Initial Branch Research Articles

Vortex-induced vibrations of an elliptic cylinder of low mass ratio: Identification of new response branches

The classical resonance branches that construct the response of a freely vibrating circular or elliptic cylinder at low Reynolds numbers, Re, are “initial” and “lower.” The existence of additional response branches, if any at low Re via alteration of controlling parameters, is unavailable in the literature. In this computational work, relating to a low mass ratio (m* = 1) and zero damping, i.e., m*ζ = 0 transverse-only vortex-induced vibrations of an elliptic cylinder over Re = 50–180, four response branches that are unreported in the literature are identified. The lock-in at such a low mass ratio is non-classical, and the new response branches are resolved close to the lock-in boundaries. These additional branches are designated as extended initial branch, extended lower branch, terminal branch, and quasi-periodic desynchronization branch. The method proposed by Kumar et al. [“Identification of response branches for oscillators with curved and straight contours executing VIV,” Ocean Eng. 164, 616–627 (2018b)] has been employed to identify the branches by locating the Re region concerning the change of slope and discontinuous jumps of oscillation frequency. It is further shown that branching at a low mass ratio depends on structural damping, oscillator shape, and degree-of-freedom.

Effect of surface roughness on vortex-induced vibrations of a freely vibrating cylinder near a stationary plane wall

The effects of surface roughness of the vortex-induced vibration (VIV) responses of a circular cylinder near a stationary plane wall were studied using the two-dimensional unsteady Reynolds-averaged-Navier-Stokes equations and the shear stress transport k−ω model coupling with a fourth-order Runge-Kutta method. A smooth cylinder and rough cylinders with three different degrees of surface roughness were selected for the study. The VIV response amplitude, structural vibration frequency, lock-in region, vortex shedding flow pattern, Strouhal number and hydrodynamic coefficient for cylinders with different degrees of surface roughness were compared. The numerical results show that for a smooth cylinder and a cylinder with small surface roughness, the reduced velocity range can be separated into four parts based on the VIV amplitude: an initial branch, an upper branch, a lower branch and a desynchronization region. However, for cylinders with intermediate and large surface roughnesses, the upper branch is absent, leaving only three branches. The lock-in phenomenon can apparently be found for all surface roughnesses, but the width of the lock-in region is not very sensitive to the variation of the surface roughness. As surface roughness increases, the Strouhal number has an increasing tendency; however, the mean drag coefficient has a decreasing tendency.

A phenomenological model for the inelastic stress–strain response of a potato tuber

In this article, we synthesise concepts from the theories of plasticity, volumetric growth, and pseudo-hyperelasticity to develop a phenomenological constitutive model for potato tuber tissue. Here, particular focus is laid on the inhomogeneity of the constitutive behaviour across different anatomical zones of a potato tuber. The internal stresses are expressed in terms of an elastic contribution to the local strains and are controlled by a kinetic memory variable that traces the past strain history. Inelastic strains, by contrast, are considered as a combination of a plastic component and a pure volumetric component mimicking the eviction of fluid. Considering tubers of cultivar Belana, we identify the relevant constitutive parameters based on stress–stretch curves obtained from single-cycle uniaxial compression experiments on samples extracted from different anatomical tuber parts. The stress–strain response of the tissue is characterised by a pronounced and well-reproducible hysteresis which displays slight stiffening along the initial loading branch. Considering the parenchyma microstructure, the significant reduction in tissue turgidity on unloading may be caused by the eviction of intracellular fluid from the parenchyma cells and an inelastic cell wall response. The experiments show that the inelastic volume change varies approximately linearly with the axial stretch. Additionally, histological analyses are presented in an attempt to quantify microstructural inhomogeneities.

