Track Modeling Research Articles

Efficient TPC data compression by track and cluster modeling

Current and future heavy ion experiments pose an increasing challenge with respect to the handling of the generated data rates. By introducing effective data compression techniques into the detector readout chain, the amount of events written to mass storage can be greatly enhanced thus improving the experimental conditions in terms of statistics. Based on a data modeling scheme highly adapted to Time Projection Chamber (TPC) data, we show that compression factors close to 10 are achievable.

Low temperature thermochronology of the southern East Greenland continental margin: Evidence from apatite (U–Th)/He and fission track analysis and implications for intermethod calibration

The southern coast of East Greenland is characterized by high topographic relief and deep fjords, but the evolution of the landscape and the low-temperature thermochronology of the region is not well understood. Here we present apatite fission-track and (U–Th)/He ages that suggest several important features of the long-term geomorphic history of this region, but which also illustrate an important discrepancy in the thermal histories derived from each technique. Apatite from bedrock of the southern coast of East Greenland between 62°N and 67°N has fission-track ages ranging from 60 to 840 Ma and (U–Th)/He ages ranging from 21 to 250 Ma. The ages generally increase with elevation and distance from the coast, and fission-track analyses show significant differences in thermal histories for the different regions. In the Kangertittivatsiaq area (c. 66–67°N) apatite fission track data and models suggest two separate periods of slow cooling: prior to c. 200 Ma and between c. 160 Ma and the late Cenozoic (more recently than c. 20 Ma), each of which was followed by a period of rapid cooling and inferred exhumation. Apatite He data in the Kangertittivatsiaq region, including crystal-size–age correlations in low-elevation samples, are most simply interpreted as recording an incision event of at least 1.5 km later than 20 Ma near the coast. This may have been caused by glacial erosion. The (U–Th)/He data also indicate an earlier phase of rapid exhumation at c. 250 Ma. In the Skjoldungen/Kap Møsting area (c. 62–64°N) approximately 200 km south of the Kangertittivatsiaq, apatite fission-track data suggest slow exhumation from c. 200 Ma into the Neogene followed by fast exhumation. The similarity of fission track ages (200 Ma) at sea level in the fjords in the Skjoldungen area (c. 62–64°N) do not suggest tilting in the hinterland related to the breakup of the East Greenland continental margin. Furthermore, the Cenozoic fission track ages and modeling fission track data suggest that pre-breakup basins may have covered the outer coast. Despite the broadly similar topographic implications of the fission-track and (U–Th)/He data, the thermal histories derived from these systems are inconsistent. Fission-track data require thermal histories that predict He ages younger than observed, and He data require thermal histories that predict fission-track ages older than observed. Similar discrepancies have also been observed in other settings characterized by long-term low-temperature thermal histories, and may reflect changes in annealing or diffusion behavior (or both) that either develop or become more apparent in such cases.

Modelling of Floating-Slab Track with Discontinuous Slab

A floating-slab track with discontinuous slab provides a spatially-varying stiffness under a constant moving load. When a train moves on such a track, even with the absence of rail roughness, a parametric excitation develops as wheels move up and down applying dynamic forces at the wheel-rail interface. The dynamic force is magnified if one of its principal frequencies matches with any of the train or the track resonance frequencies. In this paper, a new method based on a Fourier series representation is developed to couple a moving train to a track with discontinuous slab. A two-degree-of-freedom system is used to model a quarter of a train with four axles and two bogies moving on a track with constant velocity. The purpose of this work is to investigate the dynamic effect of slab discontinuity on trains running in underground railway tunnels, where the velocity is less than 100km/hr. For typical parameters of a train and a track, it is found that the force at the wheel-rail interface is only increased by 1% of its static value due to slab discontinuity. However, the dynamic effect may be more important in circumstances where high-speed or heavy-axled trains are used in underground tunnels.

Modelling of Floating-Slab Track with Discontinuous Slab

This paper presents three different methods for modelling a track with discontinuous slab under oscillating moving loads. These are the Fourier-Repeating-unit method, the Periodic-Fourier method and the Modified-phase method. The first two methods, borrowed from the literature of periodic infinite structures, are accurate if careful consideration is taken when performing numerical integrations. The third method, not presented elsewhere before, is faster and simpler; it is only valid for velocities of moving loads lower than the critical velocity of the track, but this “velocity effect” is of no consequence for underground railways. Discontinuity of slab provides a parametric excitation for moving loads over floating-slab tracks. It is shown that in the frequency range of ground-borne vibration, more vibration propagates form such tracks at resonance frequencies of the slabs, compared with tracks with continuous slabs. It is found that the velocity effect is insignificant when calculating displacements of a typical floating-slab track under oscillating moving loads with velocities less than 100km/hr. However, a correction has to be made to account for the right phase between the input force and the output displacement.

