Small Height Research Articles

Numerical Study on Overtopping Performance of Multi-stage Overtopping Wave Energy Converters

The characteristics of wave conditions with large tidal ranges and small wave heights in China's coastal waters limit the operation time of traditional single-stage overtopping devices, while the multi-stage overtopping wave energy converters can increase the overall operation time of the device by distributing the upper and lower reservoirs. To study the overtopping performance of the multi-stage overtopping wave energy converter under real sea conditions, a two-dimensional numerical model of the device is developed and verified by physical model tests. The effects of the lower reservoir opening width, slope angle combination, and slope inundation length on the overtopping performance are investigated under regular wave conditions. It is found that a smaller opening width and two 30° slope angles improve the overtopping performance of the device, while the slope inundation depth has less effect. Further, based on the full-scale prototype device, the database of overtopping in a complete tidal cycle (12h) were constructed under real sea conditions in different seasons to provide the basic data for the Wave-to-wire model of power generation simulation.

Investigation of the leakage mechanism in multi-channel GaN-on-Si SBDs

This work presented the reverse leakage current (I R) mechanisms in multi-channel GaN-on-Si Schottky barrier diodes (SBDs). The device showed excellent performances in both ON and OFF-states thanks to the advanced multi-channel tri-gate architecture. The I R is dominated by thermal field emission at 25 °C–75 °C before pinch-off of the 2-dimensional electron gas (2DEG) channel in the Schottky region, due to the thinned Schottky barrier, which turned to be thermal emission (TE)-dominated under further elevated temperatures resulted from the small Schottky barrier height. Once the 2DEG channel is pinched off by the tri-anode, the I R is firstly dominated by Poole–Frenkel emission and then is trap-assisted tunneling after the full depletion of the channels beneath the field plates. These results are supported by excellent consistency between experimental results and theoretical models, offering a key understanding of multi-channel SBDs and shedding lights on this promising multi-channel technology for future energy conversion.

Top electrode dependence of the write-once-read-many-times resistance switching in BiFeO3 films

The electrode is one of the key factors that influences and controls the resistive switching characteristic of a resistive switching device. In this work, we investigated the write-once-read-many-times (WORM)-resistive switching behavior of BiFeO3 (BFO)-based devices with different top electrodes, including Pt, Ag, Cu, and Al. The WORM-resistive switching behavior has been observed in Pt/BFO/LaNiO3 (LNO), Ag/BFO/LNO, and Cu/BFO/LNO devices. In the initial high resistance state, the Pt/BFO/LNO device shows space-charge-limited current conduction due to the large Schottky barrier height at the Pt/BFO interface, while the Ag/BFO/LNO and Cu/BFO/LNO devices exhibit Schottky emission conduction due to the small barrier height at both top electrode/BFO and BFO/LNO interfaces. In the low resistance state, the metallic conduction of the Pt/BFO/LNO device is a result of the formation of conduction filaments composed of oxygen vacancies, and yet the metallic conduction of Ag/BFO/LNO and Cu/BFO/LNO devices is due to the formation of oxygen vacancies-incorporated metal conduction filaments (Ag and Cu, respectively). The observed hysteresis I-V curve of the Al/BFO/LNO device may be attributed to oxygen vacancies and defects caused by the formation of Al–O bond near the Al/BFO interface. Our results indicate that controlling an electrode is a prominent and feasible way to modulate the performance of resistive switching devices.

Improved Technology for Rounding Graphite: Machine Structure and Industrial Test

The graphite, which is treated to be potato-shaped, is widely applied in Li-ion batteries as the anodic material. Sequential batch shaping is the main method at present. However, the small height of the shaping cavity of the existing structure leads to the problem of low processing capacity and high cost. In this work, a new structure of the shaping machine was developed with the aim of shaping graphite by large output and costless. The equipment system for graphite rounding in a pilot scale at a treatment amount of 25 kg raw material each run was established. The results showed that the ratio of the diameters of the final product by an undersized percentage corresponding to 10% was 11.15 μm, 50% was 18.94 μm, and 90% was 29.54 μm, and tap density was 0.945 g/cm3, the yield reached 48%, under the optimized conditions of 1833 rpm rotating speed of shaping disk, 2646 rpm rotating speed of classifier, and 40 min shaping period. All the above characteristics of the rounded graphite are in line with the requirements for applying in the anode of Li-ion batteries. In short, the present study aims to provide a new structure of the shaping machine, contributing to the efficient and cost-effective rounding of graphite and revealing the structure of the shaping machine, contributing to promoting the wide improvement of the shaping machine.

