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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]

• 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]

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]

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]

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]

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]

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]

For the purpose of both energy regeneration and directional stability enhancement, regenerative and hydraulic blended braking control of an over-actuated electric vehicle equipped with four individual on-board motors during normal straight-line deceleration is studied. System models which include the vehicle dynamics, tire, electric powertrain, and hydraulic brake models are developed. Mechanisms of directional instability of the electric vehicle during straight-line braking are analyzed. To improve the electric vehicle's safety and performance, novel compensation methods through blended braking are studied. On the basis of half-shaft torque estimation, two new regenerative braking control algorithms are proposed. Simulations of the developed control algorithms are carried out during normal straight-line braking maneuvers. The results and discussions demonstrate that the developed approaches are advantageous when compared with the conventional baseline strategy, with respect to both the directional stability and regeneration efficiency, thus validating the feasibility and effectiveness of the controller synthesis. [ABSTRACT FROM AUTHOR]

Lifting body configuration generally has weaker directional stability, hence an aerodynamic stability augmentation method is presented. In this method, the after-body?s side edges were cut to curved form, making the surface flow from expanding to compressing, the side aerodynamic force was drawn back, and the directional pressure center was drawn back simultaneously so the directional static stability was improved. In this paper, one single cone lifting body configuration was analyzed by this method，and the computational fluid dynamics method was applied in the analysis work. The analysis results showed that less cutting scope could improve the directional static stability remarkably under the moderate attack angle, but the longitude static stability, the lift to drag ratio and the lateral static stability would decrease for different levels in the same time. The main reason was that the compressing effect was decreased for the expanding effect on the side face, and the expanding effect was produced by the upwards flow coming from downside. In this paper, the lateral-directional stability influence by the side edge cutting was presented too. This method improves the directional static stability without any further directional stable rudder, it may become one of the choices for those correlative configuration design and optimization. [ABSTRACT FROM AUTHOR]

The effect of sideslip angle on the aerodynamic characteristics of a following aircraft in formation flight is investigated by experiment. Measured data from subsonic wind-tunnel testing are obtained by changing the magnitude of the sideslip angle and the relative distances between the two-5% scaled small sized jet aircraft models. The variations of aerodynamic forces and moments of a following aircraft model are measured at 49 locations on the cross-section area behind a leading aircraft. Results show the considerable changes of the aerodynamic forces and moments of the following aircraft compared to those of a single aircraft alone. The effect of the sideslip on the aircraft in formation flight is a very complex function of relative distances between two aircraft, and has a significant effect on the lateral/ directional stability of the following aircraft. Among the changes of the aerodynamic coefficients, the changes of the rolling moment coefficients are the largest. It is believed that the formation flight itself can be a very dangerous to the safety flight of the aircraft. [ABSTRACT FROM AUTHOR]

A novel gravity installed anchor (GIA) is proposed in the present work, which combines features of the GIA and the drag embedment plate anchor, with a ring fin attached to the anchor tail during free fall to enhance the directional stability and separated from the anchor body when penetrating the seabed. A systematic numerical investigation on hydrodynamic characteristics of the novel GIA is performed by the computational fluid dynamics (CFD) approach to clarify the effects of the ring fin. First, different anchor shapes for the novel GIA are compared to acquire the optimum anchor body, focusing on the drag coefficient, terminal velocity and directional stability. Second, a set of orthogonal tests and three groups of cases are designed and performed to thoroughly investigate the effects of ring fin on the hydrodynamic characteristics, from which the effects of the radius, height and thickness of the ring fin can be known on the terminal velocity and the directional stability of the anchor. Finally, empirical formulas for calculating the restoration moment coefficient and the terminal velocity of the novel GIA are constructed with high precision and efficiency, by taking into account the effects of the ring fin, which can be used to determine the optimum dimensions of the ring fin. The numerical investigation confirms that the novel GIA possesses better directional stability and higher terminal velocity compared to the OMNI-Max anchor. • A novel GIA with a ring fin (RGIA) combing the features of GIAs and drag anchors. • Systematic CFD analyses on hydrodynamic characteristics of the RGIA. • Complex effects of the ring fin on hydrodynamic characteristics of the RGIA. • Empirical formulas for calculating the terminal velocity and directional stability. • Higher directional stability and terminal velocity of the RGIA than OMNI-Max anchors. [ABSTRACT FROM AUTHOR]

