Steady-state Dynamics Research Articles

Enhancing fluid distribution in additively manufactured heat exchangers using autogenerated geometries

The heat exchanger distributor, which connects the tube carrying the medium to the heat transfer geometry, has received less attention in research studies compared to heat transfer geometries. However, the flow distribution is critical to efficiency. Therefore, a model-in-the-loop approach is presented to optimize additively manufactured distributors. A quasi-fractal distributor and all connected geometries, including pipe connections, heat transfer geometry and collector, are meshed and simulated in OpenFOAM using steady-state computational fluid dynamics. The volumetric flow rates determined from the simulation are assigned to the respective flow cross-sections during the distribution process. The flow cross-sections of the geometric model are modified within an optimization process, considering the prevailing volumetric flows. The results indicate a 64 % decrease in the standard deviation of volume flow across all 85 channels with a simple optimizer and few simulation loops. The printable geometry can be extracted directly out of Python using common file formats. The presented workflow has been proven feasible. Future improvements could involve using the automated model-in-the-loop simulation and creating optimizing algorithms considering fluid flow behavior.

Fidelity of Finite Element–Based Virtual Tire Assembly Models Used for Vehicle Noise, Vibration, and Harshness Structural-Borne Noise Performance Considering Vibrational Modal and Steady-State Dynamic Simulation

ABSTRACT The increasing presence of battery electric vehicles brings about new challenges to the noise, vibration, and harshness performance of tires. One of the new challenges involves the expansion of frequency range for structural-borne noise virtual predictions. Current standard virtual tire simplifies the tire geometry as an axisymmetric body, neglecting the effect of complex tread pattern. It is perceived that this simplification can lead to prediction error for a tire’s structural-borne noise performance at mid-frequency range (250∼500 Hz). This study investigates how different tread pattern representation affects the structural-borne noise prediction. This study uses linear, steady-state dynamics finite element simulations of a modified SAE J2710 test and traveling sinusoid test. The resulting frequency responses of the virtual tires and the computational time to obtain each frequency response are compared. The comparison shows that while including the 3D tread pattern does show some differences under certain conditions, it is not necessary to use this technique for every case, especially during the early evaluation stage.

Analysis of steady-state dynamics and stability of particle dampers considering the friction effect

This study analyzes the steady-state dynamics and stability of a structure with a particle damper considering the friction effect between the particle and container, with a focus on whether the system can maintain stable-state motion for an extended period. The determination of friction’s contribution and the maximum allowable gap clearance for steady-state motion is demonstrated through the solution of motion of the primary structure with a particle damper subjected to low-frequency vibration conditions. Additionally, stability analysis is conducted to assess if initial disturbances cause deviations from the original stable state and identify necessary parameters for stability when the system parameters are uncertain. Analytical descriptions for the stability of the system are derived. The effects of friction on the dynamics and stability regions of the particle dampers are systematically revealed, where the theoretical and numerical models are mutually verified and supported by the cases of previous studies. Results show that the inclusion of the rolling friction effect will disrupt the steady-state motion as gap clearance approaches the optimal value. As the coefficient of rolling friction increases, the stability region’s area gradually decreases with a notable leftward shift of its right boundary. This shift ultimately leads to a leftward shift in the optimal vibration reduction curve. In the range of gap clearance variation allowing for steady-state motion with two symmetrical impacts per cycle, the relative velocity of the particle is more effective and intuitive to reveal the vibration reduction mechanism of particle dampers than other perspectives such as momentum, energy, and phase.

Applying assessment methods to diversified farming systems: Simple adjustment or complete overhaul?

In response to criticism of current specialized and input-intensive agriculture, diversified farming systems (DFS) have increased in popularity. The most advanced forms of DFS include perennial components (e.g., perennial crops, trees), functionally different plants and livestock, and landscape heterogeneity. These characteristics make it more difficult to assess DFS in agricultural sciences, which have focused to date mainly on low-diversity systems. We provide an overview of the main methodological issues involved in assessing DFS, and their potential solutions. We identify five key methodological challenges for assessing DFS: i) combining conceptual frameworks from different disciplines to develop a holistic view of DFS multi-performance; ii) characterizing DFS structure from a functional perspective to define the relevant spatial extent to assess them; iii) considering DFS ontogeny i.e. the time required for DFS to establish, reach maturity and achieve a dynamic steady state when assessing their performance; iv) aggregating and mapping multiple performance indicators to integrate the range of products and services generated by DFS and to reveal potential synergies and antagonisms; v) defining and characterizing the reference systems used to compare DFS, as systems might differ in history, composition, management, soil-climate, and sociotechnical conditions. These challenges underline the need to overhaul assessments in agricultural sciences (e.g., agronomy, animal science, economics, ecology) to identify whether, and under what conditions, DFS are relevant and sustainable options for farmers. They also come with available options for researchers to proceed with this overhaul.

