Fourth Mode Research Articles

Characterization of Three-Mode Combination Internal Resonances in Electrostatically Actuated Flexible–Flexible Microbeams

Abstract Nonlinear intermodal coupling based on internal resonances in MEMS resonators has advanced significantly over the past two decades for various real-world applications. In this study, we demonstrate the existence of various three-mode combination internal resonances between the first five flexural modes of electrostatically actuated flexible–flexible beams and dynamic modal interaction between three modes via internal resonance. We first calculate the natural frequencies of the beam as a function of the stiffnesses of the transverse and rotational springs of the flexible supports, utilizing both analytical formulation and finite element analysis (FEA). Following this, we identify six combination internal resonances among the first five modes and use applied DC voltage to validate the exactness of one commensurable internal resonance condition (ω2=ω5−ω4). Subsequently, we studied a detailed forced vibration analysis corresponding to this resonance condition by solving the five-mode coupled governing equations through numerical time integration and the method of multiple scales. The results compellingly exhibit three-mode intermodal coupling among the second, fourth, and fifth modes as a function of excitation amplitude and frequency. Alongside this, intriguing nonlinear phenomena such as threshold behavior, saturation phenomena, and autoparametric instability are observed. Finally, this paper provides a systematic methodology for investigating three-mode combination internal resonances and related nonlinear dynamics, offering significant insights that could be used in observing phonon or mechanical lasing phenomena in MEMS resonators.

Analysis of unsteady wake flow in centrifugal pump volute by using mode decomposition method

To analyze the coherent structure of wake flow in volute and its corresponding frequency information, dynamic modal decomposition (DMD), classic and spectral proper orthogonal decomposition (SPOD), were employed to decompose the transient flow field of the centrifugal pump volute. The snapshot set was constructed by means of the velocity field data at different moments in volute based on the large eddy simulation (LES) approach. The basic principles of the DMD, POD, and SPOD methods were compared in detail, and the decomposition results of the three methods on the wake flow structure in volute were compared and analyzed. The analysis results show that DMD can decompose the wake flow into coherent structures with different frequencies, including the basic steady-state structure, the dynamic modal flow field structure characterizing rotor–stator interaction (the first three modes with frequencies of 145.81, 291.61, and 437.43 Hz, respectively), and dissipative modal flow field structure characterizing fragmentized vortex (the fourth mode with a frequency of 486.03 Hz) in the volute. The POD can decompose the wake flow into flow structures with different energy levels. The first four modal energies account for more than 66% of total energy, which represents the large-scale structure with higher energy, and its dominant frequencies correspond to the blade passing frequency (145 Hz) and its frequency multiplication (290 Hz). The SPOD can not only decompose the complex wake flow into structural features of different energy levels but also has single-frequency characteristics of its modal structures. Compared with DMD and POD methods, the SPOD has the advantages of both, and can reflect the evolution characteristics of the wake flow in the volute.

Solar-powered adsorption desalination utilizing composite silica gel with a humidification-dehumidification desalination system

This work comes in light of addressing crises of freshwater scarcity, energy demand, and climate change to investigate innovative configurations of hybrid adsorption desalination integrated with a humidification dehumidification system powered by solar energy or waste heat in four operation modes. The investigation includes economic cost analysis and system performance using raw silica gel and silica gel/CaCl2 adsorbents under the weather data of Assiut-Egypt. System performance has been evaluated regarding daily water production, gain output ratio, and cooling effect using TRNSYS and MATLAB software. The combined configuration with heat recovery (the fourth mode) using silica gel/CaCl2 gives a relatively high freshwater production (69 m3/ton.day in June) compared with the basic adsorption desalination system using raw silica gel (7.1 m3/ton.day in June). Silica gel/CaCl2 in the first mode presented the highest cooling effect (555 W/kg) in June compared with silica gel in the primary system (197 W/kg). The third configuration's solar-powered silica gel/CaCl2 system shows a clear superiority of 1.8 in gain output ratio, compared with the basic system with and without heat recovery (0.54 and 0.4, respectively). The third configuration also provided the cheapest freshwater production among all configurations at 2 $/m3 in June.

