Derivation Of Transfer Function Research Articles

Derivation of Transfer Function of an IPMC Actuator Based on Pseudo-Rigid Body Model

In this article an effort has been made to derive the transfer function of an ionic polymer metal composite (IPMC) actuator. The transfer function obtained is based on the experimental deflection data and following the pseudo-rigid modeling technique. Initially an experiment is conducted with an IPMC actuator to measure its bending characteristics with input voltages. Subsequently expression for bending moment with radius of curvature is established. IPMC has been modeled then following the pseudo-rigid body modeling technique as fix-pin support type of cantilever mode with end-moment loading and its derivation is explained in detail. Based on the experimentally obtained bending moment, IPMC has been modeled to obtain the distributed force, spring constants, characteristic radius factor, and pseudo-rigid body angles. Energy based dynamic model of the IPMC actuator has been formulated following the Lagrangian principle based on the tip position in 2D. Transfer function is then obtained with respect to pseu...

Another Simple Method of Spectral Correction to Obtain Robust Eddy-Covariance Results

The eddy-covariance method is the state-of-the-art tool to measure mass and energy fluxes, though many measuring systems (particularly closed-path systems) show strong spectral attenuation that causes significant underestimates of actual mass fluxes. The standard way to correct these underestimates is to use theoretically derived transfer functions. Practical implementation has shown that the attenuation, especially of closed-path systems, is underestimated by this method, even when the additional tube damping is considered. This paper introduces and tests three alternative site-specific and hardware specific correction methods based on spectral analysis, which typically enhance—additionally to the classical correction—the calculated mass fluxes based on closed-path analysers, as their inevitable tubing and the filters used cause additional flow attenuation. Two of the three methods are based on a site-specific and hardware specific transfer functions, the third uses direct comparison of cospectra. Primarily the methods based on transfer functions proved to be easy-to-handle once established for the specific set-up and measurement site. They represent practical and robust methods to correct for spectral attenuation.

Frequency Control Design for Offshore Wind Farm Grid With LCC-HVDC Link Connection

This paper considers the formal design for the grid frequency control in an offshore wind farm connected with line-commutated converter high voltage dc (HVDC) link. The control paradigm is based on using the grid frequency control to regulate the HVDC rectifier firing angle or dc-link current and hence control the power flow in the system. The dynamic behaviors of the system are verified by comparing the response from derived transfer functions and PSCAD simulations; hence the grid frequency controllers are designed. The control system performance has been validated by simulations of normal operation and fault regimes. The work provides a good basis for wider research investigation into wind farm operation.

Dynamic properties of the Quaternary sedimentary rocks and their influence on seismic site effects. Case study in Bucharest City, Romania

Bucharest is one of the cities most affected by earthquakes in Europe. Situated at 150–170 km distance from Vrancea epicentral zone, Bucharest had suffered many damages due to high energy Vrancea intermediate-depth earthquakes. For example, the 4 March 1977 event produced the collapse of 32 buildings with 8–12 levels, while more than 150 old buildings with 6–9 levels were seriously damaged. The studies done after this earthquake had shown the importance of the surface geological structure upon ground motion parameters. New seismic measurements are performed in Bucharest area aiming at defining better elastic and dynamic properties of the shallow sedimentary rocks. Down-hole seismic measurements were performed in a number of 10 cased boreholes drilled in the Bucharest City area. Processing and interpretation of the data lead to the conclusion that shallow sedimentary rocks can be considered weak in the area, down to 150–200 m depth. Seismic wave velocity values and bulk density values presented in the paper associated with local geology are useful primary data in the seismic microzonation of Bucharest City. They are used as 1D models to derive transfer functions and response spectra for the stack of sedimentary rocks in several parts of Bucharest area, leading to a better knowledge of the local site amplification and associated frequency spectra. In a recent study the H/V spectral ratio using Nakamura’ s method was applied on the seismic noise measurements in 22 sites in Bucharest City in order to derive the fundamental period associated with these sites. The values confirm the previous results, showing a dominant resonance in the period range of 1.25–1.75 s. The fundamental periods obtained with Nakamura’ s method are in good agreement with those computed on the basis of geological and geotechnical data in boreholes, which show an increase of the fundamental period in the Bucharest area from south to north, in the same direction as the increase of the thickness of the Quaternary deposits above the Fratesti layer which is considered the bedrock in the area.

