Forced Response Research Articles

MULTI-AEROELASTIC PHENOMENA MODELLING PART I: THE DEVELOPMENT OF WHOLE LPC MODEL FOR CIVIL TURBOFAN ENGINE

Abstract Aeroelastic phenomena in the low pressure compression (LPC) system of civil turbofan engines can cause a significant high cycle fatigue (HCF) risk to LPC components. Currently, the mechanical integrity risk to the LPC components is assessed by performing multiple, discrete aeromechanical simulations, which require large resources and incur high time cost. Therefore, the development of a comprehensive modelling simulation approach is necessary to assess multiple phenomena and components simultaneously that can provide accurate results within design timescales. This paper presents the methodology for generating a common, system level model for investigating multiple aeroelastic phenomena in fan and outlet guide vanes (OGVs). The development of a high fidelity, full annulus CFD model of the whole low pressure compression system is described. Time accurate unsteady CFD simulations are then conducted at multiple flight conditions. These information-rich simulation models are interrogated to extract various parameters of interest to assess multiple aeroelastic phenomena such as, 1EO fan forced response, fan alternating passage divergence (APD) forced response, OGV buffet, and OGV resonant forced response etc. In the second part of this paper, the application of this modelling methodology is demonstrated to evaluate and to better understand the efficacy of OGV asymmetric cyclic patterns.

Impact of sacroiliac interosseous ligament tension and laxity on lumbar spine biomechanics under vertical vibration: a finite element study

Objective To investigate the impact of tension and laxity in the sacroiliac interosseous ligament on lumbar spine displacement and force response in vibration environments. Methods A finite element model of the lumbar-pelvis, previously crafted and rigorously validated, was used to simulate ligament tension and laxity by adjusting the elastic modulus of the SIL under a sinusoidal vertical load of ±40 N at 5 Hz. Comparisons of lumbar spine horizontal and axial displacements as well as annulus fibrous stress, nucleus pulposus pressure, and facet joint force were performed, respectively. Results With the elastic modulus of the SIL varying by +50, −50, and −90%, the maximum vibration amplitude changed by +20.00, −175.00, and −627.27% for lumbar horizontal displacement, +30.00, −157.14, and −627.22% for lumbar axial displacements, +5.88, −19.35, and −245.16% for annulus fibrous stress, +10.00, −25.00, and −157.14% for nucleus pulposus pressure, as well as +6.54, −20.13, and −255.37% for facet joint force, respectively. Conclusion In contrast to static environments, large laxity of the SILs not only diminishes lumbar spine stability in vibrational settings but also significantly amplifies dynamic loads, thereby heightening the risk of lumbar spine vibratory injuries and low back pain disorders.

A robust hybrid estimation method for local bearing defect size based on analytical model and morphological analysis.

This paper presents a robust hybrid method using an analytical model and morphological analysis for estimating defect sizes on bearings, addressing inaccuracies in traditional peak-based approaches. First, a spatial contact analytical model is developed to analyze roller movement through defects. Numerical results indicate that radial defect sizes significantly impact dual-impulse intervals for accurate estimation, while axial size has minimal effect. An analysis of contact deformation, force, and vibration response reveals that the defect entry aligns before the first low-frequency peak, and the exit aligns after the first high-frequency peak, preceding the second low-frequency peak. Finally, testing of the derived model on four samples, incorporating vibration characteristics and geometry, achieves a minimum estimation error of 0.03%, demonstrating high accuracy and practical value.

Aerosol-Induced Changes in Atmospheric and Oceanic Heat Transports in the CESM2 Large Ensemble

