Countermeasure Techniques Research Articles

Centrifuge modelling for seismic retrofit design of an immersed tube tunnel

A centrifuge testing program was conducted to assess the earthquake performance of countermeasure retrofit techniques for an existing concrete tunnel embedded in a liquefiable sandy deposit. In a series of three separate heavily instrumented model tests, a tunnel section-foundation system was studied first without retrofitting, and then with a densified-wall and a gravel-wall liquefaction countermeasure techniques. The test results provided valuable insights into the underlying mechanism and effectiveness of each countermeasure and served as basis for calibration and validation of computational modelling of the George Massey Tunnel seismic retrofit design. Test results showed that the implemented countermeasures significantly reduced the tunnel movements. The gravel-wall technique was found to be particularly effective in reducing the extent of liquefaction as well as reinforcing the tunnel-foundation system against earthquake induced deformations. The centrifuge test results and the calibrated numerical model studies led to a final ground improvement scheme that included both stone column densification and seismic gravel drains.

Prediction of the degradation of the carrier‐to‐noise plus interference ratio concerning a site diversity system suffering from differential rain attenuation

Rain‐induced attenuation is a factor of utmost importance in designing a satellite link since it can strongly deteriorate the availability and performance of an Earth‐space path. Availability and performance are key criteria for the reliable design process. In the present paper the statistics of carrier‐to‐noise plus interference ratio under rain fade conditions are examined, given that the interference is caused by an adjacent satellite operating at the same frequency, and taking also under consideration double site diversity protection as a countermeasure technique. The method presented herein is based on a model of convective rain cells and the lognormal assumption for the point rainfall statistics. Numerical results have been obtained for heavy rain climatic regions and very large availability times, to examine how effective site diversity can be, not only for lowering fade margins but for compensating severe interference effects. Moreover, the elaboration of the numerical results has revealed how the optimum design of the satellite link can be achieved by selecting proper values for some critical parameters of the system.

NUMERICAL ANALYSIS OF EMBANKMENT FOUNDATION LIQUEFACTION COUNTERMEASURES

Computational simulations are presented for a unique series of centrifuge tests conducted to assess the performance of liquefaction countermeasure techniques. In these centrifuge tests, the dynamic response of an embankment supported on a liquefiable foundation (medium sand) is investigated. The experimental series included: (i) a benchmark test without a liquefaction countermeasure, (ii) foundation densiflcation below the embankment toe, and (iii) use of a sheet-pile containment enclosure below the embankment. This series of experiments documents a wide range of practical liquefaction response mechanisms (including countermeasure implementation). In order to numerically simulate the above centrifuge tests, a new calibrated soil stress-strain constitutive model is incorporated into a two-phase (solid-fluid) fully coupled Finite Element formulation. Comparison of the computational and experimental results demonstrates: (i) importance of post-liquefaction dilative soil behavior in dictating the dynamic response and deformation characteristics of the embankment-foundation system, and (ii) capabilities and limitations of the numerical modeling procedure.

Dynamic fade restoration in Ka‐band satellite systems

AbstractAtmospheric precipitation can seriously affect the propagation of centimeter and millimeter electromagnetic waves. As a consequence, in some applications, it is necessary to make use of a fade countermeasure technique in order to satisfy the system availability and quality requirements. This study analyses the performance of a satellite‐based system in geo‐stationary orbit operating at 20 GHz, dynamically assigning the antenna directivity pattern to counteract tropospheric attenuation. The on‐board power is spatially distributed over the covered region to minimize, at any time, the number of users undergoing outage because of the tropospheric attenuation. Both the aspects of broadcasting and telecommunication services are addressed. The reflector antenna of the system is supposed to be illuminated by a cluster of feeds driven by a set of excitation coefficients, continuously modified and optimized according to the meteorological information derived by processing METEOSAT satellite data and ECMWF (European Centre for Medium‐Range Weather Forecasts) data. Copyright © 2002 John Wiley & Sons, Ltd.