Primary and secondary resonance phenomenon for two-layer liquid sloshing in a rectangular container under horizontal excitation

Laboratory experiments were conducted to study primary and secondary resonant sloshing in a laterally excited rectangular container containing two-layer stratified liquids. The findings revealed that primary resonance of the free surface or the separation surface occurs when the forcing frequency closely matches the corresponding natural frequency. Some intriguing phenomena, such as the sudden wave amplitude increase and the downward shift in resonant peaks, can be observed due to the soft-spring effect. Secondary resonance arises when superharmonic or sub-harmonic frequencies associated with liquid sloshing closely align with the natural frequencies of the system. For the free surface, the secondary resonances of the first five modes occur at forcing frequencies closely related to a third of the first mode, half of the second mode, a third of the third mode, a quarter of the fourth mode, and a fifth of the fifth mode natural frequency of the free surface, respectively. Furthermore, secondary resonance can also manifest under other forcing conditions, such as when the harmonic at a fractional multiple is near the second mode natural frequency of the free surface. Regarding the separation surface, it is worth noting that secondary resonance occurs due to the dominant contribution of fractional harmonics of the forcing frequency. To the best of the authors' knowledge, this is the first systematic investigation of primary and secondary resonance behaviors in a two-layer liquid system.

Investigation of the unsteady pressure fluctuation mechanism in a regenerative flow pump based on proper orthogonal decomposition

The regenerative flow pump (RFP) derives its name from the circular flow pattern akin to a vortex. However, the presence of numerous vortices results in highly turbulent flow and pressure fluctuation. This study delves into the characteristics of the internal unsteady flow in two distinct RFP models featuring different blade shapes. Numerical simulations are employed to obtain the pressure field, which is subsequently scrutinized using the proper orthogonal decomposition (POD) method. The results show that the average pressure in the peripheral direction undergoes minimal variation during the flow developing stage, experiences a sharp increase in the fully developed stage, and finally exhibits substantial changes in the stripper. The transient pressure in the time domain fluctuates periodically, and the dominant blade passing frequency in the frequency domain demonstrates a similar trend along the circumferential direction as the average pressure. Moreover, the fluctuating intensity of pressure diminishes along the impeller's rotating direction but intensifies significantly in the stripper. Comparative analysis indicates that the exchange intensity is influenced by the flow at different developmental stages, and the exchange flow conditions could reflect the fluctuating intensity. Furthermore, the study reveals that the frequency amplitude of the time coefficient gradually decreases as the mode order increases. The first and second modes exhibit a gradually changing trend associated with pressure increase patterns, whereas the third and fourth modes highlight the emergence of localized modulation phenomena linked to exchange flow. Thus, the POD method offers a unique perspective for comprehending the flow mechanisms within RFPs.

Lightweight and High-Stiffness Metal Optical Systems Based on Additive Manufacturing.

To build a long-wave infrared catadioptric optical system for deep space low-temperature target detection with a lightweight and wide field of view, this work conducted a study that encompasses a local cooling optical system, topology optimization-based metal mirror design, and additive manufacturing. First, a compact catadioptric optical system with local cooling was designed. This system features a 55 mm aperture, a 110 mm focal length, and a 4-degree by 4-degree field of view. Secondly, we applied the principles of topology optimization to design the primary mirror assembly, the secondary mirror assembly, and the connecting baffle. The third and fourth modes achieved a resonance frequency of 1213.7 Hz. Then, we manufactured the mirror assemblies using additive manufacturing and single-point diamond turning, followed by the centering assembly method to complete the optical assembly. Lastly, we conducted performance testing on the system, with the test results revealing that the modulation transfer function (MTF) curves of the optical system reached the diffraction limit across the entire field of view. Remarkably, the system's weight was reduced to a mere 96.04 g. The use of additive manufacturing proves to be an effective means of enhancing optical system performance.

Nonlinear vibrations of a slightly curved Maxwell viscoelastic pipe conveying two phase flow under various boundary conditions

Two phase flows are common in pipeline engineering, and most times, the assumption of single phase flow is usually assumed. In this paper, the dynamics of a slightly curved Maxwell viscoelastic pipe conveying two phase flow under four boundary conditions; cantilever, simple supported, clamped simply supported and clamped clamped supported is investigated. Eigenfunction expansion was used to discretize the PDE into four modes. The linear analysis results show that the Maxwell viscoelastic parameter has no significant effect on the first and the second modes of the vibration, but on the third and fourth modes for the three boundaries conditions considered. The void fraction has effects on the frequency and critical velocity only if the densities of the components of the two phase fluid are significantly large. The nonlinear dynamics shows that Maxwell viscoelastic parameter reduces the bifurcation position and changes the bifurcation point from being sharp to a gentle curve at the bifurcation point. Further results were presented for the Maxwell parameter and velocity of fluid and temperature loading on the pipe, which are very important to understanding the behavior of Maxwell viscoelastic pipe conveying two phase flow.

