Littérature scientifique sur le sujet « Primary delay modelling »

The advancement of construction equipment is a trend in the construction industry, with numerous benefits. However, using inappropriate construction equipment causes delays in construction projects, affecting the firm's reputation. A number of research studies on overall delay have been conducted globally. Even so, there is a lack of research on construction delays caused by inappropriate construction equipment. The aim of this paper is to investigate the inappropriate construction equipment delay factors and their effects on the firm's reputation. Based on the issues identified in the focus group interviews and the literature survey, a questionnaire survey was conducted to assess the impact of these factors on the progress of Indian construction projects. The primary constraint was that all 300 responses were collected in person from construction professionals to avoid lethargic responses that could skew the results. Pearson correlation coefficients were used to determine the positive strength of each factor's relationship. A t-test was used to see if there was a significant difference between the respondents' firm categories. Structural Equation Modeling (SEM) was used to validate the effective relationship between the causes of delays due to inappropriate construction equipment and its impact on company's reputation. All of the factors examined by the SEM analysis evidenced that the inappropriate construction equipment factors are correlated among themselves and combined to impact the reputation of the company. Recommendations are made to overcome the inappropriate equipment delay factors. Doi: 10.28991/cej-2021-03091717 Full Text: PDF

Background: Women with ST-segment elevation myocardial infarction (STEMI) experience greater delays for percutaneous coronary intervention-facilitated reperfusion than men. Whether women and men benefit equally from current strategies to reduce ischaemic time and whether there are gender differences in factors determining delays is unclear. Methods: Patient delay (symptom onset to first medical contact) and system delay (first medical contact to percutaneous coronary intervention-facilitated reperfusion) were compared between women ( n=967) and men ( n=3393) in a Swiss STEMI treatment network. Trends from 2000 to 2016 were analysed, with additional comparisons between three time periods (2000–2005, 2006–2011 and 2012–2016). Factors predicting delays and hospital mortality were determined by multivariate regression modelling. Results: Female gender was independently associated with greater patient delay ( P=0.02 vs. men), accounting for a 12% greater total ischaemic time among women in 2012–2016 (median 215 vs. 192 minutes, P<0.001 vs. men). From 2000–2005 to 2012–2016, median system delay was reduced by 18 and 25 minutes in women and men, respectively ( P<0.0001 for trend, P=n.s. for gender difference). Total occlusion of the culprit artery, stent thrombosis, a Killip class of 3 or greater, and presentation during off-hours predicted delays in men, but not in women. A Killip class of 3 or greater and age, but not gender or delays, were independently associated with hospital mortality. Conclusions: STEMI-related ischaemic time in women remains greater than in men due to persistently greater patient delays. In contrast to men, clinical signs of ongoing chest discomfort do not predict delays in women, suggesting that female STEMI patients are less likely to attribute symptoms to a condition requiring urgent treatment.

Cognitive radio networks (CRNs) rely on sensing of the licensed spectrum of a primary network to dynamically ascertain underutilized portion of the spectrum, thus affording additional communication opportunities. In a CRN, a single homogeneous spectrum access, such as interweave only deprives the secondary users (SUs) of channel access during handoff, particularly at high primary network traffic. Therefore, providing quality-of-service (QoS) to multi-class SUs with diverse delay requirements during handoff becomes a challenging task. In this paper, we have evolved a Markov-based analytical model to ascertain the gain in non-switching spectrum handoff scheme for multi-class SUs employing hybrid interweave-underlay spectrum access strategy. To satisfy the QoS requirements of the delay-sensitive traffic, we have analyzed the impact of hybrid spectrum access scheme for prioritized multi-class SUs traffic. The results show substantial improvement in spectrum utilization, average system throughput and extended data delivery time compared to conventional CRN using interweave only spectrum access. This demonstrates the suitability of the proposed scheme towards meeting QoS requirements of the delay-sensitive SU traffic while improving the overall performance for delay-tolerant SU traffic as well.

Delay and throughput are important metrics for network performance. We analyze the end-to-end delay of cognitive radio ad hoc networks for two traffic models: backlogged and geometric, respectively. By modelling the primary users as a Poisson point process and the secondary network deploying multihop transmissions, we derive the closed-form expression for the end-to-end delay in secondary networks. Furthermore, we optimize the end-to-end delay in terms of the hop number and the secondary transmission probability, respectively. The range of the optimal hop number and the equation satisfied by the optimal transmission probability are obtained for backlogged source models. The equation met by the optimal hop number is presented for geometric source models.

