Iterative Calculation Method Research Articles

Analysis of aerodynamic characteristics of drone wing based on CFD

In order to improve the aerodynamic characteristics of the drone wings, CFD method was used to simulate and calculate the lift coefficient, drag coefficient, and lift-drag ratio under different relative inflow velocities, as well as the velocity and pressure fields under different attack angles. Modal calculations were conducted on the wing to obtain the first four modal shapes, providing a basis for analyzing flutter characteristics. An iterative calculation method of incompressible potential flow-boundary layer based on surface element method was combined with the software XFOIL to optimize the airfoil at low wind speeds. The results indicate that the airfoil is susceptible to stall at high angles of attack, with the pressure of the separation flow being nearly equivalent to that at the separation point. Subsequent to separation, there is an increase in differential pressure resistance, resulting in a marked rise in the drag coefficient. At the optimized angle of attack, the lift-drag ratio of the optimized wing increases by 12.58 %, while there is a decrease of 0.084 % in lift coefficient and an increase of 11.21 % in drag coefficient.

Heat transfer performance of regenerative cooling in the presence of supersonic combustion based on two-way decoupling method

As a promising active cooling method for aero engines, regenerative cooling with endothermic hydrocarbon fuel plays an important role in thermal protection systems. However, simply assuming the thermal boundary conditions for the numerical simulation of regenerative cooling as either Dirichlet or Neumann boundary conditions is often unsuitable, as the combustion process exhibits complex three-dimensional (3D) characteristics. We propose a novel multi-step iterative calculation method in this work to simulate the coupled flow and heat transfer between supersonic combustion in the combustor and regenerative cooling outside. The method captures the main features of the supersonic combustion including different shockwave structures, and generates a realistic 3D distribution of heat flux as the boundary condition for the regenerative cooling study. With improved simulation, the result shows that regenerative cooling significantly reduces the peak temperature of the combustor by 58.5% with a mass flow rate of 1 g/s. A local high-temperature region is observed on the coupled wall inside the combustor near the injector, where the flame is primarily concentrated. Increasing the mass flow rate by 100%, from 1 g/s to 2 g/s, leads to a reduction in the maximum wall temperature by up to 15.7%.

Prediction of Wind Turbine Gearbox Oil Temperature Based on Stochastic Differential Equation Modeling

Aiming at the problem of high failure rate and inconvenient maintenance of wind turbine gearboxes, this paper establishes a stochastic differential equation model that can be used to fit the change of gearbox oil temperature and adopts an iterative computational method and Markov-based modified optimization to fit the prediction sequence in order to realize the accurate prediction of gearbox oil temperature. The model divides the oil temperature change of the gearbox into two parts, internal aging and external random perturbation, adopts the approximation theorem to establish the internal aging model, and uses Brownian motion to simulate the external random perturbation. The model parameters were calculated by the Newton–Raphson iterative method based on the gearbox oil temperature monitoring data. Iterative calculations and Markov-based corrections were performed on the model prediction data. The gearbox oil temperature variations were simulated in MATLAB, and the fitting and testing errors were calculated before and after the iterations. By comparing the fitting and testing errors with the ordinary differential equations and the stochastic differential equations before iteration, the iterated model can better reflect the gear oil temperature trend and predict the oil temperature at a specific time. The accuracy of the iterated model in terms of fitting and prediction is important for the development of preventive maintenance.

Analysis of the Effect of Sampling Probe Geometry on Measurement Accuracy in Supersonic Gas Flow

The accuracy of sampling of gas components has a significant impact on the measurement of various performance parameters in the combustion chamber of an aero-engine. In order to investigate the effect of the probe geometry of a six-point gas sampling probe on sampling accuracy in supersonic gas flow, a three-dimensional probe gas flow characteristic solution model is established through numerical simulation methods of components of transport and fluid–solid coupling. Probes with three angles of 28°, 30°, and 32° and an optimized conical probe are constructed. The sampling accuracy of the probes with different geometries is compared and evaluated by the deviation of the component volume fraction before and after sampling and the resulting combustion efficiency error. This paper presents a set of calculation methods for solving the relative deviation of volume fraction by an iterative method based on the ideal gas law and the Redlich–Kwong equation (R-K equation). The method is designed to solve the exact component volume fraction problem in the simulation calculation. The study results demonstrate that the 28° and optimized conical probes improve sampling accuracy more effectively than the original 30° structure. The deviation of the volume fractions of the two structures is less than 1.7%, and the combustion efficiency error is less than 0.09%. The developed iterative calculation method can significantly reduce the theoretical calculation error to less than 0.06%. The experimental data of the test bench are in good agreement with the simulation results, thereby demonstrating the reliability and accuracy of the sampling probe following structural optimization.

