Surface Of Cylinder Research Articles

Investigation of a Near-Field Cylinder Wake in the Subsonic, Transonic, and Supersonic Regimes

The near wake of a circular cylinder in a high-Reynolds-number regime is investigated using the particle image velocimetry technique for an inflow Mach number spanning 0.3 to 2. The mean flow and turbulent kinetic energy field for different Mach number cases are presented. Furthermore, the influence of the Reynolds and Mach number effects is examined based on the mean separation point along the cylinder surface, which is extracted from complementary schlieren visualization measurements, and the literature. The wake width for the supersonic inflow case is found to be an order of magnitude smaller physically than the subsonic case with an identical cylinder diameter. Additionally, the swirl strength criterion is used to identify the eddies present within the wake, and the eddy size and convection velocity are characterized based on the spatiotemporal correlations. The result suggests that the mean wake features for the subsonic and supersonic cases are very different. Moreover, the interaction of eddies generated at the cylinder’s top and bottom shear layers leads to the large-scale features present in the wake, and the differing paths followed by the eddies between the subsonic and supersonic cases are responsible for the variation in the observed wake width.

Simultaneous investigation of flow and thermal fields inside a square duct with a built-in heated circular cylinder

Air-based cooling methods are widely used for heat exchange and thermal management, due to their potential for heat removal with minimal complexity and operating costs. However, the physical mechanisms involved in these processes are not yet fully understood, due to the complexities involved in the many interacting underlying sub-processes pertaining to the energy transfer from the surface to the bulk fluid. When dealing with turbulent flows involving heat transfer, one needs to delineate the coupled effects of velocity and temperature to ascertain the heat transfer dynamics. Here, we present the first-ever application of an advanced methodology based on the concept of two-color laser-induced phosphorescence (2cLIP) and particle image velocimetry (PIV), elucidating the mechanisms involved in the heat transfer from the surface of a cylinder placed inside a confined square duct. The potential advantage of the technique is in measuring the whole-field velocity and thermal fields simultaneously by incorporating modifications to the conventional PIV systems through the usage of a single tracer (BAM:Eu+2) for measuring the velocity and temperature fields. This aids in reducing the costs and complexities involved in setting up separate systems for measuring the temperature field distributions. Measurements reported here, were performed for the Reynolds numbers of 270 and 360, and for the heat flux levels of 10, 12 and 15 W. Experimental observations revealed that, with an increase in the mass flow rate from 3.06×10-4 (kg/s) to 4.08×10-4 (kg/s), the heat removal rate from the surface of the cylinder was enhanced. Also, the heat transfer was witnessed to enhance in the rear portion of the cylinder, in the case of increased cylinder heat input at constant mass flow rate. Also, a local peak in the heat transfer coefficient was indicative of the flow separation from the cylinder surface. The spatio-temporally averaged Nusselt number (Nu¯D) was witnessed to be higher for higher mass flow rate and was seen to increase with increasing cylinder heat input at constant mass flow rate. To the best of the knowledge of the authors, the work reported is one of the first attempts to carry out the simultaneous, whole-field, non-intrusive measurements of flow and heat transfer in a confined channel fitted with a heated cylinder using Thermographic-PIV technique.

Modeling Developable Surfaces using Quintic Bézier and Hermite Curves

The nature of the developable surfaces has similarities to the industrial materials that are not amenable to stretching. Regarding the benefit, the developable surfaces are widely used to model plat-metal-based industry products such as automobiles, ship hulls, and ducts. For this reason, we introduce a new approach for designing developable surfaces limited by two space curves. The method consists of these steps. First, we define a generalized cone and a cylinder surface by posing restrictions: a fixed summit point of the cone has to be outside a plane; a static nonzero constant vector is unparallel to the plane; and two quintic Bézier curves are placed on the different sides of the plane. Second, computing the control points on the plane is determined by the intersection between the control lines of the cone/cylinder surface and the plane. Third, using these obtained control points, we evaluate the required boundary curves profile and the shape of the developable Bézier surfaces, that are limited by these quintic Bézier curves. Finally, we also apply this method to design the developable Hermite surfaces. As a result, this introduced method can provide the equations and procedures for modeling developable surfaces with boundary curves in space. Also, it is useable to design these surfaces in many arches and shapes. Moreover, this method is effective for modifying and adjusting the desired boundary curves profile of the surfaces.