Hysteretic Interference of Magnetic Field of a Moving Linear Inductor

Coordinate distributions U(x) were calculated for the electric voltage across a magnetic field sensor scanning a magnetic carrier with recordings of pulsed magnetic fields from a linear inductor moved discretely with a given pitch above the magnetic carrier surface. The magnetic carrier was acted upon with pulses of one direction and with oppositely directed pulses. The characteristics of the magnetic field sensors used in experimental studies were expressed as analytical arctangent functions. An arctangent initial curve and hysteresis branches of the dependence of electric voltage U(H) across the magnetic field sensor on magnetic field strength when the sensor scans a magnetic carrier are presented. These curves correspond to the distribution of remanent magnetization in the magnetic carrier in a pulsed magnetic field. The sensitivity of the magnetic field sensors used in the calculations was $${{\gamma }_{{{\text{max}}1}}} = $$ 1.0 mV cm/A, $${{\gamma }_{{{\text{max}}2}}} = $$ 0.26 mV cm/A, $${{\gamma }_{{{\text{max}}3}}} = $$ 2.8 mV cm/A. Sequences are established in which the remanent magnetization changes in the magnetic carrier exposed to unipolar and bipolar magnetic-field pulses. Hysteretic interference is represented as the interference of the distributions of the electric voltage across the sensor in a pulsed magnetic field U(x) along the coordinate x. The results of calculations of the magnitude of electric voltage U across the sensor are presented for layers of aluminum foil with a thickness on the order of 0.05 mm by hysteretic and anhysteretic methods. It is shown that the use of hysteretic interference can increase threefold or more the sensitivity of measuring instruments.

Undamped transverse-only VIV of a diamond cylinder at low Reynolds numbers

There have been only a few investigations lately to analyze the flow-induced vibrations of a diamond cylinder, i.e. a square cylinder inclined at 45 ∘ to the free-stream at low and high Reynolds numbers, Re. However, for transverse vortex-induced motions of diamond cylinders at low Re, features of response branching, mean surface pressure, wake modes and fluid loading are less explored. We investigate numerically at Re=100, undamped hydroelastic vortex-induced vibrations of a diamond cylinder over a well-resolved U∗ range of 1 to 12. The order of magnitude of the maximum response as well as branching of response of the diamond oscillator are analogous to those of the circular cylinder and depart considerably from the ones of a square cylinder at zero incidence. Interestingly, the mean lift from this nominally symmetric cross-section deviates from zero at U∗ values of 3.5 and 4.2 corresponding to the quasi-periodic initial branch and periodic lower branch, respectively. At U∗=3.5 corresponding to low amplitude oscillations, three distinct asymmetric wake modes are identified: asymmetric 2S and two one-sided modes of different nature. The well known asymmetric P+S mode is identified at U∗=4.2 relating to high amplitude oscillations.

Purification of mercury-contaminated water using new AM-11 and AM-14 microporous silicates

Water is an essential resource on Earth and the maintenance of its quality led to the incentive of water reuse programmes. Among the most relevant contaminants, mercury is recognized for its toxicity and biomagnifications along the food chain, reason why its removal from aqueous solutions was studied in this essay using two microporous materials for the first time. The ability of a niobium silicate, called AM-11 (Aveiro-Manchester No 11), and of a vanadium silicate, AM-14 (Aveiro-Manchester No 14), were assessed under batch conditions, at fixed temperature and pH. These microporous materials were synthesized and characterized by SEM, PXRD, ICP-OES, TGA and elemental analysis. Because of their excellent ion exchange properties, equilibrium and kinetics assays were performed using only a few mg dm−3 of material. The most relevant two- and three-parameter isotherms were used to fit the experimental data. Langmuir isotherm adjusted better the AM-11 data (deviation of 3.58 %, Radj2=0.980, AIC=52.8), predicting a maximum uptake of 161 mg g−1, while the AM-14 data were better fitted by the Temkin model (deviation of 3.92 %, Radj2=0.985, AIC=54.2). The kinetic study was performed using Elovich, pseudo-first order and pseudo-second order models. The pseudo–second order and Elovich equations provided the best fits for both materials. The Elovich equation achieved a better correlation in the initial branch while the pseudo-second order expression was more efficient for the horizontal branch. The intraparticle diffusivities of counter ions were also assessed using a kinetic model based on the Nernst-Plank equations. Performance of these two microporous materials to remove mercury has been compared with other sorbents, highlighting their potential as ion exchangers.