Simultaneous measurement of solid concentration and solid moisture in gas–solid two-phase flow using a dual-modality electrical sensor

Abstract In a gas–solid two-phase flow system, simultaneous measurement of solid concentration and solid moisture is essential for some applications. However, during the measurement process, solid concentration and solid moisture are coupled in the measurement signals when the measurement signal is sensitive to both solid concentration and moisture. This makes it challenging to measure them simultaneously in the same measurement field. To solve this issue, a novel measurement method is proposed in this study, which uses a dual-modality electrical sensor to achieve simultaneous measurement of solid concentration and solid moisture in gas–solid two-phase flow. The dual-modality electrical sensor features a simple structure and captures measurement signals of capacitance and angle of dielectric loss within the same measurement section. With the above signals which are both sensitive to solid concentration and moisture, an iterative correction calculation method is adopted to achieve the simultaneous measurement of solid concentration and solid moisture. During the calculation process, the measured parameters are decoupled and continuously corrected until the related error values meet the threshold requirement. Numerical simulation experiments under three typical distributions and physical experiments under roping flow are carried out to verify the proposed measurement method. The results prove the effectiveness of the proposed measurement method in the simultaneous measurement of solid concentration and solid moisture for gas–solid two-phase flow.

A Novel Method to Calculate Water Influx Parameters and Geologic Reserves for Fractured-Vuggy Reservoirs with Bottom/Edge Water

In practical oilfield production, the phenomenon of water influx typically shortens the water-free recovery period of wells, leading to water flooding and causing a sharp decline in the production well yields, bringing great harm to production. Water invasion usually occurs as a result of the elastic expansion of the water as well as the compaction of the aquifer pore space. However, it can be due to the special characteristics of fractured-vuggy reservoirs such as non-homogeneity and the discrete distribution of the pore spaces. It is challenging to use traditional seepage flow theories to analyze the characteristics of water influx. Also, reservoir numerical simulation methods require numerous parameters which are difficult to obtain, which significantly reduces the accuracy of the results. In this study, considering the driving energy for water influx, a water influx characteristic model was obtained by fitting a graph plate. Subsequently, an iterative calculation method was used to simultaneously obtain water influx volume and OOIP. The aquifer to hydrocarbon ratio was determined by fitting the water influx curve with the graphic plate. Results show that the calculation method is sensitive to the values of reservoir pressure and the crude oil formation volume factor. After applying the method to one field case, it was discovered that water influx performance can be characterized into two types, i.e., linear water influx and logarithmic water influx. In the early stages, the water influx rate of logarithmic water influx is greater compared to linear water influx. However, the volume and energy of waterbody are limited, and the water invasion phenomenon occurs almost exclusively within a short period after the invasion. On the other hand, the volume of waterbody invaded by linear water influx is larger, and it can maintain a stable rate of water influx. The results of the study can provide theoretical support for the waterbody energy evaluation and dynamic analysis of water influx, as well as the control and management of water in these types of reservoirs.

Analytical method for calculating internal forces and deformations in foundation pit support under asymmetric loading

Sheet pile walls are significant forms of foundation pit supports that are widely employed in foundation pit support projects in combination with inner bracing. The complex geological conditions, surrounding environments, and earthwork excavations associated with foundation pits generally lead to noticeable asymmetric loading on a support system, posing challenges for accurately calculating the internal forces and deformations. To study the calculation methods for the internal forces and deformations in foundation pit support structures and bracing systems under asymmetric loading, a new model was established for foundation pits subjected to asymmetric unbalanced force loading on opposite sides. This method provides an adjusting technique for bracing forces on both sides based on the principle of equalizing axial forces, thereby providing a calculation approach for the stress and deformation of the foundation pit support system. Additionally, the developed axial force iterative calculation method was compared with numerical analysis methods to analyze the stress and deformation patterns in the support structure, which validated its effectiveness and accuracy.