Discharge Randomness and Attraction Process of Epoxy Surface on Discharge Channel in SF6 Gas Under Uniform Electric Field

It is generally believed that due to the electric field distortion effect and the photoemission process of the solid surface, the discharge channel near the solid surface trends to develop along the surface than that in bulk gas. One way to improve insulation performance is to avoid the solid surface from participating in the gas discharge process. However, the mechanism of the solid surface’s effect on the gas discharge process is still unclear. In this paper, we recorded high-speed framing pictures of the discharge process in SF6 gas near the epoxy surface under lightning impulse voltage in the uniform electric field. The arc pictures show that the attraction effect of the solid surface to the discharge channel is related to the surface shape, gas gap height, and distance from the discharge channel to the solid surface. Besides, discharge randomness also plays a role, which is more obvious in the cylinder insulator than in the conical insulator, for the surface with conical shape could easily attract and arrest the discharge channel to its surface. According to the pictures of discharge process near the cylinder surface, we found that the photoemission process occurs in the streamer stage but has little effect on the attraction effect. The leader initiates after the streamer bridges the gas gap, and its random stepped walk could induce the attraction effect from the solid surface: only when the random stepped leader deflects close to the solid surface, the discharge channel could be further attracted to the solid surface by the electrostatic force, especially its normal component. The result indicates that there are three points to prevent the solid surface from participating in the gas discharge process and further improve insulation performance: choose a cylinder shape (avoid a conical shape), keep the surface away from the high electric field area where discharge may start, and reduce the normal component of the surface electric field.

Effects of taper ratio on the aerodynamic forces and flow field of two tandem square cylinders

To explore the influence of taper ratio on aerodynamic characteristics of tandem square cylinders, three-dimensional (3D) large eddy simulations of flow around two tandem square cylinders at the Reynolds number (Re) = 2 × 103 are carried out with a spacing ratio G/D = 4, where G is the cylinder center-to-center distance and D is the cylinder width. Different taper ratios of ξ = 0%, 5%, 10%, and 15% are considered. The influence of taper ratio on aerodynamic coefficient, wind pressure coefficient, mean, and instantaneous flow fields are comprehensively studied. The mechanism of variation in flow fields is revealed, and the mathematical relationship between the taper ratio and aerodynamic characteristics is established, which can provide theoretical reference for design and construction of tandem structures. The results indicate that the taper ratio has significant influence on the mean force coefficient, fluctuating force coefficient, surface mean and fluctuating pressure coefficients, and vortex shedding frequency (fvs). As increase in the taper ratio, the mean force in the along-wind direction, fluctuating force in the across-wind direction, and surface pressure of the two cylinders will be decreased, but the vortex shedding frequency will be increased. The taper ratio has negligible influence on the flow separation location of the upstream cylinder. However, reattachment location of the shear layer moves backward along the leeward surface of the downstream cylinder, and width of the shear layer gradually becomes narrower and closer to surface of the two cylinders. The vortex shedding strength and vortex energy distribution of the two cylinders will be reduced as a result of the narrower shear layer. Meanwhile, coherence and periodicity of the vortex shedding will also be weakened, which results in reduction in the aerodynamic forces and increase in the vortex shedding frequency.

