Vertical Disturbance Research Articles

Vertical “Half-and-Half” Syndrome with Ipsilateral Pseudoabducens Palsy due to Rostral Midbrain Lacunar Infarction

Vertical "half-and-half" syndrome, characterized by contralateral upward and ipsilateral downward gaze palsy, is a rare variant of vertical eye movement disturbance. Similarly, pseudoabducens palsy, manifesting as abductive palsy despite no lesion to the pons, constitutes another rare type of eye movement disturbance. Both conditions have been associated with lesions in the thalamo-mesencephalic junction. We present a rare case report detailing a patient exhibiting vertical "half-and-half" syndrome with ipsilateral pseudoabducens palsy following a left lacunar infarction of the thalamo-mesencephalic junction. Additionally, we discuss the potential underlying mechanisms contributing to this rare combination of eye movement disorders.

Implications of vertical stability control on the SPARC tokamak

To achieve its performance goals, SPARC plans to operate in equilibrium configurations with a strong elongation of κareal∼1.75 , which in turn will destabilize the n = 0 vertical instability. However, SPARC also features a relatively thick conducting wall that is designed to withstand disruption forces, leading to lower vertical instability growth rates than usually encountered. In this work, we use the TokSyS framework to survey families of accessible shapes near the SPARC baseline configuration, finding maximum growth rates in the range of γ≲100 s−1. The addition of steel vertical stability plates has only a modest ( ∼25% ) effect on reducing the vertical growth rate and almost no effect on the plasma controllability when the full vertical stability system is taken into account, providing flexibility in the plate conductivity in the SPARC design. Analysis of the maximum controllable displacement on SPARC is used to inform the power supply voltage and current limit requirements needed to control an initial vertical displacement of 5% of the minor radius. From the expected spectra of plasma disturbances and diagnostic noise, requirements for filter latency and vertical stability coil heating tolerances are also obtained. Small modifications to the outboard limiter location are suggested to allow for an unmitigated vertical disturbance as large as 5% of the minor radius without allowing the plasma to become limited. Further, investigations with the 3D COMSOL code reveal that strategic inclusion of insulating structures within the VSC supports are needed to maintain sufficient magnetic response. The workflows presented here help to establish a model for the integrated predictive design for future devices by coupling engineering decisions with physics needs.

Stochastic flutter analysis of a three-degree-of-freedom airfoil under vertical turbulence disturbance

This paper investigates the nonlinear stochastic dynamic response of a three-degree-of-freedom(3-DOF) airfoil with high substructural nonlinearity under vertical turbulent disturbances. Considering a two-dimensional flow field, the Dryden turbulence model is used to describe the vertical turbulent disturbance, and a nonlinear stochastic aerodynamic model based on the Theodorsen theory is established for the stochastic flutter problem of the wing. An analysis is conducted to reduce the dimensionality of the airfoil system and solve the critical flutter velocity of the system. The Monte-Carlo method is applied to analyze the stochastic P-bifurcation problem of the system, and the effects of parameters such as the incoming velocity, turbulence scale and intensity on the stochastic dynamics behavior of the system are clarified. It is shown that the amplitude of the steady-state oscillation of the system increases with the incoming velocity and turbulence intensity, whereas the critical flutter speed decreases with increases in these parameters.

Event-triggered sliding mode control for 2-D Roesser model with mismatched disturbance

This paper is concerned with designing two-dimensional event generators and sliding mode controllers for discrete-time two-dimensional systems described by the celebrated Roesser model with external mismatched disturbance. First of all, aimed at the characteristics of the Roesser model, the horizontal and vertical disturbance observers and sliding surface functions are established for the addressed two-dimensional systems, respectively. Then based on the disturbance estimation and rejection technique, a modified reaching law and its corresponding sliding mode controller are designed to achieve the system robustness and disturbance attenuation. To reduce the resource usage, the event-triggered strategy is further incorporated in the design of sliding mode control law. Moreover, the stability of the sliding-mode dynamics is analyzed by resorting to the Lyapunov stability theory. Finally, a simulation example is presented to verify the effectiveness of the proposed method.

