Counterclockwise Direction Research Articles

Numerical Study on the Influence of Solutal Buoyancy on Mixed Convection Heat and Mass Transfer in Skewed Domain

This study examines how variations in solutal buoyancy force affect mixed convection heat and mass transfer in a skewed domain. The thermal buoyancy is fixed at 105 for all the cases and mixed convection is induced due to the rotation of a cylinder in clockwise and counterclockwise directions. The solutal buoyancy is varied by changing the buoyancy ratio (0.5, 1, and 1.5). In the present investigation, OpenFOAM 5.0 has been employed to compile the heat and mass transfer solver by coupling energy and concentration equations with Soret and Dufour parameters. The Navier-Stokes equation along with Boussinesq term is included for mixed convection flow analysis. The cylinder rotation is kept constant to maintain the Reynolds number at 1000 at a fixed Richardson number of 1. It is found that for natural convection flow with a stationary cylinder, the heat and mass transfer are higher and stable at low buoyancy ratios. However, for mixed convection flow cases, the increase in heat and mass transfer is maximum and periodic with higher buoyancy ratios.

Numerical simulation of a non-Newtonian nanofluid on mixed convection in a rectangular enclosure with two rotating cylinders

Non-Newtonian fluid flows are a present advancement in industrial heat transfer and fluid mechanics, with numerous applications in engineering field as well as in real life such as food industry, petroleum refiners, biological processes, biomedical engineering, chemical engineering, etc. As a result, this numerical investigation explore the heat transfer and fluid flow behaviour of a mixed convective non-Newtonian power-law nanofluid ( Al 2 O 3 - H 2 O ) in a rectangular enclosure. The physical model is considered as a two-dimensional rectangular enclosure consisting two rotating hot cylinders ( T H )in the middle part of the cavity, where one moving clockwise and the other counter-clockwise directions. The left and right walls of the chamber are taken relatively low temperature ( T C ) while the remaining top and bottom walls are insulated. The important thermophysical property, viscosity, depends on the fluid shear rate, and the thermal conductivity depends on the fluid temperature. The related governing equations are solved by using the finite element method, and to describe the response surfaces the response surface methodology (RSM) is applied. The influence of the relevant non-dimensional parameters, Prandtl number ( Pr = 6.2 ), Reynolds number ( Re = 10 , 100, 200 and 400), power-law index (n = 0.6, 0.8, 1.0 and 1.4), Richardson number ( Ri = 1.0 , 2.0, 4.0 and 6.0), and nanoparticle volume fraction ( ϕ = 0.00 , 0.01, 0.02 and 0.04), are explained with physical interpretation by using streamlines, isotherm lines, velocity profile, temperature profile, and average Nusselt number ( Nu av ). To visualise the response surfaces, 2D and 3D contour plots are explained using the RSM. It is concluded that by adding nanoparticle into base fluid, the rate of heat transfer developed significantly. Same phenomena exhibits for larger magnitudes of Ri and Re . And, by increasing the value of n from 0.6 to 1.4, the Nu av would go down by 39.8 percent.

Concept and Design of Cutting Tools for Osseodensification in Implant Dentistry

Osseodensification is an innovative surgical instrumentation technique based on additive (non-cutting) drilling using special burs. It is known from the literature, that the osseodensification burs should operate in a clockwise direction to drill holes and in a counterclockwise direction to compact the osteotomy walls. For these purposes, the burs have special design features, like conical contour shape, increased number of helical flutes, and negative rake angle on the peripheral part. However, although other parameters and features of the burs define their overall performance, they are not described sufficiently, and their influence on surgical quality is almost unknown both for clinicians and tool manufacturers. The purpose of the present research is to identify the key design features of burs for osseodensification and their functional relationship with the qualitative indices of the procedure based on an analytical review of research papers and patent documents. It will help to further improve the design of osseodensification burs and thereby enhance the surgical quality and, ultimately, patient satisfaction. Results: The most important design features and parameters of osseodensification burs are identified. Thereon, the structural model of osseodensification bur is first represented as a hypergraph. Based on the analysis of previous research, functional relationships between design parameters of osseodensification burs, osseodensification procedure conditions, and procedure performance data were established and, for the first time, described in the comprehensive form of a hypergraph. Conclusions: This study provides formal models that form the basis of database structure and its control interface, which will be used in the later developed computer-aided design module to create advanced types of burs under consideration. These models will also help to make good experimental designs used in studies aimed at improving the efficiency of the osseodensification procedure.