We investigate a class of abstract stochastic integrodifferential delay equations dependent upon a family of probability measures in a separable Hilbert space. We establish the existence and uniqueness of a mild solution, along with various continuous dependence estimates and Markov (weak and strong) properties of this solution. This is followed by a convergence result concerning the strong solutions of the Yosida approximations of our equation, from which we deduce the weak convergence of the measures induced by these strong solutions to the measure induced by the mild solution of the primary problem under investigation. Next, we establish the pth moment and almost sure exponential stability of the mild solution. Finally, an analysis of two examples, namely a generalized stochastic heat equation and a Sobolev-type evolution equation, is provided to illustrate the applicability of the general theory.

Abstract An apparent delay is occurred in GPS signal due to both refraction and diffraction caused by the atmosphere. The second region of the atmosphere is the ionosphere. The ionosphere is significantly related to GPS and the refraction it causes in GPS signal is considered one of the main source of errors which must be eliminated to determine accurate positions. GPS receiver networks have been used for monitoring the ionosphere for a long time. The ionospheric delay is the most predominant of all the error sources. This delay is a function of the total electron content (TEC). Because of the dispersive nature of the ionosphere, one can estimate the ionospheric delay using the dual frequency GPS. In the current research our primary goal is applying Precise Point Positioning (PPP) observation for accurate ionosphere error modeling, by estimating Ionosphere delay using carrier phase observations from dual frequency GPS receiver. The proposed algorithm was written using MATLAB and was named VIDE program. The proposed Algorithm depends on the geometry-free carrier-phase observations after detecting cycle slip to estimates the ionospheric delay using a spherical ionospheric shell model, in which the vertical delays are described by means of a zenith delay at the station position and latitudinal and longitudinal gradients. Geometry-free carrier-phase observations were applied to avoid unwanted effects of pseudorange measurements, such as code multipath. The ionospheric estimation in this algorithm is performed by means of sequential least-squares adjustment. Finally, an adaptable user interface MATLAB software are capable of estimating ionosphere delay, ambiguity term and ionosphere gradient accurately.

In this paper, we consider an SI epidemic model incorporating additive Allee effect and time delay. The primary purpose of this paper is to study the dynamics of the above system. Firstly, for the model without time delay, we demonstrate the existence and stability of equilibria for three different cases, i.e. with weak Allee effect, with strong Allee effect, and in the critical case. We also investigate the existence and uniqueness of Hopf bifurcation and limit cycle. Secondly, for the model with time delay, the stability of equilibria and the existence of Hopf bifurcation are discussed. All the above show that both additive Allee effect and time delay have vital effects on the prevalence of the disease.

The consideration of payments to contractors is not only a legal obligation but a necessity for assuring the continuity and completion of a construction project. However, consistent payments to facilitate project cash flows are uncommon in the construction industry. Within the context of a small island developing state, this paper aims to uncover leading risks factors the contributing to implications of delayed payments, on contractors’ cash flows and uncover any causalities and effects on relationships among these factors. A two-tiered quantitative approach was adopted. Firstly, a compiled list of delay factors was collated from the literature review. Semi-structured interviews were conducted with experienced construction professionals to determine the factors’ relevance and applicability in Trinidad and Tobago. A closed-ended survey questionnaire was subsequently developed and administered to primary construction stakeholders. Secondly, the responses obtained were collated, validated, and ranked using the relative importance index. A confirmatory factor analysis (CFA) was carried out using SPSS, and thereafter, SPSS Amos was used to determine the best-fit Structural Equation Model (SEM). The results strongly indicate that the issue of delayed payments is very prevalent within public sector projects. Unstable political climates and the delay in employers’ issuance of variation orders were found to be the main causes of delayed payments within the industry. Delays in sub-contractor and supplier payments as well as an increase in the contractor’s debt are the leading effects of delayed payments on the contractor’s cash flows. Based on these findings, a risk response framework was outlined to assist small to medium-contracting enterprises cope with payment delays, both locally and internationally. This research contributes to the advancement of construction management knowledge by informing construction professionals and policy makers of the implications of delaying approved payments, the consequential causes and effects, and a risk response technique to mitigate the negative effects on contractors’ cash flows. Doi: 10.28991/CEJ-2023-09-01-05 Full Text: PDF

