Empirical Transfer Function Research Articles

Application of non-stationary shear-wave velocity randomization approach to predict 1D seismic site response and its variability at two downhole array recordings

Accounting for uncertainties in seismic site response is crucial to improving the performance of one-dimensional (1D) ground response analyses (GRAs) at downhole array recording sites. In addition to site effects, uncertainties in 1D-GRAs can also be contributed from the seismic source and/or path. Though often representing not more than one percent of the distance (path) from the source, site conditions are known to have an enormous influence on ground shaking. In this study, we focus on the site shear-wave velocity (VS) structure, which is the main ingredient for estimating the variability of site response. As such, VS can manifest aleatory uncertainties related to the effects of small-scale spatial heterogeneities within the near surface, thus VS can substantially modify ground shaking during earthquakes. We apply a novel VS randomization approach to propagate the small-scale heterogeneities of VS to estimate seismic site response within a non-stationary probabilistic framework. The randomization approach generates samples of VS profiles that are used to perform several 1D-GRAs and obtain an averaged site response and related variability. The proposed method is implemented on data recorded at two downhole array sites with different subsurface soil conditions: a soft soil site on Treasure Island (California, United States of America) and a rock outcrop site in Cadarache (South-East France). We show that synthetic surface-to-borehole transfer functions from 1D-GRAs provide an acceptable fit to the empirical transfer functions from low-motion earthquake records and succeed in reproducing most of the site-specific seismic response variability. The remaining mismatch between transfer functions is likely due to insufficient precision on the seismic bedrock and the impedance contrast. The variability in site response is discussed with emphasis on the role of VS small-scale heterogeneities, attenuation, and input motion incidence angle in ground motion variability for the site and soil conditions at both locations.

Improving the insulin therapy for diabetic patients using optimal impulsive disturbance rejection: Continuous time approach

The paper proposes a new model-based optimization approach to improve the clinical efficiency of compensatory insulin bolus treatment in diabetic patients, aiming to mitigate the consequences of diabetes. The most important contribution of this paper is a novel methodology for determining the optimal parameters of insulin treatment, namely the size and timing of insulin boluses, to effectively compensate for carbohydrate intake. This concept can be seen as the so-called optimal model-based bolus calculator. The presented theoretical framework deals with the problem of optimal disturbance rejection in impulsive systems by minimizing an integral quadratic cost function. The methodology considers a personalized empirical transfer function model with static gains and time constants as the only parameters assumed to be known, making the bolus calculator more straightforward to implement in clinical practice. Contrary to other techniques, the proposed methodology considers impulsive insulin administration in the form of boluses, which is more feasible than continuous infusion. In contrast to the conventional bolus calculator, the proposed algorithm allows for maximizing therapy performance by optimizing the relative time of insulin bolus administration with respect to carbohydrate intake. Another feature to highlight is that the solution of the optimization problem can be obtained analytically, hence no numerical iterative solvers are required. Additionally, the continuous-time domain approach allows for a much finer adjustments of the insulin administration timing compared to discrete-time models. The proposed approach was validated in an in-silico study, which demonstrated the importance of systematically determined insulin–carbohydrate ratio and the relative delay between disturbance and its compensation. The results showed that the proposed optimal bolus calculator outperforms the traditional suboptimal formula.

Derivations of transfer functions for estimating ship underwater radiated noise from onboard vibrations

The adverse impacts of underwater radiated noise (URN) from marine vessels on marine life are increasingly recognized. URN estimation and subsequent monitoring could be used to track URN and take measures to reduce it in sensitive environments (e.g., a marine life protected area). Two common analytical radiated noise power approximations and two empirical methods are assessed for URN estimation. The assessments were carried out by testing the methods on data from acoustic range measurements of an ORCA-class training vessel of the Royal Canadian Navy, named Patrol Craft Training (PCT) Moose and a DAMEN Combi Freighter 3850, named Heinz G. The analytical approximations are called equivalent radiated power and power from volume velocity; both are used to estimate URN directly from the onboard ship vibration measurements. The empirical methods are based on the correlations of onboard vibrations with measured URN, from which the derived transfer functions. The analytical and empirical transfer functions are compared. A statistical energy analysis model of PCT Moose is also used to estimate onboard vibrations from the ship’s engine, generator, and propeller specifications for URN estimation at the design stage.

