Dynamic Simulation Program Research Articles

Determination of the burning velocity of gas/dust hybrid mixtures

Abstract The laminar flame speed is an essential input for Computational Fluid Dynamics simulation programs aiming to predict the effects of explosions. In this study, an approach to assess fundamental flame propagation properties from the analysis of the flame velocity as a function of its stretching and hydrodynamic instabilities was developed. A numerical tool was developed to analyse videos of propagating flames in order to estimate their unstretched burning velocities. Markstein’s theory, developed for gases and assuming a linear relation between the flame stretch and its speed, was then extended to dust clouds and hybrid mixtures of starch and methane. At first, the approach was validated with pure methane and was extended to pure starch and hybrid mixtures of both compounds. Finally, it appears that hybrid mixtures, especially when the gas concentration is greater than the lower explosive limit, can present a synergetic effect enabling faster flame propagation with regard to pure gas flames. Indeed, the stretching of a gas flame is strongly influenced by the addition of dusts. Nevertheless, for lower gas concentrations and larger dust concentrations called ‘dust-driven regime’, the presence of powders tends to limit the flame velocity to that of the less reactive compound, i.e. the dust.

Regularized immersed boundary-type formulation for fast transient dynamics with fluid-structure interaction

The present article deals with fast transient phenomena involving fluids and structures undergoing large displacements and rotations, associated with non-linear local behavior, such as plasticity, damage and failure. In this context, classical Arbitrary Lagrangian Eulerian approaches reach a limit where it is not possible to update the fluid grid to follow the structural motion without encountering entangled fluid cells forcing the simulations to stop. So-called immersed boundary approaches are thus frequently preferred in this situation, since they allow breaking the topological connection between the fluid and structural meshes and retrieve the expected level of robustness to handle complex structural motions. Their potential for efficient, robust and accurate simulations at the industrial level has been proven. However, it appears that the classical implementation of such approaches still imposes some constraints over the fluid mesh with respect to the structural mesh in terms of cell sizes, due to the expression of the kinematic links between fluid and structural velocities, which must be improved. It is demonstrated in the present article that an extended regularized framework can be designed to overcome the current drawbacks, but it comes with a significant increase of computational complexity and requires an extension of the classical software features encountered in fast transient dynamics simulation programs.

The Importance of Internal Heat Gains for Building Cooling Design

This paper aims to investigate the effect of internal heat gains on the cooling load of a building. The house occupied by three adult men is selected as the case study for paper. The house is in the third floor of the apartment. The apartment has four flats and it has no insulation around the external walls. The heat dissipation from lighting devices, electrical equipment and the occupants are calculated by using the DesignBuilder v4 Beta release simulation program. The temperature of the house is observed during three weeks by using hobo data loggers and calibration of the measurements is made with respect to weather data file of the flat. Detailed schedule based on time of operation and occupancy is prepared to get more accurate results. Annual energy consumption and cooling load of the house is determined by using the dynamic simulation program.

Theory and calibration of the Pierre 2 stochastic rock fall dynamics simulation program

The use of computer models to determine rock fall hazards is increasingly common, with increasingly complex models being developed. In most practical applications, slopes potentially affected by rock falls are characterized in general terms only, thus a simpler model is desirable to reduce the parameter uncertainty. The model presented here utilizes a lumped-mass representation of the rocks. Key features are the stochastic roughness angle to represent contact geometry variability, hyperbolic restitution factors, and a stochastic shape factor, which have been developed considering impact mechanics theory. Together, these features can yield realistic results for linear and angular velocity, bounce height, runout distance, and normal restitution factors greater than one while still being easy to calibrate. The model calibration has been carried out using detailed, full-scale experiments from a talus slope in France, a hard rock quarry in Austria, and a weak bedrock and talus slope in Japan. An observed rock fall event in British Columbia was modeled as a pseudoforward analysis to demonstrate the model validity. The usefulness of the model as a design tool has been demonstrated by using the simulation results as inputs for a hypothetical barrier design application, and calculating the reliability of the design values.

