Low Mode Research Articles

Tuning of a Viscous Inerter Damper: How to Achieve Resonant Damping Without a Damper Resonance

Inerter dampers are effectively employed to mitigate and dampen structural vibrations in slender or high-rise buildings. The simple viscous inerter damper, with a viscous dashpot placed in series with an inerter, is designed to create resonant vibration damping, although the damper itself is without an internal resonance. The apparent resonant behavior is instead obtained by increasing the damper inertance until the two lowest modes of the considered building model interact, whereafter the viscous coefficient is adjusted until the desired response mitigation is achieved. The present modal interaction tuning requires that the reduced-order single-mode dynamic model of the building includes both inertia and flexibility from the (other) modes otherwise discarded by the model reduction. While the inertia correction adjusts the modal mass of the inerter damper, the corresponding flexibility introduces the apparent damper stiffness that creates the desired damper resonance. Thus, the accurate representation of other modes is essential for the design and resonant tuning of the simple viscous inerter damper. The resonant damper performance by the non-resonant viscous inerter damper is illustrated by a numerical example with a 20-story building model, for which the desired resonant modal interaction requires an inertance of almost ten times the entire translational building mass.

Effects of turbulence spreading and symmetry breaking on edge shear flow during sawtooth cycles in J-TEXT tokamak

The effect of sawteeth on plasma performance and transport in the plasmas of tokamak is an important issue in the fusion field. Sawtooth oscillations can trigger heat and turbulence pulses that propagate into the edge plasmas, and thus enhance the edge shear flow and induce a transition from low confinement mode to high confinement mode. The influences of turbulence spreading and symmetry breaking on edge shear flow with sawtooth crashes are observed in the J-TEXT tokamak. The edge plasma turbulence and shear flow were measured using a fast reciprocating electrostatic probe array. The experimental data were analyzed using methods such as conditional average and probability distribution function. After sawtooth crashes, the heat and turbulence pulses in the core propagate to the edge, with the turbulence pulse being faster than the heat pulse. Figures 1 (a)-(e) show the core electron temperature, and the edge electron temperature, turbulence intensity, turbulence drive and spreading rates, Reynolds stress and its gradient, and shearing rates, respectively. Following sawtooth crashes, the edge electron temperature increases and the edge turbulence is enhanced, with turbulence preceding temperature. The enhanced edge turbulence is mainly composed of two parts: turbulence driven by local gradient and turbulence spreading from core to edge. The development of the estimated turbulence spreading rates is prior to that of the turbulence driving rates. The increase in the turbulence intensity can cause the enhancements of the turbulent Reynold stresses and its gradient, thereby enhancing shear flows and radial electric fields. Turbulence spreading leads to the development of edge Reynolds stresses and shear flow faster than edge electron temperature. The Reynolds stress arises from the symmetry breaking of the turbulence wave number spectrum. After sawtooth collapse, the joint probability density function of radial and poloidal wave numbers of turbulence intensity became highly skewed and anisotropic, exhibiting strong asymmetry, as seen in the figures 1 (f) and (g). The development of turbulence spreading flux at the edge is also prior to the particle flux driven by turbulence, indicating that turbulent energy transport is not simply accompanied by turbulent particle transport. These results show that turbulence spreading and symmetry breaking can enhance turbulent Reynolds stress, thereby driving shear flows, after sawtooth crashes.

The spectrometer development of CosmoCube, lunar orbiting satellite to detect 21-cm hydrogen signal from cosmic dark ages

Abstract The cosmic Dark Ages represent a pivotal epoch in the evolution of the Universe, marked by the emergence of the first cosmic structures under the influence of dark matter. The 21-cm hydrogen line, emanating from the hyperfine transition of neutral hydrogen, serves as a critical probe into this era. We describe the development and implementation of the spectrometer for CosmoCube, a novel lunar orbiting CubeSat designed to detect the redshifted 21-cm signal within the redshift range of 13 to 150. Our instrumentation utilizes a Xilinx Radio Frequency System-on-Chip (RFSoC), which integrates both Analog-to-Digital Converters (ADCs) and Digital-to-Analog Converters (DACs), tailored for the spectrometer component of the radiometer. This system is characterized by a 4096 FFT length at 62.5 kHz steps using a Polyphase Filter Bank (PFB), achieving an average Effective Number of Bits (ENOB) of 11.5 bits throughout the frequency of interest, from 10 MHz to 100 MHz. The spectrometer design is further refined through loopback tests involving both DAC and ADC of the RFSoC, with DAC outputs varying between high (+1 dBm) and low (-3 dBm) power modes to characterize system performance. The power consumption was optimized to 5.45 W using three ADCs and one DAC for the radiometer. Additionally, the stability of the ADC noise floor was investigated in a thermal chamber with environmental temperatures ranging from 5○C to 40○C. A consistent noise floor of approximately -152.5 dBFS/Hz was measured, with a variation of ±0.2 dB, ensuring robust performance under varying thermal conditions.