Behavior of a Rock Mass in Uplift Field Tests of Rock Anchors

AbstractRock anchors are high-capacity reinforcement measures used to stabilize large-scale infrastructures. According to the literature, they can fail in one of the four ways: (1) steel tensile failure; (2) tendon–grout interface failure; (3) grout–rock interface failure; and (4) rock mass uplift failure. Rock mass uplift field tests were performed in a limestone quarry to test this fourth failure mode. The tests were designed to induce rock mass failure around rock anchors. The ground surface heaved asymmetrically around the anchors and the pre-existing joints in the rock mass tended to open first. The seismic activity in the rock mass was greatest close to the anchor, decreasing with distance. The failure crater in the rock followed the joint sets in the rock mass, and the shape was partly controlled by the pre-existing joints. The apex angle of the failures was measured to be between 125 and 140$$^{\circ }$$ ∘ . The horizontal stress in the rock mass increased when the anchor was pulled, indicating load arching around the anchor. The observed failure was a combination of rock mass uplift and grout–rock bond failure. The measured anchor capacity was much higher than the estimated rock mass capacity using the recommended design methods of the Norwegian Public Roads Administration.

Equatorial wave diagnosis for the Atlantic Niño in 2019 with an ocean reanalysis

Abstract. The propagation of equatorial waves is essential for the onset of Atlantic Niño, but diagnosing waves with ocean reanalysis or in situ data remains a challenge. This study uses an ocean reanalysis to diagnose the wave energy transfer route during the 2019 event. The climatological values and the anomaly in 2019 at each grid point are decomposed into the first four baroclinic modes based on their local density profiles. The decomposed geopotential can well reproduce the displacement of the thermocline during the event. Wave energy flux is calculated by means of a group-velocity-based scheme. In addition to detecting wind-forced Kelvin waves and reflected Rossby waves, the wave energy flux reveals another possible energy transfer route along the western boundary, where some off-equatorial wave energy can excite coastally trapped Kelvin waves and transfer back to the equatorial Atlantic. Five transects are selected, across which the passing wave energy fluxes in 2019 are integrated. The results suggest that the Kelvin waves in the third and fourth mode are locally forced, while the wave energy in the second mode is more likely from the off-equatorial region. Therefore, in the autumn of 2019, the second-mode Kelvin waves can deepen the thermocline ahead of other modes from September, serving to precondition the Niño event.

Impact of stratospheric variability on subseasonal temperature reversals during late winter over the mid-high latitudes of East Asia

Significant phase shifts in winter surface air temperature (SAT) anomalies have successively occurred in East Asia (EA) during recent years, leading to detrimental effects on socio-economic activities. In this study, we identify the fourth principal mode of month-to-month SAT variations over EA in winter (November–February) using the Season-reliant Empirical Orthogonal Function (S-EOF) analysis. The fourth S-EOF mode (S-EOF4) represents subseasonal SAT reversals over the mid-high latitudes of EA during late winter (January–February), with cold (warm) anomalies over Northeastern Asia in January and widespread warm (cold) anomalies over midlatitude EA in February. Results indicate that the cold-to-warm S-EOF4 is associated with a northward shift of the Siberian High in January and a quasi-barotropic low-pressure system over the Ural region in February. The formation of the S-EOF4 is accompanied by stratospheric temperature anomalies over eastern Siberia–Alaska in January. Stratospheric warming corresponds to cold-to-warm transitions over the mid-high latitudes of EA, and vice versa. Further investigation suggests that stratospheric warming would simultaneously lead to a weakened Arctic stratospheric polar vortex (SPV), which mainly stretches into Northern Eurasia and directly influences cold anomalies over Northeastern Asia in January. The delayed impact of stratospheric variability on the reversal of EA SAT anomalies is accomplished by an “ocean bridge” of the midlatitude North Atlantic sea surface temperature (SST) anomaly. The weakened SPV promotes anomalous westerly winds in the midlatitude North Atlantic and generates a significant SST cooling, which then regulates a cyclonic anomaly over the Ural region and results in warm anomalies over the midlatitude EA in February. The bridge role of the North Atlantic SST anomaly is well supported by a linear baroclinic model. In addition, the deepening of the Aleutian Low in December could significantly enhance the climatological wavenumber 1, serving as the tropospheric precursor of stratospheric warming. These findings contribute to an in-depth comprehension of EA subseasonal temperature variability, offering valuable insights for enhancing seasonal prediction strategies.