Subclinical Left Atrial Remodeling in Healthy Adults with Left Ventricular 'Rigid Body Rotation'-Detailed Analysis from the Three-Dimensional Speckle-Tracking Echocardiographic MAGYAR-Healthy Study.

Background. While the basal region of the left ventricle (LV) rotates in a clockwise (cw) direction, the apical regions of the LV rotate in a counterclockwise (ccw) direction in healthy circumstances. Although LV rotational mechanics help optimize LV ejection, in some cases, LV twist is missing. This clinical situation, when the LV base and the apex rotate in the same cw or ccw direction, is called LV 'rigid body rotation' (LV-RBR). Three-dimensional speckle-tracking echocardiography (3DSTE) seems to be optimal for the simultaneous assessment of the LV and the left atrium (LA). Therefore, the present study aimed to determine the features of LA remodeling in healthy adults having 3DSTE-derived LV-RBR as compared to subjects with normally directed LV rotational mechanics. Methods. This study consisted of 165 healthy subjects (mean age: 33.1 ± 12.3 years, 75 males), from which 156 individuals showed normally directed LV rotational mechanics, while 9 cases had LV-RBR. Results. When LV-RBR subjects were compared to subjects with normally directed LV rotational mechanics, all LA volumes were increased with preserved LA stroke volumes and (non-significantly) reduced LA emptying fractions. When subgroups were compared with each other, it has been clarified that an enlargement of the LA with increased volumes was limited only to ccwLV-RBR cases. While reduced global peak LA longitudinal strain could be detected in LV-RBR subjects as compared to subjects with normally directed LV rotational mechanics, which was limited to cases with the ccw form of LV-RBR (15.1 ± 4.7% vs. 26.6 ± 9.0%, p < 0.05), the global peak LA radial strain was increased in subjects with cwLV-RBR (-23.4 ± 6.3% vs. -14.7 ± 8.0%, p < 0.05). Increased global LA radial strain at atrial contraction could be detected in LV-RBR subjects (-9.9 ± 7.1% vs. -5.2 ± 5.2%, p < 0.05), which was present in both ccw and cw LV-RBR cases. Conclusions. In healthy adults presenting LV-RBR, subclinical LA remodeling could be detected in both forms of LV-RBR, but more pronounced in those who present a counterclockwise-oriented form.

A comparative study on bone density before and after implant placement using osseodensification technique: a clinical evaluation

BackgroundDental implant success critically depends on the primary stability of the implant, which is significantly influenced by the bone density at the osteotomy site. Traditional drilling techniques for osteotomy preparation often compromise bone volume and quality. This study aimed to evaluate the impact of osseodensification, a novel osteotomy preparation technique, on bone density and implant stability. The technique utilizes specialized drills that operate in a counter-clockwise direction to compact autografted bone laterally and apically, preserving and enhancing bone density.MethodsA total of 32 patients undergoing dental implant surgery were included in this study. Pre-operative and post-operative bone densities at the apical, mesial, and distal regions of the osteotomy sites were measured using Dentascan (CT) and analyzed with Radiant DICOM software. The study utilized osseodensification drills for osteotomy preparation, comparing pre-operative and post-operative bone densities to assess the technique’s efficacy.ResultsThe study found a statistically significant increase in bone density post-operatively (p < 0.001), with the greatest improvement observed in the distal region, followed by the mesial and apical regions. The findings underscore osseodensification’s effectiveness in enhancing bone density and primary stability, with the distal region exhibiting the highest bone density.ConclusionOsseodensification represents a significant advancement in implant dentistry for osteotomy preparation. By preserving and increasing bone density through compact autografting, this technique not only improves primary stability but also offers potential benefits in indirect sinus lifting and alveolar ridge expansion. The study advocates for the broader adoption of osseodensification drills in clinical practice to achieve better outcomes in dental implantology.Trial RegistrationThis study received ethical approval from The Research Ethics Committee at King Khalid University’s under Approval no. ECM#2024 − 216. Additionally, it was registered with ClinicalTrials.gov, identifier no: NCT06268639.Graphical

The early dodder gets the host: decoding the coiling patterns of Cuscuta campestris with automated image processing.

