Dimensional Dynamic Model Research Articles

Numerical Assessment of Earth to Air Heat Exchanger with Variable Humidity Conditions in Greenhouses

Earth to air heat exchangers are widely utilized to cool or heat passive buildings for energy savings. They often need to deal with high humidity air conditions, especially in the greenhouse due to plant transpiration, and the condensation phenomenon is frequently observed during the cooling process. To evaluate the effect of humidity and condensation on thermal performance, a three dimensional computational fluid dynamic (3D-CFD) model was developed. The distribution of relative humidity in each pipe was investigated, and the impact of inlet air relative humidity on the integrated performance of the earth to air heat exchanger was discussed. The effects of inlet air temperature and volume flow rate were also analyzed. Moreover, the influence of the heat exchanger configurations on the performance of the air condensation was researched. The results indicated that condensation had few effects on the airflow distribution uniformity of the earth to air heat exchanger, while it acted observably on the thermal performance. In addition, humid air in a small diameter pipe tended to condense more easily. Humidity and condensation should be taken into consideration for the design of earth to air heat exchangers in greenhouses during engineering applications.

Progress in multiphase computational fluid dynamics

This paper is primarily concerned with the development of three dimensional (3-D) multiphase computational fluid dynamics models for use in Pressurized Water Nuclear Reactor (PWR) design and analysis. These models were developed during the last 40 years, that is, during the time since the first NURETH meeting in 1980. The major topics in this paper include: the development of a 3-D two-fluid model for the MCFD prediction of phase distribution in turbulent adiabatic and diabatic bubbly flows. The mechanistic prediction of departure from nucleate boiling (DNB), and the direct numerical simulation (DNS) of bubbly flows. While significant progress has been made in the modeling and prediction of bubbly flows, specific recommendations are made in this paper for further improvements and for the extension of this type of MCFD model to other flow regimes.

Significant reduction in size of an ambient air vaporizer by employing novel configuration of reverse flow vaporization

Ambient air vaporizers re-gasify liquefied industrial gases such as air, nitrogen, oxygen, natural gas etc. by using renewable heat energy from atmosphere. Moisture of air freezes and deposits over the fin surfaces that is defrosted after each half-cycle to prevent deterioration of heat transfer beyond a limit. For continuous vaporization, two sets of vaporizers switch flows between them after each half-cycle. While one operates in working mode, the other is switched off for complete defrosting. In this paper, the concept of reverse flow vaporization is proposed that employs only one set of vaporizer and the flow direction of vaporizing fluid is reversed with valves in each half-cycle. It uses the concept of partial defrosting instead of complete defrosting that helps to improve the efficiency of operation. A one dimensional dynamic heat transfer model is developed to determine the frosting and defrosting phenomena under natural convection. Defrosting model includes preheating and melting stages of reverse flow vaporization. Data from experiments on frosting and defrosting over the pipe agrees well with those obtained from the numerical model. Total length required for an ambient air vaporizer working with reverse flow reduces by 28% for the given environmental conditions and 8-hour half cycle.

Anode state observation of polymer electrolyte membrane fuel cell based on unscented Kalman filter and relative humidity sensor before flooding

Water flooding occurs at the output region of the anode side, which is one of the main reasons for performance degradation of automotive fuel cell systems. If liquid water saturation ratio in gas diffusion layers can be observed and regulated within a suitable range, water flooding in anode channels can be avoided. For this purpose, a zero dimensional dynamic model which focuses on the internal states (such as liquid water saturation ratio in gas diffusion layer) for the anode side before water flooding is presented. A nonlinear state observer for the anode side is designed using the unscented Kalman filter algorithm. Influences of the relative humidity sensor and initial values of internal states on the observation results are analyzed. The results show (1) four key internal states (e.g., water vapor pressure, hydrogen and nitrogen pressure, average liquid water saturation ratio) can be observed using this method, and the time constant of the sensor has a smaller influence on the observer than the signal noise. (2) With a suitable sensor (noise power <10−8 bar2), the relative errors of the partial gas internal states can be within ±5%, while the relative error of the average liquid water saturation ratio in the gas diffusion layer can be within ±10%. (3) When the purging valve is controlled based on the liquid water saturation ratio, it is possible to avoid water flooding on the anode side.