Reconstituting the dynamic steady states of actin networks in vitro.

Reconstituting the dynamic steady states of actin networks in vitro.

Inertia suppresses signatures of activity of active Brownian particles in a harmonic potential.

A harmonically trapped active Brownian particle exhibits two types of positional distributions-one has a single peak and the other has a single well-that signify steady-state dynamics with low and high activity, respectively. Adding inertia to the translational motion preserves this strict classification of either single-peak or single-well densities but shifts the dividing boundary between the states in the parameter space. We characterize this shift for the dynamics in one spatial dimension using the static Fokker-Planck equationfor the full joint distribution of the state space. We derive local results analytically with a perturbation method for a small rotational velocity and then extend them globally with a numerical approach.

On the Efficiency Impacts of Berthing Priority Provision

Facing intensified interport competition in the global container shipping market, an increasing number of ports choose to offer berthing priority for carriers to increase their attractiveness. This study is the first to theoretically analyze the efficiency impacts of such prioritization. Specifically, this study models the steady-state dynamics for each terminal in a biterminal port as a prioritized queuing system. We explore the equilibrated shipping flow distribution and resulting total system cost (i.e., bunker consumption cost and waiting time cost) with and without priority provision, along with their major analytical properties. Then, we examine the “second-order” effects of these priority schemes on just-in-time (JIT) arrivals, an increasingly popular green port management tool. Specifically, we investigate how the equilibrium state associated with JIT arrivals could change with priority berthing. These analyses generate some interesting results, including (1) the total system cost increases or remains unchanged when a priority scheme is implemented under a symmetric port with equal service capacities for both terminals; (2) under the asymmetric biterminal case, however, it is also possible that berth prioritization could reduce the total system cost, and such phenomenon occurs only if the terminal which offers prioritization owns larger service capacity; (3) the results indicate that the “price of prioritization” could reach [Formula: see text] in port operation when the berth loading is heavy, implying that priority provision may significantly harm the operational efficiency; and (4) lastly, priority provision has a negative second-order effect on JIT strategies in a symmetric port, and such negative effect may neutralize the positive ones. Those theoretical results are validated by numerical experiments, and some of them are also supported by empirical data. The results provide important practical implications for the decision making of the port (or terminal) agencies. Funding: This work was supported by the National Natural Science Foundation of China [Grants 72371143 and 72188101]. Supplemental Material: The online appendix is available at https://doi.org/10.1287/trsc.2022.0411 .

Chloroplast thiol redox dynamics through the lens of genetically encoded biosensors.

Chloroplasts fix carbon by using light energy and have evolved a complex redox network that supports plastid functions by (i) protecting against reactive oxygen species and (ii) metabolic regulation in response to environmental conditions. In thioredoxin- and glutathione/glutaredoxin-dependent redox cascades, protein cysteinyl redox steady states are set by varying oxidation and reduction rates. The specificity and interplay of these different redox-active proteins are still under investigation, for example to understand how plants cope with adverse environmental conditions by acclimation. Genetically encoded biosensors with distinct specificity can be targeted to subcellular compartments such as the chloroplast stroma, enabling in vivo real-time measurements of physiological parameters at different scales. These data have provided unique insights into dynamic behaviours of physiological parameters and redox-responsive proteins at several levels of the known redox cascades. This review summarizes current applications of different biosensor types as well as the dynamics of distinct protein cysteinyl redox steady states, with an emphasis on light responses.

Formation mechanism of α particles in glycogen: Testing the budding hypothesis by Monte-Carlo simulation

Glycogen, a complex branched glucose polymer and a blood-sugar reservoir in animals, comprises small β particles joined together into composite α particles. In diabetic animals, α particles fragment more easily than those in healthy animals. Finding evidence for or against postulated mechanisms for α-particle formation is thus important for diabetes research. Insight into this is obtained here using Monte-Carlo simulations, including addition and loss of glucose monomer, branching and debranching, based on earlier simulations which were in acceptable agreement with experiment [Zhang et al., Int J Biol Macromolecules 2018, 116, 264]. One postulated mechanism for α-particle formation is “budding”: occasionally a glucan chain temporarily protrudes from the particle, and if its growing end is sufficiently far from its parent particle, it propagates to a new linked particle. We tested this by simulations in which an “artificial” bud (a chain extending well outside the average particle radius) is added to a glycogen molecule in a dynamic steady state, and the system allowed to evolve. In some simulations, the particle reached a new steady state having an irregular dumbbell shape: a rudimentary α particle. Thus ‘budding’ is a possible mechanism for α particles to form. If no simulations had shown this behaviour, it would have refuted the postulate.

