Trim Analysis Research Articles

Longitudinal Air-Breathing Hypersonic Vehicle Nonlinear Dynamic Simulation with Different Control Inputs

<div>The air-breathing hypersonic vehicle (AHV) holds the potential to revolutionize global travel, enabling rapid transportation to low-Earth orbit and even space within the next few decades. This study focuses on investigating the nonlinear dynamic simulation, trim, and stability analysis of a three-degrees-of-freedom (3DOF) longitudinal model of a generic AHV for variable control surface deflection, <i>δ<sub>e</sub></i> and <i>δ<sub>r</sub></i>. A simulation is developed to analyze the burstiness of the AHV’s nonlinear longitudinal behavior, considering the complete flight envelope across a wide range of Mach numbers, from <i>M</i> = 0 to 24, for selected stable <i>M</i>. The presented simulation assesses trim analysis and explores the dynamic stability of the AHV through its flight envelope and bifurcation method analysis is carried out to gain insight and validate the dynamic stability using eigen value approach.</div>

Detail and structural design of a fixed-wing BWB UAV

The current study focuses on the development of a prototype BWB UAV for highway traffic monitoring by supporting a Cooperative Intelligent Transport System (C-ITS). This system allows the monitoring of traffic conditions at large roads and highways. Having determined the mission requirements and concluded the aerodynamic conceptual and preliminary design phases, high fidelity CFD simulations are performed, aiming to calculate the key aerodynamic and stability characteristics of the platform and to optimize its performance throughout the mission. More specifically, regarding the aerodynamic vehicle design, results concerning the calculation of stability derivatives, control surfaces sizing, trim analysis and flight envelope (V-n diagram) are presented, along with the respective methodologies. Considering the structural design of the aircraft, a combination of layout, FE simulations and parameterized design tools were employed, allowing the design and sizing of the skin and the internal structural parts. The parts are mainly made of composite and additively manufactured nylon materials. Coupled interaction loops are conducted among the aerodynamic and structural analyses to optimize the overall performance of the aerial vehicle, maximizing the aerodynamic efficiency, and reducing the structural weight. Finally, the study is concluded by the presentation of the manufactured prototype of the UAV, which satisfies all the structural, aerodynamic, stability and performance requirements for the established highway traffic monitoring mission.

Trim Analysis and Structured H-Infinity Control of Wing-Docked Multibody Aircraft

A wing-docked multibody aircraft is a novel configuration being explored as a balanced solution between efficiency and structural resilience for very long-endurance aviation. The presence of wingtip hinges complicates the dynamics and control of this class of aircraft but has thus far only been analyzed in specific cases. In this work, we make a comprehensive exploration of parameter space of the multibody trim problem and stability and demonstrate the treatment of the control problem using the robust H∞ synthesis technique. We propose a simplified simulation approach to the static trim analysis and demonstrate key observations relating to the configurations and open-loop dynamic stability of multibody aircraft in general. An interpolated parameter-scheduling model using the hinge angle as a scheduling parameter is established, based on which the structured multimodel H∞ synthesis method is employed to synthesize the robust flight controllers. Simulation results show that the designed controllers are capable of configuration control within the range of possible trim solutions and have also achieved good control effectiveness in path following and disturbance rejection. The proposed trim analysis and control techniques serve to provide a systematic benchmark study on wing-docked multibody aircraft dynamics, which is valuable to the development of this research area.

Pseudospectral-Method-Based Framework for Rotorcraft Stability and Trim Analysis

The paper demonstrates applications of pseudospectral-method-based framework to rotorcraft dynamics. The framework is developed to incorporate blade-to-blade symmetry (fast-Floquet) to reduce computational time. The methodology is applied to compute Floquet exponents of an isolated rotor in forward flight using the periodic eigenvector equations, and computational performance is assessed. The framework is also applied to a trim problem that determines time-varying control input for equilibrium, as well as meets stability criteria in the form of minimum damping of the system at a prescribed value. Through the applications considered, the paper brings out the advantages of the use of the pseudospectral framework, particularly its amenability to problems that involve optimization.

