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The verticality of a dynamically installed anchor (DIA) during free fall in water is vital for successful installation of the anchor within the seabed. Two lines, a deployment line and a mooring chain, are usually used to install a DIA. The mooring chain is prereleased to the seabed surface, presenting a catenary profile in the seawater. When the anchor is released and falls freely in the seawater, the verticality of the anchor is affected by the tension on the pad eye resulting from the connected mooring chain. Therefore, a vertically hanging arrangement method for the mooring chain is proposed, which is effective in reducing the tilt angle of the anchor during free fall in water compared with the traditional catenary arrangement method. Model tests are subsequently designed to justify the effectivity of the vertical-hanging arrangement of the mooring chain. Finally, a theoretical framework is established to predict not only the fall velocity but also the tilt angle of the DIA during free fall in water, with the deployment line and mooring chain taken into consideration. [ABSTRACT FROM AUTHOR]

Introduction. Road safety is largely determined by the technical condition of the vehicle, and especially control systems. The braking system is one of them. To improve its efficiency, various assistive electronic systems are now widely used. These systems control the vehicle through wheel braking mechanisms. Brake pads are a constituent element of a friction-type wheel brake mechanism. The efficiency of the vehicle braking system depends on its quality, regardless of the presence of auxiliary electronic systems. The use of brake pads with a wide spread of friction coefficients can have a significant impact on braking performance.Materials and methods. To conduct experimental studies, a methodology for conducting them and processing experimental data was developed, as well as a laboratory setup was made. Arduino Uno R3 analog-to-digital converter was used as an instrumental component of the stand for converting mechanical movements into an electronic signal.Results. In accordance with the proposed methodology, four pairs of brake pads were tested. As a result of processing the experimental data, it was found that the difference in the values of the friction coefficients of the brake pads can cause a difference in the magnitude of the braking forces on the wheels from 8 to 19%.Discussion and conclusions. The difference in the coefficients of friction of the brake pads has a significant impact on the magnitude of the braking forces and the stability of the vehicle during braking. One of the reasons for this may be the poor quality of the pad material or a violation of operating conditions. The proposed improved technique for determining the coefficients of sliding friction makes it possible to obtain more accurate values through the use of an analog-to-digital converter, reducing the influence of the accuracy of measuring instruments and the human factor.

One of the important operational properties of a car that ensures traffic safety is the stability of the car. The loss of stability of the car is a negative phenomenon leading to the occurrence of road accidents. Currently, a number of electronic systems are used to eliminate the loss of stability of the car. But most of them are aimed at eliminating the loss of stability, and not at preventing this condition. Depending on the driving mode of the car (traction, free run), the stability of its movement is evaluated by various parameters. These parameters can be used to quickly assess the stability of the vehicle, but this requires adequate techniques that take into account the main parameters of the car that affect its stability when driving, as well as traffic conditions. The currently existing methods and expressions for calculating the stability parameters of a car have a number of assumptions. This does not reduce their value, but somewhat reduces the accuracy. The purpose of this work was to increase the stability of the car by developing a method for quickly assessing its stability in traction mode. In theoretical studies, it was found that the stability coefficient can be used to assess the stability of a car with all-wheel or rear-wheel drive. It is equal to the ratio of the stabilizing moment of the car to the perturbing one. If this coefficient is greater than one, the car will be stable. The expression for its calculation includes a number of design and operational parameters of the vehicle. Expressing from it the acceleration values corresponding to the values of the stability coefficient greater than one, we get the maximum permissible accelerations that ensure stable movement of the car. Based on this, a method of operational assessment of the stability of the car was proposed, which consists in comparing the maximum permissible accelerations of the car with the actual ones. To improve the accuracy of calculations of the maximum permissible accelerations, it is proposed to determine the height of the center of mass of the car depending on its actual mass using linear interpolation. The scientific novelty of this work is the proposed method of operational assessment of the stability of the car, based on a refined methodology for calculating the maximum permissible accelerations. To calculate the values of the maximum allowable accelerations according to the proposed method, a computer program was developed. The direction of further research is to assess the adequacy of the proposed method by conducting experimental studies.