We developed an in-house Python-based image analysis pipeline to investigate the movement patterns of Cuscuta. Our analysis unveiled that the coiling and circumnutation movements of Cuscuta are regulated by its intrinsic circadian rhythm. Cuscuta spp., commonly known as dodders, are rootless and leafless stem parasitic plants. Upon germination, Cuscuta starts rotating immediately in a counterclockwise direction (circumnutation) to locate a host plant, creating a seamless vascular connection to steal water and nutrients from its host. In this study, our aim was to elucidate the dynamics of the coiling patterns of Cuscuta, which is an essential step for successful parasitism. Using time-lapse photography, we recorded the circumnutation and coiling movements of C. campestris at different inoculation times on non-living hosts. Subsequent image analyses were facilitated through an in-house Python-based image processing pipeline to detect coiling locations, angles, initiation and completion times, and duration of coiling stages in between. The study revealed that the coiling efficacy of C. campestris varied with the inoculation time of day, showing higher success and faster initiation in morning than in evening. These observations suggest that Cuscuta, despite lacking leaves and a developed chloroplast, can discern photoperiod changes, significantly determining its parasitic efficiency. The automated image analysis results confirmed the reliability of our Python pipeline by aligning closely with manual annotations. This study provides significant insights into the parasitic strategies of C. campestris and demonstrates the potential of integrating computational image analysis in plant biology for exploring complex plant behaviors. Furthermore, this method provides an efficient tool for investigating plant movement dynamics, laying the foundation for future studies on mitigating the economic impacts of parasitic plants.

Mixed convection and sensitivity analysis of impinging jet flow of engine oil on rotating heated cylinder with high Prandtl numbers

This work investigates the impinging engine oil jet flow on a rotating heated cylinder with high Prandtl numbers through a combination of convection and sensitivity analysis. The impinging jet has an inlet in the middle of the upper wall and two outlets on its left and right sides. The outlets experience zero gradients, and the inlet is thermally cold. The finite element method (FEM) is used to solve the governing equations. The heated cylinder can rotate clockwise and counter-clockwise direction at ω and −ω, respectively. The impinging jet’s upper and lower walls are kept at a cold temperature (Tc). The Prandtl number (10≤Pr≤1000), Reynolds number (100≤Re≤300), angular rotational velocity (−30≤ω≤30), and Richardson number (Ri=1) are among the important parameters that have been numerically simulated. Streamlines, isotherms, velocity, temperature, local and average Nusselt numbers, and sensitivity analysis are used to display the results. Higher Reynolds and Prandtl numbers correspond to an increase in the local Nusselt number. When the Prandtl number rises from Pr=50 to 100 and Pr=1000 at ω=0, the average Nusselt number, Nu¯, increases by 28.2% and 191.85%. A sensitivity analysis was performed using variance analysis (ANOVA). The sensitivity for Pr, Re, and ω is positive at the highest level of Pr, lowest and medium levels of ω, and increases with higher levels of Re.

Numerical Simulation of the Effects of Compartment Height, Fire Source Location, and Vent Location on Compartment Fire Phenomena with a Ceiling Vent

In this study, the numerical simulations of the effects of compartment height, fire source location, and vent location on the compartment fire phenomena with a ceiling vent were performed. Under the same fire source and vent location conditions, the compartment height of 5.5 m showed a higher mass flow rate across the vent than that of 11 m. For the fire source at the center, the vent on the left showed a lower mass flow rate than that at the center for both compartment heights. For the fire source on the left, the vents on the right and left exhibited the lowest mass flow rates at the compartment heights of 5.5 m and 11 m, respectively. Moreover, for the fire source on the left, a macroscopic rotational flow in the clockwise direction was observed at the compartment height of 5.5 m, whereas at the compartment height of 11 m, macroscopic rotational flows in the clockwise and counterclockwise directions appeared at its lower and upper portions, respectively. It was confirmed that these macroscopic rotational flows were closely related to the change in the mass flow rate across the vent with the vent location. The compartment height of 11 m had a lower average temperature inside the compartment than that of 5.5 m, which was because of the increase in the surrounding wall area. In addition, under each compartment height condition, the changes in the average temperature inside the compartment with the fire source and vent locations were minor.