Time-resolved ion energy measurements using a retarding potential analyzer for electric propulsion applications.

To completely characterize the evolving state of a plasma, diagnostic tools that enable measurements of the time-resolved behavior are required. In this study, a gridded ion source with superimposed oscillations was utilized to verify the functionality of a high-speed retarding potential analyzer (HSRPA), at frequencies equivalent to the low frequency oscillations occurring in Hall effect thrusters (HETs). The verification of this device provides an effective alternative to existing diagnostics for measuring time-resolved ion energies. Retarding potential analyzers (RPAs) have established themselves as a fundamental diagnostic in the field of electric propulsion (EP), enabling the measurement of ion energy distributions within the plumes of EP thrusters. The work presented here has demonstrated the capability of a standard RPA in conjunction with high-speed circuitry and data fusion techniques to produce time-resolved ion energy distribution functions (IEDFs) at higher frequencies and beam potentials than have previously been investigated. Tested frequencies ranged between 20 and 80kHz with 10V peak-to peak oscillations at a mean beam potential of 570V. In addition, measurements were conducted with several waveforms, functioning as the superimposed oscillation, including a sine wave, triangle wave, and noisy sine wave. Data from the HSRPA were successfully reconstructed into time series utilizing two data fusion techniques: the empirical transfer function method and shadow manifold interpolation. Time-resolved IEDFs were produced at all frequency set points and waveforms. This investigation has demonstrated the HSRPA effectiveness at producing time-resolved measurements under conditions similar to those occurring in HETs.

Empirical transfer functions for foam glass aggregates insulation used in flexible pavement layered systems

Pavement design in cold regions is challenging due to the difficult conditions of soils, humidity, and temperatures. Insulation layers have been identified as a suitable solution for these conditions. Due to their unique engineering properties, foam glass aggregates (FGAs) are a promising material for use as an insulating granular layer in pavement design. However, understanding their mechanical performance is critical for predicting long-term layer and pavement behavior. In this laboratory study, an empirical transfer function was developed using an environmental and heavy vehicle simulator and an experimental pavement built in an indoor test pit. The study aimed to determine the allowable number of load repetitions for an FGAs insulation layer and to develop an empirical transfer function that can be used as part of a mechanistic-empirical pavement design procedure. This article proposes a linear relationship between permanent deformation, the number of load cycles, and the equivalency factor between the effect of resilient strain, or vertical stress, and allowable damage. The proposed empirical transfer functions allow defining an allowable number of load repetitions for a characteristic resilient strain or vertical stress and an allowable damage. The allowable damage can be modulated with respect to road classification, and a damage value of 0 % to FGAs layer can be considered as a safety factor. The findings of this study provide valuable insights into the use of FGAs as an insulating granular layer in pavement design in cold regions.

Data-driven modeling of hydrodynamic loading using NARX and harmonic probing

Optimizing floating wind turbines and their mooring systems requires validated computational models that predict wave-frequency and low-frequency hydrodynamic loads. Low-frequency loads are crucial for determining extreme offsets and tension in mooring lines and are generally described by a quadratic transfer function. The quadratic transfer function, obtained with numerical tools, accurately predicts low-frequency loads in mild sea states. However, since the existing numerical methods are based on potential and perturbation theory, they generally fail to accurately predict low-frequency loads in moderate-to-extreme sea states where current, viscous, and beyond-second-order potential effects become significant. Developing a procedure for empirical transfer function estimation is, therefore, necessary to overcome these limitations. This paper describes an existing framework for estimating any higher-order transfer functions from experimental data. The framework employs a nonlinear auto-regressive model based on Kriging to establish a causal input/output relationship between the wave-elevation and hydrodynamic force histories exerted on the floater. Then, higher-order transfer functions are extracted using harmonic probing. The procedure was validated by estimating the linear surge transfer function of the INO WINDMOOR 12 MW floater using synthetic data. The data-driven results showed an excellent agreement with the theoretically computed transfer function.

