Inverse Simulation Technique Research Articles

Vestiges of the Ancient: Deep-Time Noble Gas Thermochronology

Ancient rocks have survived plate tectonic recycling for billions of years, but key questions remain about how and when they were exhumed to the surface. Constraining exhumation histories over long timescales is a challenge because much of the rock record has been lost to erosion. Argon and helium noble gas thermochronology can reconstruct deep-time <350 °C thermal histories by using the distinct temperature sensitivities of minerals such as feldspar, zircon, and apatite, while exploiting grain size and radiation damage effects on diffusion kinetics. Resolution of unique time–temperature paths over long timescales requires multiple chronometers, appropriate kinetic models, and inverse simulation techniques to fully explore and constrain possible solutions. Results suggest that surface histories of ancient continental interiors are far from uninteresting and may merely be misunderstood.

Efficient and Robust Inverse Simulation Techniques Using Pseudo-Spectral Integrator with Applications to Rotorcraft Aggressive Maneuver Analyses

This paper intends to propose new inverse simulation techniques to cope with the numerical stability and accuracy problems frequently encountered with the integration inverse simulation methods widely used today. To achieve this, the pseudo-spectral method is adopted as a time integrator of the aircraft motion equations. In addition, the quasi-Newton and fixed-point iterative methods are applied to solve the resultant nonlinear algebraic equations in an efficient manner. These algorithms are integrated into a moving horizon framework to guarantee fast numerical convergence. The proposed methods are applied to the analyses of rotorcraft aggressive maneuvers such as popup, pirouette, and depart/abort mission-task-elements defined in the rotorcraft handling qualities requirements, ADS-33E-PRF. Numerical properties of the proposed methods are thoroughly investigated to clarify the effect of the numbers of quadrature nodes and time-horizon segments, and the level of maneuver aggressiveness on the robustness and efficiency of the analyses. Numerical efficiency and robustness of the present method are identified using specially designed performance measures such as the number of iterations to obtain a converged solution, functional residuals at the final solutions, and the variation of the adaptive relaxation factor. The results show that the present approach can provide extremely fast solutions of the inverse simulation problems and presents strong robustness to the level of maneuver aggressiveness, long-term simulation, and solution control parameters. Therefore, it is worthwhile to use the present techniques as one of the inverse simulation methods.

Analysis of grip and pinch strength using inverse dynamics simulation technique.

Grip strength is the function of musculotendinous action across the finger joints and varies while dealing objects of varying size and shape. Increasing object size requires greater effort by the fingers to grip. The main objective of this study is to analyse the variation in grip and pinch strength exerted on objects of various sizes and shapes in a short span of time. OpenSim 3.3 is open-source musculoskeletal modelling software used for performing simulations in a dynamic environment. The generic wrist model in OpenSim has movements on index finger and thumb only, for study purpose. Objects of various sizes were designed and imported in OpenSim. This study determines the joint moments exerted by the fingers during grip activities. Original model was modified and custom joints were placed in the proximal and distal phalanx joints of the fingers. This allowed the finger segments to undergo translational and rotational movements. Coordinates of the custom joints were adjusted to provide constraints in the joint movement to hold the objects in position. For grip strength, objects of various sizes and shapes were imported to OpenSim. Simulation was carried out for gripping the objects for a specified time period. The force generated by the synergistic movements of finger segments was compared among grip and pinch of different objects. This method is used to determine the grip and pinch strength by handling objects of different shapes and sizes under the influence of time.

Inverse Modelling for Prediction of Coating Material Diffusivity and Lag Time of Controlled-Release Coated Urea Granule

Controlled release fertilizer (CRF) has attracted a lot of interest because of its advantages for ecosystem in terms of enhancement of nutrient utilization and reducing nutrient loss from leaching and volatilization, etc. While a number of research studies on novel coating material to control the release of nutrients, modelling has a significant role in predicting release behaviour and determining good CRF design that matches the nutrient requirement from the plants. The present study proposes a solution to predict coating material parameters based on multi-diffusion model and preliminary experimental results using inverse simulation technique. In addition, the solution showed an advantage in prediction the release of nutrient, i.e., the reduction in experimental time which plays an important role in investigation novel coating material and designing of CRFs which are matched the nutrient uptake from plants. Hence, this solution reduces experimental cost and time to researchers, who investigated novel CRFs.