Experimental research on vortex-induced vibrations of flexible circular cylinders at low Reynolds number: revealing atypical branches

This study presents the experimental results of 31 cantilevered flexible circular cylinders, subjected to vortex-induced vibrations, with different materials, diameters and lengths. Diameter and length ranges are 1.56 mm ≤ D ≤ 3.19 mm and 30 cm ≤ L ≤ 40 cm, respectively. Tested materials are aluminum, bronze, copper and stainless steel. A total of 1905 experimental points were obtained and processed with the Particle Velocimetry technique. A Matlab code was developed to obtain the maximum amplitude for several Reynolds number through the synchronization regime. Reynolds number range is 75 ≤ Re ≤ 1050. Results illustrate the existence of four different groups corresponding to different maximum amplitude behaviors. As some of these behaviors are not yet reported in the literature, each branch is distinguished and explained in detail. One group presents two local maximum amplitudes and the global maximum is not located in the initial branch as usually expected. In order to classify all the groups, several parameters were analyzed. The slope of reduced velocity vs Reynolds number resulted in the best parameter. This parameter, and therefore the classification of a given cylinder, can be predicted through a 2D polynomial linear fit by knowing only the L/D and mass damping ratios.

Excitation and Damping Fluid Forces on a Cylinder Undergoing Vortex-Induced Vibration

In the context of flow-induced vibration, the component of the hydrodynamic coefficient in-phase with the velocity of an oscillating body, $C_v$, can be termed `positive excitation' or `negative damping' if $C_v>0$. While this empirical approach is of long standing in the literature it does not account for distinct physical mechanisms that can be associated with fluid excitation and fluid damping. In this work, we decompose the total hydrodynamic force into a drag component aligned with the time-dependent vector of the relative velocity of a cylinder oscillating transversely with respect to a free stream and a lift component normal to the drag component. The drag and lift components are calculated from laboratory measurements of the components of the hydrodynamic force in the streamwise and cross-stream directions combined with simultaneous measurements of the displacement of an elastically mounted rigid circular cylinder undergoing vortex-induced vibration. It is shown that the drag component only does negative work on the oscillating cylinder, i.e. it is a purely damping force as expected from theoretical considerations. In contrast to this the lift component mostly does positive work on an oscillating cylinder, i.e. it is the sole component providing fluid excitation. In addition, the new excitation (lift) coefficient, $C_L$ displays the same scaling as the linear theory predicts for the traditional excitation coefficient, $C_v$, even though $C_L$ is two orders of magnitude higher than $C_v$. More importantly, while $C_v$ depends on the mechanical properties of the hydro-elastic system, according to linear theory, we provide here evidence that $C_L$ depends solely on fluid-dynamical parameters. Finally, an effective drag is calculated that represents the dissipation of energy within the fluid, and it is found that the effective drag is not equal to the mean value of the drag component. The effective drag provides complementary information that characterizes the state of the wake flow. Its variation suggests that the wake can dissipate the kinetic energy most vigorously at the end of the initial branch.