Simulation of vehicle–track interaction with flexible wheelsets, moving track models and field tests

Vehicle–track dynamic interaction emerged as a key multi-aspect subject following the development in high-speed and high axle-load trains. In this context, wheelset structural flexibility and track flexibility are the two main factors that contribute to high frequency content of the wheel–rail forces and influence the vehicle–track damage. Appropriate wheelset and track flexibility models are hence of great importance in pertinent numerical simulations. The present study comprises vehicle–track dynamic simulations considering wheelset structural flexibility and advanced moving track models. Simulated wheel–rail forces are then validated against measured data. The effects of the wheelset structural flexibility and track flexibility on the wheel–rail forces are investigated in the frequency range 0–150 Hz. The influence of track modelling and pertinent data on the simulation results is particularly assessed through a set of moving track models. Measured track data, i.e. irregularities, roughness and flexibility support the simulations. It is confirmed that track flexibility with appropriate modelling and data is important when examining the vehicle–track interaction. In the present case study, the influence of wheelset structural flexibility on the lateral wheel–rail forces is quite significant too.

Solid sediment load history of the Zambezi Delta

We calculate the solid sediment load history of the Zambezi River for the last 120 Ma (i.e. Middle Cretaceous–Recent times). Our starting point is a detailed grid of two-dimensional seismic reflection profiles, calibrated by well-log information. After conversion from two-way travel time to depth, we made simple assumptions about the compaction history in order to construct isochore maps of solid sediment load and yield as a function of geological time. Our results show that solid sediment load has varied by ∼1 order of magnitude over the last 120 Ma. There have been three periods of elevated flux. The first period occurred in Late Cretaceous times (90–65 Ma) and was synchronous with the rapid denudation of southern Africa recognised by, for example, apatite fission track modelling. The second period occurred in Oligocene times (34–24 Ma) during proposed rapid regional uplift of Southern Africa. The youngest phase of elevated flux started in Late Miocene times (10 Ma) and has continued to increase rapidly through to the present day. A large proportion of this increase can be attributed to a doubling of the size of the Zambezi catchment during the Pliocene. At other times, we suggest that load variations can be used to bound the uplift history of the region, which encompasses the catchment. Finally, changes in the shape of the Zambezi Delta through time suggest that the Mozambique current, which sweeps through the Mozambique Channel from northeast to southwest, initiated at the start of the Miocene.

Adjacent track erasure analysis and modeling at high track density

The issues of the adjacent track erasure problems have been studied for high track density (TPI) situations using dc erasure at adjacent tracks. It is found that a significant portion of the BER degradation is due to the stray field from the vicinity of the write gap. Finite element method (FEM) calculations were carried out for studying the field in the vicinity of the write gap. Furthermore, we have incorporated FEM results into micromagnetic simulation of conventional media to simulate the actual side writing and erasure processes. The simulation results confirmed the RMS loss of SNR due to multiple adjacent dc erasure. The obtained experimental results indeed are quite consistent with the modeling results.

Remote detection of derailment of a wagon of a freight train: theory and experiment

The paper discusses the possibility to detect derailment of a train's wagon by measuring vibrations of the rails under the locomotive. Both theoretical and experimental studies have been carried out, followed by a comparison of their results. For the theoretical modelling of the railway track, a Timoshenko beam resting on discrete, equidistantly spaced supports is used. The steady-state response of the beam to a load that either uniformly moves along the beam or uniformly `jumps' from support to next support is investigated at a point, which remains at a fixed distance from the moving load. The load that moves along the beam is used to model the `normal motion' of a train's wheelset, whereas the `jumping' load is employed to model the action of a derailed wheelset. It is shown that the effect of the derailed wheel-set consists of an amplification of the rail's response in the frequency band that surrounds the natural frequency of the sleeper's vibrations. This theoretical prediction is confirmed experimentally. A method of processing the measured data is proposed that allows for stable detection of the derailment. A maximum distance between the locomotive and the derailed wagon is estimated, at which the detection is possible.