On the development of a generalized atmospheric boundary layer velocity profile for offshore engineering applications considering wind–wave interaction

Within industrial standards, effects due to wind–wave interaction on the marine atmospheric boundary layer (ABL) may be included via the Charnock sea-surface roughness parameter for open-sea and near-coastal waters. This roughness parameter does not accommodate the wide variety of wave states possible, nor does it modify the ABL to include speed-up effects resulting from an undulating wave profile. In an attempt to provide an updated definition of the general ABL profile for offshore wind engineering applications, an experimental and numerical study is performed to assess the interaction of the ABL on a fixed wave geometry. By extracting the mean velocity field during the wind–wave interaction, bespoke values of the velocity profile power exponent and wind risk factor can be obtained. A range of wave heights and wave lengths are considered from which a Kriging surrogate model is trained to supply the relevant wind profile parameters depending on the wave state. These newly garnered parameters enable the practitioner to define a reference wind velocity, and then adjust the velocity profile characteristics to contain the influence of the wave. This approach provides a new inlet velocity condition that can be used within computational wind engineering investigations without the need to explicitly model the wave surface, as well as flexibility in specifying the underlying wave conditions. Application of the re-calibrated velocity profile shows that wind forces are significantly greater throughout an offshore wind turbine (OWT) swept blade area when large (H= 15 m) and small (H= 1.5 m) wave heights are compared.

Hybrid Model Predictive Control of a Two-Body Wave Energy Converter with Mechanically Driven Power Take-Off

In this paper, a variable damper is proposed to regulate the efficiency of a two-body wave energy converter (WEC) with mechanically driven power take-off (PTO). The variable damper introduces logic constraints into the WEC system, which can be translated into a mixed logical dynamical form with the dynamics of real-valued variables, the dynamics of logic variables, and their interactions. A hybrid model predictive control (MPC) method is used to determine the control inputs, which has the capacity to handle various constraints. The performance is assessed through simulations to evaluate the effectiveness of the proposed method. The achievable performance improvements of the proposed hybrid MPC are shown by means of comparative analysis with uncontrolled WEC devices. The results show that the proposed hybrid MPC has a high requirement on the lower bound of the variable damper and the maximum damping is used only at low relative velocities to achieve the optimum phase, like latching control. The hybrid MPC performs exceptionally well under wave conditions with a small significant wave height and long wave period, improving the power generation of the uncontrolled system up to 22.5%. And, the prediction error has a significant effect on hybrid MPC performance, especially for long prediction horizon.

Li + HF and Li + HCl Reactions Revisited I: QCT Calculations and Simulation of Experimental Results.

The Li + HF and Li + HCl reactions share some common features. They have the same kinematics, relatively small barrier heights, bent transition states, and are both exothermic when the zero point energy is considered. Nevertheless, the pioneering crossed beam experiments by Lee and co-workers in the 80s (Becker et al., J. Chem. Phys. 1980, 73, 2833) revealed that the dynamics of the two reactions differ significantly, especially at low collision energies. In this work, we present theoretical simulations of their results in the laboratory frame (LAB), based on quasiclassical trajectories and obtained using accurate potential energy surfaces. The calculated LAB angular distributions and time-of-flight spectra agree well with the raw experimental data, although our simulations do not reproduce the experimentally derived center-of-mass (CM) differential cross section and velocity distributions. The latter were derived by forward convolution fitting under the questionable assumption that the CM recoil velocity and scattering angle distribution were uncoupled, while our results show that the coupling between them is relevant. Some important insights into the reaction mechanism discussed in the article by Becker et al. had not been contrasted with those that can be extracted from the theoretical results. Among them, the correlation between the angular momenta involved in the reactions has also been examined. Given the kinematics of both systems, the reagent orbital angular momentum, , is almost completely transformed into the rotation of the product diatom, j'. However, contrary to the coplanar mechanism proposed in the original paper, we find that the initial and final relative orbital angular momenta are not necessarily parallel. Both reactions are found to be essentially direct, although about 15% of the LiFH complexes live longer than 200 fs.