Empirical Transfer Function Estimation With Differential Filtering and Its Application to Fine Positioning Control of Galvano Scanner

Fast and precise point-to-point (PTP) positioning control is a critical technology for improving the throughput and product quality of industrial machines. This study aims to investigate the frequency response function (FRF) estimation method with differential filtering (ETFE-Diff: empirical transfer function estimation with differential filtering) that uses the input and output signals of PTP motion during processing operation and to apply ETFE-Diff to a feedforward (FF) compensation adjustment. In this study, the principle of ETFE-Diff for FRF estimation was clarified, compared to the existing FRF estimation methods, i.e., empirical transfer function estimation and local rational modeling. Moreover, the effectiveness of ETFE-Diff for FF compensation adjustment in improving positioning accuracy of a galvano scanner as an industrial servo system was experimentally demonstrated.

Quantification of uncertainty in linear wave energy hydrodynamic models from experimental data

Considerable testing and modeling are required in order to fully realise, efficiently develop, and successfully industrialise the wave energy converters (WECs). Numerical modeling, full-scale measurements, and scaled prototype testing are the various methodologies that can be applied to model WECs and predict the dynamic response. Mathematical WEC models form the basis of model-based energy maximising control and directly affect the ability of model-based controllers to maximise energy capture. Linear WEC models are attractive in leading to simpler control designs, but may not cover the complete operational space. One solution is to identify a range of linear models at different operating points, which give a measure of the underlying nonlinear behaviour [1], [2]. This model set can then be used to extract a nominal model, and an associated uncertainty region, which can be used as a basis for a robust WEC controller synthesis process, such as articulated in [3].
 Recently, such an approach has been adopted using data generated from a high-fidelity numerical computational fluid dynamics (CFD) model [4]. However, numerical wave tanks (NWTs) and physical wave tanks differ significantly in terms of the range of tests which can be performed, and the contamination which can affect the measurements used to determine the data-based models e.g. measurement noise, numerical effects, wave reflections, etc [5]. As a result, the determination of nominal models and uncertainty regions in a physical wave tank may provide some advantages (and disadvantages) which need to be examined carefully. In addition, the range of post-processing techniques which could, or should, be applied to the different experimental/numerical domains, to improve the fidelity of the identified models, may differ between domains.
 In this paper, experimental testing of a WEC, by recreating a wave field similar to real-life conditions and a small-scale version of the device, is used to understand the hydrodynamic behaviour and to obtain an accurate dynamic model for WECs, which are considered to be essential towards optimal WEC design. Physical wave tank experiments, even though having their own disadvantages, overcome some difficulties of CFD-based NWT experiments, most notably huge computation time, problems in accurate representation of viscous fluids, uncertainty in the specification of an appropriate turbulence model, and propagation of incident waves [6]. 
 In this study, representative linear models of a point-absorber type WEC from a physical wave tank in the wave basin at Aalborg University are determined which give insight into the system dynamics and provide a basis for robust control of WECs. Among different stimulation techniques to excite the system dynamics in physical wave tank tests, the particular types of excitation signals covering the complete range of frequencies and amplitudes of the system dynamics, while considering limitations on the range of excitation signals or the wave tank reflections, are adopted for the determination of representative linear models. Moreover, a full investigation is carried out to ascertain the appropriate post-processing needed to optimise the signals as the basis for model identification. The model identification includes the non-parametric frequency response by means of empirical transfer function estimate (ETFE). 
 

Data-driven analysis for disturbance amplification in car-following behavior of automated vehicles

This paper presents a data-driven framework to quantitatively analyze the disturbance amplification behavior of automated vehicles in car-following (CF). The data-driven framework can be applied to unknown CF controllers based on the concept of empirical frequency response function (FRF). Specifically, a well-known signal processing method, Welch's method, together with a short time Fourier transformation is developed to extract the empirical transfer functions from vehicle trajectories. The method is first developed assuming a generic linear controller with time-invariant CF control features (e.g., control gains) and later extended to capture time-variant features. The proposed methods are evaluated for estimation consistencies via synthetic data-based simulations. The evaluation includes the performances of the linear approximation accuracy for a linear time-invariant controller, a nonlinear controller, and a linear time-variant controller. Results indicate that our framework can provide reasonably consistent results as theoretical ones in terms of disturbance amplification. Further it can perform better than a linear theoretical analysis of disturbance amplification, particularly when nonlinearity in CF behavior is present. The methods are applied to existing field data collected from vehicles with adaptive cruise control (ACC) on the market. Findings reveal that all tested vehicles tend to amplify disturbances, particularly in low frequency (< 0.5 Hz). Further, the results demonstrate that these ACC vehicles exhibit time-varying features in terms of disturbance amplification ratio depending on the leading vehicle trajectories.