Impact of time resolution on estimation of energy savings using a copula-based calibration in UBEM

Urban Building Energy modelling (UBEM) has emerged in the last decade as an important tool to accelerate energy transition in the building sector. To fulfil one of its major purposes - forecasting energy savings for potential energy conservation measures at an urban scale, several challenges are still to be addressed. Two key challenges include: 1) the need to calibrate models with a large number of unknown parameters across numerous buildings (either individually or through archetype representation); 2) the limited availability of high-resolution measured data, which raises concerns about calibrated models based solely on yearly values for accurate energy savings forecast. This study addresses these challenges using a case study of 35 buildings in a district in Stockholm, Sweden. Firstly, a new iterative Approximate Bayesian Computation (ABC) method for calibration is proposed, incorporating a copula-based sampling process at each iteration. Secondly, the new calibration process is applied with three different time resolutions to examine the impact of data resolution on forecasted energy usage, particularly when applied to a classical energy conservation measure. Results demonstrate the efficiency of the new method across the 35 buildings, facilitating the rapid population of a final joint distribution for the nine unknown parameters considered in each building. While the marginals may be strongly influenced by the time resolution, the forecasted energy consumption remains identical across the three analysed time resolutions. However, a noticeable difference is observed when the ECM pertains to a formerly unknown or known parameter.

A new iterative method for simultaneous computation of several eigenpair derivatives of a large matrix

A new iterative method is proposed to simultaneously compute several eigenpair derivatives of a large matrix analytically dependent on parameters. By using the Krylov subspaces augmented with the eigenvectors that one wants to differentiate, computation of several eigenpair derivatives is reduced to solving several small linear least square problems at each iteration. Convergence properties of the proposed method are analyzed. A strategy is provided to accelerate the convergence of the proposed method. Finally the efficiency of the proposed method is illustrated with some numerical examples.

An Iterative Calculation Method for Internal Forces and Deformation of Curved Tunnel Lining

The accurate prediction of lining forces and deformations is crucial for the design of arched tunnel lining. However, in traditional tunnel structural mechanics methods, the distribution shape of the surrounding rock elastic resistance (SRER), as well as the zero point and maximal point locations of SRER, are not clearly defined. In this paper, an iterative calculation method is proposed based on the gradual convergence of the unitized values of SRER and total displacement (TD) of the lining, and the one-to-one functional relationship between the two in the stability process of the surrounding rock and lining. In this method involves using the initial displacement caused by the pressure of the surrounding rock pressure is used to initiate the iterative process, and iterative calculation is carried out until the errors between the unitized value of SRER and the unitized value of TD of the lining structure meet the error requirements. This enables precise determination of the SRER and TD. In order to verify the effectiveness of the proposed method, a case study is conducted on the tunnel of Lianghe Expressway tunnel in Yunnan province, China. The results showed that when the semi-lining structure is divided into unit blocks and the average error of consistency is required to be less than 1e-3, it takes about 20 iterations are needed to meet the error requirement. Furthermore, the accuracy of the calculated results is verified through site-measuring experiments. This method provides an effective tool for failure analysis of arched tunnel lining structures.

Effect of Different Anchorage Reinforcement Methods on Long-Term Maxillary Whole Arch Distalization with Clear Aligner: A 4D Finite Element Study with Staging Simulation.

The objective of this study was to examine how various anchorage methods impact long-term maxillary whole arch distalization using clear aligners (CAs) through an automated staging simulation. Three different anchorage reinforcement methods, namely, Class II elastics, buccal temporary anchorage device (TAD), and palatal TAD, were designed. Orthodontic tooth movement induced by orthodontic forces was simulated using an iterative computation method. Additionally, the automatic adjustment of the CA was simulated through the application of the thermal expansion method. The results indicated that the palatal TAD group had the largest retraction of incisors, followed by the buccal TAD group and the Class II elastic group, while the least was in the control group. The largest distal displacements and efficiency of molar distalization for the first and the second molars were noticed in the palatal TAD group. Arch width increased at the molar and premolar levels in all groups. The FEM results suggested palatal TAD had the best performance considering anterior teeth anchorage maintenance, both sagittally and vertically. However, attention should be paid to the possible increasement of arch width.

