Hydrostatic Component Research Articles

Calculation of key parameters of tropospheric mapping function based on random forest method

The tropospheric mapping functions (MFs) play a crucial role in estimating the delay of electromagnetic waves as they traverse the troposphere, particularly in space geodetic techniques like GNSS and VLBI, where these waves are the primary measurement tool. Currently, empirical models that rely on non-meteorological parameters are commonly used to calculate MFs, offering convenience but often yielding less accurate results in regions with volatile climates. Such inaccuracies can lead to errors in slant total delays reaching the meter-level, subsequently affecting other data products. Although authoritative bodies periodically release essential meteorological parameters for MF calculation or provide ready-made MF products, these often come with a delay of several days or require specific authorization. To address this, we introduced a method leveraging the random forest (RF) model to rapidly derive key MFs from surface observations. Experimental results indicate that the RF model significantly enhances the accuracy of MFs, with improvements exceeding 60% for the hydrostatic component and over 20% for the wet component, effectively eliminating seasonal systematic deviations; although it is somewhat inferior to the MFs from VMF3-FC, RF does not require an internet connection and can independently train and construct models, making it very suitable for independently operated systems. We further trained a series of RF models using varied sample spaces and analyzed their performance under different combinations of feature dimensions and time spans. This analysis suggests that an optimal balance exists when considering the challenges in acquiring sample data, training time, model size, computational efficiency, and accuracy.

Investigation on the thermal characteristics of double-driven hydrostatic lead screw micro-feed system

The micro-feed system of the dual-drive hydrostatic lead screw (DDHLS) can overcome the accuracy limitations inherent in traditional hydrostatic lead screw through the process of differential synthesis, thereby achieving exceedingly low speeds and exceptional precision in feed operations. Nevertheless, due to the complex structural form of DDHLS, both heat generation and heat dissipation are different from conventional hydrostatic functional components. Therefore, for DDHLS micro-feed system, it is necessary to deeply investigate its thermal performance and evolution rules to improve its thermal stability. Based on the analysis of multi-field coupling, the accurate thermal model of the DDHLS micro-feed system is formulated. Taking into account the variable viscosity of the oil film and the heat dissipation conditions within the oil film region, the thermal behavior of DDHLS feed system is analyzed systematically. The accuracy of the thermal performance model of DDHLS feed system is verified by experiments. The findings indicate that the DDHLS micro-feed system has better thermal performance than the dual-axis differential feed system based on rolling components. Furthermore, optimizing the heat dissipation pathway of the DDHLS can significantly mitigate the thermal effects exerted by the hydrostatic nut assembly on the screw.

Deformation health diagnosis of RCC dams considering construction interfaces based on monitoring data and numerical simulation

The health diagnosis procedure applied to determine the deformation of a roller compacted concrete (RCC) dam is different from that of a conventional concrete dam. Hence, in this study, a deformation health diagnosis model was established for an RCC dam considering the construction interfaces by combining the hydrostatic component simulated using ABAQUS (2016) with the temperature and aging components calculated using a statistical method. The combined method can help monitor the structural health of RCC dam and determine the physical meaning and statistical law of the deformation of RCC dams. During the simulation process, the geometric characteristics of the construction interfaces were modeled using the interface equivalent expansion method. The material properties were modeled using multi-output least-squares support vector regression optimized with the Jaya algorithm. A case study demonstrated that the established deformation health diagnosis model has good fitting and prediction ability. The model and methods proposed in this study provide a new idea for the behavior analysis and numerical simulation of mass composite structures similar to RCC dams.