Numerical study of hydrodynamic characteristics in a moving bed biofilm reactor

The moving bed biofilm reactor (MBBR) has certain advantages, such as high wastewater treatment efficiency, low maintenance and operating costs, and simple operation. It has emerged as a valuable option for small decentralized facilities. The filling ratio, aeration mode and aeration intensity are the main factors that affect the performance of MBBRs in wastewater treatment. However, the information that concerns the used criteria that pertain to the process design for the MBBR is not adequate. In this study, a three dimensional computational fluid dynamics (CFD) model was constructed and the maximum error was only 1.98%, which was much smaller than the traditional 2D-CFD model. The filling ratio, aeration mode and aeration intensity of MBBR were optimized by CFD model from the point of view of fluid mechanics. The results show that the fluidization performance of the filling is the best under the one-side aeration mode with 30% filling ratio. The cost-performance ratio of the reactor with 30% filling ratio was 1.53, 25% and 35% filling ratio were only 1.17 and 1.14 respectively. Increasing the aeration intensity could improve the fluidization performance. However, the effect of high aeration intensity on the fluidization performance of the carrier was limited and the energy consumption increased greatly. The results revealed that when the aeration intensity increased from 0.07 min−1 to 0.13 min−1, the proportion of the carrier area increased by 16.56%. The proportion of the carrier area with an aeration rate of 0.20 min−1 was only 4.23%, which is higher than 0.13 min−1. The main factors that control the fluidization of the carrier were the range of the flow zone and the flow velocity of the liquid. Increasing the range of the flow zone could facilitate the flow of the carriers. The critical value of the flow velocity of the liquid in the flow zone was 0.04 m/s. These results could guide the optimization design of the filling ratio and the aeration conditions and provide a theoretical basis for the application of MBBR.

Horn ultrasonic‐assisted pregelatinized starch with various streamline patterns as a green process: Computational fluid dynamics and microbubble formation of process

AbstractThe ultrasound‐assisted pregelatinization starch (UAPS) is considered as a physical method for starch modification. In this study, the effect of ultrasonic control parameters, including power, probe size, temperature, and time was investigated in order to predict microbubble formation and cavitation process as a two dimensional axisymmetric computational fluid dynamics (CFD) model to optimize the UAPS process. The cavitation phenomenon and the bubble dynamics were further investigated with regards to the mentioned parameters. Results showed that with the increase in probe diameter from 20 mm to 100 mm, a new pattern of streamlines were generated at the bottom of the container, increasing the turbulence among bubbles. This is mainly due to collapsing bubbles, resulting in a huge amount of energy released which accelerates heat and mass transfer to the fluid. According to the results obtained from the dynamics of bubbles, the maximum radius of the bubbles had a rising pattern with the increase in the probe size (from 20 to 100 mm), amplitude (from 25 to 45%) and temperature (from 35 to 65°C); moreover, the energy of the bubble slightly increased with the increase in liquid temperature and probe size.Practical applicationsThe physical modifications of starch structure are more widely employed since it is safer and without impurities, which have strong effects on different component functionalities. Pregelatinization is one of the most popular industrial methods of physically modifying starch. Pregelatinized. The ultrasound‐assisted pregelatinized starch as physical modification offers many advantages, mainly the declined utilize of chemicals and processing time, serving as an environment‐friendly processing technology, high selectivity method. Use of computational fluid dynamics is a suitable approach to assessing the data pertaining to the physical features of the ultrasonication process. We underscored the importance of filling the gaps of knowledge concerning modeling sonication process to produce the efficient ultrasound‐assisted pregelatinized starch under various ultrasound power, probe size and fluid temperature to predict microbubble formation, heat and energy transfer.

