Analytical Calculation Method Research Articles

Comparing Numerical and Analytical Methods for Heat Loss Determination of District Heating Systems

Energy efficiency assessment considers the heat losses in district heating systems. For instance, life cycle assessments of such engineering structures require knowledge of the heat losses during their use phase. Therefore, it is essential to have the most accurate knowledge of the heat losses of a district heating system. In this study, three different methods for the determination of specific heat losses for buried preinsulated steel pipes are compared. The first method involves an analytical calculation in accordance with EN 13941, while the second utilizes an equivalent circuit approach. The third method employs finite element analysis. The objective was to evaluate the accuracy of the methods, the achievable range of results, and the effort required to solve the respective calculation algorithms. Therefore, typical 2-dimensional cross sections including different pipe diameters were selected. In situ measurements were not part of this study. Consequently, the analysis centres on the deviation between the methods. All three methods determine the heat loss in both the supply and return pipes. While the analytical calculation method cannot determine temperatures in the soil, the equivalent circuit method can handle more complex tasks and gives detailed results at predefined points in the model. With the finite element method, a high degree of detail can be achieved, but the requirements for solving the algorithms increase. An emerging trend in district heating involves reducing operational temperatures in both new and existing networks. This will change the relation between heat losses and heat delivered to the customers. Subsequently, an increasing interest in the actual heat losses and the precision of calculation is expected within this development. Therefore, it remains essential to evaluate the performance of different models

An analytical calculation method of SiC MOSFET junction temperature based on thermal network theory and Laplace transform

An analytical calculation method of SiC MOSFET junction temperature based on thermal network theory and Laplace transform

A methodology for the selection of low friction/anti-seize coating in applying bolted joints of ITER blanket modules

The application of bolted joints with the Spiralock®/Selflock® technology for remote handling system in fusion machines leads to develop a methodology for selection a low friction/anti-seize coating in applying sliding surfaces of high-loaded threaded fasteners. This study discusses the analytical engineering method for calculation the maximum/minimum allowable friction coefficients in the thread and on the bearing surface during the tightening/untightening procedure. Calculations were made to determine the maximum/minimum allowable coefficient of friction in threaded pairs used for the ITER Blanket Module Connections and enhanced flux First Wall Panel fasteners (bolts with a regular metric thread/nuts with a self-locking thread, Spiralock®/Selflock® technology) of the ITER fusion experimental reactor under maximum torque conditions of the robot manipulator (remote handling system) and tensile load (preload) generated in the bolt during the tightening/untightening procedure. Design features of the Spiralock® technology were derived for calculation the working ranges of thread friction coefficient in the threaded pairs of the Blanket Module Connection and enhanced Heat Flux First Wall Panels fasteners at different coefficient of thread proportionality values (ζ=0.45–1.00). The lowest thread friction coefficients were obtained by the coefficient of thread proportionality ζ=1.00: 0.022≤μth≤0.171 for the M24 × 3 SB Electrical strap central bolts, 0.013≤μth≤0.047 for the М52 × 4 Outboard Flexible Cartridge central bolts, 0.010≤μth≤0.055 for the M64 × 4 Inboard Flexible Cartridge central bolts. The new method of determining the total tightening torque of the M24 × 3, M52 × 4, M64 × 4 bolted joints fastened to the Spiralock® female thread under conditions of elastoplastic, plastic deformation was applied to assess the suitability the solid lubricating coating MoS2 (VNIINP-212) under preload force Fa=10–1200 kN. The performed design verification indicated the significant differences in the calculated tightening torque obtained according to the standard and proposed method for the Spiralock® female thread by the plastic deformation of the tip of bolt thread and change of sliding friction coefficient depending on the contact pressure.