Mechanical properties and soil failure process of interface between grouser of tracked mining vehicle and deep-sea sediment

Tracked mining vehicles (TMVs) are key equipment in deep-sea mining systems and can easily slip when walking on soft sediments on the seabed. Thus, it is important to investigate the effect of track parameters and grounding-specific pressure on the shear interaction between mining vehicles and sediment. The sediment was simulated using a mixture of bentonite and water, and a shear test of the track with a single grouser and sediment was conducted. A numerical model of the track–sediment shear test was established, and the shear strength and failure mode of the sediment soil under the track action were examined. The results demonstrate that the peak shear strength of the track–sediment interface increases with an increase in the grounding-specific pressure, gradually increases with an increase in grouser height, and tends to stabilize at a given level of grouser height. Owing to the presence of the grouser, the deep-sea sediment transitions from the elastic state to the plastic state faster than the typical clay during the shear test. The variation law of peak shear strength at the track-sediment interface with the height of track grouser under different grounding-specific pressures was analyzed, and a modified shear stress-displacement relationship model was proposed. Wedge failure is the predominant method of failure for a single-grouser shear sediment soil at various heights. The primary factor affecting the horizontal disturbance range is the grouser height, and the range increases as the grouser height increases; the primary element affecting the vertical disturbance range is the grounding-specific pressure, and the range increases as the grounding-specific pressure increases. The relationship of the grouser height and cohesiveness with the interfacial shear strength was examined and a new shear stress–displacement relationship model that can accurately capture the shear mechanical behavior between the track and sediment under various grouser heights was proposed. In conclusion, the study findings could serve as a guide for the engineering design of a TMV walking system.

Experimental and numerical simulation on the sliding process of roof rock blocks triggered by dynamic disturbance

With the excavation of underground opening, the roof rock block may fall under external dynamic disturbance. In this paper, the roof rock mass was simplified as a rock block system composed of trapezoidal rock blocks. A series of experiments and numerical simulations were performed to study the sliding process of the key block under the horizontal static clamping load and vertical impact disturbance. The propagation of stress wave in the block system were captured and analyzed by using high-speed camera and digital image correlation technique. The results reveal that a pendulum-type wave was generated due to the propagation and superposition of stress waves in the block system. Therefore, the governing mechanism of the sliding displacement of the key block was clarified based on the propagation of incident stress waves or pendulum-type waves. Meanwhile, it is found that the sliding distance of the key block decreases in a power function with the increasing friction coefficient, or decreases in a parabolic function with the increasing trapezoid internal angle. Finally, a case study on the roof block sliding of the roadway at a gold mine was conducted, and it is concluded that the sliding of the key block resulted from the coupled effects of “shear driving” and “low friction” driven by stress wave propagation, regardless of a single or multi-layer rock block system. These results may provide technical guideline for preventing rock-falling accidents caused by blasting disturbances in underground mining.

Physical Mechanism of the Development and Extinction of the China Southwest Vortex