Short Landing for Flying-Wing Unmanned Aircraft with Thrust Vector

The task of achieving a safe and short landing for a flying-wing unmanned aircraft with a three-bearing-swivel thrust vector is highly challenging. The process is further complicated due to the need to switch between multiple control modes, while also ensuring the protection of the flight boundaries from environmental disturbances and model uncertainties to ensure flight safety. To address this challenge, this paper proposes a short-landing strategy that employs mixed control using lift fans, thrust vectors, and aerodynamic control surfaces. The extended state observer (ESO) is integrated into the inner angular rate control and outer sink rate control to account for environmental disturbances and model uncertainties. To ensure flight safety, the attainable linear and angular acceleration is calculated through a trim analysis to determine the command value of velocity and angle of attack during a short landing. Additionally, a flight boundary protection method is employed which includes an additional command value of the angle of attack, resulting in a higher probability of a successful landing. This paper provides a detailed description of the short-landing strategy, including the control objectives for each phase. Finally, a Monte Carlo simulation is conducted to evaluate the effectiveness and robustness of the short-landing strategy, and the landing accuracy is assessed using the circular error probability metric.

Flare folding wing tips for static and gust loads alleviation

The Passive gust load alleviation device can effectively simplify the control system by relying on the adaptive deformation of the structure. This research examines the influence of using folding wingtips during flight as a means of reducing static loads and gusty loads. Effects of hinge direction, wing-tip weight, stiffness and wing-tip centre of gravity on static and gust alleviation performance has been examined. The results show that the flare folding wing-tip can significantly reduce the static load and gust load of the aircraft. In a static aeroelastic trim analysis, a folding wingtip can increase span by 25% without increasing the wing root bending moment and decrease the trim angle of attack by 0.14°. In the gust response analysis, the maximum bending moment of wing root can be decrease by nearly 50% compared with the fixed wing-tip, only 17% higher than the baseline model without a wing-tip.

Nolinear Static Aeroelastic Analysis and Optimization for High-Altitude Solar-Powered UAV With Large Aspect Ratio

According to the static aeroelastic characteristics of Solar-Powered UAV (SP-UAV) with large aspect ratio, this paper develops a nolinear aeroelastic analysis method which takes into account both the calculation accuracy and efficiency. Firstly, we establish the finite element model of the geometric nonlinear structure, which is verified by the static test of the whole UAV to reduce the calculation error caused by the simplified method of structure model. Then, the aerodynamic model of SP-UAV is established by using Curved Vortex Lattice (CVL), and the structure-aerodynamic coupling interpolation is realized by the Thin Plate Spline-interpolation (TPS) method, so as to complete the full static aeroelastic analysis. The analysis indicate that the calculated results of the longitudinal trim are well match the first flight condition. In particular, considering the elevator efficiency loss occurred in longitudinal trim analysis of the UAV, we design an optimization scheme to improve the efficiency of the elevator by about 15%. The simulation results show that the loss of elevator efficiency of flexible solar UAV with high aspect ratio is non-negligible, with the maximum value higher than 40% under high dynamic pressure. In actual flight, the speed of UAV must be reduced as much as possible to minimize the loss of rudder efficiency, while the elastic control method should be considered in flight control.

Longitudinal Trim and Stability Analysis of Generic Air-Breathing Hypersonic Vehicle using Bifurcation Method

The Air-breathing Hypersonic Vehicle (AHV) can meet the futuristic goals of rapid global travel, to Low-Earth Orbit and into space in near-term decades. This paper presents the study of the trim and stability characteristics of the 3DOF longitudinal model of the generic AHV. Longitudinal 3DOF AHV simulation is developed with the aerodynamic model for trim analysis considering the complete flight envelope for Mach number from M=0 to 24. Dynamic model simulation of the 3DOF AHV is performed for the trim conditions and stability of the AHV flight for the complete envelope. Bifurcation Analysis is implemented with the longitudinal 3DOF AHV model for trim analysis and stability for the complete AHV flight envelope.