Abstract The total poleward energy transport (PET) is set by the top of atmosphere radiation flux and is therefore sensitive to any process which can alter those fluxes, particularly in the shortwave. One example is the direct and indirect effects of anthropogenic aerosols, which increase the local reflection of solar radiation back into space. The historic emission of sulfur dioxide, which peaked in the northern midlatitudes during the 1980s, has been proposed as a primary contributor to historic anomalies in cross-equatorial energy transport, as well as related processes such as a shift in the tropical rainband. In this study, we analyze simulations from the Community Earth System Model, version 2 (CESM2), large ensemble and single-forcing projects to better understand the forced response of PET to historical forcings. First, analysis of the single-forcing project reveals that the position of the intertropical convergence zone (ITCZ) responds in a nonlinear manner to greenhouse gas forcing in CESM2. This type of nonlinearity has been found previously in the context of the aerosol-only simulations in the CESM2 single-forcing project but may be the first identification of a similar effect in the greenhouse gas–only simulations. Second, through analysis of the full CESM2 large ensemble simulations, we find that anomalous heat transport occurred in both the atmosphere (through the mean meridional circulation and atmospheric eddies) and the oceans (through the Atlantic and Indo-Pacific sectors) due to a variety of related processes including the Hadley cells, the midlatitude storm tracks, the Atlantic meridional overturning circulation (AMOC), and the Pacific wind-driven subtropical gyre. Significance Statement In this study, we investigate how the Earth system changed the transport of energy from the tropics to the poles in response to historic pollution. We analyze a large number of climate model simulations of the recent past (1850 to present) and find that historic emissions of sulfur dioxide caused the model to transport more energy in the form of stronger ocean currents, stronger storms, and stronger prevailing winds. This is because the modeled currents in the Atlantic were too sensitive to historic pollution and transported too much warm water northward.

Emergence of biphasic versus monotonic response of actin retrograde flow and cell traction force with varying substrate rigidity

Emergence of biphasic versus monotonic response of actin retrograde flow and cell traction force with varying substrate rigidity

Non-linear dynamic behavior of T0 and T90 mesopelagic trawls based on the Hilbert–Huang transform

Although adopting the T90 mesh orientation on the trawl net can improve the selectivity of the trawl codend, it is unknown whether the T90 mesh orientation influences the dynamic behavior of the trawl system. Therefore, this study uses non-linear dynamic analysis to examine the effect of mesh orientations, mesh size, and twine diameter on the mesopelagic trawls' fluttering motions and hydrodynamic force responses. Three trawls are designed with different mesh orientations (T0 and T90), mesh sizes (40 mm and 60 mm), and twine diameters (0.96 mm and 1.11 mm) on the codend and codend extension sections of the trawl model based on Tauti's law. These trawls are tested in a flume tank under various flow velocities and catch sizes. A time-frequency analysis method based on the Hilbert–Huang transform is utilized to analyze each trawl's dynamic responses, including motions and drag force responses. The results are compared with those obtained through Fourier analysis using power spectral density. The results highlight that the oscillation amplitude of the surge motion of the T90 trawl is higher than that of the T0 trawl. In contrast, the T90 trawl's heave motion oscillation amplitude is smaller. The dominant frequency of the periodic high-energy coherent structures of the surge and heave motions are detected at a low frequency. The surge and heave motions of the T0 trawl have a greater response to the current components with lower frequencies than that of the T90 trawl. An increase in mesh size, a decrease in twine diameter, and a change in mesh orientation decrease the drag force. The inherent characteristic oscillations of the drag force response for the three trawl models are synchronized with the low-frequency characteristic of surge and heave motions. The gravity periods of the low-frequency mode components of drag force, surge motion, and heave motion for the T90 trawl are higher than those for the T0 trawls. In other words, the T90 trawl is more stable and selective than the T0 trawl. The findings of this study offer important information for comprehending and enhancing the selectivity of trawls in marine mesopelagic fisheries, particularly for exposing the effects of mesh orientation and design parameters on trawl performances.

Real-time prediction of structural responses in deep-water jacket platforms using Ada-STLNet: A comprehensive analysis with prototype monitoring data

Real-time prediction of the mechanical behaviors based on prototype monitoring data is crucial for ensuring the integrity and safety of deep-water jacket platforms. As complex nonlinear systems, these platforms’ response exhibit varying temporal trends, dynamic spatial correlations, and load dependencies. This makes accurate prediction of future axial force and bending moment responses a significant challenge. In this paper, a novel deep learning method called Adaptive Spatio-Temporal Load Network (Ada-STLNet) is proposed aiming to address the issue of multi-node axial force and bending moment response prediction of deep-water jacket platform. Our model utilizes an enhanced graph convolution (EGCN) and self-attention mechanism for efficient spatial correlation modeling in multi-node response, LSTM for long sequence temporal feature capture. It integrates spatial and temporal, along with load-aware modules to capture intricate patterns in structural responses. Additionally, a multi-gated coupling mechanism with two independent gating modules is designed to adaptively represent the complex dependencies of structural responses, ensuring model stability and robustness. Extensive experiments conducted on prototype structural monitoring data from a deep-water jacket platform in the South China Sea demonstrate that Ada-STLNet outperforms six traditional models, including HA, SVR, KNN, MLP, LSTM, and GRU, across various prediction steps. The proposed model exhibits superior accuracy, particularly in short-term predictions, achieving up to 62.80% improvement in MAE and 48.11% in RMSE for axial force predictions compared to the second-best model. Ablation studies confirm the effectiveness of each component within Ada-STLNet. This research highlights the potential of Ada-STLNet for reliable and accurate prediction of structural responses, contributing significantly to the field of marine engineering.