In this paper, a typical vortex system based on quasi-linear thermal-dynamic equations to reflect the development and extinction of the China Southwest Vortex is established using the vortex motion stability method combined with the outer environmental field and cumulus convective latent heat release. The development and extinction of the China Southwest Vortex in catastrophic weather systems are studied from the aspects of stability and development mechanisms for the primary-stage China Southwest Vortex, the transition mechanism from the primary-stage China Southwest Vortex to the mature vortex, and stability and development mechanisms of the mature China Southwest Vortex. The results show the following: (1) the convergence and divergence of the surrounding flow field is the main factor influencing the development and extinction of the primary-stage China Southwest Vortex, while gravity wave disturbance is the main driving force for the maintenance and development of the primary vortex. Based on the convergence of the external flow field, the gravity wave disturbance must exceed the critical frequency, or the vortex will tend to die out. (2) The convergence and divergence of the surrounding flow field is also the main factor for the transition from the primary vortex to the mature vortex. Based on the convergence of the surrounding flow field, the primary vortex transforms into a mature vortex only when the gravity wave disturbance strongly exceeds the critical frequency and causes the vertical disturbance to become unstable. (3) The convergence and divergence of the external flow field is also the main factor for the development and extinction of the mature China Southwest Vortex. In the early stage, the vortex can be maintained and developed as long as the surrounding flow field converges. In the case of the divergence of the external flow field, the vortex may be maintained for a short time, but eventually dissipates when the gravity wave disturbance exceeds the critical frequency. In the later stage, under the convergence of the surrounding flow field, the vortex can be maintained when the gravity wave disturbance exceeds the critical frequency. However, with the divergence of the surrounding flow field, the vortex may be maintained for a short time, but it will eventually dissipate when the gravity wave disturbance is extremely strong. In addition, the observations of the evolution of China Southwest Vortexes and gravity wave activities under the influence of southwest airflow and atmospheric disturbance in the Western Sichuan Plateau–Sichuan Basin are explained by the above physical mechanism. It is also pointed out that the heating effect can be an obstacle to the development of the China Southwest Vortex by increasing the critical frequency of gravity waves during unstable layer formation, and the divergent environment flow field under the condition of stable layer formation. Therefore, this paper deepens the understanding of the evolution process and anomalous mechanisms of the China Southwest Vortex.

Analysis of Cyperus esculentus–Soil Dynamic Behavior during Rotary Tillage Based on Discrete Element Method

Considering the problems of low soil fragmentation rates, high working resistance, and high energy consumption in the harvesting process of Cyperus esculentus in China, a method of Cyperus esculentus harvesting based on counter-rotation digging is proposed. The mechanism of interaction between the rotary tillage blade and Cyperus esculentus–soil is systematically investigated, and the vertical and horizontal disturbance performance of the positive and counter-rotating harvesting methods on soil and Cyperus esculentus is compared and analyzed. The results of the experiment showed that the intensity of soil and Cyperus esculentus disturbance by counter-rotation increased by 166.67% and 297.78%, respectively, and the effective disturbance time of soil and Cyperus esculentus increased by 133.33% compared to that of positive rotation. The working depth and rotation speed of the rotary tillage blade were the most significant for soil and Cyperus esculentus disturbance intensity. The working depth increased from 150 mm to 170 mm, and the soil disturbance intensity increased by 17.91% and 21.37% for positive and counter-rotating operation, respectively, and the rotation speed of the rotary tillage blade increased from 270 rpm to 330 rpm, and the soil disturbance intensity increased by 28.85% and 35.29%, respectively. Compared with the positive rotation operation, the Cyperus esculentus counter-rotation soil fragmentation rate increased by 4.09%, the Cyperus esculentus damage rate decreased by 10.69%, and the buried fruit rate decreased by 7.38%. This paper helps to understand the interaction mechanism between the rototiller and Cyperus esculentus–soil and lays a theoretical foundation for the subsequent design and optimization of the Cyperus esculentus digging device.

A hybrid sliding mode controller design for vibration suppression in a hydraulic suspension system with vertical load disturbance

Anti-disturbance vibration control is a crucial component in a hydraulic suspension system. However, random input excitation and prolonged service can cause hydraulic suspension system parameters to drift, leading to system vibration with suppression failure. The resulting states of nonlinearity and disturbance will lead to a gradual deterioration of pressure control. Therefore, designing a viable controller for a hydraulic suspension system that considers system nonlinearity, computing capacity, and sensor configuration is essential. To address this need, we present a double-layer control strategy in this work. A hybrid sliding mode control algorithm based on the reference skyhook and groundhook model is proposed to regulate the expected force of reverse compensation. An output controller is then applied based on the expected force observer to mitigate low-frequency vibrations to realize a steady state. A logic rule is designed to ensure that the two controllers work to suppress sprung mass vibration, and a comprehensive system model is derived to help characterize system nonlinearities and design the hybrid sliding model controller. Numerical and physical validations are then carried out to demonstrate the feasibility of the strategy and test the performance of the controller. The experimental results show that the hybrid sliding mode controller can suppress vibration under disturbance excitation and reduce the vibration acceleration to a 2.3 m/s2 random response when system parameters vary.

