Numerical Mode Research Articles

Research on gas-liquid interface parameters related to thermal performance of frost-free evaporator of air source heat pump

Direct spray frost-free air source heat pumps (FFASHPs) base on liquid desiccant solutions are a more promising renewable energy technology for developing net-zero emission buildings. In order to improve the thermal performance of the frost-free evaporator, a numerical mode was established based on the penetration theory and the two-film theory to reveal the interfacial heat and mass transfer mechanism of LiCl solution falling film absorption on the air side of the frost-free evaporator. The distribution characteristics of temperature, water vapor concentration, effective diffusion coefficient, morphology, velocity and pressure at the interface under different air Reynolds numbers and temperatures were analyzed. The results show that the distribution uniformity of interface parameters has a greater effect on heat transfer performance than its average value. The critical Reynolds number is 391.0 under the present study, and the distribution uniformity of interface parameters and the intensity of interface fluctuation are improved, and the thermal performance reaches the peak. The COP of FFASHP system can be improved effectively when the frost-free evaporator is operated under the critical condition matching its parameters. The purpose of the study is to provide theoretical support for the performance improvement and efficient operation of frost-free evaporators.

Analysis and mitigation of uncertainties in damage identification by modal-curvature based methods

The objective of this paper is to address and reduce the uncertainties associated with measurement noise and discretization in damage identification methods based on modal curvature analysis. The experimental case study considers the local reduction in the bending stiffness of a slender beam under free-free and simply supported boundary conditions. First, the analysis of error sources and their propagation is theoretically set up. Second, the mitigation of uncertainties in damage localization is pursued using a two-stage approach based on multiple hypothesis testing relative to the normalized indices and the definition of a combined macro-index. Finally, the Monte Carlo method is exploited to obtain the statistical error distribution of the experimental damage position and severity predictions by randomizing the numerical displacement mode shapes with the identified noise. The present analysis allows us to find the optimal number of sensors that minimizes the combination of bias and truncation errors, to highlight how sensor spacing and data noise affect damage localization, and to determine the uncertainty bounds of the predicted damage severity. The two-stage approach, enhanced by selecting thresholds related to real noise levels and tuned on SHM objectives, appears to improve identification accuracy compared to the separate use of damage indices based on absolute confidence levels.

Finding the rhythm: Humans exploit nonlinear intrinsic dynamics of compliant systems in periodic interaction tasks.

Activities like ball bouncing and trampoline jumping showcase the human ability to intuitively tune to system dynamics and excite motions that the system prefers intrinsically. This human sensitivity to resonance has been experimentally supported for interactions with simple linear systems but remains a challenge to validate in more complex scenarios where nonlinear dynamics cannot be predicted analytically. However, it has been found that many nonlinear systems exhibit periodic orbits similar to the eigenmodes of linear systems. These nonlinear normal modes (NNM) are computable with a recently developed numerical mode tool. Using this tool, the present resarch compared the motions that humans excite in nonlinear systems with the predicted NNM of the energy-conservative systems. In a user study consisting of three experiment parts, participants commanded differently configured virtual double pendula with joint compliance through a haptic joystick. The task was to alternately hit two targets, which were either aligned with the NNM (Experiments 1 and 2) or purposefully arranged offset (Experiment 3). In all tested experiment variations, participants intuitively applied a control strategy that excited the resonance and stabilized an orbit close to the ideal NNM of the conservative systems. Even for increased task accuracy (Experiment 2) and targets located away from the NNM (Experiment 3), participants could successfully accomplish the task, likely by adjusting their arm stiffness to alter the system dynamics to better align the resonant motions to the task. Consequently, our experiments extend the existing research on human resonance sensitivity with data-based evidence to nonlinear systems. Our findings emphasize the human capabilities to apply control strategies to excite and exploit resonant motions in dynamic object interactions, including possibly shaping the dynamics through changes in muscle stiffness.