Non-contact rotation of a small object using a combination of ultrasound standing and traveling waves

Noncontact transportation and separation techniques using airborne ultrasound are attractive for use in industrial fields in which micrometer- to millimeter-sized objects can be levitated, rotated, and transported in the air using acoustic standing-wave and traveling-wave fields. This paper discusses a method to rotate a small object in the air without physical contact using ultrasound. The experimental system comprises a vibrating disk with four bolt-clamped Langevin-type ultrasound transducers and two semicircular reflectors. The flexural vibration of the disk generates an acoustic standing wave between them, and a small object can be levitated at the nodal position. An acoustic traveling wave was generated in the horizontal direction in an asymmetric acoustic field by inclining one of the two reflectors, which induced rotation of the object in the clockwise or counterclockwise direction. The acoustic intensity in the circumferential direction acting on the object was then calculated, and the directions of rotation predicted by the calculations corresponded with the experimental results. Higher input currents produced higher rotation speeds; the rotation speed reached a maximum value of 6.8 ± 0.9 rps at an input current of 1.1 App.

Bidirectional all-PM Er-doped fiber laser based on a self-stabilized interferometer mode-locker

We demonstrate a bidirectional all polarization-maintaining (PM) Er-doped fiber laser based on a self-stabilized interferometer mode-locker. By utilizing mechanical sharing and multiplexing propagation directions, the laser has balanced bidirectional outputs and passively suppresses common-mode noise. We also investigate the intra-cavity pulse dynamics via numerical simulations, which coincides well with experimental observations. The self-stabilized interferometer compensates for the group delay difference between the polarization components induced by linear birefringence. The cross-phase modulation effect in the self-stabilized interferometer leads to asymmetric spectra. In addition, from 10 kHz to 1 MHz frequency range, the integrated RMS phase noise in clockwise (CW) and counter-clockwise (CCW) directions are 0.124 mrad and 0.14 mrad, respectively. The integrated RMS RIN in CW and CCW directions are 439 ppm and 464 ppm. Due to passive common-mode noise cancellation, the repetition frequency difference can be stabilized near 19 Hz in 2500 s gate time. The stability of the repetition frequency difference can reach a minimum value of 4.167 × 10−4 at a gate time of 100 s. This novel bidirectional all-PM Er-doped fiber laser based on a self-stabilized interferometer mode-locker can provide a new scheme for the construction of an all-PM dual-comb system.

Orbital angular momentum and rotational properties of off-axis vortex beams in two-dimensional media with anisotropic nonlocal nonlinearity.

By introducing anisotropy into nonlinear propagations, off-axis vortex beams exhibit significantly different characteristics compared to the isotropic case. The orbital angular momentum (OAM) is non-conservative and can periodically change between positive and negative values. Accordingly, the rotation of phase singularity can transit between clockwise and counterclockwise directions. Furthermore, the phase singularity can move to infinity when the OAM approaches zero. By using the Ehrenfest theorem, the motion of the beam center is obtained. Its trajectory can be circular and parabolic or follow other complex shapes, depending closely on the anisotropy of the nonlinearity. The rotational velocity of the beam center can be modulated by the nonlinearity anisotropy and can far exceed the initial value during its propagation. These results may find potential applications in beam shaping and optical manipulation.

Largest unit rectangles inscribed in a convex polygon

We consider an optimization problem of inscribing a unit rectangle in a convex polygon. An axis-aligned unit rectangle is an axis-aligned rectangle whose horizontal sides are of length 1. A unit rectangle of orientation θ is a copy of an axis-aligned unit rectangle rotated by θ in counterclockwise direction. The goal is to find a largest unit rectangle inscribed in a convex polygon over all orientations in [0,π). This optimization problem belongs to shape analysis, classification, and simplification, and they have applications in various cost-optimization problems.

Research on the Inhibition and Transmission Properties of Photonic Spiking Dynamics in Semiconductor Ring Lasers

Significant progress has been made in the research of all-optical neural networks in recent years. In this paper, we theoretically explore the properties of a neural system composed of semiconductor ring lasers (SRLs). Our study demonstrates that external optical signals generated by a tunable laser (TL) are injected into the first semiconductor ring laser photonic neuron (SRL1). Subsequently, the responses of SRL1 in the clockwise (CW) and counterclockwise (CCW) directions are unidirectionally injected into the CW and CCW directions of the second semiconductor ring laser photonic neuron (SRL2), respectively, which then exhibits similar spiking inhibition behaviors. Numerical simulations reveal that the spiking inhibition behavior of the SRL response can be precisely controlled by adjusting the perturbation time and intensity of the external injection signal, and this behavior is highly repeatable. Most importantly, we successfully achieve the stable transmission of these responses between the two SRL photonic neurons. These inhibition behaviors are analogous to those of biological neurons, but with a response speed reaching the sub-nanosecond level. Additionally, we indicate that SRL photonic neurons undergo a refractory-period-like phenomenon when subjected to two consecutive perturbations. These findings highlight the immense potential for the design and implementation of future all-optical neural networks, providing critical theoretical foundations and support for them.