Ship maneuvering motions are affected by so-called bank suction forces when proceeding in close proximity to channel wall. In fact, some rudder angles would be required to maintain the course and proper rudder activities are needed to be directionally stable. The authors conducted captive model tests in a channel with variations in water depth, off-centerline displacement, ship speed, hull drift angle and rudder angle. The shallow water and bank effects on the hydrodynamic force characteristics were investigated. Based on the regression mathematical model, the rudder angle and hull drift angle required at equilibrium conditions were estimated and the limiting off-centerline displacement for safe operation was proposed. Directional stability in the channel was also studied based on the eigenvalue analysis and dynamic maneuvering motion simulations. The stable/unstable zone for course keeping according to control system characteristics would be important for the maneuvering operation. [ABSTRACT FROM AUTHOR]

In a hard braking on a split-μ road, the achievement of shorter stopping distance while maintaining the vehicle in the straight line are of great importance. In this paper, to achieve these conflicting aims, an optimal nonlinear algorithm based on the prediction of vehicle responses is presented to distribute the wheel braking forces properly. The base of this algorithm is reducing the maximum achievable braking forces of one side wheels, as low as possible, so that the minimum stabilizing yaw moment is produced. The optimal property of the proposed control method makes it possible to get a trade-off between the shorter stopping distance and the less deviation of the vehicle heading from the straight line. The special case of this algorithm leads to the conventional anti-lock braking system (ABS) which generates the maximum braking forces for all wheels to attain the minimum stopping distance. However, the ABS cannot control the vehicle directional stability directly. The simulation results carried out using a nonlinear 8-DOF vehicle model demonstrate that the designed control system has a suitable performance to attain the desired purposes compared with the convectional ABS. [ABSTRACT FROM AUTHOR]

Locomotion safety is suggested to be an intrinsic property of any multi-legged system, and a concept ofNon-Tumbling Gaitis proposed. Also, a new approach, denoted asDNESM, to estimation of stability of multi-legged robots is suggested. The relationship between direction of the destabilizing force (e.g. strong sidewind, or any other kind of impact) influencing the robot, and stability margin is studied. Additionally, new stability margin is calculated in a simulation and validated experimentally. Simulation results correspond well with the results of experimental validation. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents a deep investigation on the aerodynamics of the vertical tailplane and the correct estimation of its contribution to aircraft directional stability and control, especially during the preliminary design phase. Nowadays the most used methodologies in preliminary design to estimate the contribution of vertical tailplane on aircraft directional stability and control are (i) the classical method proposed by USAF DATCOM (also presented in several aeronautics textbooks) and (ii) the method presented in ESDU reports. Both methodologies derive from NACA World War II reports of the first half of the ʼ900, based on obsolete geometries that do not represent the typical shape of a transport aircraft. The other limit is that these methods give quite different results for certain configurations, e.g. in the case of horizontal stabilizer mounted in fuselage. As shown in literature, the main effects on the sideforce coefficient of the vertical tail are due to the interactions among the aircraft components. In order to better highlight these effects, a different approach using the RANS equations has been adopted. Several CFD calculations have been performed on some test cases (used as experimental database) described in NACA reports to verify the compliance of CFD results with available experimental data. The CFD calculations (performed through the use of a parallel supercomputing platform) have shown a good agreement between numerical and experimental data. Subsequently the above mentioned effects have been deeply investigated on a new set of aircraft configurations. The configurations that have been prepared differ among them for wing aspect ratio, wing–fuselage relative position (high-wing/low-wing), vertical tailplane aspect ratio (vertical tail span versus fuselage height) and horizontal tailplane position respect to the vertical tailplane (with the aim of investigating the effect of fin-mounted T configuration, typical of regional turboprop transport aircraft). All the CFD analyses have been carefully post-processed and have been useful to obtain new curves to predict the above mentioned effects and thus to have a more accurate estimation of vertical tailplane contribution to aircraft directional stability and control. [Copyright &y& Elsevier]

This paper describes an analytical study of the lateral dynamics of multi-articulated vehicles with multiple axles. A linear planar model of vehicle dynamics is adopted for multiple-axle vehicle combinations with an optional number of trailers. Two tractor and double-trailer combinations are examined for their directional stability and response. Non-oscillatory stability and steering sensitivity in steady-state turning and lane changing are analysed using a stability factor of multiple-axle vehicle combinations. Off-tracking in the steady-state turning of multiple-axle vehicle combinations is also analysed. Numerical calculations for oscillatory stability, steering sensitivity, and off-tracking are presented for multiple-axle vehicle combinations. [ABSTRACT FROM AUTHOR]

With flat after-body, large cargo aircraft have simpler structures, less weight, and the port machine has high dependability. However, the flat after-body induces strong transverse flow and flow with high adverse gradient when the aircraft cruises, so the boundary layer on the after-body is easier to separate. Separated flow increases pressure drag, and the separated vortex worsen the pressure distributions on the both side of vertical tail when the aircraft yaws. So the yawing stability is reduced. The chine is a special aerodynamic device which is used on flat after-body. It can restrain the birth and development of vortex flow. When the aircraft yaws, the chine can also enhance yawing stability by improving pressure distributions on the surfaces of vertical tail and after-body. Because of the functions of drag reduction and stability enhancement, the chine makes the transport aircraft with flat after-body having both high load efficiency and satisfied aerodynamic performance. [ABSTRACT FROM AUTHOR]

