Numerical Computer Model Research Articles

Numerical analysis of the static performance of an annular aerostatic gas thrust bearing applied in the cryogenic turbo-expander of the EAST subsystem

The EAST superconducting tokamak, an advanced steady-state plasma physics experimental device, has been built at the Institute of Plasma Physics, Chinese Academy of Sciences. All the toroidal field magnets and poloidal field magnets, made of NbTi/Cu cable-in-conduit conductor, are cooled with forced flow supercritical helium at 3.8 K. The cryogenic system of EAST consists of a 2 kW/4 K helium refrigerator and a helium distribution system for the cooling of coils, structures, thermal shields, bus-lines, etc. The high-speed turbo-expander is an important refrigerating component of the EAST cryogenic system. In the turbo-expander, the axial supporting technology is critical for the smooth operation of the rotor bearing system. In this paper, hydrostatic thrust bearings are designed based on the axial load of the turbo-expander. Thereafter, a computational fluid dynamics-based numerical model of the aerostatic thrust bearing is set up to evaluate the bearing performance. Tilting effect on the pressure distribution and bearing load is analyzed for the thrust bearing. Bearing load and stiffness are compared with different static supply pressures. The net force from the thrust bearings can be calculated for different combinations of bearing clearance and supply pressure.

FDTD computation of shielding effectiveness of electromagnetic shielding fabric based on weave region

Numerical computation of shielding effectiveness (SE) of electromagnetic shielding fabric (EMSF) is a research difficulty, making no a suitable model for it at present. This paper proposes a partition method based on the yarn diameter and fabric weave structure. The fabric is divided into overlapping region, lateral single yarn region, longitudinal single yarn region, and interstice region according to the weave feature. A fabric structure model for FDTD numerical computation of the SE is constructed. The electromagnetic parameters of each region are tested according to the transmission and reflection method. The Yee’s grid discretization method of the structure model is given, and the absorption boundary and the excitation parameters are set to determine the physical model of the fabric. The numerical computation of the physical model is done by the East FDTD electromagnetic computation software. The computation data are compared with the actual testing data, and the results show that the computation results of the SE of the EMSF with the proposed model are satisfied. The research in this paper provides an important reference value for the design, production, evaluation, and theoretical study of the EMSF.

Direct scale comparison of numerical linear elastic moduli with acoustic experiments for carbonate rock X-ray CT scanned at multi-resolutions

Giant carbonate reservoirs hold almost 50–60% of the world's conventional hydrocarbons and are thus of major economic significance. The recently emerging Digital Rock Physics (DRP) based mechanical property predictions have been successful for sandstones when validated against laboratory results. For carbonates however the success has been limited due to their complex nature and heterogeneity. Typically experiments are conducted with core sample diameters in the order of several cm. Due to computational limitations numerical models are often of several orders of magnitude smaller than laboratory samples. In this study we used a standard carbonate rock called Silurian Dolomite to perform sonic wave experiments on two sample sizes: 1.5in. and 0.5in. diameter cylindrical cores. The latter unique size allowed us to compare our DRP based finite element method (FEM) simulations at a more compatible scale and higher image resolution. Through a multi-scale X-ray Micro-CT imaging of the same sample we studied the effect of resolution on elastic moduli simulation. We demonstrated the importance of determining Representative Volume Element (RVE) at each imaging resolution. Through determination of RVE as well as sampling of 40–55% volume fraction using non-overlapping cubes, we showed how our protocol leads to very satisfactory same scale validation of numerical linear elastic moduli predictions.

Research on numerical simulation and noise reduction of aerodynamic noise in connection section of the high-speed train

The flow field distribution characteristics of side windshields and full windshields installed in the connection section of a high-speed train were numerically computed to reduce the aerodynamic noise and improve operating environment of the high-speed train. As shown from the result, the maximum pressure was at the nose tip of the high-speed train; and the greatest flow velocity of fluid was centered in the middle section of the body, while the flow velocity at both ends of the body was relatively small. After installing a side windshield, the fluid pressure of the side was significantly lower than the upper and lower surfaces, and the pressure and turbulence intensity were greater at the corner of the connection section steps. The fluid flowed to the steps from the roof of the train, and then spread gradually down along the side, with the decreasing flow rate. Therefore, the airflow was effectively prohibited from flowing into the train through installing side windshields. However, after further installing full windshields, the pressure, flow velocity and turbulence intensity in the connection section of the high-speed train were further improved. Then, the boundary element method was applied to compute the radiation noises of two kinds of windshields installed in the connection section of the high-speed train. As shown from the result, broadband radiation noise was in the upper connection section, the maximum sound pressure level (SPL) value was between 50-100 Hz and some directivity of sound pressure was shown in the high-frequency range. A certain periodicity of sound pressure distribution was presented in the longitudinal symmetrical plane of the high-speed train. At the same observation point, the sound pressure level of full windshield was slightly reduced at most frequency points, and the maximum reduction value was 23.6 dB. Finally, the wind tunnel test was conducted on the high-speed train, and the connection section of the high-speed train was the obvious noise source, thus indicating that the research in the paper was very meaningful. Besides, from SPL comparisons of the observation point, experiments and simulations were consistent with each other whether side windshields or full windshields were installed in the connection section. As a result, the reliability of the numerical computational model and the effectiveness of the results and analysis were verified.