The stability of robot-mower motion in a specific direction is considered. The direction is regulated by means of an angular sensor and a programmable controller adjusting the motor power at one of the two drive wheels. For mower motion over a flat surface, the maximum control ratio in the drive at each of those wheels depends on the direction of initial chassis rotation. [ABSTRACT FROM AUTHOR]

This study aimed to explore the directional stability issues of a previously studied light box-wing aircraft model with a pusher propeller engine in the fuselage aft section. Earlier configurations have included the use of fuselage together with a lifting system consisting of two wings joined together at their wingtips with vertical stabilizers. However, these side vertical surfaces failed to provide the aircraft with sufficient directional stability, thus prompting the quest in this study for novel solutions that would exclude the need for a fuselage extension and a typical fin. Solutions included the use of a ducted propeller and few configurations of small "fishtail" vertical fins, which formed part of the aft fuselage itself and coupled with vortex generators on the fuselage surface to improve their interference and heal flow separation at the fuselage aft cone. The results of wind tunnel testing were supported with CFD simulations to explain the flow behavior of each of the studied solutions. Tuft visualization and computed flow patterns allowed identification of the sources of the observed low efficiency in terms of directional stability of the fishtail against a simple idle duct without a propeller. A final configuration with a duct and a modified version of the fuselage fins was achieved that provides enough yaw stability margins for a safe flight. [ABSTRACT FROM AUTHOR]

Flow separation is easily induced at the junctions of aircraft components, and for aircraft with T-type tails, in particular, it can lead to loss of directional stability under a small sideslip angle. In the reported study, improved delayed detached eddy simulation with a shear-layer-adapted length scale based on the k–ω shear-stress transport method was used to analyze and rectify the corner separation at the junctions of the horizontal and vertical parts of the tail of a demonstration aircraft. This was done to (i) suppress the flow separation caused by the complex interaction of the boundary layers on the horizontal and vertical tail parts at their junctions, and (ii) prevent the vertical tail parts from having any separated flow on their pressure and suction sides. The results showed that the main cause of the loss of directional stability was separation flow on the suction sides of the vertical tail parts. The corner flow separation was suppressed significantly by only using fairing cones at the junctions of the horizontal and vertical tail parts, thereby allowing the aircraft to maintain directional stability under a small sideslip angle. [ABSTRACT FROM AUTHOR]

The balance of lateral and directional static stability plays an important role in the lateral-directional dynamics and vehicle design. The theory of geometric influence on the lateral and directional static stability is mature for conventional aircrafts. However, the distinct configuration characteristics and flow physics for hypersonic vehicles may lead to different design theory, which is absent now. In order to solve this problem, simplified analytical models of lateral-directional static derivatives are proposed based on the simplified geometry model. It's found that the lateral and directional stability both increase as the deflection angle, dihedral angle, or angle of attack increases, whereas the influence of sweep angle can be neglected. The difference lies in that the lateral stability is proportional to dihedral angle while the directional stability is proportional to the square of dihedral angle. The reasonable accuracy is validated in comparison with the inviscid numerical solutions. Furthermore, the influence mechanism of viscous effects on the lateral and directional stability is investigated in detail based on the numerical results. It's found that the strong viscous interaction can improve the lateral stability evidently, and both the strong viscous interaction and the shear stress can lead to the increase of the directional stability. In addition, the lateral stability is slightly reduced by the chemical nonequilibrium effects. • The proposed analytical models can clearly reveal the relationship between the main geometric features and the hypersonic lateral-directional stability. • The lateral stability is proportional to dihedral angle. • The directional stability is proportional to the square of dihedral angle. • The lateral stability can be improved by the strong viscous interaction effects. • The directional stability can be improved by both the strong viscous interaction effects and the shear stress. [ABSTRACT FROM AUTHOR]

Fins play a vital role in improving the directional stability of aerial vehicles. However, airships are characterized by an inherent directional instability due to undersized fins. In this paper, a systematic approach to the design of airship fins is proposed. A constrained optimization problem is formulated to identify the optimal location, span, and chord of the airship fins. A semi-empirical aerodynamic model is used to formulate the objective function that represents the directional instability of an airship. The validity of the numerical solution acquired by minimizing the objective function with other design constraints is shown through a series of wind tunnel experiments. The result of the experiments confirms that the outcome of the fin optimization problem exhibits the best performance among the test cases, which validates the proposed methodology for designing the fins of the airship. [ABSTRACT FROM AUTHOR]