Four-stage demand models are the most popular travel demand forecasting models. Trip assignment which is the last stage in the four-stage demand modelling is a key element in travel demand forecasting process. Traffic assignment model is used to assign travel demands into the road network and predict network flows that are associated with future planning scenarios based on the estimates of link travel times. In order to calculate travel time between origin and destination, a function presenting the relationship between link delays and link flows is used. This function is known as Volume-Delay Function (VDF) and it is the fundamental component of equilibrium trip assignment models. This study aims to investigate and improve VDFs for heterogeneous traffic at different type of arterial roads in Malaysia by using the road network in Balik Pulau, Penang as a case study. Primary data such as traffic volume and speed are collected at three types of arterial roads, which are the principal arterial, minor arterial and collectors to derive the parameters required in the VDFs. In this study, the most well-known and most widely-used volume-delay function which is known as the BPR function developed by the U.S. Bureau of Public Roads was investigated and calibrated using the transportation planning software, EMME 4.1.3. The calibrated functions are then validated with field data. The output from this research is very important as better understanding of VDFs can produce better estimate of link travel times and hence better planning for future scenarios.

This thesis increased the researchers understanding of the relationship between operations and maintenance in underground longwall coal mines, using data from a Queensland underground coal mine. The thesis explores various relationships between recorded variables. Issues with human recorded data was uncovered, and results emphasised the significance of variables associated with conveyor operation to explain production.