Three-dimensional wake transition of a heated square cylinder in the presence of cross-buoyancy

The three-dimensional flow transition is examined in the wake of a heated square cylinder subjected to horizontal cross-flow perpendicular to gravity utilizing a direct numerical simulation approach. The surface of the square cylinder is heated uniformly to an elevated temperature Tw, and the amount of excess temperature is represented as the over-heat ratio ε=(Tw−T∞)/T∞, where T∞ represents the surrounding temperature. The effects of large-scale heating on the transport properties and thermal straining of the fluid particles are captured using an in-house non-Oberbeck–Boussinesq compressible model. The compressible flow governing equations (in a body-fitted coordinate system) are solved using a variant of flux-based particle velocity upwind-modified+ (PVU-M+) technique [Ahmad et al., “On the formation and sustenance of the compressible vortex rings in starting axisymmetric jets: A phenomenological approach,” Phys. Fluids 32, 126114 (2020)]. In this investigation, all computations are conducted at a low Mach number (Ma = 0.1) and air (Prandtl number, Pr = 0.71) is used as the working fluid. As the heating level rises, the shape and wavelength of the vortical structure undergo significant alterations. At Re = 250, the mode-B transition with a shorter spanwise wavelength and the mode-D transition with a longer wavelength are observed, respectively, for heating levels ε=0.0−0.2 and ε=0.8−1.0. Furthermore, for heating levels in the range 0.4≤ε≤0.6, an intermediate wavelength of the mode-E transition is detected. The temporal variation of fluid properties such as the force coefficient (CL, CD) and the Nusselt number (Nu) are shown at various heating levels. In addition, surface vorticity is examined in order to comprehend the flow dynamics near the surface of a heated square cylinder.

Flow-induced vibration of an elliptic cylinder with a splitter-plate attachment at low-Reynolds number: Self-limited oscillations

Flow-induced vibrations (FIV) of a rigid, elastically-mounted elliptical cylinder-plate assembly which is free to move in the cross-flow (transverse) direction is studied using numerical simulations. These simulations were conducted for a laminar flow at a Reynolds number of Re=100 over a reduced velocity range of Ur= 2–30, with a low mass ratio (m∗=10) and zero structural damping, for various values of the aspect ratio AR of the elliptical cylinder; namely, AR= 0.5, 0.67, 0.75, 1, 1.5 and 2. It is shown that the characteristics of the FIV response of an elliptical cylinder-plate assembly that occurs over a limited velocity range (viz., self-limited FIV) such as the vibration amplitude, the reduced-velocity range with vibrations, the nature of the branching behaviour (e.g., synchronization and non-synchronization branches in the amplitude response), and the vortex-shedding (wake) modes are strongly dependent on the aspect ratio. The self-limited FIV response of the assembly is enhanced for AR increasing from 0.75 to 1.5. However, it is found that for AR=2, the reduced-velocity range over which the FIV response occurs is significantly shortened owing to the absence of a non-synchronization branch in the amplitude response for this case. There is a critical value (AR)cri of the aspect ratio below which oscillations in an elliptical cylinder-plate assembly cannot be induced. This critical value occurs in the range 0.67<(AR)cri<0.75 for an assembly in a laminar flow at Re=100 for a fixed splitter-plate length LSP/D=0.5 (D is the equivalent diameter of the ellipsoidal cylinder). A careful analysis shows that there is close relationship between the presence of structural oscillations in the assembly and the location of flow separation points on the windward surface of the elliptical cylinder.

Artificial neural network approach for MHD mixed convection and entropy generation in a vertical annulus with time periodic thermal boundary conditions in the presence of radial and induced magnetic field