Improving the Performance of A Flat Plate Solar Collector Using Nanofluid as Working Fluid

Solar energy is the best alternative to limited fossil fuels. The foremost important means of utilizing solar energy are solar collectors. The most common types of solar collectors are flat plate solar collectors. A great deal of theoretical research has been conducted to enhance the flat plate solar collector efficiency. One effective way to increase the efficiency is by using an improved thermal properties fluid as nanofluid. In this paper, a numerical study has been made to enhance the efficiency and improve the performance of solar collector via the use of (Multi-Wall Carbon Nano Tube-water) MWCNT-H2O nanofluid instead of traditional fluid like water as working fluid under the weather of Mosul city / Iraq (36.3489° N, 43.1577° E). One dimensional dynamic model using implicit finite difference method was used. Solving energy conservation equations through the various layers of the solar system is the basis upon which the current model was based. Effects of nanoparticle volume fraction and mass flow rate on the working fluid stream temperature differences, and the thermal efficiency were studied. The mass flow rate was varied from 0.004 kg/s to 0.03 kg/s, while the volume fraction was varied from 0% to 6%. The results of "Nanofluid Based Flat Plate Solar Collector" were compared with the experimental results presented by [1]. The comparison established a good match between the current results and experimental results. The results showed an increase in the working fluid outlet and inlet temperature difference and collector thermal efficiency due to the addition of MWCNT nanoparticles. The temperature difference of "Nanofluid Based Flat Plate Solar Collector" was found 28.8⁰C at 0.014 kg/s and 6% in April, while it was 25 ⁰C at the same condition in the "Water Based Flat Plate Solar Collector case". Also, the thermal efficiency of "Nanofluid Based Flat Plate Solar Collector" was found 2.41% to 6.68% more than the "Water Based Flat Plate Solar Collector case".

Three dimensional numerical analysis of heat transfer during spray quenching of 22MnB5 steel with a single nozzle

In this paper, a three dimensional Computational Fluid Dynamics Model (CFD) model was generated for spray cooling of straight parts by using a single point nozzle. The numerical simulations of spray quenching were performed to investigate the cooling rate of a 22MnB5 hot steel blank commonly used material in the automotive industry. Experiments are carried out to examine infrared thermograph of hot steel blank surfaces during spray cooling process by using infrared thermal camera. Time dependent situations of surface temperatures, surface heat fluxes and cooling areas are investigated numerically. The 3D model with some assumptions is presented to improve the solution of numeric simulation and to meet the most appropriate acceptable results for spray cooling process. The developed 3D model will be used to investigate the heat transfer analysis of hot stamped parts during hybrid quenching to optimize the process parameters. The comparison of the numerical and experimental results showed that the presented approach can be effectively used to evaluate heat transfer during spray quenching with a single nozzle. With this research, it was clearly seen that the estimated cooling rates and the temperatures were in good agreement with the experimental cooling temperature data. By using the numerical results and experimental data obtained in this study, multi-nozzle spray apparatus which will be used to obtain different cooling rates on the parts by changing spray parameters such as spray height, spray angle, mass flow rate, the distance between nozzles and part etc. was developed for hybrid quenching process.

New soliton wave structures of nonlinear (4 + 1)-dimensional Fokas dynamical model by using different methods

The physics of the (4 + 1)-dimensional Fokas equation follows necessarily from the physical nature of the Kadomtsev–Petviashvili and Davey-Stewartson equations in wave theory. In this article, we consider the nonlinear (4+1)-dimensional Fokas partial differential equation. Two recognizable methods namely improved F-expansion and generalized exp(-ϕ(ξ))-expansion methods are proposed to investigate the new wave structures of (4 + 1)-dimensional Fokas dynamical model which have never been constructed before. As a result, new solutions are in different solitons such as dark soliton, bright soliton, combined dark-bright soliton solutions, periodic, and solitary wave solutions. The new generalized solitary wave solutions can be constructed by assigning the specific values to those parameters involved in these methods. The achieved results are compared with existing results in the literature and we found that some of results are not available in literature. The derived results are explained graphically, to understand the phenomena of the proposed model. The constructed results rendering that the consider methods in this article are simple, effective, and easy to find the solution of many other nonlinear higher-dimensional models which arise in several areas of science and engineering.

