Aki Mikkola

• D.Sc. (Tech.)
• Professor (Full) at Lappeenranta – Lahti University of Technology LUT

Smart structures based on the magnetic shape memory (MSM) effect feature giant magnetic field-induced strains and an ultra-fast response. MSM alloys could be used in a variety of applications such as digital hydraulics, microfluidic systems, soft robotics. However, practical implementation of the MSM effect is complicated by a lack of precise engin...

The real-time simulation of coupled multibody and hydraulics systems can be challenging due to the complexity, accuracy, and non-linear behavior of the modeling methods and the computational requirements. To this end, this study introduces the universal hydraulic surrogate approach instead of the conventional lumped fluid theory to solve the dynami...

The Industry 5.0 initiative seeks the sustainability and resilience of production systems through digital technologies. Derived from such an initiative, the Operator 5.0 concept surged to place the operator as the main value-creation contributor of sustainable and resilient human-machine systems. Smart service systems are data-driven services that...

In this work, the contact surface between beams with the highly deformable cross-sections are effectively constrained with the linear and cone complementarity approaches (CP). The CP approaches are tailored for an efficient numerical integration over beams’ contact surfaces in the case of non-conforming mesh with the contacting beams using nearly i...

A model-based methodology for the estimation of both lateral and vertical track irregularities is presented. This methodology, based on Kalman filter techniques, was developed for an independent and compact measuring system comprising an instrumented axle equipped with a limited set of low-cost sensors: a 3D gyroscope, a Linear Variable Differentia...

To increase productivity, reduce energy use, and minimize unplanned maintenance, manufacturers of heavy machinery must instrument their products. As explained in the literature, state and parameter estimators can successfully integrate machine sensor signals with simulation results from computational models. This leads to comparable or improved obs...

Reinforcement Learning (RL) is one of the emerging fields of Artificial Intelligence (AI) intended for designing agents that take actions in the physical environment. RL has many vital applications, including robotics and autonomous vehicles. The key characteristic of RL is its ability to learn from experience without requiring direct programming o...

Finding the unknown parameters of hydraulically driven machines such that the simulation model behaves similar to the real-world can be a cumbersome task. This could be due to number of factors in the working cycles of a physical system. This research work presents the optimization of parameters in the hydraulically driven machines using the swarm...

This paper investigates the application, design, and implementation of different adaptive sigma-point Kalman filters for nonlinear dynamic systems. It is a well-known fact that the performance of nonlinear Kalman filters depends on a prior knowledge of system noise statistics. In real-time applications, this knowledge is difficult and in some cases...

A precise evaluation of the bulk modulus is essential for the efficient simulation and accurate design of hydraulic circuits. The compression and dissolution of air bubbles in hydraulic oil can affect the density as well as the effective bulk modulus during corresponding operation. To address this phenomenon, this study presents a novel model for t...

Hydraulics is often used to actuate mechanisms in the applications of heavy machinery. In this work, a linearization approach for hydraulically driven multibody systems is presented. The approach allows linearizing the equations of motion of general multibody systems with holonomic and nonholonomic constraints, augmented with the hydraulic equation...

Artificial intelligence and mechanical engineering are two mature fields of science that intersect more and more often. Computer-aided mechanical analysis tools, including multibody dynamics software, are very versatile and have revolutionalized many industries. However, as shown by the literature presented in this review, combining the advantages...

This work introduces a surface-to-surface contact description in the context of beam-to-beam contact. The introduced contact description is formulated in the frame work of the absolute nodal coordinate formulation. Leveraging the solid element-like features of the absolute nodal coordinate beam formulation and utilizing an interpolation scheme to p...

This study investigates the discrete extended Kalman filter as applied to multibody systems and focuses on accurate formulation of the state-transition model in the framework. The proposed state-transition model is based on the coordinate-partitioning method and linearization of the multibody equations of motion. The approach utilizes the synergies...