A Multi-Strategy Improved Sooty Tern Optimization Algorithm for Concrete Dam Parameter Inversion

A original strategy for optimizing the inversion of concrete dam parameters based on the multi-strategy improved Sooty Tern Optimization algorithm (MSSTOA) is proposed to address the issues of low efficiency, low accuracy, and poor optimizing performance. First, computational strategies to improve the traditional Sooty tern algorithm, such as chaos mapping to improve the initial position of the population, a new nonlinear convergence factor, the LIMIT threshold method, and Gaussian perturbation to update the optimal individual position, are adopted to enhance its algorithmic optimization seeking ability. Then, the measured and finite element data are combined to create the optimization inversion fitness function. Based on the MSSTOA, the intelligent optimization inversion model is constructed, the inversion efficiency is improved by parallel strategy, and the optimal parameter inversion is searched. The inversion strategy is validated through test functions, hypothetical arithmetic examples, and concrete dam engineering examples and compared with the inversion results of the traditional STOA and other optimization algorithms. The results show that the MSSTOA is feasible and practical, the test function optimization results and computational time are better than the STOA and other algorithms, the example inversion of the elastic modulus is more accurate than the traditional STOA calculation, and the results of the MSSSTOA inversion are reasonable in the engineering example. Compared with other algorithms, the local extremes are skipped, and the time consumption is reduced by at least 48%. The finite element hydrostatic components calculated from the inversion results are well-fitted to the statistical model with minor errors. The intelligent inversion strategy has good application in concrete dam inverse analysis.

Inverse analysis of deformation moduli for high arch dams using the displacement reconstruction technique and multi‐objective optimization

AbstractThe inverse analysis of the deformation moduli of high arch dams based on displacement monitoring data is essential for structural safety assessment. In traditional inverse analysis methods, the deformation moduli are identified based on the single‐objective optimization and the hydrostatic component derived from the statistical model. This type of method has two main shortcomings: First, it treats the essential multi‐objective optimization problem as a single‐objective problem; second, the extracted hydrostatic component may be biased due to the multicollinearity of variables in the statistical model. This paper presents a methodology for the inverse analysis of the deformation moduli of high arch dams under a multi‐objective optimization strategy. The methodology employs empirical mode decomposition to extract the aging component from displacement monitoring data. Then, thermomechanical analysis is used to reconstruct the remaining hydrostatic and temperature components, thereby avoiding the biases encountered in solving the statistical model. The adaptive polynomial chaos expansion method is embedded in the NSGA‐III algorithm to establish and solve multi‐objective functions in the inverse analysis. Additionally, a composite decision index considering errors and test information is proposed to determine acceptable deformation moduli from the Pareto solution set. A high arch dam is selected to illustrate this methodology with static and dynamic monitoring data. The results show that the identified deformation moduli have errors of 3.8% and 7.2% in displacement and acceleration, respectively. The proposed methodology can yield deformation modulus values that are more consistent with the physical implications than those of the single‐objective optimization method.

Construction and selection of deformation monitoring model for high arch dam using separate modeling technique and composite decision criterion

Deformation prediction is important to ensure the safe and stable operation of arch dams. Statistical models are extensively applied in arch dam deformation monitoring models, which generally include hydrostatic pressure component, temperature component, and aging (irrecoverable) component. In traditional statistical models, aging component is misset, which will cause unreasonable mutual compensation of each component, resulting in overfitting of the overall model. In this paper, the deformation model based on separate modeling technology is, therefore, proposed mitigating the overfitting problem caused by misspecification of the expression of the aging component in traditional statistical models. Dam deformation components related to different effects are extracted from the deformation monitoring sequence with improved complete ensemble empirical mode decomposition with adaptive noise algorithm and equal water level condition. The correct components of the monitoring model are constructed separately. On the one hand, the fitting accuracy of the model is reflected by the coefficient of determination (R2); on the other hand, the overfitting degree of the model is quantitatively evaluated by the overfitting coefficient (OC), so that the model with high fitting accuracy and prediction accuracy is determined, that is, the optimal model is selected by using the R2-OC criterion. In this paper, displacement monitoring data from measurement points are used for analysis. The results show that the deformation monitoring model based on the separated modeling technique exhibits higher prediction accuracy and lower false alarm rate. The R2-OC criterion better reflects the degree of overfitting of the monitoring model and the real situation of arch dam monitoring and warning, which improves the accuracy of model selection.