Effect of gas density and surface tension on liquid film thickness in vertical upward disturbance wave flow

Gas–liquid annular flows, such as the flow attached to the fuel rods of boiling water reactors, is a prevalent occurrence in industrial processes. At the gas–liquid interface of such flows, disturbance waves with diverse heights commonly arise. Because the thin liquid film between two successive disturbance waves leads to the dryout on the heating surface and limits the performance of the heating components, complete knowledge of the film thickness and disturbance waves is crucial. The properties of the base film and disturbance waves have been studied extensively through experimental and analytical approaches. However, most experimental data and analysis available in the literature are limited to the near atmospheric condition, and the liquid–gas density ratio under near atmospheric conditions is much higher than in practical nuclear applications. In this study, we use nitrogen gas and water under the system pressures of 0.2 and 0.4 MPa, as well as HFC134a gas and water under the system pressure of 0.7 MPa. Therefore, the density ratio can be varied between 32 and 434. Based on our experimental data, we report a direct link between the film thickness, wave height, and dimensionless numbers. The analysis indicates the Weber number which represents the ratio of the drag force to the surface tension force is critical for the film thickness behavior. To examine this, we perform the experiments using nitrogen gas and 95% (v/v) of aqueous ethanol solution under the system pressure of 0.2 MPa. Finally, two models are proposed to predict the averaged film thickness and wave height, which are then compared with previous data.

Potential Influence of Offshore Wind Farms on the Marine Stratification in the Waters Adjacent to China

Offshore wind farms (OWFs) can influence marine stratifications, leading to fuel nutrition in the upper ocean and regulating ocean carbon fluxes. Evaluating this dynamic effect facilitates the planning of OWFs deployment for enlarging marine carbon sequestration, which is urgent in the pursuit of China’s carbon neutrality targets. However, it is impossible to observe the target influence in the planning stage of deployments, and it is impractical to build a high-resolution (100~101 m) model to cover the entire waters adjacent to China. The theoretical calculations, therefore, are the first step and top priority. The simplified theory presents two suggestions in the design of future OWF deployments in the study area. The first suggestion is made from the perspective of OWF positioning. To the east of the cities of Zhoushan, Putian, and Shantou, the oceans are dynamically sensitive to OWF deployments. The second suggestion is made from the perspective of the length scale of OWFs. A broader OWF results in a smaller vertical disturbance in the coastal waters, but the situation is opposite in the open seas. The OWF deployment strategy, proposed in the aim of ensuring idealized marine stratification responses, thus varies geographically. This study provides a panoramic view of the sensitivity of marine stratification to OWFs in the study regions. It can be seen as a steppingstone in detailed research of the target phenomenon.

Mechanical Models for Comparative Analysis of Failure Characteristics and Groundwater Inrush of Coal Seam Floors

Mining activities conducted above aquifers run the risk of groundwater outburst through fractured floor strata. However, the failure mechanism of the seam floor and the variability in its stability with varying dips remain unclear. Considering the influence of excavation-induced pressure, hydraulic pressure and strata dip, two kinds of analytical models were proposed in this study, which mainly included the hydraulic mechanical model and the key stratum model. These models were applied to comparatively investigate the failure characteristics and inrush risk of horizontal and inclined floors, and then confirmed by numerical simulation. The theoretical calculations reveal that the vertical failure ranges of horizontal and inclined floor strata exhibit approximate “inverted saddle” shapes along the inclination, and have the characteristics of symmetrical distribution and “lower-large/upper-small”, respectively, which is generally consistent with the simulated and measured observations. The theoretical maximum depths of damage within horizontal and inclined floor strata are roughly 12 m and 15 m, slightly lower than the result of numerical simulation. Compared with the remaining horizontal layer, the zone close to the lower boundary of the inclined key strata beneath the goaf incurs the most damage, which corresponds well to the distribution of vertical disturbance ranges. Therefore, the theoretical risk of groundwater outburst from the inclined floor after coal extraction is relatively higher than that from the horizontal floor. The mechanical models established in this study could elucidate the mechanism inducing floor failure and water inrush above a confined aquifer, and thus provide valuable insights for the risk assessment of water-related disasters in underground engineering.