Processing of Bistatic SAR Data From Quasi-Stationary Configurations

Standard synthetic aperture radar (SAR) processing algorithms use analytically derived transfer functions in the 2D frequency and range/Doppler domains. These rely on the assumption of hyperbolic range histories of monostatic SARs with straight flight paths. For bistatic SARs, the range histories are no longer hyperbolic, and simple analytic transforms do not exist. This paper offers two solutions for bistatic SAR data processing under the restriction of quasi-stationarity, i.e., sufficiently equal vectors of transmitter and receiver. 1) Moderately bistatic configurations can be handled satisfactorily by using hyperbolic range functions with a modified parameter, which is a solution already well known for the accommodation of curved orbits in the monostatic case. This velocity approach is shown to be of surprising range of validity even for pronounced bistatic situations. It is not to be confused with the monostatic flight path approximation, which is shown to be inapplicable for any practical case. 2) With increasing separation of transmitter and receiver, the equivalent approximation deteriorates. To cope with extreme bistatic configurations, a general approach named NuSAR is proposed, where the involved transfer functions are replaced by numerically computed ones. This paper describes how the transfer functions are computed from the given orbits and the shape of the Earth surface. In any of these two cases, the bistatic SAR data can be processed by standard SAR processors; only the conventional transfer functions need to be replaced. Neither are there time-domain prefocusing or post focusing steps required nor complicated mathematical expansions involved. The presented algorithms are also applicable to very high resolution wide-swath (or squinted) SARs on curved orbits.

Transformer winding defects identification based on a high frequency method

The transformer diagnostic methods are systematically being improved and extended due to growing requirements for reliability of power systems in terms of uninterrupted power supply and avoidance of blackouts. Those methods are also driven by longer lifetime of transformers and demand for reduction of transmission and distribution costs. Hence, the detection of winding faults in transformers, both in exploitation or during transportation is an important aspect of power transformer failure prevention. The frequency response analysis method (FRA), more and more frequently used in electric power engineering, has been applied for investigations and signature analysis based on the admittance and transfer function. The paper presents a novel approach to the identification of typical transformer winding problems such as axial or radial movements or turn-to-turn faults. The proposed transfer function discrimination (TFD) criteria are based on the derived transfer function ratios, manifesting higher sensitivity.

Voltage-Loop Power-Stage Transfer Functions With MOSFET Delay for Boost PWM Converter Operating in CCM

Open-loop transfer functions can be used to create closed-loop models of pulsewidth-modulated (PWM) converters. The closed-loop small-signal model can be used to design a controller for the switching converter with well-known linear control theory. The dynamics of the power stage for boost PWM dc-dc converter operating in continuous-conduction mode (CCM) are studied. The transfer functions from output current to output voltage, from duty cycle to output voltage including MOSFET delay, and from input voltage to output voltage are derived. The derivations are performed using an averaged linear circuit small-signal model of the boost converter for CCM. Experimental Bode plots and step responses were used to test the accuracy of the derived transfer functions. The theoretical and experimental responses were in excellent agreement, confirming the validity of the derived transfer functions

A global model of mantle conductivity derived from 5 years of CHAMP, Ørsted, and SAC‐C magnetic data

We present a global 1‐D conductivity model which is obtained by analysis of five years (2001–2005) of simultaneous magnetic data from the three satellites Ørsted, CHAMP and SAC‐C. After removal of core and crustal fields as predicted by a recent field model we used non‐polar scalar and vector observations from the night‐side sector, and interpret the field residuals in terms of a large‐scale contribution from the magnetospheric ring current and its induced counterpart. We then derive transfer functions between internal (induced) and external expansion coefficients of the magnetic potential and provide globally‐averaged C‐responses in the period range between 14 hours and 4 months. Since the satellite responses are probably influenced by induction in the oceans for periods shorter than a few days, we correct the data for this effect. Interpreting the corrected responses yields a 1‐D conductivity model which is rather similar to models derived from ground‐based data.