The discrepancy between the plow width and the tractor width leads to the asymmetry of plowing units. The geometry of the plowshare surface of the moldboard plow contributes to the generation of lateral forces on the working tool. All this leads to the imbalance of the tool and the deviation of the tractor from straight-line movement during plowing. To maintain straight-line movement, the driver has to adjust the machine every 5-10 meters, which is highly tiresome. To study the causes of lateral slips of the plowing unit, we constructed a mathematical model, which consists of the equations of controlled movement and equations of the tractor's uncontrolled shear under the action of external forces from the plow. The description of the force interaction of the drive with the ground is based on the mathematical theory of friction, taking into account anisotropy and elastic properties in contact. Based on the passive shear model, we constructed a hodograph diagram of the maximum tractor shear force from the side of the working tool. We found that the shear force reaches its maximum friction value only in the case of a translational shear, when its line of action passes through the tractor's center of gravity. In all other cases, the shift (slip) of the tractor is caused by a lower force. We formulated the features and assumptions of the model as applied to caterpillar and wheeled tractors. As a result, we found that, regardless of the direction of the lateral displacement of the plow's traction resistance, the tractor is slipped towards the plowed field. The result of the numerical experiment showed that the main reason for the slip of the wheeled plowing unit is the difference in soils along the sides of the tractor but not the deviation of the plow traction resistance.

Directional stability during the roll-out phase is crucial to the safety and reusability of the aircraft. Because of the mechanical properties, the wheel-skid aircraft is more prone to produce course instability. To address this issue, the taxiing safe set of the wheel-skid aircraft is discussed based on the reachability theory. A dynamic model of the on-ground aircraft is established firstly, considering the complex condition of the ground loads. Then, the particular Hamilton–Jacobi partial differential equation is used to obtain the safe set. According to the safe set results, the optimal control of the rudder is built in the state space. Its effectiveness is verified by the comparison with other robust methods. In addition, three structural parameters are selected to analyze the influences on the safe set. Results indicate that the maximum safe yaw angle increases from 1 ° to 9 ° at 70 m/s under the optimal control of the rudder when the steering of nose wheel is locked. The safe boundary in the middle–high-speed region expands by 43.5% under the rudder control. Because of the mechanical properties, uncontrollable deflection will appear due to the asymmetric disturbances when the longitudinal velocity is lower than 42 m/s. [ABSTRACT FROM AUTHOR]

This study aimed to explore the directional stability issues of a previously studied light box-wing aircraft model with a pusher propeller engine in the fuselage aft section. Earlier configurations have included the use of fuselage together with a lifting system consisting of two wings joined together at their wingtips with vertical stabilizers. However, these side vertical surfaces failed to provide the aircraft with sufficient directional stability, thus prompting the quest in this study for novel solutions that would exclude the need for a fuselage extension and a typical fin. Solutions included the use of a ducted propeller and few configurations of small “fishtail” vertical fins, which formed part of the aft fuselage itself and coupled with vortex generators on the fuselage surface to improve their interference and heal flow separation at the fuselage aft cone. The results of wind tunnel testing were supported with CFD simulations to explain the flow behavior of each of the studied solutions. Tuft visualization and computed flow patterns allowed identification of the sources of the observed low efficiency in terms of directional stability of the fishtail against a simple idle duct without a propeller. A final configuration with a duct and a modified version of the fuselage fins was achieved that provides enough yaw stability margins for a safe flight.

Flow separation is easily induced at the junctions of aircraft components, and for aircraft with T-type tails, in particular, it can lead to loss of directional stability under a small sideslip angle. In the reported study, improved delayed detached eddy simulation with a shear-layer-adapted length scale based on the k–ω shear-stress transport method was used to analyze and rectify the corner separation at the junctions of the horizontal and vertical parts of the tail of a demonstration aircraft. This was done to (i) suppress the flow separation caused by the complex interaction of the boundary layers on the horizontal and vertical tail parts at their junctions, and (ii) prevent the vertical tail parts from having any separated flow on their pressure and suction sides. The results showed that the main cause of the loss of directional stability was separation flow on the suction sides of the vertical tail parts. The corner flow separation was suppressed significantly by only using fairing cones at the junctions of the horizontal and vertical tail parts, thereby allowing the aircraft to maintain directional stability under a small sideslip angle.