A high sensitivity, low cost and fully decoupled multi-axis capacitive tactile force sensor for robotic surgical systems.

This paper presents the design of a multi-axis capacitive tactile force sensor with a fully decoupled output response for input normal and shear forces. A patterned elastomer is used as a dielectric layer between capacitive electrodes of the sensor that allows to achieve relatively higher sensitivity. The sensor is fabricated utilizing a low-cost rapid prototyping technique and is characterized for normal and shear forces in the range of 0 ~ 10 N and 0 ~ 3.1 N respectively. The achieved force sensitivity for the normal axis is 2.03%/N and for shear axes is 1.67%/N. The difference between the estimated force from the sensor and actual force applied is negligible, which demonstrates the accuracy of the sensor. The reliability of the sensor is analysed by performing hysteresis and repeatability tests. The hysteresis error is found to be 4.94% and 4.69% for normal and shear forces respectively. The repeatability error of the sensor is less than 5%, which shows the stability of the sensor. The high sensitivity, linear output response, high force measurement range, reliability and low cost make the proposed tactile sensor suitable for the force feedback in the robotic surgical systems.

Lessons Learned for Developing an Effective High-Speed Research Compressor Facility

Few universities in the world conduct experimental research on high-speed, high-power turbomachinery. The Purdue High-Speed Compressor Research Laboratory has a longstanding tradition of partnering with industry sponsors to perform high-TRL (technology readiness level) experiments on axial and radial compressors for aerospace applications. Early work in the laboratory with Professor Sanford Fleeter and Professor Patrick Lawless involved aeromechanics and the addition of a multistage axial compressor facility to support compressor performance studies. This work continues today under the guidance of Professor Nicole Key. While other universities may operate a single-stage transonic compressor or a low-speed multistage compressor, the Purdue 3-Stage (P3S) Axial Compressor Research Facility provides a unique environment to understand multistage effects at speeds where compressibility is important. Over the last two decades, several areas of important research within the gas-turbine engine industry have been explored: vane clocking, stall/surge inception, tip-leakage/stator-leakage (cavity leakage) flow characterization, and forced response, to name a few. This paper addresses the different configurations of the facility chronologically so that existing datasets can be matched with correct boundary conditions and provides an overview of the different upgrades in the facility as it has developed in preparation for the next generation of small-core compressor research.

A Dynamical Adjustment Approach to Estimating Forced and Internal Variability in the North Atlantic

Abstract Quantifying the relative contributions of external forcing and internal variability to North Atlantic sea surface temperature (NASST) has important implications for attributing and predicting climate changes around the North Atlantic basin. Many previous methods have approached this problem by estimating the externally forced signal directly, making assumptions about forced variability for which there is no consensus. In this work, the separation of variability is approached in a fundamentally different way that does not specify the forced response’s temporal evolution. We propose a dynamical adjustment method in which the internal, spatially uniform component of NASST is predicted based on patterns of NASST that are orthogonal to the spatially uniform pattern. When applied to preindustrial simulations, the dynamical adjustment demonstrates skill in reconstructing the NASST basin-mean variability. Applying the dynamical adjustment to historical simulations demonstrates skill in a majority of climate models although the skill is reduced relative to preindustrial simulations because external variability partly contaminates the predictors. The dynamical adjustment is compared to several other methods which directly estimate the externally forced signal. We find that dynamical adjustment performs similarly to these comparative methods despite the fundamentally different prediction method. However, methods based on different principles yield considerably different estimates of external and internal variability.