2006/2007
The efficient utilization of railway infrastructures is a primary objective in an open-market context like the European one. The capacity consumption, that is the infrastructure occupation augmented with buffers to avoid delays (referred to a time window, e.g. peak hour or day), is a measure of the utilization level of a given timetable. The standard UIC leaflet "Capacity" recommends a procedure to evaluate the infrastructure occupation, without buffers, by compressing the timetable until the blocking time stairways touch each other in the critical section. There is no recommendation about buffer times, except a well known rule of thumb about the running time supplement, which is often set to 5% of the journey time. Buffer times choice is a trade-off between efficient utilization and stability, to avoid secondary delays caused by primary delays. Given the probability distribution of the primary delays, it is possible to estimate the distribution of secondary delays and hence the buffers. In this work the primary delays are modelled following an innovative approach, that is using a family of stochastic processes called Lévy processes. These stochastic processes are defined through a very simple and general assumption: stationary independent increments. A disturbance on which there is few knowledge may reasonably be assumed to satisfy independence and stationarity properties, because independence means the future doesn't depend on the past and stationarity means the process doesn't change its structure over the time (often it is true only on large time windows). Another reasonable assumption is the path continuity, so the Lévy process reduces to a Brownian motion. The train movement is therefore modelled with a differential equation to which a Brownian motion is added, leading to a stochastic differential equation (SDE). Given the numerical approximation of the Brownian motion sample path, which is pseudo-random generated, it is possible to solve the SDE and obtain the sample path of the train. The analysis of the stochastic phenomenon requires the replication (called Monte Carlo) of the pseudo-random generation of the approximated Brownian motion sample path and the solution of a SDE to be computed many times. The result is a collection of simulated sample paths for each train scheduled. This set of collections may be used in two different ways: - estimation of the probabilistic distributions of the blocking times and consideration of the stochastic version of the blocking time stairways; - estimation of the risk, that is the probability of hindrance which corresponds to a given timetable, with the trains running in free mode (no external control, signals ignored) but counting the risky events highlighted by the signalling system. The estimation of the risk is repeated varying the number of trains, so that a relationship is built between the risk and the number of the trains or headways, from which a measure of capacity consumption is obtained given the risk level. The thesis consists of two parts, the first is made of preparation chapters while the second one is devoted to models and applications. The work begins with a chapter on capacity issues, where concepts, definitions and standards are illustrated to establish the research framework; the chapter ends with a literature review where the recent approaches are discussed and the lack of an SDE approach is highlighted. There is one stochastic approach which uses differential equations, but they are deterministic and combined with stochastic boarding time. Then a brief theoretical chapter on the Lévy processes is presented to justify the modelling choice and to introduce the Brownian motion in a reasonably acceptable way; unavoidable definitions of stochastic entities and theorems bring the reader to the presentation of the central result of the Lévy theory, that is the decomposition theorem. The Lévy-Ito decomposition theorem states that a Lévy process always decomposes as the sum of a Brownian motion with drift, a compound Poisson process and a martingale: if the sample paths are continuous, then there is only the Brownian component because the other ones have jumps in their paths. The Brownian motion introduction is followed by a theoretical chapter on the SDEs, where the symbolic meaning of dW is explained, together with two popular formulations of the stochastic integral, Ito and Stratonovich and the choice of Ito's one is justified on modelling basis. The Ito formula, that is the stochastic chain rule of calculus, and the stochastic Ito-Taylor expansion are presented as essential tools for understanding stochastic numerical methods. The chapter ends with the theorem that states the existence and uniqueness of a strong solution, that is the solution of the SDE given the driving Brownian motion Wt. The following chapter is about the numerical methods that are available to solve an SDE; at the beginning a brief review of the concepts and methods of deterministic ordinary differential equations is given. The most known and used schemes - i.e. Euler and Milstein - are presented together with their convergence and stability properties. Other schemes are briefly cited for sake of completeness. The preparation part closes with a chapter devoted to Monte Carlo simulations and the type of possible applications of the resulting collections of train paths to capacity assessment, that is estimation of the probabilistic distributions of the blocking times and estimation of the risk as probability of hindrance. Replications of Monte Carlo simulations with different timetables allow the building of the capacity-risk relationship. In the models and applications part two SDE-based models are presented, together with case studies: the first model is simple but allows some theoretical considerations to validate (in the form of bounds) the simulation results; the second model is a stochastic optimal control model. In both cases the model parameters are estimated using real life data and then the capacity-risk relationship is build through simulations. Another result of the simulation is the set of blocking/clearing time distributions for each section, which is graphically represented by plotting their key points (the mean value and extremes of the almost-sure range estimated by taking three times the standard deviation) at each section for a group of train paths. This second model describes in a more realistic way the train journey, because the mechanical equation is more suitable and the driving machine produces a force following an optimal control rule which considers both the distance from the timetable and the energy consumption. The optimal control law of the exact stochastic optimal control problem may be found by solving the Hamilton Jacobi Bellman equation, which is numerically heavy as well as difficult to solve because of instability and non-linearities. An approximated stochastic optimal control problem is solved for the more relevant part of the train travel, that is the steady state maintenance stage (initial acceleration stage and final stop stage are excluded), where the driver tries to reach the steady state determined from the planned timetable: the mechanical equation is linearized near the steady state speed and the optimal control law expression in terms of state variables is found and therefore substituted in the SDE. A parameter, the driving style, defined as the ratio of the schedule cost and the energy cost, is introduced to describe the different weights the two objectives may be given. Sensitivity analysis has been performed to determine the parameters' ranges for model applicability. The more relevant aspects of this work from a transportation research point of view are: - a new approach of computing free running times by means of stochastic differential equations has been introduced, after deep considerations about the characteristics of the stochastic perturbation; - the collection of free running times, result of a Monte Carlo simulation, can be used to estimate the distribution of primary delays, from which it is possible to derive the distribution of the secondary delays and hence choose the buffers; - the collection of free running trajectories can be used to estimate the distributions of the blocking times of the timetable stairways; - a new approach of capacity assessment based on the estimation of a relationship with the probability of hindrance by performing Monte Carlo simulations in different conditions has been introduced, together with the concept of risk-coupled capacity: capacity (and capacity consumption) depends on the maximum acceptable level of risk; - two SDE models have been introduced, together with their parameters' estimation procedures and applicability rules; - the second model is obtained solving a stochastic optimal control problem which models real life needs such as timetable observation and low energy consumption; once its closed-form expression is found, the optimal control law can also be applied in real life, provided the continuous measures of train state, i.e. its speed and position.
XIX Ciclo
1967

