The DSHplus pre- and post-processing modules

At Fluidon, we are proud to transfer the advanced pre- and post-processing modules of our proven DSHplus software to our latest product, Fluidon Cube.

In Fluidon Cube, these functions find a new home where their application is not only easier but also more comprehensive. This ongoing development will enable our users to benefit from improved efficiency and expanded analysis options.

We therefore encourage all users to switch to Fluidon Cube for future projects and take full advantage of this innovative platform. Learn more about the possibilities Fluidon Cube offers and how you can optimize your development process with it.

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In order to analyze the behavior of the duty cycle of a technical system in an adequate way, the modeling of the control strategy is always a very important but time consuming task. Until now a more or less realistic consideration of the system control within simulation tools could only be achieved through a complex modeling with the help of different control elements, like switches or other mathematical components.

The DSHplus-Director overcomes these deficits and offers the user a simple environment to define complex control strategies, including process-dependent sequential controls or safety functions.

The DSHplus-Director is an easy way to implement different sequential controls into your DSHplus model. The finite state machine allows the user to model the whole control strategy of a technical system by defining specific actions, conditions and states. Within the DSHplus-Director the user can access all state variables or parameters of the simulation model. The transitions between Director-states are described by conditions. The defined actions on the other hand can be assigned to the different states as entry or exit actions. This is all in all a very convenient way to model and simulate different control approaches in various depth of detail.

As some extra benefits the DSHplus-Director visualizes the designed control logic as a flow graph and offers a dynamic log dialog that shows which actions are performed and what conditions are met during the simulation. If the actual PLC development environment is then available in the later phases of the development process, DSHplus also offers the possibility to couple the real control program to DSHplus via an OPC interface.

Automation by Parameter Variation and Optimisation

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The DSHplus Parameter Variation Module, the DSHplus Batch Simulation Module and the DSHplus optimization Module are core modules of the DSHplus preprocessing functionality. By means of these three modules the design engineer is able to automate the simulation in order to analyze different parameter configurations or to optimize complete system set-ups. The modules are suitable for background or overnight work whereas the design engineer merely checks the results after the automatic simulation is concluded.

The DSHplus Batch Simulation Module offers the possibility to calculate pre-defined parameter sets in a batch run. Using the DSHplus Parameter Variation Module it is possible to vary each design parameter of the simulation model in arbitrary or fixed steps. The variation is realized using DOE matrixes; obtained from statistical programs such as MiniTabTM, or by user inputs. Through this the effect of different component sizes, such as pump displacement or piston diameter, or even manufacturing tolerances, such as gap height or spring stiffness, onto the system’s dynamic can be examined. In combination with the DSHplus functionality to use parametric equations in order to calculate component parameters, which are in dependence of other model parameters, it is also possible to realize constraints between components.

A HTML-based simulation report can be generated that allows a quick visual analysis of the simulation runs. This report includes a separate page for each parameter set that includes a model image, the result graphics and a legend that lists boundary condition parameter values. For a subsequent more detailed post-processing all results can be stored.

Combined with the DSHplus Optimization Module, both modules are capable of performing an automatic design parameter optimization. Herewith a real virtual engineering of fluid power system within DSHplus is possible.

The DSHplus Optimization Module uses gradient or generic search algorithms, such as the Hookes-Jeeves search algorithm or an evolution strategy, to perform an automatic variation of system parameter in defined ranges. Goal is the minimization of a quality criterion that has to be defined by the design engineer. Possible applications are an automatic search for the optimal controller gain settings, the best design parameter values, such as diameter or spring stiffness, or parameters are simply automatically tuned until simulation results match measurement data.

Frequency Analysis

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The DSHplus Frequency Spectrum (FFT), the DSHplus Frequency Analysis and the DSHplus Order Analysis are three core modules of the DSHplus Virtual Engineering Lab's postprocessing functionality.