Heat-flow determination through inverse identification in drilling of aluminium workpieces with MQL

One of the current trends in machining is the reduction or elimination of the use of cutting fluids to reduce economic and ecological costs. As a consequence, heating of the workpieces is increased, leading to greater thermal distortion. This distortion can be predicted using the finite-element method (FEM), provided heat input to the workpiece for the machining operation is known. The aim of this research is to determine the quantity and ratio of heat generated in drilling operations and to quantify the heat transferred to the workpiece based on cutting speed and feed rate. Thus, a detailed study of workpiece heating during the drilling process with minimum quantity of lubricant was conducted, and a combination of experimental and numerical data was used to obtain these parameters. The experiments were carried out on aluminium (Al2017) samples. Drilling torque and temperature of the workpiece were measured. The cutting procedure involved drilling a O10 × 15 mm blind hole using uncoated cemented carbide tools. Temperature was measured by infrared methods, and cutting torque was obtained using a piezoelectric dynamometer. The FEM model was developed using the general-purpose software ABAQUS/Standard© v6.5 and the inverse simulation technique was used to calculate heat input to the workpiece for each machining condition. As a general conclusion, an increase in cutting speed and feed rate leads to a decrease in heat input and temperature in the workpiece and thus, thermal distortion of the part.

Numerical earthquake models of the 2013 Nantou, Taiwan, earthquake series: Characteristics of source rupture processes, strong ground motions and their tectonic implication

On 27 March and 2 June 2013, two large earthquakes with magnitudes of ML 6.2 and ML 6.5, named the Nantou earthquake series, struck central Taiwan. These two events were located at depths of 15–20km, which implied that the mid-crust of central Taiwan is an active seismogenic area even though the subsurface structures have not been well established. To determine the origins of the Nantou earthquake series, we investigated both the rupture processes and seismic wave propagations by employing inverse and forward numerical simulation techniques. Source inversion results indicated that one event ruptured from middle to shallow crust in the northwest direction, while the other ruptured towards the southwest. Simulations of 3-D wave propagation showed that the rupture characteristics of the two events result in distinct directivity effects with different amplified shaking patterns. From the results of numerical earthquake modeling, we deduced that the occurrence of the Nantou earthquake series may be related to stress release from the easternmost edge of a preexistent strong basement in central Taiwan.

Researches on inverse simulation’s applications in teleoperation rendezvous and docking based on hyper-ellipsoidal restricted model predictive control for inverse simulation structure

The inverse simulation is a technique used to calculate the control action based on the expected trajectory or experimental data and has been applied successfully in the aviation field. A novel inverse simulation technique is first introduced in the fields of rendezvous and docking. The least square estimation under the hyper-ellipsoidal restriction is presented to solve inverse simulation problems. The inverse simulation structure used in this paper is based on the model predictive control scheme. The predictive model is derived by Clohessy–Wiltshire dynamics equations, and the accurate one is obtained by two-body dynamics equations. When the designed trajectories or the data obtained by teleoperation console experiments are given to the predictive model, the inverse strategy is transformed into a generalized shrunken estimation problem. Then, the continuous control signals produced by the least square theory are dispersed by the pulse width modulation method and propagated into the high-order model. The inverse simulation results of the traditional control method and the inverse strategy mentioned in this paper show that the maneuvers can be better reproduced by inverse strategy, and the proper choices of sensitive factors and the receding horizon lead to better results.

A Parameter Identification Method for Helicopter Noise Source Identification and Physics-Based Semiempirical Modeling

A new physics-based parameter identification method for rotor harmonic noise sources is developed using an acoustic inverse simulation technique. This new method allows for the identification of individual rotor harmonic noise sources and allows them to be characterized in terms of their individual non-dimensional governing parameters. This new method is applied to both wind tunnel measurements and ground noise measurements of two-bladed rotors. The method is shown to match the parametric trends of main rotor Blade-Vortex Interaction (BVI) noise, allowing accurate estimates of BVI noise to be made for operating conditions based on a small number of measurements taken at different operating conditions.

Predictive inverse simulation of helicopters in aggressive manoeuvring flight

AbstractA conventional inverse simulation does not accommodate control constraints; hence for aggressive manoeuvring flight conditions, where control inputs are close to the limits, these algorithms lose some of their applicability. A modification of the conventional inverse simulation technique that accommodates the onset of physical limits or constraints is proposed in this paper. In this way a process of constraints handling is incorporated into the inverse simulation algorithm. Therefore, the aim of this paper is to demonstrate that conventional inverse simulation can be improved in terms of the realism of the results by applying a predictive capability for applications involving manoeuvring flight. The paper gives details of the development of the predictive inverse simulation algorithm and helicopter model used and, by presenting examples of results calculated for pop-up and lateral realignment manoeuvres demonstrates that a ‘receding horizon’ predictive approach offers improvements in the realism of inverse simulation results.