Voluntary forward-looking disclosures and default risk pricing

This study examines the effects of textual and numerical information contained in voluntary forward-looking management forecast reports (MFRs) on the pricing of default risk. We find that abnormal changes in credit default swap (CDS) premiums around MFR issuance dates are inversely associated with textual quality and the extent of positive textual news conveyed in the MFR. Furthermore, we find that the negative association of CDS premiums with either textual or numerical news is qualified by the MFR’s textual quality. Collectively, our evidence implies that CDS counterparties use textual quality to verify the quality of the information disclosed in both textual and numerical modes before impounding it into the default risk price. These findings suggest that multimodal verification can enhance the overall information quality of incentive-driven disclosures.

Stable generation of Core-Shell droplets in Coaxial Electrohydrodynamic Printing by Numerical Simulation and Jet Mode Recognition

Stable generation of Core-Shell droplets in Coaxial Electrohydrodynamic Printing by Numerical Simulation and Jet Mode Recognition

A fast and efficient pseudo-direct identification method for orthotropic elastic properties of multi-layered composite plates

New types of laminated composites are continuously being developed to meet various requirements involved in engineering applications. Before mass production of these new composite materials can take place, it is necessary to identify their elastic properties. Although current identification methods based on vibration tests and optimization algorithms are highly accurate, their high computation cost is a drawback. To address this issue, this paper proposes a new method to identify orthotropic elastic properties of multi-layered composite plates. The proposed method is based on the Modal Stability Procedure, using the experimental vibration frequencies and corresponding numerical mode shapes of structures. It converges after only two or three iterations without requiring an optimization algorithm. Therefore, the computational cost of the proposed method is significantly lower than that of optimization-based methods. The effectiveness and robustness of this method are demonstrated through three examples with different material, stacking sequences, and geometries including curved plate.

Structural response of half-scale pumice concrete masonry building: shake table/ambient vibration tests and FE analysis

Seismic performance evaluation of masonry structures is of paramount importance for ensuring the safety and resilience of buildings in earthquake-prone regions. There are limited number of studies on pumice elements in the literature. In addition, there are almost no studies investigating the earthquake behavior of pumice masonry building as a whole structure. In this context, a comprehensive understanding of their seismic response and dynamic characteristics has been lacking. To address this knowledge gap, a shake-table experimental campaign was undertaken, wherein half-scale pumice masonry building was exposed to simulated seismic forces. To enhance the experimental findings, numerical simulations were performed to confirm and expand our comprehension of how the pumice masonry structure responds to dynamic forces. Integrating both experimental and numerical outcomes provides a holistic understanding of how pumice masonry buildings behave during seismic events. At the end of the experimental study, the frequency values of the pumice model were observed to decrease up to 23.5% in the modes compared to the undamaged state. In the numerical model, this value decreases up to 19.85%. For the undamaged and damaged model, the first three experimental mode shapes were similar to the numerical mode shapes. Both experimental and numerical results show that the expected damages occur in the same regions. These results show that nonlinear FE models can be helpful in determining potential damage model locations. The findings have implications for the seismic design and retrofitting of similar traditional masonry buildings, facilitating the development of resilient and sustainable engineering solutions in seismic-prone regions.

Life Assessment of Deep-Sea Observation Windows under Different Design Considerations

As a key component of deep-sea manned submersibles, the observation window is usually constructed with polymethyl methacrylate (PMMA) material. During the design of the observation windows, the consideration of actual lifespan and its influential factors is insufficient. There are no clear provisions in the widely applied specifications. In this paper, based on the continuum damage mechanics model, combined with the viscoelastic relationship of PMMA material, a series of calculations were performed on the PMMA observation window. The parametric analysis of the fatigue crack-initiation life of the observation window at various thickness-to-diameter ratios (1.6, 1.4, 1.2, and 1.0), different friction coefficients (0.1, 0.2, and 0.3), and different transition arc radii (4000 mm and 6000 mm) was carried out. The calculated crack positions in the numerical mode used for validation closely align with those in the tested window. And simulation results show that the fatigue life of the observation window gradually decreases with the decrease in the thickness–diameter ratio and the increase in the friction coefficient. However, the increase in the transition arc radius will prolong the fatigue life of the observation window, which is higher than that of the original structure.