This paper describes a floating-frame-of-reference-based (FFRF-based) recursive formulation for flexible bodies. A new definition of the joint coordinate system is introduced that makes it simpler to formulate more concise velocity transformation matrices. A path matrix, which defines the connectivity of the mechanism for the open loop system, simp...

This paper introduces a real-time co-simulation model for the prediction of the dynamics behavior of a veneer peeling lathe machine. The real-time co-simulation model introduced is described in the framework of multi-body system dynamics. It makes use of a co-simulation procedure in which a semi-recursive multi-body approach is combined with a deta...

This paper explores the usability of several beam elements based on the Absolute Nodal Coordinate Formulation (ANCF) subjected to torsional and bi-moment loading scenarios. ANCF beam element solutions are compared against an analytical solution and beam and solid finite element solutions. When subjected to bi-moment loading, most of studied higher-...

In this paper, two often-employed alternatives to the semi-recursive method are described and compared in terms of velocity transformation. The text offers a simplified way to understand the theory behind the two semi-recursive approaches. Focusing on planar cases, particular attention is given to reference and joint coordinates. Consequently, a mu...

The absolute nodal coordinate formulation (ANCF) is a nonlinear finite element approach proposed for the large deformation dynamics analysis of beam-and plate/shell-type structures. In the ANCF approach, elastic forces can be defined using three-dimensional elasticity-based continuum mechanics. This approach is often straightforward, and it makes i...

In this paper, the absolute nodal coordinate formulation (ANCF) is applied to simulate the magnetic shape memory effect. Using the absolute nodal coordinate formulation makes it possible to describe complicated or large deformation cases. The nonlinear bidirectional coupling terms between the mechanical and magnetic field are taken into account in...

This paper contributes to a recently proposed Arbitrary Lagrangian–Eulerian Modal (ALEM) approach that makes it possible to develop finite elements with variable volume suitable for modeling wire-ropes in reeving systems. Reeving systems often include motors that continuously modify the total mechanical energy. If mechanical energy dissipation is o...

In this paper, beam elements with particular emphasis on higher order elements based on the absolute nodal coordinate formulation (ANCF) are thoroughly investigated from the perspective of interpolation procedure and numerical performance. A straightforward and modularized procedure to construct the shape function is proposed. Based on the unified...

In multibody system dynamics, the equations of motion are often coupled with systems of other physical nature, such as hydraulics. To infer the real dynamical state of such a coupled multibody system at any instant of time, information fusing techniques, such as state estimators, can be followed. In this procedure, data is combined from the coupled...

The slender rods experience mechanical deformation in most practical cases. The deformation should be modeled numerically since it affects the dynamics of the entire system. This paper models flexible slender-rods in a closed-loop multibody system by considering rods as variable-length constraint equations, and updating the positions and velocities...

The numerical and computation aspects of the Knife-edge Equivalent Contact ( KEC ) constraint and lookup table ( LUT ) methods are compared in this paper. The LUT method implementation uses a penetration-based elastic contact model for the flange and a constraint-based formulation at the wheel tread. For the KEC method, where an infinitely narrow r...

The absolute nodal coordinate formulation (ANCF) approach has been successfully used to analyze bodies undergoing large deformations in multibody dynamics applications. In this study, the ANCF is extended to the analysis of coupled electromechanical systems. To this end, the electrostatic equations are solved by means of conventional plane finite e...

The absolute nodal coordinate formulation (ANCF) is a nonlinear finite element approach proposed for the large deformation dynamics analysis of beam- and plate/shell-type structures. In the ANCF approach, elastic forces can be defined using three-dimensional elasticity based continuum mechanics. This approach is often straightforward, and it makes...

The conjugate heat transfer in mixtures of a fluid and single granular clusters is studied in this paper using a novel lattice Boltzmann method (LBM) programmed for parallel computation on the graphics processing unit (GPU). The LBM is validated for heat conduction by finite volume method (FVM) in a one dimensional geometry of multi-layer composite...