Multi-resonant TVA formed by a tree of deflated composite beams with core structured fabrics

Abstract This paper presents a study on a multi-resonant tuneable vibration absorber for the control of flexural vibrations of thin structures in a low frequency band where the response is characterized by distinct lightly damped resonances of low order flexural modes. The absorber is formed by a tree of deflated composite beams made by a core structured fabric wrapped on a plastic skin. The beams have increasingly smaller length and are fixed in the middle on a mast that works as a base-post and vacuum-junction too. The fabric in each beam is made by a lattice of interlocked truss-like rigid particles. The uniform pressure exerted by the deflated skin forces the particles to jam such that the fabric moves from its natural fluid-like state to a solid state whose rigidity depends on the confining pressure exerted by the skin. Hence, each beam is characterized by a fundamental flapping vibration mode whose response resembles that of a classical mass-spring-damper vibration absorber and can be suitably tuned by adjusting the level of vacuum. The paper first analyses the working principles of single-beam and three-beams absorbers with respect to their vibration transmissibility and base impedance frequency response functions. Then, it presents the vibration control generated by the single-beam and the three-beams absorbers tuned to minimise the resonant responses of a single or three low order flexural modes of a thin plate. The paper shows that the operational frequency of each beam-absorber can be suitably adapted in a band of 8 Hz by varying the vacuum pressure in a 5 – 80 kPa range. Also, it shows that the single-beam or multi-beams absorbers reduce the resonant response of the target flexural modes by 10 to 20 dB.

Linear response of deep ocean to a moving tropical cyclone

To explore the impacts of a moving tropical cyclone (TC) on the deep ocean, a linear continuously stratified model is solved by the method of solving for the temporal and horizontal structure of each vertical mode. The response of the barotropic mode to the TC’s pressure gradient is an isostatic balance, where the sea level rise almost completely cancel the atmospheric low pressure. The response of the barotropic mode to the winds is a permanent sea level drop behind the TC. The horizontal extent of this response is determined by the distribution of the weak negative wind curl outside the core of the strong positive curl. The baroclinic response to the winds is dominated by the well-known train of near-inertial oscillation behind the TC. In addition, there is a mean upwelling and a resultant cooling. The lateral scale of the first upwelling behind the TC is determined by the size of the TC’s positive curl core; further behind in the TC’s wake, this feature spreads laterally at the group speed of inertio-gravity waves for the mode. The three-dimensional structure is then constructed by superposing these vertical modes. The position of the first upwelling peak coincides between the baroclinic modes; this alignment results in a vertical column of upwelling. Further down the wake, this coherence is gradually lost because of slight difference in the streamwise wavelength between modes. Also, lower vertical modes dominate further away from the TC track because of faster lower modes. A uniform-density ocean shows a similar columnar upwelling and downwelling pattern as a response to the same wind curl. The pressure anomaly field at the ocean bottom is dominated by the barotropic response to winds, modified by the baroclinic response. The near-inertial oscillation reaches the bottom quickly because of the columnar response.

Macro–Micro Failure Characteristics of Soft–Hard Composite Rock with Unparallel Joints: Analysis Based on DIC and AE Technique

Jointed composite rock masses are ubiquitous, where the interplay between fractures and bedding planes significantly complicates their failure mechanisms. This study conducted uniaxial compression tests on a composite rock material featuring soft and hard components with unparallel double joints. Leveraging the digital image correlation (DIC) method and acoustic emission (AE) technology, the investigation analyzed the influence of joint angles on the mechanical properties, failure modes, and crack propagation behaviors. The results indicate that the peak strength exhibits an ascending–descending–ascending trend with the variation of upper joint angle, peaking at 90°. The failure modes can be systematically categorized into three types. The failure of the specimen is predominantly influenced by the upper joint. However, when the lower joint angle is relatively flat, it becomes more prone to contributing to the failure of the specimen. The lower joint-dominated failure mode only occurs when the upper joint angle is 90°. As the lower joint angle remains at 90°, an augmentation in the upper joint angle initially leads to a decrease and subsequently to an increase in the proportion of shear cracks. In contrast, when the lower joint angle deviates from 90°, the increase of the upper joint angle initially boosts and then diminishes the proportion of shear cracks.