Doing and undoing transgender health care: The ordering of 'gender dysphoria' in clinical practice.

A formal Gender Dysphoria classification- as outlined in the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders- is a prerequisite for the reimbursement of both gender-affirming medical care and transgender mental health care in the Netherlands. Gender Dysphoria and its conceptual precursors have always been moving targets: moving due to research, policy, care practices and activism both within and outside of medicine. This raises the question of what Gender Dysphoria is exactly. To elucidate this question, we turn to the people who use the concept in clinical practice to come to a diagnosis and treatment indication: mental health professionals working in gender-affirming medical care and transgender mental health care. Using a material semiotics approach, we reflect upon how Gender Dysphoria is done in clinical practice. Based on an analysis of seventeen practice-based interviews with clinicians as well as an examination of clinical guidelines and texts, we describe four modes in which Gender Dysphoria is ordered. These modes of ordering illustrate that Gender Dysphoria is not one, but multiple. We illustrate how in the mode of isolating, Gender Dysphoria is something which is carefully isolated from mental disorders, while in the modes doing the future and narrating, Gender Dysphoria is done as a continuous and predictable object of care. Such orderings of Gender Dysphoria potentially conflict with a fourth mode of ordering: the doing of diversity in transgender health care. The study's findings provide empirical insights into how transgender health care is currently done in The Netherlands and provide a foundation on which ethical debates on what good transgender health care should entail.

Effects of temperature ratio on combustion instability in a non-premixed hydrogen-rich ram combustor

The effects of the burnt-to-unburnt temperature ratio (Tb/Tu) (reciprocal density ratio) on thermoacoustic combustion instability were investigated in a hydrogen-rich ram combustor by controlling the inlet air temperature under cruising conditions. Steady and unsteady combustion dynamics were investigated with the simultaneous measurement of combustion pressure and near-infrared (NIR) emissions. Time-resolved NIR images were analyzed using dynamic mode decomposition (DMD) to extract modes of the combustion instability, which show two oscillation modes: longitudinal (500 Hz) and flame-vortex interaction modes (2000 Hz) with a Strouhal number of approximately 0.5. The thermoacoustic combustion instability was not excited at Tb/Tu = 3.3, but was excited at Tb/Tu= 2.6 and 2.9. The DMD modes show that the structure of the vortex mode is similar to that of the fourth longitudinal mode at Tb/Tu = 2.6 and 2.9, indicating that the coupling of the vortex and the fourth longitudinal modes excited the thermoacoustic combustion instability.

Active Vibration Control Using Loudspeaker-Based Inertial Actuator with Integrated Piezoelectric Sensor

With the evolution of the aerospace industry, structures have become larger and more complex. These structures exhibit significant characteristics such as extensive flexibility, low natural frequencies, numerous modes, and minimal structural damping. Without implementing vibration control measures, the risk of premature structural fatigue failure becomes imminent. In present times, the installation of inertial actuators and control signal acquisition units typically requires independent setups, which can be cumbersome for practical engineering purposes. To address this issue, this study introduces a novel approach: an independent control unit combining a loudspeaker-based inertial actuator (LBIA) with an integrated piezoelectric ceramic sensor. This unit enables autonomous vibration control, offering the advantages of ease of use, low cost, and lightweight construction. Experimental verification was performed to assess the mechanical properties of the LBIA. Additionally, a mathematical model for the LBIA with an integrated piezoelectric ceramic sensor was developed, and its efficacy as a control unit for thin plate structure vibration control was experimentally validated, showing close agreement with numerical results. Furthermore, the LBIA’s benefits as an actuator for low-frequency mode control were verified through experiments using external sensors. To further enhance control effectiveness, a mathematical model of the strain differential feedback controller based on multi-bandpass filtering velocity improvement was established and validated through experiments on the clamp–clamp thin plate structure. The experimental results demonstrate that the designed LBIA effectively reduces vibration in low-frequency bands, achieving vibration energy suppression of up to 12.3 dB and 23.6 dB for the first and second modes, respectively. Moreover, the LBIA completely suppresses the vibration of the fourth mode. Additionally, the improved control algorithm, employing bandpass filtering, enhances the effectiveness of the LBIA-integrated sensor, enabling accurate multimodal damping control of the structure’s vibrations for specified modes.