Spatial orientation and distribution of reservoir fractures from scattered seismic energy

We present the details of a new method for determining the reflection and scattering characteristics of seismic energy from subsurface fractured formations. The method is based upon observations we have made from 3D finite-difference modeling of the reflected and scattered seismic energy over discrete systems of vertical fractures. Regularly spaced, discrete vertical fracture corridors impart a coda signature, which is a ringing tail of scattered energy, to any seismic waves which are transmitted through or reflected off of them. This signature varies in amplitude and coherence as a function of several parameters including: (1) the difference in angle between the orientation of the fractures and the acquisition direction, (2) the fracture spacing, (3) the wavelength of the illuminating seismic energy, and (4) the compliance, or stiffness, of the fractures. This coda energy is most coherent when the acquisition direction is parallel to the strike ofthe fractures. It has the largest amplitude when the seismic wavelengths are tuned to the fracture spacing, and when the fractures have low stiffness. Our method uses surface seismic reflection traces to derive a transfer function that quantifies the change in an apparent source wavelet before and after propagating through a fractured interval. The transfer function for an interval with no or low amounts of scattering will be more spikelike and temporally compact. The transfer function for an interval with high scattering will ring and be less temporally compact. When a 3D survey is acquired with a full range of azimuths, the variation in the derived transfer functions allows us to identify subsurface areas with high fracturing and to determine the strike of those fractures. We calibrated the method with model data and then applied it to the Emilio field with a fractured reservoir. The method yielded results which agree with known field measurements and previously published fracture orientations derived from PS anisotropy.

Deriving abstract transfer functions for analyzing embedded software

This paper addresses the problem of creating abstract transfer functions supporting dataflow analyses. Writing these functions by hand is problematic: transfer functions are difficult to understand, difficult to make precise, and difficult to debug. Bugs in transfer functions are particularly serious since they defeat the soundness of any program analysis running on top of them. Furthermore, implementing transfer functions by hand is wasteful because the resulting code is often difficult to reuse in new analyzers and to analyze new languages. We have developed algorithms and tools for deriving transfer functions for the bitwise and unsigned interval abstract domains. The interval domain is standard; in the bitwise domain, values are vectors of three-valued bits. For both domains, important challenges are to derive transfer functions that are sound in the presence of integer overflow, and to derive precise transfer functions for operations whose semantics are a mismatch for the domain (i.e., bit-vector operations in the interval domain and arithmetic operations in the bitwise domain). We can derive transfer functions, and execute them, in time linear in the bitwidth of the operands. These functions are maximally precise in most cases. Our generated transfer functions are parameterized by a bitwidth and are independent of the language being analyzed, and also of the language in which the analyzer is written. Currently, we generate interval and bitwise transfer functions in C and OCaml for analyzing C source code, ARM object code, and AVR object code. We evaluate our derived functions by using them in an interprocedural dataflow analyzer.

Nonlinear Transient and Distortion Analysis via Frequency Domain Volterra Series

This paper presents a novel approach for transient and distortion analyses for time-invariant and periodically time-varying mildly nonlinear analog circuits. Our method is based on a frequency domain Volterra series representation of nonlinear circuits. It computes the nonlinear responses using a nonlinear current method that recursively solves a series of linear Volterra circuits to obtain linear and higher-order responses of a nonlinear circuit. Unlike existing approaches, where Volterra circuits are solved mainly in the time domain, the new method solves the linear Volterra circuits directly in the frequency domain via an efficient graph-based technique, which can derive transfer functions for any large linear network efficiently. As a result, both frequency domain characteristics, like harmonic and intermodulation distortion, and time domain waveforms can be computed efficiently. The new algorithm takes advantage of identical Volterra circuits for second- and higher-order responses, which results in significant savings in driving the transfer functions. Experimental results for two circuits—a low-noise amplifier and a switching mixer—are obtained and compared with SPICE3 to validate the effectiveness of this method.