ТЕПЛОВИЙ РОЗРАХУНОК СУХИХ ТРАНСФОРМАТОРІВ З ЛИТОЮ ІЗОЛЯЦІЄЮ ТА З ФОЛЬГОВИМИ ОБМОТКАМИ

The method of analytical thermal calculation of dry transformers with cylindrical conductors with cast insulation and foil windings is presented. The surface and volume averaged temperatures of the magnetic system core and the wind-ings are determined from the one-dimensional non-linear substitute thermal circuit of the transformer. To clarify the temperature distribution across the cross-section of the anisotropic foil winding, the solution of the boundary value problem in the form of a two-dimensional Poisson equation with heat transfer coefficients calculated from the substitute scheme is used. Calculation example of a dry transformer with a capacity of 2500 kVA is given. Numerical CFD model-ing was performed to verify the calculation results. Bibl. 10, fig. 9, tab. 3.

Calculation method and analysis of residual stress in the strip bending roller straightening process

Taking thin gauge strip as an example, the deformation process of metal strip in bending roll straightening was studied. Based on the theory of discrete, curvature integral and elastic–plastic mechanics, the strip travel trajectory of the bending roll straightening process is analyzed, and the numerical analytical calculation method of the continuous straightening process of the strip bending roll is established. The results are verified by establishing MARC finite element simulation and designing straightening experiment. The effects of yield strength, plastic rate and bending amount on residual stress after straightening were studied. In the straightening process, with the increase of the amount of bending roll, the residual strain converges to the region Γ, and with the increase of the yield strength, the region Γ decreases. With the increase of the yield strength, the amount of bending roll and the plastic rate, the wave height increases. The results of the calculation of residual stress, finite element simulation and experiment are close and the trend is consistent. The results show that the logic of the calculation method is reasonable, and the prediction error is within the scope of engineering application, which is helpful to the realization of process intelligence in the process of bending roller straightening.

Analytical Solution for the Deformation of Pipe Galleries Adjacent to Deep Excavation

Deep excavations clearly impact adjacent existing properties and threaten their operational safety. Predicting the deformation of existing infrastructure induced by nearby underground construction is the main concern of urban underground development. This paper presents an analytical calculation method for predicting underground pipe gallery deformations induced by adjacent deep excavations. First, the authors assume the existing pipe gallery to be nonexistent in the soil and propose a solution to calculate the excavation-induced vertical movements of the soil at the position of the existing pipe gallery. Thereafter, the authors simplify the existing pipe gallery as an elastic beam on a Winkler foundation to calculate its deformation. Finally, the method is verified by the good agreement found between the calculated result and the field measurement of the construction of the Shanghai Hongqiao CBD project. The proposed analytical method of this work can provide accurate evaluation results for similar engineering projects.

Development of a Novel Lightweight Utility Pole Using a New Hybrid Reinforced Composite—Part 1: Fabrication and Experimental Investigation

This paper is the first part of a two-part paper that discusses the development of a novel lightweight and cost-effective hybrid 3D composite material and its and utilization for constructing utility poles. The main objective was to generate a material/pole with a comparable performance to the commercially available poles made of 2D fiber-reinforced polymer (FRP) and examine its feasibility. The novel hybrid composite was configured using a recently developed and marketed 3D E-glass fabric–epoxy composite reinforced with wood dowels, referred to as 3D dowel-reinforced FRPs (3D-drFRPs) hereafter. Firstly, the compressive and flexural properties of the 3D-drFRPs are evaluated. Then, the development of the 3D pole is discussed followed by the fabrication details of two 3D-drFRPs using the standard test method, and their responses are compared. For the second part, robust finite element (FE) models were developed in an LS-DYNA environment and calibrated based on the experimental results. A sophisticated nonlinear FE model was used to simulate the performances of ASTM standard-size compression and three-point bending specimens and tapered 2D and prismatic 3D poles. Moreover, the responses of equivalent 2D and 3D poles were simulated numerically, as the task could not be accommodated experimentally due to our laboratory’s deficiencies. The integrity of the numerical simulation results was validated against experimental results, confirming the accuracy of the developed model. As an example, the stiffness values for the 3-pt bending specimens and the 3D poles obtained through the simulations were very close to the experimentally obtained results, with small margins of errors of 3.2% and 0.89%, respectively. Finally, a simplified analytical calculation method was developed so practicing engineers can determine the stiffnesses of 3D-DrFRP poles very accurately and quickly.