An analytical model of seated human body exposed to combined fore-aft, lateral, and vertical vibration verified with experimental modal analysis

While most of the previous studies on biodynamics of the seated human body focused on vertical vibration in the sagittal plane, this study was designed with combined tri-axial translational vibration excitation to investigate the biodynamics in both sagittal and coronal planes. In this study, an analytical model was developed to represent the biodynamic responses of the seated human body to tri-axial translational vibration. The model consisted of thighs, pelvis, lumbar spine (L3 and L4), middle torso (thoracic spine T5-T12 and lumbar spine L1-L2), upper torso (thoracic spine T1-T6), and head (including cervical spine C1-C7). The transmissibilities from the seat to various body locations of subjects sitting with an upright backrest under single-axis and tri-axial vibration were measured. The parameters of the seated human model were determined by fitting the modelled in-line transmissibilities to the chest, L3 and pelvis along the fore-aft, lateral and vertical directions to the measured values. Five vibration modes were identified from the measured transmissibilities below 20 Hz. The first mode at 1.3 Hz featured the lateral sway of the upper body in the coronal plane. The second mode at 2.5 Hz characterised the lateral motion of the whole body accompanied by the lateral bending motion of the torso. The third mode at 3.6 Hz contained the fore-aft and pitch movements of the upper body with pitch of the pelvis. The fourth mode at 6.4 Hz included the vertical motion of the entire body with pitch of the pelvis, and the fifth mode at 10.3 Hz involved the vertical motion of the thighs with pitch and vertical motion of the pelvis. The model was verified with the measured vibration modes. This study provided a method for the identification of model parameters using the body transmissibilities and modal properties.

Influence of travelling waves on the fluid dynamics of a beam submerged in water

Inspired by the use of travelling waves for propulsion mechanisms adopted by many animals and organisms, this paper investigates the mechanism with which travelling waves in beam-like structures induce velocity in a surrounding fluid. This work focuses on the flow induced around the beam tip and provides an experimental characterisation of the phenomena. A test rig equipped with Laser Doppler Anemometry (LDA) is used to investigate the induced fluid velocity and its dependency on the modal response of the beam. Numerical simulations are performed to complement the experimental tests and provide further insight into the fluid–structure interaction. The numerical model also allows for the beam vibration envelope and vibration patterns to be obtained and correlated with the measured fluid velocity. Several geometrical variations are considered in the analysis over a range of frequencies that encompass resonant responses up to the fourth mode. The results showed that the fluid flow is only marginally affected by the change in the vibration pattern between the first-two resonant mode; the induced fluid velocity and, hence, the thrust are mostly driven by the tip velocity of the beam.

Current progress of immunotherapy based on NK cell in cancer therapy

Cancer generally refers to malignant tumor, including carcinoma, sarcoma and carcinosarcoma. This disease is caused by malignant cell hyperplasia. It is invasive and metastable. It is manifested by the continuous growth of a local mass of the body that destroys the normal tissue structure and can be transferred to other sites. It has been reported that there will be about 20 million new cases of cancer in 2020 and half of all cancer patients will die. Surgery, chemotherapy and radiotherapy, as the three standard treatment methods for cancer, plays an vital role in improving the survival rate and prolonging the survival time of cancer patients. In recent years, researchers have focused on the immune mechanism of tumors to explore the treatment of malignant tumors. Driven by the rapid development of modern molecular biology and gene engineering technology, immunotherapy has been paid more and more attention, showing good effect and application prospects, has become the world's recognized malignancy of the fourth treatment mode. Among these, natural killer cells (NK) fight cancer through their cytolytic function and the production of IFN-γ. One of the primary clinical objectives is to use their abilities for tumour immunotherapy. This article looks at advances in NK cell-based tumor therapy.