Analysis of deformation and failure mechanism of sandwich beams with lattice core under three-point bending load

This paper investigates sandwich beams with lattice cores under quasi-static bending, owing to their lightweight nature and high energy absorption capabilities. Utilizing analytical methods governing beams, an investigation into their failure mechanisms is conducted, incorporating experimental and numerical results. The influence of thickness and core cell sizes on energy absorption are examined. The analysis delves into the elastic and plastic behavior of the beam, which is refined and validated against the numerical and experimental tests and failure modes of sandwich panel beams. The alignment of analytical predictions with both experimental and numerical results in terms of mean forces, and energy absorptions was remarkably precise. Moreover, evidence has been presented that the face yield and core shear failure regions are significantly impacted by variances in core dimensions. Additionally, the thickness of core cell strands was found to be pivotal in influencing the compressive and shear strengths of sandwich panel beams.

An Improved Spectral Numerical Mode Matching Method for Simulating Fiber Bragg Gratings

An Improved Spectral Numerical Mode Matching Method for Simulating Fiber Bragg Gratings

Residual vector and solution mode analysis using semi-supervised machine learning for mesh modification and CFD stability improvement

Novel methods are studied to improve the performance of our previous mesh optimization approach for the stability improvement of unstructured-mesh finite-volume simulations. The residual vector as well as solution modes from Principal Component Analysis of solution vectors is analyzed for this purpose. After sufficient growth, instabilities appear as anomalies in the dominant numerical modes. Using standard classification algorithms, such outliers can be detected readily and much more efficiently compared to the eigenanalysis of the Jacobian matrix, which was required by the forebears of the current study. Further, it is essential to identify the correct local regions on the mesh for possible modification of vertex location and to remove the noise from the non-related cells. Hence, a synthetic vector is constructed from the working vector containing instabilities to simulate the behavior of the right eigenvectors in the solution. The results show the feasibility of residual vector analysis and principal component analysis of solution vectors for the stability improvement of finite-volume simulations. The new approach results in complete automation of the mesh optimization application.

Direct numerical simulation and mode analysis of turbulent transition flow in a compressor blade channel

The separation and turbulent transition of the flow in a compressor blade channel are investigated through direct numerical simulations (DNS) at a Reynolds number of 1.367 × 105. Based on the original DNS data, both time-averaged statistics and instantaneous vortex structures of the flow field are extensively analyzed. The vortices are visualized and studied by the Liutex method, and the streaming dynamic mode decomposition (SDMD), a low-storage variant of conventional DMD, is applied to the large datasets obtained on both pressure and suction sides. The physical quantity analyzed with SDMD is the Liutex magnitude R. The DNS results indicate that flow separation occurs on both sides of the blade. On the pressure surface, the separation is weak and the flow remains in a natural transition dominated by viscous Tollmien–Schlichting instabilities. In contrast, owing to the presence of a large laminar separation bubble, the flow experiences a separation transition governed by inviscid Kelvin–Helmholtz instabilities on the suction surface. The SDMD results suggest that a broad range of vortex frequencies exist in the transition flow, and the scale of the spatial structures is negatively correlated with the frequency of the mode. On the pressure surface, the extracted SDMD modes are primarily related to Kelvin–Helmholtz rolls, whereas on the suction side, influenced by the separated boundary layer, the modal structures exhibit greater diversity.

The Spectral Numerical Mode Matching Method for Simulating Concentric All-Fiber Sensor Structures With Metallic Films

The Spectral Numerical Mode Matching Method for Simulating Concentric All-Fiber Sensor Structures With Metallic Films

Influence of in-plane bending behaviour on textile composite reinforcement forming

The deformation of textile composite reinforcement is influenced by its fibrous composition. In-plane bending behaviour is an inherent aspect of textile reinforcement, yet it is frequently overlooked. The paper elucidates the significant influence of in-plane bending behaviour on fibre orientation during forming process and emphasizes the necessity of accounting for in-plane bending virtual work to prevent non-physical deformation mode. To this purpose in-plane bending calculation is implemented into a fibrous shell finite element by using the neighbouring elements method. Numerical spurious mode involving in-plane shear is avoided due to the new approach. Finally, the model is validated by comparing with composite reinforcement draping experiments: fibre orientations and distributions of shear angles are simulated in good agreement with experiments and give better results than the simulations neglecting the in-plane bending behaviour.

