Explicit dynamic analysis of vibrations of the sides of a washing machine

Due to advanced tools and ever more effective computers, the examination of a product's functionality in advance has become a rather routine task. Before the product design process is truly concluded, practically all the potential load cases can be examined and development risks thus significantly reduced. The following case shows the dynamic analyses of a complex product (a washing machine), where the client wanted to optimize the machine's vibrations.

Problem Definition

  • TECOS Študije primerov: Gorenje PS10 dinamična analiza vibracij ohišjavibrations of the washing machine are too strong; the desire is to compare four different shapes of a side of the machine and their effect on vibrations;
  • an alternative shape is to be proposed by the industrial design department;
  • explicit dynamic analyses are required that cannot be performed by the client themselves;
  • a simplification of a mathematical model of the problem is required to reduce calculation times.

 

Solution

The following steps have been implemented for the client:

  • definition of elements that affect the dynamic strength of the washing machine the most;
  • development of a mathematical (numerical) model of the machine - the machine's dynamic strength is mostly affected by the washing unit;
  • implementation of linear dynamic analyses of natural frequencies and different shapes of sides of the washing machine frame;
  • implementation of an explicit dynamic (time-dependent) analysis in which the dynamic response of the washing machine frame was analysed during the operation of the washing unit with eccentric weight.

Final result: we predicted the most rigid shape of the side of the washing machine, which in the provided operation regime damps the vibrations of the washing unit the most.

 

Purpose and benefits for the end customer:

  • reduced risks during the development stage due to the analysis of the model's functionality performed in advance;
  • help in the decision-making process due to an in-depth insight into the issues discussed;
  • relieving the client's own R&D team of the issues that deviate from their everyday R&D duties;
  • short response time and credible results.

 

The images and additional description of individual stages are provided below.

Definition of natural frequencies

First, the linear dynamic analyses of natural frequencies and of different shapes of the sides of the washing machine frame were performed (Figure 1). These analyses helped define the natural frequencies of different frames and potential unfavourable correlations between natural and operational frequencies of the washing unit. Such correlations may cause a resonant state or rather a significant increase in the load on the frame of the washing machine. By predicting critical areas, the suitability of different frames of machines is examined in view of potential unfavourable operating regimes.

TECOS študija primera:  Gorenje PS10 dinamična analiza - lastne frekvence in oblike ohišja

Figure 1: Analysis of natural frequencies and different shapes of the washing machine frame

Then, the explicit dynamic (time-dependent) analyses were conducted in which the dynamic response of the washing machine frame was analysed during the operation of the washing unit with eccentric weight (Figure 2 shows the model during operation). These analyses were used to observe the rigidity or rather the movements of the washing machine frame during operation (Figure 3). We were thus able to predict prior to production the most rigid shape of the side of the washing machine, which in a certain operation regime damps the vibrations of the washing unit the most.

TECOS študija primera: Gorenje PS 10 - vrtenje pralne grupe 

Figure 2: Illustration of rotation and movements of the washing unit as well as response over time

 

TECOS študija primera: Gorenje PS 10 - nihanje različnih oblik stranic ohišja pralnega stroja

Figure 3: The most suitable shape of the side is clearly evident (top right hand corner, all scales are equal).

 

Conclusions

Engineering simulations in advanced CAE software packages, such as Abaqus, enable us to gain an in-depth insight into conditions during the operation of a product. With a detailed record of the impacts of the environment (temperature field, vibration, wind, periodic unfavourable load cases, etc.), of the interaction of components (movements, forces, friction, contact problems, etc.), of various physical phenomena (e.g. heating with electricity, thermal conduction, etc.), of material properties (material or geometric non-linearity, multicomponent materials, fibre-reinforced polymers, creep properties, etc.) and of potential dynamic operating conditions (cyclic loading, major movements, etc.), a complex numerical model of the discussed problem may be developed that explores the actual conditions with great accuracy.

The main benefit of the use of simulations is evident when the numerical model of the product is made. Different combinations of loads that rarely occur in practice may quickly be applied to the product. It is in this manner that the most unfavourable operating conditions are sought and the system's response is observed, i.e. deformations, internal stress, etc. What is more important is the fact that based on findings, the product can be optimized, i.e. material can be added in areas where it lacks or removed where there is too much of it.

In the present case, we were able to show the operation of the washing machine with various shapes of the frame. The client was thus able to more easily decide on the most suitable shape of the frame. Probably the most important aspect of the process was the fact that tool designers, engineers, designers and marketing department were provided with a basis for decision-making, since they were able to see how their decisions affect the end product.

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