Electromechanical Modeling and Analysis of Motor Whine in Electric Propulsion Systems

Electric motor whine is a major source of tonal noise and vibration for electric propulsion systems. The lack of engine masking noise in electric vehicles (EVs) further pronounces the pure tones, which are annoying to the occupants. The associated vibration can cause durability issues due to resonance and lead to failure of the sub-assembly or the supporting structure. A source-level NVH assessment of electric propulsion systems in modern EVs aims to achieve first-time quality designs at the advanced design stage. Accurate modeling of the motor stator and the electromagnetic (EM) forces at the air gap between the stator and rotor are critical to the NVH assessment. This work investigates the interaction between EM force application and the stator design in all four quadrants in which the electric motor operates, including both driving and regenerative braking in both clockwise and counterclockwise directions. A finite element (FE) model of the stator is developed, and the EM forces are mapped on the stator teeth, including different clocking and application directions. The stator model is integrated in the electric drive unit (DU) model, which enables the evaluation of the NVH performance of the propulsion system due to the reversal the EM force directions. The predicted analysis results are compared with the measured mount vibration

Left ventricular deformation in the presence of left ventricular 'rigid body rotation' in healthy adults-three-dimensional speckle-tracking echocardiographic insights from the MAGYAR-Healthy Study.

During the heart cycle, the left ventricle (LV) not only shows a contraction-relaxation pattern, but LV has a rotational mechanics, as well. It is a known fact that certain pathologies may be associated with an absence of LV twist, when LV basal and apical regions rotate in the same clockwise (cw) or counterclockwise (ccw) direction called LV 'rigid body rotation' (LV-RBR), but it can also occur in healthy subjects. The present cohort study aimed to examine LV strains in healthy subjects with LV-RBR versus with normally directed LV rotational mechanics by three-dimensional speckle-tracking echocardiography (3DSTE). The study consisted of 181 healthy individuals, from which 171 cases had normally directed LV rotational mechanics (mean age: 32.5±12.3 years, 79 males) and 10 healthy subject showed LV-RBR (mean age: 35.4±11.3 years, 3 males). Complete two-dimensional (2D) Doppler echocardiography and 3DSTE were performed in all healthy individuals. None of routine 2D Doppler echocardiographic parameters showed differences between the groups examined. There were no subjects with ≥ grade 1 regurgitation on any valves or with significant stenosis on any valves. 3DSTE-derived LV volumes, global and mean segmental strains did not differ between the groups examined. Apical anterior and lateral segments showed reduced segmental LV circumferential strain (CS) (-18.9%±8.5% vs. -26.7%±10.7%, P=0.02; -27.3%±12.6% vs. -34.8%±13.2%, P=0.08, respectively) and LV area strain (AS) (-26.8%±9.8% vs -36.8%±12.0%, P=0.01; -35.7%±13.2% vs. -45.0%±14.6%) in healthy subjects having LV-RBR as compared to cases with normally directed LV rotational mechanics. These abnormalities were present only in subjects having cwLV-RBR. Although global LV deformation is normal in the presence of LV-RBR in healthy adults, reduction of apical anterior and lateral LV-CS (and LV-AS) are present in cases with cwLV-RBR only suggesting segmental deformation abnormalities.

Management of Various Cases for Implant Placement by Using Osseodensification Protocol

Abstract In recent years, implant treatment has become a popular option and is frequently preferred by patients and doctors. Initial implant stabilization is a vital element for implant-osseointegration and long-term implant success. Salah Huwais conceptualized the osseodensification technique for dental implant placement. Compared to conventional implant osteotomy practices, osseodensification allows a nonsubtractive osteotomy preparation. Specially designed burs are used in a noncutting counterclockwise direction to preserve and condense bone. The present case series aims to explain the implementation of osseodensification for dental implant insertion in the thin bony alveolar process, internal closed sinus elevation with implant placement, and immediate implant insertion in the extraction socket. Three different case reports have been discussed in detail where the osseodensification technique was used with specially designed Densah™ Bur to prepare the osteotomy and simultaneous implant placement. The study also focuses on the technique’s advantages, disadvantages, and indications, as existing in the relevant literature, along with evidence. Osseodensification is a unique procedure that prepares implant sites while conserving the alveolar bone. In the present report of three cases, satisfactory primary stability of implants with conservation of alveolus integrity was accomplished, which resulted in a shorter restoration interval for prosthetic rehabilitation.