Effects of remedial measures for mitigating embankment settlement due to foundation liquefaction

In Japan, after the Hyogoken-nambu earthquake remedial measures have often been constructed for river dikes supported on liquefiable sand beds. In this study a series of dynamic centrifuge tests was conducted to assess seismic performances of embankments with and without countermeasures and to provide a basis for establishing conventional methods to evaluate crest settlement. Three types of countermeasures used in the current practice in Japan (the solidification by the deep mixing method, the densification by the sand compaction piles and the sheet pile enclosure) were tested. It was observed that the excess pore pressure under the embankment toes tends to be higher for models with countermeasures than benchmark models without countermeasures. The horizontal displacement constraint imposed by the remedial zone is considered to be responsible for this. It was also found that the countermeasure techniques could reduce lateral deformation of the liquefied foundation sand and shear deformation of the embankment significantly, however, some embankment crest settlement was inevitable. The higher excess pore pressure under the embankment due to the existence of the remedial countermeasures resulting in an increase in contractive volume change of sand under embankment was responsible for the inevitable crest settlement. It is concluded that displacement predictions of the remediation zone as well as a volumetric strain of the liquefied sand beneath the embankment are key aspects to assess crest settlements.

Formation and Characterization of Oil–Mineral Aggregates

Oil associates with fine mineral particles in an aqueous medium not only as molecules adsorbed onto mineral surfaces, but also as a discrete phase to form microscopic oil–mineral aggregates (OMA). As it promotes the dispersion of stranded oil, this process is now believed to be instrumental in the natural recovery of oiled shorelines and in the efficacy of spill countermeasure techniques such as surf-washing (relocation of oiled sediment into the zone of wave action). To predict the fate of residual oil following spills and the effectiveness of such countermeasures, an improved understanding of the nature and properties of OMA and of the factors influencing their formation is required. Laboratory protocols and microscopical methods have been refined for the detection and classification of OMA. Three OMA types have been identified: droplet, solid and flake aggregates. Droplet aggregates are oil droplets (usually a few μm in diameter) surrounded by individual or flocculated mineral particles. Solid aggregates are mixed oil and mineral bodies of various shapes (scale of tens of μm). Flake aggregates are thin sheets that can reach the mm size range in which mineral and oil are arranged in an ordered configuration. The parameters controlling the quantity, type and size of OMA include mineral type and surface properties, quantity, viscosity and composition of the oil, and oil/mineral ratio. It is also evident that water turbulence (i.e. breaking waves, strong flood currents) greatly enhances OMA formation. Once formed, OMA appear to be very stable structures the buoyancy of which depends on the ratio of oil to mineral in each individual aggregate. OMA being on average less dense than mineral-only aggregates and even buoyant, they will be kept in suspension longer and be dispersed further than unoiled sediment. Mineral particles in OMA act as a surfactant preventing the oil from recoalescing. As OMA formation increases the surface to volume ratio of spilled oil, it prolongs and enhances oil weathering processes such as dissolution, evaporation and biodegradation.

Potential of combined spaceborne infrared and microwave radiometry for near real‐time rainfall attenuation monitoring along earth‐satellite links

AbstractThe objective of this paper is to investigate how spaceborne remote sensors, and their derived products, can be exploited to optimize the performances of a satellite communication system in the presence of precipitating clouds along the path. The complementarity between sun‐synchronous microwave (MW) and geo‐stationary infrared (IR) radiometry for monitoring the earth's atmosphere is discussed and their potential as a rain detection system within near real‐time countermeasure techniques for earth‐satellite microwave links is analysed. A general approach, consisting in estimating rainfall intensity and attenuation by polar‐orbiting microwave radiometers and temporally tracking the rainfall areas by geo‐stationary infrared radiometers, is delineated. Multiple regression algorithms for predicting rainfall attenuation from spaceborne brightness temperatures and from surface rainrate, trained by radiative transfer and cloud models, are illustrated. A maximum likelihood technique is delineated to discriminate stratiform and convective rainfall from spaceborne brightness temperatures. The differences among attenuation estimates derived from layered raining‐cloud structures with respect to those obtained from simple rain slabs, as recommended by ITU‐R, are also quantified. A test of the proposed attenuation prediction methods is performed using raingage and Italsat data acquired in Spino d'Adda (Italy) during 1994. A description of the statistical method, based on the probability matching technique, adopted to combine MW and IR data for retrieving and tracking precipitating cloud systems in terms of path attenuation and accumulated rain at ground is finally provided together with its application to a case study over the Mediterranean area during October 1998. Copyright © 2001 John Wiley & Sons, Ltd.