USAGE OF ACRYLIC ACID BASED POLYMER FOR STABILIZATION OF NICKELINE NANOPARTICLES

In this work, our team synthesized polyacrylic acid-supported Ni nanoparticles and SEM images were shown of polyacrylic acid-supported Ni nanoparticle samples at different magnifications in low electron mode at different voltages. The study examined the solubility of nickel nanoparticles depending on their concentration, and also studied the influence of the activity of acidity and ba-sicity of the medium and the concentration of nanoparticles on the overall distribution of the sus-pension. We have obtained nanoparticles of metallic nickel. To study the effect of an acidic envi-ronment on the dispersion of suspensions of nickel nanoparticles, various solutions with different alkalinity and acidity were created. Consequently, it was observed that the acidity level of the medium has minimal influence on the average particle size within suspensions of identical concen-trations. The size of nickel nanoparticles remains highly diminutive and can be readily tailored by adjusting both the polymer type and concentration in each specific context. At selected polymer concentrations that provide the same number of monofragments, PAA is the best stabilizer. Keywords: PAA, solution, suspension, nanoparticles, TEM.

Dynamically programable real-time controller for a 2D scanning fibre microscope

A programmable controller for a 2D Lissajous scanning fibre microscope is described. Source motion is based on a vibrating cantilever formed by dip-coating two cylindrical silica fibres. Orthogonal modes are excited by a piezoelectric actuator oriented at 45° to the principal axes. Back-scattered signals are detected using a mode-stripping photodiode to collect cladding modes in a dual numerical aperture confocal scheme. Optical feedback is generated by a shaped reflecting aperture with amplitude-coded reflectivity. Electrical pulses from the detector are separated into low- and high-mode feedback signals using window detectors. The low mode is excited at resonance using a phase-locked loop (PLL) containing a voltage-controlled oscillator (VCO). The high mode is driven off-resonance at a frequency derived from computer control of a second VCO. Amplitudes are corrected, and common frequency signals derived from the two motions using divide-by-N circuits are synchronised using additional PLLs. Programmable generation of Lissajous figures and imaging with dynamically variable scan density are demonstrated.

Multivalued dispersion equation for coupling between plasmons and surface optical phonons in a graphene/polar-substrate system

Dispersion equations are a common paradigm of collective excitation physics. However, in some systems, dispersion equations contain multivalued functions and their solutions are ambiguous. As an example, we consider graphene on a polar substrate where Dirac plasmons are coupled with surface optical phonons. The dispersion equation for this system contains square-root singularity. Using the initial value problem resolves this uncertainty and gives a unique solution. Particularly, we found that the lower plasmon-phonon mode, which in terms of dispersion can have a good quality factor, is almost absent in excitation spectra. The physical reason and experimental evidence of the mode collapse are discussed. Published by the American Physical Society 2024

Atomic layer deposition-enabled few-mode erbium-doped waveguide amplifiers with low differential mode gains

Atomic layer deposition-enabled few-mode erbium-doped waveguide amplifiers with low differential mode gains

Is process damping effective in the stability of robotic milling?

Chatter stability is a major constraint in milling, where low and high cutting speeds are used. At low cutting speed regime, process damping leads to increased stability, whereas at high cutting speeds lobing effect is beneficial. Excitation frequency depends on spindle speed and the number of cutting flutes on the milling tool. Hence the vibration mode governing chatter stability varies for multi-mode milling systems. In CNC milling, low frequency structural modes are stiffer than cutting spindle-holder-tool (SHT) assembly. However, robotic milling demonstrates a distinct behavior as low frequency modes are significantly more flexible. This study investigates the effect of robot structure induced low frequency vibration modes on stability limits at low cutting speeds, where process damping is expected to increase stability limits. Time domain simulations are used to explain the variation of the dominant mode from high frequency to low frequency with the decreasing spindle speed. Simulated stability diagram for the multi-mode robotic milling system is verified by experiments. It was shown that especially the vibration modes in the range of 15 to 20 Hz do not generate enough process damping force due to long vibration waves, i.e. cutting speed – to – chatter frequency ratio, when low frequency modes govern chatter stability. Simulation of stability diagrams showed that there is a spindle speed region where the stability lobes governed by the robot structure crosscut the stability lobes governed by the THS assembly. Due to the inherent effect of tool diameter (D) and number of cutting flutes (Z) on cutting speed and excitation frequency, this region shifts according to the D/Z ratio. It was shown through simulations that D/Z ratio is a critical metric to benefit from process damping without the interference of the low frequency excitation of the robotic structure. The simulation results are used to provide suggestions for milling tool selection in robotic milling, where the main conclusion is to use lower D/Z ratio, which means that using high number of cutting flutes.