Development of a steady-state computational fluid dynamics solver for transonic rotorcraft flows

The capability for solving compressible fluid flows in the rotating frame of reference is added to an existed open-source CFD solver, namely, HiSA solver. The new implementation is explained and validated using the experimental data of the Sikorsky S-76 rotor. A comparison is presented between the moving mesh results obtained from the original HiSA code and the single rotating frame results achieved through the new implementation. The comparison includes an analysis of torque and thrust values, as well as computational costs. The results imply that, for evaluating the performance of an isolated rotor or for shape optimization purposes at the transonic regime, the single rotating frame method, like the one introduced in the current work, can provide accurate results within an acceptable computational budget. Furthermore, the results show that, at least 25 revolutions are required for the transient analysis to reach an acceptable steady-state converged solution like the one obtained by the single rotating frame method.

Influence of posture during gliding flight in the flying lizard Draco volans

The agamid lizards of the genus Draco are undoubtedly the most renown reptilian gliders, using their rib-supported patagial wings as lifting surfaces while airborne. Recent investigations into these reptiles highlighted the role of body posture during gliding, however, the aerodynamics of postural changes in Draco remain unclear. Here, we examine the aerodynamics and gliding performances of Draco volans using a numerical approach focusing on three postural changes: wing expansion, body camber, and limb positioning. To this aim, we conducted 70 three-dimensional steady-state computational fluid dynamics simulations of gliding flight and 240 two-dimensional glide trajectory calculations. Our results demonstrate that while airborne, D. volans generates a separated turbulent boundary layer over its wings characterized by a large recirculation cell that is kept attached to the wing surface by interaction with wing–tip vortices, increasing lift generation. This lift generating mechanism may be controlled by changing wing expansion and shape to modulate the generation of aerodynamic force. Furthermore, our trajectory simulations highlight the influence of body camber and orientation on glide range. This sheds light on how D. volans controls its gliding performance, and conforms to the observation that these animals plan their glide paths prior to take off. Lastly, D. volans is mostly neutral in pitch and highly maneuverable, similar to other vertebrate gliders. The numerical study presented here thus provides a better understanding of the lift generating mechanism and the influence of postural changes in flight in this emblematic animal and will facilitate the study of gliding flight in analogous gliding reptiles for which direct observations are unavailable.

Steady-State Dynamics of Ganglia Populations During Immiscible Two-Phase Flows in Porous Micromodels: Effects of the Capillary Number and Flow Ratio on Effective Rheology and Size Distributions

We study experimentally the flow of non-wetting ganglia during the co-injection of n-heptane and water in a predominantly 2D PMMA micromodel, which is constructed based on a stochastic digital algorithm. The dynamics of the phase distribution patterns are recorded optically and post-processed using cluster identification and motion tracking algorithms in order to study the characteristics and the interactions between the mobile and stranded ganglia populations. We focus primarily on the effects of the capillary number (Ca) and the ratio of the injection flow rates (Q) on the observed ganglia size distributions and the effective two-phase rheology. Our experimental setup allows for the study of ganglia fragmentation and coalescence dynamics over five orders of magnitude (in terms ganglia sizes), thus offering novel physical insight on the pore-scale characteristics of different ganglia populations and on how their interactions determine the relative permeability of the non-wetting phase. We demonstrate that the rates of ganglia fragmentation and coalescence intensify at higher Ca values, as viscous forces become dominant over capillary ones, leading to a log-normal size distribution that shifts toward smaller mean values. This effect is directly correlated with the emergence of new flow paths that develop progressively through narrower pores-throats, where the continuous wetting phase sweeps ganglia with sizes smaller than the mean pore-throat diameter. These flow paths further contribute to the Darcy scale velocity of the non-wetting phase, thus leading to a power-law Darcian regime at intermediate Ca values with a scaling exponent that is found to be a function of Q.

Cooperative control of NN super twisting sliding mode and EPH methods for uncertain nonlinear systems

A cooperative control strategy is proposed based on radial basis function neural network (NN) super twisting sliding mode and error port-controlled Hamiltonian (EPH) methods to enhance dynamic performance and steady state performance of the system. First, a NN super twisting sliding mode control method is developed for system with unknown external disturbances and uncertain parameters, where NN is adopted to approximate unknown control gain, the disturbance observer (DOB) is employed to estimate the unknown lumped disturbance. The dynamic performance of the control system is enhanced. Second, the EPH control method based on DOB is developed to increase the accuracy of the control system. Lastly, NN super twisting sliding mode and EPH methods-based cooperative control strategy is developed, the superiority of the proposed method is verified through the simulation and experiments.