DESIGNING OF A NEW HARDWARE AND TECHNOLOGICAL SCHEME OF THE PROCESS OF ORGANIC SUBSTANCES MIXTURES SULPHING

The article states that surfactants based on higher alcohols fr. C12 - C14 are mainly used in a wide range of personal hygiene products, such as shampoos, foaming agents for baths, toothpastes, dishwashing liquid, and delicate laundry detergents. The use of surfactants based on a mixture of higher alcohols fr. C12 - C14 and monoethanolamides of higher fatty acids of coconut oil makes it possible to significantly improve the quality characteristics of personal hygiene products. It is stated that the main element of the apparatus and technological scheme of the sulfation process of mixtures of organic substances is a tubular film absorber. It is shown that for the sulfation of two-component mixtures of organic substances based on higher alcohols fr. C12 - C14 and monoethanolamides of higher fatty acids of coconut oil must use a tubular film absorber, which has two-stage cooling - the upper part 1/3 of the length of the absorber, the lower part 2/3 of the length of the absorber. The speed of the gasair flow is maintained at Vg = 20 m/s, the molar ratio of reagents is 1.08 : 1.0, the concentration of sulfur trioxide in the gas-air flow is 3.7% vol., the temperature of the initial reactants: liquid phase is 313 K, gas-air flow is 303 K, cooling water - 293 K. Based on such initial data, an industrial tubular absorber was calculated. The data of such a calculation are given. It is stated that the calculation of the industrial tubular film absorber was carried out according to the developed algorithm and program in the MatLab language, the iterative method of calculation was used in the program. The calculation of the number of pipes of an industrial absorber is given. It is shown that the absorber consists of the following main elements - an upper elliptical cover, a gas-air flow distribution plate, a chamber for distributing a mixture of organic substances, film formers, two cooling chambers, and a lower elliptical cover. It is stated that on the basis of an industrial tubular film absorber, a new equipment and technological scheme has been designed and presented. The main technical, economic and environmental indicators of the implementation of such a hardware and technological scheme are presented.

Thermal insulation of phenolic resin modified fly ash geopolymer

Phenolic resin has been widely used owing to its excellent thermal insulation performance. However, the application of phenolic resin in the field of geopolymer remains unexplored. Here, the foamed fly ash geopolymer samples with high porosity were prepared using phenolic resin for the purpose of foaming materials. The thermal insulation properties of these samples were evaluated by Transient Plane Source Method, and the effect of phenolic resin on pore characteristics was investigated by Mercury Intrusion Porosimetry (MIP), aim to explore how phenolic resin affects the thermal conductivity by changing the pore characteristics of geopolymer. In addition, considering that the internal gas thermal conductivity of pores with different pore sizes is also different (Knudsen effect), in order to predict the thermal conductivity more accurately, this research proposes an iterative calculation method to establish a thermal conductivity model. The results show that phenolic resin can improve the thermal insulation effect of geopolymer, and the minimum thermal conductivity of the sample is 0.17 W/m·K. In addition, according to the test results of MIP, it can be found that phenolic resin mainly promotes the porosity of micron pores (>1 μm) whereas there is slight inhibition on nano pores (<1 μm), but the beneficial effect of the increase of micron-sized pores (>1 μm) on the thermal insulation performance of geopolymer is greater than the negative influence effect of the disappearance of nano pores. Moreover, according to the results of MIP, phenolic resin can narrow the throat in the pore of the ink bottle, limit the thermal convection of the gas between the pores, and reduce the thermal conductivity. Finally, the newly modified Russell model considering the Knudsen effect can effectively predict the thermal conductivity by using the experimental data. This study provides a new method to improve thermal insulation performance of geopolymers and offers a new building insulation product.