Simultaneous radio and X-ray observations of the transitional millisecond pulsar candidate 3FGL J1544.6−1125

ABSTRACT Transitional millisecond pulsars (tMSPs) are neutron star systems that alternate between a rotation-powered radio millisecond pulsar state and an accretion disc-dominated low-mass X-ray binary (LMXB)-like state on multi-year time-scales. During the LMXB-like state, the X-ray emission from tMSPs switches between ‘low’ and ‘high’ X-ray brightness modes on a time-scale of seconds to minutes (or longer), while the radio emission shows variability on time-scales of roughly minutes. Coordinated Very Large Array (VLA) and Chandra observations of the nearby tMSP PSR J1023+0038 uncovered a clear anticorrelation between radio and X-ray luminosities such that the radio emission consistently peaks during the X-ray low modes. In addition, there are sometimes also radio/X-ray flares that show no obvious correlation. In this paper, we present simultaneous radio and X-ray observations of a promising tMSP candidate system, 3FGL J1544.6$-$1125, which shows optical, $\gamma$-ray, and X-ray phenomena similar to PSR J1023+0038, but which is challenging to study because of its greater distance. Using simultaneous VLA and Chandra observations, we find that the radio and X-ray emission are consistent with being anticorrelated in a manner similar to PSR J1023+0038. We discuss how our results help in understanding the origin of bright radio emission from tMSPs. The greater sensitivity of upcoming telescopes such as the Square Kilometre Array will be crucial for studying the correlated radio/X-ray phenomena of tMSP systems.

A Robust ALOHA and Sequential clustering-based mode estimator for low frequency oscillations in power system using synchrophasors

Accurate estimation of low frequency modes in power system are very much important for improving small signal stability. The parametric model parameters estimator known as Total least square estimation of signal parameters via rotational invariance techniques (TLS-ESPRIT) works effectively even in noisy conditions. However, this model parameter estimator requires prior information about numbers of modes of the signal. There are different Model order (MO) estimation techniques discussed in the recent past, which consider the significant eigenvalues of auto-correlation matrix (ACM) for its estimation. As the eigenvalues of ACM highly affected by bad measurements and Outliers, making these techniques inefficient and harder to automate in real time. So, to overcome aforementioned limitations, this paper proposes a robust mode estimation technique that can precisely detect the signal low frequency modes even in the presence of high variance noise and outliers. So, in this proposed work, an annihilating filter-based low-rank Hankel matrix (ALOHA) technique is implemented to obtain the rank deficient Hankel matrix to nullify the existence of noise and outliers in Phasor measurement unit (PMU) signal, thereafter approximated low rank Hankel matrix is considered for estimation of signals dominant modes. Wherein a sequential clustering technique (Sequential K-Mean++) is implemented for detection of numbers of prominent low frequency modes by segregating eigenvalues of ACM into two opponents i.e the signal and noise subspace. Thereafter the estimated MO is considered for estimation of modes through TLS-ESPRIT. The robustness of the proposed technique is validated by scheduling comparative study with recently developed techniques for synthetic signal, two area data, real PMU data of Western Electricity Coordinating Council (WECC) and oscillatory power data obtained from Western System Coordinating Council (WSCC) 9 bus system and IEEE68 bus system simulated through Real Time Digital Simulator (RTDS).