In this paper, the stability of a waveboard, a human propelled two-wheeled vehicle consisting in two rotatable platforms, joined by a torsion bar and supported on two caster wheels, is analysed. A multibody model with holonomic and nonholonomic constraints is used to describe the system. The nonlinear equations of motion, which constitute a Differe...

This paper describes an estimator incorporating the Unscented Kalman Filter (UKF) technique and multibody system dynamics, to determine the state of the flexible multibody applications. The dynamic equation of the flexible mechanism is formed using a set of non-linear equations as functions of reference and modal coordinates. Since both reference a...

Real-world products and physics-based simulations are becoming interconnected. In particular, real-time capable dynamic simulation has made it possible for simulation models to run in parallel and simultaneously with operating machinery. This capability combined with state observer techniques such as Kalman filtering have enabled the synchronizatio...

Multibody system dynamics approaches together with state estimation methods can reduce the need for a large number of sensors, especially in the digital twin of working mobile machinery. To demonstrate this, a hydraulically actuated machine was modeled using the double-step semi-recursive multibody formulation and lumped fluid theory in terms of sy...

Hydraulic machinery is a mechatronic system that is widely used in various industries such as the mining, forest, and construction industries. Computer simulation of hydraulic machinery is crucial because it can be used to affect almost everything from operational activities to the designs and features. The objective of this article is to monolithi...

Most sludges are dewatered using mechanical dewatering systems that can bring the weight percentage of the sludge solids up to a maximum of about 40 TS%. This study examined a new way to enhance pressure-filter dewatering by adding ultrasound and electrokinetics. The ultrasound adds a “stripping action” to free up bound water, and the electrokineti...

This paper analyses the stability of a waveboard, the skateboard consisting in two articulated platforms, coupled by a torsion bar and supported of two caster wheels. The waveboard presents an interesting propelling mechanism, since the rider can achieve a forward motion by means of an oscillatory lateral motion of the platforms. In this paper, the...

A line-to-line beam contact formulation in the framework of the absolute nodal coordinate formulation (ANCF) is introduced in this paper. Higher- and lower-order ANCF beam elements employ the introduced beam contact formulation. The higher- and lower-order ANCF beam elements are compared in terms of their accuracy and performance in a large deforma...

In this paper, the stability of a waveboard, the skateboard consisting in two articulated platforms, coupled by a torsion bar and supported of two caster wheels, is analysed. The waveboard presents an interesting propelling mechanism, since the rider can achieve a forward motion by means of an oscillatory lateral motion of the platforms. The system...

The estimation of the parameters of a simulation model such that the model’s behaviour matches closely with reality can be a cumbersome task. This is due to the fact that a number of model parameters cannot be directly measured, and such parameters might change during the course of operation in a real system. Friction between different machine comp...

The simulation of mechanical systems often requires modeling of systems of other physical nature, such as hydraulics. In such systems, the numerical stiffness introduced by the hydraulics can become a significant aspect to consider in the modeling, as it can negatively effect to the computational efficiency. The hydraulic system can be described by...

Dynamic simulation of mechanical systems can be performed using a multibody system dynamics approach. The approach allows to account systems of other physical nature, such as hydraulic actuators. In such systems, the nonlinearity and numerical stiffness introduced by the friction model of the hydraulic cylinders can be an important aspect to consid...

To simulate closed-loop multibody systems in effective and accurate way, the semi-recursive formulations can be used together with optimal numerical integrators. Although numerous contributions have been reported in this field, there still exists a demand to improve the computation efficiency for the faster-than-real-time simulation and hardware-in...

The concept of heads-up display can be used to provide augmented information onto the windshield of a tractor. The objective of this paper is to introduce a detailed real-time multibody model that is used in the design of a novel heads-up display unit of a tractor. To this end, a tractor is described using a multibody dynamics approach. A heads-up...

In this paper, we introduce a machine learning-based simulation framework of general-purpose multibody dynamics (MBD). The aim of the framework is to construct a well-trained meta-model of MBD systems, based on a deep neural network (DNN). Since the main advantage of the meta-model is the enhancement of computational efficiency in returning solutio...