Defect interactions in a two-dimensional sheared lamellar mesophase.

The interaction between two edge dislocations in a sheared lyotropic lamellar liquid-crystalline medium is examined. The model is a mesoscale hydrodynamic model based on a free-energy functional that is minimised for a sinusoidal concentration modulation coupled with concentration and momentum equations. The defect dynamics are analysed as a function of the system size and the Ericksen number, the ratio of the shear stress and the characteristic free-energy density for deformation. Three different regimes are observed as the Ericksen number is increased when the edge dislocations are sheared towards each other, such that there is compression of layers between the defects: (a) defect motion that reduces the cross-stream separation till there is a steady spacing with plug flow between the defects, (b) defect attraction and cancellation resulting in a well-aligned state, and (c) defect creation due to a compressional instability between the defects resulting in an increase in the disorder. When the edge dislocations are sheared away from each other, such that there is extension of the layers between the defects, two distinct regimes are observed as the Ericksen number is increased: (a) bending of layers and a plug flow between the defects at their initial separation, and (b) buckling of the layers leading to creation of more defects and a dynamical steady state between defect creation and cancellation. These regimes are found to be robust for different values of the system size, from 32 to 128 layers, and for different values of the dimensionless groups that characterise the ratio of mass/momentum convection and diffusion.

Site specifically probing the unfolding process of human telomere i-motif DNA using vibrationally enhanced alkynyl stretch.

The microscopic unfolding process of a cytosine-rich DNA forming i-motif by hemi-protonated base pairs is related to gene regulation. However, the detailed thermal unfolding mechanism and the protonation/deprotonation status of site-specific cytosine in DNA in a physiological environment are still obscure. To address this issue, a vibration-enhanced CC probe tagged on 5'E terminal cytosine of human telomere i-motif DNA was examined using linear and nonlinear infrared (IR) spectroscopies and quantum-chemistry calculations. The CC probe extended into the major groove of the i-motif was found using nonlinear IR results only to introduce a minor steric effect on both steady-state structure and local structure dynamics; however, its IR absorption profile effectively reports the cleavage of the hemi-protonated base pair of C1-C13 upon the unfolding with C1 remaining protonated. The temperature mid-point (Tm) of the local transition reported using the CC tag was slightly lower than the Tm of global transition, and the enthalpy of the former exceeds 60% of the global transition. It is shown that the base-pair unraveling is noncooperative, with outer base pairs breaking first and being likely the rate limiting step. Our results offered an in-depth understanding of the macroscopic unfolding characteristics of the i-motif DNA and provided a nonlinear IR approach to monitoring the local structural transition and dynamics of DNA and its complexes.

Flame stabilization by a highly conductive cylinder: Multiple steady-state solutions and dynamics

This study examines stabilization of a premixed flame by a circular cylinder placed perpendicularly to the uniform flow of the reacting mixture. It is assumed that the cylinder has a high thermal conductivity leading to an effectively uniform surface temperature. This temperature is not fixed, but it is determined by a thermal flame-cylinder balance. The numerical investigation is carried out on the basis of low Mach number Navier–Stokes equations coupled with the conservation equations for the energy and the fuel mass. Two models for transport coefficients are compared. The first model assumes they have constant values, and the second takes into account their change with temperature.Numerical modeling shows that within the specific range of parameters of this study the system can have several steady-state solutions corresponding to different cylinder temperatures. Moreover, at least two solutions are shown to be stable, corresponding to the hottest and coldest cylinder temperatures. The actual occurrence of one or another regime depends on the initial conditions.

Acoustic attenuation prediction and analysis of perforated hybrid mufflers with non-uniform flow based on frequency domain linearized Navier-Stokes equations

The three-dimensional frequency-domain linearized Navier-Stokes equations (LNSEs) with consideration of eddy viscosity are developed to evaluate the acoustic attenuation performance of perforated hybrid mufflers in the presence of non-uniform flow. The computations are performed in two steps: time averaged flow variables are acquired by using steady-state computational fluid dynamics (CFD) method and then mapped into the acoustic mesh, and the acoustic perturbation variables are obtained by solving frequency-domain LNSEs, where the sound-absorbing material is treated as an equivalent fluid with complex sound speed and density. The predictions of transmission losses of the two-pass perforated hybrid mufflers in the presence of non-uniform flow are in good consistencies with the measurements, which verifies the correctness of LNSEs. The effect of Mach numbers on acoustic attenuation performance of the mufflers with different filling densities and perforated components is investigated in detail. The transmission loss of the mufflers with various filling densities are increased by complex airflow in the lower frequency range. For the mufflers where not all components have been perforated, the flow lowers low-frequency resonance peak. The influence of complex airflow on acoustic attenuation performance of all configurations is weakened at higher frequencies.