In this paper, directional stability of road vehicles travelling at time-dependent forward velocity is investigated. The dynamical behaviour of the system is governed by a set of linear ordinary-differential equations with time-varying coefficients. A simple two degrees of freedom (DOF) model is considered, in order to better understand the effects of such a perturbation on the well-established bicycle model, which is frequently used in the literature as a first approach to get useful physical insights on vehicle dynamics. Numerical simulations show significative differences with respect to the prediction of the stability analysis in the case of constant forward speed. A moderately large variation on the forward velocity, indeed, can stabilise the vehicle which is statically unstable. Stability maps are obtained by means of the Floquet theory, with the aim to shed light on the modified vehicle dynamics. A final discussion is provided, which leads to outline the possible practical applications of the present investigation, together with future comprehensive studies. [ABSTRACT FROM AUTHOR]

Two trends could be observed in the evolution of road transport. First, with the traffic becoming increasingly intensive, the motor road infrastructure is developed; more advanced, greater quality, and more durable materials are used; and pavement laying and repair techniques are improved continuously. The continued growth in the number of vehicles on the road is accompanied by the ongoing improvement of the vehicle design with the view towards greater vehicle controllability as the key traffic safety factor. The change has covered a series of vehicle systems. The tire structure and materials used are subject to continuous improvements in order to provide the maximum possible grip with the road pavement. New solutions in the improvement of the suspension and driving systems are explored. Nonetheless, inevitable controversies have been encountered, primarily, in the efforts to combine riding comfort and vehicle controllability. Practice shows that these systems perform to a satisfactory degree only on good quality roads, as they have been designed specifically for the latter. This could be the cause of the more complicated car control and accidents on the lower-quality roads. Road ruts and local unevenness that impair car stability and traffic safety are not avoided even on the trunk roads. In this work, we investigated the conditions for directional stability, the influence of road and vehicle parameters on the directional stability of the vehicle, and developed recommendations for the road and vehicle control systems to combine to ensure traffic safety. We have developed a refined dynamic model of vehicle stability that evaluates the influence of tire tread and suspensions. The obtained results allow a more accurate assessment of the impact of the road roughness and vehicle suspension and body movements on vehicle stability and the development of recommendations for the safe movement down the road of known characteristics. [ABSTRACT FROM AUTHOR]

Ships can experience serious difficulties in keeping a straight course when sailing in stern-quartering seas. Design modifications like the addition of stern passive fins, or the modification of active control surfaces, are common solutions to improve the ship course-keeping. However, the success of such design modifications depends on the delicate balance between the excitation forces induced by the waves on the appended hull, the stabilization forces provided by the lifting surfaces as appended fins, and the steering forces provided by the control surfaces. This research investigates which of these aspects of a ship design play a concrete role in improving the ship course-keeping in waves. The study is carried out with the intention of looking at the different behaviors of the ship originating from different stern appendages configurations. Three modifications of stern appendages on three different ship hulls were investigated in various mild-to-rough sea conditions. The behavior of the vessels were simulated using a time domain, boundary element potential method, with the addition of semi-empirical formulations for the modelling of the stern lifting surfaces. The simulations were carried out in long crested irregular waves at three different direction, using the JONSWAP spectrum. The results showed that although larger stern appendages improve the directional stability of relatively large and slow vessels, in most cases they worsen their course-keeping ability, increasing the yaw motions. For smaller and faster vessels instead, passive and active fins tend to improve the course-keeping, because at high speed the lift provided by the appendages stabilizes the vessel. This effect is compensated by the wave excitation force at lower speed. Similarly to yaw, the roll motions increases with larger stern appendages. [ABSTRACT FROM AUTHOR]

B-double is one kind of vehicle combinations with three vehicle units structurally and widely applied in cargo transport, so its directional stability analysis is crucial but more complex than a car. Directional stability was related with vehicle operating conditions and structure parameters. A basic linear dynamic model with four degrees of freedom for B-double was developed with a special method for simplification in a calculation process. The method was verified from the simulation results with MATLAB. The step input is tractor's steering wheel angle, so the steady-state yaw rate gains with understeer gradient for three vehicle units were solved. Steady-state relative gain was also derived and has an impact on directional stability, which could be influenced by the structure parameters, such as body mass (cargo weight), tire cornering stiffness of rear axle, location of mass center, wheelbase, and location of articulated point. The results indicate that increasing body mass and tire cornering stiffness of rear axle appropriately, moving backward mass center, and moving forward articulated points could increase the understeer gradient, which results in the improvement of directional stability. It is theoretical basis for the stability tests and structure design of B-double.