On the suitability of rigorous coupled-wave analysis for fast optical force simulations

Abstract Optical force responses underpin nanophotonic actuator design, which requires a large number of force simulations to optimize structures. Commonly used computation methods, such as the finite-difference time-domain method, and finite element methods, are resource intensive and require large amounts of calculation time when multiple structures need to be compared during optimization. This research demonstrates that performing optical force calculations on 2D-periodic structures using the rigorous coupled-wave analysis method is typically on the order of 10 times faster than other approaches and with sufficient accuracy to suit optical design purposes. Moreover, this speed increase is available on consumer grade laptops, avoiding the need for a high performance computing resource.

Quasinormal mode expansion in thin elastic plates

Elastic wave manipulation using large arrays of resonators is driving the need for advanced simulation and optimization methods. To address this we introduce and explore a robust framework for wave control: quasinormal modes (QNMs). Specifically, we consider the problem for thin elastic plates, where the Green's function formalism is well known and readily exploited to solve multiple scattering problems. By studying the associated nonlinear eigenvalue problem we derive a dispersive QNM expansion, providing a reduced-order model for efficient forced response computations which reveals physical insight into the resonant mode excitation. Furthermore, we derive eigenvalue sensitivities with respect to resonator parameters and apply a gradient-based optimization to design quasi-bound states in the continuum and position eigenfrequencies precisely in the complex plane. Scattering simulations validate our approach in structures such as graded line arrays and quasicrystals. Drawing on QNM concepts from electromagnetism we demonstrate significant advances in elastic metamaterials, highlighting their potential for tailored wave manipulation. Published by the American Physical Society 2024

Fan Non-Synchronous Forced Vibration Under Crosswind

Abstract In this paper, a new aeroelastic phenomena for fans, referred to as non-synchronous forced vibration (NSFV), is presented. This type of aeroelastic instability can occur at high crosswind conditions when the flow at the intake lip separates and the disturbances caused by flow separation become unsteady. The results show that in the presence of unsteady separation in the intake, the fan can experience non-synchronous frequency excitations, which can result in resonant response in modes that are not identified by the Campbell diagram. The findings are corroborated by aeroacoustic theories. To the best of authors knowledge, this is the first time that fan forced response due to unsteady distortion is studied and the findings can unlock some of unexplained and unexpected vibrations experienced by engines.

Observed Responses of Gravity Wave Momentum Fluxes to the Madden‒Julian Oscillation Around the Extratropical Mesopause Using Mohe Meteor Radar Observations

AbstractThe 12‐year continuous observation of gravity wave momentum fluxes (GWMFs) estimated by the Mohe meteor radar (53.5°N, 122.3°E) revealed prominent intraseasonal variability around the extratropical mesopause (82–94 km) during boreal winters. Composite analysis of the December‒January‒February (DJF) season according to the Madden‒Julian Oscillation (MJO) phases revealed that the zonal GWMFs notably increased in MJO Phase 4 (P4) by ∼2–4 m2/s2, and a Monte Carlo test was designed to examine the statistical significance. The response in zonal winds lags behind the GWMF response by two MJO phases (i.e., 1/2π), indicating a “force‒response” interaction between them. Additionally, time‐lagged composites revealed that strengthened westward GWMFs occurred ∼25–35 days after MJO P4, coincident with the MJO impact on the zonal winds in the stratosphere. The analysis results also suggested that the mechanism of MJO by which the MJO influences the stratospheric circulation might involve poleward propagating effects of stationary planetary waves with zonal wavenumber one. This work emphasizes the importance of GW intraseasonal variability, which impacts tropical sources from the troposphere to the extratropical mesopause.

Improving flexible actuating behaviors of gel-based artificial muscles through chamomile polysaccharide crosslinking