The effects of submergence depth on Vortex-Induced Vibration (VIV) and energy harvesting of a circular cylinder

Vortex-Induced Vibration (VIV) is a kind of high-energy phenomena and can be used to harvest energy from ocean/river currents. In this paper, a spring-mounted circular cylinder in VIV was numerically investigated with 2-dimensional simulations to examine the effects of submergence depth on the energy conversion. The flow speed changes from 0.2 m/s to 1.3 m/s (1.61 × 104<Reynolds number<1.05 × 105), covering three different VIV branches (i.e. initial branch, upper branch and lower branch). The submergence depth changes from 0.1 m to 0.5 m. Results indicate that proximity to the free surface significantly affects the VIV responses. As the submergence depth decreases from 0.5 m to 0.1 m, the VIV amplitude is gradually suppressed resulting in a similar drop in energy conversion. The maximum energy conversion efficiency (34.7%) is achieved in the VIV upper branch with the submergence depth S = 0.5 m. When the submergence depth reaches up to the critical submergence depth S = 0.5 m, the VIV amplitude and converted power no longer increase, which means the effects of submergence depth or the disturbance from the free surface can be ignored. It is also found that when the flow speed exceeds 1.2 m/s (Reynolds number>9.7 × 104), the oscillation amplitude of the cylinder decreases to zero. In this case, the oscillation response doesn’t belong to VIV.

Study on the technique of single-layer initial arch cover method in Hongyan Village Station

Aiming at the geological characteristics of the upper soft and hard stratum in Chongqing area, taking the Hongyan Village Station of Metro Line 9 as an example, the excavation method of super-large section single-layer initial arch cover method is proposed. The finite element numerical simulation is used to analyze the horizontal and vertical displacement of the surrounding rock, the axial force and bending moment of the single-layer initial arch cover, and the axial force distribution of the anchor. It is concluded that the single-layer initial arch cover method can meet the control requirements of deformation and surface settlement of super-large section surrounding rock. The initial arch cover of H220 grill steel frame + φ25, L=4.5m hollow grouting anchor + 300mm thick C25 wet-sprayed concrete can meet the bearing capacity requirements and ensure the overall stability of the structure. The connection mode of the large arch and the side wall arch is optimized to ensure that the initial branch is completely closed and looped. Combined with on-site monitoring and measurement data, it is feasible to use a single-layer initial arch cover method at Hongyan Village Station.

Wake adjustment and vortex-induced vibration of a circular cylinder with a C-shaped plate at a low Reynolds number of 100

The vortex-induced vibration (VIV) of a circular cylinder with a C-shaped plate arranged in its wake at a low Reynolds number of 100 is numerically investigated in this work using the direct numerical simulation. Four typical streamwise spacing ratios of 1.5, 3, 4.5, and 6 are examined in the computations that were carried out for the range of reduced velocities (Ur = 2–12). In terms of shear layer reattachment, wake interference, and vortex shedding, five flow regimes are identified, i.e., the extended-body regime, the front-face reattachment regime, the shear-layer combination regime, the one-row co-shedding regime, and the two-row co-shedding regime. The wake regime is sensitive to the spacing ratio and the reduced velocity. The switching of the flow regime occurs at the transition between the initial VIV branch and the lower VIV branch, accompanying a phase jump of 180°. Furthermore, the shift of the wake regime leads to the prominent fluctuation of the response amplitude. Among the five regimes, the two-row co-shedding regime has the maximum wake width, resulting in the maximum amplitude. In contrast, the shear layers are elongated in the extended-body regime and hence the prolongation of the vortex formation length, contributing to the suppression of VIV. The best suppression is achieved by placing the C-shaped plate behind the cylinder with a spacing of 1.5D, and the reductions in the lift force and the cross-flow amplitude reach 85.5% and 94.5%, respectively.

Two-degree-of-freedom vortex-induced vibrations of a circular cylinder in the vicinity of a stationary wall

This paper presents a numerical investigation on the two-degree-of-freedom vortex-induced vibrations of a single circular cylinder near a stationary plane for gap ratio G/D = 0.6 – 3.0, normalized boundary layer thickness δ∕D=0 – 3.5, Reynolds number Re=100 and reduced velocity Ur=2 – 16, where D is the cylinder diameter. Extensive simulations are carried out to capture the features of the cylinder vibration, hydrodynamic forces, and wake flows. Three regimes are classified based on the characteristics of the vibration responses at different boundary layer thicknesses, with the largest vibration amplitude in both the streamwise and transverse directions achieved in regime II. Hysteresis exists between the initial and lower branches due to the bi-stability of the boundary layer reattachment point on the vibrating cylinder. The phase difference between the vortex lift and the displacement shows a 180°jump at the initial → lower branch transition. Within the transition, the total lift is dominated by the second harmonic.