Entropy generation with time periodic thermal boundary conditions have numerous applications in heat exchangers, electronic devices, automatic and thermal control systems. The present research focuses on mixed convective hydromagnetic electrically conducting fluid flow in a vertical annulus using thermodynamic concepts, in the presence of induced magnetic field along with entropy generation and time periodic boundary conditions. The governing equations related to the present model are solved using finite element method. Also to predict heat transport features in the vertical annulus, artificial neural network – backpropogated Levenberg Marquardt algorithm is adopted. The steady and periodic profiles of velocity, skin friction, temperature and induced magnetic field are illustrated graphically for specific range of pertinent parameters to demonstrate significant aspects of the results. It is noted that increase in Hartmann number enhances the entropy generation near the outer cylinder, which illustrates that the fluid friction and magnetic field influence is maximum at the outer cylinder surface. The Bejan number in the annulus reduces with increase in viscous heating parameter. Results indicate that raise in the Prandtl number diminishes the thermal boundary layer thickness. As a result of decrease in the intensity of heating the boundary walls, a raise in Strouhal number lowers the fluid temperature profile. The generalized correlation is expressed to predict heat transport features in the annulus using artificial neural network – backpropogated Levenberg Marquardt algorithm.

Improving the performance of parts of the cylinder piston group of marine diesel engines

For the repaired engine installed on the vessel, in order to ensure its normal operation, it is necessary to run-in. This operation consists in the running-in of rubbing surfaces to ensure the necessary surface roughness, surface shape, and an increase in the contact area of the mating surfaces. The result of proper running-in is considered to be the efficient operation of the engine, in which all engine parameters are stable, such as coolant temperature, exhaust gas temperature, fuel consumption, oil consumption. In most cases, the details of the cylinder piston group, especially the piston rings, which operate under the most extreme conditions, are responsible for all the listed engine parameters. New piston rings, with an ideal shape inserted into the piston groove of the piston, cannot ensure a tight fit to the cylinder surface during movement, in this regard, gaps appear in some places that violate the tightness of the combustion chamber. Elimination of these gaps is one of the main tasks of running-in of the mating surfaces. The main factors affecting the duration of the run-in are the macrogeometry of the piston rings, the profiles of the working surface of the piston ring and cylinder, the roughness of the surfaces, the running-in modes, lubrication and maintenance coatings. Analyzing scientific research in this field and relying on their experience, an algorithm of running-in works was formed, which was subsequently tested on engines. The final stage of the research in this direction consisted of the analysis of the positive results of the experiment and on its basis formulas for engines of different turnovers were proposed.

Local linear stability of plumes generated along vertical heated cylinders in stratified environments

The linear temporal and absolute/convective stability characteristics of a thermal plume generated along a heated vertical cylinder are investigated theoretically under the Boussinesq approximation. Special focus is given to the uniform-wall-buoyancy-flux case whereby the cylinder surface sustains the same linear temperature gradient as the environment. A competition between the axisymmetric and helical modes is a remarkable feature of the instability, distinguishing these ‘annular plumes’ from free plumes/jets for which the helical mode is generally dominant. It is found that higher surface curvature stabilises the temporal axisymmetric mode significantly, but only has moderate effects on the helical mode. The most temporally unstable perturbation mode switches from a helical into an axisymmetric mode when the Prandtl number increases beyond a critical value. Both the roles of shear and buoyancy during the destabilisation are identified through an energy analysis which indicates that, while the shear work is usually a major source of perturbation energy, the buoyancy work manifests for long-wave axisymmetric perturbation modes, and for thin cylinders and high Prandtl numbers. For the specific temperature configuration considered herein, an annular plume is always convectively unstable whereas decreasing the cylinder radius from the planar limiting case first decreases and then increases the tendency of the flow towards being absolutely unstable. The helical mode is especially susceptible to being absolutely unstable on very thin cylinders. Several conditions for the onset of cellular thermal convection and plume detrainment are proposed based on our results and a hypothesis which connects the absolute instability to the detrainment phenomenon.