Abstract The flexible actuating behaviors of gel-based artificial muscles (GBAMs) are contingent upon the properties of their hydrogel actuating membranes. While the current preparation system for these membranes is deemed flawless, the electromechanical characteristics are constrained by the inherent properties of the material. The majority of raw materials used in this process are chemically synthesized; however, Chinese herbal polysaccharides offer a convenient, environmentally friendly, and non-toxic alternative, making them a prime candidate for actuating membrane preparation. The biological activities of chamomile polysaccharide (CP) include anti-inflammatory, lipid-lowering, sugar-lowering, and OH- clearance properties. Therefore, the actuating membrane of GBAM was prepared by crosslinking sodium alginate (SA) with CP. The findings indicated that at a crosslinking ratio of 4:5 for CP-SA, the electrically actuated force density and response speed reached 20.12 mN/g and 0.09 mN/g·s, respectively. Additionally, the working life extended to 781 seconds, tremor frequency decreased by 47.67%, and tremor amplitude was 19.55% of the control group. The elastic modulus was measured at 15.44 MPa, specific capacitance reached 183.99 mF/g, and internal resistance decreased by 13.44%. Charge and discharge time was 5.73 seconds, maximum energy reached 2.7 J, and specific energy was 12.66 A·J/g, representing increases of 2.3 seconds, 64.63%, and 6.47 A·J/g compared to the control group. The deflection displacement of 6.62 mm in the CP-SA group at a crosslinking ratio of 4:5 was found to be 3.06 times greater than that of the control group. In conclusion, the actuating membrane of GBAM, synthesized through the cross-linking of CP with SA at a specific ratio, demonstrated superior properties. This innovation offers a novel perspective and direction for the advancement of GBAMs and is anticipated to significantly contribute to future developments in related fields.

Utilizing tuned mass damper for reduction of seismic pounding between two adjacent buildings with different dynamic characteristics

Today, population growth and the need for constructing adjacent buildings have raised the likelihood of pounding between adjacent buildings with different dynamic characteristics. The pounding force applied to adjacent buildings during an earthquake is intensive and may cause total or partial damage to structural elements, leading to collapse. It disturbs and complicates the functioning of buildings during and after an earthquake. Therefore, the main aim of this paper is to minimize and, if possible, eliminate the pounding force between two adjacent structures by considering three objective functions. For this aim, the tuned mass damper is utilized here. Also, this paper aims to reduce the number of collisions between different stories of adjacent buildings through a tuned mass damper system. For this purpose, two adjacent steel moment frames with six and ten stories are nonlinearly modeled and validated using the concentrated plasticity model in OpenSees. Moreover, the pounding element is nonlinearly modeled and validated. Then, tuned mass dampers (TMDs) are used on the roofs of the structures. They are optimized in stiffness, mass, and damping coefficient using the grey wolf optimization (GWO) algorithm. Nonlinear time history analysis (NLTHA) is performed under nine far- and near-field earthquakes. The pounding force and structural responses are analyzed, including maximum story acceleration, maximum inter-story drift, and base shear in the TMD-controlled and uncontrolled adjacent buildings. Finally, the Park-Ang damage index is evaluated for the structures with and without the TMD system. It has been found that the maximum pounding force, the maximum acceleration of the stories, the base shear, the drift ratio, and the number of collisions significantly reduce (or omit) in the presence of TMDs when the objective function is considered to be the minimization of the maximum pounding force. It is shown that the maximum pounding force generally declines to zero for this objective function.

High-speed microactuation in a supersonic dual-stream jet flow

Supersonic shear layers experience instabilities that generate significant adverse effects; in complex configurations, these instabilities have global impacts as they foster compounding complications with other independent flow features. We consider the flow near the exit of a dual-stream rectangular nozzle. The supersonic core and sonic bypass streams mix downstream of a splitter plate trailing edge (SPTE) just above an adjacent deck. We perform two-dimensional direct numerical simulations with laminar inflow conditions to parametrically explore the influence of active flow control, considering various actuation angles and locations. The goal is to alleviate the prominent tone associated with vortices shed at the SPTE; these vortices initiate an unsteady shock system that affects the entire flow field through a shock-induced separation and the downstream evolution of plume shear layers. Resolvent analysis is performed on the baseline flow. The identified optimal response guides the placement of steady-blowing actuators. Since the resolvent analysis fundamentally investigates the input–output dynamics of a system, it is also utilized to uncover actuation-induced changes in the forcing–response dynamics. Spectral analysis shows that the baseline flow fluctuating energy is concentrated in the shedding instability. Actuating at optimal angles based on location disperses this energy into various flow features; this affects the shedding itself, and the structure and unsteadiness of the shock system, and thus the response of the deck and nozzle wall boundary layers and the plume. The resolvent analysis indicates, and Navier–Stokes solutions confirm, that favourable control is obtained by either indirectly or directly mitigating the baseline instability.