Traveling waves at the surface of active liquid crystals.

Active liquid crystals exert nonequilibrium stresses on their surroundings through constant consumption of energy, giving rise to dynamical steady states not present in equilibrium. The paradigmatic example of an active liquid crystal is a suspension of microtubule bundles powered by kinesin motor proteins, which exhibits self-sustained spatiotemporal chaotic flows. This system has been modelled using continuum theories that couple the microtubule orientation to active flows. Recently the focus has shifted to the interfacial properties of mixtures of active liquid crystals and passive fluids. Active/passive interfaces have been shown to support propagating capillary waves in the absence of inertia and offer a promising route for relating experimental parameters to those of the continuum theory. In this paper we report the derivation of a minimal model that captures the linear dynamics of the interface between an active liquid crystal and a passive fluid. We show that the dynamics of the interface, although powered by active flows throughout the bulk, is qualitatively captured by equations that couple non-reciprocally interface height and nematic director at the interface. This minimal model reproduces the dynamical structure factor evaluated from numerical simulations and the qualitative form of the wave dispersion relation seen in experiments.

Time-delayed control of a nonlinear self-excited structure driven by simultaneous primary and 1:1 internal resonance: analytical and numerical investigation

<p>Main objective of this research to eliminate the resonant vibrations and stabilize the unstable motion of a self-excited structure through the implementation of an innovative active control strategy. The control strategy coupling the self-excited structure with a second-order filter, which feedback gain $ \lambda $ and control gain $ \beta $, as well as a first-order filter, which feedback gain $ \delta $ and control gain $ \gamma $. The coupling of the second-order filter to establish an energy bridge between the structure and the filter to pump out the structure's vibration energy to the filter. In contrast, the primary purpose of coupling the first-order filter to stabilize the closed loop by adjusting the damping of the system using the control keys $ \delta $ and $ \gamma $. Accordingly, the mathematical model of the proposed control system formulated, incorporating the closed-loop time delay $ \tau $. An analytical solution for the system model obtained, and a nonlinear algebraic system for the steady-state dynamics of the controlled structure extracted. The system's bifurcation characteristics analyzed in the form of stability charts and response curves. Additionally, the system's full response simulated numerically. Findings the high performance of the introduced controller in eliminating the structure's resonant vibrations and stabilizing non-resonant unstable motion. In addition, analytical and numerical investigations revealed that the frequency band within which the second-order filter can absorb the structure's resonant oscillation relies on the algebraic product of $ \beta $ and $ \lambda $. Furthermore, it was found that the equivalent damping of the system depends on the algebraic product of $ \gamma $ and $ \delta $, which can be employed to stabilize the negatively damped self-excited systems. Finally, it reported that although the loop delay can potentially degrade vibration control performance, the time-delay stability margin is nonlinearly proportional to the product of $ \gamma $ and $ \delta $. This finding that increasing the value of $ \gamma \times \delta $ can compensate for the adverse effects of loop delay on both system stability and vibration suppression efficiency.</p>

Acoustic Attenuation Prediction of Perforated Reactive and Dissipative Mufflers With Flow by Using Frequency-Domain Linearized Navier-Stokes Equations

To comprehensively consider the impact of complex airflow on sound propagation, a numerical approach by solving the three-dimensional (3-D) frequency-domain linearized Navier-Stokes equations (LNSEs) is proposed to accurately predict the transmission losses of perforated tube reactive and dissipative mufflers in the presence of complex airflow. The numerical computations are performed in two steps: (1) solve the time averaged flow by steady-state computational fluid dynamics (CFD) simulation and then map the results into acoustic mesh; (2) treat sound-absorbing material as an equivalent fluid and obtain acoustic perturbation variables by solving the frequency-domain LNSEs. The transmission losses of perforated tube reactive and dissipative mufflers are measured in the presence of flow and compared with the numerical predictions. The excellent consistencies between predictions and measurements validate the present approach. The influence of Mach number on acoustic attenuation performance of perforated tube reactive and dissipative mufflers is then investigated. With Mach number increases, the transmission loss of perforated tube reactive muffler increases somewhat, while the transmission loss of dissipative mufflers decreases obviously in the lower frequency range and change is limited at higher frequencies.