Experimental comparison of induction control methods for wind farm power maximization on a scaled two-turbine setup

Induction control methods offer a potential solution to minimizing wake effects that occur in large wind farms. This paper presents an experimental study on multiple induction control methods for wind farm power maximization. Wind tunnel experiments were conducted on two aligned scaled wind turbines. The upstream turbine was operated with static induction control, periodic dynamic induction control with collective pitch actuation, and dynamic individual pitch control (the helix approach). All wind farm control implementations were compared to a baseline case, which optimized the individual power extraction of both turbines. Tomographic particle image velocimetry was used to measure the wake of the upstream turbine. Based on turbine measurements, grid searches were employed to discover the optimal frequency and amplitude of the pitch actuation in the dynamic induction control cases. While static induction control showed increased wake velocities in the near wake, it did not provide an overall increase in power production of the two-turbine array. Dynamic induction control methods, especially the helix approach in the counterclockwise direction, were seen to significantly increase the total power output compared to the baseline control case. However, this improvement came with a larger amount of pitch actuation and increased fatigue loading of structural components in the fore-aft direction.

BLDC Motor based Air Dessert Cooler

Abstract: This paper proposes a new position sensorless drive for brushless DC (BLDC) motors.Growing need for high productivity is placing new demands on mechanisms connected with electrical motors. The demand for low costBrushless DC (BLDC) motor has increased in industrial applications. A simple BLDC motor control algorithm forlow cost motor drive applications using general purpose microcontrollers has been created and presented in this paper. Proposed design will allow the user to rotate the motor either clockwise or counter clockwise direction. Dependingon the rotor position the sensor will give response to the controller circuit. Then the controller circuit will fix the direction of current following to the stator. The design controller circuit is also implemented. The overall design consists of microcontroller circuit, logic gates, switching devices (MOSFET/BJT), BLDC motor, sensors.

Variations in critical current density of TSSC cable under torsional and radial loads

A 3D finite element mechanical-electric numerical model was constructed to analyze the mechanical-electric performance of TSSC cables under torsional and radial loads at 77 K. The results indicate that when subjected to torsional load, the tapes in the outermost region within the slot of TSSC cable initially exhibit a decreasing trend, gradually expanding towards the inner region. The magnitude of this decrease progressively diminishes in the direction from outer to inner. Conversely, under radial loading, the normalized critical current density of the tapes in the innermost region within the slot initially decreases and expands outward along the radius. The tapes in the middle region remain mostly unaltered, while the outer region follows a pattern of increasing from inside out and reaches its peak at layers 28 and 29. Moreover, under torsional loads, TSSC cables display a higher normalized critical current density in the counterclockwise direction compared to the clockwise direction. To enhance the critical current density performance of TSSC cables under torsional loads, it is suggested to appropriately reduce the pitch, decrease the width of superconducting tape, increase the number of stacked tapes, enlarge the width of the slot and the diameter of the diversion trench, as well as increase the inner diameter while decreasing the outer diameter of the helical core. The choice of material for helical cores is not significantly impactful. On the other hand, under radial loads, factors such as tape width, number of stacked tapes, slot width, diversion trench diameter, and inner and outer diameters of the helical core have similar effects. Additionally, increasing the pitch length or adding more slots can enhance the critical current density performance of TSSC cables. Selecting different materials for the helical core also contributes positively to this improvement.

Solitons, bifurcation and chaotics in a bidirectional mamyshev oscillator

Bidirectional mode-locked fiber lasers are able to deliver two outputs of pulses in the clockwise (CW) and counterclockwise (CCW) directions, having important applications in dual-comb spectroscopy, asynchronous optical sampling and terahertz time-domain spectroscopy. In this paper, we have experimentally demonstrated an all-fiber Er/Yb-doped bidirectional passively mode-locked Mamyshev oscillator (MO) without an external seed. Two stable mode-locked states with remarkable different characteristics are observed by adjusting the pump power. The transition process between the two mode-locked states shows chaotic behaviors, which are further investigated with numerical simulations based on the Ginzburg-Landau equation. The bidirectional MO proposed in this work is not only a good laser source, but also a good platform to study soliton dynamics, system bifurcation, and chaos in ultrafast fiber laser systems.