In this study, a developed co-simulation method, which couples 1D-fluid and 3D-structural models, has been utilised to simulate wear in a hydraulic percussion unit. The effect of wear is generally detrimental on performance and lifetime for such units, but can also cause catastrophic failure and breakdown, requiring a total overhaul and replacement of core components. One experiment of standard straight impact was performed to investigate the tolerance against seizure. The percussion unit was operated at successively increasing operating pressures, and the level of wear was registered at each step, until seizure occurred. The co-simulation model was used to replicate the running conditions from the experiment to simulate the structural response to be used as input for the wear routine to calculate the wear depth. The wear pattern from the simulations corresponds well to the wear pattern from the experiment. Further, the effect of a misaligned impact on wear development was also studied, as this is a loading situation that typically occurs for hydraulic percussion units. The study demonstrates that the simulation method used has a potential for simulating wear and predicting seizure in hydraulic percussion units.

In this dissertation, a co-simulation tool is presented that is meant to comprise a more comprehensive environment for modelling and simulation of hydraulic percussion units, which are used in hydraulic hammers and rock drills. These units generates the large impact forces, which are needed to demolish concrete structures in the construction industry or to fragment rock when drilling blast holes in mine drifting. This type of machinery is driven by fluid power and is by that dependent of coupled fluid-structure mechanisms for their operation. This tool consists of a 1D fluid system model, a 3D structural mechanic model and an interface to establish the fluid-structure couplings, which has in this work been applied to a hydraulic hammer. This approach will enable virtual prototyping during product development with an ambition to reduce the need for testing of physical prototypes, but also to facilitate more detailed studies of internal mechanisms. 

The tool has been implemented for two well-known simulation tools, and a co-simulation interface to enable communication between them has been devel-oped. The fluid system is simulated using the Hopsan simulation tool and the structural parts are simulated using the FE-simulation software LS-DYNA. The implementation of the co-simulation interface is based on the Functional Mock-up Interface standard in Hopsan and on the User Defined Feature module in LS-DYNA. The basic functions of the tool were first verified for a simple but relevant model comprising co-simulation of one component, and secondly co-simulation of two components were verified. These models were based on rigid body and linear elastic representation of the structural components. Further, it was experimentally validated using an existing hydraulic hammer product, where the responses from the experiments were compared to the corresponding simulated responses. To investigate the effects from a parameter change, the hammer was operated and simulated at four different running conditions. 

Dynamic simulation of the sealing gap, which is a fundamental mechanism used for controlling the percussive motion, was implemented to further enhance the simulated responses of the percussion unit. This implementation is based on a parametrisation of the deformed FE-model, where the gap height and the eccentric position are estimated from the deformed geometry in the sealing gap region, and then the parameters are sent to the fluid simulation for a more accurate calculation of the leakage flow. 

Wear in percussion units is an undesirable type of damage, which may cause significant reduction in performance or complete break-down, and today there are no methodology available to evaluate such damages on virtual prototypes. A method to study wear was developed using the co-simulation tool to simulate the fundamental behaviour of the percussion unit, and the wear routines in LS-DYNA were utilised for the calculation of wear.  

I denna avhandling presenteras ett co-simuleringsverktyg som är tänkt att utgöra grunden för en simuleringsmiljö för att modellera och simulera hydrauliska slagverk som används i hydrauliska hammare och bergborrmaskiner. Sådana enheter används för att generera de stora krafterna som krävs för att krossa betongstrukturer vid rivningsarbete inom byggindustrin eller för att krossa berg vid borrning av spränghål vid gruvdrift. Dessa typer av maskiner drivs av hydraulik vilket innebär att kopplade fluid-strukturmekaniskmer ligger till grund för dess funktion, varför simuleringen av sådana mekanismer utgör kärnan i detta arbetet. Co-simuleringsverktyget består av en 1D fluidsystemmodell, en 3D strukturmekanikmodell och ett interface för att skapa fluid-strukturkopplingarna, och i detta arbete har en hydraulhammare använts för att demonstrera och validera dess funktionalitet. Detta verktyg kommer att möjliggöra en simuleringsdriven produktutveckling med en ambition att reducera behovet av provning av fysiska prototyper, men det kommer också˚ att ge förutsättningar för mer detaljerade studier av interna mekanismer.