Abstract: Torpedo anchor installation is a new kind of anchoring system which is much more economical than other conventional anchoring methods. However, there are few studies on the falling velocity and drag coefficient of the torpedo anchors. In this study, seven torpedo anchors with different densities, aspect ratios, scale ratios and fin sizes were utilized to investigate their influence on the falling velocity of the anchor during acceleration. Anchors were released in a water tank and the falling process was recorded using a fast speed video camera. Accordingly, the corresponding drag coefficients against the Reynolds numbers during acceleration were calculated. The Reynolds numbers varied between 4.8×105 and 2.16×106 and the drag coefficients varied between 0.2 and 1.2. The differences between the falling velocities and the drag coefficient for anchors with different shapes, sizes, densities and directional stability were illustrated and the reasons for the differences were explained. The final drag coefficients versus the Reynolds numbers were compared with other representative models found in the literature. The influence of acceleration on the drag coefficient or falling velocity was emphasized. Finally, an Extrapolation Mathematical Model for the motion of the anchor in the fluid was proposed and the results were compared to the experimental data. [Copyright &y& Elsevier]

The so-called torpedo anchoring system is a novel and yet already intensively field-proven by Petrobras (the Brazilian oil company) offshore, Brazil. It is a pile with a specific elongated form that is buried in the sea bottom to hold mooring lines that are connected to floating production units. This is so even for very deep water (typically 1800 m). The methodology of installation of the torpedo pile so far consists of a vertical launching, starting with the torpedo above and close (typically 100 m) to the sea bottom. This installation path then occurs from the pile at the starting position with zero velocity until it reaches the bottom. During this installation, the pile travels almost freely, only dragging the mooring line. It is obvious that the object has to have a minimum directional stability to arrive vertically at the bottom. The pile becomes useless when it gets a vertical angle that is outside certain limits (typically three degrees). The present article addresses the directional stability of the torpedo pile during the installation. [ABSTRACT FROM AUTHOR]

This work is about the directional stability of truck-semitrailer vehicle, commonly used in Brazil, as a function of load parameters. For different positions of centre of gravity of semi-trailer, the curves that represent the characteristic movements and the ratio of damping for these movements during curved and straight trajectories are obtained. The influence of load and moment inertia variations for different adopted positions of the centre of gravity of semi-trailer was calculated. The results show significant changes on dynamic response of vehicle with the variations of load parameters. Thus, the operating conditions with less safety margins were determined, so they can be avoided by users. The study allows concluding that there are load conditions that although being accepted by the present legislation, must be avoided. [ABSTRACT FROM AUTHOR]

Analysis of the dynamic behaviour of road combined vehicles for sugar cane transportation. The study is about the directional stability of the type commercial combined truck semi-trailer as a function of load, of moment of inertia and of the position of the centre of gravity of set semi-trailer - load. The curves are obtained that represent the characteristic movements and the ratio of damping for these movements during curved and straight trajectories, showing the mains variations of dynamic characteristics with these variables. An articulated vehicle is modelling with acceptance of several simplifications and hypothesis, analysing a performance of vehicle and observing significant variations on dynamic response. Results show the necessity of that the users take a maximum care in relation with load conditions due to their high variability and their great influence on safety and use of these type road vehicles. [ABSTRACT FROM AUTHOR]

Aircraft directional control effectiveness is analyzed through experiments in wind tunnel. Control surfaces on low aspect ratio lifting surfaces exhibit different lifting capabilities compared to those with high aspect ratio. Such behavior must be carefully considered in the preliminary design phase to avoid any overestimation in size, weight, costs and emissions. Traditional sizing methodologies are based on coupling the effects of the wing planform (e.g. aspect ratio) at low angles of control surface deflection with the effects of wing section (e.g. chord ratio) evaluated on section data in the full range of control surface deflection, so that the non-linear aerodynamics is inherited from 2D data, completely neglecting the different aerodynamic behavior of a low aspect ratio wing at high angles of deflection. To fill this gap, an experimental wind tunnel test campaign on a generic regional turboprop aircraft model with a modular vertical tail with rudder has been performed. Results indicate that the aircraft design methodologies present in public literature underestimate the control surface effectiveness at high angle of deflections by 15% to 25%, leading to an average overestimation of control surface size. [ABSTRACT FROM AUTHOR]