As a consequence of the growing interest in wireless communications systems, much effort is being devoted to the channel characterization and modelling. This is obvious since the performance depends fundamentally on the channels under consideration, so a communication system design must be preceded by the study of channel characteristics. This chapter considers the propagation environment in which a wireless system operates. In other words, we are primarily interested in the characterization of radio links between the transmitter and the receiver antenna that will be modelled by randomly time-variant linear systems. Wireless communication channels are usually described by considering three separable phenomena, namely, path loss, shadowing, and multipath fading. In the following, we briefly overview various efforts to characterize such aspects of wireless communication channels. Firstly, in this chapter we address the estimation of signal decay due to propagation loss which is very important in the determination of the necessary transmission power and the coverage area. Although propagation loss models are sometimes quite accurate, they generally fail to predict signal fluctuations due to the effect of the terrain near the antenna. Such a phenomenon of signal fluctuations is usually called shadowing. However, the effect of multipath fading is generally more complex because it does not only change in time but also varies over frequency. As a result, this topic will also be presented in enough depth and a number of statistical models will be studied. Moreover, the various categories of fading will be discussed. Finally, a novel small-scale model derived by the author is presented in order to give a recent application of the theory.

Diverse kinetic models for iso-octane, n-heptane, toluene and ethanol i.e. main gasoline surrogates, have been investigated. The models have different levels of complexity and strong and weak points. Firstly, ignition delay times for various fuel blends have been calculated and compared with published shock tube measurements. Kinetic models which are capable of distinguishing between Primary and Toluene Reference Fuels have been used further on in a zero-dimensional Homogeneous Charge Compression Ignition engine model to predict auto-ignition. The modelling results have been compared to the experimental results obtained in a single cylinder research engine. A discussion has been made on the ability of these models to predict autoignition.

The interaction between unsteady heat release and acoustic pressure oscillations in gas turbines results in self-excited combustion oscillations which can potentially be strong enough to cause significant structural damage to the combustor. Correctly predicting the interaction of these processes, and anticipating the onset of these oscillations can be difficult. In recent years much research effort has focused on the response of premixed flames to velocity and equivalence ratio perturbations. In this paper, we develop a flame model based on the so-called G-Equation, which captures the kinematic evolution of the flame surfaces, under the assumptions of axisymmetry, and ignoring vorticity and compressibility. This builds on previous work by Dowling [1], Schuller et al. [2], Cho & Lieuwen [3], among many others, and extends the model to a realistic geometry, with two intersecting flame surfaces within a non-uniform velocity field. The inputs to the model are the free-stream velocity perturbations, and the associated equivalence ratio perturbations. The model also proposes a time-delay calculation wherein the time delay for the fuel convection varies both spatially and temporally. The flame response from this model was compared with experiments conducted by Balachandran [4, 5], and found to show promising agreement with experimental forced case. To address the primary industrial interest of predicting self-excited limit cycles, the model has then been linked with an acoustic network model to simulate the closed-loop interaction between the combustion and acoustic processes. This has been done both linearly and nonlinearly. The nonlinear analysis is achieved by applying a describing function analysis in the frequency domain to predict the limit cycle, and also through a time domain simulation. In the latter case, the acoustic field is assumed to remain linear, with the nonlinearity in the response of the combustion to flow and equivalence ratio perturbations. A transfer function from unsteady heat release to unsteady pressure is obtained from a linear acoustic network model, and the corresponding Green function is used to provide the input to the flame model as it evolves in the time domain. The predicted unstable frequency and limit cycle are in good agreement with experiment, demonstrating the potential of this approach to predict instabilities, and as a test bench for developing control strategies.

The discrete event simulation method is commonly used to support decision-making in healthcare management. It is also used in planning the prevention of tooth decay in schools. Its usefulness largely depends on the concept of the model, which reproduces a fragment of reality along with the assumptions made. The aim of this paper is to discuss particular important modeling issues, which we faced, while developing a discrete event simulation model to support decision making in caries prevention planning in a sample primary school in one of the cities in the South-West Poland. We present reflections on the assumptions for the discrete event simulation model. The first stage of the simulation study confirms the relevance of the analysis of these assumptions and that their choice was appropriate. Therefore, the developed model may be the basis for further research and, as a result, be a tool to support management in planning the prevention of tooth decay in primary schools in Poland.