A three-dimensional model for the lateral and vertical dynamics of wagon-track systems

Lateral and vertical dynamics of the wagon and track affects the maintenance and safety of the heavy haul railway operation. With a view to understanding this aspect comprehensively, a three-dimensional wagon-track system dynamics (WTSD) model is developed and presented. The model consists of a full wagon with 37 degrees of freedom (DOF), a four-layer track with discretely supported rails and a wheel-rail interface representing Kalker's creep and Hertzian contact parameters. The model has been validated using two sets of field data: one dealing with vertical impact due to the flat wheel and the other dealing with lateral hunting. The effect of detailed track modelling on lateral hunting is discussed, and the capability of the three-dimensional WTSD model in predicting lateral impact is demonstrated.

Thermochronological constraints on the timing and magnitude of Miocene and Pliocene extension in the central Wassuk Range, western Nevada

Apatite fission track and (U‐Th)/He thermochronological data provide new constraints on the timing of faulting and exhumation of the Wassuk Range, western Nevada, where east dipping normal faults have accommodated large‐magnitude ENE‐WSW oriented extension. Extensional deformation has resulted in the exhumation of structurally coherent fault blocks that expose sections of preextensional mostly granitic upper crust in the Grey Hills and central Wassuk Range. These fault blocks display westward tilts of ∼60° and expose preextensional paleodepths of up to ∼8.5 km, based on the structural reconstruction of tilted preextensional Tertiary andesite flows that unconformably overlie Mesozoic basement rocks. Apatite fission track and (U‐Th)/He thermochronological data from the fault blocks constrain the onset of rapid footwall exhumation at ∼15 Ma. Fission track modeling results indicate rapid fault block exhumation occurred between ∼15 and 12 Ma, which is in agreement with Miocene volcanic rocks that bracket the tilting history. In addition, fission track and (U‐Th)/He data suggest reduced rates of cooling following major extension, as well as renewed cooling related to active, high‐angle faulting along the present‐day range front starting at ∼4 Ma. Thermochronological data from structurally restored fault blocks indicate a preextensional Miocene geothermal gradient of 27° ± 5°C/km. The thermochronological constraints on the timing of extensional faulting and the eruptive history in the Wassuk Range imply a model for extension where crustal heating and volcanism precede the onset of rapid large magnitude extension, and where synextensional magmatism is suppressed during the highest rates of extension.

Storm Track Dynamics

This paper reviews the current state of observational, theoretical, and modeling knowledge of the midlatitude storm tracks of the Northern Hemisphere cool season. Observed storm track structures and variations form the first part of the review. The climatological storm track structure is described, and the seasonal, interannual, and interdecadal storm track variations are discussed. In particular, the observation that the Pacific storm track exhibits a marked minimum during midwinter when the background baroclinicity is strongest, and a new finding that storm tracks exhibit notable variations in their intensity on decadal timescales, are highlighted as challenges that any comprehensive storm track theory or model has to be able to address. Physical processes important to storm track dynamics make up the second part of the review. The roles played by baroclinic processes, linear instability, downstream development, barotropic modulation, and diabatic heating are discussed. Understanding of these processes forms the core of our current theoretical knowledge of storm track dynamics, and provides a context within which both observational and modeling results can be interpreted. The eddy energy budget is presented to show that all of these processes are important in the maintenance of the storm tracks. The final part of the review deals with the ability to model storm tracks. The success as well as remaining problems in idealized storm track modeling, which is based on a linearized dynamical system, are discussed. Perhaps on a more pragmatic side, it is pointed out that while the current generation of atmospheric general circulation models faithfully reproduce the climatological storm track structure, and to a certain extent, the seasonal and ENSO-related interannual variations of storm tracks, in-depth comparisons between observed and modeled storm track variations are still lacking.

Tropical cyclone track and intensity prediction: The generation and assimilation of high-density, satellite-derived data

The impact of recent scientific and technological advances in tropical cyclone track, intensity and structure modeling is discussed. Since the early 1990s, developments have occurred in remote sensing, data assimilation procedures, numerical models and high performance computing. In particular, there is now quasi-continuous high spatial and temporal resolution data coverage over the previously data-sparse oceans where tropical cyclones spend most of their life cycles. There has been a rapid development of data assimilation methodologies capable of using these data to initialize high-resolution prediction models. Model developments have reached a stage of maturity where the representation of many of the physical processes necessary for improved tropical cyclone track and intensity prediction are now included. Finally, available computer power has reached the teraflop range. Most operational centers have high performance computers capable of tropical cyclone modeling at resolutions necessary for skillful track and intensity simulations. This article focuses on combining all of the above developments in a tropical cyclone data analysis and prediction system. The system has produced statistically significant reductions in the mean forecast error statistics for tropical cyclone track predictions and resulted in far more realistic simulations of tropical cyclone intensity and structure. A large number of tropical cyclones have been modeled, with emphasis on those classified as being “difficult” storms to predict accurately. These difficult storms are most responsible for rapidly growing forecast errors. Our results are illustrated by case studies of such tropical cyclones.