Drag of a shear-thickening suspension on a rotating cylinder

We investigate experimentally the two-dimensional flow of a shear-thickening suspension around a rotating cylinder to which a constant torque is applied. While for low torques both the drag and the flow are steady and close to those for a Newtonian fluid, above the onset torque for discontinuous shear thickening the average velocity of the cylinder saturates and large periodic oscillations of the cylinder velocity are observed. The oscillations result from a hydrodynamic instability of the flow: slow-acceleration phases are followed by high-deceleration phases, triggered by the propagation of a thickening front, and so on. The slow-acceleration phases set the oscillation period, which is limited by the cylinder inertia and inversely proportional to the applied torque. Combined analyses of the cylinder motion and the flow reveal that the front typically nucleates when the shear rate at the cylinder surface reaches the discontinuous shear-thickening threshold. In addition, the characteristics (duration, stress) of the deceleration are set by the interplay between the thickening front propagation and the suspension and cylinder inertiae or the container size. Since for a slow acceleration the shear rate at the cylinder surface is essentially the cylinder angular velocity, this description of the unsteadiness elucidates the saturation of the average velocity. More generally, it illustrates how the hydrodynamics of a shear-thickening suspension with a strongly re-entrant rheology can lead to a marginally re-entrant, although steep, drag curve.

Effects of superhydrophobicity on VIV control of a circular cylinder

We conducted an experimental study on the vortex-induced vibration (VIV) dynamics of cylinders featuring a specific superhydrophobic band. The superhydrophobic band refers to the pattern where the cylinder's surface is featured with equispaced bands of normal surface and superhydrophobic coating in an alternate manner. The experiments were conducted over a range of reduced velocities from Ur = 3 to 11, corresponding to Reynolds numbers between 1500 and 5900. To capture the near-field wake of the cylinders, a time-resolved particle image velocimetry (TR-PIV) system was employed, while the hydrodynamic forces were acquired using a six-component load cell. We found that the fully coated cylinder consistently displays the smallest amplitude of oscillation in the VIV initial branch, achieving a maximum reduction of approximately 38.9% at Ur = 5.0. Upon applying a superhydrophobic coated band, the patterned cylinder experiences a substantial enhancement in VIV amplitude (about 22.5% at Ur = 5.0) compared to the normal cylinder. On the other hand, in the VIV lower branch, the patterned cylinder effectively suppresses oscillation, whereas the fully coated cylinder exhibits slightly larger oscillation amplitudes than the normal cylinder. This finding agrees well with the trend of lift forces. The analysis of phase-averaged flow structures suggests that this difference can be attributed to the delayed vortex shedding from the superhydrophobic surface and the emergence of three-dimensional vortex structures created by the superhydrophobic band.

NUMERICAL INVESTIGATION OF FORCED CONVECTION HEAT TRANSFER ON INLINE CYLINDERS IMMERSED IN A POROUS MEDIA

In the present study, forced convection heat transfer on eight inline cylinders immersed in a 10 × 10 × 30 cm packed bed of porous medium is numerically explored with a range of Reynolds numbers from 1100 to 2250. The airflow passes through eight cylinders with an inline arrangement, each having a diameter of 15 mm and a length of 10 cm, immersed in a horizontal porous channel at a constant heat flux of 2000W/m2. The commercial program ANSYS Fluent R.19 simulates the changes in pressure drop and temperature distribution by changing the Reynolds number and porosity. The dimensions of each porous pack are 10x10 cm in cross-section, 5 cm in length, and 5 cm in spacing from the next porous pack. The porosity values are (0.4001, 0.39112, and 0.3822). The general shape of all temperature contours shows that the high porosity near the cylinder wall enhances heat transfer from the heated cylinder surface. After that, the air temperature gradually decreases when going away from the cylinder surface. It can also be seen that the pressure drop decreases as particle diameter increases.