A survey of motion planning techniques for humanoid robots

This paper provides a brief survey of motion planning techniques for humanoid robots. Among various related topics that constitute the broad framework of motion planning of humanoid robots, this paper covers two actively researched topics, namely, bipedal locomotion planning based on low dimensional dynamical models and multi-contact problems that involve non-coplanar and non-scheduled contact. For each of these two classes of planning problems, after reviewing the theoretical background and commonly used problem formulation, existing planning methods are classified based on their concepts and their respective advantages and shortcomings are discussed.

Controlling reformation rate for a more uniform temperature distribution in an internal methane steam reforming solid oxide fuel cell

Internal methane reformation capability makes the SOFC technology favorable for integration with the existing infrastructure. Methane steam reformation (MSR) reaction happening at the entrance of the fuel channel is endothermic while exothermic fuel cell reactions dominate the remaining of the cell. Consequently cold spots occur near the inlet while hot spots occur farther down the electrode resulting in steep temperature gradients. To alleviate this problem, it is suggested that MSR reaction can be slowed down to extend methane conversion to a broader fuel cell region. Rejecting the heat released during the fuel cell reaction with MSR, temperature gradients can be flattened for a more uniform distribution. In this study a three dimensional computational fluid dynamics model is developed to investigate the potentials of controlling the MSR rate for improved thermal characteristics of an SOFC. Modification of the catalytic activity by changing anode material and microstructure is considered as the means of controlling reaction rate. Also the effect of fuel stoichiometry and interconnect material on the thermal gradients are analyzed. It is suggested that the anode material can be engineered to have a more balanced temperature distribution and relaxed thermal stresses during methane fueled SOFC operation.

Uneven development and the balance of payments constrained model: Terms of trade, economic cycles, and productivity catching-up

This paper addresses (I) the transition dynamics incompatibility between the BPCM and the Prebisch-Singer hypothesis (PSH) (II) the causes of cyclical volatility in developing countries. In order to discuss these issues, we expand the Dutt (2002) model adding: (a) a productivity gap dynamics in which the south has a catching-up element; (b) a labor market dynamics, by including a wage curve in the relationship between employment rate and economic activity; and (c) a labor supply dynamics that considers the labor transfer issue between traditional and modern sectors. The result is a four dimensional dynamic model that represents a lagged developing economy constrained by its balance of payments. We find that our model converges and generates damped cycles. Fragile economies show an oscillatory decline in terms of trade, reinforcing an uneven development pattern between north and south. Industrialization and higher learning capabilities, however, can change the adjustment to a catching-up scenario.

Data Assimilation for a Quasi-Geostrophic Model with Circulation-Preserving Stochastic Transport Noise

This paper contains the latest installment of the authors’ project on developing ensemble based data assimilation methodology for high dimensional fluid dynamics models. The algorithm presented here is a particle filter that combines model reduction, tempering, jittering, and nudging. The methodology is tested on a two-layer quasi-geostrophic model for a beta -plane channel flow with O(10^6) degrees of freedom out of which only a minute fraction are noisily observed. The model is reduced by following the stochastic variational approach for geophysical fluid dynamics introduced in (Holm in Proc R Soc A 41:20140963, 2015) as a framework for deriving stochastic parameterisations for unresolved scales. The reduction is substantial: the computations are done only for O(10^4) degrees of freedom. We introduce a stochastic time-stepping scheme for the two-layer model and prove its consistency in time. Then, we analyze the effect of the different procedures (tempering combined with jittering and nudging) on the performance of the data assimilation procedure using the reduced model, as well as how the dimension of the observational data (the number of “weather stations”) and the data assimilation step affect the accuracy and uncertainty of the results.