Heavy-wheeled vehicles with articulated hydraulic steering systems are widely used in construction, road building, forestry, and agriculture, as transport units and tool-carriers because they have many unique advantages that are not available in car steering systems, based on the Ackermann principle, such as—high cross-country mobility, excellent maneuverability, and high payload and lift capacity, due to heavy axles components. One problem that limits their speed of operation and use efficiency is that they have poor directional stability. During straight movement, articulated tractors' deviate from a straight line and permanent driver correction is required. This limits the vehicles' speed and productivity. In this study, we describe a driver-aid system concept that would improve the directional stability of articulated vehicles. Designing such a system demands a comprehensive knowledge of the reasons for the snaking phenomenon and driver behaviors. The results of our articulated vehicle directional stability investigation are presented. On this basis, we developed models of articulated vehicles with hydraulic steering systems and driver interaction. We next added the stabilizing system to the model. A simulation demonstrated the possibility of directional stability improvement. [ABSTRACT FROM AUTHOR]

• A theoretical framework for determining the stability of negative stiffness metamaterials in a uniform field is established. • The concepts of directional stability and semi-directional stability are proposed. • Metamaterials with different physical feature distributions are designed and prepared to achieve directional stability. Negative stiffness metamaterials have been widely studied due to their unusual properties and potential applications in shape reconfiguration, shock isolation, and reusable energy absorption, but their stability in fields has been less studied. In this work, a theoretical framework for determining the stability of negative stiffness metamaterials in a uniform field is established. More importantly, the concepts of directional stability and semi-directional stability are proposed for the metamaterials that have different stability in different field directions; metamaterials with different physical feature distributions are designed and prepared to achieve such ability, and the finite element simulation is used for theory verification and parameter study. The proposed metamaterial has the potential to be applied as field direction detectors and field-sensitive electrical relays. [ABSTRACT FROM AUTHOR]

Two trends could be observed in the evolution of road transport. First, with the traffic becoming increasingly intensive, the motor road infrastructure is developed; more advanced, greater quality, and more durable materials are used; and pavement laying and repair techniques are improved continuously. The continued growth in the number of vehicles on the road is accompanied by the ongoing improvement of the vehicle design with the view towards greater vehicle controllability as the key traffic safety factor. The change has covered a series of vehicle systems. The tire structure and materials used are subject to continuous improvements in order to provide the maximum possible grip with the road pavement. New solutions in the improvement of the suspension and driving systems are explored. Nonetheless, inevitable controversies have been encountered, primarily, in the efforts to combine riding comfort and vehicle controllability. Practice shows that these systems perform to a satisfactory degree only on good quality roads, as they have been designed specifically for the latter. This could be the cause of the more complicated car control and accidents on the lower-quality roads. Road ruts and local unevenness that impair car stability and traffic safety are not avoided even on the trunk roads. In this work, we investigated the conditions for directional stability, the influence of road and vehicle parameters on the directional stability of the vehicle, and developed recommendations for the road and vehicle control systems to combine to ensure traffic safety. We have developed a refined dynamic model of vehicle stability that evaluates the influence of tire tread and suspensions. The obtained results allow a more accurate assessment of the impact of the road roughness and vehicle suspension and body movements on vehicle stability and the development of recommendations for the safe movement down the road of known characteristics.

This paper presents a study on the dynamic modelling of a land-yacht, i.e. a ground vehicle that is propelled by wind energy through the use of a vertical airfoil. First, a non-linear dynamic model of the land-yacht motion is derived using a compact matrix notation. Then, an introduction to the study of the performance and handling characteristics is presented. It is considered the vehicle response to input commands, i.e. steering to follow the desired course and adjusting the sail angle according to environmental conditions, that is, wind intensity and direction. The model demonstrates the performance in terms of maximum longitudinal speed and the effects on handling behaviour of the major vehicle design and operational parameters, including location of the centre of gravity and centre of effort, and forward speed, and it leads to conclusions of practical significance concerning directional control and stability. [ABSTRACT FROM AUTHOR]