Dynamic Simulation and Analysis of the Space Shuttle Main Engine with Artificially Injected Faults

Securing the safety and the reliability of liquid-propellant rocket engines (LREs) for space vehicles is indispensable as engines consist of many complex components and operate under extremely high energy-dense conditions. Thus, health monitoring has become a mandatory requirement, especially for the reusable LREs that are currently being developed. In this context, a dynamic simulation program based on MATLAB/Simulink was developed in the current research on the Space Shuttle Main Engine (SSME), a partly reusable engine. Then, a series of fault simulations using this program was conducted: at a steady state operating condition (104% Rated Propulsion Level), various simulated fault conditions were artificially injected into the simulation models for the five major valves, the pumps, and the turbines of the SSME. The consequent effects due to each fault were analyzed based on the time responses of the major parameters of the engine. It is believed that this research topic is an essential pre-step for the development of fault detection and diagnosis algorithms for reusable engines in the future.

A generalised model of electrical energy demand from small household appliances

Accurate forecasting of residential energy loads is highly influenced by the use of electrical appliances, which not only affect electrical energy use but also internal heat gains, which in turn affects thermal energy use. It is therefore important to accurately understand the characteristics of appliance use and to embed this understanding into predictive models to support load forecast and building design decisions. Bottom-up techniques that account for the variability in socio-demographic characteristics of the occupants and their behaviour patterns constitute a powerful tool to this end, and are potentially able to inform the design of Demand Side Management strategies in homes.To this end, this paper presents a comparison of alternative strategies to stochastically model the temporal energy use of low-load appliances (meaning those whose annual energy share is individually small but significant when considered as a group). In particular, discrete-time Markov processes and survival analysis have been explored. Rigorous mathematical procedures, including cluster analysis, have been employed to identify a parsimonious strategy for the modelling of variations in energy demand over time of the four principle categories of small appliances: audio-visual, computing, kitchen and other small appliances. From this it is concluded that a model of the duration for which appliances survive in discrete states expressed as bins in fraction of maximum power demand performs best. This general solution may be integrated with relative ease with dynamic simulation programs, to complement existing models of relatively large load appliances for the comprehensive simulation of household appliance use.

Analysis of vehicle dynamics under sadden cross wind

In this paper, the way of calculating aerodynamic forces acting on a vehicle passing in the region of sadden cross wind was presented. The CarDyn, a vehicle dynamics simulation program, developed by the author was used. The effects of the cross wind were studied with a fixed steering wheel simulation. On the base of computer simulations the car cross wind sensitivity were determined, and vehicle responses such as lateral offset, side acceleration and yaw angular velocity are presented.

Building performance simulation modeling techniques

This research aims at demonstrating techniques in complex dynamic building energy simulation methods that greatly reduce the otherwise very time-consuming - in particular cases even week-long - computation time of simulation models, however marginal difference arises in the energy results of the simulations. Different test simulations were created to examine how to simplify the models without altering the energy and comfort results, which lead to reduce also the working hours spent on building the model. The building physics behavior of the zones, heating and cooling equipment in the complex model were studied and tested to understand how those can be used, merged or simplified in order to speed up both computation time and model building phase. The IDA ICE complex dynamic building energy simulation program offers two methods - periodic and dynamic - for calculation, which were compared in this program. Test simulations provide information about possible differences between the results of these calculatio...