No Evidence of Winter Warming in Eurasia Following Large, Low-Latitude Volcanic Eruptions during the Last Millennium

Abstract We critically reexamine the question of whether volcanic eruptions cause surface warming over Eurasia in winter, in the light of recent modeling studies that have suggested internal variability may overwhelm any forced volcanic response, even for the very largest eruptions during the Common Era. Focusing on the last millennium, we combine model output, instrumental observations, tree-ring records, and ice cores to build a new temperature reconstruction that specifically targets the boreal winter season. We focus on 20 eruptions over the last millennium with volcanic stratospheric sulfur injections (VSSIs) larger than the 1991 Pinatubo eruption. We find that only 7 of these 20 large events are followed by warm surface temperature anomalies over Eurasia in the first posteruption winter. Examining the 13 events that show cold posteruption anomalies, we find no correlation between the amplitude of winter cooling and VSSI mass. We also find no evidence that the North Atlantic Oscillation is correlated with VSSI in winter, a key element of the proposed mechanism through which large, low-latitude eruptions might cause winter warming over Eurasia. Furthermore, by inspecting individual eruptions rather than combining events into a superposed epoch analysis, we are able to reconcile our findings with those of previous studies. Analysis of two additional paleoclimatic datasets corroborates the lack of posteruption Eurasian winter warming. Our findings, covering the entire last millennium, confirm the findings of most recent modeling studies and offer important new evidence that large, low-latitude eruptions are not, in general, followed by significant surface wintertime warming over Eurasia.

On the Inverse Correlation Between the Thermosphere Winter Helium Bulge and Solar Activity: Impact of Gravity Wave Drag From the Mesosphere

AbstractUnderstanding the temporal and spatial variations in the ideal inert tracer helium can provide insight into the dynamic evolution of the thermosphere. The magnitude of the thermospheric winter helium bulge was inversely correlated with the level of solar activity. However, this feature has been found to be not reproduced by the Thermosphere‐Ionosphere Electrodynamic General Circulation Model (TIEGCM), and the associated physical mechanisms remain unknown. Using the Thermosphere‐Ionosphere‐Mesosphere Electrodynamic General Circulation Model (TIME‐GCM), we found that mesospheric gravity wave drag (GWD) is a factor contributing to this inverse correlation. Specifically, the summer‐to‐winter circulation in thermosphere becomes the main cause of the helium bulge, as mesospheric GWD can play a role in strengthening this circulation. The GWD contributions to temperature change below the lower thermosphere do not depend prominently on solar activity. However, because the temperature impacts on the pressure gradient force are height‐integrated according to the background temperature of the neutral gas, the higher background temperature in the thermosphere at the solar maximum corresponds to a relatively weaker response in pressure gradient force in the thermosphere. Therefore, the response of the thermospheric circulation that might be expected to accompany increasing solar activity is suppressed due to the influence of mesospheric GWD, which results in a decrease in the magnitude of the winter helium bulge with increasing solar activity. Thus, our results demonstrated that lower atmosphere forcing can play a significant role in the response of thermospheric helium to solar activity.

Data-driven modeling of subharmonic forced response due to nonlinear resonance

Complex behavior in nonlinear dynamical systems often arises from resonances, which enable intricate energy transfer mechanisms among modes that otherwise would not interact. Theoretical, numerical and experimental methods are available to study such behavior when the resonance arises among modes of the linearized system. Much less understood are, however, resonances arising from nonlinear modal interactions, which cannot be detected from a classical linear analysis. Academic examples of such phenomena have been known, but no systematic method has been developed to detect and model nonlinear resonant interactions purely from numerical or experimental data. Here, we develop such a data-driven methodology that identifies nonlinear resonant response on low-dimensional spectral submanifolds (SSMs) of the dynamical system. Our approach is generally applicable to nonlinear resonances, but we specifically focus here on one particular behavior: subharmonic response in forced nonlinear systems without any resonance among the linearized frequencies of the unforced system. We first illustrate analytically how such a response is born out of a nonlinear resonance hidden in the conservative limit of the system. We then show how this effect can be identified and modeled purely from data. As our main example, we isolate and model previously unexplained response patterns in fluid sloshing experiments.