencies used (130–220 kHz). The damping coefficients given by all four compact models underestimate the measured damping coefficient by approximately 20%. The reasons for this underestimation are discussed by studying the various flow components in the models.