The Effect of Wire Mesh on Premix Combustion with Butane Fuel in Bunsen Burners

Combustion is an important process in a variety of industrial, laboratory and household applications, and the use of devices that control the characteristics of the fire is essential. Bunsen burner is one of the common laboratory equipment used to produce flames in experiments and heating processes. Wire mesh is placed above the Bunsen burner to control air flow and has a crucial role in premix combustion by affecting efficiency, stability and heat distribution. In this study, an experimental investigation will be carried out on Bunsen burners using wire mesh 30, 40, and 50. Furthermore, parameters such as flame stability, flame height, and combustion speed will be measured. The results of this study indicate that the looser the wire mesh density, the burning speed tends to decrease. When using wire mesh 30, the value of the combustion velocity reaches 3.09 cm/s. Meanwhile, when using wire mesh 50, the value of the combustion velocity increased to 3.24 cm/s. This indicates that the wire mesh is getting tighter, air and fuel flow can move faster, thus increasing the combustion velocity. In addition, the density of wire mesh also affects the high flame produced. By using wire mesh 30, the flame height reached 29.69 mm, while using wire mesh 50, the flame height reached 21.56 mm. This shows that the higher the wire mesh density, the flame tends to be more stable and has a smaller height.

Effect of Different Feed Particle Size on Gastrointestinal Tract Morphology, Ileal Digesta Viscosity, and Blood Biochemical Parameters as Markers of Health Status in Broiler Chickens.

The study is focused on how the physical structure of the feed affects the health status of broiler chickens. The aim of this study was to evaluate the influence of feed particle size in broiler diets on gastrointestinal tract morphology, digesta viscosity, and blood biochemical parameters. A total of 90 one-day-old male Ross 308 broiler chickens were randomly divided into three different experimental groups (with five replicates per pen), with 6 birds per cage. The first experimental group (Coarse) was fed with the coarsest particle size, with feed with a geometric mean diameter (GMD) of 1111.26 µm, the next group (Medium) was fed with a less coarse feed size of GMD 959.89 µm, and the last group (Fine) was fed a diet with a fine feed particle size of GMD 730.48 µm. The use of coarse feed particle size in the diet had a positive effect on the gizzard weight and small intestinal villi height and crypt depth, which increased the surface area intended for digesting nutrients. The use of finely ground particles in the feed increased the level of gamma-glutamyl transferase and at the same time, decreased the level of urea, which could indicate adverse changes in the liver.

Viscosity measurements of glycerol in a parallel-plate rheometer exposed to atmosphere

Glycerol is a hygroscopic fluid that spontaneously absorbs water vapour from the atmosphere. For applications involving glycerol, care must be taken to avoid exposure to humidity, since its viscosity decreases quickly as water is absorbed. We report experimental measurements of the viscosity of glycerol in a parallel-plate rheometer where the outer interface is exposed to atmosphere. The measurements decrease with time as water is absorbed from the atmosphere and transported throughout the glycerol via diffusion and advection. Measured viscosities drop faster at higher relative humidities, confirming the role of hygroscopicity in the transient viscosities. The rate of viscosity decrease shows a non-monotonic relationship with the rheometer gap height. This behaviour is explained by considering the transition from diffusion-dominated transport in the narrow-gap regime to the large-gap regime where transport is dominated by inertia-driven secondary flows. Numerical simulations of the water absorption and transport confirm this non-monotonic behaviour. The experimental viscosity measurements show unexpectedly fast decreases at very small gap heights, violating the parallel-plate, axisymmetric model. We propose that this drop-off may be due to misalignment in the rheometer that becomes non-negligible for small gaps. Theoretical considerations show that secondary flows in a misaligned rheometer dominate the typical secondary inertial flows in parallel-plate rheometers at small gaps. Finally, simulations in a misaligned parallel-plate system demonstrate the same sharp drop-off in viscosity measurements at small gap heights. This modelling can be used to estimate the gap height where misalignment effects dominate the transient glycerol viscosity measurements.