Creep-Fatigue Life Property of P91 Welded Piping Subjected to Bending and Torsional Moments at High Temperature

Abstract In recent years, the role of thermal power plants has shifted from providing a baseload to providing supplemental supply to compensate for fluctuations in the output of renewable energy sources. Thus, the operation of these plants involves frequent startup and shutdown cycles, which lead to extensive damage caused by creep and fatigue interactions. In addition, the piping utilized in thermal plants is subjected to a combined stress state composed of bending and torsional moments. In this study, a high-temperature fatigue testing machine capable of generating such a bending-torsional loading was developed. Creep-fatigue tests were conducted on P91 steel piping with weldment. The results clarified that the creep-fatigue life was reduced by the superposition of the torsional and bending moments and that it was further reduced by a holding load. It was shown that the creep-fatigue life of piping with weldment can be estimated accurately using the equivalent bending moment, which is composed of the torsional and bending moments. It was also confirmed that crack occurred in the heat-affected zone (HAZ) of the welded part, which has been often observed in actual thermal power equipment. From the finite element analysis, it was identified that cracking was initiated in the HAZ due to the accumulation of creep strain and increase in the hydrostatic pressure component during a holding load.

Deformation critical threshold estimation of Xiaowan ultrahigh arch dam with time-varying grey model

The structural behavior of the Xiaowan ultrahigh arch dam is primarily influenced by external loads and time-varying characteristics of dam concrete and foundation rock mass during long-term operation. According to overload testing with a geological model and the measured time series of installed perpendicular lines, the space and time evolution characteristics of the arch dam structure were analyzed, and its mechanical performance was evaluated. Subsequently, the deformation centroid of the deflective curve was suggested to indicate the magnitude and unique distribution rules for a typical dam section using the measured deformation values at multi-monitoring points. The ellipse equations of the critical ellipsoid for the centroid were derived from the historical measured time series. Hydrostatic and seasonal components were extracted from the measured deformation values with a traditional statistical model, and residuals were adopted as a grey component. A time-varying grey model was developed to accurately predict the evolution of the deformation behavior of the ultrahigh arch dam during future operation. In the developed model, constant coefficients were modified so as to be time-dependent functions, and the prediction accuracy was significantly improved through introduction of a forgetting factor. Finally, the critical threshold was estimated, and predicted ellipsoids were derived for the Xiaowan arch dam. The findings of this study can provide technical support for safety evaluation of the actual operation of ultrahigh arch dams and help to provide early warning of abnormal changes.

Solid-liquid coupling of in-phase and out-of-phase vibrations for two piezoelectric disks

Theoretical analysis is used to solve the solid–liquid coupled vibration characteristics for two piezoelectric disks in a limited space and verified with experimental measurements. Based on the Navier–Stoke equation and equilibrium of motion, the Rayleigh-Ritz and energy methods were developed to analyze the solid–liquid coupled system. Following an entire systematic procedure, two piezoelectric disks immersed in hydrostatic compressible fluids were analyzed using the piezoelectric constitutive equation to perform the in-phase and out-of-phase vibration. The full-field, non-contact, optical technique, called amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI), was applied to experimentally measure the vibration properties in a solid–liquid coupling system, including the mode shapes and resonant frequencies. The experimental results are presented in good agreement with the theoretical solutions and finite element calculations. Under the solid–liquid coupled system, the distributions of pressure fields and velocity vectors of fluids were also determined in the correspondent vibrating modes. Finally, it is interesting to show the tendency to close the same resonant frequency both on the in-phase and out-of-phase vibrations when the fluid depth increases. The research outcomes can provide a guide in the design of hydrostatic components.

Optimized deformation monitoring models of concrete dam considering the uncertainty of upstream and downstream surface temperatures

Measured data-driven deformation monitoring models of concrete dams are reliable scientific approaches for analyzing the operational state of dam structures. Considering the complexity of dam structural behavior, the existing models are established on the basis of a series of assumptions, which also contribute to the uncertainty of the analyzing results. In view of the fact that classical deformation monitoring models are insufficient in effectively accounting for the hysteresis effect of upstream and downstream surface temperature on the structural behavior of dams, this research analyzes the construction theory of deformation models and adopts the chi-square distribution to determine the weight of antecedent surface temperature. A model taking the weighted air and water temperature measurements as variables for thermal deformation and accounting for the hysteresis effect of surface temperature is then proposed. Meanwhile, to make up for the weakness of the proposed model to be applied in situations where little recorded water temperature data is available, a variant form of the proposed model is also presented. For further improvements in the prediction performance, a Long Short-Term Memory (LSTM) network-based model optimized by Genetic Algorithm (GA) is introduced. An engineering example demonstrates that the proposed model efficiently lowers the uncertainty aroused by surface temperature, that is, it quantitatively considers the hysteresis effect and, to some extent, separates the temperature component mixed with the hydrostatic component. And the GA-LSTM network significantly promotes the prediction performance of the monitoring model, which provides a new method for dam deformation prediction.