A superconducting gravimeter on the island of Heligoland for the high-accuracy determination of regional ocean tide loading signals of the North Sea

SUMMARY The superconducting gravimeter GWR iGrav 047 has been installed on the small offshore island of Heligoland in the North Sea approximately at sea level with the overall aim of high-accuracy determination of regional tidal and non-tidal ocean loading signals. For validation, a second gravimeter (gPhoneX 152) has been setup within a gravity gradiometer approach to observe temporal gravity variations in parallel on the upper land of Heligoland. This study covers the determination of regional ocean tide loading (OTL) parameters based on the two continuous gravimetric time-series after elimination of the height-dependent gravity component by empirical transfer functions between the local sea level from a nearby tide gauge and local attraction effects. After reduction of all gravity recordings to sea level, both gravimeters provide very similar height-independent OTL parameters for the eight major diurnal and semidiurnal waves with estimated amplitudes between 0.3 nm s−2 (Q1) and 11 nm s−2 (M2) and RMSE of 0.1–0.2 nm s−2 for 2 yr of iGrav 047 observations and a factor of 2 worse for 1.5 yr of gPhoneX 152 observations. The mean absolute OTL amplitude differences are 0.3 nm s−2 between iGrav 047 and gPhoneX 152, 0.4 nm s−2 between iGrav 047 and the ocean tide model FES2014b and 0.7 nm s−2 between gPhoneX 152 and FES2014b which is in good agreement with the uncertainty estimations. As by-product of this study, OTL vertical displacements are estimated from the height-independent OTL gravity results from iGrav 047 applying proportionality factors ${\rm d}h/{\rm d}g$ for the eight major waves. These height-to-gravity ratios and the corresponding phase shifts are derived from FES2014b. The OTL vertical displacements from iGrav 047 are estimated with amplitudes between 0.4 mm (Q1) and 5.1 mm (M2) and RMSE of 0.1–0.7 mm. These OTL amplitudes agree with FES2014b within 0.0 (M2) and 0.8 mm (K1) with a mean difference of 0.3 mm only. The OTL amplitudes from almost 5 yr of GNSS observations show deviations of up to 6 mm (M2) compared to vertical displacements from both iGrav 047 and FES2014b, which suggests systematic effects included in the estimation of OTL vertical displacements from GNSS. With the demonstrated accuracy, height-independent sensitivity in terms of gravity and vertical displacements along with the high temporal resolution and the even better performance with length of time-series, iGrav 047 delivers the best observational signal for OTL which is representative for a large part of the North Sea.

Incorporating the Benefits of Geosynthetic into MEPDG

One of the most effective ways to increase the longevity of pavement structures is through the integration of geosynthetic reinforcement. Geosynthetics are synthetic materials such as geotextiles, geogrids, or geocomposites that are added to the interface between the subgrade and the base layer of a pavement structure. To evaluate the effect of various parameters on the structural benefits of geosynthetic reinforcement on the pavement structure of low-volume traffic flexible pavements, a finite element (FE) study was performed using the ABAQUS program. These parameters included the geosynthetic type, geosynthetic tensile stiffness, subgrade stiffness, and base thickness. The FE rutting curves for the 100 cycles were calibrated using the mechanistic–empirical (M-E) transfer functions, which were then used to calculate the long-term rutting curves. The traffic benefit ratio (TBR) was initially calculated based on the calibrated rutting curves for each pavement layer. The calculated TBRs were then used as an input in AASHTOWare to compute the base effective resilient modulus (MR-eff) and the factor of base course reduction (BCR). The results showed that adding one layer of geosynthetics enhanced the rutting performance of pavement structures significantly (up to 8.9 in TBR, 322% in MR-eff, and 64% in BCR). Geogrids showed higher benefits than geotextiles due to the interlocking between base aggregates and geogrid aperture. The values of TBR, MR-eff, and BCR increase with the increasing tensile stiffness of the geosynthetics and the rutting target and with the decreasing subgrade stiffness. The results also demonstrated peak values of TBR, MR-eff, and BCR for a base thickness of 25.4 cm.