Computational fluid dynamics modeling of abutment scour under steady current using the level set method

The scour and deposition pattern around an abutment under constant discharge condition is calculated using a three dimensional (3D) Computational Fluid Dynamics (CFD) model. The Reynolds-Averaged Navier Stokes (RANS) equations are solved in three dimensions using a CFD model. The Level Set Method (LSM) is used for calculation of both free surface and bed topography. The two-equation turbulence model (k-ε and k-ω) is used to calculate the eddy viscosity in the RANS equations. The pressure term in the RANS equations on a staggered grid is modeled using the Chorin's projection method. The 5th order Weighted Essentially Non-Oscillatory (WENO) scheme discretizes the convective term of the RANS equations. The Kovacs and Parker and Dey formulations are used for the reduction in bed shear stress on the sloping bed. The model also used the sandslide algorithm which limits bed shear stress reduction during the erosion process. The numerical model solution is validated against experimental results collected at the Politecnico di Milano, Milan, Italy. Further, the numerical model is tested for performance by varying the grid sizes and key parameters like the space and time discretization schemes. The effect of varying bed porosity has been evaluated. Overall, the free surface is well represented in a realistic manner and bed topography is well predicted using the Level Set Method (LSM).

Study on the evolution of dynamic performance of high-speed EMU after long-term service

In order to find the influence of wheel and rail wear about dynamic performance of the high-speed railway vehicle in the actual operation process, a high dimensional strong nonlinear dynamic model of the high-speed vehicle is established, and measured wheel profile is used to characterize contact geometry between wheel and rail, and relationship between stiffness of steering rubber joint and dynamic performance of railway vehicle is studied in different wheel/rail wear state. Results show, With the increment of wheel and rail wear and equivalent conicity, that stability of hunting motion of vehicle decreases, stability and safety of the vehicle all deteriorate. Moreover, with the increment of longitudinal steering joint stiffness, critical speed, lateral stability and safety of vehicles increases gradually. When it goes above 17.5MN/m, with the increments of critical speed, lateral stability and safety tend to be stable. With the increment of lateral steering joint stiffness, critical speed of vehicle tends to increase first and then decrease, and finally tends to be stable around 5MN/m, which reaches the maximum when the stiffness is 2.5MN/m. Lateral stiffness of steering joint has little influence on lateral stability of the vehicle; At low equivalent conicity, vehicle running safety decreases slightly with the increment of lateral stiffness of steering joint, while equivalent conicity increases, the vehicle running safety deteriorates sharply with the increase of lateral stiffness of steering joint. In conclusion, in order to adapt to different equivalent conicity, the optional range of longitudinal stiffness of steering joint is suggested to concentrated in 5∼17.5MN/m, while its lateral stiffness is suggested to be within 2∼5MN/m.

Arising wave propagation in nonlinear media for the (2+1)-dimensional Heisenberg ferromagnetic spin chain dynamical model

In this study, we study the (2+1)-dimensional nonlinear Schrödinger kind equation which illustrates the non-linear spin dynamics of (2+1)-dimensional Heisenberg ferromagnetic spin chains (HFSCs) through bilinear and anisotropic interactions in the semi-classical limit. This model also illustrates the ferromagnetic materials of magnetic ordering. Two analytical schemes are employed to study the equation namely, improved auxiliary equation and generalized Riccati mapping methods. We construct dark and bright solitons, combined bright–dark solitons, periodic waves, solitary waves and elliptic solutions to this equation. We give graphical presentations of the 2D and 3D of some achieved solutions. The obtained results of this investigation might be useful to explain the physical structure of this model. The achieved results of HFSC show the effectiveness and reliability of the proposed techniques.