Primary Modes of Northern Hemisphere Snowfall Particle Size Distributions

Abstract A comprehensive understanding of snowfall microphysics is crucial for enhancing the accuracy of remote sensing snowfall retrievals. However, variations in regional and seasonal snow particle size distributions (PSDs) contribute substantial uncertainty. Here, we examine snowfall PSDs from across the Northern Hemisphere, applying principal component analysis (PCA) to disdrometer observations with the aim of identifying dominant modes of variability across varying regional climates. The PCA revealed three empirical orthogonal functions (EOFs) that account for a combined 95% of the variability across the dataset, which are attributed to latent linear embeddings of snowfall intensity (EOF1), snowfall character (EOF2), and snowfall regime (EOF3). Examining point clusters with the highest combined EOF values reveals six distinct modes of variability [i.e., principal component (PC) groups] with unique PSD traits. These groups are then correlated with environmental factors using data from collocated vertically pointing radar, surface meteorology, and reanalysis to assist in assigning physical attributes. The first and second PC groups, linked to EOF1’s intensity embedding, are described by their PSD intercepts, snowfall rates, and reflectivity and Doppler velocity values, representing low- and high-intensity snowfall modes, respectively. The third and fourth PC groups, associated with EOF2’s character embedding, are defined by temperature, fall speed, and density, indicative of cold, fluffy snowfall and warm, dense snowfall, respectively. The fifth and sixth PC groups, related to EOF3’s regime embedding, are distinguished by their PSD slope, snowfall rate, and reflectivity profiles, signifying shallow, weak convective systems with small particles and deep, stratiform snowfall events with large aggregates, respectively. Significance Statement This research enhances our understanding of varying snow particle size distributions in the Northern Hemisphere, offering valuable new insights for improving future remote sensing–based snowfall retrieval algorithms. Using a statistical technique called principal component analysis, we found that 95% of the variability in observed snowfall could be explained by three primary features: how intense the snowfall is, how dense the particles are, and the depth of the storm. We identified six unique snowfall groups, each with its own set of traits, such as the snow being light and fluffy, or heavy and packed. By linking these traits to external environmental observations, we can better understand the driving physical mechanisms within each group.

Exploring the convective core of the high-amplitude δ Scuti star TIC 120857354 with asteroseismology

ABSTRACT Based on 2-min cadence TESS data, 20 confident independent frequencies were identified for the star TIC 120857354. The Kolmogorov–Smirnov test reveals a rotational splitting of 2.40 $\mu$Hz and a uniform frequency spacing of 74.6 $\mu$Hz. Subsequently, five sets of rotational splittings were discerned, including a quintuplet and four pairs of doublets, aligning with the characteristics of p-mode rotational splitting. Based on the sets of rotational splittings and the uniform frequency spacing, we finally identified four radial modes, six dipole modes, and 10 quadrupole modes. Furthermore, we found that the frequency separations within the $\ell$ = 2 sequences show a decreasing trend towards lower order modes, analogous to the $\ell$ = 0 sequences. A grid of theoretical models were computed to match the identified frequencies, revealing that TIC 120857354 is a main-sequence star with M = 1.54 $\pm$ 0.04 $\mathrm{M}_{\odot }$, Z = 0.015 $\pm$ 0.003, $T_{\rm eff}$ = 7441 $\pm$ 370 K, $\log g$ = 4.27 $\pm$ 0.01, R = 1.52 $\pm$ 0.01 $\mathrm{R}_{\odot }$, L = 6.33 $\pm$ 1.53 $\mathrm{L}_{\odot }$, age = 0.53 $\pm$ 0.07 Gyr, and $X_\mathrm{ c}/X_0$ = 0.84 $\pm$ 0.05. In-depth analyses suggest that $\ell$ = 2 may be p-dominated mixed modes with pronounced g-mode characteristics, enabling us to probe deeper into interiors of the star and determine the relative size of the convective core to be $R_\mathrm{ c}/R$ = 0.092 $\pm$ 0.002.

Modal Complexity Factors as indexes for modal parameter identification in Operational Modal Analysis of coupled dynamic systems

Vibration analysis seeks to extract the modal parameters of a mechanical system by means of experimental measurements. Natural frequencies, damping ratios and mode shapes are identified from the measurements data from experimental or operational modal analysis. Modal shapes can show real or complex values. The degree of complexity of a modal shape can be measured by the Modal Complexity Factors (MCF). Among others, modal complexity can be due to non-uniformly distributed damping. In complex mechanical systems like a robot, complex modes are expected due to its active and non distributed damping. In turn, in a metallic workpiece real modes are expected. In the robotic machining of thin workpieces, both the robot and the workpiece constitute a coupled dynamic system, operating within the same frequency range. This work proposes the use of MCFs as indexes to determine if each mode corresponds to the workpiece or the robot. Experimental results of an operational modal analysis show a lower mode complexity for the workpiece modes and a higher complexity for the robot frequencies. MCFs show a good performance in separating modes of such coupled systems due to the different damping nature of the robot and the workpiece.