4H-SiC Surface Structures and Oxidation Mechanism Revealed by Using First-Principles and Classical Molecular Dynamics Simulations

The 4H-SiC(000-1)C and (0001)Si surface reconstructed structures and the oxidation processes of these surfaces are investigated using a first-principles calculation method. The most stable reconstructed 4H-SiC(000-1)C and (0001)Si surfaces have p-bonded chains. In the topmost SiC bilayer, half of Si and C atoms exchange their positions and C-C or Si-Si bonds formed densely below the surfaces. When we place a SiO2 layer on the p-bonded chain (000-1)C surface, C-C bonds are formed more densely below the interface. We simulate a sequence of O2 molecules arrivals at an interface of tridymite-phase-SiO2 and 4H-SiC(000-1)C. Dissociated O atoms at the interface tended to make bonds with Si atoms. The C-C bonds in the SiC substrate break easily and a local C surface occasionally appears. We have examined how the surface structure changes through an O2 molecule exposure by using a classical molecular dynamics simulation program and confirmed the formation of C-C bonds below the surface and the interface.

Hourly Calculation Method of Air Source Heat Pump Behavior

The paper describes an hourly simplified model for the evaluation of the energy performance of heat pumps in cooling mode maintaining a high accuracy and low computational cost. This approach differs from the methods used for the assessment of the overall energy consumption of the building, normally placed in the so-called white or black box models, where the transient conduction equation is deterministically and stochastically solved, respectively. The present method wants to be the expression of the grey box model, taking place between the previous approaches. The building envelope is defined using a building thermal model realized with a 3 Resistance 1 Capacitance (3R1C) thermal network based on the solution of the lumped capacitance method. The simplified model evaluates the energy efficiency ratio (EER) of a heat pump through the determination of the hourly second law efficiency of a reversed Carnot cycle. The results of the simplified method were finally compared with those provided by EnergyPlus, a dynamic building energy simulation program, and those collected from an outdoor test cell in real working conditions. The results are presented in temperatures and energy consumptions profiles and are validated using the Bland-Altman test.

Performance Analysis and Optimization of Distributed Workflows in Heterogeneous Network Environments

Large-scale e-science features complex DAG-structured workflows comprised of computing modules with intricate inter-module dependencies. Mapping such workflows in heterogeneous network environments and optimizing their end-to-end performance are crucial to the success of scientific collaborations that require fast system response and smooth data flow. We construct analytical cost models and formulate workflow mapping as optimization problems for minimum end-to-end delay and maximum frame rate. The difficulty of these problems essentially arises from the topological matching nature in the spatial domain, which is further compounded by the resource sharing complicacy in the temporal dimension. For unitary processing applications, we develop a workflow mapping algorithm based on a recursive critical path optimization procedure to minimize the latency; while for streaming applications, we conduct a rigorous workflow stability analysis and develop a layer-oriented dynamic programming solution based on topological sorting to identify and minimize the global bottleneck time. The accuracy of the proposed exact delay calculation algorithm is verified in comparison with an approximate solution, a dynamic distributed system simulation program, and a real network deployment, and the performance superiority of the proposed mapping approaches are illustrated by extensive simulation-based comparisons with existing algorithms and verified by large-scale experiments on real-life scientific workflows through effective system implementation and deployment in real networks.

Semi-Active Method of Motion Stabilization Applied to Mechanical System with the Constant Reaction Force Vibroisolation (CRF) – Model Study

The use of the CRF vibration isolation system with zero natural frequency for machinery and equipment in the Earth's gravity field requires stabilization of motion because of its high susceptibility. For this purpose, an additional spring element with a low elastic coefficient “k1” and a semi-active damper “c (t, x, v, ff)”, was included in the vibration isolation system and parallel-attached to the CRF vibroisolator. Investigation of the effect of the additional element to stabilize the motion of the mechanical system was carried out by a numerical simulation of its motion. The simulation was based on a physical and mathematical model of the system including the spring and the magnetorheological damper (MR). The mathematical model was then used to develop a dynamics simulation program of the system and conduct simulations using sample data in order to study transitional processes and their stability. Simulation results indicate a substantially improved stability of motion in the system. Stability studies of motion were also combined with an analysis of power distribution in the system. The aim of this study was to determine energy efficiency of the system developed, defined as the ratio of the RMS power of the exciting force to RMS power of the elastic force. The resulting energy efficiency of CRF vibroisolation was equal to 5168 for a simulation period of 6 seconds.