A reinforcement learning backstepping‐based control design for a full vehicle active Macpherson suspension system

This paper presents a reinforcement learning backstepping-based control scheme for the design of a full vehicle active suspension system such that both the superior ride comfort and stabilization are achieved. It is well known that the traditional backstepping control scheme is suitable to solve higher order nonlinear system based on the strict-feedback form; however, the disadvantage of the procedure requires computing the derivatives of virtual control signals, which is a very complex task. Therefore, a reinforcement learning scheme using the deep deterministic policy gradient (DDPG) control strategy is developed to replace the process of finding virtual control force in backstepping method. It not only avoids the complexity of analytically calculating the derivatives of the virtual control signals, but also retains the systems robustness when there exist random disturbances from road irregularities. To verify the performance of the proposed active suspension control scheme, the random road unevenness profiles according to ISO 8608 is considered as vertical and lateral disturbance input excitation of a full-vehicle suspension system. Compared with conventional passive suspension system and backstepping control scheme, the proposed approach can be demonstrated to not only effectively improve ride comfort under random road excitation, but also improve the transient response and robustness.

Contribution of Fire Emissions to PM2.5 and Its Transport Mechanism Over the Yungui Plateau, China During 2015–2019

AbstractAir pollution over the Yungui Plateau (YGP) in southwestern China can be caused by the transport of biomass burning aerosols from Southeast Asia; however, the magnitude and mechanisms of such long‐range transport have not been fully investigated. Here, we studied the impacts of fire emissions on vertical PM2.5 over the YGP and the transport mechanisms of PM2.5 during the fire seasons (March–April) of the neighboring Indo‐China Peninsula (ICP) region in 2015–2019 using ground‐based monitoring data, reanalysis of meteorology, and GEOS‐Chem model simulations. Average daily PM2.5 concentrations of 36.06 ± 14.86 μg m−3 were measured at 16 ground stations in the YGP with the highest value of 53.77 μg m−3 at Xishuangbanna, the nearest station to the ICP. Model simulations showed that fire emissions contributed approximately 50%–60% of the vertical PM2.5 over the YGP at a height of 3–4 km, with larger contributions in meridional than zonal cross‐sections. Four weather patterns with low pressure over the YGP were identified as favorable conditions for smoke transport. The pattern with the lowest pressure over the northern YGP and the strongest vertical wind disturbance was the most favorable for the eastward transport of fire air pollution to the YGP. Another pattern, which had the strongest southerly wind, promoted smoke aerosols to climb from eastern Myanmar and northern Laos/Vietnam to the YGP. Through these typical pathways, ICP biomass burning significantly impacted PM2.5 pollution in southwestern China.

Study of the process of deflagration flame behavior in disturbance conditions

To evaluate the effect of the disturbance airflow on the methane deflagration flame, a deflagration experiment is conducted in a closed duct. The effects of three disturbance airflow levels and two disturbance positions on the deflagration flame dynamics, including the variation of flame propagation behavior, disturbance mechanism, and deflagration overpressure development are investigated. The experimental results show that the vertical disturbance of the airflow disrupts the original structure of the deflagration flame, increasing the inherent instability and turbulence of the flame. The increase in the initial pressure of the disturbance airflow can increase the flame turbulence intensity, propagation velocity, the maximum value of the deflagration overpressure and the rate of overpressure rise. The contribution of the disturbance airflow at the initial acceleration position of the flame to the characteristic parameters of deflagration is more prominent. The experimental results complement and explain the propagation behavior of deflagration flame in a non-static environment. It provides suggestions on the prevention and protection of combustible gas deflagration risks in complex environments.