РЕКОМЕНДАЦИИ ДЛЯ МОДЕЛИРОВАНИЯ ЭЛЕМЕНТОВ ИЗ СТАЛЬНЫХ ТОНКОСТЕННЫХ ПРОФИЛЕЙ

Despite the increase in the growth rate of construction with the use of steel thin-walled sections, the building code for the design and calculation of these structures has a number of conventions and indicates the preferred use of the results of experimental studies in the design. Fullscale tests are generally not available during design, so numerical modelling is a correct alternative. The analysis of existing scientific literature shows that there is no consensus among researchers regarding the main parameters of the models and the modelling algorithm in general, so the aim of the paper is to develop recommendations for modelling thin-walled sections. The results of the study for object made from a coupled sigma profile under axial compressive force conditions let us develop key recommendations for modelling including the use of finite element type, finite element mesh parameters, the mechanism of application of boundary conditions, external loads and other model parameters. The results were verified by analytical methods of thin-walled sections calculation. The obtained convergence of the results indicates the possibility of using these recommendations in the design and calculation of thin-walled structures.

An Analytical Steady Heat Flow Calculation Method for District Heating Networks

An Analytical Steady Heat Flow Calculation Method for District Heating Networks

Analytical Expression of the Mirror Coefficient by Joint Analytical Calculation Method

Analytical Expression of the Mirror Coefficient by Joint Analytical Calculation Method

Utility and Application of a Versatile Analytical Method for MMF Calculation in AC Machines

Utility and Application of a Versatile Analytical Method for MMF Calculation in AC Machines

Multi-physical Field Analysis Method for Enclosed Isolated Phase Busbar of Hydropower Station

In this paper, geometrical modelling and finite element multi-physical field analysis method are carried out for the actual layout of the enclosed isolated phase busbar (EIPB) of a hydropower station, for the horizontal and vertical connection parts that can hardly be considered in the analytical calculation process. The finite element model is able to accurately represent the main structure of the EIPB by reasonably simplifying some of the components. Meanwhile, the finite element model incorporates the coupling of magnetic field and transient structural field, allowing for analysis of the magnetic field distribution, stress-strain distribution, modal analysis, and harmonic response of each component of the EIPB. It is capable of analyzing the vibration response of the complex horizontal-vertical structure EIPB under different excitations. This method can overcome the limitations of analytical calculation methods in calculating complex structure EIPBs. It can also provide valuable guidance for the structural optimization design of future EIPBs.

Intact stability analysis of crane barge due to loading orientation effect during heavy lifting operation

Changes in the position of the lifting load on the crane barge during heavy lifting operation significantly affect the stability of the vessel. The changes in stability during this heavy lifting operation must be analysed to prevent operational failures. This study conducted an intact stability analysis of the crane barge during lifting of topside structures in the installation phase. The analysis was performed with variations in the position of the lifted load from starboard to bow for every 15° change in the crane angle. The stability results of the Crane Barge for all variations, using both analytical and numerical methods, have met the IMO requirements. The extreme condition occurred in load case 8, with a maximum GZ value of 2.904 m at a 22° angle and an area of 103,894 m.deg. The comparison of the stability results of the crane barge during the structural lifting operation using analytical calculation and numerical methods indicates that the overall validation error values have met the ±5% requirement according to the ABS Rules. However, when considering the corrections for changes in the lifting load moment in the analytical calculation, stability error values increase significantly as the heeling angle of the vessel increases.