Railway formation design by elasto-plastic FEM mechanistic-empirical approach

A design method for conventional railway track formations to limit deformations in fine-grained subgrades is proposed. It is based on previous performance-based design methods with the important distinction that two-dimensional mechanisms are considered. Advanced hardening plasticity constitutive models are used for the subgrade to predict permanent deformation under a single loading directly, rather than by elastic analysis and approximate empirical transfer functions, before using empirical relationships to predict permanent deformation accumulation of the subgrade under successive loadings. The approach was validated by back-analysis of a laboratory test and full-scale trial. A parametric study identified a strong correlation between mobilised subgrade shear strength and permanent strain and between mobilised track bearing capacity and permanent subgrade deformation – correlations that could streamline design significantly. A strain rather than stress-based criterion for subgrade failure was found to be more appropriate since it takes account of the contribution of ballast strength at resisting permanent strain in the subgrade. The benefits of geogrids in granular layers on subgrade strains can be directly assessed using this method. Simple, approximate equations to determine permanent subgrade strain and deformation are derived that could be used for rapid non-FEM based optioneering prior to more rigorous, time consuming, analysis being performed.

Probability Distributions of Asphalt Pavement Responses and Performance under Random Moving Loads and Pavement Temperature

Asphalt pavements are damaged by traffic load repetitions. Conventionally, the allowed number of load repetitions until pavement failure is calculated based on empirical transfer functions from deterministic pavement mechanical responses to performance. However, the mechanical responses and damage to the pavement are uncertain under a random realistic traffic load and pavement temperature. Therefore, the non-deterministic problem—that is, the probability distributions of asphalt pavement responses and performance under random moving loads and pavement temperatures—was investigated in this study. Random factors include the load pressure, vehicle wandering, speed, and temperature inside the asphalt layer. A combination of the response surface and first-order reliability methodologies was recommended to calculate the probability of mechanical responses at any point within the pavement, for reasons of computational efficiency. The accuracy of this method was verified by a Monte-Carlo simulation. Then, the effects of the mean values and standard deviations of the random factors on the probability distributions of the mechanical responses were discussed. Finally, probability distributions of pavement performance (i.e., probability density distributions of cumulative damage for fatigue failure and rutting after repeated random loads) were calculated using transfer functions and the probability distributions of the mechanical responses; thereby, the failure probability of the pavement after a given number of load repetitions was obtained. The results show that the previous deterministic analysis could not fully reflect the random characteristics of pavement mechanical responses under realistic random moving loads, and the mean values and standard deviations of the random factors have significant effects on the probability distributions of mechanical responses and performance. The failure probability of the pavement after a given number of load repetitions can be used as a guide to reliability-based pavement design. This study on the probability distributions of asphalt pavement responses and performance exhibits the potential to understand pavement behavior and could be beneficial as a complement during reliability-based pavement design.

Uncertainty estimation in wave energy systems with applications in robust energy maximising control

Under control action, wave energy devices typically display nonlinear hydrodynamic behaviour, making the design of energy maximising control somewhat onerous. One solution to approach the optimal performance for nonlinear control problem under model mismatches is to employ a linear control strategy, which can be robust to linear model mismatches. However, accurate characterisation of the uncertainty in the linear model is vital, if the controller is to adequately capture the full extent of the uncertainty, while not being overly conservative due to overestimation of the uncertainty. This paper describes a procedure, employing CFD-based numerical tank experiments, to accurately produce a nominal linear empirical transfer function model, along with an accurate estimate of the uncertainty bounds in that linear model, due to hydrodynamic uncertainty. A robust control case study is provided, illustrating the nominal model estimation process, and its corresponding uncertainty set, including the complete procedure, required to generate the robust controller. Robust control results, on the fully nonlinear CFD model, are provided to demonstrate the efficacy of the modelling and control philosophy.

Can modeling soil heterogeneity in 2D site response analyses improve predictions at vertical array sites?