DOA Estimation of Multiple Coherent Targets Using Weight Vector Orthogonal Decomposition in TDM-MIMO HF-Radar

In recent years, MIMO high-frequency surface wave radar (MIMO-HFSWR) plays an increasingly important role in sea surveillance because of its wide-area surveillance capabilities. In signal processing, the coherent targets with the same distance and speed can only be distinguished in the angle dimension. However, HF radar’s angular resolution is poor because of the restrictions of the aperture, which causes aliasing of targets on the range–angle (RA) spectrum. Traditional super-resolution algorithms, such as MUSIC, are also inapplicable because of the targets’ coherence. Therefore, the spatial smoothing algorithm is usually used to realize the decoherence of echo at the cost of array aperture. The loss of array aperture makes the algorithm fail when there are too many targets in the echo. Aiming at this problem, this paper proposes an iterative calculation method (iterative calculation via weight vector orthogonal decomposition, IC-WORD) to estimate the angle of multiple coherent targets. Through the verification of simulation, it is proved that IC-WORD has better performance than the traditional spatial smoothing algorithm. More specifically, IC-WORD can correct spectral peak shift, improve angle measurement accuracy, and still operate stably under the condition of multiple coherent targets. This paper also uses the measured data from one of the most advanced HFSWR stations in China to validate the algorithm, which makes the paper have strong practical significance.

An Iterative Method for the Simulation of Rice Straw-Based Polyol Hydroxyl Moieties

Bio-derived polyol products have gained global interest as a green and sustainable substitute for fossil-based polyols in a diverse range of polyurethane (PU) applications. According to previous studies, PU properties are highly influenced by the reaction kinetics during their formation. One major factor affecting this is the reactivity of their polyol’s functional hydroxyl moieties that are classified as primary, secondary, and hindered-secondary. However, experimental quantitative characterization of these polyol hydroxyl moieties remains a challenge in the field due to various factors affecting them, including extensive time requirements, the need for substantial and expensive resources, large potential errors, and the generation of wastes, as well as health and safety considerations. In this study, the molar fraction of primary, secondary, and hindered-secondary hydroxyl moieties of a petroleum-based polyol (V490) and a rice straw-based polyol were determined via an iterative computational method. The method employed a MATLAB script that can simultaneously solve multiple differential equations involving PU gelling reaction kinetics and thermodynamics. In this manner, numerical combinations of the fraction of each type of hydroxyl moiety are generated by looping together the respective numerical fractions for each moiety. The best-fit combinations of the fractions of the mixed polyol’s hydroxyl moieties were successfully found via curve fitting of the simulated and experimental gelling temperature profile with an average numerical deviation of less than 1%. Thus, the method presented in this study offers a faster and more reliable characterization of the polymeric reaction kinetics than the experimental and conventional computational methods for product property enhancement and development in the field.

Long-term optimization of the hydrogen-electricity nexus in France: Green, blue, or pink hydrogen?

We model the optimal hydrogen and electricity production and storage mix for France by 2050. Moreover, an iterative calculation method to represent electrolyzer lifetime based on functioning hours in linear programming is developed. We provide a central scenario and study its sensitivity to the cost of electrolyzers, to hydrogen demand and to renewable energy deployment potential. The proportion of electrolysis to methane reforming with CO2 capture and storage in hydrogen production is sensitive to the cost of electrolyzers, with the former providing around 60% in the central scenario. However, the system cost as well as the hydrogen and electricity production costs are much more robust, thanks to the wide feasible near-optimal solutions spectrum.The electricity production mix is almost fully renewable in the central scenario, while nuclear power has a significant role only if the potential of wind & solar limits their deployment, or if CO2 capture and storage is not authorized. Furthermore, exclusion of reformer-based hydrogen from fossil gas with CO2 capture induces negligible additional cost to the hydrogen-electricity coupled system (below 1%). Therefore, in the current European resilience and sovereignty context, a robust low-carbon hydrogen development strategy would be prioritizing green hydrogen to other low-carbon hydrogen supply options.