This chapter describes research into physics-based real-time simulation from a business perspective and provides guidance for further studies. Despite the increasing amount of research into simulator-driven design and production, little progress has been made towards understanding the complexities of its implementation, its effect on business model...

https://lutpub.lut.fi/handle/10024/162826

This chapter introduces an implementation of gamification for the simulation modeling of agricultural heavy machinery. The objective of this study is to demonstrate how adding a gamification platform can both streamline the development process for a complex machine and enhance its marketing. To achieve this objective, a farm tractor is described wi...

The product development of complex machinery is moving away from a focus on technical features to an emphasis on user experience throughout the product lifecycle. The advent of new real-time simulation techniques is enabling end user participation in product development and active collaboration throughout the entire product lifecycle. Using an exam...

While the adoption of digital twins among industrial companies is growing due to rapid developments in available solutions, the utilization of digital twins as a part of company operations and management is a new phenomenon. As a result, the long-term functionality of the digital-twin lifecycle is not well understood. Because of the small number of...

This paper introduces a procedure in the field of computational contact mechanics to analyze contact dynamics of beams undergoing large overall motion with large deformations and in self-contact situations. The presented contact procedure consists of a contact search algorithm which is employed with two approaches to impose contact constraint. The...

This study introduces an inertial measurement unit-based measurement system for resolving the dynamic lean angle of a ski pole during double poling while cross-country skiing. The measurement system estimates both the pole lean angle and pole–terrain contact events. Reported are results from 20 trials providing validated estimates of ski pole lean...

Machinery devices often consist of mechanical mechanisms that are actuated by fluid power systems. In many applications, the mechanical system can be modelled and analysed in terms of the multibody system dynamics. Fluid power systems, in turn, can be analysed via the lumped-fluid theory, with which simulation of fluid power systems requires smalle...

Contact description plays an important role in modeling of applications involving flexible multibody dynamics. Example of such applications include contact between a belt and pulley, crash-worthiness analysis in aerospace and automotive engineering. Approaches such as the linear complementarity problem (LCP), nonlinear complementarity problem (NCP)...

The simulation of mechanical devices using multibody system dynamics (MBS) algorithms frequently requires the consideration of their interaction with components of a different physical nature, such as electronics, hydraulics, or thermodynamics. An increasingly popular way to perform this task is through co-simulation, that is, assigning a tailored...

In co-simulation, a number of subsystems sharing details of a system, are coupled to exchange data. The subsystem level development of each package enhances the computational efficiency, and more sophisticated packages can be created. However, the data exchange is not always straight forward as different packages can be developed by different resea...

Semi-recursive formulations and their various versions have made it possible to describe complex nonlinear systems such as vehicles precisely while still solving the relevant equations of motion in real time. An optimal combination of an efficient multibody formulation and a fast numerical time integration scheme are needed to accurately simulate c...

Real-time simulation models based on multibody system dynamics can replicate reality with high accuracy. As real-time models typically describe machines that interact with a complicated environment, it is important to have an accurate environment model in which the simulation model operates. Photogrammetry provides a set of tools that can be used t...

Applying a semi-recursive multibody approach enables the solution of the equations of motion of a complex system in real time. This makes it possible to conduct human-in-loop simulations and analyse the user experience. The idea of recognizing the user experience to produce more efficient, competitive, and user-friendly products has been limited th...

The Arbitrary Lagrangian-Eulerian (ALE) formulation provides a high-efficiency approach to simulate the moving contact behaviors in mechanical systems using the relative movement between material points and mesh nodes. Two approaches have been widely adopted to obtain the governing equations of ALE elements, namely, (i) Lagrange's equations for non...

Age-related reduction in muscle force generation capacity is similarly evident across different lower limb muscle groups, yet decline in locomotor performance with age has been shown to depend primarily on reduced ankle extensor muscle function. To better understand why ageing has the largest detrimental effect on ankle joint function during locomo...