Abstract The development of actuators for flight control surfaces based on electrical technologies had a breakthrough in the last decade. Nevertheless, servo-hydraulic systems are still widely used. Servo Hydraulic Actuators (SHA) have the advantages of precise positioning, high dynamic response and being a jam-free solution in case of failures, but they present low energy efficiency. Digital hydraulics has become a topic of interest in improving energy efficiency in the fluid power community. A Digital Hydraulic Actuator (DHA) for aircraft is being developed to be used in primary flight control surfaces. The DHA concept is based on secondary control with multi-chamber cylinders and shows an energy efficiency gain with a similar response when compared to SHA. However, the opening and closing times of on/off valves are different and uncertain. These aspects may result in short circuits, bringing energy losses, or in blocked chambers, which may cause pressure peaks or cavitation. Consequently, the DHA system may have a lower energy efficiency or presents vibration due to fluid blocking. The present paper presents a solution for these issues and the reliability evaluation of the DHA. The opening and closing times issues are addressed using the synchronization between on/off valves through a method to find the correct time for valve opening control. As a result, the synchronization of pressure shifting without knowledge of the response times of on/off valves was accomplished. Moreover, when used periodically, this method can estimate future failures in valves due to a change of the required time delay. In order to evaluate the system reliability, FTA models were developed considering valve and pressure line failures, modelling how the failures affect force availability to move the control surfaces. The resulting FTAs were reduced to the minimum cut-sets that lead to force profiles that are insufficient for a safe flight and also may lead to an aircraft crash. Considering that the on/off valves have similar failure rates to those of servo valves, the results show that DHA and SHA have comparable reliability levels.

Experiments were conducted to better understand the flow physics associated with axial flow mixers in pipes. Specifically, the dependence of the downstream mixing evolution on the velocity ratio of the secondary to primary stream was explored. Experiments were conducted in a 25.4 mm diameter water pipe flow loop (25,700 ≤ RD ≤ 28,500), in which a fluorescein dye was coaxially injected. The injection tube diameter was 1.5 mm. Three velocity ratios, VR = 0.5, 1.0 and 2.0 were explored, where VR = Vjet/Vmain. The present results indicate that the effects of velocity ratio on the mean concentration are primarily evident in the near-field flow downstream of the injector, while concentration variance measurements indicate a primary influence at intermediate axial locations. Analysis of higher order moments and flow visualizations suggest that these influences are associated with the injected flow conditions. Two-dimensional LIF analysis of the coherent jet breakup region showed an instability in this transition related to injector flow Reynolds number. The present concentration measurements do not indicate the exponential variance decay commonly used for modelling mixing in pipes. Far field data exhibit low wavenumber motions as predicted by the recent theory of Guilkey et al. (1997).

In the high temperature component design the accumulation of creep strain during the primary stage cannot be ignored, since most the allowable design strain occurs in this stage, for which appropriate modelling is needed. In this work a mechanism based model for primary creep has been derived assuming that the creep rate in the transient regime can be given as a fraction of the steady state creep rate and as a function of the internal stress. Taking into account that the apparent activation energy varies with the internal stress and that the internal stress kinetic can be given as a function of strain, an exponential form of the creep rate vs creep strain has been obtained. The proposed model has been applied to high chromium steel P91 and the evolution of the decay constant and scaled activation volume with the applied stress has been determined.

Abstract The formation of water droplets within condensing steam turbines is a complex process that occurs at supersaturated, non-equilibrium conditions and is influenced by the unsteady segmentation of blade wakes by successive blade rows. This is often referred to as ‘wake chopping’, and its effect on the condensation process is the subject of this paper. The practical significance is that thermodynamic ‘wetness losses’ (which constitute a major fraction of the overall loss) are strongly affected by droplet size. Likewise, droplet deposition and the various ensuing two-phase phenomena (such as film migration and coarse-water formation) also depend on the spectrum of droplet sizes in the primary fog. The majority of wake-chopping models presented in the literature adopt a stochastic approach, whereby large numbers of fluid particles are tracked through (some representation of) the turbine flowfield, assigning a random number at each successive blade row to represent the particle’s pitchwise location, and hence its level of dissipation. This study contributes to the existing literature by adding: (a) a comprehensive study of the sensitivity to key model parameters (e.g., blade wake shape and wake decay rate); (b) an assessment of the impact of circumferential pressure variations; (c) a study of the implications for wetness losses and (d) a study of the implications for deposition rates.