Structural identification of super high arch dams using Gaussian process regression with improved salp swarm algorithm

Structural identification is critical for evaluating the operation of high arch dams, and has become an important topic. This paper proposes a novel inverse analysis framework combining an improved salp swarm algorithm and Gaussian process regression to identify the material parameters of concrete dams. First, the hydrostatic component is separated from the prototype measured data using the multiple linear regression method. Subsequently, the Gaussian process regression is adopted to build the mapping relationship between elastic modulus and the calculated relative hydrostatic component of the dam. Finally, the improved salp swarm algorithm is used to estimate the real elastic modulus of the dam by minimizing the discrepancy between the measured and calculated relative hydrostatic components. The performance of the proposed method is verified on a real concrete arch dam with sufficient monitoring data. Results show that the proposed inverse analysis method can identify the material parameters accurately and efficiently.

Residual Stress Distribution in a Copper-Aluminum Multifilament Composite Fabricated by Rotary Swaging.

Rotary swaging is a promising technique for the fabrication of clad Cu/Al composites. Residual stresses appearing during the processing of a special arrangement of Al filaments within the Cu matrix and the influence of the bar reversal between the passes were studied by (i) neutron diffraction using a novel evaluation procedure for pseudo-strain correction and (ii) a finite element method simulation. The initial study of the stress differences in the Cu phase allowed us to infer that the stresses around the central Al filament are hydrostatic when the sample is reversed during the passes. This fact enabled the calculation of the stress-free reference and, consequently, the analysis of the hydrostatic and deviatoric components. Finally, the stresses with the von Mises relation were calculated. Hydrostatic stresses (far from the filaments) and axial deviatoric stresses are zero or compressive for both reversed and non-reversed samples. The reversal of the bar direction slightly changes the overall state within the region of high density of Al filaments, where hydrostatic stresses tend to be tensile, but it seems to be advantageous for avoiding plastification in the regions without Al wires. The finite element analysis revealed the presence of shear stresses; nevertheless, stresses calculated with the von Mises relation show similar trends in the simulation and in the neutron measurements. Microstresses are suggested as a possible reason for the large width of the neutron diffraction peak in the measurement of the radial direction.

A nonhydrostatic oceanic regional model, ORCTM v1, for internal solitary wave simulation

Abstract. The Oceanic Regional Circulation and Tide Model (ORCTM), including a nonhydrostatic dynamics module which can numerically reproduce internal solitary wave (ISW) dynamics, is presented in this paper. The performance of a baroclinic tidal simulation is also examined in regional modeling with open boundary conditions. The model control equations are characterized by three-dimensional and fully nonlinear forms considering incompressible Boussinesq fluid in Z coordinates. The pressure field is decomposed into the surface, hydrostatic, and nonhydrostatic components on the orthogonal curvilinear Arakawa-C grid. The nonhydrostatic pressure determined by the intermediate velocity divergence field is obtained via solving a three-dimensional Poisson equation based on a pressure correction method. Model validation experiments for ISW simulations with the topographic change in the two-layer and continuously stratified ocean demonstrate that ORCTM has a considerable capacity for reproducing the life cycle of internal solitary wave evolution and tide–topography interactions.