Investigation into the vibration characteristics of agricultural wheeled tractor-implement system with hydro-pneumatic suspension on the front axle

Before predicting the vibration characteristics of a tractor/implement system with front axle hydro-pneumatic suspension, it is essential to develop a dynamic model. The nonlinear stiffness and damping calculation equations for hydro-pneumatic suspension are derived and the complete three dimensional multibody dynamic model of the wheeled tractor/implement system is presented in this paper. The construction of the model considers the effect of implement and passive rub cabin suspension as well as front axle hydro-pneumatic suspension together. The vibration responses and the corresponding power spectral densities (PSD) of driver seat, cabin, chassis and implement under different forward speed and field road conditions gathered from the simulation using the models are in good agreement with experimental results, demonstrating the effectiveness of the proposed model. A comparative investigation on the dynamic effects of a passive cabin suspension, implement and front axle hydro-pneumatic suspension under four cases was made. The effects of front axle suspension and the implement on the rollover limit chart for the tractor system were also studied. Simulation results showed that the front axle hydro-pneumatic suspension will deteriorate the ride comfort of drivers but will improve pitch and roll stability. Passive cabin suspension plays a more important role in improving the ride comfort of drivers than the front axle hydro-pneumatic suspension does, while compromising the pitch stability to some extent. The implement will raise the riding comfort of drivers and the pitch stability of tractors, but dramatically worsen the roll stability. The presence of the front axle suspension and the implement improves the minimum slope angle and reduces the maximum slope angle. Furthermore, the effect of the initial nitrogen volume, the pressure of energy accumulators, and the orifice diameter of the small throttle valves on the vibration characteristics of the tractor system with the large throttle valve closed or fully opened is also investigated.

Complex surfaces to the fractional (2 + 1)-dimensional Boussinesq dynamical model with the local M-derivative

This manuscript finds new solutions to the fractional (2 + 1)-dimensional Boussinesq dynamical model with the local M -derivative with the help of the modified exponential function method. Many new complex singular and travelling wave solutions are successfully obtained. For deeper investigation of gravity waves propagation on the water surface, 2D and 3D graphs along with contour simulations via several computational programs are used.

Mass and Heat Transfer Coefficients in Automotive Exhaust Catalytic Converter Channels

Mass and heat transfer coefficients (MTC and HTC) in automotive exhaust catalytic monolith channels are estimated and correlated for a wide range of gas velocities and prevailing conditions of small up to real size converters. The coefficient estimation is based on a two dimensional computational fluid dynamic (2-D CFD) model developed in Comsol Multiphysics, taking into account catalytic rates of a real catalytic converter. The effect of channel size and reaction rates on mass and heat transfer coefficients and the applicability of the proposed correlations at different conditions are discussed. The correlations proposed predict very satisfactorily the mass and heat transfer coefficients calculated from the 2-D CFD model along the channel length. The use of a one dimensional (1-D) simplified model that couples a plug flow reactor (PFR) with mass transport and heat transport effects using the mass and heat transfer correlations of this study is proved to be appropriate for the simulation of the monolith channel operation.

The Analysis and Forecasting of Tennis Matches by using a High Dimensional Dynamic Model

SummaryWe propose a high dimensional dynamic model for tennis match results with time varying player-specific abilities for different court surface types. Our statistical model can be treated in a likelihood-based analysis and can handle high dimensional data sets while the number of parameters remains small. In particular, we analyse 17 years of tennis matches for a panel of over 500 players, which leads to more than 2000 dynamic strength levels. We find that time varying player-specific abilities for different court surfaces are of key importance for analysing tennis matches. We further consider several other extensions including player-specific explanatory variables and the match configurations for Grand Slam tournaments. The estimation results can be used to construct rankings of players for different court surface types. We finally show that our proposed model produces accurate forecasts. We provide evidence that our model significantly outperforms existing models in the forecasting of tennis match results.