D-Q Axis Inductance Analytical Calculation for Fractional-Slot Distributed Winding IPM Motor Based on Big-Small Pole Space Method

The d-q axis inductance is the crucial parameter for the interior permanent magnet (IPM) motor. In order to facilitate the design, analysis, and optimization of IPM motors, it is of great significance to develop an accurate and simplified inductance analytical calculation method. Among the existing calculation methods, the magnetic equivalent circuit (MEC) has advantages in the inductance calculation of the IPM motor due to the simple modeling, the fine processing of the saturation region and the visualization of the magnetic field distribution. However, the traditional MEC method is only applicable to the IPM motor with integer-slot distributed winding (ISDW) or fractional-slot concentrated winding (FSCW), while lacking of in-depth research on fractional-slot distributed winding (FSDW). The magnetic circuit topology of FSDW IPM motors is not as single as that of FSCW/ISDW IPM motors. It leads to problems in the traditional MEC method when dividing the d/q axis flux path in FSDW motors. To solve this problem and expand the applications of MEC method, a big-small pole space (BSPS) method is proposed after fully considering the common characteristics of MMF distribution and reluctance distribution in FSDW motors, which fills the gap of MEC method applied to FSDW motors. The BSPS method divides the d-axis flux path according to the asymmetry of the d-axis magnetomotive force (MMF). Based on the divided flux paths, an improved nonlinear MEC model that considers the saturation of stator and rotor is established to calculate d- and q-axis inductances. The results of finite element analysis (FEA) verify the validity of the proposed MEC model with different geometry parameters. Experimental results of an 84-pole/360-slot FSDW I-type IPM wind generator further confirm the validity of the proposed MEC model

Numerical and analytical method of calculation of dynamic strength of modernized air springs for high-speed electric trains

The article presents a new design of a pneumatic suspension device for the high-speed electric train “AFROSIAB”, Uzbekistan. The authors developed a numerical-analytical method for the calculation of dynamic strength of modernized pneumatic springs for high-speed electric trains; an algorithm and a program for the Mathcad 15 programming environment were built. The design given in the article is protected by the Patent of the Republic of Uzbekistan for invention No. IAP 04632 [1].

КОНТРОЛЬ НАПРУГИ ЗАНУРЮВАНИХ ЕЛЕКТРОДВИГУНІВ

The methods and means of voltage control on the clamps of submersible electric motors of electric drills are considered. The peculiarities of the submersible electric motor as a consumer of electrical energy when it is powered by three-phase voltage via a cable line with asymmetric electrical resistances of the phases are revealed. The main downhole factors influencing the functioning of the submersible electric motor that rotates the drill bit during drilling of deep oil and gas wells are analyzed. The impact of the temperature of the drilling fluid on the value of the active resistance of the cable cores and the drill pipe in deep drilling conditions has been updated. The results of the analysis of known technical solutions and concepts regarding the possibility of voltage control on the clamps of submersible motors, which would implement its physical measurement in industrial conditions, are presented. A method of analytically calculating the phase voltages on the clamps of the submersible electric motor of the electric drill, which is powered by an electric cable with asymmetric electric resistances of the phases, is proposed. The possibility of practical implementation of a laboratory installation based on the proposed method of calculating phase voltages on the clamps of the submersible electric motor of an electric drill is shown. For the practical implementation of the method of analytical calculation of phase voltages on the clamps of a submersible electric motor, the feasibility of using digital processing of signals from current and voltage transmitters located on the surface during oil or gas well drilling is substantiated. The advantages of the proposed method of controlling the voltage on the clamps of the submersible electric motor of the electric drill are the consideration of the electrical parameters of specific power supply cables obtained as a result of auxiliary measurements, and the possibility of technical implementation on a modern element base. The development and implementation of a device for monitoring phase voltages on the clamps of the submersible electric motor of an electric drill will increase the operational reliability and efficiency of drilling wells with an electric drill, which will reduce their cost.