Investigation of Load Characteristics in Cold Upsetting of High-Strength Steel

Decreasing the amount of heating energy in hot forging has been required to alleviate global warming. Some forming conditions of low-friction and high-aspect-ratio billets are effective in reducing load to exchange hot forging to cold forging. It is helpful to decrease the amount of hot forging if other conditions are found to reduce the forming load of high-strength steel. In this study, the effect of the elastic deformation of a forging die on the load is investigated. The load increased when a high-strength material is compressed using a die made of tool steel. Experimental and analytical results show that the flat tool surface has a deep elastic concave, that inhibits the free flow of the material and increases the hydrostatic pressure component, resulting in increases in the surface pressure and load. Therefore, when a cylindrical billet of bearing steel is compressed by 70% using a die made of carbide, the load is reduced by 20% compared with that when using the tool made of tool steel. The tool made of carbide is effective for suppressing the load increase caused by the concave due to elastic deformation.

Self-organized quantum dots in marginally twisted MoSe2/WSe2 and MoS2/WS2 bilayers

Moiré superlattices in twistronic heterostructures are a powerful tool for materials engineering. In marginally twisted (small misalignment angle, θ) bilayers of nearly lattice-matched two-dimensional (2D) crystals moiré patterns take the form of domains of commensurate stacking, separated by a network of domain walls (NoDW) with strain hot spots at the NoDW nodes. Here, we show that, for type-II transition metal dichalcogenide bilayers MoX2/WX2 (X=S, Se), the hydrostatic strain component in these hot spots creates quantum dots for electrons and holes. We investigate the electron/hole states bound by such objects, discussing their manifestations via the intralayer intraband infrared transitions. The electron/hole confinement, which is strongest for θ < 0.5°, leads to a red-shift of their recombination line producing single-photon emitters (SPE) broadly tuneable around 1 eV by misalignment angle. These self-organized dots can form in bilayers with both aligned and inverted MoX2 and WX2 unit cells, emitting photons with different polarizations. We also find that the hot spots of strain reduce the intralayer MoX2 A-exciton energy, enabling selective population of the quantum dot states.

The dilatation line in an elastic wedge

A solution for a dilatation line which occupies an arbitrary position in an elastic wedge with free surfaces and an arbitrary apex angle is found for the first time. The analytical expressions are given in the Mellin space for the stress fields of the dilatation line. It is shown that the free surfaces of the wedge strongly affect upon the stress fields. The axial and hydrostatic stress components are not equal to zero outside the dilatation line. They are strongly inhomogeneous and can change their signs, while their magnitude is comparable with that of the other non-vanishing stress components. They also demonstrate strong non-monotonic and alternating dependence on the wedge apex angle. For the wedge apex angles of 180° and 360°, the non-vanishing stress components of the dilatation line are represented in an explicit form. The results obtained can be used for solving similar problems for long elastic dilatation inclusions of arbitrary cross section embedded to wedge-shaped elastic bodies. The paper is devoted to the memory of our friend and colleague Igor Sevostianov who gave a great contribution to micromechanics of composite and porous materials.

The Effect of the First and Second Stress Invariants (Hydrostatic and Deviatoric Stresses) on the Compressibility Function

Experimental work was carried out to investigate the separate roles of the hydrostatic and deviatoric components of stress tensor (Using the First and the second invariants and ). The results were expressed in term of stress dependent shear compliance and apparent compressibility function in the time temperature region of the test (up to seconds at the region of the relaxation).&#x0D; The Compressibility Function showed no significant change, when increasing the hydrostatic stress and keeping the deviatoric stress constant, and by varying and keeping constant the change is about 10 for the stress combination of tension-torsion.&#x0D; The volume was found to increase with time when increasing and keeping constant.&#x0D; In the case of and the deviatoric stress played the major role. All these effects could be rationalized by the idea of the time dependent free volume. If the free - volume increases with time by increasing this could explain the difference in the effect of and on and explain the creep less than recovery.&#x0D; There is no difference between the compressibility function in creep and recovery (to within the experimental scatter of ()).&#x0D; A small increase in B was detected with time, the maximum difference between the lowest and highest is .