Acoustic Analysis and Sound Quality Assessment of a Quiet Helicopter for Air Taxi Operations

This paper investigates tonal and broadband noise for rotor designs used on urban air mobility vehicles. Quiet helicopter rotor designs with varying tip speeds and blade numbers are studied for the tonal and broadband noise at the same mission specification. The rotor aerodynamics in edge-wise forward flight are calculated using the blade element theory coupled with a dynamic inflow model and the moment-balance trim analysis. Loading noise and thickness noise are obtained using the lifting-line loading distribution and the dual-compact thickness noise model in PSU-WOPWOP. With the forward flight capability developed in UCD-QuietFly, broadband noise, including trailing-edge noise, trailing-edge bluntness noise, and airfoil stall noise, is predicted. Psychoacoustic metrics, such as fluctuation and roughness, are used to quantify the human subjective annoyance levels. The relative importance between tonal noise and broadband noise is investigated for various design cases and operating conditions. It is found that broadband noise is the dominant noise source for the rotor designs with low tip speeds and fewer blades, while tonal noise is dominant for the high-tip-speed designs. A low tip speed and more blades are found to be the preferable design features in terms of psychoacoustic metrics.

Frequency Domain Analysis of F-16 Aircraft in a Variety of Flight Conditions

Examining the flight quality of an aircraft to ensure the stability of the aircraft, increase maneuverability, and make the aircraft easier to control by the pilot necessitates an examination of the natural stability of the system. Within the scope of the paper, the frequency domain response of the F-16 aircraft dynamics is analyzed using Simulink models considering two different flight regimes because the frequency-domain methods have many distinct and important advantages over time-domain methods. Aerodynamic, propulsive, and atmospheric databases are used to create the nonlinear model. The trim analysis for cruise flights is carried out to obtain trim parameters. The aircraft is numerically linearized using the small perturbation theory. The linearized dynamics for each trim condition are used to create transfer functions for each input. The linear model is subsequently examined in the frequency domain to obtain information about the dynamic behavior of the aircraft, and flight quality analysis was examined by considering the lateral and longitudinal modes of the aircraft by international standards. It has been clearly understood the stability augmentation system design has critical importance for the modes with unstable or long steady-state duration.

Frequency Domain Analysis of F-16 Aircraft in a Variety of Flight Conditions

Examining the flight quality of an aircraft to ensure the stability of the aircraft, increase maneuverability, and make the aircraft easier to control by the pilot necessitates an examination of the natural stability of the system. Within the scope of the paper, the frequency domain response of the F-16 aircraft dynamics is analyzed using Simulink models considering two different flight regimes because the frequency-domain methods have many distinct and important advantages over time-domain methods. Aerodynamic, propulsive, and atmospheric databases are used to create the nonlinear model. The trim analysis for cruise flights is carried out to obtain trim parameters. The aircraft is numerically linearized using the small perturbation theory. The linearized dynamics for each trim condition are used to create transfer functions for each input. The linear model is subsequently examined in the frequency domain to obtain information about the dynamic behavior of the aircraft, and flight quality analysis was examined by considering the lateral and longitudinal modes of the aircraft by international standards. It has been clearly understood the stability augmentation system design has critical importance for the modes with unstable or long steady-state duration.