An Intelligent Automatic Sea Forecasting System Targeting Specific Areas on Sailing Routes

Sailing vessel navigators always want to receive state-of-the-art prompt and accurate marine weather-forecasting services. However, the weather-routing services by private sectors are expensive. Further, forecasting results from public institutes are usually free, and they are not in real-time or numerical modes, so they are not quite suitable for small-size or offshore vessels. In this study, an intelligent system was constructed for delivering sea forecasting at specific areas according to the navigator’s order. The system can automatically obtain web-based forecasting charts issued from multi-source meteorological agencies and convert the regional information into numerical text at requested points. During this step, several intelligent algorithms, like the OpenCV digital image processing algorithm and the YOLO wind vector deep learning recognition method, were applied. By applying this state-of-the-art system, navigators on board do not need to download different institutional graphics (usually with large stream bytes) to explore the future states of the sea surface in a specific area in the sailing route but can obtain the multi-source text forecasting information just by sending the area coordinates to a designated email address. The field tests confirmed that this auto-intelligent system could assist the navigator within a few minutes and thus greatly enhance the navigation safety with minor text-based communication costs. It is expected that by improving the efficiency of marine services and bringing in more artificial intelligence technology, maritime security would be more sustainable.

Asteroseismic g-mode period spacings in strongly magnetic rotating stars

ABSTRACT Strong magnetic fields are expected to significantly modify the pulsation frequencies of waves propagating in the cores of red giants or in the radiative envelopes of intermediate- and high-mass main-sequence stars. We calculate the g-mode frequencies of stars with magnetic dipole fields which are aligned with their rotational axes, treating both the Lorentz and Coriolis forces non-perturbatively. We provide a compact asymptotic formula for the g-mode period spacing and universally find that strong magnetism decreases this period spacing substantially more than is predicted by perturbation theory. These results are validated with explicit numerical mode calculations for realistic stellar models. The approach we present is highly versatile: once the eigenvalues λ of a certain differential operator are pre-computed as a function of the magnetogravity and rotational frequencies (in units of the mode frequency), the non-perturbative impact of the Coriolis and Lorentz forces is understood under a broad domain of validity and is readily incorporated into asteroseismic modelling.

Assessment of the rotational stiffness of single-riveted joints in a steel lattice girder by modal analysis

Wrought-iron and mild-steel riveted lattice girders are widespread structural components of the French metallic construction heritage of 1850–1930. Many rafters and purlins of roof structures of train sheds or market halls are made of flat and angle bars assembled with single-riveted joints. The assessment of the mechanical properties of those joints is key to sensitive and targeted retrofitting operations. Despite its influence on the buckling risk of lattice girders, the out-of-plane rotational stiffness of the joints has not been investigated yet. To fill this gap, experimental and numerical investigations based on modal analysis techniques were carried out on a riveted steel lattice girder dating from 1930. The measured natural frequencies and mode shapes were used to update a finite-element model of the girder. The results suggest that the single-riveted joints exhibit a rigid behaviour in the out-of-plane direction. When numerically varying the rotational joint stiffness, two indicators seem to be relevant, one based on the study of mode shapes, and the other one linked to the presence of additional numerical modes compared to the experimental measurements. Furthermore, a numerical study was conducted to assess the potential use of the findings to develop a modal-based damage detection method for riveted joints. With only one measurement point on each lattice web member, an indicator named ΔECOMAC, derived from the enhanced coordinate modal assurance criterion (ECOMAC) proposed in the literature, appears capable of detecting and localising one or several joints presenting a loss of stiffness. Overall, this paper shows that experimental modal analysis can be an efficient tool for assessing single-riveted joints in old steel lattice girders.