MORPHOLOGICAL CHARACTERS VARIABILITY OF THE A4-10 WINTER WHEAT LINE UNDER CURRENT CLIMATE CONDITIONS

Currently, wheat plants know permanent evolutions of productive potential, of quality and of different resistances. The morphology of the plant in general, as well as the production elements: ears, grains and mass of a thousand grains, know true performances. The expression of the morphological characters of the plants is, however, closely related to the natural provision of water. Being a plant that capitalizes on moisture, frequently encounters periods of deficit, especially during the period of depositing dry matter in the grains. The intensity of these drought periods causes some decreases in the expression of plant and grain morphology respectively. In the present research, the appearance of the plants is compared together with the production elements obtained in three different years, namely one with a favorable background and two dry years. From the obtained data, the plants of line A.4-10 affected by drought had a smaller height by 3-7 cm and stem thicknesses reduced by 0.15 mm. The length of the ear was shorter by 1.5 cm, the number of grains in an ear was 18 less, and the mass of the grains was also reduced by 0.9 g. The mass of a thousand grains decreased by about 3 g. Correlations between characters were positive and statistically well supported. Straw length was negatively correlated with the other characters, possibly due to the reduced waist obtained in its breeding.

PRELIMINARY RESEARCH ON THE PLANT STATUS OF SEVERAL WHEAT VARIETIES IN RELATION TO NITROGEN MINERAL FERTILIZATION

The study evaluated the variation of plant height in relation to nitrogen fertilization, and took place within the Didactic and Experimental Resort (DER) of the University of Life Science "King Mihai I" from Timisoara. Six wheat varieties were studied, three with smaller height (C3 – Montecarlo, C4 – Venezio, C5 – Combin) and three with larger height (C1 – PG102, C2 – Falado, C6 – Pitar). Variable doses of nitrogen (ammonium nitrate) were applied in the range of 0-280 kg N a.s. ha-1 (a.s. – active substance). In the experimental conditions (chernozem soil) and associated with the climatic conditions, according to the genetic specificity, the wheat varieties considered in the study used the applied fertilization in a different way. The height of the plants varied between 63.67±1.45 - 73.00±1.15 cm in the C1 variety; 62.33±0.88 - 73.67±2.33 cm for the C2 variety; 56.67±1.20 - 63.67±1.45 cm for the C3 variety; 54.00±2.08 - 62.67±3.18 cm for the C4 variety; 59.00±0.58 - 70.00±1.15 cm in the C5 ace; 67.33±1.76 - 77.67±1.20 cm for the C6 variety. The data series presented a normal distribution, and a close relationship with the N doses (r=0.994 for the variety C1; r=0.980 for the variety C2; r=0.984 for the variety C3; r=0.979 for the variety C4; r=0.985 for the variety C5; r=0.983 for the C6 variety). Based on the PCA, the wheat varieties studied were positioned specifically in relation to the applied fertilization; PC1 explained 92.498% of variance, and PC2 explained 4.134% of variance. The cluster analysis facilitated the clustering of variants from the perspective of wheat varieties (Coph.corr.=0.732) and from the perspective of fertilization (Coph.corr.=0.727). A ranking of the wheat varieties was obtained based on the plant height values (Ph), in response to the applied fertilization. The variation of Ph depending on the doses of N was described by polynomial equations of degree 2 and 3, under conditions of statistical safety.

Evaluation of blast mitigation performance of cylindrical explosion containment vessels based on water containers

Using liquid materials with specific geometries can enhance the explosion-proof properties of confined structures. This approach is promising because bulk water has multiple blast mitigation mechanisms and adds almost no extra mass. In this study, a method of using water-filled containers to reduce both the peak and permanent deformation of cylindrical explosion containment vessels (CECVs) is investigated through experiments and numerical simulations. Several explosion experiments were performed to evaluate the blast mitigation of the empty containers and the bulk water with multiple thicknesses and heights in terms of dynamic deformation and afterburning suppression. The experimental results indicated that the bulk water with a larger thickness and a smaller height had better protective performance, which provided up to an 80.1% reduction in permanent deformation compared with no mitigant. Numerical models were established using LS-DYNA and verified by the deformation-time history curves measured in the experiments. The energy conversion process during the explosion was analyzed through the numerical simulations, and the results showed that water absorbed most of the detonation energy that should have been transferred to the steel shell, proving that momentum extraction of water was a significant mitigation mechanism for the internal blast in CECVs. Another significant mitigation mechanism was the shadowing effect of water, which changed the spatial distribution of the blast loading acting on the steel shell, especially for water containers with larger thickness and smaller height.