Early Experiences Porting the NAMD and VMD Molecular Simulation and Analysis Software to GPU-Accelerated OpenPOWER Platforms.

All-atom molecular dynamics simulations of biomolecules provide a powerful tool for exploring the structure and dynamics of large protein complexes within realistic cellular environments. Unfortunately, such simulations are extremely demanding in terms of their computational requirements, and they present many challenges in terms of preparation, simulation methodology, and analysis and visualization of results. We describe our early experiences porting the popular molecular dynamics simulation program NAMD and the simulation preparation, analysis, and visualization tool VMD to GPU-accelerated OpenPOWER hardware platforms. We report our experiences with compiler-provided autovectorization and compare with hand-coded vector intrinsics for the POWER8 CPU. We explore the performance benefits obtained from unique POWER8 architectural features such as 8-way SMT and its value for particular molecular modeling tasks. Finally, we evaluate the performance of several GPU-accelerated molecular modeling kernels and relate them to other hardware platforms.

Comparison of numerical simulation and experimental study on indoor air quality of air-conditioned office building in desert climate

This paper is a study of the air temperature distribution of an air-conditioned office room equipped with a double-glazed window in a desert climate. The study includes both experimental and theoretical works using a computational fluid dynamics (CFD) simulation program. The experimental results were compared with the CFD program results. The commercial computational fluid dynamics ANSYS CFD V.13.0, solver FLUENT software, and three-dimensional flow finite difference of k-e for analysis and validation experimental work were used. The main objective of the study is to evaluate the temperature difference between the outdoor and indoor environments, as well as the distribution of air temperature in the room. The computational results for internal air temperatures of the office ranged from 23°C to 26°C, while the airflow velocity was low at less than 0.3 m/s. The temperature differences between the indoor and outdoor spaces varied between 9 °C and 15 °C. Good agreement was achieved between the computed and measured temperature results. The error percentage varied from 0.3% to 0.8%. The experimental and numerical results showed that well-designed double glazing can reduce the emission of sunshine and heat inside desert buildings, even using the northeastern facade, in sunny climates.

다물체 동역학을 이용한 타워크레인 운송 모델링 방법 연구

When a tower crane is carried by a transporter in shipyard, the height and length of the tower crane should be adjusted to meet the safety guidelines. Since the guidelines came from the field experience, the safety limitation needs to be analyzed by a computer simulation. In this paper, modeling methods are addressed to implement the appropriate transportation simulation of a tower crane. For the relation between the tower crane and the transporter, normal contact force, friction force, and kinematic constraints are compared. Assignment of relevant linear acceleration and angular velocity is considered for the transporter to start or move on an inclined ground surface. By using the examined modeling methods, the dynamic motion of tower crane transportation is analyzed by a dynamic simulation program, and comparison between the simulation result and analytic solution is made to verify the feasibility of the modeling methods.

Development of a Gas Dynamic and Thermodynamic Simulation Model of the Lontra Blade Compressor™

The Lontra Blade Compressor™ is a patented double acting, internally compressing, positive displacement rotary compressor of innovative design. The Blade Compressor is in production for waste-water treatment, and will soon be launched for a range of applications at higher pressure ratios.In order to aid the design and development process, a thermodynamic and gas dynamic simulation program has been written in house. The software has been successfully used to optimise geometries and running conditions of current designs, and is also being used to evaluate future designs for different applications and markets.The simulation code has three main elements. A positive displacement chamber model, a leakage model and a gas dynamic model to simulate gas flow through ports and to track pressure waves in the inlet and outlet pipes. All three of these models are interlinked in order to track mass and energy flows within the system.A correlation study has been carried out to verify the software. The main correlation markers used were mass flow, chamber pressure, pressure wave tracking in the outlet pipe, and volumetric efficiency. It will be shown that excellent correlation has been achieved between measured and simulated data. Mass flow predictions were to within 2% of measured data, and the timings and magnitudes of all major gas dynamic effects were well replicated.The simulation will be further developed in the near future to help with the optimisation of exhaust and inlet silencers.