Abstract This paper describes the validation of a novel floating wind turbine simulation tool based on an existing finite element offshore structural analysis solver that recently has been extended to simulate offshore wind turbines. Given the growing importance of offshore wind in the decarbonization strategy of many countries, and particularly the predicted exponential future growth in floating offshore wind, the requirement for validated numerical modelling tools to support detailed engineering design is now greater than ever. The tool combines a unique structural analysis solver incorporating a 3D hybrid beam-column element featuring fully-coupled axial, torsional and bending deformation modes, with the open-source aerodynamic modelling software FAST, to enable it to perform fully coupled aero-hydro-structural simulation of offshore wind turbines. The validation process focuses on a floating semi-submersible platform hosting a 5MW turbine, which is the reference model used in the international research project Offshore Code Comparison Collaboration Continuation (OC4). This is a code-to-code verification project sponsored by the International Energy Agency (IEA) which benchmarks a range of simulation codes for offshore wind turbine modelling. Beginning with fundamental test cases, such as static equilibrium, eigen-analysis, and free-decay simulations, the scenarios advance in complexity to include current loading, regular and random wave excitation, in conjunction with both steady and turbulent wind inflow. The new tool generates results which exhibit a close correlation with the OC4 benchmark data, thereby validating the numerical modelling approach. Although primarily focused on the semi-submersible, the validation programme also considers the same 5MW turbine hosted by a jacket substructure in shallower water, illustrating the versatility of the modelling tool to simulate fixed support structures in addition to floating. Given the scope of the validation effort, this paper presents a representative sample of results only. A more comprehensive report covering the other load cases can be provided to interested readers by the authors. This paper complements the research work undertaken in OC4, further substantiating its insights into the dynamic responses of floating offshore wind turbines. The new tool offers advantages for non-linear structural simulation via its innovative finite element solution technique, and detailed hydrodynamic modelling via its established and proven numerical models. The combination underlines the benefits of exploiting synergies between offshore oil and gas and offshore wind.

Safety of nuclear reactor needs to be assessed against different categories of Postulated initiating events. Advanced Heavy Water Reactor is natural circulation light water cooled and heavy water moderated pressure tube type of reactor. Inventory of the system is important parameter in determination of flow characteristics of this natural circulation reactor. In view of this, various events that cause changes in PHT system inventory are analysed in this paper. One of the reason for decrease in coolant inventory is hypothetical Loss of coolant accident (LOCA) This event is of very low probability but important from designing engineered safeguard system of a reactor. Loss of coolant accident in a nuclear reactor can cause voiding of the reactor core due to expulsion of primary coolant from break. In such, a situation the reactor core experiences very low heat removal rate from the nuclear fuel though the decay heat generation continues even after tripping of the reactor. Heat generation in the reactor core is due to various sources such as decay heat, stored heat etc, can lead to heating of fuel elements. However, Emergency core cooling systems of the reactor are actuated and prevent undesirable temperature rise. These events are called design basis events and focus is on adequacy of Emergency Core Cooling System (ECCS) and fuel integrity. The scenarios, phenomena encountered and consequences depend upon size and location of break, system characteristics, and actuation and capability of different protection and engineered safeguard systems of the reactor system. Moreover, this reactor has several passive features to ensure safety of this reactor. which are considered in analyzing these events. Events under category of decrease in coolant inventory includes loss of coolant accidents due to break at different locations of different sizes. Various locations considered in this paper are steam line, inlet header, inlet feeder, ECCS header, downcomer, pressure tube, Isolation condenser inlet header, instrument line break at inlet header and steam drum. The paper also considers scenario emerging due to malfunctions like relief valve stuck open. Causes for events under category of increase in coolant inventory are Increase in Drum level controller set point, Inadvertent valving in of Accumulators and Inadvertent valving in of Gravity driven water pool (GDWP). Last two events are not analysed as they are not possible. The analysis for the above events is complex due to various complex and wide ranges of phenomena involved during different pies under this category. It involves single and two phase natural circulation at different power levels, inventories and pressures, two-phase natural circulation under depleted inventory conditions. Coupled neutronics and thermal hydraulics behaviour, Phenomena under LOCA, phenomena during ECCS injection, direct injection into fuel rod, advanced accumulator injection., vapour pull through and coupled controller and thermal hydraulics. Modelling of these phenomena for each event is discussed in this paper. In this paper summary of analyses for representive event is presented.