Intermittency in free vibration of a cylinder beyond the laminar regime

Vortex-induced vibration of a circular cylinder that is free to move in the transverse ($Y$) and streamwise ($X$) directions is investigated at subcritical Reynolds numbers ($1500\lesssim Re\lesssim 9000$) via three-dimensional (3-D) numerical simulations. The mass ratio of the system for all the simulations is $m^{\ast }=10$. It is observed that while some of the characteristics associated with the $XY$-oscillation are similar to those of the $Y$-only oscillation (in line with the observations made by Jauvtis &amp; Williamson (J. Fluid Mech., vol. 509, 2004, pp. 23–62)), notable differences exist between the two systems with respect to the transition between the branches of the cylinder response in the lock-in regime. The flow regime between the initial and lower branch is characterized by intermittent switching in the cylinder response, aerodynamic coefficients and modes of vortex shedding. Similar to the regime of laminar flow, the system exhibits a hysteretic response near the lower- and higher-$Re$ end of the lock-in regime. The frequency spectrum of time history of the cylinder response shows that the most dominant frequency in the streamwise oscillation on the initial branch is the same as that of the transverse oscillation.

The Hepatic Central Vein: Anatomical and Molecular Links to Perivenous Liver Biology

The hepatic central vein, the initial branch of the hepatic veins, occupies the central position in the classic liver lobule. The endothelial cells of the vein contain organelles showing secretory modality and are supported by a thin wall containing collagenous matrix and a layer of myofibroblasts. Perivenous hepatocytes differ in ultrastructure from periportal heatocytes and stably express glutamine synthetase serving as a reliable biomarker . Central veins are a primary source of Wnt2, Wnt9b and R-spondin3. These angiocrines participate in the cellular-molecular circuitry of the Wnt/s-catenin and R-spondin-LGR4/5-ZNRF3/RNF43 signaling modules associated with perivenous hepatocytes. These modules regulate hepatic metabolic zonation and perivenous gene expression. The structures of the molecules of these signaling pathways have been elucidated. Expression of glutamine synthetase and cytochrome P4502E1 is indicator of s-catenin activity in liver injury and regeneration . The production, transport and secretion of lipidated Wnts in Wnt-producing cells and their passage in the extracellular matrix to contact responder cells have been described. The modes of Wnts and R-spondin3 release from cental vein endothelial cells and passage in the wall matrix to reach perivenous hepatocytes are unknown. GS + , Axin2 + , Tbx3 + , HNF4a + and CPS - perivenous hepatocytes exhibit stem cell properties, subserving homeostatic hepatocyte renewal. The hepatic central vein constitutes an anatomical niche of perivenous hepatocyte stem cells and provides a molecular link to perivenous hepatic biology.

The effect of cubic stiffness nonlinearity on the vortex-induced vibration of a circular cylinder at low Reynolds numbers