Adaptive mode decomposition based on the instantaneous frequency basis space

Signal decomposition has attracted increasing interest in various applications in recent years. This paper proposes a new mode decomposition algorithm, called “mode decomposition based on the instantaneous frequency basis space” (IFBMD), to decompose complex chirp signals superposed with multiple-mode signals with a low-frequency instantaneous frequency (IF). In IFBMD, a global optimization algorithm is combined with an alternating iterative computation method to extract the optimal IF of the modes from the low-frequency IF basis space. In addition, to avoid the limitation of a fixed number of modes, an adaptive IFBMD is designed based on a scale-factor iteration approach that can extract modes successively. This new scaling-factor updating method can be widely usable to improve other mode-decomposition algorithms. Compared with other well-known algorithms, IFBMD has been proved to be superior in performance.

Soft Decision Decoding with Cyclic Information Set and the Decoder Architecture for Cyclic Codes

The soft decision decoding algorithm for cyclic codes, especially the maximum likelihood (ML) decoding algorithm, can obtain significant performance superior to that of algebraic decoding, but the complexity is much higher. To deal with this problem, an improved soft decision decoding algorithm based on a cyclic information set and its efficient implementation architecture are proposed. This algorithm employs the property of the cyclic codes to generate a series of cyclic information sequences by circularly shifting, constructing the cyclic information set. Then, a limited number of candidate information sequences are efficiently generated using an iterative computation method, and the candidate codewords are generated using the very concise encoding method of the cyclic codes. Furthermore, the efficient hardware architecture based on systolic arrays is also proposed to generate candidate information sequences and to select the optimal candidate codewords. An emulation platform is constructed to verify the error correction performance and to determine the optimal decoder parameters. Emulation results indicate that, with appropriate parameter selection, the proposed decoding algorithm can achieve a bit error rate approaching the ML performance while maintaining low complexity.

Dynamic characteristics of a spur gear pair under the coupled effects of angular misalignment fault and tooth modification

Angular misalignment is a common fault in gearbox manufacturing and installation, which directly affects the meshing characteristics of the gear pair. Tooth axial modification is considered to be a useful way to suppress angular misalignment. However, accurate determination of contact characteristics, e.g., contact stiffness and friction, caused by the coupled effects of angular misalignment and tooth modification is difficult. To settle this problem, this article put forward a method on the strength of the slice coupling and nonlinear Hertzian contact calculation. With the proposed model, the meshing errors caused by angular misalignment and tooth axial modification are derived. Then the influence of nonlinear Hertzian contact and friction on time-varying mesh stiffness (TVMS) is considered in each sliced tooth. In addition, an iterative computation method is proposed to calculate the proposed analytical model. Further, a dynamic model is developed to study the influences of angular misalignment and tooth axial modification on gear dynamic characteristics. Finally, the analytic model is validated by an experimental setup for a spur gear pair with ideal installation, misalignment and tooth axial modification. Results show that the proposed model is effective and efficient for predicting the dynamic response of the spur gear pair under the coupled effects of angular misalignment and tooth modification.

A double-layer iterative analytical model for mesh stiffness and load distribution of early-stage cracked gear based on the slicing method

To reveal the coupling relationship between the time-varying mesh stiffness (TVMS) and the load distribution along the tooth width direction (TWD) of gears with early-stage crack (ESC), a double-layer iterative analytical model for the TVMS and load distributions of gears is proposed considering the effects of the non-uniformly distributed load (NDL) along TWD caused by the ESC. In the proposed model, an analytical model of tooth torsional deformation and a parallel slice stiffness model of the tooth pair with ESC are separately developed based on the slicing method. On this basis, a double-layer iterative calculation method for the TVMS and load distributions is proposed, in which the coupling relationships between the slice stiffness and load distribution along TWD as well as the TVMS and load distribution between the meshing tooth pairs are respectively presented with the inner- and outer- layer iterations. Finite element (FE) models are established to verify the proposed double-layer iterative model. The effects of crack parameters and applied torque on the tooth torsional deformation, TVMS, and load distributions of the gear with ESC are finally investigated based on the proposed model. The results show that the proposed model can realize the accurate and fast decoupling calculation of the TVMS and load distributions of gears with ESC. This study can provide a basis for the establishment of the refined ESC fault diagnosis method and the rapid evaluation of the load distributions of gears with asymmetric errors or faults along TWD.