Multibody dynamics of vehicle systems can be simulated in real time using semi-recursive-based formulations and their various versions, which are normally described in terms of relative coordinates. To efficiently and accurately simulate closed-loop vehicle multibody systems, a semi-recursive formulation must be optimally combined with a numerical...

The Arbitrary Lagrangian-Eulerian (ALE) formulation provides a high-efficiency approach to simulate the moving contact behaviors in mechanical systems using the relative movement between material points and mesh nodes. Two approaches have been widely adopted to obtain the governing equations of ALE elements, namely (i) Lagrange's equations for non-...

Fully autonomous earth-moving heavy equipment able to operate without human intervention can be seen as the primary goal of automated earth construction. To achieve this objective requires that the machines have the ability to adapt autonomously to complex and changing environments. Recent developments in automation have focused on the application...

A real-time multibody model of an off-road vehicle can be used to analyze the dynamics of tasks, such as loading and/or transferring material from deformable ground. This analysis requires an accurate description of the mechanics, hydraulic actuators, and the terrain. The objective of this paper is to introduce a novel, real-time capable, deformabl...

Digital tools have become indispensable for the testing and modification of prototypes in mobile and industrial machine manufacturing. Data that are extracted from virtual experimentation and analysis are both affordable and valuable, due to their repeatability and because they are close to real-world observations. Expert knowledge is a prerequisit...

New directions in wastewater treatment consider not only the adequate purification efficiencies but also water and material recovery for recycling and reuse. Freeze crystallization offers the potential for the simultaneous separation of water (ice) and material (i.e., salts and nutrients) from wastewater using a single wastewater purification proce...

The dynamics of helical gear-shaft systems are characterized by three-dimensional (3D) meshing contacts that have significant variations in the location and size of the contact area, resulting in noise that is unavoidably transmitted to the gearbox through the shaft. Accurate and efficient predictions of the dynamic behaviors of helical gear and sh...

In this paper, a machine learning-based simulation framework of general-purpose multibody dynamics is introduced. The aim of the framework is to generate a well-trained meta-model of multibody dynamics (MBD) systems. To this end, deep neural network (DNN) is employed to the framework so as to construct data-based meta-model representing multibody s...

The structure of water in its solid state (ice) is complex. A number of process parameters and the chemistry of the freezing aqueous solution influence ice crystal growth and ice characteristics such as crystalline structure, impurity inclusions, and appearance. The resulting variation in ice properties makes determining mechanical properties chall...

The multibody system dynamics approach allows describing equations of motion for a dynamic system in a straightforward manner. This approach can be applied to a wide variety of applications that consist of interconnected components which may be rigid or deformable. Even though there are a number of applications in multibody dynamics, the contact de...

A finite-element based absolute nodal coordinate formulation (ANCF) is applied to dynamic analysis of high-speed rotating shafts. To this end, a four-node higher-order ANCF beam element with third-order derivatives in the axial and cross-section directions is studied. Using a number of eigenfrequency, static and dynamic benchmark tests, it is shown...

Dynamics of complex mechanical systems can be modeled and solved efficiently, often even in faster-than-real-time by employing semirecursive formulations and their various versions. To simulate complex mechanical systems accurately and efficiently, an optimal combination of a multibody formulation and a numerical time integration scheme is critical...

In this paper, a tailored four-step Adams–Bashforth–Moulton (ABM) algorithm is applied to a semirecursive formulation to perform a real-time simulation of a semitrailer truck. In the ABM algorithm, each integration step involves two function evaluations, namely predictor and corrector. This is fundamentally different when compared to the classic fo...

In geographical regions with sub-zero temperatures, natural freezing can potentially be used as an energy-efficient purification technique for industrial wastewaters. The utilization of this technique requires knowledge of the effect of impurities on the strength of the ice to enable the effective harvesting of produced ice. Previous studies of the...

A lightweight wheel structure developed for rotor and stator use in large diameter direct-drive wind turbine generator is presented. The wheel structure uses layered sheet-steel elements to form the spokes and rim. This novel wheel structure is assumed to be more flexible than the existing conventional machine designs. Concerns with the dynamic res...