Design on the fairwater shape and its influence on the radiation noise of submarines

Firstly, a numerical computation model of submarine radiation noise was established to obtain the radiation noise of the submarine, which was compared with the experimental results, thus verifying the validity of the model. As indicated by the computational result, the submarine fairwater played a significant impact on radiation noise at the front section, whose structure was therefore necessary to be studied. In the paper, there were several different type submarine fairwaters. Large eddy simulation (LES) and boundary element method (BEM) were applied to conduct the numerical computation for the vortex flow field and acoustic characteristics of the original fairwater, the fairwater with fillet and the streamline fairwater. Furthermore, the impact and suppression effect of the fairwater’s type on wall pressure fluctuations and flow-induced noise were analyzed. As shown from the research, the vertical fairwater with fillet or the streamline fairwater can significantly improve the flow quality, thus considerably reducing the pressure fluctuations and flow-induced noise. The paper is conductive to the academic research of flow noise of submarine as well as the new submarine design in the future.

Physical characterization of hematopoietic stem cells using multidirectional label-free light scatterings.

An experimental setup capable of measuring simultaneous 2D scattered light angular distribution from two directions to study cell morphology without the use of bio-labels was developed. Experiments with hematopoietic stem cells (CD34+ cells) show good agreement with detailed numerical simulations of light scattering. Numerical simulations and computer models of cells are used to identify physical features of cells with the largest scattering cross sections. This allows for determination of size, geometry of the nucleus and distribution of mitochondria in hematopoietic stem cells by means of our label-free method.

Experimental and Numerical Analysis of Tensile Properties of Textile Reinforced Concrete with Steel Fibres

The topic of this article is the experimental and numerical testing of tensile strength of glass textile reinforced cement-based composites with steel fibres. Cement-based composite is similar to high-performance concrete, with its maximal compressive strength higher than 100 MPa. We used thirty six dogbone-shaped specimens for uniaxial tensile loading with three different kinds of textile reinforcement. The difference between reinforcement was in its weight of 1 m2 of textile. We focused on maximal tensile stress in specimens and the ductile behaviour after first cracking occurred. We will compare results from experimental testing made on different types of reinforcement and results from numerical computer model. Tensile stress was generated by loading with constant increase of displacement.

Performance Optimization of Vehicle Handling and Stability Using Multiple Surrogate Models

Abstract Handling and stability are key performances characteristics of vehicles. A vehicle with good handling performance can be controlled precisely by drivers and help avoid accidents. In this paper, the handling and stability optimization was conducted based on a multi-body dynamic vehicle model. Considering the large computational assumption numerical model calculation, surrogate modeling techniques were introduced in this study. The non-dominated sorting genetic algorithm version II (NSGA-II) method was applied in the optimization of each surrogate model. A comparison study on three different surrogate models was conducted to understand their performance in engineering problems. It showed that the simultaneous usage of different surrogate models was essential for obtaining the best possible design.

High-order numerical schemes based on difference potentials for 2D elliptic problems with material interfaces

Numerical approximations and computational modeling of problems from Biology and Materials Science often deal with partial differential equations with varying coefficients and domains with irregular geometry. The challenge here is to design an efficient and accurate numerical method that can resolve properties of solutions in different domains/subdomains, while handling the arbitrary geometries of the domains. In this work, we consider 2D elliptic models with material interfaces and develop efficient high-order accurate methods based on Difference Potentials for such problems.