Molecular dynamics simulation of the Stribeck curve: Boundary lubrication, mixed lubrication, and hydrodynamic lubrication on the atomistic level

Lubricated contact processes are studied using classical molecular dynamics simulations for determining the entire range of the Stribeck curve. Therefore, the lateral movement of two solid bodies at different gap height are studied. In each simulation, a rigid asperity is moved at constant height above a flat iron surface in a lubricating fluid. Both methane and decane are considered as lubricants. The three main lubrication regimes of the Stribeck curve and their transition regions are covered by the study: Boundary lubrication (significant elastic and plastic deformation of the substrate), mixed lubrication (adsorbed fluid layer dominates the process), and hydrodynamic lubrication (shear flow is set up between the surface and the asperity). We find the formation of a tribofilm in which lubricant molecules are immersed into the metal surface—not only in the case of scratching, but also for boundary lubrication and mixed lubrication. The formation of a tribofilm is found to have important consequences for the contact process. Moreover, the two fluids are found to show distinctly different behavior in the three lubrication regimes: For hydrodynamic lubrication (large gap height), decane yields a better tribological performance; for boundary lubrication (small gap height), decane shows a larger friction coefficient than methane, which is due to the different mechanisms observed for the formation of the tribofilm; the mixed lubrication regime can be considered as a transition regime between the two other regimes. Moreover, it is found that the nature of the tribofilm depends on the lubricant: While methane particles substitute substrate atoms sustaining mostly the crystalline structure, the decane molecules distort the substrate surface and an amorphous tribofilm is formed.

Location of Small Points on an Elliptic Curve by an Equidistribution Argument

Abstract Let $E$ be an elliptic curve defined over a number field $K$ without complex multiplication. If $\Gamma \subset E(\overline{K})$ is a subgroup of finite rank, a very special case of a conjecture of Rémond predicts that points of small height in $E(K(\Gamma ))$ lie in the division group of $\Gamma $. Using an equidistribution argument, we will show that this conjecture is true for groups of rank arbitrarily large.

Research on Symmetrical Integrated Matrix Transformer Applied to Full-Bridge LLC Resonant Converter for CM Noise Cancellation

The planar transformer is widely used in DC-DC power converters due to the small leakage inductance and low height. However, the big overlapping area between primary and secondary windings in the planar transformer generates large parasitic capacitance, which brings serious common-mode (CM) noise problems. The full-bridge LLC resonant converter can meet the premise of CM noise cancellation since the noise sources on the primary and secondary sides have same magnitudes and opposite phases. Therefore, the symmetrical planar transformer design is more conducive to the attenuation of CM noise. This paper analyses symmetrical winding arrangements with minimal winding loss for the transformer in the full-bridge LLC resonant converter. Based on this, the symmetry of the reverse integrated matrix transformer (RIMT) and forward integrated matrix transformer (FIMT) composed of two elemental transformers is investigated. The scattering parameter <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> is used to evaluate the symmetry of RIMT and FIMT. It is found that the two CM <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> curves of RIMT are not consistent even though the windings have been arranged symmetrically. In contrast, the CM <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> curves for FIMT are almost overlapped. This implies that FIMT is symmetrical and capable of CM current cancellation. Finally, the CM noises of the full-bridge LLC resonant converter using RIMT, RIMT with a balance capacitor, and FIMT are tested. Experimental results show that the CM noise for the converter using FIMT is lowest. Especially at the switching frequency, the CM noise is reduced by more than 20 dBμV.

Experiment and simulation of slurry flow in irregular channels to understand proppant transport in complex fractures

Slurry flow and proppant placement in irregular fractures are crucial to evaluate hydraulic fracturing stimulation but need to be better understood. This study aims to investigate how irregular fracture affects proppant transport and distribution using laboratory experiments and micro-scale numerical models. The unresolved method of the computational fluid dynamics (CFD) and the discrete element method (DEM) considers Saffman lift force, Magnus force, and virtual mass force to accurately capture the frequent interaction between proppant and slickwater. Experimental results validated the reliability of the optimized CFD-DEM model and calibrated primary parameters. The effects of crack height and width, bending angle, and distance between the crack and inlet on particle distribution were studied. The results indicated that the improved numerical method could rationally simulate proppant transport in fractures at a scale factor. The small crack height causes downward and upward flows, which wash proppant to the fracture rear and form isolated proppant dunes. A wider region in the fracture is beneficial to build up a large dune, and the high dune can hinder particle transport into the fracture rear. When the crack is close to the inlet, the primary fracture without proppants will close to hinder gas production. The smaller the bending angle, the smaller the proppant dune. A regression model can precisely predict the dune coverage ratio. The results fundamentally understand how complex fractures and natural cracks affect slurry flow and proppant distribution.