Comparison of the Newton–Raphson Method and genetic algorithm solutions for nonlinear aircraft trim analysis

As the number of unknowns in trim analysis increases, the problem becomes more complicated, and traditional methods begin to fail. Common problems with conventional methods may be an ill-conditioned matrix, rounding errors, and division by zero. Furthermore, these methods are likely to find the local optimum, not the global optimum. In such cases, hybrid use with intelligent methods such as genetic algorithms is recommended. In this study, a flight situation that the Newton–Raphson method has for difficulty in solving is selected for a six-degree-of-freedom nonlinear trim analysis. Trim analysis was performed using the Newton–Raphson method, genetic algorithm, and by their hybrid use, respectively. The Newton–Raphson method had convergence problems despite very good initial guesses. The genetic algorithm was able to solve the same problem by itself. The unknowns in trim analysis, such as deflection angles of an elevator, a rudder, and an aileron, have physical limits, whereas the constraints make conventional methods more complicated, and the ability to use these limits in the genetic algorithm narrows the solution space and reduces the computation time. The hybrid use of the GA and Newton–Raphson method significantly increased the performance of the Newton–Raphson method and eliminated the convergence problem. It has been shown that a 6-degree-of-freedom trim problem, which traditional numerical methods such as the Newton–Raphson method have for difficulty in solving, can be solved easily and effectively with the hybrid use of the GA and the Newton–Raphson method. The strength of the proposed hybrid method to solve a highly nonlinear trim problem was demonstrated.

Longitudinal Trim and Dynamic Stability Analysis of a Seagull-Based Model

Understanding the mechanisms of trim and flight stability in birds is critical to guide the design of bionic micro air vehicles. The complex movements (plunging, sweeping, twisting) and morphing of wings always keeps the flapping flight of birds in dynamic equilibrium, which makes it difficult to determine the critical factors of trim and stability. Hence, a model has been developed that takes real complex movement and the calculation of unsteady aerodynamics into consideration. Two trim methods, including wash-out and forward-sweep, have been used to achieve equilibrium in the longitudinal direction. It is interesting to find that these two methods are both important to realize a larger take-off weight, lower power consumption, and stronger longitudinal stability. This implies that the seagull probably uses both of them to obtain the requirement of equilibrium and stability, which further inspires the design of seagull-inspired micro air vehicles.

Multidisciplinary conceptual design for a hybrid-electric commuter aircraft

AbstractThe electrification of the commuter aircraft is instrumental in the development of novel propulsion systems. The scope of this work aims to explore the design space of a parallel hybrid-electric configuration with an entry into service date of 2030 and beyond and determine the impact of other disciplines on conceptual design, such as components positioning, aircraft stability and structural integrity. Three levels of conceptual sizing are applied and linked with a parametric aircraft geometry tool, to generate the aircraft’s geometry and position the components. Subsequently, the structural optimisation of the wing box is performed, providing the centre of gravity of the components placed inside the wing, that minimise the induced stresses. Furthermore, the stability and trim analysis follow, with the former being highly affected by the positioning of components. Results are compared to a similar aircraft with entry into service technology of 2014 and it is indicated that in terms of block fuel reduction the total electrification benefit increases with the increase of degree of hybridisation, if aircraft mass is kept constant. On the other hand, if battery specific energy is kept constant, similar block fuel reduction is possible with lower hybridisation degrees. The potential for improvement in terms of carbon dioxide emissions and block fuel reduction ranges from 15.73% to 21.44% compared to the conventional aircraft, for levels of battery specific energy of 0.92 and 1.14 kWh/kg respectively. Finally, the component positioning evaluation indicates a maximum weight limitation of 240 kg for the addition of an aft boundary layer ingestion fan to a tube and wing aircraft configuration, without compromising the aircraft static stability.