Properties of a pair of fracture networks produced by triaxial deformation experiments: insights on fluid flow using discrete fracture network models

Results of a series of deformation experiments conducted on gabbro samples and numerical models for computation of flow are presented. Rocks were subjected to triaxial tests (σ1 > σ2 = σ3) under σ3 = 150 MPa confining pressure at room temperature, to generate fracture network patterns. These patterns were either produced by keeping a constant confining pressure and loading the sample up to failure (conventional test: CT), or by building up a high differential stress and suddenly releasing the confining pressure (confining pressure release test: CPR). The networks are similar in overall density but differ primarily in the orientation of smaller fractures. In the case of CT tests, a conjugate fracture set is observed with one dominant fracture zone running at about 20° from σ1. CPR tests do not show such a conjugate pattern and the mean fracture orientation is at around 35° from σ1. Discrete fracture network (DFN) methodology was used to determine the distribution of flow and hydraulic head for both fracture sets under simple boundary conditions and uniform transmissivity values. The fracture network generated by CT and CPR tests exhibit different patterns of flow field and hydraulic head configurations, but convey approximately the same amount of flow at all scales for which DFN models were simulated. The numerical modelling results help to develop understanding of qualitative differences in flow distribution that may arise in rocks of the same mineralogical composition and mechanical properties, but under the influence of different stress conditions, albeit at similar overall stress magnitude.

Simulation and optimization of computer numerical control-milling model for machining a spiral bevel gear with new tooth flank

Distinguished with the traditional tooth flank of spiral bevel gears, an accurate spherical involute tooth profile is of obvious advantages for the design and manufacture. For obtaining the gear model with enough tooth flank accuracy, simulation and optimization methodologies of computer numerical control-milling model are proposed. Initially, it gives an identification of the spherical involute tooth flank based on an improved formation theory. A universal simulation machining of the universal multi-axis computer numerical control-milling center is proposed to obtain an initial model. Then, in order to get/for getting improved tooth flank accuracy of the initial gear model, it presents some optimization methods included in the applications which are (1) non-uniform rational B-spline reconstruction by the Skinning method and (2) an overall interpolation based on Energy method. Finally, some given numerical examples are utilized to verify the form error of tooth flank. In addition, a closed-loop experiment scheme is provided to verify the validity of proposed methods.

FIRE CHARACTERISTICS FOR ADVANCED MODELLING OF FIRES

This paper summarizes the material and fire properties of solid flammable/combustible materials /substances /products, which are used as inputs for the computer numerical fire models. At the same time it gives the test standards for their determination.

Numerical analysis of flow instability in the water wall of a supercritical CFB boiler with annular furnace

In order to expand the study on flow instability of supercritical circulating fluidized bed (CFB) boiler, a new numerical computational model considering the heat storage of the tube wall metal was presented in this paper. The lumped parameter method was proposed for wall temperature calculation and the single channel model was adopted for the analysis of flow instability. Based on the time-domain method, a new numerical computational program suitable for the analysis of flow instability in the water wall of supercritical CFB boiler with annular furnace was established. To verify the code, calculation results were respectively compared with data of commercial software. According to the comparisons, the new code was proved to be reasonable and accurate for practical engineering application in analysis of flow instability. Based on the new program, the flow instability of supercritical CFB boiler with annular furnace was simulated by time-domain method. When 1.2 times heat load disturbance was applied on the loop, results showed that the inlet flow rate, outlet flow rate and wall temperature fluctuated with time eventually remained at constant values, suggesting that the hydrodynamic flow was stable. The results also showed that in the case of considering the heat storage, the flow in the water wall is easier to return to stable state than without considering heat storage.

Improvement of Code Behavior in a Design of Experiments by Metamodeling

It is now common practice in nuclear engineering to base extensive studies on numerical computer models. These studies require running computer codes in potentially thousands of numerical configurations and without expert individual controls on the computational and physical aspects of each simulation. In this paper, we compare different statistical metamodeling techniques and show how metamodels can help improve the global behavior of codes in these extensive studies. We consider the metamodeling of the Germinal thermomechanical code by Kriging, kernel regression, and neural networks. Kriging provides the most accurate predictions, while neural networks yield the fastest metamodel functions. All three metamodels can conveniently detect strong computation failures. However, it is more challenging to detect code instabilities, that is, groups of computations that are all valid but numerically inconsistent with one another. For code instability detection, we find that Kriging provides an interesting tool.

Pores distribution statistical analysis for metal foams obtained by casting-dissolution process

Interesting properties of metal foams such as light weight, good energy absorption and low thermal conductivity, have promoted the development of new processes to improve properties without sacrificing productivity. This study aims to verify the uniformity pore distribution in an aluminum alloy foam obtained by Casting - Dissolution Process, using a nondestructive analysis. In order to evaluate mechanical properties of a metal foam using computational numerical models, the use of a small reconstructed section of the sample representing an entire volume of metal foam, was validated. In conclusion, it was possible to determine that all parts of the sample have the equivalent superficial area and volume.