Analysis of Transmission Characteristics of Gaussian Monocycle Pulses for Silicon Integrated Antennas

Ultra wideband (UWB) signal transmission characteristics of Si integrated antennas were investigated and analyzed by measurement and high accuracy simulation program with integrated circuit emphasis (HSPICE). The transfer functions were derived from a three-dimensional (3D) electromagnetic field simulator. HSPICE simulation was performed using the derived transfer functions. The measured results were compared with HSPICE results in terms of the scattering parameter and the received signal. Moreover, the effect of load impedance on the receiving antenna was investigated, and the peak-to-peak voltage of the received signal was improved by increasing the load impedance.

Channel model of broadband power-line communication network with ring topology

The growing interest in using electrical power networks as an alternative broadband communication medium has spurred many to study the channel characteristics and to formulate channel models of these power networks. Existing channel-modelling techniques for power-line communications (PLC) typically assume that the power networks are connected in tree or radial topology. This assumption is not entirely valid as many electrical circuits in residential homes, commercial and industrial facilities may be wired in ring topology. Using the concept of scattering parameters a novel method derives analytical expressions for the channel transfer function and input impedance of ring-based PLC networks. The derived transfer function and input impedance are successfully verified against measurements conducted on a practical electrical power network in the frequency band from 1 to 30 MHz.

Reference biospheres for post-closure performance assessment: inter-comparison ofSHETRAN simulations and BIOMASS results

Example Reference Biosphere 2B (ERB2B) is a hypothetical river catchment, described inthe IAEA-sponsored BIOMASS study on biosphere aspects of post-closure radiologicalsafety assessments for repositories for solid radioactive wastes. In ERB2B, a radioactivelycontaminated aquifer interacts with the soils and sediments of the river catchment. A‘semi-distributed’, lumped-parameter model (SDLP) was set up for the site as part of theBIOMASS study. In the model, empirically derived transfer functions are used to reducethe complexity of real hydrological transport systems to readily calculable mass-balanceaccounting routines. In this work, a physically based, spatially distributed modellingsystem SHETRAN was set up for the site and comparison made with the existing SDLPmodel.The work has shown that, using standard soil properties in SHETRAN, the soilrapidly saturates and much of the hydrologically effective rainfall (precipitation lessevapotranspiration) is lost as saturation-excess surface runoff. This is contrary to theassumptions in the SDLP model. The difficulty arose from the original formulation ofcatchment characteristics in BIOMASS. Specifically, there was a large water volumeentering the soils from precipitation together with an upward flux of groundwater acrossthe lower boundary of a substantial part of the catchment. This water had to be lost fromthe catchment in some way and the thinness of the soil zone precluded dominance ofsubsurface, lateral flow over surface runoff. Increasing the saturated conductivity from1 to 20 m d−1 reduced the surface flows to similar values to those assumed in the SDLP model (this couldalso have been achieved by increasing the soil depth). Even with the high saturatedconductivity there were still major differences between the two representations. In thewoodland on the upper slopes of the valley, the SHETRAN simulation was slightly wetterthan the SDLP model, whereas in the shrubland and marshland near the river it was drierthan the SDLP model. In the SDLP model, subsurface lateral flows are ignored ifthere is surface flow, and deep subsurface flows are ignored if there are shallowsubsurface flows. In the SDLP model, there is a major assumed change in flow regimebetween summer and winter. This is not the case in the SHETRAN simulation.Overall, this work illustrates the problems of using ‘semi-distributed’, lumped-parametermodels without prior calibration against a physically based model and the potential forimplying unexpected and possibly implausible hydrological characteristics through thespecification of flows without considering whether they could occur for realistic soil depthsand properties. As there is a need for application of such SDLP models, particularly whenundertaking probabilistic calculations, it is suggested that, in future, explicit hydrologicalmodelling should be undertaken first, so that a physically realistic representation can beproduced as a basis for assessment studies of the migration of radionuclides or othercontaminants.