PCCI-DI Combustion Simulation for Significant Reduction of NOX and PM for GENSET Engine

Improvements in engine combustion are required due to the stringent pollution norms. This can be achieved either by making improvements in the combustion or by equipping after-treatment devices to control engine emission levels. PCCI is one of the popular techniques used to enhance the combustion. In this work, Diesel-RK software is used for the simulation. The main and pre-injection timings are altered to give the benefits in power and emissions. Based on a literature survey, the fourth and fifth modes are finalized for PCCI combustion simulation. The amount of total fuel injected was kept the same to compare the performances in DI and PCCI modes. The simulation results show the reduction in soot (PM) and NOx simultaneously with the help of PCCI concept at lower BMEP levels. The results show a decrease in PM by up to 26%, a reduction in NOx by up to 30% and an increase in power by 2%.

DOMINANT SPATIOTEMPORAL MODES OF ARCTIC SEA ICE DURING 2000–2020

This study quantifies drastic variations of Arctic sea ice during 2000–2020. Four dominant modes revealed 32.18%, 14.6%, 9.34% and 8.25% of the total variance of sea ice concentration over the Arctic. The first two dominant modes have exhibited seesaw structures on the Atlantic and Pacific sectors of the Arctic over the past 20 years: Sea ice increased in the southwest of Greenland and reduced in the northeast; sea ice decreased drastically in the Bering Sea but increased in the Okhotsk Sea. An overall increase of sea ice in the Arctic occurred in the third dominant mode, while a seesaw structure appeared in the Barents Sea in the fourth dominant mode. At the end, the influence of the Arctic atmosphere and upper-ocean state on the Arctic sea ice variation was investigated.

An Analytic Solution for the Dynamic Behavior of a Cantilever Beam with a Time-Dependent Spring-like Actuator

The purpose of this study is to derive an analytical solution for a cantilever beam with a novel spring-like actuator that behaves like a time-dependent spring and to study the dynamic behavior of the system. A time-dependent spring was set at the free end of the cantilever beam to model the novel spring-like actuator. First, the boundary conditions were transformed from being nonhomogeneous to being homogeneous using the shifting function method. The solution of the analytic series was then obtained by using the expansion theorem method. The correctness of the proposed analytical solution was verified by comparing the results with those obtained via the separation of variables in the special extreme case of a constant spring coefficient. We took the free end of a cantilever beam with harmonic spring stiffness and an external periodic unit load as an example. The influence of the actuator parameters, such as the effect of the magnitude and the frequency of the time-dependent spring stiffness on the resonance frequency, was investigated. An important new result was found, i.e., that the resonance frequency is clearly dependent on the magnitude and the frequency of the spring-like actuator in the first two modes, but not in the third and fourth modes. In practical engineering applications, system resonance can be avoided by adjusting the magnitude and frequency of the actuator.

Optimal phase compensation for a rotor-AMB system considering interface contact

Rotor-Active magnetic bearing (rotor-AMB) systems offer significant advantages in power consumption and are increasingly being applied in fluid machinery. However, in such machinery, the impeller and the rotor are commonly connected by bolt fastening. Once a certain pre-tightening force is applied to the bolted connection and the interface contact between the rotor and the impeller is formed, the flexible modal vibration will be excited when the rotor is levitated. The conventional Proportional-Integral-Derivative (PID) controller is limited in this vibration suppression and it is essential to increase the damping at bending mode to inhibit vibration. However, the calculation of the optimal phase compensated is based on the rotor-AMB model considering interface contact. In this work, the effect of the interface contact is equivalent to massless spring units, and the disturbance generated by spring units is acted upon the mechatronic system in the way of positive feedback. The detailed description of the transfer function from the disturbance to rotor deformation at fourth bending mode is obtained by theoretical model and system identification. The optimal phase of the system needed to inhibit the disturbance is determined by minimizing the gain of the transfer function at fourth bending mode. A combination of PID control and phase compensation is implemented in the experiment. The results show that the optimal phase is 50° as the calculation and the optimal phase compensation control can sufficiently inhibit the modal vibration.