Abstract The OMNI-Max anchor, a newly developed gravity installed anchor, offers a cost effective anchoring solution with improved reliability for deep-water mooring facilities. However, the anchor final penetration depth is relatively shallow in the soil with high strength gradient. A booster, which can be attached at the tail of the OMNI-Max anchor, is designed with the aim to improve both the anchor directional stability and terminal velocity, such that the anchor can penetrate deeper into the seabed and consequently gain higher holding capacity. The objective of this paper is to investigate the directional stability and terminal velocity of the OMNI-Max anchor and hybrid anchor (i.e. an OMNI-Max anchor with a booster) based on the computational fluid dynamics (CFD) approach. The numerical simulation results demonstrated that the booster is beneficial in moving the position of the hydrodynamic centre towards the anchor rear, hence the directional stability of the hybrid anchor is improved. Moreover, the anchor terminal velocity was increased from 22.44 m/s to 32.01 m/s by the aid of a booster. Finally, an optimised design on the booster geometry was performed to ensure that the hybrid anchor can obtain high terminal velocity and maintain directional stability at the same time. Highlights • The hydrodynamic characteristics of OMNI-Max anchor are investigated. • The booster structure was optimised to improve both the terminal velocity and directional stability of hybrid anchors. • The efficiency of the booster on the terminal velocity of OMNI-Max anchor was investigated. [ABSTRACT FROM AUTHOR]

To accurately estimate the navigation safety of a barge in still water and waves, computational fluid dynamics (CFD) was used to calculate the hydrodynamic force on the barge and simulate the flow field to comprehensively study the effect of skeg for wave drift force and directional stability of the barge. With respect to the wave drift force, the steady surge force and steady sway force are found to decrease due to the skeg effect in both short and long wavelength regions. The overall steady yaw moment tends to be reduced by the skeg. As the drift angle increased, the sway force and yaw moment also increased. The changing trend in the sway force varied with the angular velocity, depending on the installation of the skeg, and it was noted that the yaw moment value significantly increased because of the skeg. Owing to the effect of the skeg installed on the barge, the yaw damping lever became larger, while the sway damping lever became smaller regardless of waves. It was confirmed that the directional stability was improved both in still water and head waves.

Heavy-wheeled vehicles with articulated hydraulic steering systems are widely used in construction, road building, forestry, and agriculture, as transport units and tool-carriers because they have many unique advantages that are not available in car steering systems, based on the Ackermann principle, such as—high cross-country mobility, excellent maneuverability, and high payload and lift capacity, due to heavy axles components. One problem that limits their speed of operation and use efficiency is that they have poor directional stability. During straight movement, articulated tractors’ deviate from a straight line and permanent driver correction is required. This limits the vehicles’ speed and productivity. In this study, we describe a driver-aid system concept that would improve the directional stability of articulated vehicles. Designing such a system demands a comprehensive knowledge of the reasons for the snaking phenomenon and driver behaviors. The results of our articulated vehicle directional stability investigation are presented. On this basis, we developed models of articulated vehicles with hydraulic steering systems and driver interaction. We next added the stabilizing system to the model. A simulation demonstrated the possibility of directional stability improvement.

The plate shaped gravity installed anchor (GIA) provides a potential alternative to deepwater mooring systems as its dynamic installation and diving behavior. However, the anchor final penetration depth in seabed soils, especially in soils with high strength gradient, is relatively shallow due to the limited impact velocity and large contact area between the anchor and the surrounding soil. An innovative booster concept is put forward in this study to increase the anchor final penetration depth by increasing the kinetic energy during free fall in water and gravitational energy during dynamic penetration within seabed. The booster is attached to the rear of the anchor during installation and can be retrieved after installation for reuse. The present study performed model tests with the aim of investigating the working efficiency of booster on the impact velocity of the GIA during free fall in the water column. A mini motion tracing device (MTD) is developed to record the anchor free fall history in water. The hydrodynamic characteristics, including the terminal velocity, drag coefficient and directional stability, for the GIA were studied. A series of experimental cases were subsequently conducted to study the effects of the adding booster on the impact velocity and directional stability of the GIA. The testing results demonstrated that both the directional stability and the release height can be improved for the GIA with a booster, thus the anchor impact velocity is increased. The anchor kinetic energy is significantly increased due to the additional mass and increased impact velocity by the booster, which ensures the anchor to be embedded deeper within seabed. [ABSTRACT FROM AUTHOR]