The DSHplus Frequency Spectrum computes the representation of a time-domain signal in the frequency domain. The frequency spectrum can be generated via a Fourier transformation of the signal. Baron Jean Baptiste Fourier showed that any waveform that exists in the real world can be generated by adding up sine waves. A major use of the frequency domain is to resolve small signals at certain frequencies in the presence of large ones at other frequencies. The DSHplus Frequency Spectrum is integrated into the DSHplus online graphic. The frequency spectrum is computed immediately after the simulation run stopped.

The DSHplus Frequency Analysis Module computes the frequency response of a system. The transfer function is subsequently displayed in a Bode-diagram depicting amplitude and phase shift. There are two methods available to calculate the mean value of the spectrum the Root-Mean-Square method (RMS) and the Peak-Hold method. If the raw data are contaminated with noise the DSHplus Frequency Analysis Module offers different cross correlation functions in order to identify the usable signal and computes the coherence value of the two signals. By means of two boundary lines a data interval suitable for the calculation can be chosen. If the data is not periodic a weighting function - such as Hanning or Blackman Harris - can be assigned to improve the calculation.

By means of the parameter block size and percentage of the blocks overlap the DSHplus Frequency Analysis Module it able to perform a sliding window analysis of the data.

The calculated frequency data can be stored to a file, including also complex power spectrum values of input and output. The Bode-diagram can be printed or copied. Input or output of the frequency analysis may be any variable in the simulation model or measurement data that has been imported into DSHplus.

The DSHplus Order Analysis computes a spectrogram. The horizontal axis represents time or rpm, the vertical axis is frequency. The third dimension indicating the amplitude of a particular frequency at a particular time is represented by a color of each point in the image. As representation of the spectrogram a top view or a rotatable 3D surface is available. If the excitation is linear increasing with time, individual frequency orders can be extracted from the signal.

Look-up Tables

Look-up tables are indispensable for the dynamic simulation of fluid systems. Mathematically, a look-up table is a set of data points of a sampled function F with N variables, which can also be empirical. The look-up table maps input values onto the output value by linear interpolation between the samples data points.

The wide range of application for look-up tables is reaching from nonlinear component behavior, such as the flow area of valve metering edges or the stroke-dependent working diameter of an airspring, to the representation of measured component behavior, such as cylinder friction, valve pressure drop or the flow rate of a constant pump.

In practical applications, the output value of a look-up table very often depends on more than one input value. While it is possible to describe a valve’s flow area or the stroke dependent working diameter through a simple x-y relation, for the representation of measured valve flow already two input values (valve opening and pressure difference) are required and for a fixed displacement pump flow the number of required input values increases to three (speed, system pressure, fluid temperature). In the case of a variable displacement pump the tilt angle would add a fourth input value.

The DSHplus look-up table editor is the administration module for making and modifying the look-up tables of the DSHplus components. 1-D look-up tables are described as an x-y set of points. Within the range of the look-up table intermediate values are derived from linear interpolation. An extrapolation outside of the table’s range is not carried out, the respective final value of the table is kept constant.

Higher dimensional look-up tables may be based on Cartesian coordinates or line-based look-up tables.

In a Cartesian table all data points form a grid structure with an output value assigned to each input value on either axis. This type of look-up table is suited for numerically derived data where all output values can be exactly calculated. In case of measurement values the Cartesian form poses to be problematic because data for the exact grid points is hard to obtain and requires complex postprocessing of the raw data. Line-based tables are ideally suited for measurement data, a 2D-look-up table e.g. is constituted of several 1D-tables, which may all have different data point spacing. An example would be a set of measurements of flow vs. pressure drop of a valve for different valve openings.

3D-look-up tables are made by combining 2D-tables, there is no limitation in number or type, line-based and Cartesian tables can be mixed.

To create look-up tables DSHplus offers two modules. Using the Look-up Table Generator data curves e.g. from a manufacturer data sheet are digitalized into a 1D-look-up table. The DSHplus Data Interpolator can create 2D-tables from an arbitrary amount of unsorted x-y-z data points.

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