Dynamic responses of a bituminous concrete core rockfill dam on layered overburden under seismic wave input

The dynamic nonlinearity, overburden stratification characteristics and oblique incidence of seismic waves in soil greatly increase the difficulty of determining the free field of a dam foundation, which restricts seismic input accuracy. Based on the potential function theory, this paper constructs a transfer relationship between the wave amplitude matrix at the top layer of a dam foundation with overburden and the wave amplitude matrix at any layer and obtains the shear strain of the soil through Fourier inverse transformation. Then, the equivalent linearization method is adopted to depict the nonlinearity of the soil. An analytical calculation method for the free field of a dam foundation with layered overburden under inclined seismic waves is proposed. This method can not only forward the free field according to the incident wave in the deep part of the foundation but also directly invert the free field according to the seismic motion on the ground surface, and the inversion efficiency is high. Using a nonlinear viscous-spring boundary element developed by the authors, combined with the free field, a wave input method for a dam foundation with a layered overburden under inclined seismic waves is established. The maximum error between the numerical solution under wave input and the analytical solution is only 5%. The computational precision of the method is high. Finally, the dynamic responses of a bituminous concrete core rockfill dam on a layered overburden are studied. The results show that an upstream buoyancy and oblique incidence are the main reasons for a larger acceleration on the upstream side of the dam than on the downstream side. As the incident angle increases, the differential distribution becomes more significant, and the amplification coefficient of the anti-seepage system also increases. When the incident angle is 25°, the horizontal and vertical amplification coefficients at the top of the core wall increase by 12.8% and 25.2% compared to the vertical incidence, respectively. The accelerations of the dam are overestimated under uniform seismic input, and the amplification coefficients of the dam crest are overestimated by 52.3% and 39.8% compared with the wave input, respectively. The wave input reasonably solves the problem of seismic input for a dam foundation with layered overburden, considers the inclined seismic waves, and can reflect the seismic waves propagation characteristics. The wave method provides a solid foundation for the seismic safety of rockfill dams with layered overburden.

О направленном излучении сверхкоротких электромагнитных импульсов и фрактальной геометрии пространства-времени

Theoretical and experimental investigations of propagation of ultrashort electromagnetic pulses (US EMP) are needed to develop new technologies of creation of modern special engineering. The analytical method of field calculation of travelling antenna waves taking into account reflection of fracture and redistribution of currents in wires because of losses of radiation energy from fractures is considered. The calculations of V-antenna, the field of radiation of a horn system and the pulse radiation of the antenna with a reflector are presented. Experimental investigations of UWB EMP propagation carried out on the basis of the theory developed by S.A. Podosenov are the base of creation of modern radiotechnical complexes. Simultaneously the main conceptions of space-time fractal geometry of deterministic structures are introduced.

Analytical method of DC input impedance for stability analysis of IPM motor drive system

AbstractThis paper proposes an analytical calculation method of frequency characteristics of DC input impedances of an IPM motor drive system for design and stability analysis by the impedance method. The proposed method is based on an averaged frequency model linearized at an operating point. The developed small‐signal model considers control principles and mechanical perturbations. It is an analog and digital mixed model which is controlled by a digital signal processor system. Analysis examples of frequency characteristics for the impedance method by the proposed method are investigated and validated analytically and experimentally.

Analytical calculation method of a liquid-cooling eddy current brake considering magnetic saturation and skin effect

In this article, a clear and concise analytical method for predicting the performance of a Liquid-cooling eddy current brake (LC-ECB) is proposed. The LC-ECB has a coolant channel in the rotor to allow direct cooling of the inner surface of the stator. The static air-gap magnetic field distribution is obtained by the dynamic magnetic equivalent circuit (MEC) method, and the magnetic flux leakage and global magnetic saturation effects are fully considered. The magnetic field intensity distribution function of the eddy current reaction magnetic field is derived for the first time based on Ampere circuital theorem. Considering the local magnetic saturation and skin effect, a novel double-iteration algorithm based on the conservation principle of magnetic pressure drop is applied to obtain the transient air-gap flux density distribution, and then the brake torque expression is obtained. The finite element method (FEM) and experimental results show that the proposed method is feasible and effective. The new model is easy to program and can be easily used in the initial design and optimization of LC-ECB.