Track Structure Modeling With Nucars™ and Its Validatation

SUMMARYThis paper presents the development of a methodology for simulating flexible track structures in the *NUCARS™ vehicle/track interaction multi-body simulation program. Several different track modeling methods were evaluated and example results arc compared. The implementation of the chosen track model in NUCARS is described. Simulations and comparisons with test data from three research and test programs are presented. This paper discusses the limitations of the methodology and the ongoing development of the NUCARS software to improve the simulation of track structure interaction with vehicle dynamics.

Simulation of Hurricane Risk in the U.S. Using Empirical Track Model

This paper describes a new technique for modeling hurricane risk in the United States. A storm track modeling approach is employed where, for each hurricane, the entire track as it crosses the ocean and makes landfall is modeled. The central pressure is modeled as a function of the sea surface temperature. The approach is validated through comparisons of simulated and observed key hurricane statistics (central pressure, translation speed, heading, and approach distance) along the U.S. coastline. The simulated and observed landfall rates of intense hurricanes (Saffir-Simpson Scale 3 and higher) also are compared on a regional basis along the coast. The model is able to reproduce the continuously varying hurricane climatology along the U.S. coastline, and it provides a rational means for examining the hurricane risk for geographically distributed systems such as transmission lines and insurance portfolios.

The link between physics and chemistry in track modelling.

The physical structure of a radiation track provides the initial conditions for the modelling of radiation chemistry. These initial conditions are not perfectly understood, because there are important gaps between what is provided by a typical track structure model and what is required to start the chemical model. This paper addresses the links between the physics and chemistry of tracks, with the intention of identifying those problems that need to be solved in order to obtain an accurate picture of the initial conditions for the purposes of modelling chemistry. These problems include the reasons for the increased yield of ionisation relative to homolytic bond breaking in comparison with the gas phase. A second area of great importance is the physical behaviour of low-energy electrons in condensed matter (including thermolisation and solvation). Many of these processes are not well understood, but they can have profound effects on the transient chemistry in the track. Several phenomena are discussed, including the short distance between adjacent energy loss events, the molecular nature of the underlying medium, dissociative attachment resonances and the ability of low-energy electrons to excite optically forbidden molecular states. Each of these phenomena has the potential to modify the transient chemistry substantially and must therefore be properly characterised before the physical model of the track can be considered to be complete.

99/03005 Genesis of coal-generated oil in Konggu-4 well in Huanghua depression, China

We calculate the solid sediment load history of the Zambezi River for the last 120 Ma (i.e. Middle Cretaceous–Recent times). Our starting point is a detailed grid of two-dimensional seismic reflection profiles, calibrated by well-log information. After conversion from two-way travel time to depth, we made simple assumptions about the compaction history in order to construct isochore maps of solid sediment load and yield as a function of geological time. Our results show that solid sediment load has varied by ∼1 order of magnitude over the last 120 Ma. There have been three periods of elevated flux. The first period occurred in Late Cretaceous times (90–65 Ma) and was synchronous with the rapid denudation of southern Africa recognised by, for example, apatite fission track modelling. The second period occurred in Oligocene times (34–24 Ma) during proposed rapid regional uplift of Southern Africa. The youngest phase of elevated flux started in Late Miocene times (10 Ma) and has continued to increase rapidly through to the present day. A large proportion of this increase can be attributed to a doubling of the size of the Zambezi catchment during the Pliocene. At other times, we suggest that load variations can be used to bound the uplift history of the region, which encompasses the catchment. Finally, changes in the shape of the Zambezi Delta through time suggest that the Mozambique current, which sweeps through the Mozambique Channel from northeast to southwest, initiated at the start of the Miocene.