A multi-frequency TDMA/TDM system for a VSAT terminal network operating in Ka band

FH-JFDA (Frequency Hopping-Jitter Free Demand Assignment) is a satellite access scheme suitable for VSAT systems and designed for the Ka band (20–30 GHz). It uses the FH-TDMA (Frequency Hopping-Time Division Multiple Access) technique on the in-bound link towards the hub station, and the TDM (Time Division Multiplexing) technique on the out-bound link, from the hub towards the traffic stations. Each traffic station is allowed to transmit to the hub in temporal slots assigned by the hub itself, generally hopping among different TDMA carriers at each data burst transmission. The hub station retransmits the data received by using two TDM carriers modulated at different bit rates. It tries to maintain the same temporal position of the real time data packets when it switches between the two carriers in order not to introduce any further jitter on data. The fade countermeasure system adopted is based on the up-link power control and on data bit rate changing. This paper describes the FH-JFDA MAC protocol, the algorithm for assigning the transmission temporal slots, the algorithm adopted by the hub station for mapping the TDMA transmissions onto the TDM links, and the fade countermeasure technique used. The results of the investigation on one particular parameter of the system, which influences the choice of the TDMA assignment procedure, are also presented. A possible realization of the system using two transponders of the Italsat National coverage payload is also included in the paper, and the performance of the fade countermeasure system is evaluated.

Propagation modeling and system strategies in mobile-satellite urban scenarios

Land mobile satellite (LMS) systems require fade countermeasure techniques since they suffer from limited fade margins and severe channel degradations. In the view of complete statistical models for LMS systems in urban areas, this paper deals with several specific mobile satellite urban configurations, such as a long straight street lined on both sides by buildings and a crossroad. Propagation effects are modeled as time series of received power by means of a ray-tracing method, which is used in combination with an orbit generator. The time series results are then postprocessed to simulate the impact of propagation mechanisms and satellite motion on fade mitigation techniques, satellite handover, and diversity. This original approach inherently accounts for the correlation between a number of very different but simultaneous effects that influence system performance. Exemplary results are finally discussed to stress the capability of the time-series approach.

Simulator for advanced fighter radar EPM development

In order to develop electronic protection measures (EPM) for airborne intercept radars, it is necessary to fully understand the often complex effects of different types of electronic countermeasure (ECM) techniques on the radar operation. To aid in this effort, a software-based high-fidelity simulator called SAFIRE has been developed. SAFIRE models target clutter and ECM signal returns on a pulse-by-pulse basis for arbitrarily long scenario durations. Conventional air-to-air processing modes that are typically used in airborne intercept radars for search and track functions are also modelled. The capabilities of SAFIRE are described, with particular emphasis on the ECM model. The ECM model is based on a modern coherent jammer which uses digital radio frequency memory (DRFM) technology to generate false targets and smart noise for sophisticated ECM techniques. Sample results from SAFIRE are presented to illustrate its utility in analysing the effects of such ECM techniques on the radar processing. Benchmark timing results for SAFIRE code execution are also provided, which indicate that for many jamming scenarios of interest, the code execution is only about five times slower than real time. This is a significant feature since the scenario durations that are required for these studies are often relatively long.

Detection of landmines (Review Paper)

Detection of landmines is a problem concerning both military and peacekeeping forces. This paper reviews literature on strategic minefield layouts, modern mine clearing, and mine countermeasure techniques based on mechanical methods. Discusses hydraulic and signal processing techniques, ion-trap mobility spectrometer, subsurface probing radar and few other novel methods employed for this purpose. The specialised directions that the landmine detection methods are taking are clearly pointed out.