Simulation of soil organic carbon under different tillage and stubble management practices using the Rothamsted carbon model

In addition to its important effect on soil quality and crop productivity, soil organic carbon has also been identified as a possible C sink for sequestering atmospheric carbon dioxide. The Rothamsted carbon model, RothC, has been widely tested in many countries. The source of carbon input into soils consists of below-ground and above-ground plant biomass. The model requires users to estimate carbon inputs, rather than being directly simulated by the model. Measured above-ground dry matter and crop yields are often used to estimate the amount of carbon input. Theoretically, if above-ground stubble is neither removed from the field nor burnt at the site, the stubble retention factor is set as 1.0, otherwise, it is 0.0 or a value between 0.0 and 1.0, depending on the proportion left in the field. In this study, the RothC model is used to simulate SOC in a long-term field experiment (1979–2004) near Wagga Wagga, NSW, which involved different crop rotation, tillage and stubble management practices. The simulation showed that modelled SOC adequately matched observed SOC in the stubble burnt treatments, but failed to simulate the stubble retained treatments. The root mean squared errors (RMSE) were 2.86 and 2.18 t C ha −1 for no-tillage (NT) and cultivated treatments (CC) when stubble was burnt, and 9.93 (NT) and 11.51 t C ha −1 (CC) when stubble was retained, respectively. Using an inverse simulation technique, results showed that when the stubble retention factor was ≤26%, the simulated SOC can match well the observed SOC, yielding RMSE of 2.33 t C ha −1 or lower. The results suggested that a large fraction of the surface-retained stubble was lost before entering soil to be sequestrated as SOC.

HYBRID INVERSE METHODS FOR HELICOPTERS IN AGGRESSIVE MANOEUVRING FLIGHT

The need to implement a process of constraints handling into conventional inverse simulation represents an important problem. To achieve this, a modification of the conventional inverse simulation technique which includes predictive capability is proposed in this paper. After giving details of the development of the predictive inverse simulation algorithm, the paper demonstrates the applicability of the developed methodology on two aggressive helicopter manoeuvres: pop-up and lateral realignment.

Pilot modelling and inverse simulation for initial handling qualities assessment

AbstractThis paper describes the development of an approach to handling qualities investigation that can be applied at an early stage in t he design of the vehicle. It makes use of inverse simulation techniques, together with a pilot model to provide an integrated description of the man-machine control system. In order to incorporate pilot effects into data generated by inverse simulation, the output from an inverse simulation run is applied as input to a closed-loop system model that includes the vehicle dynamics and a simple parametric model of the pilot. Parameters of the pilot model are determined by optimisation and the pilot effect is added to the system output. Validation of the approach is achieved through a case study involving a predefined mission task involving a lateral manoeuvre. Equalisation characteristics estimated for each pilot are compared with those found by inverse simulation for the same manoeuvre. This approach may be applied using a simple real-time simulation on a desk-top computer and could be of value in identifying any potential deficiencies in a helicopter flight control system at an early stage in its development

Modification of a generalized inverse simulation technique for rotorcraft flight

Inverse simulation techniques have been employed for several years to analyse the manoeuvrability, operational suitability and conceptual design of helicopters. Much of the published work has used specially constructed (algebraic) models of the aircraft. Recently, integration methods have been used successfully with conventional simulation models, although with some important simplifying assumptions made regarding the dynamics of the main rotor, principally the omission of coupled lead/lag and rotorspeed degrees of freedom. This paper will present the current state-of-theart in helicopter inverse simulation—inserting a complete, validated, rigid-body rotorcraft model inside an integration-based algorithm. It is found that the additional rotor dynamics destabilize the inverse algorithm, resulting in severe oscillations in certain unconstrained states, most notably body pitch and roll angles. Analysis of the dynamics of the inverse system shows that these oscillations are manifest by lack of robustness in the inverse algorithm. Several new modifications to the inverse algorithm are shown to reduce these instabilities considerably.

A nonlinear inverse simulation technique applied to coaxial rotor helicopter maneuvers

As compared with the maneuvering flight studies for single main rotor helicopters, the corresponding studies for coaxial rotor helicopters are relatively poor. In this paper, the maneuvering flight governing equations for coaxial rotor helicopters is established. By introducing induced velocity interference factor analysis, the coaxial rotor aerodynamic interference can be taken into account. With the combination of coaxial rotor helicopter control features and nonlinear inverse simulation technique, the governing equations for maneuvering flight can be solved so as to determine helicopter control input, control force and moment, and helicopter body attitudes which are needed for performing a specified maneuver. Good results of the sample calculations of level turn and lateral jink maneuvers are obtained and simply analyzed.