The vortex-induced vibration (VIV) of a circular cylinder elastically supported by linear and cubic springs is investigated numerically at low Reynolds numbers. The cylinder has a low mass ratio and zero structural damping. Nine dimensionless cubic stiffness nonlinearity strength values are considered. It is found that within the parameter space examined, the VIV response for the linear and softening springs can be divided into four regimes, namely the initial, upper, lower and desynchronised regimes. When the softening spring nonlinearity gets stronger, there exist a reduction in the peak amplitude and shifts in the initial-upper branch and upper-lower branch transitions to lower Reynolds number ranges. In contrast, as the hardening spring nonlinearity increases, the response envelope moves to a higher Reynolds number range and the profile of the initial and upper branches becomes smoother with the lower branch gradually disappearing. In the hardening spring case, the beating response is observed near the low end of the initial branch up to the high end of the initial branch. The modulations in the vibration amplitude gradually diminish with increasing Reynolds number. The cubic spring results coincide with those of the linear spring when they are presented with the equivalent reduced velocity. Due to the low Reynolds number range considered, the majority of the vortex shedding is in the 2S mode. The wake in the cases with smaller vibration amplitudes exhibits a single-row configuration. Whereas, a double-row vortex street is mainly observed in the upper branch. Disorders in the wake are found to be associated with beating responses which have larger vibration amplitudes.

Vortex-induced vibration of a single degree-of-freedom flexibly-mounted horizontal cylinder near the free surface

This paper reports findings from an experimental study on vortex-induced vibration of a horizontal, flexibly-mounted cylinder positioned near the free surface of fluid flow. The cylinder is allowed to oscillate in the vertical direction only. Oscillation amplitude and frequency data are presented as a function of reduced velocity and dimensionless depth from the free surface. Data are presented for cases of decreasing depth from where the resting cylinder is fully-submerged until its centerline is even with the free surface of the water. For a fully-submerged cylinder, VIV behavior is consistent with published findings of similar systems, producing a well-documented lock-in region with initial, upper, and lower branches. Broadly, as the cylinder is raised from the fully-submerged case, the amplitudes diminish and the lock-in region decreases in range and shifts toward higher reduced velocities. When the cylinder is very near the surface, a second region of oscillations occurs at higher reduced velocities. This region emerges in cases where the cylinder’s top edge is half a diameter below the free surface. For a short range of depths, the lock-in region and the non-zero amplitude region at higher reduced velocities coexist. But after a critical depth, the lock-in region disappears and oscillations are observed only at the higher reduced velocity region. Multi-frequency oscillations and regions of hysteresis are observed for some cases of low depth and high reduced velocity.

Experimental Investigation of Vibration Response of A Free-Hanging Flexible Riser Induced by Internal Gas-Liquid Slug Flow

The vibration response of a free-hanging flexible riser induced by internal gas-liquid slug flow was studied experimentally in a small-diameter tube model based on Froude number criterion. The flow regime in a curved riser model and the response displacements of the riser were simultaneously recorded by high speed cameras. The gas superficial velocity ranges from 0.1 m/s to 0.6 m/s while the liquid superficial velocity from 0.06 m/s to 0.3 m/s. Severe slugging type 3, unstable oscillation flow and relatively stable slug flow were observed in the considered flow rates. Severe slugging type 3 characterized by premature gas penetration occurs at relatively low flow rates. Both the cycle time and slug length become shorter as the gas flow rate increases. The pressure at the riser base undergoes a longer period and larger amplitude of fluctuation as compared with the other two flow regimes. Additionally, severe slugging leads to the most vigorous in-plane vibration. However, the responses in the vertical and horizontal directions are not synchronized. The vertical vibration is dominated by the second mode while the horizontal vibration is dominated by the first mode. Similar to the vortex-induced vibration, three branches are identified as initial branch, build-up branch and descending branch for the response versus the mixture velocity of gas-liquid flow.