The development and testing of an intraruminal slow-release bolus designed to limit radiocaesium absorption by small lambs grazing contaminated pastures

The accident at the Chernobyl nuclear power plant in 1986 resulted in levels of radiocaesium in animal-derived food products above national intervention limits in a number of countries. In upland areas of the United Kingdom (UK) radiocaesium activity concentrations in the meat of some sheep exceeds (in 1998) the local intervention limit of 1000 Bq kg −1 and measures are still in place to restrict the entry of such animals into the human food chain. The use of many established countermeasure techniques is difficult due to the nature of animal management in the affected areas. This paper describes a study to develop and test a bolus containing the radiocaesium binder ammonium ferric hexacyanoferrate (AFCF) suitable for administration to small lambs of hill-sheep breeds used in the UK. It was found that a bolus 14 mm × 50 mm in size, and containing 20% AFCF, could be safely administered to lambs of 10 kg. An increase in the AFCF content above 20% resulted in too rapid a breakdown of the bolus. Administration of three boli per lamb reduced the 137 Cs activity concentration in muscle by circa 50% between 3 and 8 weeks following administration of the boli. After 12 weeks the reduction in the 137 Cs activity concentration was 30%. We conclude that the AFCF bolus developed could be effectively used to reduce the radiocaesium activity concentration in lambs within hill and upland areas of the UK.

Analysis of the interference due to differential rain attenuation induced by an adjacent path on a triple-site diversity Earth-space system

The reliable design of satellite communication systems requires the consideration of interference effects. Interference caused by differential rain attenuation from an adjacent Earth-space system is taken under consideration. In particular, a method to predict rain differential attenuation statistics used for single/double site Earth-space systems is extended to include triple-site diversity ones. The modified method is again based on a model of convective rain cells as well as on the lognormal assumption for the point rainfall rate distribution at the location under consideration. In an analogous fashion with the (C/N) ratio, a "(C/I) diversity gain" is also adopted here and some very useful remarks concerning the effectiveness of the triple-site diversity protection as a countermeasure technique are deduced. As a general conclusion, it can be stated that the triple-site scheme not only reduce the potential large attenuation margins significantly, but also leads to the establishment of the minimum separation between satellites operating under permitted interference levels.

Millimeter waves for short-range multimedia communication systems

A framework for the performance characterization of short-range communications systems is developed with the intention of investigating the feasibility of new multimedia wireless services at millimeter waves (MMWs). Both narrow- and wide-band systems are considered for mobile and/or fixed users. This paper aims at defining and evaluating proper metrics to characterize the service quality for the user and jointly takes the propagation characteristics, the transmission techniques, and the multiple access protocols into account. The definition of service-oriented metrics is emphasized. Three different real scenarios operating at MMW are investigated with a unified perspective: intelligent transport systems, wide-band local-area networks, and local multipoint distribution systems for interactive video services. The role played by the MMW band in the development of these services is discussed. In each scenario, accurate propagation analysis is carried out and suitable countermeasure techniques are pointed out in order to join suitable service-quality levels. The methodology considered is based on both analytical and semianalytical tools for performance evaluation.

Foundation Liquefaction Countermeasures for Earth Embankments

A centrifuge-testing program is conducted to assess the earthquake performance of countermeasure retrofit techniques for a liquefiable foundation under an existing embankment. Currently, such testing results offer a valuable alternative to actual full-scale dynamic response, which is virtually nonexistent for retrofitted embankments. The response of a cohesive highway embankment supported on a loose saturated sand layer is analyzed under dynamic base excitation conditions. In a series of five separate model tests, this embankment-foundation system is studied first without, and then with the following four different liquefaction countermeasure techniques: densification, cement deep-soil-mixing, gravel berms, and sheet-pile enclosure. The underlying mechanism and effectiveness of each countermeasure are discussed based on the recorded dynamic response. Effects of each countermeasure on both foundation excess pore pressures and embankment deformations are analyzed and compared. The implemented countermeasures are found to reduce embankment vertical deformations by a maximum of about 50%. However, in some cases cracking and lateral spreading of the embankment are practically eliminated. Thus, retrofit techniques that constrain lateral flow of the underlying liquefied soil are deemed to be particularly effective in preserving overall embankment integrity.