Torpedo anchors are an innovative and cost-effective technology in marine foundation engineering; however, there is a lack of systematic and comprehensive studies on the influence of torpedo anchor geometry on its hydrodynamic characteristics, especially the effect of anchor fin configuration on the hydrodynamic characteristics is rarely reported in the existing literature. Therefore, this study investigates the influence of geometric characteristics of both finless and finned torpedo anchors on their terminal velocity, drag coefficient and installation directional stability in water through CFD numerical analysis in a systematical manner. The considered geometric characteristics include the center of gravity position, shape and angle of anchor tip, shaft and fin aspect ratio, fin number, fin thickness, fin shape, fin position and fin area. Based on the obtained numerical results, some practical design recommendations and impact weighting charts of different anchor geometric factors are provided, which enables a quick qualitative and quantitative assessment of torpedo anchors. In addition, a simple weight-based approach for estimation of terminal velocity and drag coefficient of torpedo anchors considering multiple geometric configuration factors is proposed, which may provide some reference and scientific guidance for experimental and engineering design of torpedo anchors. • The effect of torpedo anchor geometry configuration on its hydrodynamic performance was systematically investigated. • Some practical design recommendations and impact weighting charts of different anchor geometric factors were provided. • A simple weight-based approach for estimation of terminal velocity and drag coefficient of torpedo anchors was proposed. [ABSTRACT FROM AUTHOR]

Aircraft directional stability and control are related to vertical tail design. The safety, performance, and flight qualities of an aircraft also depend on a correct empennage sizing. Specifically, the vertical tail is responsible for the aircraft yaw stability and control. If these characteristics are not well balanced, the entire aircraft design may fail. Stability and control are often evaluated, especially in the preliminary design phase, with semi-empirical methods, which are based on the results of experimental investigations performed in the past decades, and occasionally are merged with data provided by theoretical assumptions. This paper reviews the standard semi-empirical methods usually applied in the estimation of airplane directional stability derivatives in preliminary design, highlighting the advantages and drawbacks of these approaches that were developed from wind tunnel tests performed mainly on fighter airplane configurations of the first decades of the past century, and discussing their applicability on current transport aircraft configurations. Recent investigations made by the authors have shown the limit of these methods, proving the existence of aerodynamic interference effects in sideslip conditions which are not adequately considered in classical formulations. The article continues with a concise review of the numerical methods for aerodynamics and their applicability in aircraft design, highlighting how Reynolds-Averaged Navier-Stokes (RANS) solvers are well-suited to attain reliable results in attached flow conditions, with reasonable computational times. From the results of RANS simulations on a modular model of a representative regional turboprop airplane layout, the authors have developed a modern method to evaluate the vertical tail and fuselage contributions to aircraft directional stability. The investigation on the modular model has permitted an effective analysis of the aerodynamic interference effects by moving, changing, and expanding the available airplane components. Wind tunnel tests over a wide range of airplane configurations have been used to validate the numerical approach. The comparison between the proposed method and the standard semi-empirical methods available in literature proves the reliability of the innovative approach, according to the available experimental data collected in the wind tunnel test campaign. [ABSTRACT FROM AUTHOR]

The safe hard braking of a turned vehicle requires short stopping distance while maintaining the vehicle in the path. To achieve the first aim, a wheel slip controller is designed to calculate the maximum braking force of each wheel according to the tire/road conditions. For the second aim, a new optimal multivariable controller for integrated active front steering and direct yaw moment control is analytically developed to control the vehicle directional stability directly. Since the required stabilizing external yaw moment has to be produced by reducing the maximum achievable braking forces of one side wheels, it leads to increase the stopping distance and should be kept as low as possible. In an effective way to manage the integrated control inputs, a fuzzy logic is defined to determine the weight factor of each control input in the integrated optimal control law. This logic is defined using the stability index obtained by the phase plane analysis of nonlinear vehicle model. Therefore, the proposed controller can be tuned automatically for different driving conditions. The simulation results carried out using a validated vehicle model demonstrate that the integrated control system has a better performance compared with stand-alone braking and steering systems to attain the desired purposes. [ABSTRACT FROM PUBLISHER]