Effect of crossflow oscillation Strouhal number on circular cylinder wake

The wake flow features and aerodynamic characteristics of a circular cylinder in an oscillating crossflow were experimentally investigated. The study focused on crossflow oscillation Strouhal numbers that were smaller than the natural wake vortex-shedding Strouhal numbers. Crossflow oscillations were generated using a downstream rotating plate method. The flow evolution processes were observed using laser-light sheet assisted smoke flow visualization technique. Wake instability and time-averaged velocities were assessed using a one-component hot-wire anemometer and particle image velocimetry. Pressure distributions on the cylinder's surface were quantified using a linear pressure scanner, obtaining pressure coefficient distributions and drag forces. The wake instability Strouhal number, velocity vectors, streamline patterns, and recirculation bubble geometries in the wake region of the circular cylinder were determined. The wake turbulence properties were analyzed using the triple-decomposition method, including turbulence intensities and Lagrangian integral length and time scales. The results of natural and oscillating crossflows were compared. The wake vortex-shedding Strouhal number was lower than the natural Strouhal number but higher than the crossflow oscillation Strouhal number. It was primarily influenced by the oscillation Strouhal number and the Reynolds number of the crossflow. Critical crossflow Reynolds and oscillation Strouhal numbers were identified, beyond which the wake vortex-shedding Strouhal number reached a constant value. The crossflow oscillation intensity did not significantly affect the wake vortex-shedding behavior. The study provided quantitative descriptions and discussions of recirculation bubble geometries and statistical turbulence properties. Furthermore, the crossflow oscillations led to a substantial reduction in the drag coefficient experienced by the circular cylinder.

Convenient Conformal Transmissive Metasurface Antenna Embedded on Arbitrary Cylindrical Surface

Conformal metasurface antenna embedded on the platform with an arbitrary shape is of great significance for communication systems in practical applications. Herein, a convenient design strategy for conformal transmissive metasurface antenna with arbitrary cylinder surface is presented. First, a novel‐phase compensation concept for curved surface is inspired by ray‐tracing technique. Then, by using arc differentiation and numerical integration, the meta‐atoms’ coordinates calculation method is analyzed for arbitrary cylindrical surface. Next, the electromagnetic responses of planar and curved transmissive meta‐atoms are discussed, and conformal metasurfaces in single‐quadratic surfaces are simulated to validate the feasibility of the design strategy. Finally, for potential applications, three combined quadratics conformal metasurface antennas with capabilities of beam focusing, beam deflecting, and vortex generation are designed and measured. It is indicated in the results that the three conformal metasurface antennas with combined quadratic cylinder surfaces can transform the spherical wave efficiently into the plane wave, deflected beam, and vortex beam, respectively, verifying the validity of the designs. The convenient strategy has good generality and flexibility because it is applicable to arbitrary cylindrical metasurface with a specific alignment function, which has promising perspective in practical applications, and offers a novel approach to design conformal antennas without changing aerodynamic shapes of platforms.

Research on protection methods for 70 MPa on-board Type IV hydrogen storage cylinders under localized fire conditions

When hydrogen fuel cell vehicles (HFCVs) occur fires, the localized fire protection methods for on-board hydrogen storage cylinders can reduce the failure possibility of cylinders. This paper describes an experimental study of 70 MPa Type IV on-board hydrogen storage cylinders exposed to localized and engulfing fires. A three-dimensional (3D) computational fluid dynamics (CFD) model is developed to simulate the effects of various protection methods on the heat transfer characteristics of cylinders. The results demonstrate that both fire-protection coatings and fire-protection baffles effectively reduce the maximum temperature of cylinder surfaces and enhance the fire resistance of cylinders under localized fire conditions. Specifically, using a 2 mm thick fire-protection coating and a circular fire-protection baffle with a width equal to 100% of the cylinder diameter proves to be more suitable protection methods. These measures significantly decrease the risk of explosion and leakage in Type IV hydrogen storage cylinders during localized fire conditions.

