# Introduction

Introduction

## Library

UsersGuide

## Description

The package **HydraulicsByFluidon** is a **modelica** library
for the one-dimensional simulation of fluid-power systems. The models are
based on the **lumped parameter** approach. The library consists of
various hydraulic components and predefined hydraulic fluids. In order to enable
the user to create custom components, the library specific component interfaces are
provided as well.

__Minimal working example__

Each model created by using the HydraulicsByFluidon package requires the **Liquid**
and **Environment** blocks to be added:

The environment block provides the simulation with information about the
**environmental conditions**, e.g. the ambient pressure or the value of
the gravitational constant. The liquid block determines the hydraulic fluid
that is used, which is why **every** hydraulic component in a model has to be connected to it. In
order to save the user the trouble of connecting the liquid block to each
component manually, the option **forwardFluidProperties** is included in certain
components. If this option is used, the user has to connect the liquid block to each
hydraulic circuit only once since the fluid information is forwarded between the components.

__Fundamentals of the lumped parameter approach__

In hydraulic engineering, the lumped parameter approach assumes that the state of a cross-section within a hydraulic system is fully described by the (mass) flow rate and the pressure. Due to numerical limitations, the application of the lumped parameter approach is usually restricted to systems with low to moderate dynamic effects. In the lumped parameter approach, there are three fundamental types of hydraulic elements:

- Resistor
- Capacitor
- Inductor

**ideal loss**without any inertia or hydraulic stiffness. Its constitutive equation can be expressed as follows:

This equation states that the mass flow rate is assumed to be proportional to the n-th power of the pressure drop across the component. The exponent can vary between 1 and 0.5, depending on the flow regime.

By contrast, the capacitor corresponds to an **ideal hydraulic spring** without any losses or inertia.
Mathematically, its behaviour is described by the following differential equation:

According to this model, the temporal change in pressure is proportional to the difference in incoming and outgoing mass flows, multiplied with the bulk modulus and divided by the density and volume of the fluid in the respective component.

The inductor is an **ideal inertia** without any losses or stiffness. It is mathematically described by the following equation:

This equation is the hydraulic formulation of Newton's second law of motion. It states that the temporal change in mass flow rate is equal to the pressure difference across the component, multiplied by the cross-sectional flow area and divided by the length of the component.

__Solution procedure__

These fundamental elements can be used alone or in combination to model actual hydraulic components.
If components modeled through these elements are connected to a circuit model, they form a
system of coupled ordinary differential equations which has to be solved numerically. The
solving algorithm works in a staggered way: based on the initial pressure distribution,
the resistors and inductors calculate **flow rates**. These flow rates are then used as boundary
conditions for the capacitors, which calculate the new **pressure distribution** in return. After
this step, the whole procedure is repeated. Due to the algorithm structure outlined above,
reasonable initial pressures have to be assigned to components that are based on capacitor
elements, e.g. simple volumes.

Instructions regarding the use of individual components can be found in the respective component's documentation.

__Component library__

The User's Guides for the Component library can be accessed here.