Inverse Modeling of Chlorine Concentration in Pipe Networks under Dynamic Condition

The Surface Water Treatment Rule under the Safe Drinking Water Act and its amendments require that the water utilities maintain a detectable disinfectant residual throughout the distribution system at all times. A new computer model is presented to directly calculate the chlorine concentrations needed at the source(s) to have specified residuals at given locations in a pipe network in unsteady flow conditions by using an inverse method. Unlike the forward solution method, which calculates the source chlorine concentration by a trial-and-error procedure, the inverse solution technique presented in this paper directly calculates the source concentration required to meet a specified value at a particular point in the network. The dynamic flows and pressures are first calculated by solving the governing equations by an implicit finite-difference scheme subject to appropriate boundary conditions. For chlorine concentrations at various pipe sections and at each node, the one-dimensional transport equation is modified for the advection dominated flow. This modified transport equation is then discretized by using the four-point implicit finite-difference scheme and solved simultaneously together with the junction mass balance equations. A first-order reaction rate for chlorine decay is assumed and a flow-weighted averaging procedure is used to calculate the complete mixing of chlorine at the junctions. For the verification of the inverse method, the computed results are compared with those determined by direct simulations. An excellent agreement is observed between the inverse method and direct simulation technique.

Inverse and optimal control for precision aerobatic maneuvers

Control input histories are determined for flying precision three-dimensional acrobatic maneuvers using inverse- control and optimization methods. A point-mass model is used with three controls, angle of attack, bank angle, and thrust. Bounds are placed on normal load factor, thrust, and angle of attack. By choosing cylindrical coordinates for the position vector and spherical coordinates for the velocity vector, simple inverse solutions are found for precision acrobatic maneuvers. Requiring constant radius and constant helix angle produces nonlinear feedback laws for angle of attack and bank angle. Numerical results are presented for an F4H aircraft performing barrel rolls. EROBATIC maneuvers are the ultimate art of flying. They re- quire keen reflexes in the pilot and close coordination of the various controls. The acrobatic aircraft must be structurally sound, have a large wind area, and have an engine that is powerful rel- ative to its weight. The American Pitts special, with a composite structure and a modified engine, achieves a thrust/weight ratio well above 1. Most fighters can also perform such maneuvers because of their powerful engines (e.g., the maximum thrust/weight ratio of an F-16 ranges between 1.0 and 1.4). Acrobatic maneuvers are an integral part of a fighter pilot's tactics in aerial combat and help him to recover from unexpected flight conditions such as spins.1 For example, a high-g barrel roll is often effective against an attacker closing from astern. Immelman or split-S maneuvers are standard methods of disengaging from combat.2 In conventional flight control design, the aircraft dynamics are assumed linear and time invariant about some nominal equilibrium flight trajectory. These assumptions are not valid in aerobatic maneu- vers because they generally involve large changes in aircraft altitude and attitude. This study develops a systematic approach to determine the control inputs for specified aerobatic maneuvers. The approach uses inverse and optimal control methods to generate feedforward control histories. A unified approach for analyzing precision aero- batic maneuvers is presented by specifying the flight path as either a horizontal or a vertical helix. These specifications are then used in inverse analysis to generate the controls. If the resulting controls are not feasible or if terminal conditions are not met, optimal control methods are used to satisfy the constraints while minimizing the deviations from the ideal aerobatic maneuver. Uehara et al.3 considered minimum time loop maneuvers using a point-mass model. They showed that the controls are mainly on the control boundaries (i.e., bang-bang). A similar study by Shinar et al.4 used an energy state model. They showed that by using this reduced-order model, the solution can be expressed in a feedback form. In recent years, inverse control methods have been used to analyze large-amplitude aircraft motions. Kato and Sugiura5 pre- sented an aileron roll maneuver as an example of inverse analysis of aircraft motion. In their example, however, the inverse control magnitudes are not feasible. Hess et al.6 found the inverse controls for the same maneuver using an inverse simulation technique. A rigid-body model was used in both cases. In another paper by Kato7

Inverse simulation of large-amplitude aircraft maneuvers

Inverse simulation techniques are computational methods that determine the control inputs to a dynamic system that will produce desired system outputs. Such techniques can be useful tools for the analysis and evaluation of problems associated with maneuvering flight. As opposed to current inverse simulation methods that require numerical time differentiation in their implementation, the proposed technique is essentially an integration algorithm. It is applicable to cases where the number of inputs equals or exceeds the number of constrained outputs. The algorithm is exercised in determining the trim conditions and then the control inputs that force a nonlinear model of an F-16 fighter to complete large-amplitude maneuvers.

Generalized technique for inverse simulation applied to aircraft maneuvers

Inverse simulation techniques are computational methods that determine the control inputs to a dynamic system that produce desired system outputs. Such techniques can be powerful tools for the analysis of problems associated with maneuvering flight. An algorithm is developed that serves as an efficient inverse simulation tool for analyzing maneuvering flight. As opposed to current inverse simulation methods, which require numerical time differentiation in their implementation, the generalized technique offered is essentially an integration algorithm. Examples of inverse solutions for a large-amplitude aircraft maneuver and a nap-of-the-Earth helicopter maneuver are presented.