Experimental investigation on the three-dimensional oblique interaction of an internal solitary wave with a horizontal finite-length cylinder

An experiment on the oblique interaction of an internal solitary wave (ISW) with a horizontal finite-length cylinder was conducted in a gravitationally stratified fluid flume. The multi-measuring technique, which was composed of the multichannel conductivity-probe array, dyeing identification and particle image velocimeter (PIV), was used to study the coupling wave–flow structure, and the three-component micro-amplitude force sensor was used to measure the horizontal longitudinal, horizontal transverse and vertical forces on the cylinder. Based on the experimental observations and measurements, a theoretical analysis method of the three-dimensional force on the cylinder interacting with an ISW at any angle was established for the experimental analysis. The ISW force on the cylinder is composed of the wave force, the friction force and the disturbance force, in which three components of the wave force in the horizontal longitudinal, horizontal transverse and vertical directions can be estimated by the Morison formulas corresponding to those component velocities perpendicular to their respective directions, the dynamic friction force depends on the tangential velocity at the surface of the cylinder, additionally the disturbance force composed of the reduced gravity and the vortex shedding lift is considered in the vertical direction. Furthermore, it is found that the wave–flow structure of the ISW at its windward side, leeward side and inside its wave profile dominates the three-dimensional force on the horizontal finite-length cylinder, of which its characteristics change with key factors such as the interaction angle between the cylinder and the ISW, the incident ISW amplitude and the cylinder-submerged depth. When the interaction angle increases, the same order of the horizontal transverse force at a certain angle as the increasing horizontal longitudinal force can be gotten, and the ”double peak” of the vertical force can be made. With the increase of the incident amplitude, the magnitude of the three-dimensional force always increases, but its direction is unchanged. For different submerged depths, the vertical force depends on the ratio of the reduced gravity or the vortex shedding lift or their resultant force to the vertical disturbance pressure. However, the understanding of the oblique interaction mechanism of an ISW with a horizontal finite-length cylinder provides direct insight into the intrinsic characteristics of the damage to the safety of marine and offshore structures in the actual ocean.

Adaptive Fuzzy PID Control Strategy for Vehicle Active Suspension Based on Road Evaluation

The paper proposes a fuzzy proportion integral differential (PID) control strategy based on road estimation to meet the different performance requirements of active suspension for comfort and safety under different road conditions in view of the uncertainty of vehicle suspension parameters and random road perturbations. First, flexible neural tree (FNT) is used to estimate the vertical disturbance of road within uncertain vehicle parameters in which the Fourier transform of the autocorrelation function is used to fit the road power spectrum density (PSD). In order to compensate for the delay and realize the real-time estimate of road conditions, an online fuzzy evaluation strategy for road condition is developed by integrating the fitted road PSD and the real-time suspension performance. After that, an adaptive fuzzy PID control strategy is developed based on the adaptive suspension control performance, which is supposed to realize the adaptive adjustment of control parameters for different road conditions. The simulation experimental results show that the online fuzzy evaluation strategy can effectively reflect the change in road condition, and the proposed adaptive fuzzy PID control strategy can work for adjusting the parameters adaptively, according to the changes in road conditions and therefore meet the control performance requirements under different road conditions.

Riddles wrapped inside an enigma. Lupemban MSA technology as a rainforest adaptation: revisiting the lanceolate point.