This study uses a database of 21 vertical borehole arrays in California to examine whether a two-dimensional (2D) site response analysis framework that accounts for soil heterogeneity via spatially correlated random fields can explain misfits observed from prior one-dimensional (1D) ground response modeling. The main hypothesis is that the overprediction of ground motion at site modal frequencies, consistently observed in many site response validation studies, is caused by soil heterogeneity and 2D/three-dimensional (3D) wave propagation effects that cannot be captured by 1D analyses. We apply classical “within” boundary conditions for borehole input motion along with equivalent incident wave motions derived using a framework developed here to help elucidate the effects of the down-going wave on observed fundamental mode resonances. Results from 2D and 1D analyses are compared to observations using a transfer-function-based taxonomy and residuals of other intensity measures (IMs) including response spectra. The uncertainty in predicted IMs is estimated from the many realizations of 2D models. This 2D approach was found capable of scattering seismic waves and producing transfer function variability resembling the observed event-to-event variability in empirical transfer functions (ETFs). For several sites that exhibit less down-going wave effects in ETFs (i.e. flatter peaks) and/or higher variability in ETFs, median transfer functions from 2D analyses provide a significantly better estimate of the median ETF than conventional 1D deterministic analyses, especially at fundamental modes. In contrast, for some of the sites that are well represented by 1D methods (e.g. Wildlife Liquefaction Array and Treasure Island), 2D methods with generic levels of spatial variability may over-represent the heterogeneity and consequently underpredict amplifications at higher mode frequencies.

Amplification Behaviour of Compressional Waves in Unconsolidated Sediments

Similar to horizontal earthquake motions, vertical motions are amplified depedent on the local site conditions which can be critical for the safety of certain structures. Production of natural gas in Groningen, the Netherlands, results in reservoir compaction causing low magnitude, shallow earthquakes which are recorded with a borehole seismic network. These recordings form an excellent data set to understand how shallow unconsolidated subsurface geology influences the amplification behaviour of compressional waves (P-waves). First, we present borehole and single-station techniques (amplification factors, empirical transfer functions (ETF) and V/H spectral ratio implementations) to quantify vertical amplification. We show that vertical-wave incidence is a reasonable assumption. All techniques are capable of emphasising the sites with strong amplification of vertical ground motion during an earthquake. Subsequently, we compare ETF with single-station methods with the aim to develop proxies for vertical site-response using spectral ratios. In a second step, we link vertical site-response with shallow subsurface conditions, like the P-wave velocity and peat content. To better understand the amplification mechanisms, we analytically simulate P-wave propagation. In the simulations, we compute synthetic transfer functions using realistic subsurface conditions and make a comparison with the ETF. The simulations support the hypothesis that thin layers of shallow gas, originating from the Holocene peat, result in wave amplification. We observe strong vertical site-response in particular in the eastern part of Groningen, with industrial facilities and pipeline infrastructure in the region. Here, if high vertical amplifications are persistent at large earthquake magnitudes, appreciable levels of vertical loading may be expected. This study demonstrates that vertical motions should be assessed separately from horizontal motions, given that the amplification behaviour of P-waves is affected by distinctive mechanisms.

Development of a seismic site-response zonation map for the Netherlands

Abstract. Earthquake site response is an essential part of seismic hazard assessment, especially in densely populated areas. The shallow geology of the Netherlands consists of a very heterogeneous soft sediment cover, which has a strong effect on the amplitude of ground shaking. Even though the Netherlands is a low- to moderate-seismicity area, the seismic risk cannot be neglected, in particular, because shallow induced earthquakes occur. The aim of this study is to establish a nationwide site-response zonation by combining 3D lithostratigraphic models and earthquake and ambient vibration recordings. As a first step, we constrain the parameters (velocity contrast and shear-wave velocity) that are indicative of ground motion amplification in the Groningen area. For this, we compare ambient vibration and earthquake recordings using the horizontal-to-vertical spectral ratio (HVSR) method, borehole empirical transfer functions (ETFs), and amplification factors (AFs). This enables us to define an empirical relationship between the amplification measured from earthquakes by using the ETF and AF and the amplification estimated from ambient vibrations by using the HVSR. With this, we show that the HVSR can be used as a first proxy for site response. Subsequently, HVSR curves throughout the Netherlands are estimated. The HVSR amplitude characteristics largely coincide with the in situ lithostratigraphic sequences and the presence of a strong velocity contrast in the near surface. Next, sediment profiles representing the Dutch shallow subsurface are categorised into five classes, where each class represents a level of expected amplification. The mean amplification for each class, and its variability, is quantified using 66 sites with measured earthquake amplification (ETF and AF) and 115 sites with HVSR curves. The site-response (amplification) zonation map for the Netherlands is designed by transforming geological 3D grid cell models into the five classes, and an AF is assigned to most of the classes. This site-response assessment, presented on a nationwide scale, is important for a first identification of regions with increased seismic hazard potential, for example at locations with mining or geothermal energy activities.