Nonlinear Aeroelastic Analysis for Highly Flexible Flapping Wing in Hover

Aeromechanics of highly flexible flapping wings is a complex nonlinear fluid–structure interaction problem and, therefore, cannot be analyzed using conventional linear aeroelasticity methods. This paper presents a standalone coupled aeroelastic framework for highly flexible flapping wings in hover for micro air vehicle (MAV) applications. The MAV-scale flapping wing structure is modeled using fully nonlinear beam and shell finite elements. A potential-flow-based unsteady aerodynamic model is then coupled with the structural model to generate the coupled aeroelastic framework. Both the structural and aerodynamic models are validated independently before coupling. Instantaneous lift force and wing deflection predictions from the coupled aeroelastic simulations are compared with the force and deflection measurements (using digital image correlation) obtained from in-house flapping wing experiments at both moderate (13 Hz) and high (20 Hz) flapping frequencies. Coupled trim analysis is then performed by simultaneously solving wing response equations and vehicle trim equations until trim controls, wing elastic response, inflow and circulation converge all together. The dependence of control inputs on weight and center of gravity (cg) location of the vehicle is studied for the hovering flight case.

A Coupled CFD/Trim Analysis of Coaxial Rotors

A numerical simulation method of computational fluid dynamics (CFD) coupling with a trim analysis for coaxial rotor systems is described in this paper. The trim analysis is implemented using a rotorcraft flow solver, rFlow3D. Six target forces and moments, which are the thrust of the coaxial rotor system, the rolling and pitching moments for each upper and lower rotor, and the torque balance for yaw control, are considered as the trim conditions. The blade pitch angles of both upper and lower rotors are adjusted to satisfy the target trim conditions through the trim analysis by being loosely coupled with the CFD solver. Verification of the trim analysis method and validation of the prediction accuracy of aerodynamic performance are performed based on previous experimental and numerical studies in hover and forward flight using the lift-offset conditions. It is shown that the predicted hover performances of the torque-balanced coaxial rotors are in excellent agreement with the experimental data. It is also verified that the lift-offset conditions in forward flight are simulated using this established trim analysis. Furthermore, reasonable agreements with other computational results are indicated.

HTSQualC is a flexible and one-step quality control software for high-throughput sequencing data analysis

Use of high-throughput sequencing (HTS) has become indispensable in life science research. Raw HTS data contains several sequencing artifacts, and as a first step it is imperative to remove the artifacts for reliable downstream bioinformatics analysis. Although there are multiple stand-alone tools available that can perform the various quality control steps separately, availability of an integrated tool that can allow one-step, automated quality control analysis of HTS datasets will significantly enhance handling large number of samples parallelly. Here, we developed HTSQualC, a stand-alone, flexible, and easy-to-use software for one-step quality control analysis of raw HTS data. HTSQualC can evaluate HTS data quality and perform filtering and trimming analysis in a single run. We evaluated the performance of HTSQualC for conducting batch analysis of HTS datasets with 322 samples with an average ~ 1 M (paired end) sequence reads per sample. HTSQualC accomplished the QC analysis in ~ 3 h in distributed mode and ~ 31 h in shared mode, thus underscoring its utility and robust performance. In addition to command-line execution, we integrated HTSQualC into the free, open-source, CyVerse cyberinfrastructure resource as a GUI interface, for wider access to experimental biologists who have limited computational resources and/or programming abilities.

Aerodynamic Characterization of Hypersonic Transportation Systems and Its Impact on Mission Analysis

This paper aims to provide technical insights on the aerodynamic characterization activities performed in the field of the H2020 STRATOFLY project, for the Mach 8 waverider reference configuration. Considering the complexity of the configuration to be analyzed at conceptual/preliminary design stage, a build-up approach has been adopted. The complexity of the aerodynamic model increases incrementally, from the clean external configuration up to the complete configuration, including propulsion systems elements and flight control surfaces. At each step, the aerodynamic analysis is complemented with detailed mission analysis, in which the different versions of the aerodynamic databases are used as input for the trajectory simulation. eventually, once the contribution to the aerodynamic characterization of flight control surfaces is evaluated, stability and trim analysis is carried out. The comparison of the results obtained through the different mission analysis campaigns clearly shows that the accuracy of aerodynamic characterization may determine the feasibility or unfeasibility of a mission concept.