Modal Approximation of Distributed Dynamics for a Hydraulic Transmission Line With Pressure Input-Flow Rate Output Causality

Based on analytical results obtained in the frequency domain, modal approximation techniques are employed to derive transfer function and state space models applicable to a pressure input-flow rate output causality case of a transmission line. The causality case considered here arises while modeling short connection lines to hydraulic accumulators. However, the modal approximation results presented apply also to other cases where the linear friction model is considered applicable. It is highlighted that the results presented can reduce the overall order of the hydraulic system model containing the transmission line being considered.

A Duhamel Integral Based Solution for the Sideways Heat Equation Applied to the Non-intrusive Temperature Measurement

In the present study, an inverse heat conduction problem is considered, the Sideways Heat Equation, which is a model of a problem, where one wants to determine the temperature on both sides of a thick wall, but where one side is inaccessible to measurements. Considering the problem of an intrinsic thermocouple attached to a slab, and no thermal contact, a transfer function is proposed. It is based on Duhamel Integral and the measured response is approximated by a quasi-periodical function. The derived transfer function is the product of two transfer functions, for the slab and for the intrinsic thermocouple respectively. To validate the present model, a comparison with actual measurements is carried out. It was found that the present model can predict the inner temperatures more accurately than the previous model, which did not take into account the effect of the thermocouple.

An Improved Acoustic Model for Active Noise Control in a Duct

This paper presents a model of sound propagation in a duct, for the purpose of active noise control. A physical model generally different from those explored in much of the literature is derived, with non-constant acoustic load impedance at the one end, and a coupled disturbance loudspeaker model at the other end. Experimental results are presented which validate the derived transfer function.

Critical values of trace elements in soils from the viewpoint of the transfer pathway soil - plant

The development of soil limiting values of the protection of the quantity and mainly quality of the crop production tends from empiric values towards critical values, based on ecotoxicity. We present an attempt to derive transfer functions by the means of multiple regression analysis. The substitution of trace elements contents in crops in the prediction equations for fodder or food standards or phytotoxicity limits satisfies the present ecotoxicological demands. We preferred polyfactor relations to simple ones. The exceeding of reference values must be verified by the determination of the hazardous transfer in the field. Therefore the reference values are called testing values. They were derived especially for Cd, Pb, As, Cu, Zn, Ni and Mn. For some trace elements, only protective values can be set up (especially for Cr, Hg, but also for Tl, Be, V). They reflect minimum values that guarantee growing crops without any risks. Experimental data (pot trials) were compared with results obtained in field investigations. The resulting critical values were also compared with the values proposed in Germany.

WA-PLS diatom-based pH, TP and DOC inference models from 42 lakes in the Abitibi clay belt area (Québec, Canada)

The relationship between surficial sediment diatom species and measured environmental variables was explored in lakes from the Abitibi region of western Quebec. Diatom assemblages in 42 lakes were identified and their relationship with measured environmental variables was examined using multivariate statistical methods. Canonical correspondence analysis with forward selection and Monte Carlo permutation tests revealed that the three environmental variables pH, TP and DOC each accounted for statistically significant fractions of the variation in diatom taxa. A training set with 164 modern diatom taxa was used to derive transfer functions for lake-water pH, TP and DOC using weighted-averaging-partial-least-squares (WA-PLS) techniques. The models were developed to infer lake water pH, TP and DOC within the ranges 4–8 for pH, 2.75–30.0 μg l−1 for TP, and 2.9–18.5 mg l−1 for DOC. These quantitative inference models may now be used to help identify and estimate the effects of natural disturbances on the biogeochemistry of Abitibi lakes during their historical development.

Phase noise transfer in resonant optical cavities

We study theoretically and experimentally the field circulating in a resonant optical cavity when the phase of the incident field and the length of the cavity exhibit fluctuations about their mean values. With a simple model we derive transfer functions which relate the spectral density of phase noise of both the input field and the cavity length to that of the circulating field. In agreement with the standard steady state result, we find that phase noise in the incident field is low pass filtered by the cavity. Cavity length fluctuations are found to be high pass filtered in their transfer to the circulating field. These results are used to present a control loop model of the cavity-laser system. We verify the model experimentally with a Pound–Drever–Hall discriminator and apply it to a discussion of the stability of a frequency reference at 532 nm.