WEATHERING AND DISPERSION OF NAPHTHENIC, ASPHALTENIC, AND WAXY CRUDE OILS

ABSTRACT The chemical composition and physical properties of a crude oil determine the behavior of the oil and the way its properties will change when the oil is spilled at sea. Reliable knowledge of the oil's behavior will enable the most effective countermeasure techniques to be used in a spill situation. A diverse range of crude oils is coming into production in the North Sea. The weathering behavior and chemical dispersibility of three very different crude oils—Troll (naphthenic), Balder (asphaltenic), and Nome (waxy)—have recently been thoroughly investigated through bench- and meso-scale experiments. The naphthenic crude oil was also exposed to full-scale studies in the North Sea. This study shows that emulsion formation, the viscosity of emulsion, and the potential for dispersing emulsions by dispersant treatment may vary greatly for the different crude oils. It would be impossible to predict these differences with existing oil-weathering models based on fresh oil properties alone. Especially for abnormal (e.g., highly asphaltenic, waxy) crude oils, the weathering and dispersibility behavior can be revealed only by experimental work. The findings have important implications for effective oil spill response planning, particularly for estimating the most appropriate “window of opportunity” and for optimizing a dispersant application strategy for crude oils.

屋根雪の滑雪制御に関する基礎的考察

The effectiveness of roof snow control by sliding mechanism on the sloped roof is widely recognized, but many problems are remained to systemize the techniques on removing roof snow.This paper presents fundamental study on the factors; characteristics of roof snow damage, regional characteristics of the damage, methods of removing roof snow, the frame on the systemization of roof snow control, and the state of studies on roof snow behavior, that are required in the systemization of the techniques on roof snow control.From the study, it is clarified that the techniques on roof snow control should be supported by prediction technique and countermeasure technique against to the roof snow damage. The prediction technique is required to know roof snow behavior and damages occurred by roof snow. The systemization of roof snow control is strongly required in deep snow area of Japan. Furthermore it is required to organize the knowledge obtained by observational, experimental, or analytical approach.

96/06567 The behaviour in bomb-derived caesium-137 fallout in catchment soils

After a nuclear accident the removal of contaminated soils and plants with radiocaesium and radiostrontium generally leads to the production of huge quantities of radioactive waste. Some countermeasure techniques studied within the European RESSAC programme (Rehabilitation of Soil and Surfaces after an Accident) are aimed at restoring the environment with a minimal waste production. They remove only the most contaminated part of the environment, the soil surface, or the tree leaves. The Decontaminating Vegetal Network (D.V.N.) mechanically removes less than 1 cm of soil, facilitated by the deliberate sowing of seeds to produce a turf with a substantial binding root-network. An organic polymer gel has also been tested for removing a soil layer of only a few millimetres thickness by mechanical brushing. Initial results from testing of these techniques are promising. Recently, another programme has been launched in which the use of non-lethal defoliation of trees has been tested to minimise foliar absorption and translocation leading to contamination of wood.

Error rate for optimal follower tone-jamming

The performance of a countermeasure technique in the presence of the optimal follower multitone jammer is evaluated for frequency-hopped spread spectrum (FHSS) communications. It is shown that, with a certain probability, the optimal jammer will have dual tones in a frequency channel.

On a follower tone-jammer countermeasure technique

A countermeasure technique to a follower tone-jammer is evaluated for frequency-hopped spread spectrum communications. This technique utilizes randomized decisions by the transmitter and the receiver to lure the jammer into helping the communicator's performance part of the time. It is shown that the proposed technique reduces the bit error rate of the system.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>