Is shift-work associated with increased risk of rectal cancer? A meta-analysis.

e15600 Background: Globally, more than 1.8 million people were diagnosed of colorectal cancer (CRC) in 2018, with over 30% of CRC in the rectum. Shift-work, involving circadian disruption, sleep deprivation and lifestyle changes, was designated as a probable cause of cancer by The International Agency for Research on Cancer. Previous studies investigating the impact of permanent night-shift work and rotating shift-work on rectal cancer risk showed controversial results. Thus, this meta-analysis was conducted. Methods: A comprehensive literature search on PubMed was conducted to identify all relevant studies published prior to January 2021 according to the established inclusion criteria. The quality assessment was performed by the Newcastle-Ottawa Scale (NOS). The pooled odds ratio (OR) and 95% confidence intervals (CI) were calculated to estimate the association between the shift-work and rectal cancer risk. Based on heterogeneity significance, random-effect or fixed-effect model was used. Subgroup analyses were conducted to explore the night-shift and rotating-shift, respectively. Sensitivity analysis and publication bias detection were performed, and trim and fill analysis was also conducted. All statistical analyses were performed using RevMan software (version 5.3; Cochrane library) and STATA 15.0 statistical software (Stata Corp., College Station, TX), and all P values were two-tailed, the test level was 0.05. Results: Thirty-seven articles were obtained from database searching. Three articles involving 1,063 rectal cancer cases were included. All studies were considered moderate to high quality. All included studies investigated on the association between shift-work and rectal cancer risk. A statistically significant association between shift-work and increased rectal cancer risk was found (OR 1.53, 95%CI: 1.31, 1.79, P< 0.00001, I 2 = 35%). In subgroup analyses, night-shift work was associated with a non-statistically significant increased risk of rectal cancer (OR 1.25, 95%CI: 0.47, 3.32, P = 0.66, I 2 = 93%). In contrast, Rotating-shift was associated with a statistically significant increased rectal cancer risk (OR 1.35, 95%CI: 1.10, 1.65, P = 0.004, I 2 = 6%). Sensitivity analysis confirmed the stability of the result. Funnel plot, Egger's test (t = 1.69, P = 0.341), and Begg's test (z = 1.04, P = 0.296) found no publication bias of analysis. Trim and fill analysis on fixed-effect model showed the pooled OR kept stable after adding two “missing” studies (OR 1.403, 95%CI: 1.224, 1.609, P <0.05). Conclusions: The current meta-analysis demonstrates that shift-work is associated with increased rectal cancer risk. However, no association between night-shift work and rectal cancer risk was found. In contrast, association between rotating-shift work and increased rectal cancer risk was found. More original studies on this topic are needed to further explore shift-work impacts on rectal cancer risk.

A Trimming Design Method Based on Bio-Inspired Design for System Innovation

The application of design knowledge determines the innovativeness of a technical scheme obtained by trimming (a tool for problem analysis and solving in TRIZ). However, limitations in the knowledge, experience and expertise of designers constrain the range of design knowledge that they can apply, thus reducing the effectiveness of trimming. In this paper, biological strategies are introduced to the trimming process to compensate for limitations imposed by the insufficient professional knowledge of designers, thereby improving design innovation. Therefore, this paper proposes a new design method that combines the trimming method and bio-inspired design (BID). First, a trimming analysis of the target system is carried out. Taking the missing functions of the trimmed system as a potential breakthrough point, a keyword search mode based on “V(verb)O(object)P(property) + the effect/features of the associated function” is used to search for biological prototypes in the biological knowledge base. Second, a fuzzy comprehensive evaluation method is used to analyze the biological prototypes from three dimensions, namely, compatibility, completeness and feasibility, and the best-matching biological prototype is selected. Finally, the biological solution is transformed into an engineering design scheme through a resource derivation process based on structure–function–attribute analogies. The proposed method can expand the range of design solutions by adding biological strategies as a new resource to solve trimming problems. The feasibility and effectiveness of the method are verified by redesigning a steel tape armoring machine.