Stress analysis of primary support arch cover excavation in metro station based on 3D geomechanical model experiment

By considering a certain subway station of Qingdao Metro Line 1 as the research object, a 3D geomechanical model was established to analyze the stress and deformation characteristics of the surrounding rocks of a large-span subway underground station under primary support arch cover excavation. Fiber grating sensors, resistance strain gauges, earth pressure gauges, and multipoint displacement meters were arranged to monitor changes in stress and displacement of surrounding rock masses in the tunnel. The vault surrounding rock experiences excavation disturbance and rapid release stress, which consequently stabilizes. The excavation response of the arch foot to the monitoring section is gentler than the vault stress. Further, the horizontal stress of the sidewall sustains slow release, and the primary support stress increases rapidly, slows down, and finally stabilizes. The initial stress of the initial branch increases slightly after the first rapid growth, and the final trend is stable. During the process of advancing of the tunnel face, deformation undergoes three main stages, namely, slow, abrupt, and stable deformation, with continuing arch cover excavation. Although the surface subsidence is consistent with the vault subsidence, it has a lower value than the vault subsidence. The influence of the surface subsidence caused by excavation is larger than that of the vault subsidence, and the influence of axial subsidence on the tunnel is approximately 15 m. The primary support arch cover excavation can be successfully applied to large-span hard-rock metro stations whose surrounding rock grade is II–III; this provides a theoretical basis and reference for similar projects.

Improving defense innovation programs to enhance force readiness

Purpose The purpose of this study is to evaluate Department of Defense (DoD)-backed innovation programs as a means of enhancing the adoption of new technology throughout the armed forces. Design/methodology/approach The distribution of 1.29 million defense contract awards over seven years was analyzed across a data set of more than 8,000 DoD-backed innovation program award recipients. Surveys and interviews of key stakeholder groups were conducted to contextualize the quantitative results and garner additional insights. Findings Nearly half of DoD innovation program participants achieve no meaningful growth in direct defense business after program completion, and most small, innovative companies that win follow-on defense contracts solely support their initial sponsor branch. Causes for these program failures include the fact that programs do not market participants’ capabilities to the defense community and do not track participant companies after program completion. Practical implications Because the DoD does not market the capabilities of its innovation program participants internally, prospective DoD customers conduct redundant market research or fail to modernize. Program participants become increasingly unwilling to invest in the DoD market long term after the programs fail to deliver their expected benefits. Originality/value Limited scholarship evaluates the efficacy of DoD-backed innovation programs as a means of enhancing force readiness. This research not only uses a vast data set to demonstrate the failures of these programs but also presents concrete recommendations for improving them – including establishing an “Innovators Database” to track program participants and an incentive to encourage contracting entities and contractors to engage with them.

Flow-induced vibration of tandem circular cylinders with selective roughness: Effect of spacing, damping and stiffness

Abstract Flow Induced Vibrations (FIV), and particularly Vortex Induced Vibrations (VIV) and galloping, of two locally rough, rigid, circular cylinders in tandem are studied by varying the stiffness of the supporting springs, the linear viscous damping, and the cylinder spacing. The test parameters are: mass ratio set to 1.34, center-to-center spacing of 1.57, 2.0 and 2.57 diameters; spring-stiffness 400 N/m ∼ 1200 N/m, damping-ratio 0 . 02 ζ 0 . 26 , and Reynolds number 30,000 ⩽ Re ⩽ 120,000, which falls in the TrSL3 flow regime. The virtual spring-damping system Vck developed in the Marine Renewable Energy Laboratory (MRELab) enables embedded computer controlled change of viscous-damping and spring-stiffness for fast and mathematically correct oscillator realization, without including the hydrodynamic force in the closed control loop. Experimental measurements for the oscillatory response of both cylinders, are studied to reveal the interaction of upstream and downstream cylinders. All the experiments were conducted in the Low Turbulence Free Surface Water (LTFSW) Channel of the MRELab of the University of Michigan. The main findings are: (1) In the range of spacing tested, for all the values of K and ζ , the upstream cylinder’s amplitude response is enhanced due to the presence of the downstream cylinder. This effect is very strong in galloping. (2) With the exception of the initial branch of VIV, the downstream cylinder’s amplitude response is also enhanced but with higher standard deviation in two tandem oscillating cylinders. (3) Three oscillation patterns are identified in galloping: In-phase, out-of-phase, and alternating between the two in a given experiment. (4) Four interactive zones are identified.