Energy-maximising experimental control synthesis via impedance-matching for a multi degree-of-freedom wave energy converter

We present, in this paper, an experimental framework for design and synthesis of impedance-matching-based (IM) controllers capable of maximising energy extraction in inherently multi degree-of-freedom wave energy converter (WEC) systems, and its subsequent application to the Intertial Sea Wave Energy Converter (ISWEC) device, by incorporating recent advances in IM-based theory. In particular, we consider a 1/20th scale prototype of the ISWEC system, tested as part of a larger experimental campaign conducted within the tank facilities available at Università degli Studi di Napoli Federico II, subject to a variety of wave conditions. We adopt two different control structures to realise an approximation of the IM principle, fully tuned based upon interpolation of a particular (experimentally obtained) non-parametric empirical transfer function estimate, which defines the optimal frequency-domain input-output response for energy-maximising behaviour. Furthermore, a performance comparison between controller tuning based upon traditional linear boundary element method models, and the presented experimental approach, is also offered, showing that the latter can consistently outperform the former in realistic scenarios, for the set of analysed sea-states.

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A variable speed refrigeration system (VSRS) has been applied to various industrial fields because of its excellent energy saving performance and partial load response capability. In this paper, an optimal servo controller for a variable speed oil cooler system was investigated to obtain precise temperature control performance against disturbance and model uncertainty. A state space model for controller design was derived from empirical transfer function. The controller was designed as a servo type to follow the step command strictly while minimizing an evaluation function of the secondary form for state variable and input energy. Especially, the weighting matrix, a key parameter in an optimal servo controller design, was automatically designed to meet design specifications using genetic algorithm (GA). The validity of the suggested controller was confirmed through MATLAB-based simulations and actual experiments. Moreover, the optimality and ease of design of the proposed optimal servo controller were demonstrated by comparing results with a conventional PI controller.

2D Geotechnical site-response analysis including soil heterogeneity and wave scattering

This study describes an approach for modeling wave scattering and the spatial variability of ground motion in geotechnical site-response analysis by modeling soil heterogeneity through 2D correlated random fields. Importantly, the required site-specific inputs to apply the proposed approach in a practical setting are the same as those associated with conventional 1D site-response analysis. The results, which are affected by wave scattering attenuation, are compared to those from conventional laterally homogeneous 1D site-response analyses and 1D analyses with randomized velocity profiles extracted from heterogeneous 2D velocity model realizations. A sensitivity study, involving 5400 2D model realizations, investigates the influence of random field input parameters on wave scattering and site response. The computed ground surface acceleration waveforms and transfer functions show that this method is capable of scattering seismic waves. Multiple ground-motion intensity measures are analyzed to quantify this influence and distinguish between the effects of 1D vertical heterogeneities and averaging across many nodes and realizations, from the effects of wave scattering and 2D ground-motion phenomena. The redistribution of ground-motion energy across wider frequency bands and scattering attenuation of high-frequency waves in the 2D analyses resemble features observed in empirical transfer functions computed in other studies. While analyses with 1D randomized velocity profiles are able to replicate median results from 2D analyses for some low-frequency intensity measures (e.g. transfer functions at [Formula: see text] Hz, and spectral acceleration at the fundamental period), medians and standard deviations of high-frequency intensity measures (e.g. transfer function at [Formula: see text] Hz, [Formula: see text], and Arias intensity), which are influenced by wave scattering, are not appropriately captured. Given the equivalent input information requirements as conventional 1D analysis, and the availability of large computational resources, we advocate that the proposed 2D (and eventually 3D) approach is a fruitful path forward to improve the modeling of site-response physics and realize improved predictive capabilities.