An advanced Bayesian parameter estimation methodology for concrete dams combining an improved extraction technique of hydrostatic component and hybrid response surface method

It is very important to estimate the mechanical parameters based on monitoring data for investigating the operation behavior of concrete dams. In this paper, an advanced Bayesian parameter estimation method for concrete dams is proposed. The Empirical Mode Decomposition (EMD) is adopted to extract the aging component of the observed deformation sequence, and the hydrostatic component is separated from the remaining periodic term through the statistical regression model (SRM). A hybrid response surface method (HRSM) is proposed as a surrogate model for finite element method (FEM) simulation. The likelihood function, which reflects the error between the observed and simulated deformation, is constructed, then the Bayesian formula for parameter estimation is established. The transitional Markov chain Monte Carlo (TMCMC) algorithm is used to obtain the parameter posterior distribution. The proposed method is applied to estimate the elastic modulus of the GD concrete dam, the parameter posterior distribution is obtained through the fusion of monitoring information and parameter prior information. This method can also avoid the issues of multiple solutions and unreasonable parameter combinations, which may exist in traditional deterministic inversion methods. The case study shows that the proposed method has good applicability in the parameter estimation of concrete dams.

Feasibility of early fatigue damage evaluation using the Neutron diffraction method

One of the most successful applications of the Neutron Diffraction (ND) method is the evaluation of residual stress, specifically in welded structures, and many examples exists in the literature. The present study explores the feasibility of applying the ND method to the evaluation of early high-cycle fatigue damage (i.e. the damage prior to formation of fatigue micro- or macro-cracks). In metals and advanced alloys early fatigue damage is normally associated with the accumulation of irreversible and highly localised micro-plastic strains. These strains change the micro-strain/stress field on various scale levels. In this study we attempt to measure these changes applying the ND method to G350 steel fatigue samples, which have been relieved from residual stress and subjected to various degrees of high-cycle fatigue damage. Multiple measurements of the strain/stress field in each sample have been undertaken using the ND method with an incoming beam of 0.5×0.5 mm2. The outcomes demonstrate that it is feasible to evaluate severe fatigue damage using the ND method, and, in general, the severity of the fatigue damage correlates relatively well with the averaged hydrostatic component of the residual stresses measured by the ND. However, more accurate evaluation may require higher spatial resolution (smaller gauge length) and, possibly, a larger number of measurement points to improve the quality of the experimental data.

Cascade earthquake and tsunami hazard assessment: A deterministic perspective for engineering purposes

Preventive management strategies are evolving towards multi-hazard risk estimates. Commonly, the multi-hazard characterization is pursued following a probabilistic approach. However, scenario-based evaluations can provide complementary key insights of relevance to design critical facilities.In this paper, an alternative deterministic analysis was explored to characterize the cascade seismic and tsunami actions of a 1755-alike Great Lisbon Earthquake and Tsunami event oriented to the container terminal of Sines deep-water seaport, Portugal, which is in expansion to increase the current 2.3 million TEU capacity to 7.1 million TEU.The analysis accounts source, propagation and site effects uncertainties influencing the multi-hazard estimates for different structural configurations representing the different stages of the extension plans for the infrastructure.The target-hazard assessment assumes ground motion acceleration and tsunami hydrostatic and hydrodynamic quantities as explanatory variables, respectively obtained from ground motion prediction equations and non-linear Shallow-Water equations. The intensity measures inherent to each of the inextricable candidate sources, Scandidate, were characterized over 864 seismic and 144 tsunami simulations and then compared to key-thresholds to identify the scenarios with damaging potential, Seligible. The quantities of each Seligible were assessed varying the earthquake and tsunami intensity measures as leading measures to define a set of combined worst-case scenarios for the infrastructure, Sworst. The cascading loading patterns for structural design purposes are then derived following the European and North American code provisions for earthquake and tsunami actions, respectively.The prediction of the cascading loading pattern at the terminal container of the Sines port quantifies PGA around 0.37 g for a seismic displacement-controlled behavior and peaks of hydrostatic and hydrodynamic components values around 1000 kNm−1 for tsunami force-controlled behavior during both the inflow and outflow cycles. A brief correlation between indicative action values and structural resistance of the current constructive solution raises awareness for the high probability of structural collapse of the pile-supported wharf due to an extreme 1755-alike Great Lisbon Earthquake and Tsunami threat, which would disrupt the port's operations and compromise its role as lifeline structure in case of emergency.