A resonance-avoiding modal balancing method for multimodal balancing of high-speed flexible rotors

Abstract Conventional balancing methods for high-speed flexible rotors typically necessitate costly and potentially hazardous balancing tests conducted near their critical speeds. This paper first demonstrates the feasibility of achieving multi-mode balancing using measurements taken below the first critical speed, based on traditional modal balancing methods and rotor modal parameters. However, while theoretically viable, this approach is highly susceptible to measurement noise, complicating its practical implementation. To address this issue, we propose an innovative resonance-avoiding modal balancing (RAMB) method specifically designed for multi-mode balancing. In RAMB, balancing is performed mode by mode in a forward manner, effectively integrating the correction weights of lower modes into the balancing equation. This strategy eliminates the need to operate the rotor at unbalanced critical speeds, enhancing the effectiveness of multi-mode balancing while ensuring measurement safety. The effectiveness of both the conventional method and the RAMB approach is validated through numerical simulations and experimental tests as well. The results show that RAMB significantly enhances the vibration suppression over the entire operating speed range while avoiding resonance measurements and exhibits comparable robustness to noise, confirming the validity and superiority of the proposed balancing method

Low mode interactions in water wave model in triangular domain

We study gravity water waves in a domain with inclined lateral boundaries that make a 45°angle with the horizontal axis. We consider free surface potential flow and a simplified model that contains quadratic nonlinear interactions among the normal modes. The particular geometry leads to classical semi-explicit expressions for the normal modes and frequencies, and we use this information to compute the mode interaction coefficients. We further use a partial normal form to compute the amplitude dependence of nonlinear frequency correction of the lowest frequency mode. We indicate the general computation and present numerical results for a truncations to a system for the two lowest modes.

Goffin's cockatoos use object mass but not balance cues when making object transport decisions.

Utilising weight cues can improve the efficiency of foraging behaviours by providing information on nutritional value, material strength, and tool functionality. Attending to weight cues may also facilitate the optimisation of object transport. Though some animals' ability to assess weight cues has been determined, research into whether they can apply weight assessment during practical decision making is limited. In this study, we investigate whether Goffin's cockatoos (Cacatua goffiniana) account for relative weight and unequal versus equal weight distribution when making object transport decisions, and whether sensitivity to these cues varies depending on transport mode. We conducted a series of binary choice experiments in which birds could choose to transport one of two identical, non-functional, equally rewarded objects differing only in overall weight (experiment 1) or weight balance (experiment 2) over a short distance. We found that in experiment 1, Goffin's cockatoos preferred to transport light objects over heavy objects and seemed to rely more on weight cues to inform decisions over time, whereas in experiment 2, weight balance cues were ignored. Contrary to our predictions, Goffin's cockatoos did not show increased preference for lighter or more balanced objects when employing higher energy transport modes (flight) compared to lower energy modes (walking). We suggest that this may be due to an insufficient difference in physical effort between transport modes due to the short distance travelled. These findings provide the first evidence of weight cues being considered to optimise object transport in birds.

OpenFOAM modelling of air ingress into the high vacuum for fusion reactor safety

The underexpanded jet induced by loss of vacuum accidents (LOVA) can significantly impact the fusion reactor management, since it poses safety problems associated with hydrogen risks and radioactivity to the environment. To characterize the air ingress process into the high vacuum environment, simulations were performed with OpenFOAM modelling in a representative small-scale fusion facility. The general features of the thermodynamic parameters, such as density, pressure, velocity, and temperature, were analyzed, and also characterized the wall friction velocity and the formation of the Mach disk within the underexpanded jet. Proper orthogonal decomposition (POD) method was applied to compare the fluid dynamic behaviors of the jet subjected to different thermodynamic conditions. The results show that the rapid expansion and acceleration of the jet leads to a decrease in density and an accumulation of the gas along the centerline. The high jet velocity will result in a lower jet temperature and raise the temperature of the surroundings, which also triggers the formation of recirculation zones, and the gradual development of Mach disk structure, also, the higher wall friction velocity will further contribute to the complex air ingress dynamics. Moreover, it is observed that the ideal gas and real gas model appear similar fluid dynamic structures and energy modes during the pressure and velocity development, and only subtle differences appear in the low energy contribution POD modes. The main differences of the energy modes are captured in the momentum field between these different thermodynamic conditions. The observations can contribute to fusion safety management and appropriate thermodynamic modelling selection in such applications.