Space-time variational material modeling: a new paradigm demonstrated for thermo-mechanically coupled wave propagation, visco-elasticity, elasto-plasticity with hardening, and gradient-enhanced damage

We formulate variational material modeling in a space-time context. The starting point is the description of the space-time cylinder and the definition of a thermodynamically consistent Hamilton functional which accounts for all boundary conditions on the cylinder surface. From the mechanical perspective, the Hamilton principle then yields thermo-mechanically coupled models by evaluation of the stationarity conditions for all thermodynamic state variables which are displacements, internal variables, and temperature. Exemplary, we investigate in this contribution elastic wave propagation, visco-elasticity, elasto-plasticity with hardening, and gradient-enhanced damage. Therein, one key novel aspect are initial and end time velocity conditions for the wave equation, replacing classical initial conditions for the displacements and the velocities. The motivation is intensively discussed and illustrated with the help of a prototype numerical simulation. From the mathematical perspective, the space-time formulations are formulated within suitable function spaces and convex sets. The unified presentation merges engineering and applied mathematics due to their mutual interactions. Specifically, the chosen models are of high interest in many state-of-the art developments in modeling and we show the impact of this holistic physical description on space-time Galerkin finite element discretization schemes. Finally, we study a specific discrete realization and show that the resulting system using initial and end time conditions is well-posed.

Simulation of Drag Crisis in Flow Past a Circular Cylinder using 2D Computations

The unsteady incompressible 2D Navier-Stokes equations are solved using a finite element method with Streamline-Upwind/Petrov-Galerkin (SUPG) and Pressure-Stabilizing/Petrov- Galerkin (PSPG) stabilization terms for high Reynolds number (105 to I06) flow past a cylinder to stimulate drag-crisis. The mean drag coefficient for various Re are compared with experimental data. It is observed that the low at Re =106 separates much later, from the cylinder surface as compared to that at Re =105. The wake at Re =106 is narrower than that at Re = 105. The time-averaged flow field shows a standing bubble just downstream of the flow separation point for the Re = 105 flow. The bubble is not observed for the flow at Re = 106. The energy spectrum of the flow exhibits the characteristics of 2D isotropic turbulence.

Emission and Lubrication Performance of Hazelnut Oil as A Lubricant

The aim of this study is to search the tribological and emission performances of hazelnut oil as a lubricant in one cylinder two-stroke gasoline engine and simulation-testing machine. The tribological and emission performances of mineral oil and hazelnut oil as lubricant were compared. In the experiments, simulation-testing machine and one cylinder two-stroke gasoline engine were used to determine the tribological performance of these two lubricants. The wears on the surfaces of cylinder were analyzed to examine the lubricant performances. In addition to lubrication performance, exhaust emissions of the lubricants were also measured. To observe the effects of different kinds of cylinder surface materials, TiN, CrN and gray cast iron coated cylinder surfaces were used in simulation testing machine. The wear as well as the soot formation on the cylinder surfaces increased when hazelnut oil was used as the engine lubricant. However, hazelnut oil exhibited good lubrication properties in simulation testing machine. When hazelnut oil was used, CO and HC emissions increased while CO2 emission decreased.

Strength damage behavior analysis of silicon carbide(SiC) ceramic cylindrical shells under hydrostatic pressure based on the state-based peridynamics

Ceramics are one of the most promising materials for pressure-resistant shells of submersibles due to their exceptional mechanical properties. However, ceramics are brittle materials, and the occurrence of strength damage is inevitably accompanied by the generation and propagation of cracks. A new state-based peridynamic damage model is established, the relation between critical elongation and critical energy release rate for tensile and compression fracture is deduced innovatively, to investigate the strength damage behavior of silicon carbide (SiC) cylindrical shells under hydrostatic pressure. The findings demonstrate that by increasing cylinder thickness, the structural damage pressure can be significantly improved. Moreover, the initial damage zones, are located on the internal surface of shell and induced by the compression fracture, and evenly scattered at 90° around the circular direction. As pressure increases, tensile damage zones emerge on the external surface of cylinder. The failure zones on the interior and exterior walls of the shell propagate along the circumferential direction firstly, then extend toward the middle surface until the damage zones completely penetrate the entire thickness, and the cylinder loses its load-bearing capacity.