Verktyget har implementerats för två˚ välkända simuleringsprogram, och för att möjliggöra kommunikationen mellan dessa utvecklades ett co-simuleringsinterface. Simuleringen av enhetens hydrauliska funktion genomförs i systemsimuleringsverk-tyget Hopsan och strukturdelen simuleras i LS-DYNA, ett finita elementprogram. Co-simuleringsinterfacet är baserat på standarden Functional Mock-up Interface mot Hopsan, och på User Defined Feature modulen i LS-DYNA. Verktygets grundläggande funktionalitet verifierades med hjälp av enkla modeller som representerar slagverkets grundläggande mekanismer. Funktionaliteten verifierades först för co-simulering av en komponent och sedan för co-simulering av flera komponenter, vilket är ett krav då slagverket består av flera rörliga delar. De strukturella delarna i dessa modeller simulerades dels som helt stela och dels som helt elastiska för att successivt öka komplexiteten hos modellen. Vidare genomfördes en mer omfattande validering baserad på experimentella mätningar på en kommersiellt tillgänglig hydraulhammare. Denna validering bestod av jämförelser mellan experimentella och simulerade resultat, och utifrån denna kunde man konstatera att simuleringsmetoden ger en god överensstämmelse inte bara för de grundläggande mekanismerna utan också för de mekanismer som är kopplade till vågutbredning i fluiden och strukturen. För att undersöka effekterna av en parameterförändring genomfördes experiment där hydralhammaren kördes vid fyra olika arbetsvillkor, och därefter jämfördes resultaten med simulerade resultat från motsvarande arbetsvillkor.

Tätningsspalten är en fundamental mekanism hos slagverket och den används för att styra den grundläggande rörelsen hos slagverket. Funktioner och rutiner utvecklades och implementerades i verktyget för att ge förutsättningar för en kopplad fluid-struktursimulering av dynamiska tätningsspalter, med en ambition att förbättra beräkningen av läckageflödet genom spalten. Implementationen är baserad på en rutin som parametriserar den deformerade FE-modellen vid tätningsspalten och beräknar spalthöjd och det excentriska läget, vilka sedan skickas till fluidsimuleringen för att användas vid beräkning av läckageflödet.

Slitage i slagverk är en oönskad skademekanism som kan resultera i försämrad prestanda eller orsaka allvarliga haveri, vilka kan ge upphov till produktionsbortfall. Då metodik för att studera sådana skador saknas för virtuella prototyper i dagsläget, presenteras i denna avhandling ett förslag på hur sådana mekanismer kan analyseras genom simulering. Metoden baseras på att simulera slagverkets fundamentala mekanismer med hjälp av co-simuleringsverktyget och i den efterföljande analysen används slitagerutinerna i LS-DYNA för att beräkna slitaget.   

This Licentiate of Engineering thesis concerns modelling and simulation of hydraulic percussion units. These units are often found in equipment for breaking or drilling in rock and concrete, and are also often driven by oil hydraulics, in which complex fluid-structure couplings are essential for their operation.

Current methodologies used today when developing hydraulic percussion units are based on decoupled analyses, which are not correctly capturing the important coupled mechanisms. Hence, an efficient method for coupled simulations is of high importance, since these mechanisms are critical for the function of these units. Therefore, a co-simulation approach between a 1D system simulation model representing the fluid system and a structural 3D FE-model is proposed.

This approach is presented in detail, implemented for two well-known simulation tools and evaluated for a simple but relevant model. The Hopsan simulation tool was used for the fluid system and the FE-simulation software LS-DYNA was used for the structural mechanics simulation. The co-simulation interface was implemented using the Functional Mock-up Interface-standard.

The approach was further developed to also incorporate multiple components for coupled simulations. This was considered necessary when models for the real application are to be developed. The use of two components for co-simulation was successfully evaluated for two models, one using the simple rigid body representation, and a second where linear elastic representations of the structural material were implemented.

An experimental validation of the co-simulation approach applied to an existing hydraulic hammer was performed. Experiments on the hydraulic hammer were performed using an in-house test rig, and responses were registered at four different running conditions. The co-simulation model was developed using the same approach as before. The corresponding running conditions were simulated and the responses were successfully validated against the experiments. A parameter study was also performed involving two design parameters with the objective to evaluate the effects of a parameter change.

This thesis consists of two parts, where Part I gives an introduction to the application, the simulation method and the implementation, while Part II consists of three papers from this project.

In this study a previously developed co-simulation method that is based on a 1D system model representing the fluid components of a hydraulic machinery, within which structural 3D Finite Element (FE) models can be incorporated for detailed simulation of specific sub-models or complete structural assemblies, is further developed. The fluid system model consists of ordinary differential equation sub-models that are computationally very inexpensive, but still represents the fluid dynamics very well. The co-simulation method has been shown to work very well for a simple model representing a hydraulic driven machinery. A more complex model was set up in this work, in which two cylinders in the hydraulic circuit were evaluated. Such type of models, including both the main piston and control valves, are necessary as they represent the real application to a further extent than the simple model, of only one cylinder. Two models have been developed and evaluated, from the simple rigid body representation of the structural mechanics model, to the more complex model using linear elastic representation. The 3D FE-model facilitates evaluation of displacements, stresses, and strains on a local level of the model. The results can be utilised for fatigue assessment, wear analysis and for predictions of noise radiation.