Experimental study of floating bridge global response when subjected to waves and current

The present paper investigates the wave- and current-induced responses of the Bjørnafjord phase 5 K12 floating bridge concept based on small-scale model tests. Due to the extensive length of the bridge concept combined with relatively small wave heights governing the design, the experimental model represents a truncated section of the original bridge concept. This truncated section includes a stay-cable tower and ten floating pontoons supporting a horizontally curved bridge girder at varying altitude. The bridge girder truncation points coincide with the tower column and the location just above the first moored pontoon. The girder boundary conditions are simplified as fixed for all degrees of freedom (DOF) on either side of the model while allowing for free rotation around the longitudinal and vertical axes at the location above the otherwise moored pontoon. The instrumentation of the experimental model includes three DOF translational motions captured at 13 locations along the bridge and six DOF motion of each pontoon. Force transducers are used to capture axial forces in all ten tower stay-cables and at the two ends of the bridge girder, while strain gauges capture shear forces and bending- and torsional moments measured at 12 locations along the bridge girder.The dynamic properties of the model are investigated by subjecting the model to both regular waves and broad-banded, long-crested waves, propagating at two different wave directions corresponding to waves travelling in and out of the fjord. These tests are performed with and without collinear current to investigate the effect of current on the bridge responses. Subsequently, the effect of current is investigated for two important long-crested wave conditions, i.e. the 100-year wind wave condition and the 10000-year swell wave condition. For both wave conditions the model tests are performed without current and with 1-year and 10-year current velocities, respectively. Finally, the short-term response from the long-crested wind and swell wave conditions without current are compared to those of short-crested waves without current.Results show that both current and the directional distribution of the waves have a significant influence on the structural responses. It is recommended that both effects are properly accounted for in any future design.

On the dimension of dual modules of local cohomology and the Serre's condition for the unmixed Stanley–Reisner ideals of small height

In this paper, we focus on the dimension of dual modules of local cohomology of Stanley–Reisner rings to obtain a new vector. This vector contains important information on the Serre's condition (Sr) and the CMt property as well as the depth of Stanley–Reisner rings. We prove some results in this regard including lower bounds for the depth of Stanley–Reisner rings. Further, we give a characterization of (d−1)-dimensional simplicial complexes with codimension two which are (Sd−3) but they are not Cohen–Macaulay. By using this characterization, we obtain a condition to equality of projective dimension of the Stanley–Reisner rings and the arithmetical rank of their Stanley–Reisner ideals. Moreover, our characterization allows us to compute the h-vectors and give a negative answer to a known question regarding these vectors.

Wake Control of Flow Past Twin Cylinders via Small Cylinders

The drag and lift force of a twin-cylinder structure are often greater than those of a single cylinder, causing serious structural safety problems. However, there are few studies on the passive control of twin cylinders. The study aimed to investigate the performance of passive drag reduction measures using small cylinders on twin cylinders at a Reynolds number of 100. The effects of small cylinder height (HD/D = 0~1.0, D is the side length of the twin cylinder) and cross-sectional shape on fluid force and flow structures were studied by direct numerical simulations. The control mechanism was analyzed using high-order dynamic mode decomposition (HODMD). The results showed that significant drag reduction occurred in the co-shedding state, particularly when the gap length of the twin cylinders L/D = 6.0. The small control cylinders with HD = 0.6, by contrast, showed the best performance in reducing the mean drag and fluctuating lift of the twin cylinders. It reduced the mean drag of the upstream cylinder (UC) by 2.58% and the downstream cylinder (DC) by more than 62.97%. The fluctuating lift coefficient for UC (DC) was also decreased by more than 70.41% (59.74%). The flow structures showed that when the flow hit UC under the action of small control cylinders, a virtual missile-like aerodynamic shape was formed at the leading edge of UC. In this way, the gap vortex consisted of two asymmetric steady vortices and the vortex length significantly increased. This was also confirmed by HODMD. The coherence modes in the gap were suppressed and thus the interaction between gap flow and wake flow was mitigated, which resulted in the fluid force reduction.