The Central African Stone Age is very poorly known when compared to the higher-resolution records of East and Southern Africa. Early Stone Age (ESA) archaeology is effectively absent from the rainforest zone, with the early Middle Stone Age (MSA) Lupemban industry representing the earliest sustained archaeological signature. Uranium-series dates of approximately 265 ka BP for the Lupemban at Twin Rivers (Zambia), although queried, suggest a precocious late Middle Pleistocene dispersal of early Homo sapiens into the equatorial rainforest belt. Lupemban palaeohabitat interactions and attendant behavioural and technological repertoires are key to its evolutionary significance, but investigation is hampered by the widespread vertical disturbance of stratigraphic profiles and the formation of 'stone-lines'. The Lupemban takes in a range of implement types and technologies, including core-axes, prepared core technology (PCT) points, blades and backed blades. But it is the elongated bifacial lanceolate point-some exquisitely made and many exceeding 30 cm in length-that defines the industry. Remarkably, unequivocal examples of these iconic artefacts have never been the focus of detailed techno-typological scrutiny. In this paper, I advance understanding of the Lupemban by initiating a re-consideration of lanceolate points at Kalambo Falls, Zambia, and discuss their implications for the Lupemban's evolutionary significance. This article is part of the theme issue 'Tropical forests in the deep human past'.

Variability and composition of amino acids and amino sugars in sediment cores of the Changjiang Estuary

Understanding the sources, compositions and degradation states of sedimentary organic matter (SOM) in estuarine regions can provide significant information about regional carbon and nitrogen cycles. Amino acids (AAs), amino sugars (ASs), total organic carbon (TOC), total nitrogen (TN) and stable carbon isotopic composition (δ13OC) were investigated in six sediment cores of the Changjiang Estuary. The concentrations of ASs ranged from 0.60 to 3.11 μmol g−1, and accounted for 1.7 ± 0.7% of TOC and 2.1 ± 0.9% of TN. The concentrations of AAs ranged from 5.18 to 11.66 μmol g−1 and accounted for 8.1 ± 1.7% of TOC and 17.4 ± 3.9% of TN. Relatively coarse and fresh SOM was mainly deposited in the nearshore (e.g., station B6), whereas fine and degraded SOM occurred in the offshore area (e.g., station A7-4). The relationships between median grain size and AA-C% and degradation index (DI) revealed that fine-grained particles adsorbed older SOM, but sandy sediments were correlated with relatively fresh SOM. Diatoms were the main contributor of marine SOM and high primary production increased the burial of fresh SOM. TOC and TN contents and their degradation states did not exhibit distinct trends with core depth, possibly due to frequent vertical disturbance. Additionally, bacterial OM contributed 0.4–23.7% to TOC and 0.6–30.6% to TN in the sediment cores. The hypoxia of the water might have further promoted the proportion of bacterial OM in the sediments.

Lift Disturbance Cancellation with Rapid-Flap Actuation

Mitigation of vertical aerodynamic disturbances by means of a simple mechanical flap is investigated experimentally. A wall-to-wall NACA 0006 wing is bisected about the midchord for a 50%-chord flap length. Experiments are performed in a water tunnel at a chord-based Reynolds number of . The wing is driven in a sinusoidal vertical plunge motion as a spatially uniform, temporally varying surrogate to a vertical disturbance. Concurrently, the flap is actively deflected in a survey of kinematic parameters designed to suppress the influence of a plunge-induced disturbance. Plunge rates explored amount to disturbances incurred over a temporal range from one convective time to eight convective times. Two methodologies are employed to guide selection of flap deflection phase and amplitude necessary to preserve the baseline zero-lift state () of the undisturbed wing. In the first method, Theodorsen’s model is applied to arrive at an analytical solution to flap kinematics for a given prescribed plunge history. The theoretical derivation makes the standard assumptions of attached flow, planar wake, and no leading-edge vortical formations. Direct force measurements reveal reduction in lift transients by flap actuation of up to 87%, verifying the applicability of Theodorsen’s classical model. Further improvement is sought in a second method where empirical state-space modeling is formulated for lift cancellation. In this approach two separate lift models for wing plunge and flap deflection are constructed independently, and their superposition is employed to approximate the total lift in combined plunge and deflection motions. It is shown that although the empirical state-space approach performs similar to the inviscid theory of Theodorsen’s model, the empirical model proves more effective in suppressing the formation of the leading-edge vortex induced by plunge.