99/03003 Formation condition of coal as oil-source rock and assessment of oil generation Turpan-Hami basin, China

We calculate the solid sediment load history of the Zambezi River for the last 120 Ma (i.e. Middle Cretaceous–Recent times). Our starting point is a detailed grid of two-dimensional seismic reflection profiles, calibrated by well-log information. After conversion from two-way travel time to depth, we made simple assumptions about the compaction history in order to construct isochore maps of solid sediment load and yield as a function of geological time. Our results show that solid sediment load has varied by ∼1 order of magnitude over the last 120 Ma. There have been three periods of elevated flux. The first period occurred in Late Cretaceous times (90–65 Ma) and was synchronous with the rapid denudation of southern Africa recognised by, for example, apatite fission track modelling. The second period occurred in Oligocene times (34–24 Ma) during proposed rapid regional uplift of Southern Africa. The youngest phase of elevated flux started in Late Miocene times (10 Ma) and has continued to increase rapidly through to the present day. A large proportion of this increase can be attributed to a doubling of the size of the Zambezi catchment during the Pliocene. At other times, we suggest that load variations can be used to bound the uplift history of the region, which encompasses the catchment. Finally, changes in the shape of the Zambezi Delta through time suggest that the Mozambique current, which sweeps through the Mozambique Channel from northeast to southwest, initiated at the start of the Miocene.

Vehicle-Track Dynamics in the Mid-Frequency Range

During the last years railway companies have observed increasing problems with track damage like rail corrugation, deterioration of ballast or unround wheels. Since the origin of these damages is suspected in the mid-frequency dynamics, research activities in the frequency range from 50 up to 500 Hz have been initiated. The article demonstrates that in comparison to the low and high frequency range the knowledge about physical effects in the mid-frequency range is poor. Apart from a historical literature review on vehicle and track modelling, recently published methods and models are collated and problems in their mathematical treatise are mentioned. Regarding the vehicle, the paper shows the development starting with Klingel's massless wheelset model and ending with sophisticated elastic multibody system models. Concerning the track, different mathematical approaches in frequency and time domain are compared. In the mid-frequency range the pad, ballast and subsoil properties play an important role. Hence, the missing of experimentally validated models of these components is crucial. First attempts have been performed, which take into account the subsoil as layered half-space and the ballast as an assembly of viscoelastic rods. Besides the short time dynamics the article gives also an overview of the modelling of the wear phenomena mentioned above. An investigation of such long-term effects requires complex models of the entire vehicle-track system. The few wear models found in literature are discussed and first results are mentioned.

Fission track and numerical thermal modeling of differential exhumation of the Glarus thrust plane (Switzerland)

Geometry and differences in metamorphic grade along the Glarus thrust (external European Alps) can be explained by a restoration of the hanging wall some 10 km toward the south, and back rotation of the thrust plane into a ramp–flat–ramp geometry. The apatite fission track (FT) age pattern from the area suggests that isotherms were parallel to the thrust plane during cooling of the rocks along the thrust plane below the apatite closure temperature. Two forward modeling programs that both produce time–temperature paths are used to constrain the thermal and structural evolution of differential exhumation along the Glarus thrust. (a) A two-dimensional finite-difference thermal model is used to examine differential exhumation of the thrust plane, starting from an assumed horizontal position of the middle part of the Glarus thrust at some 10 Ma when parallel to the paleo-isotherms. Five locations in the crustal section corresponding to locations on a final horizontal and vertical sampling traverse record their time–temperature ( t– T) history during exhumation along particle paths. The near-surface temperature distribution is strongly influenced by the development of a simplified step-like topographic relief, which causes all modeled samples to reach the surface at the end of the modeled time period. (b) The calculated t– T paths of these five modeled samples were used to forward model apatite FT data based on an existing annealing model. By comparison between synthetically generated FT data and actual measured FT samples, the exhumation history of the Glarus Alps was evaluated with respect to its thermal and temporal brackets. Several parameters such as the location of the rotation point, the thermal gradient, and the topography have significant influence on model results. Best-fit models produce results that are consistent with independent geological and geophysical information.

Modeling of military aircraft noise in support of environmental impact mitigation

The Military Training Area in Labrador, Canada is used by NATO Alliance air forces of the United Kingdom, Germany, and the Netherlands, and is managed by the Canadian Department of National Defence (DND). Protection of the natural environment is a major consideration in the management of the training area. This paper describes a computer-based noise propagation model that will be used to support environmental management. The paper demonstrates its use in planning flying training sorties to mitigate short-term environmental impacts, and also its use in assessing environmental effects of the flying activity over the longer term. The model enables DND to maximize the extent of the range available for flight training by accurately calculating noise levels on the ground, and hence the degree and method of noise impact mitigation that is appropriate. The noise propagation model is used in conjunction with other computer-based tools for flight track modeling, terrain modeling, and specifying locations of noise-sensitive areas (typically wildlife habitats which may change in location during the training period). Other projects are aimed at investigating and evaluating acceptable levels of noise impact, in terms of consequences on wildlife viability in these habitats.