VISIR-I: small vessels – least-time nautical routes using wave forecasts

Abstract. A new numerical model for the on-demand computation of optimal ship routes based on sea-state forecasts has been developed. The model, named VISIR (discoVerIng Safe and effIcient Routes) is designed to support decision-makers when planning a marine voyage. The first version of the system, VISIR-I, considers medium and small motor vessels with lengths of up to a few tens of metres and a displacement hull. The model is comprised of three components: a route optimization algorithm, a mechanical model of the ship, and a processor of the environmental fields. The optimization algorithm is based on a graph-search method with time-dependent edge weights. The algorithm is also able to compute a voluntary ship speed reduction. The ship model accounts for calm water and added wave resistance by making use of just the principal particulars of the vessel as input parameters. It also checks the optimal route for parametric roll, pure loss of stability, and surfriding/broaching-to hazard conditions. The processor of the environmental fields employs significant wave height, wave spectrum peak period, and wave direction forecast fields as input. The topological issues of coastal navigation (islands, peninsulas, narrow passages) are addressed. Examples of VISIR-I routes in the Mediterranean Sea are provided. The optimal route may be longer in terms of miles sailed and yet it is faster and safer than the geodetic route between the same departure and arrival locations. Time savings up to 2.7 % and route lengthening up to 3.2 % are found for the case studies analysed. However, there is no upper bound for the magnitude of the changes of such route metrics, which especially in case of extreme sea states can be much greater. Route diversions result from the safety constraints and the fact that the algorithm takes into account the full temporal evolution and spatial variability of the environmental fields.

Thermal Technical Failures of Critical Construction Details

The paper deals with thermal technical failures of building structures that arise due to bad solution of construction details. For the purpose of this paper several construction details were selected. These construction details show a fault. The details were thermal technical evaluated by using a numerical computational model. In addition to the thermal technical assessment of these construction details it was also suggested possible solution to problems that arise in these places of building structures.

Absorbable energy monitoring scheme: new design protocol to test vehicle structural crashworthiness

In vehicle crashworthiness design optimization detailed system evaluation capable of producing reliable results are basically achieved through high-order numerical computational (HNC) models such as the dynamic finite element model, mesh-free model etc. However the application of these models especially during optimization studies is basically challenged by their inherent high demand on computational resources, conditional stability of the solution process, and lack of knowledge of viable parameter range for detailed optimization studies. The absorbable energy monitoring scheme (AEMS) presented in this paper suggests a new design protocol that attempts to overcome such problems in evaluation of vehicle structure for crashworthiness. The implementation of the AEMS involves studying crash performance of vehicle components at various absorbable energy ratios based on a 2DOF lumped-mass-spring (LMS) vehicle impact model. This allows for prompt prediction of useful parameter values in a given design problem. The application of the classical one-dimensional LMS model in vehicle crash analysis is further improved in the present work by developing a critical load matching criterion which allows for quantitative interpretation of the results of the abstract model in a typical vehicle crash design. The adequacy of the proposed AEMS for preliminary vehicle crashworthiness design is demonstrated in this paper, however its extension to full-scale design-optimization problem involving full vehicle model that shows greater structural detail requires more theoretical development.

Numerical Modeling of Cooling Conditions of Thermoplastic Injection-Molded Parts

The basic information characterizes the process of plastic injection molding and questions connected with computer simulation and numerical modeling of the phenomena setting during the injection molding were presented in the article. The results of the numeric simulation of the injection process of the molded part were obtained and analyzed for several models of injection mold cooling systems with different construction. Numerical simulation was conducted in the aim of the optimization of the conditions of the cooling of molded part in dependence from chosen factors connected with the parameters of the injection process and the dimension accuracy.

Time-Dependent Analysis of Prestressed Cable Nets

AbstractIn this paper, time-dependent nonlinear numerical and analytical computational models suitable for rheological analysis of prestressed cable nets subjected to creep effects are presented. The principal aim of this contribution is to describe a developed design computational tool for a theoretical simulation of the time-dependent behavior of cable nets and predict their rheological characteristics. For this purpose, a modified finite-element method for the time-dependent analysis of materially linear and geometrically nonlinear cable nets is proposed. Creep constitutive equations in the logarithmic form are incorporated into the finite-element model to express the current lengths of cables as the functions of creep strain increments. As an extension of the Irvine approach, a geometrically nonlinear time-dependent analytical static solution of taut flat cable nets over an orthogonal square plan is presented. The cable net is replaced by an equivalent membrane. Creep strain is incorporated into the c...