Evaluation of sustainability and energy optimization of existing buildings: the development of new technologies for Zero Energy buildings

The aim of this research is to exploit the structural paradigm “tensegrity” at the level of secondary structures, in order to respond to the natural environment by changing their mechanical and HVAC properties. According to standards of European and Italian Laws, rating systems LEED and operating principles of tensegrity, technological, functional and prestational parameters are defined in order to design innovative Smart Facade System. A tensegrity plate – designed for a particular study case - will be developed, assembled and tested by different dynamic simulation programs to evaluate potentially the effects of applying this envelope technology.

Solar Thermal Cooling on the Northernmost Latitudes

Abstract The national priority axis is increase of renewables (RES) use in Latvian Energy sector; therefore, new solutions for Electricity, Heat and Cold production are sought for. Solar energy is available at the same time when there is need to cool rooms, so Solar Cooling systems are suitable also for Latvian conditions. In Latvia such systems are not used yet, so it is important to assess the potential of these systems. The sunlight duration and intensity depends on the season, weather conditions and geographical position of a country. As compared with the annual global solar radiation incident on horizontal surfaces in sunny regions (2200 kWh/m2), in the northern Europe is half as much (1100 kWh/m2). The solar energy potential defined for Latvia as technically achievable by 2020 is: for electricity 0.01 TWh and for heat 0.04 TWh. As shown by experimental studies, the application of solar collectors in Latvia can give good results. The energy of solar radiation can be employed for 1700-1900 hours annually. Due to a gradual increase in the comfort level, the demand for space cooling will grow in the near future. Solar cooling can be an alternative for electrically-powered compression-type chillers that currently are the most common in the Baltic States. The solar cooling system installed in the Institute of Physical Energetic is the first of the type in EU which is built at the latitudes higher than 55 degrees of north. Taking into account the fact that there were no systems plants of this type at so “cold” latitudes, first of all the models in PolySun were to be validated, and a dynamic simulation program containing the five-years meteorological data was to be developed. The solar cooling system has been optimized using multiple simulations. The influence of the system's different elements on its operation is evaluated. The optimal model developed for the given climatic conditions is described.

Thermal performance of a vertical solar hot water storage tank with a mantle heat exchanger depending on the discharging operation parameters

This study presents the numerical investigations to predict the influence of the operating parameters during discharging/consumption mode on the thermal performance of a new designed vertical solar storage tank (SST) with a mantle heat exchanger installed in a solar domestic hot water (SDHW) system. It is assumed that the tank is initially stratified during its previous heat storing/charging operation. Meanwhile, the collector loop is assumed to be active. Three-dimensional (3D) unsteady Computational Fluid Dynamics (CFD) simulation program (Fluent 14.0) was constructed based on the actual operation conditions and the actual geometry of a mantle solar storage tank (MSST). The laminar model was thought for treating convection in the flow field. The governing equations in the cylindrical coordinate have been used in the simulation of flow fields inside the mantle storage tank where realistic boundary and initial conditions were applied and discretised by employing the finite volume method. Validation of the unsteady flow computation results with experimental data found in the literature has shown a good agreement. The obtained results from the computer simulations were discussed and concluded as depending on the thermal stratification parameters. The results show that for higher values of Grashof number, the pre-established thermal stratification is well preserved during the discharging operation mode and thus supplied hot water for usage as long as possible. In order to increase levels of thermal stratification or have least mixing inside the tank during the consumption period, the tank inflow Reynolds number should be kept below certain values. In these cases, the storage tank is enabling to provide proper amount of hot water with a proper temperature for consumption purposes.

分子動力学プログラムMXDORTO用可視化ソフトウェアMDVISの開発

分子動力学プログラムMXDORTO用可視化ソフトウェアMDVISの開発