Dynamic Analysis of a High-Performance Prosthetic Leg: Experimental Characterisation and Numerical Modelling

In recent years, significant improvements in the design of leg blade prosthetics have been carried out. After several advances in material and topological optimisations, sport-purpose feet prosthetics have reached high-level performances, allowing athletes with limb loss to participate in various sport activities at a competitive level. Since the knowledge of prosthetic mechanical behaviour is crucial for its optimal design, specific studies are required to meet the anthropometric characteristics of the athlete. This research work is focused on investigating the dynamic behaviour of a running blade prosthetic and developing a validated prosthetic model, placing particular emphasis on the definition of suitable material properties. An experimental modal analysis is performed on the Cheetah Xcel, Össur lower limb prosthetic. In contrast with what has already been presented in the literature, a roving hummer test under free–free conditions is proposed here to avoid the uncertainties due to constraint conditions. For the first time, blade prosthetic dynamic characteristics in free–free conditions are presented. Additionally, a novel Finite Element model of the prosthetic is developed and tuned on the basis of the experimental results. The modal assurance criterion index is exploited to compare experimental and numerical mode shapes. Starting from frequency response functions, the first six mode shapes are experimentally identified in the frequency range up to 750 Hz, including both bending and torsion. As expected, the bending in the vertical plane constitutes the primary mode shape: this kind of flexion enhances energy storage, enabling athletes to achieve an optimal running gait. This study shows the dynamic modal behaviour of a lower limb prosthetic in free–free conditions and demonstrates that a traditional isotropic material is not suitable in describing its dynamic features. The development of a model that exploits orthotropic material properties improves the alignment between experimental and numerical outcomes. This result is in agreement with the material composition of the prosthetic, which consists of carbon fibre layers.

Combining uncertain machine learning predictions and numerical simulation results for the extreme value analysis of cyclone-induced wave heights – Application in Guadeloupe

Assessing return level RL (with return period typically ranging from 100 to 500 years) for extreme waves in cyclone-prone regions is often made problematic by the lack of sufficient representative samples to properly fit the extreme value probability distributions. Motivated by the Guadeloupe context (French West Indies), we address this problem when the wave numerical model is too expensive to be run a large number of times. A possible option is to use a machine learning (ML) model in place of the long-running numerical mode. By construction, ML predictions are however uncertain, because they are learned from a limited number of pre-calculated wave simulation results. We propose to account for this type of error along the inference of the parameters of the extreme value probability distribution within an Approximate Bayesian Computation (ABC) scheme. Using a subset of the database of numerically computed HS for Guadeloupe (for approximately 700 synthetic cyclones representative of 1000 years of cyclonic activity), we train a random forest (RF) regression model to relate the cyclone characteristics (radius, atmospheric pressure, distance to cyclone eye) to HS. The quantile RF model is then used to model the prediction error within the ABC scheme. By comparison to the 100-year and 500-year RL reference solutions (calculated using the entire database), we show that the ML-based approach achieves low bias and high reliability of the RL estimates at locations both along Guadeloupe coasts and in deep ocean environments for low sample size (down to ∼70). Provided that the prediction error is low-to-moderate, integrating this type of uncertainty improves the performance of the ML-based approach, and decreases the computational burden of the return level estimation.

Effect of steel grid on enhancing seismic performance of bridge pier with low reinforcement ratio: Shaking table test and numerical simulation

The railway bridge piers with large cross section and low reinforcement ratio are easy to damage under earthquakes in China. The steel grid has been proved to be an effective strengthening method to improve the cyclic behavior using quasi-static test. In this study, shaking table tests were conducted to investigate the seismic response of three pier specimens. Experimental results indicated that the steel grid delayed the crack development and occurrence of uplifting-rocking phenomenon for the railway pier. For strengthened piers, about 7.5%-51.4% reduction, 9.1%-21.9% and 7.6%-27.4% enhancement is measured for displacement of pier top, acceleration of pier top and energy dissipation. To obtain the effect of design parameter variation of steel grid on seismic damage (i.e., the horizontal distance between steel grid and the surface of pier specimen, steel grid area and vertical spacing of steel grid), the numerical analysis mode of strengthened pier was established. The mechanical model of steel grid obtained by deriving the equivalent spring calculation method is used in the numerical simulation model. The results show that the horizontal distance variety between steel grid and surface of pier specimen has the most obvious impact to strengthening effect, while the vertical spacing of steel grid is the least. The smaller horizontal distance between steel grid and the surface of pier specimen, the higher steel grid area and shorter vertical spacing of steel grid are the most significant to reduce the different damage probability of the bridge pier.